Optometry Updates

CONTACT LENSE

2009-01-13T06:53:00.000-08:00

Monthly, Bi-weekly, Daily, conventional/yearly disposable contact lense, Toric lense, Color lense, Extended wear lense (day & night), Prosthetic lense

3 months disposable color lens

rm 65 a box for Blincon color lens (no astigmatism correction). 1 box has 2 pieces.

rm 180 for 1 pair of Blincon custom made color toric lens.

rm 90 a piece for Blincon BB color toric lens. 5 colors available : Hazel, Brown, Grey, Green, Blue

Monthly normal lense

rm 45 a box for Sauflon 55 UV. 1 box has 6 pieces.

rm 120 for a box of B&L purevision 2. (6 pieces in a box). buy 1 box free 1 extra piece.

rm 45 a box for AIR optix. 1 box has 3 pieces. BUY 4 BOXES FOR RM 170

rm 60 a box for O2 optix. 1 box has 6 pieces.

rm 45 a box for Acuvue clear. 1 box has 6 pieces.

rm 40 a box for Bausch & Lomb (B&L) Softlens 59. 1 box has 6 pieces.

rm 45 for a box of B&L Softlens 38 monthly lens. 1 box has 6 pieces.

rm 80 for a box of B&L purevision normal lens. (6 pieces in a box). buy 1 box free 1 extra piece. Buy 4 boxes for rm 300 only.

rm 50 for a box of Freshkon 38 monthly disposable lens.(6 pieces in a box)

rm 50 for a box of Freshkon 55 monthly disposable lens.(6 pieces in a box)

rm 55 for a box of focus visitint monthly disposable lens.(6 pieces in a box)

rm 60 for a box of Sauflon Bioclear monthly disposable lens.(6 pieces in a box)

rm 100 for a box of Sauflon clariti (silicon hydrogel) monthly disposable lens.(6 pieces in a box)

rm 45 for a box of BIOMEDIC 55 monthly disposable lens.(6 pieces in a box)

rm 50 for a box of BIOMEDIC 38 monthly disposable lens.(6 pieces in a box)

rm 95 for a box of Biofinity monthly disposable lens.(6 pieces in a box). Buy 1 box free 1 extra piece

Monthly toric lense

rm 90 a box for Bausch & Lomb Softlens toric lens. (1 box has 6 pieces). buy 1 box free 1 piece.

rm 75 for a box of B&L purevision toric lens. (3 pieces in a box). buy 1 box free 1 piece.

rm 110 for a box of Freshkon N-hance toric monthly disposable lens.(6 pieces in a box), buy 1 box free 1 piece

rm 40 for a PAIR of Freshkon N-hance toric monthly disposable lens.(2 pieces ONLY)

rm 110 for a box of Sauflon-Bioclear toric monthly disposable lens.(6 pieces in a box). Buy 1 box get 1 extra free piece.

rm 80 for a box of Air Optix toric lens. (3 pieces in a box), free 1 extra piece for every box purchase.

rm 95 for a box of Biomedic toric monthly disposable lens.(6 pieces in a box). Buy 1 box get 1 extra free piece.

rm 110 for a box of Biofinity toric monthly disposable lens.(6 pieces in a box). Buy 1 box free 1 extra piece.

Daily normal lense

rm 75 a box for Johnson & Johnson 1 day Acuvue daily lens. 30 pieces in a box.

rm 75 for a box of Acuvue moist daily lens. (30 pieces in a box). Buy 7 boxes free 1 box.

rm 70 for a box of Freshkon EveryDay daily disposable lens.(32 pieces in a box)

rm 80 for a box of B&L Softlens daily disposable lens (40 pieces).

rm 60 for a box of focus daily disposable lens. (30 pieces in a box)

rm 90 for a box of Acuvue TruEye daily lens. (30 pieces in a box). Buy 7 boxes free 1 box

rm 60 for a box of Biomedic daily lens. (30 pieces in a box)

rm 80 for a box of focus daily aqua comfort plus disposable lens. (30 pieces in a box)

Daily toric lense

rm 100 for a box of focus dailies toric daily lens.(30 pieces in a box)

rm 100 for a box of B&L toric daily lens.(30 pieces in a box).

Monthly color lense

rm 40 for freshlook colourblend monthly lens. 1 box has 2 pieces.

rm 35 for Freshkon colour fusion monthly lens. 1 box has 2 pieces.

rm 40 for Freshkon mosaic monthly colour lens. 1 box has 2 pieces.

rm 40 for Freshkon Dezigner monthly colour lens. 1 box has 2 pieces. Buy 3 boxes free pos laju.

rm 50 for Blincon sweeties or BB monthly colour lens. 1 box has 2 pieces.

Daily color lense

rm 45 for a box of freshlook daily color lens. (10 pieces in a box), available in Grey, Blue, Green, and Hazel

Bi-weekly normal & toric lense

rm 70 a box for Acuvue 2, bi-weekly lens. (6 pieces in 1 box).

rm 55 for a box of Acuvue advance PLUS, bi-weekly lens (6 pieces in a box). buy 7 boxes free 1 box.

rm 85 for a box of Acuvue Oasys, bi-weekly lens. buy 3 free 1 till promotion ends. (6 pieces in a box)

rm 105 for a box of Acuvue Oasys toric lens, bi-weekly lens. buy 4 boxes for rm 380 only. (6 pieces in a box). Buy 1 box free 1 extra piece.

Extended monthly wear lense (can sleep with the lens on)

rm 110 for a box of Focus Night & Day monthly disposable lens. (3 pieces in a box)

Cosmetic lense (eyes big like Barbie doll eyes)

rm 40 for a box of Freshkon Alluring Eye color monthly disposable lens. (2 pieces in a box) mystical black, winsome brown, Mesmeric Black and Magnetic Grey.

rm 90 for a box of Acuvue define daily disposable lens. (30 pieces in a box)

rm 30 for a box of Freshlook Illuminate daily disposable lens. (10 pieces in a box)

Multifocal soft contact lens

rm 160 for a box of B&L softlens multifocal. (6 pieces in a box). buy 1 box free 1 extra piece

rm 100 for a box of ciba vision Air optix multifocal lens. (3 pieces in a box). buy 1 box free 1 extra piece

rm 105 for a box of Cooper-vision Proclear multifocal. (3 pieces in a box). buy 1 box free 1 extra piece

Conventional / yearly soft lense

Rm 75 for 1 piece of Oculus normal flexcon conventional soft lense.

Rm 200 for 1 piece of Oculus flexcon toric conventional soft lense.

Rm 225 for 1 piece of Oculus flexcon toric blue tint conventional soft lense.

Overnight Orthokeratology-Associated Microbial Keratitis.

2007-01-18T03:34:00.000-08:00

Orthokeratology is designed to reduce myopia and astigmatism temporarily by flattening the corneal curvature. Several investigations in the 1970s and 1980s using a flat-fitting polymethyl methacrylate (PMMA) lens for orthokeratology showed unpredictable and uncontrollable results. However, as the design and materials used for orthokeratology contact lenses have evolved, orthokeratology with overnight wearing of gas permeable material (overnight orthokeratology) has shown more promising results.

The new generation of designs, collectively termed reverse geometry contact lens, contained the base curve and reverse curve. The base curve is designed to be flatter than the central corneal curvature. The secondary curve radius is steeper than the base curve radius, which can be used to improve the centration and stability of the lens. Advances in oxygen transmissibility (Dk/t) of rigid gas permeable materials are further influencing the current practice of orthokeratology. All these current trends in orthokeratology contribute to more predictable, stable, and safer effect than the older version of designs.

Complications reported with orthokeratology include corneal epithelial edema, abrasion or staining of the cornea, keratoconic change, and induced astigmatism. Among these problems, corneal epithelial staining is the most common phenomenon observed in overnight orthokeratology. Corneal epithelial damage can cause the break down of the corneal epithelial barrier and increase the risk of corneal infection. Many cases of infectious keratitis associated with orthokeratology including Pseudomonas aeruginosa, Acanthamoeba, and Serratia marcescens have been reported.

As orthokeratology treatment of myopia has become increasingly popular in Taiwan during the past 10 years, many cases of corneal infection have been observed. This study was conducted to review the clinical and microbiologic features and the outcomes of overnight orthokeratology-associated microbial keratitis.

DISCUSSION

Orthokeratology lenses are designed to flatten the central cornea. Their base curve is usually flatter than the anterior corneal curvature. Alteration of the corneal shape and remolding of the corneal epithelium have been reported as the possible mechanisms in changing refraction. Changes in the cornea that include corneal epithelial edema, abrasion, and staining of the cornea can occur in orthokeratology lens wearers. In our study, 90% of microbial keratitis were located at the central cornea. The high incidence of microbial keratitis at this central location in orthokeratology lens wearers coincided with the design of orthokeratology lenses that most compressed the central cornea and damaged the central corneal epithelium, thus predisposing the central cornea to an increased risk of infection.

Besides lens design, the night-wearing strategy of orthokeratology lenses may be another important risk factor of infection. Wearing extended-wear lenses overnight, even if only for one or two nights at a time, increases the risk of ulcerative keratitis compared with use of the lenses solely during the day. Thus, the risk of infection in overnight orthokeratology should not be overlooked. Other possible complications associated with orthokeratology lenses include corneal scarring, permanent corneal warpage, keratoconic changes in the cornea, induced astigmatism, and corneal thinning.

The prevalence of myopia in school children is high in Taiwan. Although the role of orthokeratology in arresting or slowing the progression of myopia is still not clear, orthokeratology has gained popularity for school children in Taiwan because of its publicized claim of halting myopia progression. However, children may not be able to manipulate or clean the lenses properly. Poor lens hygiene and possible corneal trauma during lens insertion and removal may predispose children to increased risk of corneal infection.

Although the new generation of RGP lenses for overnight orthokeratology have higher oxygen transmissibility, and hence might have lower infection rates, several cases of microbial keratitis associated with overnight orthokeratology have been reported including Pseudomonas, Acanthamoeba, Fusarium, and Serratia infection. Pseudomonas aeruginosa and Acanthamoeba are the most important pathogens causing microbial keratitis associated with overnight orthokeratology, accounting for 47.1% (16/43) and 20.6% (7/34) of cases, respectively.

Presently, all the eyes displayed the complete disappearance of corneal infiltrates and re-epithelization after using antimicrobial medications. No urgent therapeutic surgery was needed to control the infections. Previous reports confirm the success of the strategy in the majority of patients. Acanthamebic infection associated with orthokeratology can require months to heal. In our series, the mean time for re-epithelization with acanthamebic infection (112 days) was much longer than cases with nonacanthamoebic infection (6.6 days). The poor epithelization of these cases may be caused by drug toxicity or concomitant steroid usage, because these patients had been treated empirically with a variety of commercially available antibiotics and antibiotic-steroid combination before being referred to our hospital.

In a previous study regarding the clinical characteristics of microbial keratitis, we demonstrated the better medical treatment result of bacterial infection compared with acanthamebic infection. Early diagnosis is essential for successful treatment of acanthamebic keratitis. Delays in diagnosis and treatment can result in an extensive involvement of ocular tissue and poor visual outcome, as exemplified by patient 8. Therefore, the possibility of acanthamebic keratitis in users of orthokeratology lenses could not be overlooked. Where the clinical presentations are characteristic, vigilance should be heightened for acanthamebic keratitis, and laboratory examination mandatory.

The visual outcomes in our study varied from 20/20 to hand motion only. Because all the patients had a sequela of corneal opacity, the density, size, and location of the corneal opacity are key factors influencing visual outcome. Other complications such as cataract and secondary glaucoma also affect the visual prognosis.

We attempted to identify the specific data of orthokeratology lenses, including the brand and type of lenses, fitting characteristics, diameter, power, and base curve of lenses, and the corneal topographic changes; however, the details were unavailable to us because the orthokeratology lenses were not fitted at our hospital. Although the design and material of orthokeratology lenses are continuously evolving, the long-term effect and safety of overnight orthokeratology warrants further evaluation and continuous monitoring.

CONCLUSIONS

Patients and ophthalmologists should not overlook the risk of microbial keratitis after overnight orthokeratology. Parents should be educated on the importance of proper lens hygiene and the need for immediate ophthalmic consultation when symptoms of keratitis occurred.

Acanthamoeba and Gram-negative bacilli, including Pseudomonas aeruginosa, are the most common pathogens causing microbial keratitis associated with overnight orthokeratology in this series. Patient education, early diagnosis, and proper antimicrobial treatment are helpful in preventing and eradicating the infection.

Infectious Keratitis Related to Overnight Orthokeratology.

2007-01-15T03:23:00.000-08:00

Orthokeratology is defined as the temporary reduction, modification, or elimination of myopia by the programed application of a rigid contact lens. This procedure was first reported in the early 1960s when the “orthofocus” technique was described. The technique of traditional orthokeratology contact lens fitting, where the base curve radius of lenses was designed to be flatter than the central corneal curve, had lost favor because earlier controlled clinical studies showed it was unpredictable and modest in its ability to correct myopia. However, with the advent of reverse-geometry contact lens designs and new rigid gas-permeable (RGP) materials with high oxygen transmissibility, clinical interest in orthokeratology has been renewed.

Mountford conducted a study of orthokeratology in which patients wore reverse-geometry contact lenses on an overnight basis. This strategy was reported to significantly enhance the predictability and efficacy of the orthokeratology in reducing myopia. Nichols and his co-workers also reported satisfactory results from overnight orthokeratology. The theory underlying overnight orthokeratology is that, as the RGP lenses are worn, the cornea is reshaped, and the level of myopia is reduced as the patient sleeps. The lenses are removed on waking, and good vision is maintained without correction through the day.

However, overnight wear is known to be a risk factor for infectious keratitis, a serious and vision-threatening complication, as in all contact lens use. Previous case reports have specifically documented the occurrence of this rare complication of overnight orthokeratology. We have reported 6 patients with pseudomonal keratitis related to overnight orthokeratology. Here, we extended the observation period to include 21 eyes in 20 subjects with infectious keratitis associated with overnight orthokeratology to investigate patient histories, microbial culture results, clinical courses, and visual outcomes.

DISCUSSION

Overnight orthokeratology is gaining increased popularity for the treatment of myopia in children because good vision can result without the aid of glasses or contact lenses in the daytime. Another reason for its usage becoming popular among children is that some parents often have the false belief that orthokeratology itself can halt or even reverse the progression of myopia, especially in our locality, where the myopia rate increases from 20% at 7 years to 61% at 12 years, 81% at 15 years, and 84% at 18 years. As is inherent in the practice of orthokeratology, subjects seen for correction generally are children with excellent best corrected visual acuity. Although the risk of infection with overnight orthokeratology is rarely reported, this complication can be devastating. Furthermore, it is likely that many cases of infection are not reported, or some mild cases may have been encountered and treated in local practices. Thus, the reported number of infections likely underestimates the true incidence of the problem.

Overnight wear is a principal risk factor for infectious keratitis among all types of contact lens users. Several studies have shown that overnight contact lens wear, including wear of high-oxygen-transmissibility RGP lenses, impairs the epithelial barrier because of the reduced oxygen transmission through contact lens. In addition, lack of eye movements that help disrupt the bacterial glycocalyx and spreads lysozyme over the corneal surface can render the eye more susceptible to bacterial infection.

Ren et al establish the importance of lens oxygen transmissibility in controlling P. aeruginosa binding to the corneal epithelium, not the lens. Their follow-up report shows that a hyper-oxygen-permeability (Dk) RGP polymer that produces no lens-wear-related increases in P. aeruginosa binding to the cornea in an alignment fit does produce increased P. aeruginosa binding in an orthokeratology reverse-geometry design. As described before, we were unable to get the details of orthokeratology protocols in our patients. The most popular overnight orthokeraology lenses in our locality are Paragon HDS (paflufocon B with a Dk of 58), Paragon HDS (paflufocon D with a Dk of 100), Boston Equalens II (oprifocon A with a Dk of 85), and Siflufocon A (fluorosilicone acrylate polymer with a Dk of 81). Further epidemiologic studies would confirm if the new hyper-Dk RGP lenses provide less risk for infectious keratitis.

The reverse-geometry orthokeratology lenses are similar to traditional orthokeratology contact lens, but the base curvature of these lenses is designed to be flatter than the central corneal curvature. The reverse geometry design means that the secondary curve radius is steeper than the base curve radius. At the secondary curve junction, the lens and cornea form a tear reservoir exhibiting a band of midperipheral fluorescein pooling. This design improves the centration and stability of the lens on the cornea. However, compressive forces exerted by these lenses in the redistribution of corneal epithelium may damage the corneal surface, especially when it is already compromised from overnight lens wear. This may lead to an increased risk for infections. The locations and sizes of the corneal ulcers complicating orthokeratology could imply an improper fitting or dislocation of the contact lens. Unfortunately, we were not able to get the premorbid lens-fitting conditions. Further study to evaluate the relationships among the locations of corneal ulcers, lens fitting, and topography of compressed cornea is warranted.

Lens hygiene is important in contact lens wear and so would be expected to play a role in the infection related to orthokeratology. Most of our patients claimed they cleaned the lens strictly. Indeed, the fact that 12 patients had worn RGP lenses for more than a year attests to the diligence of their cleaning regimen and handling of the lenses. However, sampling of 4 available contact lens solutions produced positive culture results. Similar results have been published. Instilling in young children, who are enrolled in an orthokeratology program, and their parents the sense of the importance of proper lens hygiene and having them habitually use the standard cleaning procedure is thus very important.

Concerning the bacterial infections observed in the present study, the English literature review contains several case reports of infectious keratitis occurring after overnight orthokeratology. Of these 16 reported cases, 9 were caused by P. aeruginosa, one was Serratia marcescens, and 5 were Acanthamoeba; one had a negative culture result. A 16-case series of infection after orthokeratology has been reported in the Chinese literature. Taken together with our observations, P. aeruginosa is the most frequently isolated pathogen. This is not surprising, because P. aeruginosa is also the most common pathogen of contact lens-related corneal ulcers. Adherence of P. aeruginosa to RGP lenses and exfoliated epithelial cells has been studied.

Whereas Acanthamoeba keratitis was observed in only a single instance of overnight orthokeratology in the present study and in a previous study, Sun, et al from China reported 4 cases of Acanthamoeba keratitis complicated with overnight orthokeratology, and a report in the Chinese literature described a higher ratio (8 of 16 cases) of Acanthamoeba keratitis infection after orthokeratology. The known risk factors include swimming with contact lens still in place, washing lenses with tap water, or irregular disinfection for the patients with Acanthamoeba keratitis were not elaborated in these studies. The high ratio reported in the Chinese study might reflect geographic variation. However, Acanthamoeba should be taken into consideration in a patient with an atypical keratitis after overnight orthokeratology treatment. The early diagnosis and the prompt initiation of treatment with PHMB could make the visual outcome of Acanthamoeba keratitis favorable, as in our patient 13.

Our culture-positive rate (13/21, 61.9%) is consistent with that observed in other studies of contact lens-related corneal ulcer. Among the 8 culture-negative corneal ulcers, 7 of the involved eyes had received prior topical antibiotic therapy elsewhere. The negative culture results may have been a consequence of the tendency of local ophthalmologists to prescribe fluoroquinolones or other antibiotics for treatment of a corneal ulcer before referral of the patient to our hospital, a tertiary center.

When a contact lens wearer presents with a small corneal ulcer, it is crucially important to distinguish a noninfectious corneal infiltrate from infectious microbial keratitis. The presence of a moderate amount of pain, an overlying epithelial defect, surrounding corneal edema, or anterior chamber reaction in the patients with small corneal ulcers in our series suggested the diagnosis of infectious keratitis. This diagnosis was bolstered by the response of the patients to antibiotic treatment.

We reported a big series, may be the biggest one so far, of cases of infectious keratitis associated with overnight orthokertology. As overnight orthokeratology increases in popularity, the incidence of related infections will also likely increase. The long-term safety of overnight orthokertology should be evaluated thoroughly. Eye care practitioners who perform overnight orthokeratology have an obligation to warn their patients of this potential vision-threatening complication. Part of this obligation entails educating patients to the importance of strict adherence to proper contact lens hygiene. Patients must be informed to seek prompt medical attention when they experience signs or symptoms of infectious keratitis. Once an infection develops, the ophthalmologist needs to be aggressive in culturing and identifying the responsible organism. Prompt and aggressive management of this potentially vision-threatening complication can result in preserving useful vision.

Conclusions:

Infectious keratitis is a potential complication of overnight orthokeratology that may cause significant visual impairment. Parents of children who consider overnight orthokeratology should evaluate the benefit of temporary myopia reduction and the risk of infection.

Vitrectomy and gas tamponade without internal limiting membrane peeling for myopic foveoschisis.

2007-01-12T03:41:00.000-08:00

Macular retinoschisis with foveal detachment is a condition that occasionally occurs in highly myopic eyes with posterior staphyloma and is also known as myopic foveoschisis. With the use of optical coherence tomography (OCT), it has been estimated that the prevalence of macular retinoschisis in highly myopic eyes with posterior staphyloma ranged from 9% to as high as 34%. Although the exact pathogenesis is uncertain, it has been postulated that myopic foveoschisis is a result of vitreous traction and may have a role in the formation of myopic macular hole.

Patients with myopic foveoschisis have variable severity of visual impairment and they may be asymptomatic due to the underlying myopic chorioretinal degeneration. In symptomatic patients with reduced vision or central metamorphopsia, pars plana vitrectomy with internal limiting membrane (ILM) peeling and gas tamponade have been shown to result in the resolution of myopic foveoschisis with visual improvement. The rationale of ILM peeling is to remove the macular traction that might have caused the myopic foveoschisis and the associated retinal detachment. This is similar to the basis of ILM peeling in idiopathic and myopic macular holes for improving macular hole closure rates. ILM peeling may also remove collagen fibres and cell debris which are frequently observed in the inner surface of ILM removed from patients with myopic foveoschisis.

Despite evidence suggesting that vitrectomy with ILM peeling is beneficial for the treatment of myopic foveoschisis, it remained unclear whether ILM peeling is essential in treating myopic foveoschisis. ILM peeling is technically challenging due to its transparency and friability. In highly myopic eyes, ILM removal is even more difficult as the ILM in highly myopic eyes seems to be thinner and tends to fragment into pieces during its removal. The use of dye staining like indocyanine green or trypan blue has improved the visualisation of ILM for removal but potential retinal toxicities have been demonstrated in both laboratory and clinical studies. Therefore, it will be of interest to determine whether vitrectomy without ILM peeling will be sufficient in treating myopic foveoschisis. The purpose of this prospective study is to evaluate the outcomes of vitrectomy and gas tamponade without ILM peeling for the treatment of highly myopic patients with symptomatic visual impairment as a result of myopic foveoschisis.

DISCUSSION

The pathogenesis of myopic foveoschisis is poorly understood and traction caused by premacular vitreous cortex has been postulated to contribute to its development. Another proposed factor is the posterior ectasia associated with posterior staphyloma in high myopia, resulting in a “stretch retinoschisis”. A degenerative process involving the posterior retina may be another factor associated with myopic foveoschisis as a previous study has shown posterior pole microcystoid degeneration in myopic patients with foveoschisis using OCT.

The level of visual impairment in patients with myopic foveoschisis is variable and vitrectomy with ILM peeling and gas tamponade has been demonstrated to be useful in treating symptomatic cases. Kanda and coworkers reported both anatomical and visual improvements after vitrectomy with ILM peeling and gas tamponade in two highly myopic eyes with myopic foveoschisis. Kobayashi and Kishi carried out a prospective study to evaluate the use of vitrectomy with ILM peeling in nine eyes of seven patients with myopic foveoschisis.

Foveal reattachment was achieved in eight (88.9%) of the nine eyes after surgery; one eye developed a microhole at the macula during brushing of the retinal surface with a silicone tipped cannula for removal of premacular vitreous cortex. All eyes had visual improvement postoperatively. In another study conducted by Ikuno and associates, vitrectomy with ILM peeling was performed in six eyes with myopic foveoschisis. Five (83.3%) eyes had complete resolution of the myopic foveoschisis and one eye had partial resolution. Although there was a lack of complete foveal reattachment in all cases, all cases had visual improvement postoperatively. Despite results from these studies, it remained unclear whether ILM peeling was necessary for treating myopic foveoschisis and the ideal surgical approach remained speculative.

The rationale of ILM removal in epiretinal membrane surgery is to ensure complete removal of any residual microscopic epiretinal membrane that may be present on the ILM in order to minimise epiretinal membrane recurrence. Likewise, in patients with myopic foveoschisis, the aim of ILM peeling is to obtain complete relief of macular traction by complete removal of the premacular membrane and vitreous cortex that may reside on the ILM. Another reason to peel the ILM is due to its rigidity and ILM removal may allow the retina to conform better to the posterior staphyloma. ILM peeling may also help to remove the collagen fibre and cellular components that may be present in ILM in eyes with myopic foveoschisis. However, ILM peeling may be technically more difficult in patients with myopic foveoschisis as a result of the associated retinal thinning at the macula. This may predispose complications like iatrogenic macular hole to occur due to surgical trauma. It would therefore be useful to determine whether pars plana vitrectomy without ILM peeling followed by gas tamponade could result in similar success compared with ILM removal.

In our study, seven (77.8%) of the nine eyes had complete resolution of the myopic foveoschisis and resulted in visual improvement postoperatively. Benhamou and coworkers have previously described the outcome of pars plana vitrectomy without ILM peeling in three eyes with myopic foveoschisis associated with vitreous traction. The thickness of the retinoschisis and visual acuity remained the same after the operations and one eye developed a macular hole shortly after vitrectomy. It appeared that gas tamponade was not used in their patients. In our study, with the use of gas tamponade, we achieved similar anatomical and visual results compared with previous studies in which vitrectomy and ILM peeling was performed for myopic foveoschisis. Our results suggest that without ILM peeling, vitrectomy alone followed by gas tamponade may be useful for treating symptomatic patients with myopic foveoschisis.

There are several limitations in our study. Firstly, only a small number of patients were included and a longer period of follow up with more cases will be beneficial in demonstrating the long term recurrence rate of myopic foveoschisis in these patients. Secondly, histological analysis was not performed on the removed epiretinal membrane specimens and it remained uncertain whether small pieces of ILM were actually removed inadvertently in small areas together with the premacular epiretinal membrane. Another limitation was that not all patients uniformly received combined cataract and vitreoretinal surgery. In more than 50% of eyes, concurrent cataract surgery was performed together with vitrectomy. None of these patients had visually significant cataract and cataract surgery was carried out to avoid subsequent lens surgery.

In summary, vitrectomy and gas tamponade without ILM peeling appears to have favourable visual and anatomical outcomes for treating myopic foveoschisis in highly myopic eyes with posterior staphyloma. Further prospective controlled studies in the future will be useful in demonstrating the effects of ILM peeling compared with no ILM peeling on the outcome of vitrectomy for myopic foveoschisis.

Acanthamoeba Keratitis During Orthokeratology.

2007-01-09T03:54:00.000-08:00

Infection is a serious adverse reaction of contact lenses, and its risk increases with continuous wear. Ulcerative keratitis has complicated orthokeratology in which a contact lens is worn to mold the cornea. Many reported cases of microbial keratitis associated with orthokeratology are caused by Pseudomonas aeruginosa, but Acanthamoeba is becoming recognized as a prevalent cause. I report a culture-confirmed case to highlight this emerging problem.

DISCUSSION

Orthokeratology reshapes the cornea by programed fitting of rigid gas-permeable contact lenses that may involve overnight lens wear. Bacterial keratitis is the most common infectious complication. However, several patients, mostly teenagers, have developed amoebic keratitis during orthokeratology.

Acanthamoeba keratitis is an emerging problem of orthokeratology that largely affects younger contact lens wearers. Rigid lenses are associated with Acanthamoeba keratitis, but Acanthamoeba keratitis occurs more often with soft than with hard lenses. The risk of ulcerative keratitis with rigid gas-permeable contact lenses is greater when they are worn overnight, but why the spectrum of microorganisms infecting patients undergoing orthokeratology might differ from that of other rigid contact lens wearers is unclear.

Eye-care practitioners commented 25 years ago that “orthokeratology remains experimental” and should “not be practiced on children until it has undergone appropriate clinical trials.” The practice of orthokeratology has evolved and grown, but definitive studies are still needed to determine the incidence and predisposing factors of infectious complications. Warning patients and parents about vision-threatening complications should be part of contact lens fitting.

Results:

A 16-year-old girl developed laboratory-confirmed acanthamoebic keratitis during orthokeratology for myopic reduction. Recent case reports suggest that Acanthamoeba is a cause of microbial keratitis associated with gas-permeable contact lenses among teenagers and young adults undergoing orthokeratology.

Conclusions:

Acanthamoeba keratitis is an emerging complication of orthokeratology in young myopes.

Post-LASIK Corneal Flap Displacement Following Penetrating Keratoplasty for Bullous Keratopathy.

2007-01-06T03:41:00.000-08:00

With improved microsurgical techniques, penetrating keratoplasty (PKP) has become a more common and successful procedure, with approximately 35,000 surgeries performed annually. Visual rehabilitation following a penetrating keratoplasty is often challenging because of anisometropia and astigmatism. Most patients will not tolerate more than 3 diopters of anisometropia because of image size disparity or astigmatism of greater than 1.5 to 3 diopters.

Rigid gas-permeable (RGP) contact lenses have been the mainstay of refractive rehabilitation following PKP. However, surgical options may be the only alternative to treat post-PKP refractive error. Kirkness et al reported a series of 201 corneal transplants for keratoconus and found that 18% of patients required refractive surgery for the correction of post-PKP astigmatism.

With the demonstrated success of photorefractive keratectomy (PRK) in treating myopia and astigmatism, PRK has been studied and used to treat post-penetrating keratoplasty refractive errors. However, significant haze following PRK is especially problematic in patients who have undergone prior keratoplasty. The corneal haze may reduce best spectacle-corrected visual acuity (BSCVA), induce regression and irregular astigmatism, and cause visual symptoms including haloes, blurred vision, and glare. Maloney and colleagues described a 29% incidence of corneal haze in patients undergoing PRK for visual rehabilitation following PKP.

Laser in situ keratomileusis (LASIK) has been demonstrated to offer patients the opportunity to be visually rehabilitated following a corneal transplantation. The first series of LASIK following penetrating keratoplasty reported a mean reduction of myopia from 7.58 diopters to 1.14 diopters and cylinder from 3.64 diopters to 1.48 diopters. BSCVA improved or remained the same in 21 of 23 patients, and all patients had less than 3 diopters of anisometropia. Additional studies have confirmed the safety and efficacy of LASIK following PKP for the management of residual refractive errors. Although LASIK has revolutionized the visual rehabilitation of the corneal transplant patient, no surgical procedure is risk-free. The purpose of this study is to report 3 patients who experienced flap dislocation following penetrating keratoplasty for bullous keratopathy.

DISCUSSION

All 3 patients had bullous keratopathy as the indication for penetrating keratoplasty, and all had peripheral corneal edema at the time of the LASIK procedure, with flap slippage occurring at a mean of 7 days postoperatively (range 3 to 14 days). The incidence of flap dislocation in this population of eyes following PKP was 1.85% compared with an incidence of 1.22% of complete and partial flap dislocation after LASIK in normal corneas. The incidence of flap dislocation in a recent study of LASIK following PKP of 57 eyes was as high as 9%. The peripheral corneal edema was the common factor in these 3 post-LASIK patients who had had a prior PKP for bullous keratopathy. To our knowledge, this is the first report of a series of patients experiencing corneal flap dislocation following LASIK after PKP for bullous keratopathy.

The final results of treatment of flap slippage were varied. One patient had a 2-line loss of BSCVA after flap slippage and underwent flap suturing, with an UCVA of 20/40 and a return to preoperative BSCVA of 20/25. One patient had a flap suturing with no change in BSCVA of 20/40. The final patient initially had a 5-line loss of BSCVA following flap repositioning, and underwent a repeat PKP for decreased visual acuity due to irregular astigmatism. His final BSCVA demonstrated a 2-line decrease in BSCVA.

This small case series highlights the importance of the endothelial pump function in maintaining the adherence of the LASIK flap. The corneal flap following LASIK is initially held in place by suction created by the pumping function of the endothelium against an intact epithelium. Any evidence of epithelial or stromal corneal edema is a sign that the endothelial pump function has been reduced below the natural swelling pressure of the cornea, and the adherence of the flap may not be adequate to prevent flap slippage.

Risk for development of corneal edema is increased in corneal grafts because of their decreased number of endothelial cells. The mean human endothelial cell density starts at about 4000 cells/mm2 in the first decade of life. As the eye ages, the average cell density gradually levels off to approximately 2600 cells/mm2 by age 40 but decreases to less than 300 cells/mm2 in patients with bullous keratopathy. The average cell density of donor corneas is around 2665 cells/mm, but grafts undergo a more rapid and continual decline in endothelial cell count than do normal corneas, with cell loss of 7.8% per year for the first 5 postoperative years, followed by a 4.7% annual decline for years 5-10. This is contrasted to a 0.5% per year decline in normal controls.

If the corneal endothelial barrier is injured, the corneal thickness can increase more than two-fold. A wounded endothelial barrier will cause a much greater increase in corneal thickness than a damaged epithelial barrier. The corneal stroma swells once the barrier or metabolic pump function is damaged because of the hypertonicity of the stromal milieu, which contains collagen, proteoglycans, and salts that are hypertonic to both tears and aqueous humor. These factors contribute to the corneal stromal swelling pressure, which has been determined to be approximately 60 mm Hg. The corneal stroma will also become edematous if the endothelial barrier is disrupted because the normal intraocular pressure of 15 mm Hg will be unopposed, and aqueous will diffuse into the stroma.

Even if a corneal graft is clear and nonedematous before LASIK, the surgeon needs to consider the possibility of endothelial compromise from the LASIK procedure itself. Although some studies have found no long-term endothelial effects of LASIK, 1 study does demonstrate post-LASIK changes in corneal morphology. Jones and colleagues found no effect on the endothelium in 98 eyes followed up to 12 weeks after LASIK. Pérez-Santonja and associates who followed patients over 6 months found that endothelial parameters in contact lens wearers actually improved after LASIK because of the discontinuation of contact lens wear. One study of 4 patients who underwent LASIK after penetrating keratoplasty and were followed for 12 months found no change in the endothelium. However, changes in endothelial cell morphology, probably related to transient corneal edema, were noted at 15 minutes postoperatively by Kim et al. Although these changes resolved by the first postoperative day, they could compromise endothelial pump function in postkeratoplasty eyes.

As part of the LASIK evaluation in postkeratoplasty eyes, we recommend a careful examination of the corneal graft for evidence of corneal edema. Because corneal endothelial function is best measured by corneal pachymetry, the pachymetry should be reviewed not only for adequate post-LASIK bed thickness but also for evidence of edema. Specular microscopy may be performed if there is clinical suspicion of low endothelial cell density. Once epithelial edema or bullae have occurred, the pump function of the endothelium has been overwhelmed, resulting in decreased flap suction, which increases the risk of flap dislocation.

For LASIK performed on a postkeratoplasty eye with Fuchs dystrophy or pseudophakic bullous keratopathy, or any postkeratoplasty eye in which the endothelial pump function may be marginal, we recommend an 8.5-mm-diameter superior hinge flap, particularly when the peripheral host bed has frank edema. None of the cases in this series had a superior hinge combined with an 8.5-mm-diameter corneal flap. If the peripheral cornea is edematous and the pump function of the endothelium is decreased, it is more likely the peripheral flap will elevate and dislocate following a blink. A larger flap will have a greater surface area over the peripheral edematous bed, and the edge of the flap may elevate, whereas the smaller diameter flap has less tissue overlying the edematous peripheral bed and is less likely to elevate. We recommend a superior flap for patients who undergo LASIK following PKP for bullous keratopathy because the natural gravitational effect will tend to hold the flap in place better than a nasal hinge flap.

We also recommend that patients with endothelial compromise who undergo LASIK wear protective shields for a longer than normal period and be followed closely to reduce the risk of flap slippage. Endothelial cell density may be helpful in all patients after corneal transplant in whom refractive surgery is being considered. Eyes with corneal transplants may lose endothelial cells at a more rapid rate than normal eyes and not always display typical guttata; therefore, specular microscopy may also be helpful in recognizing those eyes at risk for poor failure.

Furthermore, for eyes undergoing LASIK after PKP, consideration could be given to suturing edematous flaps to prevent a flap dislocation. Another consideration is increasing the use of topical steroids every 2 hours in corneal transplant patients because of the slight increase in cornea rejection caused by the trauma of the surgery and the fact that the endothelial cells may experience some disruption in function, which can be ameliorated by additional steroids. We suggest that endothelial compromise should be added to the list of risk factors for flap dislocation.

Conclusion:

Flap displacement may occur following LASIK in patients who have undergone PKP for bullous keratopathy. The endothelial pump function, which is vital to maintaining flap adherence, may be compromised in these patients. We suggest that patients with a history of PKP and endothelial compromise who undergo LASIK wear protective shields for a longer than normal period and be followed closely to reduce the risk of flap slippage.

Refractive Errors in Children With Vision Impairment.

2007-01-03T03:27:00.000-08:00

Emmetropization is the reduction in neonatal refractive errors that occurs after birth. This process uses a visual feedback system with successful emmetropization thought to be dependent on good retinal image quality, accurate focusing, and intact visual pathways. Ocular disease may affect one or more of these requirements, disrupting the emmetropization process and resulting in refractive error persistence or development.

Although the majority of research in the field of refractive error control and myopia development typically involves normally sighted children, the study of the refractive errors of children with ocular and visual pathway defects can provide further insights into the underlying mechanisms of emmetropization. For example, it has been suggested that the location of retinal pathology may play a role in the type of refractive error that occurs. Conditions that cause retinal image degradation such as cataracts and ptosis appear to be associated with myopia and failure of emmetropization. Similarly, children with visual pathway defects are also likely to have large refractive errors, although there is no specific trend in terms of the type of error observed. Because children with vision impairment often have associated mental and/or physical disabilities, characterizing the refractive anomalies present in the pediatric vision-impaired population would assist the clinician in the prescription of suitable vision correction.

The causes of vision impairment in children based on data collected from children attending schools for the visually impaired or records from low-vision clinics vary greatly between regions. For example, the high socioeconomic status of children in countries such as the United States, Nordic region (Denmark, Finland, Iceland, and Norway), and Australia has virtually eliminated the infectious and nutritional diseases that are still the major causes of childhood blindness in developing countries. In third world countries, infections and poor nutrition predominate as factors associated with vision loss. Corneal ulcerations, toxoplasmosis, and other ocular scars account for 43.5% of vision impairment in Brazil and 22.0% in Africa, whereas these causes only account for 2.0% in Australia.

In 1982, Lovie-Kitchin and Bevan reported data from a retrospective study of 398 vision-impaired children from the Pediatric Low Vision Clinic (PLVC), a statewide service for children with vision impairment based in Brisbane, Australia. These authors found that primary congenital nystagmus was the most common cause of vision impairment in children, accounting for 17.6% of the sample size. Other causes were congenital cataracts (15.8%), rubella syndrome (9.3%), albinism (7.5%), primary optic atrophy (6.3%), secondary optic atrophy (5.0%), and the remaining 38.5% consisted of many less frequent conditions such as ectopia lentis, rubella retinopathy, retinoblastoma, and congenital glaucoma. In a more recent study in the United States, the most common causes of vision impairment in 2 to 20 year olds were congenital cataracts (13%), optic atrophy (13%), albinism (13%), glaucoma (8.1%), retinitis pigmentosa (8.1%), and chorioretinal degeneration (8.1%).

DISCUSSION

This study analyzed the ocular conditions and the relative frequency and magnitude of refractive errors in children with vision impairment, and the effect of age and type of ocular disease. This study included data on more children with vision impairment than has been reported in the past in Australia. Few studies have examined the refractive errors of children across a range of different conditions that cause vision impairment.

Cause of Vision Impairment

The relative proportion of children with aphakia or cataract leading to vision impairment has decreased significantly (from 15.8% in 1982 to 5.73% in 2002). Improvements in surgical techniques and compulsory vaccinations (e.g., rubella) are likely factors in reducing the prevalence of rubella cataracts in children. CVI has now become the most frequent cause of vision impairment. In 1982, CVI was virtually unheard of (accounting for 0% of proven diagnoses); within 20 years, it has surged to 27.6%. Advancements in technology in recent times have resulted in increased survival rates of premature low-birth-weight babies, and this presumably accounts for some of the observed increase in CVI and ROP numbers. Some of the increase in the number of children with CVI may also be due to diagnosis as more referrals of these children are now made for support service assessment.

Although the data was not significant, more boys than girls appeared to have conditions such as albinism, retinitis pigmentosa, aphakia, cataracts, and CVI. Fifty-eight percent of the records were from male children and the remaining 42% were from female children. This is consistent with previous reports of vision impairment being more common in boys (percentage of boys in study samples ranges from 54 to 60). This tendency for boys to have more vision problems does not appear to have altered over time. Although some of this difference is clearly the result of the sex-linked genetic nature of some conditions causing vision impairment, other reasons may exist for the gender differences; perhaps male babies are less resilient than female babies or more like to be damaged by adverse environmental conditions during gestation.

Refractive Errors Associated With Vision Impairment

The principal finding of this study is that vision impairment in children is likely to be associated with ametropia. Fewer than 25% of vision-impaired children had refractive errors within ± 1 D. In contrast, almost 80% of normally sighted children satisfy this refractive error criteria (except in Asia, where many develop myopia). The small proportion of children in our study with refractive errors between ± 1 D (23%) is similar to that reported by Nathan and colleagues (30%). The leptokurtotic characteristic of the distribution of refractive states of the normal population is not apparent in the total low-vision group nor, more significantly, within the individual age bands. The refractive error distribution of children with vision impairment resembles a bell-shaped curve rather than the significantly leptokurtotic distribution displayed by normally sighted children.

The large refractive errors of children with vision impairment suggests that the process of emmetropization fails in most cases in which visual quality is reduced, whereas eyes of normally sighted children undergo a process of emmetropization. In normally sighted children, the (Gaussian) distribution of refractive errors at birth changes to a significantly non-Gaussian adult distribution in which there is a preponderance of refractive errors around emmetropia or slight hyperopia. The relative frequency distribution of children with vision impairment begins as a normal distribution, but instead of becoming a narrower distribution, the distribution becomes more Gaussian-like with an associated decrease in kurtosis. Furthermore, the standard deviation of the refractive errors of a group of children with vision impairment is much greater than that of a group of normally sighted children. For the entire group, the standard deviation was 6.00, which was markedly larger than the 0.82 to 0.95 reported for normally sighted children. This suggests that the majority of children with vision impairment do not undergo normal emmetropization.

The mean spherical equivalent refractive errors of children with vision impairment differ from that of normally sighted children. Compared with a recent study of normally sighted children, the mean refractive error of children with vision impairment is less hyperopic or more myopic compared with normally sighted children. The large variation of refractive errors in children with vision impairment and the deviation of the refractive error from the norm demonstrate a relationship among ocular disease, image processing deficits, and inaccurate emmetropization.

Whereas statistical comparison of the variation of refractive errors of the group of children with vision impairment and that of children with normal vision (based on published data) was possible, statistical comparison of the means was not possible as a result of large differences in the standard deviations of the two groups of data. Unpaired two-tailed t-tests could not be used because the two-sample standard deviations were statistically different and hence violated the assumption of t-tests. Wilcoxon signed rank test, the nonparametric version of t-test, could be used if a full dataset for normally sighted children were available. Our study did not include a control group of normally sighted children because this information is already well described in the literature and only children with visual impairment attended this clinic.

Refractive Errors Associated With Specific Conditions

Few reported studies have examined the refractive errors of such a large range of ocular conditions. Nathan and colleagues’ study presents a good base for comparisons owing to its similar subject population (Melbourne, Australia versus Brisbane, Australia) with similar age ranges (to 16 years versus to 17 years) and similar ocular disease classifications. Of the eight conditions in common, only two conditions showed good correlation in spherical equivalent refractive errors: ROP and rod monochromatism. Differences between the studies were observed for the other conditions, for example, coloboma and retinitis pigmentosa. Such differences could be attributed to the difference in time frame of the studies (1985 versus 2002) and thus differences in health care. Our refractive data are similar to that reported in studies that have examined only one ocular condition. For example, our results for albinism (+2.19 ± 2.96 D), CVI (+0.92 ± 3.03 D), and retinitis pigmentosa (-0.97 ± 5.63 D) are similar to that reported by Wildsoet et al. (+1.07 ± 4.67 D), Tuppurainen (+1.54 ± 1.58 D), and Sieving et al. (-2.04 ± 4.07 D) for albinism, CVI, and retinitis pigmentosa, respectively.

The relative frequency distribution of astigmatic refractive errors in children with vision impairment shows a preponderance of low (0 to 1 D) astigmatic errors (69.9%). Nathan and colleagues demonstrated a similar result (64.8%). However, this is quite different from normally sighted children (18.4%). It has been shown that the prevalence of astigmatism in normal infants is high (42%), but the prevalence declines sharply after 6 months of age to reach a minimum of 5% from 6 to 10 years, and then slowly rises after that. Data of Abrahamsson and colleagues also support the view that astigmatism decreases in power as the infant grows older, and this change is especially notable between the first and second year of life. This does not seem to be the case for vision-impaired children. The relative frequency of low amounts of astigmatism decreased with age with an associated increase in higher amounts of astigmatism.

Seven of the 10 most common ocular conditions in the sample population showed higher astigmatic refractive errors in older age groups. Hence, there appears to be a relationship between image processing deficits, i.e., visual impairments, and higher amounts of astigmatism.
Children with vision impairment showed increasing frequency of anisometropia with age (relative frequency of anisometropia more than 1 D: 13.0% at 0 to 2 years, 25.1% at 6 to 8 years, and 30.5% at 12 to 14 years). In normally sighted children, anisometropia is rarely found with prevalence in the range of 1.4 to 7.7%. In cross-sectional studies covering several age groups, the prevalence of anisometropia in normally sighted children is independent of age. This apparent stability is the result of anisometropia decreasing in some children and developing or increasing in others. This difference in anisometropia further supports the conclusions that the coordination of eye growth of visually impaired children is not regulated as well as normally sighted children.

CONCLUSIONS

The causes of vision impairment in children have changed since the 1970s, with CVI now being the most common cause of vision impairment. Children with vision impairment often have an associated ametropia suggesting that the emmetropization system is also impaired.

Vitreoretinal surgery for macular hole after laser assisted in situ keratomileusis for the correction of myopia.

2006-12-30T03:21:00.000-08:00

Laser assisted in situ keratomileusis (LASIK) has become one of the most popular options for the correction of low to moderate myopia worldwide. However, vitreoretinal complications including endophthalmitis, retinal tear and detachment, retinal haemorrhage, and choroidal neovascular membrane have been reported.

Chan and Lawrence have reported three eyes of three myopic patients that developed a macular hole in one eye after bilateral LASIK or photorefractive keratectomy (PRK). Ruiz-Moreno et al recently reported a case of a macular hole in a myopic eye after LASIK. We previously reported in a letter to the editor 10 eyes (10 patients) with full thickness macular hole development after bilateral LASIK for the correction of ametropia.

DISCUSSION

Our findings support previous studies that showed the characteristics and demographics of myopic macular holes to be different from those of idiopathic macular holes. Myopic macular holes tend to develop in young subjects and may be associated with a retinal detachment surrounding the macular hole.

In the present series, posterior vitreous detachment was not present before and was documented after LASIK on 42.8% of eyes. Luna et al have used kinetic ultrasonography to demonstrate vitreoretinal alterations after LASIK, including partial or total PVD in 24% (12 eyes) in high myopes. Their findings are consistent with similar results in almost half of myopic eyes with macular hole after LASIK in our series.

Macular hole surgery can achieve substantial VA improvement for myopic eyes, but the results do not seem to be as favourable as those reported for typical idiopathic macular holes in recent series. In our series, only four (28.5%) eyes out of 14 had a VA outcome of 20/40. Case 12 was our only case with loss of VA after vitrectomy. However, silicone oil removal and cataract extraction are still pending, and could potentially improve final VA. Our results should be interpreted with caution, since multiple surgeons with different surgical techniques and training participated in this study.

The pathogenesis of macular hole remains controversial. Certainly, vitreofoveal traction is felt to be the predominant force together with pre-existing degenerative changes in the fovea. Chan and Lawrence have stated that LASIK surgery has certain features that may induce postoperative vitreoretinal interface changes. For instance, the acute intraocular pressure rise associated with the mechanical stretch of the vitreous base induced by the suction ring as well as the shock waves generated by the excimer laser may lead to vitreoretinal traction. Retinal breaks and detachment have also been reported to occur after laser in situ keratomileusis.

Our findings are not generalisable to all myopic eyes that undergo LASIK. However, myopia is a risk factor for macular hole formation. It is possible that vitreomacular interface changes occurring after laser in situ keratomileusis may predispose certain myopic eyes to form a macular hole. Nevertheless, there are not enough hard data in the literature to determine if these are just myopic holes that would have developed anyway regardless of LASIK.

OCT before LASIK may be helpful to identify those eyes at risk for the development of a macular hole. Chan et al have recently introduce the concept of a stage 0 macular hole based on OCT observations of the vitreoretinal interface in fellow eyes of patients with unilateral idiopathic macular holes, and to evaluate the subsequent risk of progression to a full thickness macular hole. In a retrospective observational case series of 94 patients with a unilateral stage 2, 3, or 4 full thickness macular hole. They found that in 27 (28.7%) of 94 clinically normal fellow eyes, OCT detected an abnormality of the vitreoretinal interface but normal foveal anatomy.

Eyes with severe and moderate vitreoretinal abnormalities seemed to share characteristic features on OCT that increased their risk of macular hole development (stage 0 macular hole). Univariate analysis revealed that the presence of a stage 0 macular hole was significantly associated with an almost sixfold increase in the risk of macular hole formation. They concluded that a stage 0 macular hole has a normal biomicroscopic appearance clinically, but has salient features on OCT as a result of oblique vitreous traction. Optical coherence tomographic findings consist of a normal foveal contour and normal retinal thickness and must include the presence of a preretinal, minimally reflective, thin band inserting obliquely on at least one side of the fovea. The presence of a stage 0 macular hole in the fellow eye is a significant risk factor for the development of a second macular hole.

An important limitation of our study is that, owing to its retrospective nature, OCT was not performed before LASIK. In addition, follow up was not consistent and it is possible that patients who developed a macular hole after LASIK were seen by other ophthalmologists outside of our institutions. Thus, we did not attempt to determine the incidence of macular hole formation after LASIK.

In summary, we present 14 eyes of 13 patients with no presurgical sign of a macular hole, which developed a full thickness macular hole after laser in situ keratomileusis. Our study shows that vitreoretinal surgery can be successful in restoring vision for most myopic eyes with a macular hole after LASIK. Vitreoretinal interface changes may have a role in macular hole formation after LASIK for the correction of myopia. Future prospective investigation involving a large number of myopic eyes with ultrasonic or ocular coherence tomographic studies may be valuable for determining vitreoretinal interface changes before and after LASIK.

Eye growth changes in myopic children.

2006-12-27T01:19:00.000-08:00

The reported rates of myopia progression (-0.70 dioptres (D) per year in Singapore children and -0.63 D per year in Hong Kong children) among myopic children in east Asian countries are among the highest in the world. The knowledge of changes in biometric patterns in myopic children will enable a better understanding of stimuli influencing growth patterns and continued shifts in refraction. Most previous studies have evaluated biometry parameters at one point of time in cross sectional studies. Changes in biometry parameters were documented in the Correction of Myopia Evaluation Trial (COMET) of 469 children aged 6–11 years with myopia between -1.25 and -4.5 D: the increase in axial length was 0.75 mm in the single vision lens group (n = 234) over a 3 year period. There are few reports describing the risk factors for changes in biometric parameters, although from cross sectional analysis of 2583 school aged children in the Collaborative Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) study, boys and older children had longer axial lengths.

There are few community based or school based longitudinal data describing risk factors influencing changes in biometry parameters in myopic children. We aimed to evaluate the pattern of biometry parameter changes and associated factors in young myopic children aged 7–9 years followed prospectively for 3 years in Singapore.

DISCUSSION

In our study, the 3 year increases in axial length (mean = 0.89 mm) and vitreous chamber depth (0.92 mm) in Singapore children are high. In contrast, the 3 year changes in anterior chamber depth, lens thickness, and corneal curvature were minimal. Children who were young, female, and who had myopic parents were more likely to have greater axial length increases. No associations between near work activity and biometry parameter changes were found.

The 3 year increase in axial length is high (0.89 mm), but similar to the single vision lens group of a Hong Kong study of myopic children aged 7–10.5 years (n = 133) enrolled in a trial evaluating progressive lenses, who showed similar increases in axial length (0.32 mm per year = 0.96 mm over 3 years). In the COMET trial, the rate of increase in axial length was slightly lower in myopic children aged 6–11 years in the single vision lens group: 0.75 mm over 3 years. In contrast, in a university study of 149 Norwegian engineering students (mean age of 20.6 years) across the refractive error range with a mean 3 year refractive change of -0.52 D, the 3 year change in axial length was 0.34 mm. Differences in the refractive error range, subject age limits, interethnic composition, and overall dropout rates, however, limit the conclusions from comparing the results of these studies.

Greater changes in axial length in younger children and females parallel the greater changes in refraction in the same age and sex patterns in this Singapore cohort. In our study, children who had one or two parents with myopia had greater increases in axial length change compared with children without any myopic parents. In a 24 year longitudinal study of 122 US children, the odds ratio of incident myopia for two myopic parents versus none was 5.09 (95% confidence interval (CI) 1.69 to 14.49). Previously, most epidemiological investigations have been cross sectional in nature. A cross sectional study of adults aged 17–45 years showed that if there were one or more highly myopic parent, the odds ratios of mild (SE -1.25 to -2.5 D), moderate (SE -3.75 to -4.75 D), and high myopia (SE at least -5.0 D) were 2.5, 3.7, and more than 5.5, respectively. In the Orinda Longitudinal study of 716 children aged 6–14 years, children with two myopic parents had more myopic refractive error compared with children with one or no myopic parents. Few studies, however, have evaluated the effect of parental history, a possible marker of shared common family environment or genetic susceptibility, on biometric parameter changes.

In the Finnish children’s study, reading was significantly associated with the progression of myopia. To our knowledge, there are few studies that have evaluated the effects of reading on the change in axial length. Reading in books per week was not associated with greater increases in axial length in our study. The initial cross sectional analysis of SCORM data showed that children who read more and who had myopic parents had larger axial lengths. The lack of any significant effects of lifestyle and familial risk factors on longitudinal changes on axial length change could perhaps be attributable to the narrow age range of the population, the rather young cohort, relatively short follow up, misclassification of near work activity, or to the possibility that the role of near work differs between myopia onset and myopia progression.

The rapid progression of myopia in our study is accompanied by elongation of the eye in the axial dimension. The posterior segment changes in severely myopic eyes include the stretching of the retina and the development of optic disc crescents and other pathological changes. In Singapore children, corneal power appears to have a minor role in the progression of myopia, consistent with the pattern found in other longitudinal studies. In a 2 year follow up study of 142 Hong Kong children aged 6–17 years with refractive error from -7.5 to +3.5 D, the myopic shifts in refractive error were driven by increases in axial length and vitreous chamber depth. Contrary to our findings, the flattening of the cornea (but only in the horizontal meridian) was associated with the progression of myopia in Hong Kong children. Lens thinning does not explain the shift of refractions towards the myopic direction, and among adult clinical microscopists, this effect is also minimal.

The advantages of our study include the relatively large sample size, the low dropout rate, and the availability of longitudinal biometry parameters in a school based cohort in a myopia endemic country. The 3 year dropout rate was 18.4% and children who withdrew from the study were not significantly different from children who did not withdraw.

In summary, the 3 year increase in axial length is high (0.89 mm). Axial length changes are greatest in the first 2 years of the study and highest in younger children, females, and children with a parental history of myopia. Children who read more were not more likely to have greater changes in biometry parameters. The rate of progression of myopia was significantly associated with changes in vitreous chamber depth.

Conclusions:

The 3 year change in axial length of Singapore children aged 7–9 years at baseline was high and greater in younger children, females, and children with a parental history of myopia. Myopia progression was driven largely by vitreous chamber depth increase.

Overnight Corneal Reshaping versus Soft Disposable Contact Lenses: Vision-Related Quality-of-Life Differences.

2006-12-24T23:34:00.000-08:00

Overnight corneal reshaping (OCR) or corneal refractive therapy (CRT) is a nonsurgical method of improving vision and decreasing dependence on glasses or traditional contact lenses. To compare patients’ experiences and preferences between OCR lenses and 2-week disposable soft lenses, currently the most commonly used mode of contact lens correction, we conducted a crossover study in which each subject wore each type of lens for 8 weeks.

DISCUSSION

Soft disposable lenses provide clear, comfortable vision correction for millions of wearers (approximately 33 million in the United States—nearly 12% of the U.S. population—representing approximately 50% of those who need vision correction between the ages of 18 and 34). Even so, many SCL wearers are not comfortable wearing lenses all day or for all activities. At the end of 2004, it was estimated that there were 50,000 OCR wearers in the United States. Previous studies have documented the corneal responses to OCR lenses and to soft disposable lenses. Soft disposable lenses have been used since the late 1980s, whereas Paragon’s CRT lens was granted U.S. Food and Drug Administration approval in June of 2002. Given the chance to experience these 2 modes of lens wear, two thirds of our study subjects preferred OCR lenses. This study population was mildly to moderately myopic. As such, these results must be considered relevant for such patients only.

The outcomes in this study show some definite differences between OCR and SCL wear. First, logMAR acuity with SCL was better than acuity with OCR. Even so, subjects’ rating of their vision was not significantly different between the 2 modes. Second, subjects felt less activity-restricted, had fewer symptoms of discomfort, and felt less dependent on correction while in the OCR mode but were more affected by glare while wearing the OCR lenses. It is apparent that subjects separate vision from comfort. As described in the “Results,” subjects who chose OCR rated their symptoms 20 points better (less symptoms) with OCR than with SCL.

On the other hand, subjects choosing SCL rated their clarity of vision 23 points higher with SCL and glare 40 points better with SCL. Wavefront testing that is becoming standard in LASIK evaluations may explain some of the reasons for the glare/visual distortions. A recent study of higher-order aberrations in clinically successful OCR cases showed significant increases in third-order (coma-like) and fourth-order (spherical-like) aberrations. Their study concluded that the increases in higher-order aberrations correlated with the amount of the myopic correction. It would be very helpful to be able to predict which patients will be bothered by glare/aberrations before treatment, but this study’s data could not be used to make that distinction.

Comparing mean OCR results on the RQL-42 with the normative data shows close similarities on all attributes except “glare” (lower with OCR, 58.3 vs. 76.4 in the normative data or more bothersome with OCR), “symptoms” (better with OCR, 90.3 vs. 79.2 in the normative data), and “dependence on correction” (better with OCR, 94.6 vs. 42.3 in the normative study or less dependent with OCR). The SCL mean results showed very close correlation to normative data on all attributes.

Although SCL are easy to wear, both the SCL preference group and the OCR preference group rated their symptoms as better with the OCR lenses. Subjective choice in this study showed a majority (67.7%) choosing to continue with OCR lenses.

In comparing alternative modes of vision correction, one study compared RQL-42 scores for a group of patients with OCR (CRT) versus a group of patients undergoing LASIK. That study showed no significant vision-related quality-of-life differences between the 2 groups at 3 months after treatment. These data suggest that OCR may compete with or complement LASIK as a result of similar candidate profiles. Another study compared RQL-42 of OCR with silicone/hydrogel lenses worn for 30 days continuously showing a significant difference in the “dependence on correction” attribute (possibly because of the nature of the instrument questions). The other attributes did not show statistically significant differences.

Safety in various modes of contact lens wear is a serious consideration. In this study, there were no adverse events with OCR or SCL. However, the 8-week follow up in this study was not long enough to establish relative safety or frequency of adverse events with either mode of lens wear. Previous studies have evaluated risk of adverse events while wearing soft disposable contact lenses on a daily-wear basis. Estimates are between one in 1500 and one in 15,000 soft lens wearers per year having events of microbial keratitis. There have been no studies as to the incidence of microbial keratitis with OCR, although there are published case reports of these events that total 41 cases worldwide (7 in the United States and 34 in other countries).

The strengths of this study were:

1) It was a randomized crossover study in which each subject wore both modes, they were their own control.

2) The RQL-42 is a validated instrument and there are normative data for refractive quality-of-life attributes.

3) The study outcomes were subjective and patient-focused.

4) Investigator bias was minimized because most of the outcomes were based on the patient’s self-report, not on investigator evaluations.

Also, there was equal sponsorship by the manufacturer of each mode of lens wear. One weakness of the study is that most patients attracted to the study stated they were interested in these “new” type lenses. Subjects may have been somewhat biased toward the OCR lens mode because of their interest in OCR or because of problems with their current lenses (a large majority previously wore SCL). Also, there was no cost to subjects for lenses in the study. Cost factors could influence patient preferences in a clinical practice setting. The study only dealt with subjects who had lower levels of myopia and therefore does not provide information on OCR versus SCL use in subjects with moderate to high myopia.

Visual acuity was good with both modes of lens wear but slightly better with SCL. However, this difference alone was not enough to determine overall preference. Our data show that of those subjects who experienced both modes of lens wear, 67.7% preferred OCR with a decreasing OCR preference as myopic refractive error increased. Lens preference is likely influenced by factors in addition to visual acuity. As the RQL-42 findings show, attributes like dependence on correction, glare, symptoms, and activity limitations differ between lens types and play a role in the patient’s overall assessment of their lens preference.

Conclusion.

In subjects with mild myopia who experienced both SCL and OCR, better visual acuity and less glare resulted from SCL wear, whereas activity limitations, symptoms, and dependence on refractive correction were less troublesome with OCR wear. When the study was completed, 67.7% chose OCR lenses worn only while sleeping, whereas 32.3% preferred 2-week disposable soft lenses worn during the day as their preferred correction.

Choroidal neovascularisation in pathological myopia: an update in management.

2006-12-21T23:39:00.000-08:00

Pathological myopia is a common cause of visual impairment worldwide. High myopia is more common in Asian populations, with rates of 9–21%, compared with 2–4% in white people. The pathogenesis of high myopia is associated with progressive and excessive elongation of the eyeball. In highly myopic eyes, the collagen fibres are pathologically abnormal and the smaller fibres have less cross linking than those in emmetropic eyes. These factors predispose the development of various degenerative changes involving the sclera, choroid, and retina.

VITREORETINAL MANIFESTATIONS AND LACQUER CRACKS IN HIGH MYOPIA

The vitreoretinal manifestations in pathological myopia are associated with varying degrees of visual loss and they include posterior staphyloma, diffuse or patchy chorioretinal atrophy, retinal pigment epithelial atrophy, lacquer cracks, spontaneous subretinal haemorrhages, and macular choroidal neovascularisation (CNV). Lacquer cracks are formed by ruptures in Bruch’s membrane, in which small haemorrhages may develop, and predispose high myopes to rapid visual loss. Small fibrovascular tissue ingrowths may cause elevated pigmented circular lesions (Fuchs’ spots).

CHOROIDAL NEOVASCULARISATION IN PATHOLOGICAL MYOPIA

Incidence of myopic CNV

Macular CNV is the most vision threatening complication of myopia. It is also the most common cause of CNV in young individuals in many countries, accounting for 62% of CNV in patients aged 50 years or less in one series. The risk of developing myopic CNV is 5–11%. Among pre-existing myopic CNV patients, more than 30% will develop CNV in the fellow eye within 8 years. Clinical findings predisposing to myopic CNV include patchy chorioretinal atrophy and lacquer cracks.

Clinical features of myopic CNV

Typically, myopic CNV is a small, flat, greyish, subretinal membrane which is less than 1 disc diameter in size and is located between the neurosensory retina and retinal pigment epithelium (RPE) (type 2). Whereas the CNV secondary to age related macular degeneration (AMD) is usually in the sub-RPE space (type 1). Most myopic CNV is subfoveal or juxtafoveal with minimal subretinal fluid or exudate.

Fluorescein angiographic findings of myopic CNV

Myopic CNV tends to have a classic pattern of leakage on fluorescein angiography (FA). With the aid of stereoscopic FA, CNV may appear as plaque-like elevation with pigmented halo and sharply defined borders. In one series, 83% (100/120 eyes) showed the classic angiographic pattern with transit phase hyperfluorescence followed by minor leakage in late phases.

Indocyanine green angiographic findings of myopic CNV

Indocyanine green angiography (ICG-A) provides supplementary information to FA. Since myopic CNV are usually small with minimal leakage, it may be difficult for FA to distinguish CNV from mild hyperfluorescence caused by other lesions. ICG is minimally absorbed by RPE and blood and so allows better differentiation of CNV from other pathologies, especially if haemorrhage is present. ICG-A may also allow more precise CNV localisation and feeder vessel detection.

Optical coherence tomographic findings of myopic CNV

Optical coherence tomography (OCT) produces high resolution cross sectional images of the retina and is useful in evaluating the morphology of various macular pathologies, including CNV. OCT can provide supplementary information while making treatment decisions by demonstrating various stages and activities of myopic CNV, providing clues to CNV location, and identifying optimal cases for submacular surgery. For instance, the CNV located anterior to and separated from the RPE layer, appearing as an optically clear zone around the CNV on OCT, may be the best candidates to be considered for surgical removal.

Multifocal electroretinogram abnormalities in myopic CNV

Multifocal electroretinogram (MfERG) provides topographic retinal mapping through simultaneous stimulation of different locations, giving a longitudinal assessment of retinal function in myopic CNV, with a moderate to strong correlation between visual function by MfERG and visual acuity (VA). MfERG is also useful for monitoring changes in retinal function after photodynamic therapy (PDT).

MANAGEMENT OF CNV IN PATHOLOGICAL MYOPIA

Natural history

A predominance of myopic CNV in females (67%) may reflect oestrogen receptor expression in CNV and the external influence of oestrogen. Unlike CNV in AMD, more than 50% of affected patients have a presenting age of 50 years or less. Presenting VA depends on CNV location; subfoveal involvement is usually associated with VA between 20/40 and 20/100.

In order to determine the optimal management for patients with myopic CNV, studies over the natural history of myopic CNV become vital but results are conflicting.A few studies have reported favourable outcome with observation alone, while others have described a poor prognosis. The discrepancy in visual outcome may be partly attributed to insufficient duration of follow up of most studies.

Fried et al studied 55 eyes with Fuchs’ spots with a mean duration of 5 years and 63% of eyes were noted to have stable or improved vision. A limitation of the study was 23% of eyes did not have angiographic evidence of CNV. In another study by Avila et al, 70 eyes with myopic CNV were followed for a mean of 3.4 years and 96% of the CNV regressed or remained stable.

Tabandeh et al reported the natural outcome of 22 patients with myopic CNV aged 50 or more after a mean follow up of 4.1 years and 73% had a final visual acuity of 20/200 or worse. Secretan et al had made a 5 year observation of 50 eyes with juxtafoveal or extrafoveal myopic CNV; all lesions became subfoveal with a mean visual acuity of 20/160.

A recent study conducted by Yoshida et al reported the long term visual outcome of 27 eyes with a minimum follow up of 10 years; 70.4% of eyes had a baseline visual acuity better than 20/200 while 55.5% of eyes still retained visual acuity of better than 20/200 after 3 years. However, by 10 years, 96.3% of eyes had a visual acuity of 20/200 or worse. This study confirmed the poor long term prognosis of myopic CNV with observation.

Several studies have evaluated the prognostic factors in patients with myopic CNV. In a retrospective review of 73 eyes in 63 patients with myopic CNV, patients aged more than 40 years at onset had poorer initial VA and significantly reduced VA during follow up. To determine the influence of age on the outcome, Hayashi et al demonstrated that younger patients, smaller CNV, and better initial visual acuity were more likely to have a good prognosis. Kojima et al observed that chorioretinal atrophy is the main cause of poor long term visual prognosis in myopic CNV and older age and larger CNV were factors for the atrophy. These studies on the natural history of myopic CNV give us the clues that active interventions should be considered for patients with myopic CNV.

Direct thermal laser photocoagulation: visual outcomes and complications

Once the only treatment, thermal laser photocoagulation is of limited benefit in myopic CNV. In a study by Jalkh et al, of 19 eyes with extrafoveal CNV all had a dry atrophic photocoagulation scar a mean 29.2 months after direct thermal laser with 11% having visual improvement. In another study, laser photocoagulation resulted in complete closure of myopic CNV but VA had deteriorated in all the 16 study eyes at the final follow up. In a comparison of laser photocoagulation and natural history by Secretan et al, laser treated eyes had statistically better VA at 2 years but this difference was insignificant after 5 years. Similarly, initial beneficial effects of laser photocoagulation in juxtafoveal myopic CNV were insignificant after 3 years in another series. Such late failure is generally due to expansion of the laser scar (atrophic creep) which is seen in 92–100% of the treated eyes. CNV recurrence, which can occur in up to 72% of the treated eyes, in which 36% were subfoveal, may be due to secondary lacquer crack development.

Photodynamic therapy with verteporfin

The selectivity and efficacy of PDT is the result of differential clearance of verteporfin in the blood and preferential binding to CNV endothelial low density lipoprotein receptors. Activation by diode laser generates reactive oxygen species which occlude abnormal CNV. Selective choriocapillary endothelial damage is the major mechanism of action of PDT. Sparing of damage to the neurosensory retina, RPE, and optic nerve makes PDT particularly useful in treating subfoveal CNV. Phase I/II studies, as well as larger phase III/IV studies, have demonstrated PDT’s ability to reduce visual loss in patients with subfoveal CNV caused by AMD and pathological myopia.

Subfoveal myopic CNV

The VIP study is the largest study addressing the efficacy and safety of PDT with verteporfin in treatment of subfoveal CNV caused by pathological myopia. One hundred and twenty patients were randomised into the verteporfin treated and placebo treated groups. At 12 months, 72% of verteporfin treated eyes compared with 44% of placebo treated eyes had a visual loss of fewer than eight letters, which was the primary outcome measure. Moreover, 14% of verteporfin treated group compared with 33% of placebo group developed moderate visual loss of 15 letters or more. The treatment benefits such as visual improvement by one line or more and better median visual acuity persisted in the second year. The primary outcome benefit, however, was no longer statistically significant by that time, which may be the result of subtle adverse effects on neurosensory retina and RPE as well as the loss of PDT efficacy.

Montero and Ruiz-Moreno also reported a series of 33 eyes with subfoveal myopic CNV treated with PDT. The mean VA improved from 0.22 at baseline to 0.26 at 12 months and those aged more than 55 had worse final vision than younger patients. Development of subretinal fibrosis after PDT correlated with the size of the CNV and refractive error.Ergun et al carried out a retrospective study on 36 eyes that had PDT for subfoveal CNV; at 2 years, 19.4% had gained three lines or more of vision, 55.6% remained stable, and 25.0% had lost three lines or more after a mean 3.2 treatments. Age and baseline VA were the only factors significantly associated with visual outcome by multivariate analysis.

In a prospective study of Asian eyes with subfoveal myopic CNV, mean best corrected VA remained at baseline levels after 24 months of follow up; 14 (63.6%) eyes had stable or improved vision while six (27.3%) eyes had gained more than three lines. A mean 2.3 PDT sessions were required compared with 5.1 in the VIP study. All the reviewed studies showed that PDT for subfoveal myopic CNV is well tolerated.

Recurrent subfoveal myopic CNV after laser photocoagulation

Bandello et al retrospectively reviewed 12 eyes that underwent PDT for subfoveal recurrence after laser photocoagulation for extrafoveal myopic CNV. At 12 months, PDT treated eyes had a median two line improvement versus one line loss in controls.

Recurrent subfoveal myopic CNV after macular translocation

Macular translocation relocates the macular neurosensory retina overlying the CNV to a healthier area of RPE and choriocapillaris. Despite initial postoperative success, recurrent CNV may develop. As further focal laser photocoagulation may compromise newly translocated fovea, PDT is an option. Chan et al reported a successful single application of PDT in recurrent CNV after limited macular translocation, with complete closure, visual improvement, and no recurrence after 24 months.

Juxtafoveal myopic CNV

Over 75% of untreated juxtafoveal myopic CNV patients have moderate to severe visual loss within 10 years with laser photocoagulation having limited benefit because of subfoveal expansion of laser scarring. All three PDT treated juxtafoveal myopic CNV patients had visual improvement with resolution of CNV after 12–24 months. After 12 months and a mean of 2.3 PDT treatments, mean visual improvement of 1.8 lines was seen in 11 eyes with juxtafoveal myopic CNV. However, the long term safety of PDT requires confirmation since post-treatment lacquer cracks may occur predisposing to recurrent CNV and RPE atrophy with consequent adverse effects on visual outcomes.

Extrafoveal myopic CNV

Gelisken et al reported a series of three patients with extrafoveal myopic CNV who all had improvements in VA and complete regression of CNV after one PDT treatment and a mean follow up of 3 years.

Submacular surgery for CNV in pathological myopia

Submacular surgery has been evaluated for myopic CNV in several studies with differing outcomes. Most earlier studies were small case series and larger series had conflicting results. After a mean 16 months of follow up, VA improved by at least two lines in 45% and remained stable in 37% of 65 eyes with subfoveal myopic CNV in a study by Bottoni et al. Uemura et al reported 48 patients who underwent removal of subfoveal myopic CNV; VA improved in 39% and remained unchanged in 26% after a mean follow up of 24 months. However, no significant change in VA was observed in 22 patients who had removal of myopic CNV after a mean follow up of 29.3 months in Ruiz-Moreno and de la Vega’s series. Variable CNV recurrence rates of 8–57% and postoperative RPE atrophy have been reported.

Macular translocation surgery for myopic CNV

Machemer and Steinhorst first developed macular translocation surgery for repositioning the neurosensory retina overlying the CNV onto an area of healthier RPE and choriocapillaris. Macular translocation surgery has been performed for CNV caused by AMD as well as pathological myopia. Several surgical methods have been developed and commonly used methods are macular translocation with 360 degree retinotomy, and limited macular translocation (LMT).

Limited macular translocation

LMT has the advantage of being less invasive compared with macular translocation with 360 degree retinopathy. Hamelin et al reported that patients having limited macular translocation for myopic CNV had better outcome compared with submacular surgery for CNV removal.

Glacet-Bernard et al also reported the outcome of limited macular translocation for nine eyes with myopic CNV. After a mean follow up of 10 months, visual acuity improved in 67% of eyes and remained unchanged in the remaining. Ichibe et al reported the outcome of 10 patients with foveal translocation using scleral imbrication and all patients had improvement in vision after surgery. In a similar study by Fujii et al, LMT was performed in 11 eyes with myopic CNV but the results were less favourable. After a mean follow up of 9.8 months, 36% of eyes had improvement in vision, with 36% and 27% having stable or decreased vision respectively.

In the series by Tano et al, 17 eyes received LMT with both scleral infolding or scleral outfolding techniques. The fovea was displaced inferiorly and was completely separated spatially from the original CNV in 12 of 17 eyes (71%). Visual acuity initially improved by two lines or more in 14 eyes (82%), but the proportion dropped and only 29% could maintain the improvement of two lines or more at the final follow up. Final visual acuity was worse than best postoperative visual acuity in the majority (71%). The transient visual improvement may be jeopardised by recurrence of CNV and progressive atrophy of the retina/RPE/choroid. Mateo et al reported a series of 79 eyes and all had completed 2 years of follow up. The mean presenting VA was 20/125, and the mean VA at the 2 year follow up was 20/80.

Smaller and less predictable postoperative foveal displacement is the main disadvantages of LMT. Complications include retinal detachment, retinal breaks, and macular folds. Transient visual improvement may also be jeopardised by CNV recurrence and progressive atrophy. The potential visual impairment after surgery and the inadequate movement of the retina from the CNV might compromise the surgical results for LMT for myopic CNV.

Macular translocation with 360 degree retinotomy

Macular translocation with 360 degree retinotomy has the advantage over LMT in allowing a greater foveal displacement. The fovea is more likely to be translocated to a healthier area with less chance of being affected in case of recurrence. The surgical steps are technically more demanding and have been described previously by Fujikado et al. Sequential or simultaneous extraocular muscle surgery are performed to counter-rotate the globe to avoid postoperative diplopia. Fujikado et al reported the results of 11 patients who underwent macular translocation with 360 degree retinotomy and simultaneous muscle surgery for myopic CNV.

After a mean follow up of 6.2 months, vision improved in eight eyes with two eyes remaining unchanged and only one eye had visual loss. Seven (64%) eyes had a final visual acuity of 20/50 or better. In the extended report of 51 eyes (Ohji et al, American Academy of Ophthalmology meeting, 2004) visual improvement of three lines or more was found in 55% of eyes; stable vision and worsened vision were 25% and 20%, respectively; 47% could achieve the final vision of 20/40 or better.

One of the main disadvantages of macular translocation with 360 degree retinotomy is more extensive surgical manipulations. Complications include retinal detachment, proliferative vitreoretinopathy, postoperative diplopia, recurrent CNV, and severe hypotony. The potential significant gain in visual acuity after surgery needs to be weighed against the manual dexterity required, complications, postoperative care, surgical costs, and facilities. Macular translocation with 360 degree retinotomy is usually considered for second eye patients with subfoveal CNV and healthy neurosensory retina.

Other treatments for myopic CNV

A randomised, controlled pilot study of radiotherapy over 2 years in 39 patients with subfoveal myopic CNV found a significantly smaller increase in CNV size in the treatment group and no decline in VA compared with significantly decreased vision in controls. The results, however, need to be weighed against the possible risks of malignancy and other complications after radiotherapy, particularly in younger patients. Costa et al reported using ICG mediated photothrombosis for CNV focal ingrowth sites in six patients with myopic CNV. After 48 weeks, five patients had improved and one had stable vision. No adverse events were noted. The long term efficacy of this treatment remains to be elucidated.

PERSPECTIVES FOR THE FUTURE

Recently, several new treatments have been proposed for CNV of AMD and many trials have been undertaken. Corticosteroids may be beneficial in patients with CNV, because of their dual anti-inflammatory and anti-angiogenic actions. The use of an intermediate acting intravitreal corticosteroid like triamcinolone acetonide in combination with PDT has been shown to be promising in treating CNV in AMD. Anecortave acetate is an synthetic angiostatic cortisol, but unlike triamcinolone or other corticosteroids, the glucocorticoid effect that causes cataract and elevated intraocular pressure has been removed. The drug is administered at 6 month intervals through a posterior juxtascleral route. The results were encouraging for AMD and the study demonstrated that anecortave acetate at a dose of 15 mg was safe, and statistically significant at 12 months compared with a placebo for stabilisation of vision (less than 3 logMAR line change), prevention of severe vision loss (decrease of more than or =6 logMAR lines), and inhibition of lesion growth but was not statistically superior to the placebo for vision improvements of more than or =2 logMAR lines. A pivotal trial to compare anecortave acetate and PDT with verteporfin has indicated that the two therapies were not statistically different from each other. Stabilisation of vision (less than 3 logMAR line change) was shown in 45% of patients with anecortave acetate, compared to 49% for PDT at 1 year follow up.

Vascular endothelial growth factor (VEGF) is responsible for ocular neovascularisation and blockade of VEGF may lead to regression of neovascularisation. Pegaptanib (Macugen) is an aptamer that is administered intravitreally every 6 weeks. It binds specifically with the VEGF165 isoform, and has the effects of antiangiogenesis, anti-inflammatory, and antivascular leakage. It was approved by the US Food and Drug Administration for AMD in December 2004 and it works for all types of CNV in AMD in reducing moderate and severe vision loss significantly at the 12 month follow up. Ranibizumab (rhuFab, Lucentis) is a humanised anti-VEGF antibody fragment produced by recombinant antibody production techniques. It is injected intravitreally and the smaller fragment can penetrate through all layers of the retina.

Ranibizumab, alone or in combination, has been demonstrated to be safe, well tolerated, and effective in reducing vascular leakage in preclinical studies. All potential treatments for CNV in AMD might provide strategic hopes in also treating the CNV of pathological myopia. Nevertheless, CNV with various aetiology might behave differently and might have diverse treatment complications. Further clinical trials on myopic CNV are warranted to clarify these issues.

CONCLUSION

Long term visual prognoses in patients with myopic CNV are relatively poor, with almost 90% having vision of 20/200 or less after 5–10 years. PDT and macular translocation surgery are effective treatments for myopic CNV, although confirmation of long term efficacy and safety await further assessment. PDT is, in general, safe and well tolerated for most patients with active myopic CNV, vision of 20/200 or better, and who can understand the concept of preventing visual loss after treatment. Macular translocation with 360 degree retinotomy is practically reserved for second eye patients with subfoveal CNV, baseline vision of 20/40 or less, and who can accept the potential risk of the surgery. Together with the newer therapeutic agents and combination therapy, the prognosis for patients with myopic CNV will hopefully become better.

Five year follow up of laser in situ keratomileusis for all levels of myopia.

2006-12-18T23:30:00.000-08:00

Though laser in situ keratomileusis (LASIK) surgery is now one of the most common operations performed worldwide, few studies have been published on long term outcome and safety.

Photorefractive keratectomy (PRK) and LASIK have been shown to be comparable in terms of refractive outcome and visual performance for both myopic and hyperopic corrections. LASIK has become more popular because it is a pain free procedure and gives faster visual rehabilitation. However, LASIK is a more invasive procedure than PRK. LASIK surgery involves the formation of a flap at a level of 160 µm from the corneal surface. This, theoretically, could disturb the organisation of collagen fibres that make up the corneal stroma at this level which could lead to compromise in corneal strength. Thus, there has been concern expressed over the long term refractive and biomechanical stability associated with LASIK surgery.

PRK has been shown to offer long term stability for up to 12 years. In contrast, the longest follow up of myopic LASIK has been 6 years and it showed modest results in terms of refractive, and visual outcome for high myopes. In this study we report the long term refractive stability for all levels of myopic correction and we review patient satisfaction with this procedure.

DISCUSSION

LASIK surgery is still a controversial issue despite almost 10 years of experience and eight million patients treated worldwide. The recent publication by the National Institute of Clinical Excellence (NICE) in the United Kingdom, although fundamentally flawed, highlighted the need for long term evaluation of the procedure. Several studies have published good short term results for LASIK surgery; however, few have addressed long term outcome.

Sekundo et al, in a study of 33 eyes with 6 years of follow up, reported a cumulative unaided visual acuity of more than 0.4 logMAR in 66% of patients and only 46% of patients were within plus or minus 1.0D of attempted correction at the end of the study. Furthermore, they reported that 75% of their patients experienced night-time glare, yet 81% of patients were quite happy with overall result.

The long term results for PRK showed that postoperative refraction remained stable over 12 years. In 68 patients studied, it was found that 75% of those who underwent a -2.0D correction and 65% of patients who received a -3.0D correction were within 1D of intended correction at 12 years. This fell to 25% and 22% for patients having a -6.0D and -7.0D correction, respectively. The 5 year results for hyperopic LASIK were recently reported by Jaycock et al. They reported that at 5 years post-treatment 71% of eyes treated for +1.0 to +3.0D of hyperopia were within plus or minus 1.0D of intended correction, whereas only 37.5% of those between +3.5D and +6.0D were within plus or minus 1.0D of intended correction.

In contrast with Sekundo’s study where the mean preoperative SE was -11.4D, the patients in our study had a broader range of preoperative refraction (mean SE = -4.83, range = -1.5 to -13D). Sixty per cent of eyes were within plus or minus 0.5D and 83% within plus or minus 1.0D of attempted correction at 5 years. Furthermore, 89% of eyes had a cumulative unaided vision of 6/12 or better with 57% having a visual acuity of 6/6 or better. The superior results are no doubt because of the inclusion of mild myopes in the study population. But if we exclude the high myopes in the study the results are even better, with 93% having an unaided vision of 6/12 or better. Our findings show that LASIK surgery is predictable for mild to moderate myopia; however, beyond -6.0D its efficacy decreases with a trend towards myopia over 5 years. However, though we see a myopic trend over 5 years it is notable that 96% of patients would have the surgery again and 96% are currently happy with their level of vision.

Like many other studies glare is a common side effect. We were unable to assess changes in glare sensitivity as these measurements were not performed preoperatively. In contrast with Sekundo’s study, which reported glare in 75% of patients only 24% of our patients reported haloes/glare. Contrast sensitivity was not recorded preoperatively in our patients therefore we were unable to compare the levels of contrast sensitivity preoperatively to those at 5 years. Contrast sensitivity is important in the evaluation of patients post-LASIK as it has been found that contrast sensitivity can be poor in the presence of good Snellen acuity. However, the evidence so far seems to suggest that LASIK causes a temporary reduction in contrast sensitivity with gradual normalisation by at least 6 months. The range of methods available for the measurement of contrast sensitivity and the difficulties producing ambient conditions suitable for accurate assessment often deters surgeons from performing this exam in routine practice. Furthermore, even a slight decrease in contrast sensitivity can be within the normal range of a healthy control population.

Overall, there was a 5% re-treatment rate during the 5 years. These re-treatments were performed in the first 6 months after surgery. All three patients were high myopes with spherical equivalents of -13D, -8.5D, -9.5D, and -6D, respectively. Following re-treatment at 5 years two eyes have achieved their best corrected visual acuity, one eye is within one line of best corrected acuity, and one eye is within two lines of best corrected acuity.

No patient developed corneal ectasia and 6% of patients reported dry eyes with only 4% requiring tear substitutes at 5 years.

Importantly, the safety profile of LASIK in this study is excellent. No eye lost more than one line of best spectacle corrected vision and 31 eyes gained one line of vision.

In conclusion, the findings in this study are significant. It is the largest long term outcome study published to date showing good unaided visual results with excellent safety profile. Overall patient satisfaction with the procedure is high with 98% reporting that they would have the surgery again. The emergence of better laser nomograms, safer keratomes, larger optical zones, and improved understanding of aberrations and their significance will lead to improvements in patient outcome in the future.

Post-LASIK Infectious Crystalline Keratopathy Caused by Alternaria.

2006-12-15T23:19:00.000-08:00

Infectious keratitis is a known complication of laser in situ keratomileusis (LASIK) surgery. Alvarenga et al have reported 3 cases of post-LASIK infectious keratitis resembling infectious crystalline keratopathy (ICK), caused by nontuberculous mycobacteria. We herein report a fourth case of ICK after LASIK, which was caused by Alternaria species.

DISCUSSION

ICK is an uncommon corneal infection. It is usually caused by gram-positive bacteria and fungi and has been reported after corneal transplantation, topical anesthetic abuse, persistent epithelial defect, chronic herpetic keratitis, corneal scar, ocular cicatricial pemphigoid, and LASIK.

The various causative organisms, which have been isolated from cases of ICK, include Streptococus species, Staphylococcus species, Peptostreptococcus, Pseudomonas aeruginosa, Candida tropicalis, Candida albicans, and nontuberculous Mycobacterium. Only one previous case of ICK caused by Alternaria species has been reported after penetrating keratoplasty. To the best of our knowledge, no case of ICK has been reported because of this organism after LASIK surgery. In general, the occurrence of fungal keratitis after LASIK surgery is uncommon.

Alvarenga et al described 3 cases of post-LASIK infectious keratitis that presented as infectious crystalline keratopathy caused by Mycobacterium chelonae, a nontuberculous Mycobacterium. In these cases, fortified topical antibiotics, flap amputation, or keratoplasty was required to control the infection.

The increasing use of broad-spectrum topical antibiotics may provide a noncompetitive environment for Alternaria species to grow and cause opportunistic infection, because these organisms are generally present in external ocular flora. Furthermore, the prolonged use of topical corticosteroids, as was present in our case, may enhance the growth of fungi by suppressing the host immune response.

We recommend early institution of the fortified topical antibiotics along with excision of LASIK flap for control of interface infection. In cases of infectious keratitis after LASIK, where smear and cultures are negative, based on the clinical impression, an early institution of antifungal therapy may be a therapeutic option, especially in nonresponsive cases where antibiotics and corticosteroids have been used for prolonged periods of time. It is possible that an earlier intervention with appropriate antifungal medications such as 5% natamycin may have helped in controlling the infection in our case, thus obviating the need for an emergent penetrating keratoplasty.

Conclusions:

Alternaria species fungus may cause ICK after LASIK.

Implantation of Verisyse Phakic Intraocular Lens to Correct Myopic Refractive Error After Penetrating Keratoplasty in Pseudophakic Eyes.

2006-12-12T23:11:00.000-08:00

Penetrating keratoplasty (PK) is proven as an effective and highly successful means to treat a variety of corneal pathologies. In fact, PK is the most common and most successful transplant surgery performed in the United States. However, even with substantial progress aided by sophisticated tissue banking and the preservation and distribution of corneal grafts, a high postoperative refractive error continues to be a major obstacle in restoring optimal visual acuity.

Many clinical approaches have been taken in an attempt to correct post-PK refractive errors, including the use of contact lenses and spectacles. Contact lens correction is often limited by the increased incidence of dry eyes, corneal neovascularization, blepharitis, and ocular surface abnormalities after corneal transplant. The high level of anisometropia and astigmatism associated with PK limits spectacle correction. Surgical approaches including relaxing incisions, wedge resections, and radial keratotomy have been reported, but may yield unpredictable outcomes. Piggybacking of posterior chamber intraocular lens (PCIOL) and intraocular lens (IOL) exchanges offer alternative options for correcting such refractive errors. With the recent advent of minus power IOLs, piggyback implantation has been reported to be quite effective in treating high myopia after PK. PCIOL exchange is another possibility but may be associated with unpredictable complications. Laser in situ keratomileusis (LASIK) and Photorefractive keratectomy (PRK) may also be used to effectively treat refractive errors and astigmatism after penetrating keratoplasty but may be associated with undesirable complications and unstable correction.

Artisan phakic IOLs (PIOLs) have been used effectively to treat high myopia or hyperopia with or without astigmatism in phakic, aphakic, and pseudophakic patients after corneal transplant. We describe 2 pseudophakic patients who had successful unilateral implantation of the Verisyse (Advanced Medical Optics, Santa Ana, CA) PIOL for the correction of myopic refractive error after corneal transplant.

The preoperative evaluation of these patients included a complete eye examination and measurement of the manifest refraction (MR), uncorrected visual acuity (UCVA), best spectacle corrected visual acuity (BSCVA), endothelial cell density (ECD), anterior chamber depth (ACD), topography, and corneal pachymetry. MR, UCVA, and BSCVA were measured at each postoperative visit. ECD was measured at the most recent postoperative visit.

Pachymetry measurements were taken using the Orbscan IIz (Bausch & Lomb, Rochester, NY). Keratometry was performed using the Atlas Corneal Topography System 991 (Zeiss Humphrey Systems, Dublin, CA). ACD was measured using IOL Master (Zeiss Humphrey Systems). Three corneal endothelial cell images were obtained from each eye using the TOPCON SP2000P Non-Contact Specular Microscope (Topson Medical Systems, Paramus, NJ). The ECD was calculated for each image using TOPCON IMAGEnet 2000 software, and the average was recorded.

DISCUSSION

We report the use of the Verisyse PIOL as an alternative method for correcting myopia after PK in pseudophakic patients. Several studies involving Artisan PIOL implantation in different patient populations have shown the efficacy, predictability, and stability of this treatment. LASIK has been an effective treatment option after corneal transplant for certain patients. However, LASIK has been associated with a higher rate of complications in patients after corneal transplant, including flap complications, wound dehiscence, and graft rejection.7 Furthermore, LASIK may be unpredictable, with the tendency to regress in highly myopic patients, and retreatment is often needed. Kwitko et al have reported progressive changes in refraction and topography in 35.7% of patients who have undergone LASIK after PK.

PRK provides another surgical option, particularly in cases with insufficient corneal thickness for LASIK. However, PRK in postkeratoplasty patients has been associated with corneal graft haze, astigmatism, regression of treatment, and unpredictable refractive outcomes. Mitomycin-C has shown promise in reducing PRK-associated corneal haze, but its effect on grafted corneas is unknown and needs to be studied.

Iris supported IOL implantation may offer several advantages over PRK and LASIK in certain patients. Compared with LASIK, the use of Artisan lens to treat moderately high myopia resulted in better UCVA, BSCVA, and contrast sensitivity, and a lower enhancement rate. Patients also gave the Artisan lens a higher rating of subjective quality of vision. Furthermore, implantation of PIOLs requires no direct manipulation or ablation of the donor cornea. Finally, the simple insertion and ability to exchange and remove this lens offers further advantage.

The effect of iris supported IOLs on the integrity of the corneal endothelium is controversial. The possibility of accelerated endothelial cell loss is concerning, particularly in patients who have had a corneal transplant. In normal adult eyes, the average rate of endothelial cell loss is 0.6% per year. Studies have shown an increased rate of endothelial cell loss after PK, with an ECD decrease of 34.0% ± 22.0% in year 1, a 7.8% annual loss in years 3 to 5, and a 4.2% annual loss in years 5 to 10. Mean cell loss 5 years after transplantation has been estimated at 59%. Studies of endothelial cell loss associated with iris supported PIOL implantation in normal phakic eyes have shown high variability.

At its highest, endothelial cell loss has been reported to be approximately 8% at 12 months, 9% at 2 years, and 11% at 3 years. These studies suggest that most of the endothelial damage was caused by cellular insult during the surgery. In contrast, another study reported a slight gain in endothelial cell density at 2 years after surgery. Recently, an evaluation by Pop and Payette of the United States Food and Drug Administration Ophtec Study involving 765 normal phakic eyes showed no significant decrease in ECD up to 2 years after Artisan PIOL implantation.

The patients in our report experienced a significant decrease in central ECD beyond what was expected for PK patients. At least 2 publications have addressed the issue of endothelial cell loss in corneal transplant patients after Artisan PIOL implantation. Moshirfar et al published a case report that involved 2 phakic and relatively young patients with a previous history of PK who experienced no significant endothelial cell loss 6 months after PIOL implantation. Specific information regarding the ECD in these patients was not reported. However, review of these patients' records revealed that endothelial cell loss at the last follow-up was -3.2% at 14 months (case 1) and +36.4% at 24 months (case 2). Another study by Nuits et al, which involved 16 eyes receiving Artisan PIOL implants after PK, reported a cell loss of 7.6% ± 18.9% at 3 months, 21.7% ± 22.3% at 6 months, and 16.6% ± 20.4% at last follow-up (8.4 ± 4.9 months).

While high variability among endothelial cell loss exists in patients who have undergone PK, several risk factors have been associated with a higher level of endothelial cell loss and graft failure. Low donor ECD, older donor age, aphakia, pseudophakia, and older recipient age have all been identified as significant risk factors for increased loss of endothelial cells after PK. Both patients in our study were older, pseudophakic, and received older donor tissue with a lower average ECD compared with those in the previous case report by Moshifar et al, which automatically places them at higher risk for endothelial cell loss. In addition, implantation of PIOLs is a relatively new procedure for American surgeons, and surgical inexperience may be a factor in the variability seen in these small population studies. Furthermore, the surgeries of both the patients in this study were performed under topical anesthesia. Performing the procedures under local block may have resulted in less tissue manipulation and less cell loss during surgery.

There may be several reasons why the patients in the study by Nuijts et al experienced a lower rate of ECD loss than that seen in our cases. First, the population in their study was quite variable. The patients ranged from 39 to 82 years of age, and 12 of the 16 patients were pseudophakic. This was reflected in the large deviation from the mean in the calculation of endothelial cell loss. The older pseudophakic graft recipients may have experienced high endothelial cell losses that were buffered by the minor losses observed in the younger healthier individuals in their study. However, no comparison was made between the phakic, aphakic, pseudophakic, younger, or older patients with regard to endothelial cell loss. Furthermore, the interval between PK and PIOL implantation in the study of Nuijts et al was from 34 to 90 months, whereas the interval in our study was 16 to 24 months. It is unclear what interval between PK and PIOL implantation is acceptable. Patients with a longer intervals may further progress through the wound repair phase and establish a more stable ECD, which may be more resilient to additional intraocular procedures.

Patients with pre-existing pathology seem to experience a significant decrease in ECD after PIOL implantation, whereas young phakic patients with no significant ocular history may experience virtually no decrease in ECD. The endothelium in older pseudophakic patients may be less resilient to the surgical trauma occurring during PIOL implantation. The point at which the endothelium loses its physiologic capacity to adapt to increased levels of stress is unknown, and further studies are required for a better understanding of the effects of the multiple surgeries on the endothelium.

In our study, we expect endothelial cell loss to be similar to the loss seen in other PK patients who have undergone subsequent cataract surgery when matched for recipient and donor age and pretransplantation ECD. Hsiao et al report a decrease in ECD of 7.3% in 14 patients undergoing cataract extraction and IOL placement after PK. However, this loss was not statistically significant because of the small sample size. At this point, it is not clear what effect the PIOL implant will have on the accelerated endothelial cell loss in pseudophakic patients with PK.

One drawback of this study is that we cannot discern with certainty what portion of the ECD is caused by the actual implantation of the lens during surgery and what may be caused by the possible accelerated cell loss secondary to the implanted lens. In addition, as mentioned previously, both patients had significant risk factors for increased endothelial cells loss after PK because of their demographic, and we cannot determine what amount of cell loss may be simply caused by their posttransplantation status. Future studies that more closely examine postoperative ECD changes immediately after surgery and at 1 week, 1 month, 3 months, and 6 months would be helpful in determining the nature of this loss and the endothelial response to PIOL implantation over time.

The Verisyse iris-supported IOL may provide an effective alternative method for correcting high myopia and astigmatism after corneal transplant. PIOL implantation has been considered a safe and effective elective surgery for the treatment of myopia by the recent Food and Drug Administration approval of Verisyse lens in healthy phakic eyes. We believe that some pseudophakic PK patients have significant ocular pathology and are left with no appropriate alternative methods for restoring functional visual acuity. The long-term outcome and effects on endothelial survival in patients after PK and PIOL has yet to be determined, but our 2 patients have thus far benefited from this procedure.

Future improvements in surgical technique and instrumentation may reduce the endothelial cell loss, making this procedure a more attractive alternative, For some patients, PIOL implantation may prove to be an acceptable approach that warrants further study. No doubt additional work is necessary to determine which refractive technique has the safest and most effective profile for this category of patients. Therefore, studies with longer follow-up and larger populations comparing the implications and effectiveness of PRK, LASIK, piggybacked PCIOLs, and PIOLs is needed for this group of patients.

Conclusion:

The Verisyse PIOL may provide an alternative method to correct high myopia for anisometropia in pseudophakic patients after PK. In this report, PIOL implantation was associated with a decrease in ECD. Further studies are required to determine the long-term effects and ultimate safety of PIOL placement on the integrity of the cornea endothelium after corneal transplant in pseudophakic patients.

Laser photocoagulation for choroidal neovascularisation in pathologic myopia.

2006-12-09T23:01:00.000-08:00

Introduction

Myopia, commonly called short-sightedness, is characterised by the need for optical correction with lenses of negative power to achieve maximum distance visual acuity. Several ocular diseases such as retinal detachment, glaucoma and, in particular, choroidal neovascularisation (CNV), are more common in people with higher levels of myopic refractive error. Choroidal neovascularisation is the occurrence of newly formed vessels in the macula that often leads to a fibrotic pigmented scar causing a blind spot in the centre of the visual field.

Epidemiology

The prevalence of any level of myopia varies among different ethnic groups. Its prevalence in the US was about 25% in one study whereas a recent review reported values as high as 70% to 90% in Asian populations. In a multicentre study in the US myopia was four times more prevalent in children of Asian descent than in white children.

The degenerative form of myopia, called high or pathologic myopia (PM), is associated with potentially blinding conditions such as retinal detachment, macular degeneration and glaucoma. Pathologic myopia has been defined in recent reviews as a refractive error of at least -6 diopters or -8 diopters. Complications of pathologic myopia may occur at lower levels but they are more common when refractive error is -8 diopters or worse.

The prevalence of PM has been reported to be up to 2% in the US but it is much more common in Asian countries. In Eastern Europe 1% of the population is affected by myopia of at least -6 diopters and up to 8% of the Japanese population is affected. In a survey of 11,000 students aged 18 in Taiwan myopia of at least -6 diopters was found in 24% of girls and 18% of boys. The prevalence of a defect of -8 diopters or more is 0.2% to 0.4% in the US and 1% of the general population in Japan.

Pathologic myopia is associated with excessive and progressive elongation of the eyeball. This results in a variety of fundus changes such as hypopigmentation, tilted optic nerve and lacquer cracks (breaks in Bruch's membrane), with or without posterior staphyloma (deformity of the eyeball profile at the posterior pole). As elongation of the globe is a key feature of PM an axial length of 26 mm or 27 mm has been adopted as a biometric definition. A value of 26.5 mm or more has been adopted as an inclusion criterion in a recent therapeutic randomised controlled trial.

Pathologic myopia is an important cause of blindness and visual impairment, especially in the 50 to 75 years age range. Choroidal neovascularisation is the most common vision-threatening macular complication observed clinically in PM; for example, PM was found to be the cause of CNV in 60% of people under the age of 50 who were seen at a referral clinic.

As for age-related macular degeneration, CNV associated with PM may become bilateral. In a study of 325 highly myopic eyes of 218 patients, approximately 1 in 10 developed myopic CNV in 130 months average follow up. The incidence of CNV in the fellow eyes of patients with pre-existing myopic CNV was significantly higher than that in eyes of patients without pre-existing CNV (35% compared to 6%). Lacquer cracks at the macula were a risk factor for this event. Combining the overall 10% cumulative incidence estimate from this study with the prevalent number of people with myopia -8 diopters of more, an approximate 11-year cumulative incidence rate of 2 to 4 per 10,000 would be obtained.

Presentation and diagnosis

Early symptoms of CNV include blurred central vision and metamorphopsia (objects appear distorted). Although CNV due to PM is usually associated with less retinal destruction than in age-related macular degeneration the disease carries a substantial risk of severe visual loss. Visual acuity will become 6/60 (20/200) or worse in 40% to 75% of affected eyes within a few years from the first diagnosis of CNV. The visual prognosis is worse among patients aged 50 or more. People with bilateral CNV usually have a level of central visual loss that causes impairment of activities such as reading, driving, recognising faces and finding small objects. Orientation is usually mildly or not impaired except in the most severe cases. The disease may have a substantial economic impact on individuals and families because most people affected are of working age.

Choroidal neovascularisation in PM is usually readily diagnosed with fundus examination. The CNV is often seen as a subretinal elevation with a varying degree of hyperpigmentation that may be associated with subretinal fluid and haemorrhage. After several months the CNV often evolves to a macular fibrotic scar. In the long-term a large area of chorioretinal atrophy centred in the macula may occur around the central hyperpigmented CNV, a picture called Foster Fuchs' spot. Fluorescein angiography is necessary for diagnosis when CNV is suspected on the basis of symptoms and fundus examination. It usually shows a hyperfluorescent spot corresponding to the CNV that leaks dye during the exam. Fluorescein leakage is usually mild with respect to lesions seen in age-related macular degeneration and it is more evident in recent and active than in scarred lesions. Moreover, fluorescein angiography provides more accurate information about the location of the CNV with respect to the centre of the macula, called foveola and commonly identified as the centre of the foveal avascular zone (FAZ). The proximity of the CNV border to the centre of the FAZ is the main criterion used for anatomical classification of myopic CNV. Only lesions that are not subfoveal are usually considered for photocoagulation.

Treatment options

During the last three decades laser photocoagulation has been the only effective means of treating CNV associated with PM and age-related macular degeneration. Its effectiveness in the latter disease was demonstrated by the studies of the Macular Photocoagulation Study (MPS) Group. Its use in subfoveal lesions has been limited to a few select cases and only in patients with age-related macular degeneration because normal retinal tissue is also destroyed at the treatment site causing an absolute scotoma. Since myopic CNV has been reported to be subfoveal in 1/2 to 3/4 of eyes at presentation photocoagulation can rarely be applied.

Recently, photodynamic therapy has greatly expanded the possibility of safely treating myopic CNV. However, the randomised controlled trial that evaluated photodynamic therapy for myopic CNV had limited power to truly assess its effectiveness due to its limited sample size. Other treatment modalities, such as submacular surgery or macular translocation, have not gained popularity because their effectiveness has never been demonstrated in large randomised controlled studies and because of safety concerns.

Discussion

Given the insufficient data reporting and the small size of the two randomised controlled studies in this review the effectiveness of laser photocoagulation for treating myopic non-subfoveal CNV remains unestablished. However, only initial and final visual acuity were reported. Therefore, it was impossible to extract sufficient data for comparisons at fixed time intervals as per protocol. Furthermore, the small number of eyes assigned to the three wavelengths (nine per group) allowed for little power to detect even clinically meaningful differences in visual and anatomic outcomes. The follow up was also too short to allow for a sufficient part of the disease course to be observed. Follow up was always less than two years, the limit considered appropriate in this review.

Follow up at the first time-point varied markedly. Survival analysis can take account of loss to follow up, provided that patients enrolled during a certain period are carried on to the date representing the end of the study. Under such a design it is unlikely that other factors potentially associated with treatment are responsible for loss to follow up. However, such analysis was not available in this publication. Furthermore, in 1990 a differential loss of control participants was reported.

Observational studies are prone to several sources of bias, especially if retrospective. In Secretan 1997 there was an imbalance of baseline visual acuity, which was significantly worse in untreated eyes. The authors tried to reduce bias with stratified analyses by baseline visual acuity group. They found a significant difference in favour of photocoagulation at two years. No difference was found at five years, a pattern that is similar to that in one randomised study included in this review. While comparisons between groups can be biased in an observational study it may be useful to provide other types of data, such as on safety. In Secretan 1997, CNV recurrence was 72% at five years among treated eyes, with 64% of eyes having a dry scar at the last examination. The mean largest linear diameter of laser scar in disc diameters increased from 0.38 mm at baseline to 0.83 mm at one year, up to 1.56 mm at five years for those who needed only one laser. For eyes with recurrence, these values were 0.47 mm, 1.27 mm and 1.72 mm respectively. Although visual prognosis was not correlated to laser scar enlargement, this complication of photocoagulation could be a cause of delayed visual loss. The risk of inadvertent photocoagulation of the foveola with immediate visual loss is also unknown.

Conclusions

Implications for practice

Laser photocoagulation of CNV that does not involve the fovea has been shown to be effective in reducing the risk of further visual loss in age-related macular degeneration and in other types of CNV. However, its effectiveness for treatment of CNV associated with pathologic myopia is only presumptive, despite its widespread use during the last three decades. Observational studies suggest that the enlargement of the laser scar might lead to retinal pigment epithelial atrophy involving the foveal centre in the long-term, a picture similar to the natural course in some eyes affected by this disease. When ophthalmologists offer laser photocoagulation as a treatment option for myopic patients with non-subfoveal CNV they should state that it is able to anatomically stop the lesion growth in some cases, but that the balance between the possible resulting visual benefit and harm is unclear.

Immunohistochemical Findings After LASIK Confirm In Vitro LASIK Model.

2006-12-06T22:47:00.000-08:00

In recent years, laser in situ keratomileusis (LASIK) became an established surgical procedure to correct refractive error. Numerous patients have undergone this treatment that can be considered a safe procedure within biologic limits. However, one aspect still in discussion is the wound-healing process in the created interface that leads to an easily removable flap even years after treatment.

Although we have learned quite a lot from experimental animal models and in vivo confocal studies, histologic studies on human LASIK-treated eyes that are required to study and better understand the complete tissue reaction in vivo so far are limited to case reports of corneas, most of them with postoperative complications. They demonstrated absence of bridging collagen fibrils and cells between the flap undersurface and the stromal bed and epithelial ingrowth. To date there are only a few case reports of corneas with prior uncomplicated LASIK: in one case, epithelial plugs under the flap margin, regeneration of nerve fibers in the anterior stroma, and a restricted expression of fibronectin and tenascin at the wound area were described. By comparing LASIK wound healing after 3 and 20 months, Anderson et al could demonstrate a reduction of reactive wound repair like epithelial ingrowth, reactive keratocytes at the wound margin, and irregular collagen fibrils in the wound bed. Recently, Mootha and colleagues showed vacuolization and pyknosis of keratocytes as a consistent histopathologic finding in a series of donor corneas with prior LASIK.

To gain further insight in morphologic changes of human eyes after LASIK surgery, we recently established an in vitro LASIK model using human donor eyes. This in vitro model showed similarities to studies of animals treated with LASIK, but has not yet been confirmed in the human in vivo situation. To test the validity of the human in vitro model, one donor with a complete history and follow-up of a LASIK procedure was obtained from the eye bank of the Department of Ophthalmology in Munich. The LASIK treatment in this donor showed no complications during the observation period of 8 months in vivo.

DISCUSSION

Immunohistochemical studies of donor corneas with prior successful LASIK surgery revealed a similar staining pattern as cultured corneas in the in vitro LASIK model presented recently. Staining for fibronectin in the donor corneas was consistent along the complete incision line, whereas staining for collagen type I and laminin did not show alterations in the central interface. The difference in fibronectin staining of the LASIK interface in human LASIK eyes with clinical complications, where the presence of fibronectin was restricted to regions of epithelial cell ingrowth, and in rabbit LASIK eyes might be due to differences in the sensitivity of the antibody or in the method of sectioning (cryosections versus paraffin sections).

Consistent with other studies of human LASIK eyes, no staining for collagen type III could be detected in the central region of the LASIK interface. However, similar to the rabbit LASIK eyes, collagen type III was faintly present at the peripheral incision side. In contrast to the donor corneas after LASIK, in our previously published human in vitro LASIK model, collagen type III staining was present in the central area of the human flap. This might most likely be explained due to a demasking of collagen type III following the culturing process immediately after LASIK procedure.

The lack of pronounced morphologic changes in the central area of the LASIK interface, which only showed little accumulation of fibronectin, supports the hypothesis of reduced wound-healing reactions after performing this surgical procedure. Only at the rim zone of the incision, scar tissue formation can appear and might form an incomplete fixation zone for the corneal flap. Due to this impaired healing process, even years after the LASIK procedure, a corneal flap displacement can occur.

In summary, our histologic findings confirm the well-known clinical phenomenon that wound-healing reactions are marginal after uncomplicated LASIK treatment. Because animal models often have limitations in comparison with the human situation and some differences exist between human and rabbit LASIK treated eyes, similar findings in the in vivo situation after LASIK treatment and in the recently introduced human in vitro model strengthen the reliability of the latter model for further studies concerning LASIK.

Conclusion:

Histologic findings in donor corneas with prior LASIK treatment confirm histologic observations in a recently introduced human organ culture LASIK model. This strengthens the reliability of the latter LASIK model for further studies concerning wound healing after LASIK surgery.

Hypermetropia-Succeeded Myopia After Hyperbaric Oxygen Therapy.

2006-12-03T22:54:00.000-08:00

Hyperbaric oxygen (HBO) therapy is used in the treatment of a number of medical conditions, including decompression sickness, carbon monoxide poisoning, arterial gas embolism, anaerobic infections, and other disorders characterized by local ischemia. The patient breathes 100% oxygen at a pressure of 200 to 240 kPa in a hyperbaric chamber. HBO therapy has been shown to stimulate growth of capillaries, fibroblast proliferation, and collagen synthesis in ischemic tissue.

Temporary refractive changes toward increased myopia or reduced hypermetropia is a frequently reported ocular side effect in patients undergoing prolonged periods of daily HBO therapy. We present an atypical case in which a hypermetropic shift followed the myopic shift in a patient after each of two series of hyperbaric oxygen exposures.

DISCUSSION

A myopic shift is commonly described in HBO-treated patients. The myopic shift found in this patient was within the range of collated data from other patients treated with a standard HBO therapy protocol. After cessation of the hyperbaric oxygen exposure, the myopic shifts tend to revert to baseline values. Recently, a temporary hypermetropia (+2.00 D) was observed as an initial phenomenon in a single patient who recovered by 8 to 9 weeks after completed treatment. The patient in our case report showed relatively slow changes in refraction and terminated with a longlasting low-level hypermetropia, which is difficult to explain on an osmotic basis.

Sufficient changes in central corneal power, anterior chamber depth, and axial length of the eye or accommodative tonus have not been found to explain the degree of ocular refractive changes in HBO-treated patients. Although the exact mechanism remains obscure, the myopic shift has been attributed to refractive index change within the crystalline lens. Ultrasonographic measurements showed no change in total lens thickness.

Oxidative stress has been proposed to cause an aggregation of proteins in the lens nucleus with an implication of increased refractive index and a consequent myopic shift. Some support for this notion has been provided from studies on guinea pig lenses: in vivo treatment with HBO resulted in a decrease in the water-soluble and an increase in the insoluble protein proportion. However, it should be noted that increases in insoluble protein on extraction may not necessarily represent increased aggregation in the intact lens, because high levels of water-insoluble protein have been found in clear bovine lenses. The relatively high level of insoluble proteins extracted from older lenses is more likely to reflect an age-related increase in aggregation on extraction, because older proteins may be more vulnerable to abrupt changes in their immediate environment.

A manifestation of protein aggregation in the intact lens is opacification or loss of clarity and this has been reported after HBO treatment in human and guinea pig lenses. Recently, a study conducted by Bantseev et al. showed that HBO treatment of guinea pig lenses results in a decrease in sharp focusing of laser rays. This may result in a loss of optical quality but should not necessarily be interpreted as an increase in light scatter if, like in Bantseev et al.'s findings, all rays that are traced through the lens cross the optic axis at some point. Furthermore, results from guinea pig lenses may not reflect the situation in the human lens, because the former contains [zeta]-crystallin, a protein not found in its human counterpart.

If indeed, the refractive changes after HBO treatment are attributable to changes in the lens proteins, it is not clear how this may occur. The total amount of protein in the lens must remain the same so there cannot be any overall reduction or increase in protein concentration. Any change in response to HBO therapy would therefore have to relate to how the proteins and water interact and/or in their respective distributions. This would result in a change in the refractive index within the lens. Whether this change affects the entire lens or is restricted to cortical or nuclear regions is not known. The refractive index in the lens is relatively constant in the nuclear region and manifests as a gradient in the cortex. To contribute to the refractive shifts reported in this study, maximal amplitude of 3.00 D (range –1.37 D to +1.62 D) in the right eye and 2.75 D (range –1.25 D to +1.50 D) in the left eye, the fluctuation in nuclear refractive index would need to be around ±0.005 for nuclear refractive indices of 1.401 to 1.411. This would, according to the Gladstone-Dale formula, equate to changes in local protein concentration of around 3 mg. Given that there can be no overall loss or gain of protein but only a redistribution of protein and water in localized regions, these calculated values would be very likely to manifest as opacities by slit lamp examinations.

Because no such reduction in the clarity of the lens nucleus was found, any changes to the structure of the lens were most likely to have occurred in the cortex. A change in cortical refractive index would not require an overall increase or decrease in magnitude, but only very slight changes in the gradient sufficient to alter the refractive power to a measurable degree.

The underlying causes for the refractive changes reported in this study are not clear, and it is not possible to reach any conclusions from a single case. The long-term low hyperopic shift may simply be reflecting a progression that would have occurred without HBO therapy, because such changes in presbyopes are not uncommon. However, this is the first reported case in which a hypermetropic shift has immediately succeeded a myopic shift in a patient after each of two series of HBO treatments. Any explanation needs to take into account that significant increases and decreases in ocular refractive power can occur in patients treated with a standard HBO therapy protocol without causing clinically detectable loss of lens transparency or reduction in best-corrected visual acuity.

Long-Term Complications of Iris-Claw Phakic Intraocular Lens Implantation in Weill-Marchesani Syndrome.

2006-11-29T06:09:00.000-08:00

The treatment of patients with high myopia has generated controversy in recent years. Optical correction of high myopia with spectacles produces image minification, optical aberrations, limited field of vision, and a poor cosmetic appearance because of the thickness of the lenses. Contact lenses largely resolve these issues, although they entail problems of intolerance and complications derived from their use. Hence, surgical procedures, such as epikeratoplasty, automated lamellar keratomileusis, excimer laser photorefractive keratectomy, laser in situ keratomileusis, phakic intraocular lens (IOL) implantation, and refractive lens exchange have been introduced to correct high myopia.

The implantation of an IOL to correct high myopia was first discussed during the 1950s by Strampelli and Barraquer. Since then, several phakic anterior chamber IOLs (ACIOL) have been developed. Worst et al performed the first implantation of the iris-claw phakic IOL.

DISCUSSION

Weill-Marchesani syndrome is a rare connective tissue disorder characterized by short stature, brachydactyly, joint stiffness, and characteristic eye abnormalities, including microspherophakia, ectopia lentis, severe myopia, and glaucoma. Both autosomal recessive and autosomal dominant modes of inheritance have been described, and a gene for the recessive Weill-Marchesani syndrome has recently been mapped to chromosome 19p13.3-p13.2.

The characteristic small, spherical shape of the lens combined with zonular laxity predisposes the eye to pupillary block and angle-closure glaucoma in Weill-Marchesani syndrome. Asaoka et al reported a case and postulated a mechanism of chronic angle closure glaucoma secondary to frail zonular fibers and spherophakia in Weill-Marchesani syndrome. In our case, gonioscopic examination revealed angle closure glaucoma as well. Our patient also had 3+phacodonesis indicative of loose zonular fibers. Although iris-claw IOLs should theoretically not disturb the angle; nasal and temporal peripheral anterior synechiae contributed to further impairment of outflow and poor control of glaucoma.

Phakic ACIOL implantation is an effective surgical procedure to correct high myopia; however, there is a concern regarding long-term endothelial cell loss. Several articles have been published to assess the effect of iris-claw lenses on endothelial cells. Menezo et al 1 studied 94 eyes of 62 patients with myopia of -7.00 diopters or higher who underwent Worst-Fechner IOL implantation. Three years after surgery, 58 eyes (61%) had an uncorrected visual acuity of 20/40 or better and the mean endothelial cell loss was 17.9% at 5 years after surgery, whereas the percentage of hexagonality and the coefficient of cell variation tended toward preoperative levels. The same group reported 4-year follow-up results and suggested that there was a slight, progressive cell loss after implantation with return of morphometric changes to the preoperative levels. They concluded that endothelial loss occurred primarily during the surgical procedure.

Landesz and coauthors reported the long-term results of the Artisan 5-mm optic iris-claw myopia lens in 67 eyes of 38 consecutive patients with preoperative myopia ranging from -5.38 to -28.00 D. With a mean follow-up of 35 months, 67.2% of the patients had a postoperative residual refraction within ±1.00 D of emmetropia. Mean endothelial cell loss was 5.5% at 6 months, 7.21% at 12 months, 9.1% at 24 months, and 10.9% at 36 months.

Although Artisan phakic IOL has been widely used around the world over the years, it only received United States Food and Drug Administration (FDA) approval in September 2004. It is called the Verisyse lens in the United States. Pop and Payette published the initial results of endothelial cell counts of 765 eyes enrolled at 25 North American sites in the FDA Ophtec clinical trial of the myopic Artisan IOL. The mean preoperative endothelial cell count was 2631 ± 442 cells/mm2. Percentage change from baseline at 6, 12, and 24 months was -0.09% ± 16.39%, -0.87% ± 16.35%, and -0.78% ± 17.41%, respectively. The decrease was not statistically significant. No relationships were noted between endothelial cell loss and patient age or implant power.

Ophtec does not advocate Artisan phakic lens implantation in eyes with an anterior chamber depth (ACD) below 2.6 mm. The current FDA approval indications for the Verisyse are for the ACD to be no less than 3.2 mm. The original ACDs are reported to be reduced by 28 to 34% after implantation. Current ACDs in our patient are 2.63 mm OD and 2.40 mm OS. Although we were not able to identify the exact model of the iris-claw lens and preoperative ACD values are not available for our case, peripheral anterior synechiae could have further reduced the anterior chamber angle depth. The surgeon should always consider ACD before implantation of a phakic ACIOL, especially in eyes that are at increased risk for glaucoma.

To the best of our knowledge, there is no report of phakic IOL implantation to correct myopia secondary to microspherophakia in Weill-Marchesani syndrome. It is possible that the lower endothelial cell count and corneal edema in the left eye could be attributable more to the dislocated phakic IOL and the additional repositioning procedure in that eye. Nevertheless, cell counts in both eyes are significantly lower than normal for such a young age, although we do not have any data regarding preoperative endothelial cell counts.

In conclusion, iris-claw phakic IOL implantation may be an effective surgical procedure to correct high myopia in select patients; however, the surgeon should consider the risk of long-term complications in such a young patient with an unusual condition.

An Evaluation of Keratometry in 6-Year-Old Children.

2006-11-26T04:50:00.000-08:00

The ability to determine corneal curvature or corneal refractive power with a high degree of accuracy and repeatability is important in both clinical and research situations. Reproducible keratometry is especially important for cataract surgery and in monitoring changes in corneal curvature over time. Many studies have documented changes or lack of changes in corneal power with age and its role in the development of myopia and progression of astigmatism. Findings in these studies need to be interpreted in light of the repeatability of the keratometers and other instruments used.

A variety of instruments capable of performing keratometry are in current clinical and research use. The IOLMaster (Carl Zeiss Meditec AG, Germany) and the RK-F1 AutoRef-Keratometer (Canon Inc., Japan) are two relatively new instruments. The IOLMaster semi-automatically performs measurements of axial length, corneal curvature, anterior chamber depth, and corneal diameter using non-contact techniques. The RK-F1 fully automatically performs keratometry and autorefraction.

Although a number of studies have reported excellent repeatability and accuracy of axial length measurement by the IOLMaster compared to ultrasound, few have assessed the repeatability of keratometry by this instrument, and no study has assessed the repeatability of keratometry when used in young children. To our knowledge, no reports have assessed the repeatability of keratometry by the RK-F1, or the comparability between the RK-F1 and the IOLMaster.

DISCUSSION

Repeatability

In the current study on 6-year-old children, both the IOLMaster and RK-F1 gave highly repeatable keratometry measurements, with similar limits of repeatability between the two instruments. There was greater variability of differences along the steepest meridian for both instruments, resulting in wider 95% limits of repeatability for the steepest meridian than the flattest meridian. This is probably a mathematical artefact arising from the use of the derived variable (refractive power), calculated from radius of curvature.

To our knowledge, the repeatability of keratometry by the RK-F1 has not been examined in previous studies, while those that examined keratometry by the IOLMaster did not examine its repeatability in children. Santodomingo-Rubido et al studied the repeatability of keratometry in a group of 52 adults with no ocular pathology using the vectorial method described by Thibos The mean differences in mean corneal radius and J0 and J45 vectors were all negligible. The 95% limits of repeatability for these variables ranged from 0.03 to 0.05 mm (equivalent to differences of approximately 0.17 to 0.29 D). However, direct comparison with our study is difficult due to the different methods of analysis.

Keratometry in the current study was performed before and after the instillation of cyclopentolate as there is little evidence to support an effect of cyclopentolate on its repeatability. In Heatley et al's study of patients at a cataract clinic, no change in mean keratometry along the flattest and the steepest meridians, or in mean keratometry was found on repeated measurements in the group that did not receive phenylephrine or tropicamide (34 subjects). In the group that did receive these mydriatics (47 subjects), a significant but small difference was found for mean keratometry along the steepest meridian (difference of group mean 0.08 D). Liang et al studied the effects of cycloplegia on repeatability by examining the change in the degree of agreement between the handheld Nikon Retinomax K-Plus and the on-table Topcon KR8100 autokeratometer in two cohorts of children (aged 2 to 12 years), one of which received cycloplegia. The authors found a significant change in agreement between the two instruments for the horizontal meridian of both eyes but only for the vertical meridian in the left eyes. However, the results of these studies may have been affected by the performance of applanation tonometry on the subjects and by interindividual variability that was not controlled for by the use of between-group comparisons. In contrast, Dobson et al used the Nikon Retinomax K-Plus keratometer to measure corneal curvature in 250 children aged 3-5 years and found no change in corneal curvature when measured with and without pupil dilation using cyclopentolate.

Comparability

The systematically steeper keratometry readings given by the IOLMaster compared to the RK-F1 represents approximately a one step change in refractive error correction. This difference was not related to the difference in estimates of principal axis. The 95% limits of agreement represent maximum deviations from the mean difference within which 95% of differences in measurements can be expected to lie. Thus, using the RK-F1 as the arbitrary reference, in 95% of measurements, the IOLMaster would give keratometry values along the flattest meridian that are as much as 0.08 D flatter or as much as 0.66 D steeper. Similarly, keratometry along the steepest meridian may be as much as 0.29 D flatter or 0.65 D steeper than the RK-F1.

To our knowledge, a comparison between the IOLMaster and RK-F1 has not been conducted before. However, the IOLMaster has been compared to the Javal-Schiotz keratometer and the EyeSys videokeratoscope. In that study, it was found that the IOLMaster gave steeper keratometry readings than did both the Javal-Schiotz keratometer (mean difference of mean corneal radius, -0.03 mm) and the EyeSys videokeratoscope (mean difference of mean corneal radius, -0.06 mm). These differences are equivalent to approximately 0.17 D and 0.34 D, respectively (calculated assuming one corneal radius is 7.70 mm and refractive index is 1.3375). In a study of 252 eyes of 134 patients aged 7 to 94 years, Nemeth et al also found that the IOLMaster gave significantly steeper keratometry readings than a Javal-type keratometer (mean difference ± SD of 0.17 ± 0.48 D). These differences are comparable to the differences with the RK-F1 found in the current study.

Systematically higher keratometry for both the flattest and the steepest meridians between the IOLMaster and RK-F1 may be due to the difference in the area of central cornea measured by each instrument. Previous studies have documented that the central cornea is more curved than the peripheral cornea. The RK-F1 measures a more peripheral part of the cornea than the IOLMaster because it uses a larger mire size.

Application

The findings of the current study have implications for clinical practice and research. Highly repeatable keratometry is desirable in both settings, especially when follow up is required. It should be noted that although there is no significant mean difference in keratometry on repeated measurements in both instruments, the 95% limits of repeatability are within 0.2 D (for the flattest meridian) or 0.35 D (for the steepest meridian) of the mean difference. This is important clinically and needs to be taken in consideration when repeated measures are performed over time.

The systematic difference of keratometry between the two instruments should be noted in situations when keratometry by these two instruments are being compared. In clinical practice, it should be noted that the IOLMaster may give keratometry values up to about 0.3 D flatter or 0.6 D steeper than the values given by RK-F1.

Conclusions:

Keratometry was highly repeatable for both the IOLMaster and RK-F1 instruments when used in young children. These instruments would be suitable for use in monitoring changes of corneal curvature over time. Small significant systematic differences in keratometry between the two instruments were also found.

Exacerbation of Avellino Corneal Dystrophy After LASIK.

2006-11-23T04:45:00.000-08:00

Avellino corneal dystrophy is an autosomal dominant stromal corneal dystrophy originally described in descendants of the Avellino, Italy region. This dystrophy is caused by a specific mutation at codon 124 of the BIGH3 gene on chromosome 5. Avellino dystrophy shares clinical features with both granular and lattice corneal dystrophies. BIGH3 gene analysis has been used to differentiate these disorders because of the unique mutation associated with each dystrophy.

Exacerbation of Avellino dystrophy after LASIK has been reported in Koreans. Jun et al described 7 patients with Avellino dystrophy that had worsening of their disease after LASIK. The number of affected patients is growing rapidly, now with more than 30 cases in Korea with known disease exacerbation after LASIK (E.K. Kim, unpublished data). Herein, we describe the first reported case of exacerbation of Avellino dystrophy after LASIK in either a white patient or one from North America. Potential mechanisms of disease progression and treatment strategies are discussed.

CASE REPORT

A 25-year-old white female was referred to the Cornea Service at Emory University for evaluation of decreased vision in both eyes 14 months after uneventful bilateral LASIK for a refractive error of approximately -8.00 D OU. The treating physician had observed "2 or 3 small, white, central, subepithelial opacities" in both eyes preoperatively.

Two months postoperatively, the patient complained of mild glare in both eyes when outdoors. Uncorrected visual acuity (UCVA) was 20/25-OD and 20/20-OS. Examination showed mild dry eye, but no corneal opacities were noted in the medical record. She was treated with artificial tears.

Over the next several months, the patient noted progressive loss of vision and increasing glare in both eyes. Six months postoperatively, UCVA was 20/25-OU. Numerous white, central, subepithelial opacities were now seen in both corneas, and the patient was diagnosed with mild diffuse lamellar keratitis. Loteprednol etabonate 0.2% was initially prescribed twice daily but was discontinued, and the opacities progressed.

By 1 year postoperatively, UCVA had fallen to 20/50 OD and 20/70 OS. Manifest refraction of -1.75 + 0.75 × 138 OD and -1.75 + 0.75 × 055 OS yielded visual acuities of 20/20 in each eye. Further progression of the corneal opacities in each eye prompted referral to the Cornea Service at Emory.

At this examination, UCVA was 20/60 OD and 20/70 OS, improving to 20/20 in each eye with refraction (-2.00 + 1.00 × 132 OD and -2.00+ 0.75 × 054 OS). Slit-lamp examination showed discrete corneal opacities within and posterior to the interface between the flap and stromal bed in each eye. The opacities were white, granular in appearance, 0.1-0.3 mm in diameter, and the intervening stroma was clear. The ophthalmologic examination was otherwise unremarkable. The patient's family history was pertinent for an undetermined corneal abnormality in her maternal grandfather and mother. Neither of these family members ever received treatment of this condition. Slit-lamp examination of the patient's mother revealed similar corneal deposits in each eye.

Venous blood was drawn from the patient and extracted DNA sent for polymerase chain reaction testing and DNA sequencing of the BIGH3 gene. Her DNA was heterozygous for the R124H (Avellino dystrophy) mutation and negative for the R555W (granular dystrophy) mutation.

After discussion with the patient, spectacle correction was prescribed and observation of the corneal deposits was recommended. She was discouraged from pursuing LASIK enhancement. Her examination has remained stable over the ensuing 7 months.

DISCUSSION

This is the first reported case of exacerbated Avellino dystrophy after LASIK in North America or in a white patient; however, others will undoubtedly follow with the increasing numbers of LASIK procedures being performed. Some of these patients will be difficult to recognize preoperatively because of minimal corneal involvement.

Insight into factors that trigger phenotypic expression of stromal dystrophies is growing. Transforming growth factor beta (TGF-[beta]) is a family of cytokines produced by epithelial cells and keratocytes that is involved in the corneal wound healing response. The activity of TGF-[beta] increases in response to corneal injury and excimer laser surgery.

TGF-[beta] directly activates the BIGH3 gene causing overexpression of the gene product keratoepithelin. Specific mutations in this gene have been shown to cause Avellino dystrophy, along with forms of lattice dystrophy, granular dystrophy, and corneal dystrophy of Bowman's membrane. Upregulation of TGF-[beta], therefore, should enhance abnormal corneal protein deposition in these dystrophies.

LASIK could exacerbate stromal dystrophies by several mechanisms. Flap creation triggers release of proinflammatory cytokines, including TGF-[beta], through epithelial and stromal cellular injury. The interface between the flap and stromal bed also likely enhances protein deposition by serving as a potential space for accumulation. Choi et al have also recently shown that ultraviolet (UV) light exposure increases TGF-[beta]1 production in cultured human corneal fibroblasts. This discovery has potentially deleterious implications for the use of the 193 nm excimer laser in patients with mutations of the BIGH3 gene. The recurrence of stromal dystrophies after phototherapeutic keratectomy, sometimes quickly after ablation and more dense than prior to ablation, may be explained by UV exposure.

Treatment options for exacerbation of Avellino dystrophy after LASIK include observation or debridement of the flap interface. Jun et al performed flap elevation with manual debridement of the deposits on 1 patient. Although much of the interface was cleared and visual acuity improved in this patient, the deposits reaccumulated and vision declined to the predebridement level within 6 months. Another patient who was treated with debridement and mitomycin C has remained recurrence-free for greater than 6 months.

Inoue et al have shown that recurrence after phototherapeutic keratectomy tends to be less severe in patients with heterozygous mutations of the BIGH3 gene in Avellino dystrophy than it is in patients with homozygous mutations. This genetic determination may guide the form and timing of treatment and also provide prognostic information. These patients should avoid LASIK enhancements and environmental UV exposure. If elevation of the flap is performed for enhancement or interface debridement, mitomycin C or specific TGF-[beta] blocking antibodies should be used.

CONCLUSIONS

LASIK may be contraindicated in patients with Avellino dystrophy because it can exacerbate the deposition of corneal opacities postoperatively. Preoperative evaluation of LASIK candidates should include a careful family history and corneal examination. Genetic testing is indicated in those who may carry the genetic mutation for Avellino dystrophy, even if there are minimal or no corneal abnormalities present.

Biometric characteristics of developing eyes.

2006-11-20T04:25:00.000-08:00

The changes in ocular dimensions that occur between the ages of 6 and 14 years, and the components that are important in the development of the eye and maintaining emmetropia are well known. Over this age range, when the prevalence of myopia may increase rapidly, the major changes are an increase in vitreous chamber depth and a decrease in the power of the crystalline lens. Any imbalance between these two components will lead to a refractive error of the eye, primarily myopia.

One reason for conducting studies on eye growth during childhood is to provide insights as to how an eye that becomes myopic differs from an eye that remains essentially emmetropic. Identifying how aspects of the myopic eye differ from the emmetropic eye before the onset of the condition offers the possibility of predicting the refractive outcome of children. Sorsby approached the issue by examining correlations between refractive error and the various ocular components in children aged 3 to 13 years and concluded that there was no change in corneal power, crystalline lens power, or anterior chamber depth beyond 13 years of age. He did not identify differences between the growth of myopic and nonmyopic eyes other than to observe that myopia developed from a failure of the lens or cornea to compensate for an increase in axial length.

There are reports that in myopia, the cornea has a steeper radius of curvature, the lens power is reduced, the lens is thinner, and the axial length is greater than in nonmyopic eyes. However, there are few studies that have specifically examined the differences between eyes that become myopic and those that do not before the onset of the condition. Such a predictive approach would necessarily define the myopic eye as one that ultimately develops myopia and would require a different analysis of longitudinal data from that of previous work.

The Nepal Longitudinal Study of eye growth and development of refractive error was conducted from 1992 to 2000 when detailed biometric data were collected from children at the Srongtsen Bhrikuti Boarding School at Boudha on the outskirts of Katmandu in Nepal. The distribution of these children in terms of age at first examination and the number of examinations and the distribution of refractive error have been previously reported. The reason for conducting this study in Nepal was that the students at this school were predominantly of Tibetan origin with very few from other ethnic backgrounds. Additionally, children who entered the school at kindergarten age almost invariably completed their secondary schooling, leaving at approximately age 18 years. The school was well endowed and conducted a rigorous academic program. Some results from this project have been published previously.

DISCUSSION

Previous studies on ocular dimensions and refractive error have followed different lines of inquiry. Sorsby et al. examined the correlations between the various components and refractive error as a means of understanding the nature of the coordination shown in emmetropia and to give an explanation of why refractive errors occur. Longitudinal studies provide more information on changes that occur with age and usually compare the rate of change in ocular dimensions with refractive error to give a clue as to the ocular component contributing to the refractive error.

The analysis of our data was based on establishing two refractive error groups, myopic if the error was ever less than -0.50 D, irrespective of the age at which this occurred, and nonmyopic. Our groups were chosen on the basis of refractive error; there can therefore be no analysis using this variable such as how refractive error varies with age. Our decision to use this classification related to the question of how children who became myopic might differ from those that remained emmetropic or hypermetropic. Some children may have been placed into the myopia group based on measurements taken at an early age and subsequently developing higher degrees of myopia. A child we observed to develop say more than -0.50 D myopia for the first time at age 17 years would also have been placed into the myopia group. It is conceivable that some of the nonmyopic group may have become myopic at a time subsequent to our measurement period. In this case, a misclassification of these children would have occurred in our cohort. Any misclassification may result in the observed differences being smaller than the true differences. Nevertheless, we have demonstrated a statistically significant difference between our groups, and when this aspect is taken into consideration, our results are all the more compelling.

The major findings are discussed subsequently in terms of the various ocular components.

Cornea

We found that the radius of curvature of the cornea flattened by 0.08 mm for both groups. The corresponding decrease in corneal power amounted to 0.44 D, assuming a keratometer calibration refractive index of 1.3375. This flattening of the cornea occurred up to the age of approximately 15 years, and our model suggested little subsequent change. Whereas there was no significant difference in the rate of change in corneal radius of curvature between the two groups, there was a significant difference in the absolute radius values between the two groups. The myopia group demonstrated a steeper radius of curvature, by 0.09 mm, at all ages. Sorsby 1 concluded that a good correlation between corneal power and axial length existed for emmetropia, but that this broke down for refractive errors up to -4.00 D. The inference was that myopic eyes tended to have corneas of higher power. However, Sorsby admitted that the data on the cornea was equivocal for those beyond ages 10 to 12 years. Previous cross-sectional studies have generally failed to show any change in the cornea over this age range.

Friedman et al. reporting results from longitudinal data from the Orinda Longitudinal Study of Myopia gave a decrease in corneal power of 0.33 D over a 3-year period for subjects aged 8.8 to 14.5 years. Our reduction of 0.44 D over a 12-year period for children aged 6 to 18 years would tend to support their findings given that most of the change that we measured was apparent before 15 years of age. There was nothing in our results that suggested the rate of change was different in myopia; the cornea for subjects in the myopia group was always steeper than those in the nonmyopia group.

Anterior Chamber

There was a significant difference in the rate of increase in anterior chamber depth between the two groups, with the nonmyopia group increasing by 0.05 mm and the myopia group increasing by 0.19 mm. The increase in the anterior chamber depth may be attributed in the main to a decrease in lens thickness. Sorsby found an increase of 0.05 mm/year but did not find any correlation between anterior chamber depth and axial length or refractive error, and concluded that anterior chamber depth did not materially influence the development or degree of refractive error. This may well be correct with the increase in anterior chamber depth associated with the decrease in lens thickness involved in the emmetropization process. Larsen also found an increasing anterior chamber depth up to the age of 13 years. He further reported a negative correlation between chamber depth and refractive error, i.e., a deeper anterior chamber in myopia. These results concur with our findings.

Crystalline Lens

Thickness

We found a thinning of the crystalline lens with age of 0.20 mm for the myopia group and 0.14 mm for the nonmyopia group. These results are similar to those of Zadnik et al., who reported lens thinning of almost 0.20 mm for all refractive groups between 6 to 10 years and a largely constant thickness to age 14 years. They also reported a trend for children with myopia to have thinner lenses. Our results suggested that lens thinning continued to age 18 years, although the rate decreased with increasing age. Furthermore, our model suggested that the crystalline lens in the eye that developed myopia may be initially thicker than that in nonmyopia; a difference in the rate of thinning of -0.005 mm/year was apparent between the groups.

Equivalent Refractive Index

The equivalent refractive index increased with age with no significant difference in the rate of change between the two groups. At age 6 years, the index was 1.425 and for age 18 years, it had increased to 1.431 for the nonmyopia group. The method used to obtain the refractive index was an iterative procedure based on the Purkinje image from the posterior surface of the lens and the refractive error, a solution being based on the premise that only one refractive index will satisfy the other two measures. In an earlier report using this technique and based on cross-sectional data from this project, we reported a mean value of 1.4252, but as a result of the nature of the study, we could not show a change with age. Mutti et al. calculated a refractive index to produce agreement between the measured ocular components and the refractive error for 519 school children and obtained a similar value of 1.427. Because the posterior radius of curvature of the lens determined by phacometry is dependent on the refractive index of the lens, there is an inherent error in this method, and although they appreciated this interaction, no clarification of any corrections was offered.

In a later study Mutti et al. used an iterative procedure for determining equivalent refractive index and found a refractive index at age 6 years of 1.427, which reduced up to age 10 and then increased to 1.4305 by age 14 years. Our mean values were 1.425 at age 6 years, 1.429 at age 14 years, and 1.432 by age 18 years. Given the different populations and measurement techniques, the results are remarkably similar, although it must be said that small differences in refractive index have a marked effect on lens power.

Surface Radii of Curvatures

We found that the radius of curvature of the anterior surface increased from a mean of 9.09 mm at age 6 years to 11.90 mm at age 18 years for the nonmyopia group with corresponding values of 8.88 mm and 12.56 mm for the myopia group. The rate of flattening for the myopia group was significantly greater than for the nonmyopia group. These values are somewhat different from those obtained by Mutti et al. At age 6 years, they found an anterior radius of curvature of 10.51 mm increasing to 11.70 mm by age 14.5 years, an increase of 1.2 mm, which compares with our increase of 2.3 mm for the nonmyopia group over the same age range and an even greater change for the myopia group. Our results for the posterior lens surface are similar to Mutti et al. in which we found an increase from -5.50 mm at age 6 years to -6.19 mm at age 18 years for the nonmyopia group, a difference of 0.69 mm or a difference 0.60 mm to age 14 years. The results obtained by Mutti et al. were 6.05 mm at age 6 years increasing to 6.60 mm at age 14.5 years, a difference of 0.55 mm.

Equivalent Power

We found the lens power reduced in a regular manner up to age 18 years for both our groups, with possibly a greater rate of reduction in the myopia group. Given that the calculation of lens power is dependent on all the other measures, this is perhaps not unexpected. The reduction in power for the myopia group was 2.35 D compared with 1.64 D for the nonmyopia group, with the greater increase in the radius of curvature of the myopia group responsible for this difference. This suggests an attempt at compensation to increasing myopic defocus by an increased flattening of the anterior surface of the lens. Mutti et al. found a reduction in lens power of around 2.40 D from age 6 to 10 years with little change thereafter for all refractive error groups.

Normally, the smaller differences they report in surface radii of curvature would not be sufficient to account for the reduction in lens power with age without the reduction in refractive index over the age range 6 to 10 years, something we did not find. After age 10 years, Mutti et al. reported practically no increase in radius of curvature of the anterior surface and only a small increase in the posterior radius of curvature. Any subsequent decrease in lens power from the posterior surface was effectively nullified by the increase in refractive index after age 10 years, and little compensation by the lens was apparent after that age.

With the exception of the increase in refractive index, all the lens changes we measured tended to reduce the power of the lens in both groups with significantly greater increases in the anterior lens radius of curvature and lens thickness in those who became myopic. This suggests that the crystalline lens is involved in the emmetropization process. Mutti et al. proposed a passive mechanical model for maintaining emmetropia and to account for the observed lens changes based on a physical stretching of the lens in the equatorial direction. An alternative explanation lies in a proposed differential lens growth pattern for children that become myopic. It is known that there are many growth factors involved in the differentiation of epithelial cells beneath the lens capsule into lens fibers and that some factors originate in the retina and travel anteriorly in the eye. There are also reports that the development of the lens can be influenced by visual input. An increase in lens fiber production would lead to an increase in anterior lens surface radius, and hence a reduction in surface power, that would be partly offset by an increase in refractive index. Furthermore, such an increase in fiber production would be expected to increase the lens thickness. However, the increase in refractive index suggests a reduction in water content of the lens, which would be consistent with the observed thinning.

Our finding that the anterior surface of the lens becomes flatter in those who become myopic would suggest an attempt at maintaining emmetropia through lens fiber production rather than through a passive response of the lens to stretching in the equatorial plane. The idea of retinal control of lens growth as an emmetropization mechanism is not new. Sorsby proposed that the retina continued the function of the optic vesicle and was responsible for lens shape and eye size, and although this was in part a mechanical hypothesis proposed before our current knowledge of ocular growth factors, the concept was original.

The effect of the small increase in refractive index is to offset the reduction in equivalent power of the lens as a result of the increase in radius of curvature of the anterior and posterior surfaces of the lens. Schematic eye models such as the three-surface eye proposed by Rabbetts give relationships between lens power and vitreous chamber depth required to maintain emmetropia. A common relationship is that an increase of 1.00 mm in vitreous chamber depth requires a decrease in lens power of 2.7 D, sometimes approximated to 3 D. However, it is difficult to relate such a rule of thumb to the developing eye because it assumes that other parameters remain constant, when in fact there are concurrent changes in corneal radius of curvature, anterior chamber depth, lens thickness, and in equivalent refractive index. We found that the power of the crystalline lens reduced by 2.35 D for the nonmyopia group and 1.64 D for the myopia group, whereas the corresponding increases in mean vitreous chamber depth were 1.00 mm and 2.00 mm.

Vitreous Chamber

There were marked differences in the rate of change of the vitreous chamber depth between the two groups; we found a mean difference of 1.00 mm between the groups by age 18 years. This result is consistent with the many studies that have shown an association between axial length and refractive error. The changes in vitreous chamber depth have been reported earlier when we reported the merit of using the measurement of the rate of vitreous chamber elongation as a predictor for myopia development in children.

CONCLUSIONS

In summary, we found several differential growth patterns in the myopic group compared with those that were deemed nonmyopic. The students who became myopic had steeper corneas at all ages, greater increases in anterior chamber depth, and lenticular developmental differences involving greater lens flattening and thinning with age. These changes occurred despite the lens in the myopia group being initially thicker than the others. Furthermore, subjects in the myopia group initially had a shorter eye with greater optical power as a result of the cornea and lens. Subsequent ocular development in this group resulted in an increased rate of growth of the vitreous chamber and crystalline lens compared with those that were identified as nonmyopic.

Visual Acuity in Simple Myopic Astigmatism: Influence of Cylinder Axis.

2006-11-17T01:24:00.000-08:00

Visual acuity (VA) is the standard parameter by which the outcome of most clinical trials are judged. In particular, the relation between VA and refractive state is a matter of great interest to optometrists and ophthalmologists and especially clinical researchers. Several studies have described the effects on VA of spherocylindrical refractive errors. In 1961, Peters investigated the relation between VA and uncompensated ocular defocus. He developed charts of iso-oxyopia (lines of equal acuity) that gave expected VA in eyes of different uncompensated refractive states. In other studies relating VA and defocus, lenses were used to blur compensated eyes and VA tests of various types were used.

In most of these analyses, the traditional representation of astigmatic power in terms of sphere, cylinder, and axis was used and transformed to nearest equivalent sphere, ignoring the multivariate nature of refractive state. A three-dimensional power space for the representation of astigmatic powers as vectors and its relationship with VA gives interesting results. This space is uniform in the sense that an equal amount of defocus or a Jackson crosscylinder (JCC) lens produces blur circles of equal diameter. Using the empiric VA data compiled by Pincus, Raasch demonstrated that the single parameter that better correlates refractive errors with its associated VA is the strength (norm) of the vector that represents the refractive error in the three-dimensional power space. This theoretical model proposed by Thibos predicts that the cylinder axis has no influence on the expected VA. This result was later supported by Oechsner and Kusel using numeric simulations.

More recently, Rubin and Harris also explored the relation between VA and defocused refractive state in the context of a symmetric dioptric power space. For a single stimulus size (20/60 computer-generated letter O), they obtained the associated refractions simulated in healthy eyes by means of spheres and Jackson’s crosscylinders. They found that the experimental data represented in the dioptric power space can be fitted to surfaces of constant VA. These surfaces are in general ovoids, but it seems that when the effect of accommodation is minimized (elderly subjects), they become ellipsoids or spheres centered at the refractive compensation. They claimed that the elliptical cross-sections of these three-dimensional surfaces reveal the dependence of VA on cylinder axis. This assertion creates a discrepancy with previous results.

Discussion and Conclusions

Thibos and Raasch relate VA to a single parameter: the magnitude of the dioptric power vector u. In this approach, surfaces of constant VA in the three-dimensional power space are spheres of radius u. In this article, we confirmed this hypothesis for SMA. We found that astigmatic vectors corresponding to refractive states with the same magnitude of astigmatism, but different axis orientations have all nearly the same associated VA.

Only monocular measurements of VA have been included in this article. We designed an experimental protocol with 180 measurements of VA for each eye. To prevent the learning effect, two Internet-based VA test with random letter presentation were used. To prevent fatigue, the sessions for each eye were limited to 45 minutes per day.

It was found that when accommodation is not active, the influence of the cylinder axis is of less importance than other clinical variables such as the selected VA chart. Moreover, the same astigmatic error (same power and axis) induced in different eyes provides VA variations of higher amount than those provided by astigmatism of the same power and different axes induced in the same eye.

On the other hand, our results agree with those of Rubin and Harris to some extent. As they claimed, when there is a loss of ocular accommodation, surfaces of constant visual acuity take a nearly spheroidal form. Thus, the departure from the spherical surface in their study can be mainly attributed to accommodation, whose effect has been minimized in our study. It is interesting to note that although the experimental data of Rubin and Harris has been fitted to ellipses, many of the experimental data points lie in a circle; the authors did not comment on this particular result.

The fact that VA for an ametropic eye can be associated with a single refractive parameter could be very useful, especially in studies involving visual performance. However, additional research is needed to quantify the influence of accommodation on other types of astigmatism.

Vision Loss in Younger Patients: A Review of Choroidal Neovascularization.

2006-11-14T13:11:00.000-08:00

Choroidal neovascularization (CNV) is a common cause of blindness in the United States. It is characterized by new, abnormal blood vessels growing from the choroid through breaks in Bruch’s membrane or the basement membrane of the retinal pigment epithelium (RPE). These vessels can leak blood and fluid and are accompanied by fibrous tissue, which often leads to damage of the retinal tissues and vision loss. CNV can be classified according to its location in relation to the fovea: subfoveal CNV is located under the center of the retina; juxtafoveal and extrafoveal CNV are located at increasing distances away from the center. Vision loss is greatest, on average, when the CNV is subfoveal.

In people older than 50 years, the main cause of CNV is age-related macular degeneration (AMD); younger people can be affected by CNV as a result of other causes. In people under 50 years of age, the etiology of CNV is varied and can include pathologic myopia, ocular histoplasmosis syndrome (OHS), angioid streaks, or idiopathic causes. Regardless of cause, the vision loss caused by CNV may have a major impact on the daily lives of the people affected, especially if both eyes develop CNV over time. These people may no longer be able to perform activities such as reading, driving, and navigating independently. Consequently, some patients may have to give up work or are at least limited in the types of tasks they can perform effectively. Not only can this be a huge emotional strain, but it may also affect their career expectations and financial status—an important consideration for younger patients who may be supporting themselves and their families.

As primary healthcare providers, optometrists are in a position to take the important first step of starting the referral process for patients who potentially have CNV so that they can be treated by a retina specialist. Treatment was largely unavailable for many patients with subfoveal CNV as a result of these conditions until the introduction of verteporfin (Visudyne; Novartis Pharma AG, Basel, Switzerland) therapy. The aims of this article are to review CNV in younger patients and the treatment options available, and to discuss how optometrists might contribute to the management of CNV.

ETIOLOGY AND PATHOPHYSIOLOGY

CNV can develop as a consequence of several conditions, including pathologic myopia, OHS, angioid streaks, and idiopathic causes. The visual prognosis without treatment for patients with CNV can be poor; for example, in one study, approximately 18% of people with CNV resulting from pathologic myopia experienced vision loss to a level of 20/200 or worse in a 1-year period.

The pathogenesis of CNV is complex and the processes involved have not been completely characterized. Nevertheless, it is believed that at the cellular level, CNV develops as a consequence of processes related to wound healing and tissue repair. The normal wound-healing process consists of inflammatory, tissue-formation, and tissue-repair phases. Angiogenesis is an essential component of this normal wound-healing process, delivering oxygen, nutrients, and inflammatory cells to the site of injury, removing debris, and assisting in tissue formation and wound closure. It is believed that an identical process occurs during the development of CNV. Essentially, cellular damage is initiated by a stimulus or “injury” within the macula region such as metabolic imbalance or hypoxia, leading to release of proinflammatory cytokines. This leads to recruitment of macrophages followed by dedifferentiation of the RPE resulting in endothelial cells forming new capillaries that cross Bruch’s membrane. This process continues until normoxia or hyperoxia is established. Finally, vascular remodeling and maturation is initiated, and a mature arterial and venous supply is established.

The initial stimulus that activates the processes leading to development of CNV can arise from several sources, depending on the underlying condition. For example, in pathologic myopia, stretching of the retina can lead to development of lacquer cracks, which may trigger the initiation of a wound-healing response. Similarly, angioid streaks are associated with disruption of the elastic layer of Bruch’s membrane and may be related to several conditions, including pseudoxanthoma elasticum, Paget’s disease of the bone, or sickle hemoglobinopathies.

Development of CNV may also be initiated as a consequence of inflammatory conditions such as uveitis, probably as a response to inflammation or nonperfusion, as well as inherited macular dystrophies such as Best’s disease.

DIAGNOSIS

Clinical Signs and Symptoms

Regardless of the underlying cause of CNV, the symptoms are similar; patients tend to notice a sudden decrease in central vision. Patients affected by CNV in one eye will often subsequently develop CNV in the fellow eye. Patients who develop CNV in both eyes may become legally blind (visual acuity of 20/200 or worse in the better-seeing eye).

CNV may not be symptomatic until the late stages of the condition, and therefore it may first be detected only during a comprehensive eye and vision examination. The biomicroscopic features of CNV may vary depending on its underlying cause and the age of the patient. The hemorrhage at the site of the membrane or in the subretinal space may extend into the vitreous. In the case of subretinal hemorrhage at the level of the pigment epithelium, direct examination of the macula reveals a discrete, round-to-oval, elevated lesion. Often surrounded by a subretinal hemorrhage, the lesion appears greenish-gray or dirty brown. A halo of pigment may also surround the lesion. Other evidence of CNV includes subretinal lipid or blood (associated with an overlying thickened, detached neurosensory retina) and serous retinal pigment epithelial detachment (characterized ophthalmoscopically as a well-demarcated, dome-shaped, elevated, yellowish-orange lesion). The overlying neurosensory retina may be detached, and the separation often exceeds the boundaries of the pigment epithelial detachment, providing further evidence of CNV.

In younger patients, clinical characteristics of CNV can include all of these findings, but some of the characteristics are more typical in the younger patient. The biomicroscopic findings of CNV in younger patients are generally better defined compared with CNV in older patients with AMD. The CNV is usually visible as a grayish-green subretinal membrane, surrounded by a halo of pigmentation, sometimes with clearly visible subretinal blood, fluid, or lipid, and small in area (<1>

Other diseases can present with similar symptoms and signs of CNV. The differential diagnosis of CNV in younger patients includes exudative maculopathies such as central serous chorioretinopathy, Best’s disease, various inflammatory lesions of the choroid or retina, and branch retinal vein occlusion. Other nonexudative diseases that can simulate CNV include macular dystrophies, macular hole, lacquer cracks, and drusen. Central serous chorioretinopathy, being exudative with fluid, is the most common misdiagnosis of CNV in younger patients, but the clinical course in central serous chorioretinopathy is usually benign and self-limited. Fluorescein angiography is an extremely important tool for the accurate diagnosis of CNV.

Early Detection and Referral

The visual prognosis for patients with CNV is often poor, regardless of the underlying cause. In a retrospective study of 100 patients with CNV secondary to pathologic myopia, it was found that after 5 years, all CNV involved the center of the fovea and mean visual acuity was 20/160 in the 50 patients in the natural history group. In another retrospective study of 148 patients with subfoveal or juxtafoveal CNV secondary to ocular histoplasmosis, it was found that, after an average follow-up of 39 months, 103 eyes (70%) had visual acuity equal to or worse than 20/200. Therefore, it is paramount that the symptoms of CNV are recognized so that patients with clinical signs of the condition or unexplained symptoms can be referred promptly to a retina specialist for further evaluation and possible treatment. In general, patients should not be referred if the symptoms are consistent with and explained by another examination finding such as cataract or mild epiretinal membrane.

There is usually only a narrow window of time before the patient’s vision and quality of life will deteriorate to a level at which there is unlikely to be treatment benefit. Furthermore, there is a high risk that CNV will eventually develop in the fellow eye, and prompt treatment may avoid legal blindness.

Optometrists can facilitate the referral process by being aware of the signs, symptoms, and risk factors for CNV in younger patients. Any patient presenting with signs and symptoms indicative of CNV should be referred promptly to a retina specialist for confirmation of CNV by fluorescein angiography. Patients who are at risk of CNV should be encouraged to self-monitor for early signs and symptoms of neovascular AMD; many eye care providers recommend an Amsler grid. Detailed instructions on the use of the grid should be given to the patient. Also, the patient should be urged to pay attention to any significant change in visual acuity, even in the absence of Amsler grid changes. It is our experience that patients often present months after dramatic vision loss has occurred and, when they are asked why they did not return sooner, they say that they saw no changes on the Amsler grid. The visual acuity of an individual suspected of having CNV can also be assessed using a standard eye chart; however, this will indicate only an overall deterioration in vision, a finding that is not specific to a particular underlying condition such as CNV. If the patient has already experienced vision loss at the time of examination, it may be beneficial to also consult with an optometrist who has advanced training in, or clinical experience with, low-vision rehabilitation.

The conclusion of a comprehensive adult eye examination and vision examination should include review and discussion of the examination outcomes. Patients should be provided with information about their potential diagnosis, the prognosis of their condition, and the treatment options to aid in the management of their expectations. They should be aware of the next steps in their disease management process, which include referral to a retina specialist who will perform specialized evaluation tests. The patient should also be informed about the possible symptoms associated with CNV and be asked to return promptly in the event of any new symptoms. Otherwise, regular optometric follow-up examinations should be scheduled with their frequency related to the risk of the underlying condition as assessed by the optometrist. For example, a patient with OHS and an active lesion or a history of CNV in one eye and quiet chorioretinal scars in the fellow eye has a high risk of developing CNV and should be followed closely (e.g., initially every 3 months and then every 6 months if no activity is found).

Specialist Ophthalmic Evaluations

Retina specialists have several tools at their disposal to evaluate CNV, including biomicroscopy, ophthalmoscopy, fundus photography, fluorescein angiography, and optical coherence tomography. Fluorescein angiography is particularly useful because the fluorescent dye leaks from abnormal blood vessels of the retina or choroid and enables visualization of some pathologic vascular conditions such as fibrovascular CNV. Indocyanine green angiography (ICGA) has been shown to provide useful additional information on the composition of CNV in patients with AMD but has not been used extensively in other conditions associated with CNV. It has, however, been suggested that ICGA may be useful for detecting and describing lacquer cracks in pathologic myopia but has yet to be shown to have proven benefits in the management of any specific ocular disease.

AVAILABLE TREATMENTS

Of the many treatment modalities potentially available for younger patients with CNV, only laser photocoagulation and verteporfin therapy have been proven to be beneficial in large-scale, randomized clinical trials at this time, although other therapies may be added to these regimens over the next few years. Although the antiangiogenic agent pegaptanib sodium (Macugen®; [OSI] Eyetech and Pfizer Inc.) has recently been approved in the United States for the treatment of subfoveal CNV resulting from AMD based on the results from two phase II/III trials, there are currently no trials investigating its use for other causes of CNV, although it is likely that some retina specialists will use it for CNV in other conditions.

The treatment indicated for CNV in younger patients largely depends on its location. If the CNV is located away from the fovea (extrafoveal or juxtafoveal), laser photocoagulation may be recommended, whereas for subfoveal lesions, verteporfin therapy is the treatment of choice. Submacular surgery might be considered for some patients with CNV, although the results of randomized clinical trials evaluating this have been disappointing. Current guidelines state that there should be no lower age limit for the use of verteporfin therapy, based on clinical data from the Treatment of AMD with Photodynamic therapy (TAP) Investigation and the Verteporfin In Photodynamic therapy (VIP) Trial, although it should be noted that no data are available on the treatment of CNV in the pediatric setting. Similarly, the key studies of laser photocoagulation enrolled patients as young as 20 years of age, but there are no data from large-scale studies of children.

Laser Photocoagulation

Laser photocoagulation is administered on an outpatient basis and normally takes around 15 minutes. CNV is damaged by the heat radiating from the RPE after absorbing light from a laser beam directed at the region of CNV identified by fluorescein angiography. The MPS, in which our group participated for 15 years, proved the benefit of laser photocoagulation for extrafoveal and juxtafoveal CNV resulting from AMD, OHS, and idiopathic causes. Laser photocoagulation is usually performed with only topical anesthesia and is well tolerated. Patients typically resume their usual routines within a day.

Because the thermal effects of laser photocoagulation also damage the healthy part of the retina, it will cause the formation of a scar in the macula. This is usually well tolerated in extrafoveal locations but may be problematic for juxtafoveal lesions and very destructive for subfoveal treatment. Laser scar enlargement has sometimes been observed when treating CNV resulting from pathologic myopia. The effects of laser on retinal tissue can expand in the direction of the fovea, making juxtafoveal treatment risky. A risk of vision loss resulting from laser injury accompanies treatment of all CNV; this risk should be weighed against the potential benefit of treatment.

Verteporfin Therapy

Verteporfin therapy is a treatment, based on a photodynamic principle, for subfoveal CNV secondary to a number of diseases.

Verteporfin therapy is administered in two steps: 1) the photosensitizer verteporfin is infused intravenously in the patient’s arm; and 2) the drug is activated using a nonthermal laser applied only to the area of the eye affected by CNV. The drug accumulates preferentially in the areas of neovascularization. When the drug is activated by the laser, the CNV is occluded as a result of endothelial cell damage and thrombus formation, whereas the rest of the eye is usually unaffected by the laser or the drug. Therefore, there is less risk of damage to any viable retina overlying the CNV than with laser photocoagulation, and immediate vision loss with verteporfin therapy is less likely.

Verteporfin therapy increases the chance of stable or improved vision in patients with subfoveal CNV secondary to pathologic myopia compared with no treatment. A multinational, randomized clinical trial showed that a small percentage of patients treated with verteporfin therapy can have an improvement in vision. However, the main aim of treatment is to reduce the risk of vision loss. Smaller studies of verteporfin therapy in OHS have also shown benefit.

Furthermore, verteporfin therapy has shown some promise in treating CNV as a result of other, less common causes. These include angioid streaks, juxtafoveolar telangiectasis, and inflammatory and idiopathic causes. In small studies and case reports, verteporfin therapy has been shown to be beneficial in patients with these rare causes of CNV. Like in CNV resulting from AMD, several treatments over time were usually required, but most of the patients in these reports ultimately had complete or partial closure of the CNV and stabilization or improvement in visual acuity.

Verteporfin therapy can also have beneficial effects on contrast sensitivity, which is an important measure of a patient’s functional ability and directly related to tasks such as reading, navigating, and recognizing faces. Rehabilitation may also be facilitated by verteporfin therapy. The size of the scotoma is very significant to low vision rehabilitation for reading and other activities of daily living independent of visual acuity. A small, uncontrolled case series that aimed to determine if macular scotomas in 64 patients with neovascular AMD were affected by verteporfin therapy showed that, at 3 months, the majority (77%) of patients had stabilization or improvement in their scotomas. This finding may also extend to patients with non-AMD causes of CNV.

Patients should be advised that verteporfin therapy may involve multiple treatments; regular follow-up visits and additional courses of therapy may be required as often as every 3 months until a point of stability is reached. At follow-up visits, the presence or absence of fluorescein leakage from CNV will be determined using fluorescein angiography. If there is any leakage, presumed to be a sign of further risk of vision loss if left untreated, treatment with verteporfin is recommended in many cases. It is important for the patient to understand that verteporfin therapy is a disease-modifying therapy that attempts to slow or halt the progression of the disease. Therefore, the patient’s expectations need to be set appropriately; they are likely to experience some continued erosion of vision until their lesion stabilizes.

The most important treatment-related adverse event is acute severe visual acuity decrease (loss of more than or =20 letters or more than or =4 lines on a standard eye chart within 7 days after treatment). This was reported in three patients (0.7%) in the TAP Investigation and 10 patients (4.4%) in the AMD arm of the VIP Trial. More than half of these patients recovered their vision to within 20 letters of baseline within 3 months of treatment. It must be stressed that acute severe visual acuity decrease as an adverse event is distinct from the vision loss associated with the natural history of CNV. The risk of long-term severe vision loss without treatment is greater than the risk of acute severe visual acuity decrease with treatment in patients with AMD with predominantly classic CNV or occult with no classic CNV and presumed recent disease progression.

No cases of acute severe visual acuity decrease were reported in clinical studies involving patients with pathologic myopia or OHS; however, it is likely that there is at least some risk of severe visual acuity decrease associated with treatment in these patients. Other adverse events most commonly reported in verteporfin-treated patients in the pathologic myopia arm of the VIP Trial through 2 years included visual disturbance (19 [23%] verteporfin-treated patients; 8 [21%] patients in the placebo group) and injection site reactions (8 [10%] verteporfin-treated patients; 2 [5%] patients in the placebo group).

Patients should also be advised that they will be photosensitive after verteporfin therapy. Regulatory authorities in the United States recommend that precautions against photosensitivity be taken for 5 days after therapy; however, clinical expert opinion is that precautions are necessary for only 2 days after verteporfin therapy. Patients should wear long sleeves and pants, a wide-brimmed hat, and sunglasses and should avoid long exposure to bright lights or sunlight during this time. Exposure to ambient household light can be encouraged, because this may reduce the period of photosensitivity through a process known as photobleaching. Very few cases of photosensitivity occurred in clinical trials; provided patients follow these guidelines, the risk of a reaction is low.

Submacular Surgery

Submacular surgery is another treatment option for subfoveal CNV, although like with laser photocoagulation, the effectiveness of surgery in patients with pathologic myopia is unclear. The Submacular Surgery Trials (SST), a set of National Eye Institute-sponsored multicenter, randomized clinical trials in which we participated and that recently concluded, were designed to compare surgical removal vs. observation in patients with subfoveal CNV secondary to AMD, OHS, or idiopathic causes. In the group of patients with OHS or idiopathic causes, only a slight benefit was found in the treatment group. At the 24-month visit, 55% of 112 eyes assigned to the surgery arm had a successful outcome (defined as 24-month visual acuity better or no more than one line [seven letters] worse than at baseline) compared with 46% of 113 eyes assigned to the observation arm. Subgroup analysis showed that eyes with poorer visual acuity at baseline were more likely to benefit from surgery. In the subgroup of eyes with initial visual acuity worse than 20/100, 76% of 41 eyes in the surgery arm had a successful outcome compared with 50% of 40 eyes in the observation arm. Also, among the 42% of eyes in the surgery arm that did not develop recurrent CNV by 24 months, 74% had a successful outcome.

Submacular surgery can result in retinal damage caused by the removal of some retinal tissue with the CNV. Additional complications of submacular surgery include macular hole, retinal detachment, visual field restriction from optic nerve damage, cataract, and recurrent CNV, which can lead to poor visual outcomes. Therefore, the precise benefits and risks to the patient remain unknown and make it difficult to determine in whom surgical excision for CNV should be recommended. Further investigation may be needed to refine methods and characterize patients who might benefit from this treatment option.

VISION REHABILITATION AND LONG-TERM SUPPORT

For patients with vision loss from CNV, irrespective of whether they have received treatment, vision rehabilitation may enable them to continue performing their usual activities of daily living such as reading. In addition to referring such patients to a low-vision specialist, it may also be useful to determine the potential benefits of comprehensive low-vision rehabilitation using task-oriented evaluations. Low-vision devices may help people to continue to read when otherwise they could not. Other nonoptical measures such as orientation and mobility instruction can be used to allow visually impaired people to develop the necessary skills to navigate in a familiar environment. Such tools might enable them to maintain an independent life and may reduce the emotional burden of losing their sight. In addition, support groups for the visually impaired can provide other resources such as books on tape. When patients reach the visual acuity level defined as legal blindness, they should be encouraged to obtain assistance from government and social service agencies.

Optometrists can offer continuing, long-term care in addition to offering a portal of entry to specialists for those conditions that warrant referral. This may be particularly important for people who are bilaterally affected by subfoveal CNV resulting from pathologic myopia, OHS, angioid streaks, or idiopathic causes, because they are often affected when under the age of 50 years and may need support for over 30 years of their lives.

CONCLUSIONS

CNV is an important cause of vision loss in younger patients. CNV in this population is usually the result of pathologic myopia, OHS, angioid streaks, or idiopathic causes. Until recently, many patients with subfoveal CNV could not be treated because of the risk of central vision loss associated with laser photocoagulation. Verteporfin therapy has been proven to reduce the risk of vision loss in some patients with subfoveal CNV and is recommended for consideration in patients with pathologic myopia, ocular histoplasmosis, or those in whom the outcome with treatment is judged to be better than the natural history of the disease. Optometrists can be instrumental in the early detection and referral of patients they suspect may have CNV, thereby potentially improving long-term vision prognosis. They also have the opportunity to provide essential long-term care for these patients, including educating patients about the symptoms of CNV. They can provide low-vision aids and practical instruction on optimizing visual performance for patients who have permanent vision damage from the complications of CNV.

Diagnosis and management of Acanthamoeba keratitis.

2006-10-28T23:34:00.000-07:00

Introduction

First described in the early 1970s, a dramatic increase in cases of Acanthamoeba keratitis was observed in the early to mid-1980s. This rise was associated with the increasing use of soft contact lens wear. In 1985, the US Centers for Disease Control issued a report to alert ophthalmologists about the association between contact lens wear and this difficult infection. The use of table salt for homemade saline solution was determined to be the unifying risk factor for many of the initial cases in the epidemic. Despite the abandonment of this method of disinfection, Acanthamoeba infections continue to occur. Over the last 20 years, papers have identified other risk factors, described the clinical features and course, and a discussed multiple medical and surgical treatments, which underscore the difficult nature of treating this infection. Additional information about the history of Acanthamoeba keratitis are nicely detailed in a review by Schaumberg et al. The purpose of the present review is to discuss this body of literature since 1998, when excellent reviews were published.

Epidemiology

The incidence of Acanthamoeba keratitis may vary based on region and contact lens practices. In the UK, Europe, Hong Kong and other countries with the same contact lens fitting and hygiene, the rate of incidence is estimated at 0.33 per 10 000 hydrogel contact lens wearers per year. No recent, similar studies from the USA exist, although some have estimated the rate to be as high as 1 in 10 000 contact lens wearers annually. In 2004 and 2005, our group noted an increased incidence of new cases of Acanthamoeba, which we presented at the annual meeting of the American Academy of Ophthalmology in 2005. The incidence of Acanthamoeba in rigid contact lenses is 9.5 times lower than for soft lens wearers. Recently, however, patients using rigid contact lenses for orthokeratology have displayed high rates of Acanthamoeba keratitis. This body of literature is discussed in a separate section.

Risk factors

Contact lenses remain the most common risk factor for development of Acanthamoeba keratitis. In recent series, contact lens wear was reported in 80–86% of cases. While compliance with contact lens hygiene is often noted to be poor in patients who develop Acanthamoeba, patients are noted in these studies who disinfect regularly with multipurpose and hydrogen peroxide systems and who still develop this infection. The literature surrounding contact lens disinfection varies in methodology and subsequent results may be misleading. The unfortunate fact is that most commercially available contact lens-disinfection solutions are ineffective against Acanthamoeba.

In the last few years, silicone hydrogel lenses have become popular and accounted for 30% of new fits in 2005. The first generation of silicone hydrogel lenses, Purevision (Bausch & Lomb, Rochester, New York, USA), composed of balafilcon A, and Focus Night and Day (Ciba Vision, Duluth, Georgia, USA), composed of lotrafilcon A, were found to be very ‘sticky’ to trophozoites. Trophozoite attachment rates with these lenses were significantly higher than with conventional hydrogel lenses. These lenses are approved for continuous-wear regimens. In a large prospective study of patients in Purevision lenses, microbial keratitis was more likely in those wearing the lenses for less than the prescribed 3–4 weeks. While this study did not have any cases of Acanthamoeba infection, continuous-wear regimens obviate contact lens handling, cases and solutions. Thus, if these lenses are used, it is recommended that they be used in a continuous-wear fashion.

More recently, the same group studied the so-called second generation of silicone hydrogel lenses, Acuvue Advance (Johnson & Johnson Vision Care, New Jacksonville, Florida, USA), composed of galyfilcon A19. Trophozoite attachment rates for this lens were much lower than for the first generation and not statistically different from those of conventional hydrogel lenses. As such, it may be safer to use these lenses for daily wear. Further prospective studies are necessary to see what impact the shift to increased use of silicone hydrogel lenses has on the rates of Acanthamoeba infection.

The safest form of contact lens wear remains daily disposable lenses. There have been very few cases reported in which patients using daily disposable lenses developed Acanthamoeba keratitis. It is unclear in these reports if the patients adhered to a strict single-use regimen, and most of these patients had additional risk factors, such as swimming in contact lenses. It is crucial to educate patients on the importance on wearing the lenses once only, avoiding the risks of problems related to inadequate disinfection and overnight wear.

Orthokeratology

The practice of orthokeratology, employing a rigid contact lens to alter corneal shape and providing temporary correction of corneal power, has increased since the late 1990s, especially in Asia. Since 2001, many case reports and series have addressed infectious keratitis, especially Acanthamoeba, in patients using orthokeratology. In a review of the first 50 cases of microbial keratitis reported in overnight orthokeratology, a surprisingly high frequency (30%) of Acanthamoeba was found. It is especially concerning that this practice is usually used in teenagers, with the peak incidence in the 15–19-year age range. One study estimates that 30% of those using orthokeratology are under the age of 18 years. Inappropriate lens-care procedures, patient noncompliance, and wearing lenses despite discomfort were blamed for this high rate.

A large portion of the October 2005 issue of Cornea was dedicated to case reports and series of infections following orthokeratology from around the world. This edition also included an editorial from a member of the US Food and Drug Administration, who reported that the agency is currently evaluating whether a post-market surveillance study is the appropriate tool for addressing the question of safety issues raised by overnight orthokeratology. Any patient who is prescribed this therapy should be counseled on the associated risks of infection, including serious infections such as Acanthamoeba.

Additional risk factors

Recent studies have noted additional risk factors in 40–91% of contact lens wearers. These factors include swimming in lenses, irregular or inadequate disinfection, cleaning the lens case with tap water, minor corneal trauma, and exposure to contaminated water.

Noncontact lens wearers

The diagnosis of Acanthamoeba keratitis in the noncontact lens wearer is more difficult and often takes longer, as the suspicion for this infection is usually lower. Due to this delay in diagnosis, these patients also have worse visual outcomes. A recent case series from India presents the characteristics and outcomes of 39 noncontact lens wearers with Acanthamoeba keratitis who presented to one center in a 2.5-year period. A predisposing factor was elicited in 19/39 (48.7%) of the patients, the most common of which was trauma. The majority of these patients were misdiagnosed as having fungal keratitis, as there are high rates of fungal keratitis found in this region. The authors note that the main differences, in this series and others, from mostly contact lens-related keratitis were the lack of severe pain and rapid progression. They hypothesize that certain isolates are responsible for noncontact lens keratitis and unique to certain geographic areas. Additional speciation and susceptibility data are necessary to confirm this possibility.

Diagnosis

Making the diagnosis of Acanthamoeba is difficult. The most important step is to suspect it. Acanthamoeba keratitis is often mistaken for herpes simplex keratitis. It should be considered in any patient with a history of contact lens wear and a new diagnosis of herpes simplex keratitis, especially in those with significant pain or poor response to therapy. Numerous studies have shown that a delay in diagnosis is associated with worse visual outcome and a more severe course. Once the diagnosis is suspected, confirmation is also challenging. Corneal scrapings stained with Giemsa, periodic acid–Schiff (PAS), hematoxylin & eosin, Wright's, calcofluor white, or acridine orange stains may demonstrate the cyst and trophozoite forms.

Acanthamoeba is best cultured on nonnutrient agar overlaid with Escherichia coli, on which characteristic trails form as trophozoites move across the plate. Not all microbiology laboratories are willing or equipped to provide this culture. A recent, small case series demonstrated the ability to make the diagnosis using impression cytology and bright-field microscopy. This eliminates a large epithelial scraping and subsequent pain. The limitations of this technique are that it is only useful in early disease and requires a willing, skilled pathologist. The diagnosis is made much more easily when the disease is in its early stages and superficial in nature. Once deeper involvement of the stroma occurs, a corneal biopsy may be necessary.

Confocal microscopy is a noninvasive tool that may aid in the diagnosis of Acanthamoeba and may be useful in monitoring for improvement. The cystic form of Acanthamoeba is more distinct and appears as a double-walled, hexagonal, hyperreflective structure that is 10–25 µm in diameter. The trophozoite form is more difficult to discern, as it appears similar to normal corneal keratocyte nuclei: an ovoid, S-shaped, structure within the corneal stroma. There are different confocal microscopes available, including the Nidek ConfoScan and the Heildelberg retina tomography II (HRT II).

A recent paper from Brazil presents the findings from 15 eyes with Acanthamoeba keratitis using the Nidek ConfoScan. Cysts were easily evident at varying stromal depths. Swollen nerves were visualized, some of which were surrounded by a highly reflective area, which authors believe represent a trophozoite migrating along a nerve. A case report was recently published demonstrating the findings visualized by the Heildelberg retina tomography II. This technology, which has also been prominently displayed at many research meetings over the last few years, produces impressive, high-quality images. Limitations to confocal microscopy remain its cost and lack of standardized interpretation.

We recommend initiating treatment in the cases where the clinical picture causes a strong suspicion of Acanthamoeba but the diagnosis cannot be confirmed.

Treatment

This section discusses medical and surgical treatments of Acanthamoeba keratitis.

Medical treatment

The treatment of Acanthamoeba keratitis is challenging, as the cystic form is highly resistant and may persist for years. The first medical cure was noted in the mid-1980s through the use of propamidine 0.1% (Brolene) and neomycin 1%. Since that time, the effectiveness of the cationic antiseptic agents chlorhexidine (0.02%) and polyhexamethylene biguanide (PHMB, 0.02%) has been demonstrated. Whereas these medications are the most effective, neither is commercially available and must be obtained through compounding pharmacies. Treatment with PHMB or chlorhexidine is often combined with a diamidine, either propamidine (Brolene) or hexamidine (Desmodine).

Once again, availability of these medications is an issue, as neither is commercially available or approved for usage in the USA. Propamidine is widely available over the counter in the UK and Australia, and hexamidine is available in France. It is our practice to obtain propamidine via the Internet and provide it to patients, utilizing informed consent. Other physicians direct patients on how to obtain these medications themselves. Some feel that combination therapy is out-dated and recommend intensive topical monotherapy with either chlorhexidine or polyhexamethylene biguianide. Most cysts are resistant to neomycin – a medication which also has a fairly high hypersensitivity rate. Thus the use of neomycin is no longer recommended.

Therapy with topical PHMB (0.02%) or chlorhexidine (0.02%) with or without propamidine 0.1% should be given every hour around the clock for the first few days of treatment. Treatment is then tapered based on clinical response, but usually lasts for 2–6 months. Topical cycloplegic therapy and oral nonsteroidal drugs are helpful in the management of pain. Some also advocate the use of topical nonsteroidal drugs, although that is not our practice. Narcotic analgesics are often necessary for pain control.

Many other agents have been or are being investigated for treatment of Acanthamoeba. Topical imidazoles, when applied in a 1% solution, are effective against trophozoites, but not against cysts. They should never be used as monotherapy. Oral ketoconazole and, to a lesser extent, itraconazole penetrate into the cornea and are used by some practitioners as adjunctive therapy to PHMB and chlorhexidine. The levels obtained in the cornea via this route are likely too low to be even trophozoiticidal. Possible new therapies include antineoplastic and antimalarial medications.

The question of appropriateness and timing of topical corticosteroid use to control inflammation associated with Acanthamoeba remains a controversial one. In vitro, dexamethasone phosphate inhibits encystment of trophozoites, which may make the infection more susceptible to antiamoebic agents. It has also been demonstrated that the dead cysts which persist in the cornea cause significant inflammation. One retrospective study showed that topical corticosteroid use was not associated with medial treatment failure, although it was associated with a prolonged course of therapy. Corticosteroids suppress the activity of the macrophage, which is essential in scavenging and destroying the amoeba. Thus, in general, it is recommended to delay and limit steroid use as much as possible, utilizing it in combination with antiamoebic agents and only in those patients with severe pain, scleritis, or severe anterior-chamber inflammation. In patients with severe scleral involvement, systemic immunosuppression may be necessary and has been described using oral steroids, cyclosporine, and azathioprine.

Surgical treatment

Penetrating keratoplasty in eyes with active infection usually portends a poor outcome. Thus it is important to make every attempt to ‘quieten’ the eye before a transplant is performed. Most often this is achieved via medical therapy, but some infections may be recalcitrant to all antiamoebic agents. Lamellar keratoplasty with a conjunctival flap has been successful in some patients. Amniotic membrane transplantation for progressive stromal lesions with persistent epithelial defects may also be effective in controling inflammation and delaying penetrating keratoplasty. Initially reported by Bourcier et al. in 2004, we have used this technique on some of our more difficult cases, with good success. It is sometimes necessary to repeat the amniotic membrane transplantation to ensure complete reepithelialization.

Once eyes with Acanthamoeba are quiet, the success rate for penetrating keratoplasty is much higher. A recent cases series of patients with noninflamed eyes following successful medical treatment describes excellent visual rehabilitation, with the majority of patients obtaining better than 20/40 visual acuity. Several patients did require additional glaucoma surgery, and one patient had severe loss of vision secondary to glaucoma. The authors recommend that there should be a minimum of 3 months between the discontinuation of treatment and subsequent penetrating keratoplasty.

Conclusion

Acanthamoeba keratitis continues to be a difficult infection to diagnose and manage. The frequency of these infections may be on the rise, and it is most commonly associated with frequent-replacement soft contact lens wear. Overnight orthokeratology patients have also shown high rates of Acanthamoeba. The best chance for a good outcome is based on early diagnosis, so it is important for ophthalmologists to consider it in patients, especially in the contact lens wearer with suspected herpes simplex keratitis.

Corneal reshaping: is it a good alternative to refractive surgery?.

2006-10-23T23:14:00.000-07:00

Introduction

Over the last 3–4 years, contact lens corneal reshaping has become more popular with patients and practitioners. Overnight corneal reshaping (OCR), also called overnight orthokeratology, involves wearing a highly permeable, rigid gas-permeable (RGP) contact lens with multiple posterior curvatures to create a decrease (flattening) of the anterior corneal curvature. These specially designed lenses have a ‘reverse geometry’ configuration which means that the central curvature is flatter or less curved than the peripheral curves. The process generally takes 7–10 nights of wearing to obtain the maximum effect so that after lens removal in the morning, unaided vision remains good for all waking hours.

Generally, most patients wear the lenses every night, although some patients find that they can skip nights occasionally and still retain consistently good vision. In June 2002, Paragon CRT (Paragon Vision Sciences, Mesa, Arizona) was approved by the United States Food and Drug Administration (FDA) to be worn overnight for temporary correction of myopia. More recently, vision shaping treatment (VST) (Bausch and Lomb, Rochester, New York) received similar FDA approval for its ‘family’ of four designs of corneal reshaping lenses. The Paragon CRT lens has FDA approval for all ages for up to 6.00D of myopia and less than 1.75D of astigmatism. The VST lenses have FDA approval for up to 5.00D of myopia and 1.50D or less of astigmatism. Estimates from early 2005 as to the number of patients using OCR are over 100 000 outside the US and over 50 000 in the US (J. Jacobson, Director, Polymer Technology, personal communication, January 2005). No estimates are currently available for the number of adults versus children using these lenses.

Corneal reshaping: yesterday and today

Corneal reshaping today is nothing like the form of orthokeratology used in the late 1970s and early 1980s. Orthokeratology used a series of spherical RGP (or PMMA) lenses that were fit progressively flatter to affect a change in corneal curvature. These lenses were worn during waking hours and patients found they had improved unaided acuity for short periods of time. Practitioners found some of these patients to have corneal distortion and irregularity due to the high-riding nature of these fits.

Today's corneal reshaping lenses are dramatically different in three major ways. First, lenses are made of high-Dk (highly gas-permeable) RGP materials that are FDA approved for overnight wear. Second, as mentioned above, the posterior surface of the lens is made with multiple curves with distinct zones such that the central zone (base curve) is flatter than the peripheral curves. The unique curvatures allow carefully controlled centration, myopia reduction and corneal integrity. Third, in most cases, lenses are worn only while sleeping. The only similarity between the original orthokeratology and today's corneal reshaping is that contact lenses are worn to affect a change.

Although the process has been simplified, there is still a learning curve for practitioners to become proficient with various patients, prescriptions and lens designs.

Lens designs/techniques

There are currently five different FDA-approved corneal reshaping lenses. Each has its own proprietary design formula to determine the proper fitting relationship. The one common characteristic in each design is that the posterior surface of the lens has peripheral curvatures steeper than the central curvature. Terminology describing these curves varies amongst the brands but can be generalized as follows: base curve – the central curvature that determines the amount of myopia reduction; reverse curve – a curve significantly steeper than the base curve and much steeper than the original flat K reading; alignment curve – a curve that approximately aligns with the peripheral cornea that influences lens position on the eye and ‘floats’ the central portion of the lens on the cornea; peripheral curve – the curve used to give appropriate edge lift to allow tear flow under the lens.

Different techniques are used to fit each lens. One lens uses a fitting nomogram followed by diagnostic fit evaluation. One is strictly topography based for initial lens selection followed by topographical analysis after wearing the initial lens for one night to determine the final lens ordered. The others are fit empirically based on refraction, K readings, corneal diameter and corneal eccentricity.

Corneal changes

Post-treatment topography of corneal reshaping patients shows a central area of flattening surrounded by a steeper mid-peripheral ring somewhat similar to a post-laser in-situ keratomileusis (LASIK) topography. Proper centration of lenses is critical to give best visual acuity and to minimize the chance of subjective symptoms of glare. Detailed studies of corneal reshaping patients have consistently shown a decrease in central epithelial thickness and an increase in midperipheral epithelial thickness. The precise mechanism of these changes has been theorized to be either a compacting of the central epithelial cells or a redistribution of the epithelial cells from corneal center to the midperiphery. A number of studies have been done to evaluate changes in stromal thickness or posterior corneal curvature changes but these have failed to show a consensus.

OCR is temporary while LASIK is permanent. With OCR, lenses must be worn regularly to maintain vision improvement. Many patients enjoy the idea of good unaided acuity during their waking hours but like the security of knowing they can go back to their original myopic condition by simply discontinuing lens wear. Prior to any refractive surgery, proper informed consent requires presentation of alternatives to the procedure. Corneal reshaping is one of those alternatives and should be presented to appropriate prospective patients as an alternative to refractive surgery.

Outcomes data

Results with corneal reshaping have been evaluated from the perspective of both the doctor and the patient.

Efficacy has been evaluated in recent studies. Sorbara et al. followed 23 patients (mean refractive error -2.72 ± 1.06D sph and -0.55 ± 0.40D cyl) for 4 weeks and found unaided acuity improving to 0.00 logMAR (20/20 snellen) by day 4 and remaining consistent throughout waking hours by day 10. Unaided acuity and refractive error remained consistent through day 28. Walline et al. followed 29 children aged 8–11 years for 6 months of corneal refractive therapy. Range of myopia was from -0.75 to -5.00D with less than 1.50D of corneal toricity. At the 6-month afternoon visit, uncorrected acuity was 0.08 ± 0.15 logMAR (20/24 snellen). The mean spherical equivalent refraction at that visit was -0.16 ± 0.66D.

A study at Indiana University evaluated long-term safety and effectiveness of overnight orthokeratology. A total of 133 adults and 68 juveniles completed this 12-month study using three different lens designs. The results showed a reduction of more than 90% of original myopia at the 12-month visit. The authors concluded that the procedure is effective, there were fewer symptoms and a general decrease in slit-lamp findings over time, and safe wear of overnight corneal reshaping lenses ‘is predicated on the emphasis of clear patient direction on how to wear and take care of the lenses followed by regular examinations’ by the eye care practitioner.

The return to baseline myopia after discontinuation of corneal reshaping lenses has been studied. These two studies showed that the majority of the recovery occurs within 72 h after discontinuation of lens wear. Rates of regression were found to vary based on amount of original myopia with higher myopic corrections regressing more quickly. Uncorrected visual acuity during the immediate 16 h after lens removal remained at a level of 0.10 logMAR (20/25) or better.

Quality of vision has been analyzed in terms of acuity as well as higher-order aberrations. Two separate studies came up with similar findings. First, that unaided visual acuity was excellent (-0.07 ± 0.18 logMAR or 20/15) and there was no change in best corrected acuity. Second, there were increases in higher order aberrations (HOAs) and spherical aberration. As with LASIK, increases in HOA affect patients more with larger pupils. The spherical aberration increase was shown to reduce low-contrast unaided visual acuity.

From the perspective of the patient, Lipson et al. evaluated patients in a crossover study who wore both corneal reshaping lenses and soft disposable lenses for 2 months each. At the end of the study, 67% chose the corneal reshaping lenses as their preferred mode of correction. This study evaluated vision-related quality of life attributes scored on the NEI-RQL42 and showed no significant difference in perceived acuity with soft lenses compared with OCR lenses. For this study's population as a whole, patients wearing the OCR lenses had a mean unaided logMAR acuity of 0.10 (20/25) at the 2-month visit, while soft lens wearers had acuity of 0.06 (20/20-2). Even though acuity was slightly less with the OCR lenses, this difference alone did not explain why the majority still preferred the OCR lenses.

Another study using the NEI-RQL42 was done comparing OCR patients to LASIK patients. There were no significant vision-related quality of life differences in the two groups at the end of the study, although interestingly, there were differences noted in the two groups prior to treatment.

Safety

As discussed above, the original form of orthokeratology was considered to be safe, but lacked effectiveness. OCR has been shown to be effective, but there is little quantitative information available to support or deny its long-term safety in large numbers of patients. Prospective studies of effectiveness have known denominators that are not large enough to establish safety. Retrospective data on safety, derived from case reports and series, lack the knowledge of denominators necessary to determine the incidence of adverse events.

The most significant safety issue has been microbial keratitis in eyes treated with OCR. Watt and Swarbrick reviewed the first 50 cases of microbial keratitis reported from 2001 onward following OCR. Most cases were severe and involved the central cornea. The review noted a preponderance of Asian patients (88%). The most significant findings were the culture of Pseudomonas aeruginosa in 52% and Acanthamoeba species in 30%. The frequency of Acanthamoeba has raised an alarm because of the difficult and prolonged course of treatment and often poor outcomes. This group of organisms has been confirmed in more recent reports.

The most alarming finding, however, was the peak prevalence in children age 9–15, who accounted for 61% of cases. In a series of 28 cases from China seen over an 18-month period, the average age was 16 and all were 21 or less. It is not clear whether the predilection of infectious keratitis for young Asian OCR patients is related to patterns of OCR use in Asia or to other unknown factors. It is clear that further study is indicated, possibly as mandated postmarket surveillance. At least heightened awareness of keratitis risk and prompt reporting are indicated.

In uncontrolled studies, OCR has been shown to induce higher-order corneal aberrations after lens removal. This is associated with a decrease in low-contrast corrected visual acuity and increases with rising myopic correction. Studies comparing these findings with other forms of contact lens wear are lacking. Although it is likely that these effects are reversible, further study is necessary to document the extent of reversibility.

Candidates for overnight corneal reshaping

Candidates for this treatment include the following.

Low myopes

Low myopes are the best candidates for OCR. They respond quickly and retain very good vision during all waking hours. This group would include those who elect not to have refractive surgery but still want to enjoy good acuity without correction.

Contact lens intolerance

Dryness is the most common complaint in contact lens wearers. They often report dryness as the reason they are seeking LASIK or OCR. Patients with severe dry eyes may not be candidates for either procedure. Also, contact lens wearers bothered by allergy-related itching are ideal candidates for OCR because they wear no contacts during waking hours. Very careful lens hygiene is crucial for these patients to maintain a clean, wetable lens surface.

LASIK noncandidates

Some patients who are fearful of surgery, attracted to the temporary (reversibility) nature of OCR or are under 21 and still showing myopic progression are suitable.

Undercorrected post-LASIK patients

Patients who are still myopic following LASIK and are not candidates for enhancement can do very well with OCR. OCR has its effect on the epithelium and does not alter corneal stroma. It is recommended that only experienced OCR fitters work with post-LASIK patients.

Conclusion

Overnight corneal reshaping is a nonsurgical refractive procedure that has been shown to temporarily reduce myopia and improve unaided visual acuity. Studies have shown it to be effective and patients have found it to be a very attractive option to traditional contact lenses. Safety is an important issue with OCR. As with any procedure, there have been reports of problems. While there are no published studies to evaluate the relative risk or incidence of adverse events while wearing OCR lenses, ophthalmic journals have published case reports of adverse events over the past 7 years. The case reports do not establish the incidence of microbial infections related to corneal reshaping contact lens wear.

Risk of severe complications with corneal reshaping contact lenses is present but may be no different than with other overnight wear contact lens modalities. The FDA approved Paragon CRT 4 years ago and is watching the practice of corneal reshaping carefully while evaluating whether a postmarket surveillance study is appropriate. The FDA's current position is that practitioners must follow careful guidelines regarding patient selection, monitoring compliance with lens care and follow-up exams, informed consent, minors’ agreement to treatment and reporting of adverse events. ‘The FDA will monitor the situation and take appropriate, evidence-based regulatory action’.

Certainly, patient selection, patient education and careful monitoring of patients are critical for continued success and safety with corneal reshaping. Continued study of corneal reshaping is necessary to reduce or eliminate serious complications.

Epipolis laser in-situ keratomileusis: an evolving surface ablation procedure for refractive corrections.

2006-10-14T23:23:00.000-07:00

Introduction

Despite the fact that laser in-situ keratomileusis (LASIK) remains the undisputed leading photorefractive procedure worldwide recent surveys suggest that surface procedures are gaining ground amongst refractive surgeons.

Due to its limitations, mostly concerning postoperative pain and the well recognized risk of haze, conventional photorefractive keratectomy (PRK) is gradually being replaced by modified surface treatments that comprise the replacement of corneal epithelium onto the ablated stroma. Although not yet documented in the clinical setting, the replaced epithelium is expected to act as corneal wound healing modulator after the procedure.

Epipolis-LASIK is a recently described photorefractive procedure that comprises the replacement of the mechanically separated epithelial sheet onto the ablated corneal stroma. The main difference to laser subepithelial keratomileusis (LASEK) is the means of epithelial sheet separation that is achieved mechanically without requiring prior corneal preparation with alcohol.

The rationale of preserving the epithelial sheet for surface treatments

The wound healing responses following PRK occur at the stromal epithelial interface as a result of interactions between the regenerating epithelium and stromal keratocytes in response to injury.

The first stage of wound healing of the cornea after any surface treatment is epithelial migration, followed by epithelial hyperplasia and subsequent stromal regeneration. Cytokines secreted by the regenerating epithelium activate the process of keratocyte apoptosis and their transformation to myofibroblasts initiates the healing cascade that results in corneal haze and regression of the refractive effect, which have been related to surface photorefractive corrections.

In-vivo studies in different animal models have confirmed that the replacement of an epithelial sheet onto the ablated cornea can modulate the corneal wound healing.

Lee et al. reported reduced superficial keratocyte apoptosis in the central stroma of the leghorn chick cornea 4 h after LASEK as compared with conventional PRK. Similarly, Esquenazi et al. using the rabbit model showed a significant increase in keratocyte apoptosis 7 days after PRK as compared with LASEK for attempted myopic corrections of -7 diopters.

Song and Joo using the Sprague–Dawley rat eye model also reported that ethanol-mediated epithelial flap repositioning induced less keratocyte loss and resulted in a slower wound healing process than after conventional mechanical scraping of the epithelium.

Although results of studies on animal models cannot be directly extrapolated to humans those reports provide supporting evidence that the replaced epithelium can modulate the wound healing cascade probably in a similar way as was shown for the application of human amniotic membrane, that is, providing a mechanical barrier between the tear film and the corneal stroma.

Epipolis-LASIK evolved from LASEK with the aim of separating the epithelial flap without the use of alcohol. Using an in-house designed epikeratome we have shown that the use of the epikeratome could successfully achieve epithelial separation as a sheet that could subsequently be replaced onto the corneal stroma. Comparing specimens obtained either with the use of the epikeratome or the classic Camellin's LASEK technique using alcohol, we have shown that the mechanically assisted separation cleavage plane was deeper than that of alcohol. Confirming the findings of other investigators we have shown that alcohol assisted separations are taking place within the basement membrane whereas the use of the epikeratome can successfully separate the corneal epithelium as a sheet, preserving its basal membrane.

Trypan blue staining of mechanically separated human epithelial sheets showed that, similar to ethanol aided separations, mechanical separation also results in significant trauma of the sheet's basal cells (own unpublished data). As shown by transmission electron microscopy this trauma may due to the local shearing forces exerted during the separation to the basal part of the sheet by the detached hemidesmosome anchoring fibrils. Transmission electron microscopy has also shown that, despite the trauma, mechanically separated epithelial cells remain morphologically close to normal at least for the first 24 h after the replacement of the sheet. As evident from biomicroscopy of the operated eyes the replaced cells are eventually replaced by new epithelium, that is, the migratory phase of epithelial healing is not cancelled with this modality. Even so, the epithelial sheet's replacement has the potential of reducing the risk of haze in human corneas by disturbing the time relations between epithelial migration and keratocyte activation after the ablation.

Surgical procedure

The operative eye is anaesthetized with topical tetracaine hydrochloride 0.5% eye drops, a sterile drape is applied and a lid speculum is inserted.

After 30 s of irrigation with iced, balanced salt solution the corneal epithelium is dried and marked with a purpose designed epipolis-LASIK marker (Duckworth and Kent, Baldock, UK). The epikeratome is applied onto the operative eye and the suction is activated through a foot pedal.

The advance of the oscillating blade separates the epithelium leaving a 2–3 mm nasal hinge, the suction is released and the device is removed from the eye. The epithelial sheet is reflected nasally with the use of a moistened merocell sponge to reveal the corneal stroma to be ablated.
After the application of the excimer laser ablation the cornea is irrigated with balanced salt solution and the epithelial sheet is repositioned on the ablated corneal stroma. Preoperative marks serve so that the epithelium is replaced without significant stressing. The sheet is left to dry for 2–3 min and a therapeutic contact lens is applied on the operative eye.

Although the handling of the epithelial sheet is quite different from that of the stromal LASIK flap, the use of the epikeratome has a short learning curve for experienced refractive surgeons and provides an automated and fast modality for the separation of the epithelial sheet.

Postoperative treatment includes anti-inflammatory eye drops (diclofenac sodium 0.1%; CIBA Vision Ophthalmics, Duluth, Georgia, USA) for 2 days and combined eye drops of tobramycin dexamethasone (Tobradex, Alcon, Fortworth, Texas, USA) until the removal of the lens on the day of reepithelization. After the removal of the lens fluorometholone (FML, Allergan, Irvine, California, USA) eye drops are prescribed four times daily in a tapered dose for 5 weeks.

Epipolis-laser in-situ keratomileusis: Crete clinical experience

All eyes in our setting were operated with the Centurion SES epikeratome (Norwood Abbey EyeCare, Australia) and the Wave Allegretto (Wavelight, Enlagen, Germany) laser platform.
The mean time of epithelial healing in more than 500 eyes that have been operated on in Crete up to date is around 5 days, ranging from 3 to 7 days. The epithelial healing is complete by day 5 in the vast majority of the operated eyes. The lenses are removed on the third day after the treatment in less than 10% of the operated eyes.

The overall mean pain scores at the operation day remain below the level of burning feeling. A small percentage of about 10–15% of the operated patients, however, still report burning feeling or worse during the first two postoperative hours. The records show that this percentage decreases with time from surgery and less than 3% of the patients need oral analgesics or are prescribed eye drops of diluted topical anaesthetic (20% tetracaine in natural tears) to control pain. By the third day after the treatment a small minority of patients may complain of mild discomfort as a new symptom. In those cases the symptoms are mild and do not require any further medication than is standard.

As reported in our preliminary report of 3 months results after epipolis-LASIK on 44 eyes the visual rehabilitation after the procedure is quite slow with only 48% of the eyes having unaided vision of 20/40 or better on day 1 after the procedure. A larger series of 234 eyes confirmed this result reporting 53% of eyes having 20/40 or better on day 1 increased to 78% on the day of re-epithelization. Follow-up in the same series showed that vision improved even at 6 months after the procedure with refractive stabilization by the third month interval. At 1 year postoperatively, more than 50% of the eyes gained lines of best-corrected visual acuity. The contrast sensitivity testing in four different spatial frequencies was found equal to or better than baseline at 1 year after the procedure (Katsanevaki et al., 1-year clinical results after epipolis-LASIK for myopia, data under review).

Complications

The epithelial separation was complicated in almost 3% of the eyes treated with the first generation separators. In those eyes the cleavage plane of the separation was uneven, including a strip of corneal stroma within the epithelial sheet.

In eyes with inadvertent stromal penetration outside the treatment zone the operation was completed at the same session reversing to PRK with additional application of 0.02% mitomycin C for 12 s after the completion of the ablation.

In cases for which the crease implicated the treatment zone, the separated tissue was carefully replaced onto the corneal surface and the operation was postponed for a later date. The eyes were followed daily and received standard topical medication until the completion of surface healing. After the refractive stabilization of the eyes as shown by manifest refraction and consecutive corneal topographies in 1-month intervals after the incident, the eyes were treated with LASIK.

All the complicated eyes were followed for at least 1 year. At the last follow-up visit, all eyes are within 0.5 D of attempted correction without any line loss of best-corrected visual acuity (data to be submitted).

Evolution of epi-laser in-situ keratomileusis

The Centurion SES epikeratome operates under suction with forward oscillation of a blunt polymethyl methacrylate separator. The occurrence of inadvertent stromal incursion during epithelial separation with the first generation separators has led to optimization of the epikeratome's settings. The manufacturer redesigned the angle of the separator to be blunter and adjusted the recommendations for other parameters raising the oscillation rate from 10 800 to 12 000 rpm, lowering the speed of head advancement from 4 to 2 mm/min and raising the vacuum pressure from 630 to 640 mmHg. These changes eliminated the incidence of stromal incursions but resulted in high incidence of free sheets that were reported from different users of a specific epikeratome to a percentage of about 30% of the cases. Although free capping is not considered a significant complication in terms of safety and in the vast majority of free caps epithelial replacement is possible, third generation separators are currently under investigation aiming to achieve ideal epithelial separations in all eyes.

Apart from Norwood, other major microkeratome manufacturers have recently presented modified versions of microkeratome units that utilize proprietary blades for epithelial separations to be used as epikeratomes. The separation results that have been reported up to date are excellent but due to their relatively recent launch there are currently no peer-reviewed studies in the literature.

Conclusion

Due to the technique's relatively recent debut as well as the considerable cost to obtain appropriate instrumentation peer-reviewed clinical results currently available are limited to the experience from the University of Crete birthplace of epipolis-LASIK.

The increasing number of papers presented in international refractive meetings, however, as well as the recent epipolis–keratome launch by almost all major microkeratome manufacturing companies reflect the interest of the refractive community on the possible clinical benefits that epipolis-LASIK may offer.

As shown by the initial experience of the technique there are still remaining problems that have not yet been addressed. Epipolis-LASIK is not a pain free procedure: a certain percentage of treated patients complain of pain, especially within the first couple of hours after the procedure.
Furthermore, the visual rehabilitation is slow. Clinical data show that much like after any other surface ablation procedure unaided vision on the day of reepithelization, that is almost a week after the procedure, does not reach 20/20 in all eyes.

Long-term results, however, show evidence of excellent visual and refractive outcomes. In combination with the use of the latest generation laser platforms, epipolis-LASIK in the long term provides elimination of corneal haze, a significant percentage of eyes that gain lines of best corrected vision and unaffected contrast sensitivity. Furthermore, as any other surface ablation approach, it minimizes the risk of corneal destabilization and iatrogenic ectasia.

Bioptics: where do things stand?.

2006-10-06T10:58:00.000-07:00

Introduction: towards a definition of bioptics

Bioptics is widely performed but has never been precisely defined. Although often used to encompass the combination of various refractive procedures (even if both performed on the cornea), ‘bioptics’ has nevertheless a much narrower meaning.

Bioptics is a sequential method of treating large and complex refractive errors, aiming to improve stability and predictability, maintain a large optical zone, and preserve corneal prolate asphericity, thus limiting induced spherical aberrations. These three goals can only be achieved by the combination of refractive techniques with different mechanisms of action. This is why bioptics is normally performed using an intraocular implant [a phakic or pseudophakic intraocular lens (IOL)] associated with a modification of the corneal curvature (laser ablation, thermal shrinkage, incisions, intrastromal implant). The implant addresses most of the spherical error, while corneal surgery follows for finetuning, usually after 2–3 months.

The combinations of refractive techniques with similar mechanisms are not true bioptics. For example, the association of myopic excimer laser/intracorneal rings (both inducing a flattening of the corneal curvature) can be effective, but this combination should not be considered bioptics, because both techniques considerably alter corneal asphericity.

Bioptics with phakic intraocular lenses

Phakic IOLs and myopia, hyperopia, and presbyopia are discussed here.

Myopia: phakic intraocular lenses plus excimer laser

The combination of various models of phakic IOLs with corneal excimer laser is probably the most successful product of the bioptics concept. Myopic eyes generally have deep anterior chambers, allowing easy implantation of phakic IOLs. Moreover, subsequent laser ablation of a low residual myopic error (even if astigmatic) is simple and effective, and a wide, well centered optical zone (larger than the IOL optical zone) can be easily achieved.

Nearly all possible combinations have been investigated with good results: posterior chamber IOLs with LASIK and PRK; iris-fixated IOLs with LASIK and laser-assisted subepithelial keratectomy (LASEK); and angle-supported IOLs with LASIK and PRK. As expected, in all series laser enhancement significantly improved predictability, although in one study it proved unnecessary after IOL implantation in 43% of eyes. Most complications (pupil ovalization, anterior subcapsular opacity, iridocyclitis, dysphotopsia) were peculiar to specific phakic IOL types rather than to bioptics.

As for safety, it has been shown that LASIK maneuvers after phakic IOL implantation cause neither further damage to the endothelium nor IOL dislocation. PRK did not affect the endothelium either.

Intraocular lens-induced dysphotopsia was not worsened by laser enhancement; it was in fact improved. Residual errors contribute to halos, and their correction by corneal surgery with an adequately large optical zone is therefore beneficial. In a subjective evaluation, glare and halos were graded as ‘few’ in a study; in another series, halos after phakic IOL implantation were not increased by PRK or LASIK.

Hyperopia: iris-fixated phakic intraocular lenses plus laser-assisted in-situ keratomileusis

The correction of hyperopia by phakic IOLs is possible in only a limited number of eyes, because of shallower anterior chambers, whose depth is estimated to decrease by 20 µm per year: an anterior chamber phakic IOL in a hyperopic eye may thus require explantation 5–20 years after implantation. Such concerns account for the paucity of studies on bioptics with phakic IOLs in hyperopia. In both series, an iris-fixated phakic IOL was followed by LASIK. Iris-fixated IOL was chosen because it is supposed to be the farthest from anterior chamber angle and from the crystalline lens. The correction by IOL was aimed at leaving a myopic astigmatism, which is more easily corrected by LASIK. No additional endothelial damage was caused by LASIK; 95% of eyes were within 1 D of emmetropia, and 80% were within 0.5 D. Halos were intense in 2.6% of eyes and moderate in 36%. Predictability in this study was better than with iris-fixated toric phakic IOL without laser enhancement.

Presbyopia: angle-supported multifocal phakic intraocular lenses plus photorefractive keratectomy

Although only one case of PRK enhancement after angle-supported multifocal phakic IOL has been fully described, PRK and LASIK are frequently used to refine this form of presbyopic correction.

Bioptics with crystalline lens exchange

Crystalline lens exchange and myopia, hyperopia, and presbyopia, and bioptics after cataract surgery are discussed here.

Myopia: refractive lens exchange plus laser-assisted in-situ keratomileusis

Refractive lens exchange (improperly called clear lens extraction) consists of phacoemulsification and in-the-bag IOL implantation (as in cataract surgery) for refractive purposes. As it causes loss of accommodation, this technique is reserved for the presbyopic age. The concern about vitreoretinal complications reported in earlier studies has curbed use of refractive lens exchange in patients with myopia; however, modern phacoemulsification has shown increasing safety, and a meta-analysis has calculated a risk of retinal detachment of 1.85% in each eye 43.5 months after surgery – only slightly superior to that of nonoperated high myopic eyes (1.5%).

The safety and effectiveness of refractive lens exchange followed by LASIK enhancement have been reported in two small and in one large (64 eyes) series, showing excellent predictability (significantly improved after laser enhancement) and no retinal complications.

Hyperopia: refractive lens exchange plus excimer laser

Refractive lens exchange for hyperopia has been more readily accepted by surgeons and patients for three main reasons: low retinal risk in nonmyopic eyes, limited efficacy of corneal surgery in correcting high hyperopia, and the difficulty of placing phakic IOLs in hyperopic eyes. In addition, lens replacement deepens the anterior chamber, thus preventing angle-closure glaucoma in the long term.

All reports agree on the high safety and efficacy of refractive lens exchange followed by LASIK or PRK. The only large series, however, is characterized by a high rate (62%) of double in-the-bag IOL implantation (‘piggyback’) because higher IOL powers were unavailable: this resulted in interlenticular opacification in one-third of piggybacked eyes. Moreover, most eyes were largely overcorrected after lens surgery, requiring deeper laser ablations. The present availability of IOL powers of up to +40 D (or at least, the implantation of the second IOL in the ciliary sulcus) prevents interlenticular opacification; in addition, improved IOL formulas and intraoperative check of IOL power (e.g. by autorefractor) increase refractive lens exchange predictability, thus reducing the amount of laser enhancement. Mild to moderate halos were reported by 27% of patients.

Presbyopic lens exchange plus excimer laser

The goal of good unaided near and distance visual acuity has led to presbyopic lens exchange, in which a multifocal or a pseudo-accommodating IOL is implanted in the capsular bag. Excimer laser enhancement is not uncommon after these IOLs.

With multifocal IOLs, especially used in hyperopia, minimal residual refractive errors affect both multifocality and visual acuity and worsen halos. Therefore, attempts were made to refine presbyopic lens exchange by PRK treatment of residual errors in 12 eyes. PRK enhancement only improved distance unaided vision, with no improvements in multifocal effect or halos. These findings cast serious doubts on the theory that emmetropia (or +0.5) leads to few or no halos with multifocal IOLs.

Pseudo-accommodating IOLs require emmetropia for optimizing results, and excimer laser enhancement is needed in up to 20% of cases. Vigo et al. (L. Vigo, E. Scandola, F. Carones, presented at ESCRS, 6–10 September 2003; Munich, Germany) have treated eight eyes (seven by LASIK, one by PRK) with a -4.5 to +2.5 residual error after pseudo-accommodating IOL implantation, achieving emmetropia, good short-term accommodation, and no dysphotopsia. Unfortunately, the procedure was later abandoned because of long-term loss of accommodative ability.

Bioptics after cataract surgery

After cataract surgery, preexisting or surgically induced astigmatisms, as well as wrongly powered IOLs (a major cause of litigation), must be adequately addressed. ‘Piggybacking’ or IOL replacement can be considered, but use of the excimer laser is the most precise and least invasive approach. LASIK has been successfully employed after phacoemulsification and extracapsular extraction, the latter, however, with a 15% rate of diffuse lamellar keratitis. In the phacoemulsification studies, 82–100% of eyes treated by LASIK ended within 1 D of residual error, and no retinal, incision, or IOL complications were observed. PRK has been also successfully used after phacoemulsification in a limited case series. Possibly because of the mean patient age (75 years), a slight overcorrection of myopia was seen after LASIK and PRK.

My personal preference is for surface ablation for two reasons. First, corneal sensitivity is reduced after the age of 60 years, and the post-PRK course is normally painless. Second, dry eye is common at that age, and LASIK may induce or exacerbate symptoms. Surgically induced astigmatism is often asymmetric, however, and laser correction is therefore less precise than in congenital astigmatism.

Reverse bioptics: intraocular lenses after excimer laser

Phakic IOLs after corneal surgery and refractive lens exchange after excimer laser are discussed here.

Phakic intraocular lenses after corneal surgery

After an unsuccessful corneal refractive procedure, the temptation of a so-called enhancement is appealing to both the surgeon and the patient; however, further corneal surgery can induce recurrent haze and ectasia and is, for many reasons, poorly predictable. Thin corneas or large regressions can be conveniently approached using ‘reverse’ bioptics, i.e. phakic IOL or lens exchange after the corneal procedure. Vaz has successfully implanted iris-fixated phakic IOLs to correct residual/regressed hyperopic or myopic errors after LASIK, PRK, radial keratotomy, or intracorneal rings; two-thirds of cases ended within 1 D of emmetropia.

I have personally implanted angle-supported phakic IOLs in 12 cases of regression after myopic PRK and LASIK, which had been used improperly to address high myopic errors. Regression must be stable for at least 18 months and endothelium must be regular. Calculation of IOL power is affected by difficult subjective refraction: use of the van der Heijde formula led in my first cases almost invariably to undercorrection of myopia. I now adjust the formula by overcorrecting myopia by 10%, thus achieving better predictability. The changes induced by the surgical incision in these excimer laser-treated corneas are not relevant.

Refractive lens exchange after excimer laser

In the presbyopic age, reverse bioptics is best performed using refractive lens exchange, prudently with a monofocal IOL. Again, IOL power calculation after corneal surgery is the main issue, and many formulas have been proposed. A brilliant solution is represented by intraoperative autorefractometry, which Ianchulev et al. have recently assessed in normal eyes and in six LASIK-treated eyes, performing it during phacoemulsification, between cortical cleanup and IOL implantation. Their conclusion, in both normal and postcorneal surgery eyes, is that the spherical equivalent at autorefraction should be doubled to obtain the IOL power (e.g. with a +5 D autorefraction, a +10 D IOL should be implanted in the capsular bag). No IOL A-constant or IOL model is indicated in the paper, however.

I have found more accurate the Gills' formula (originally proposed for piggyback IOLs), in which autorefraction is multiplied by 1.3–1.5 (long eye to short eye) and +1 D is added. So, a +5 D autorefraction would indicate a +8 D IOL implant (I use it with a 118.2 A-constant). My use of the intraoperative hand-held autorefractor (Retinomax 2, Nikon, Tokyo, Japan) is as follows: when the expected IOL power is less than +8 D, autorefractometry is performed after cortical cleanup, then the is IOL chosen. In all other cases, autorefractometry is done after IOL implantation and viscoelastic removal; the IOL is then immediately exchanged if outside 1 D of desired refraction.

Bioptics for keratoconus and pellucid marginal degeneration

In keratoconus and pellucid marginal degeneration, irregular astigmatism is often associated with axial or corneal myopia. Intracorneal rings have been combined with phacoemulsification and in-the-bag IOL, with iris-fixated phakic IOLs (A. Abdel Fattah, T. El-Raggal, presented at ESCRS; 18–22 September 2004; Paris, France), and with posterior chamber phakic IOLs (E. Coskunkeven, L. Oktem, E. Ozkilik, et al., presented at ESCRS; 18–22 September 2004; Paris, France).

In cases with reduced astigmatism, pseudophakic or phakic IOL implantation should probably precede intracorneal rings (which might ultimately not be needed); in other cases, rings should be implanted first to provide reliable K readings for IOL power calculation. The published cases are few and follow-up was limited, however, and this aspect of bioptics needs (and deserves) further investigation.

Conclusion

Bioptics is worth doing. It improves vision and halos and adds no particular risks to phakic or pseudophakic IOL implantation, in either myopia or hyperopia. Reverse bioptics, with phakic IOLs or refractive lens exchange (helped by intraoperative autorefraction), is a predictable compensation for poor corneal surgery and should be preferred to laser retreatments in many cases.

The only field in which doubts persist is bioptics in presbyopic lens exchange, both with multifocal and accommodative IOLs. Here, however, the problems are in the IOLs, not in laser enhancement, which has nevertheless salvaged many eyes from poor distance uncorrected visual acuity. What bioptics cannot do is to improve halos and to maintain long-term accommodation.

The weaknesses of the present paper are several. No comparative studies between techniques exist. Most series are numerically limited, and many papers were presented but unpublished. Few studies mention dysphotopsia, and none induced aberrations.

We can imagine bioptics as the standard procedure for higher refractive errors in the future, the only drawback being increased costs. Patient age, surgeon preferences (different phakic IOLs, and LASIK vs. surface ablation), and costs will dictate the solution in each case. Improved IOL designs, laser ablation strategies, and LASIK flap creation techniques (e.g. femtosecond laser) will further expand the choices.

Summary:

Bioptics improves vision and halos and adds no particular risks to phakic or pseudophakic intraocular lens implantation in either myopia or hyperopia. Reverse bioptics, with phakic intraocular lenses or refractive lens exchange, can be used to correct regressed corneal surgery.

Corneal Asphericity and Visual Function After Wavefront-Guided LASIK.

2006-10-01T22:10:00.000-07:00

The principal theory of laser refractive surgery is that the optical power of the eye can be changed by modifying the corneal curvature. Flattening a myopic cornea corrects nearsightedness, whereas steepening a hyperopic cornea corrects farsightedness.

The majority of human corneas are aspherical in shape. Changing the shape of the corneal surface through laser refractive surgery also alters its asphericity. The degree of asphericity in a cornea can be described using a conic constant, Q. A negative conic constant is referred to as a prolate surface with the highest curvature occurring at the apex, like at the tip of an egg. A positive conic constant is referred to as an oblate surface and resembles the bottom of an egg with the top of the curvature being flatter than the rest. The Q-value is similar to the shape factor used in corneal topography, but the sign convention used for the Q-value is the opposite of that used for the shape factor.

After conventional LASIK procedures, many previously myopic eyes experience increased spherical aberration. It has been suggested that this increase is the cause of reduced visual performance. According to this theory, the increase in spherical aberration arises from flattening the cornea, and because most natural corneas are prolate, the postsurgical increase in spherical aberration results from altering the natural prolate surface. Therefore, this theory continues that good-quality vision can best be achieved with a theoretically optimal conic shape on the anterior cornea. This hypothesis is at odds with the theory that the best vision can be accomplished by correcting defocus and higher-order aberrations of the entire eye on an individual basis with a customized shape derived from the patient’s wavefront measurement.

DISCUSSION

This study did not find a correlation between corneal Q-value and visual performance. There was no evidence that preserving preoperative corneal Q-value guaranteed better visual outcomes. An oblate cornea is as likely to produce high-quality vision after surgery as a prolate cornea. In addition, the amount and direction of change in corneal asphericity had no influence on visual acuity or contrast sensitivity. Most important, amount and direction of change in corneal asphericity were not predictors of improvement in visual functions.

The theory that managing Q-value during refractive surgery can affect outcome was based on the assumption that Q-value is closely related to spherical aberration.

Mathematical modeling of the relationship among corneal asphericity, Q-value, and corneal spherical aberration using a corneal refractive index of 1.377 and corneal curvatures ranging from 41.25 to 45.25 D. Q-value is the best fit conic shape of a cornea. It does not take the central curvature of the cornea into account. With a constant Q-value, one can find a range of magnitude of spherical aberration, depending on central corneal curvature. In addition, prolate cornea (negative Q-value) only relates to negative spherical aberration when the value is more negative than -0.53. Because alteration of the corneal curvature is inherent to refractive surgery, i.e., the curvature is steepened or flattened to correct vision, constant Q-value and spherical aberration are not likely to occur simultaneously. Furthermore, other published mathematical modeling has established that no single conic shape could maximize retinal image quality.

Whereas a correlation exists between Q-value and corneal spherical aberration, it is not a perfect correlation. To further demonstrate, imagine two glass eggs, one small and one large. Both have the same asphericity (Q-value), but the difference in the radius of their curvatures causes them to have different amounts of spherical aberration. That means that even if Q-value were successfully preserved after LASIK surgery, because the corneal curvature is modified, the alteration of corneal spherical aberration is inevitable. Furthermore, retinal image quality is the cumulative result of various ocular components, which also include the posterior corneal surface and the crystalline lens. Therefore, it is not surprising to find that correlation between corneal Q-value and visual performance is nil. This finding does not contradict the findings of theoretical and experimental studies on the impact of ocular spherical aberration on visual performance. On the contrary, our findings agree with previously published findings that spherical aberration significantly affects contrast sensitivity performance. However, one should not overlook the fact that spherical aberration is just one of many aberration terms and that any of these, whether alone or in combination, affect the quality of the retinal image.

Our study did not intend to examine the individual contribution of each HOA to visual performance. It is known that RMS evaluations of the impact of HOAs on vision do not correlate well with visual performance, especially when RMS is of low magnitude. It is also known that aberrations interact to increase or decrease visual performance. Because real eyes do not exhibit isolated HOAs, and because the possible relevant combinations are extensive, we did not attempt to study the impact of each different aberration on visual performance in normal populations. However, HOA variables were applied in multivariate analysis to isolate the effect of Q-value from spherical aberrations.

In theory, ocular aberrations have more direct impact on retinal image quality than corneal aberrations, but our visual performance data showed stronger correlation of visual performance with corneal HOA than ocular HOA. In a normal population, HOAs from different optical components tend to neutralize each other, which results in much smaller overall HOAs. In addition, wavefront-guided refractive surgical technology attempts to minimize postoperative ocular aberration. Consequently, the ocular HOAs are lower both before and after surgery than the corneal HOAs. The result is a data distribution for the ocular HOAs that is approximately half that of the corneal HOAs. To analyze this limited distribution of ocular HOAs statistically would require a larger sample size than that used to analyze corneal HOAs. A larger study population than ours would be likely to show more solid effects with the ocular than with the corneal aberrations.

The role of HOAs in visual performance has been studied extensively, and they have been shown to influence visual outcomes. Current outcomes of wavefront-guided LASIK procedures reinforce these published conclusions. In addition to enhanced best-corrected visual acuity, wavefront-guided LASIK treatments have produced improved contrast sensitivity and reduced night vision complaints in some patients after surgery, all of which further uphold the findings of this study, i.e., correcting the overall optical system is likely to provide better visual outcomes.

CONCLUSIONS

Findings presented in this article reinforce that better visual outcomes are most likely to be achieved with a customized shape that corrects the overall optical system. Corneal conic constant alone does not appear to be a determining factor in postoperative quality of vision. The human eye is a complex optical system, and the quality of the retinal image depends on the combined optical effects of many elements, including, but not limited to, the anterior and posterior of cornea and crystalline lens. Based on our population data and modeling, corneal surface curvature, which is expressed as Q-value, did not by itself influence the postoperative outcome on retinal image quality in a significant way.

Progression of Adult Nearsightedness.

2006-09-28T22:41:00.000-07:00

Most myopia develops during the school years and stabilizes in the teenage years. Nonetheless, a number of individuals will show myopic changes after entering college. This may manifest as an increase in myopia in a previously myopic subject—adult myopia progression—or the onset of myopia in a previously emmetropic or hyperopic individual—adult-onset myopia. The National Research Council Committee on Vision Working Group on Myopia Prevalence and Progression reviewed over 500 articles on myopia. On the basis of the studies reviewed, the report concluded that up to 40% of low hyperopes and emmetropes entering college and military academies are likely to become myopic by the age of 25 years. Conversely, in populations in which college graduates are excluded, less than 10% of individuals become myopic as adults.

There have been a number of reports of myopia progression in adulthood. Waring et al., for example, reported a mean myopic shift of –0.65 D across 10 years in the fellow eye of 47 Prospective Evaluation of Radial Keratotomy (PERK) study patients who elected not to undergo radial keratotomy on their second eye. Adams and McBrien found that 50% of clinical microscopists reported significant myopia progression since joining the profession. A number of studies, including our own, have documented myopia progression in subjects in their thirties. This agrees with eye care practitioners’ descriptions of adult myopia progression anecdotally associated with professional or graduate school, increasing computer use, or both.

None of the aforementioned studies has demonstrated a compelling relationship between adult myopia progression and near work. Clinicians may tell their patients that their adult myopia progression is related to their computer use. Nonetheless, there is little evidence to support this assertion. Rather, the association has been based on the occupation and education levels of different groups of subjects.

We describe the design and baseline characteristics of a 5-year observational study of myopia progression in adults with detailed measures of near work and other risk factors. At study end, subjects will be categorized into those whose myopia progressed and those whose refractive error was stable. The two groups will be analyzed with respect to near work-related risk factors. In particular, two broad categories of risk factors will be assessed: the proportion of time a subject spends reading or performing other forms of near work and selected characteristics of the subjects’ ocular accommodation and vergence.

The rationale for studying near work-related risk factors is based on the clinic and research community’s belief that near work causes adult myopic progression, reports of myopic changes in occupations involving large amounts of near work, and reports of an association between myopic progression and hours of near work in university students.

The rationale for studying accommodation-related risk factors is the numerous publications implicating accommodation and vergence in the etiology of myopia. A number of researchers have hypothesized that underaccommodation, or accommodative lag, induces myopia in humans by a similar mechanism to that which produces experimental myopia in animals. This hypothesis is supported by studies in children and adults showing greater accommodative lag in myopes compared with emmetropes. Subsequent studies have shown that accommodative lag is greater in children and adults. whose myopia is increasing than in those whose myopia is stable.

Studies have also linked the interaction between accommodation and convergence—usually characterized by the accommodative convergence/accommodation (AC/A) ratio—to the etiology of myopia. Cross-sectional studies in children and adults have found that higher AC/A ratios are associated with myopia. Jiang found that adults whose myopia developed or progressed over a 2- to 3-year period had significantly higher response AC/A ratios than those whose refractive error was stable. Likewise, Mutti et al. reported that a high response AC/A ratio is a significant risk factor for the onset of myopia in children.

DISCUSSION

This article presents the baseline findings from the SPAN. In comparing our results with previous studies, it is important to remember that all of the subjects in SPAN are myopes and the analyses use refractive error (degree of myopia) rather than the presence or absence of myopia. This is particularly germane when considering the impact of family history on the refractive status of the SPAN cohort. It is not surprising that so many subjects report myopic parents and siblings, but it is surprising that myopia in a parent, particularly the subject’s mother, is related to the degree of myopia. Although the degree of myopia is not significantly associated with the reported refractive status of the subject’s father, there is a trend for higher levels in those with a myopic father.

As reported by previous researchers, the degree of myopia is related to the age of onset. In the SPAN cohort, each 1-year increase in the age at which the subject began wearing spectacles is associated with –0.16 D less myopia and early-onset myopes are significantly more myopic than late-onset myopes. Further analysis demonstrates that that the number of myopic parents is significantly related to the age of myopia onset. For example, twice as many late-onset myopes (32.1%) report no parental history of myopia as early-onset myopes (16.6%). Given that both age of onset and parental history are significantly related to the degree of myopia in our cohort, we performed a multivariate analysis to simultaneously assess the affect of these variables. In the multivariate model, age of onset (early vs. late) was significant related to degree of myopia, but parental history was no longer significant. Thus, any impact of parental refractive error on the level of myopia is mediated by the age of onset of myopia. In other words, those subjects with myopic parents have higher levels of myopia because they developed myopia at an earlier age.

The degree of myopia is higher among contact lens wearers than nonwearers, but this is probably the result of the cosmetic and functional limitations of higher-powered spectacle lenses or having spent more years as a myope and thus having greater opportunity to begin contact lens wear. As would be expected, degree of myopia was associated with increased axial length. Although less compelling, the association with anterior chamber depth and corneal power has been reported previously.

The response rate for the ESM was impressive and bodes well for the characterization of near activity in the cohort. On average, subjects spend approximately one-third of their time engaged in near activity (34.1%) with computer use contributing just over half of the activity (18.9%). Despite the cohort having been recruited from university faculty and staff, the range of near activity is quite broad (0–67.3%).

Risk Factors for Progression

The goal of SPAN is to determine the risk factors associated with adult myopia progression. The primary risk factors to be evaluated are performing near work for a greater proportion of the day, performing near tasks at a close distance, a high response AC/A ratio, and a high accommodative lag. The first two near work-related risk factors were chosen based on the longstanding, but largely unsubstantiated, assertion that adult myopia progression is associated with high levels of near activity. Of the previous studies, few examined near work as a potential risk factor for adult myopia progression, and only Kinge et al. reported an association between near work and myopia progression (r = 0.25). Reading at a closer distance has been proposed as a potential risk factor in children. An informal survey at the Eighth International Conference on Myopia in 2000 found that 31 of 47 of meeting presenters (66%) felt that environmental factors were primarily responsible for adult myopia progression, and an additional nine (19%) felt that the progression was the result of an interaction between environmental and genetic factors.

The hypothesis that increased accommodative lag is a risk factor for myopia progression is supported by both animal myopia research and accommodative studies in humans. The neonatal animal eye can compensate for refractive errors induced by convex or concave lenses. A minus lens placed in front of the cornea shifts the focal plane posteriorly. In an emmetropic eye, this results in hyperopic defocus unless the eye accommodates. In young chicks, tree shrews, and monkeys, the eye compensates over a period of days or weeks by increasing its axial growth rate until the retina has shifted to this modified focal plane. A recent report suggests that the mechanism may still be active in adolescent monkeys.

In humans, underaccommodation to a near target—accommodative lag—results in hyperopic defocus similar to that produced by a minus lens in the animal studies. A number of researchers have hypothesized that this accommodative lag induces myopia in humans by a mechanism similar to that which produces experimental myopia in animals. Studies in children and adults reported greater accommodative lag in myopes compared with emmetropes. Subsequent studies have shown that accommodative lag is greater in children and adults whose myopia is increasing compared with subjects whose myopia is stable.

Studies have also linked the interaction between accommodation and convergence to the etiology of myopia. This interaction is usually characterized by the AC/A ratio, measured as the change in convergence (or phoria) induced by a change in accommodation. Cross-sectional studies in children and adults found that higher AC/A ratios were associated with myopia. Of particular interest is a small prospective study that found that adults whose myopia developed or progressed over a 2- to 3-year period had significantly higher response AC/A ratios than those whose refractive error was stable. Likewise, it has been reported that a high response AC/A ratio is a significant risk factor for the onset of myopia in children.

The ability of SPAN to successfully identify significant risk factors depends in part on there being a broad distribution of the relevant variables in the study population. In this regard, it is important to note that there is a broad range in the proportion of near activity undertaken by the subjects. Likewise, other primary risk factors—accommodative lag and AC/A ratio—along with secondary factors like phoria show similar broad distributions. A detailed analysis of the ESM data is the subject of a future manuscript.

Public Health Significance

Myopic progression in adults is of increasing clinical interest as increasing numbers of patients undergo refractive surgery, e.g., LASIK, to correct their myopia. Adult myopic changes affect the long-term patient satisfaction with such procedures. For example, a 25 year old who is rendered emmetropic by LASIK, but whose myopia then progresses by a diopter over the next decade, will evolve into a 35-year-old –1.00-D myope (although such a refractive error may be desirable in a presbyope). Javitt and Chiang analyzed the cost-effectiveness of excimer laser photorefractive keratectomy and concluded that over a 20-year period, it was a less expensive investment than either daily wear or extended-wear soft contact lenses. Their analyses were based, however, on the premise that there were no long-term refractive changes in the postsurgery patient and that the vast majority of patients remained “glasses-free.” If patients shift in a myopic direction, then clearly refractive surgery may be a less cost-effective alternative than proposed by Javitt and Chiang.

Comparison of Multifocal and Monovision Soft Contact Lens Corrections in Patients With Low-Astigmatic Presbyopia.

2006-09-23T08:02:00.000-07:00

Currently, there are two options for the contact lens correction of presbyopia, monovision and multifocal contact lenses. The advantages and disadvantages have been examined by many studies. However, major advances in contact lens design, along with improvements in measurement techniques of visual performance and subjective quality of vision, called for a reevaluation of the current presbyopic contact lens options.

The concept of monovision was first proposed by Westsmith in the 1960s. He described a system of fitting only one eye for distance and the other eye for near. Like with any optical correction, visual acuity is a critical factor in the success of monovision. Campbell and Green first demonstrated acuity loss with loss of binocularity. The acuity loss in monovision with high-contrast charts and adequate lighting is generally agreed to be less than one line. High-contrast visual acuity loss is relatively independent of the add power. There is approximately a one-letter decrease in binocular acuity per diopter of add power. Thus, most patients are able to maintain adequate vision with monovision correction.

There is some disagreement as to whether stereoacuity is important for distance depth perception. It is thought that beyond approximately 20 feet, monocular cues are used to judge distances. Cues such as perspective, overlap, motion parallax, and size may be more important to depth perception at distance than stereoacuity. The distance stereoacuity of patients with monovision is generally accepted to be 20 to 40 sec arc, but studies show a wide range of stereoacuity loss at near with monovision fitting. Ong reported that depth perception decreased with increasing anisometropia up to +2.00 D. Levy showed a direct linear relationship between unequal acuity and loss of stereoacuity. Later studies demonstrated that stereoacuity loss worsens with increasing monocular add powers.

The first soft bifocal contact lenses became available in the United States in the 1980s. In the past 2 decades, there have been major advances in disposable soft multifocal contact lenses. With multifocal contact lenses, visual acuity varies widely depending on the design of the lens, lighting, and contrast. Studies using early designs of multifocal contact lenses found that high-contrast distance acuity was decreased by between 0.5 to 1.0 lines and low contrast by one to two lines. More recent studies using newer designs have demonstrated that high-contrast acuity is not significantly affected with bifocal or multifocal contact lenses.

Stereoacuity can also be affected by multifocal contact lenses. Reports by Sheedy on early designs of multifocal lenses showed that stereoacuity was reduced by 32 to 36 sec arc compared with binocular correction. Other studies have shown losses up to 100 sec arc. More recent multifocal designs have shown improvement such that there is no significant decrease in stereoacuity with multifocal contact lenses vs. spectacle correction.

In 2000, there were approximately 100 million presbyopes in the United States; an additional four million people become presbyopic each year. The percent of contact lens fits and refits into monovision or multifocal soft contact lenses in 2004 was 16% in the United States and ranged from 1% to 40% worldwide. Bausch & Lomb’s SofLens Multifocal (Rochester, NY) claimed approximately 50% of the market share for soft multifocal contact lenses in 2005, the largest share of any soft multifocal brand (Health Products Research data, third quarter 2005). According to a recent survey, presbyopic contact lens fits still tend toward monovision over multifocal contact lenses. Perhaps this is because of the ease of fitting monovision or because of the wide range of available lens types and powers monovision allows, or it could be because monovision is a superior modality to multifocal contact lenses. To date, no study has been conducted to evaluate both the subjective and objective performance of the SofLens Multifocal and monovision correction in patients suited for both modalities. It was the purpose of this study to determine which presbyopic lens modality performs better and is better accepted by patients.

DISCUSSION

This study demonstrated that patients can achieve better than 20/20 high-contrast distance and near visual acuity with both multifocal and monovision contact lenses. The average high-contrast binocular acuity for both lens types was, at most, two letters worse than the best-corrected spectacle acuity and not significantly different. These findings are consistent with previous studies of monovision and multifocal contact lenses that found less than one line of visual acuity loss on high-contrast charts.

Low-contrast visual acuity was worse with presbyopic contact lens correction. At distance, low-contrast visual acuity with both multifocal and monovision contact lenses was three to four letters worse than with best-corrected manifest refraction. At near, multifocal wearers lost five to six letters of vision, and monovision wearers lost two letters compared with best correction. These findings are also consistent with previous studies showing decreased low-contrast visual acuity for both lens types.

What is more important is whether the loss of a few letters of acuity is clinically relevant and important to the patient. The worst acuity for both contact lens modalities was 20/32 at near. A good benchmark for near acuity requirements is 20/40, but it is not likely that patients would be able to read so close to their threshold level for long periods of time. Also, the patients’ visual acuity was not measured at low illumination. Studies have shown a decrease in acuity from one to three lines with both monovision and multifocal contact lenses under decreased illumination. Either low illumination alone or in conjunction with low-contrast print may compromise vision to unacceptable levels with either lens modality. It is likely that reduced illumination would decrease vision with multifocal contact lenses more than with monovision, because vision with multifocal lenses is more dependent on pupil size. Therefore, it is important to consider that some patients may require reading glasses or an alternate correction for extended or difficult near reading tasks.

A limitation of this study is the fact that it did not allow for a crossover in fitting either the monovision or multifocal lenses. The dominant eye was always fitted for distance, whereas the nondominant eye was fitted for near viewing. Pilot work by Schor and Erickson claimed that correcting the wrong eye for distance can impair the success of a monovision fit. However, for most of their experiments, they only used five to eight subjects, most of whom were not presbyopic. Later studies by Schor reexamined this point using patients with presbyopia and demonstrated that ocular dominance is not a critical part of a successful monovision fit. Back and Holden also concluded that ocular dominance does not seem to play a critical role in the successful fitting of monovision. Multiple studies showed that fitting either the dominant or nondominant eye for distance had no effect on visual acuity or performance. However, if a patient’s occupation includes demanding near tasks, they may be better fitted with the near lens on their dominant eye. Both monovision and multifocal lens fitting should be adapted to the individual patient’s visual needs.

On average, stereoacuity was 79-sec arc better with the multifocal compared with monovision contact lenses. Previous studies have demonstrated a range of stereoacuity from 40-sec arc to 400-sec arc depending on the type of lens, add power, and test of stereoacuity used. Not surprisingly, most studies have consistently found better stereoacuity with multifocal contact lenses than with monovision.

This study is unique in that the patient’s stereoacuity was compared with his or her habitual near correction and thus provides more information about visual performance in the real world. There was a large range of stereoacuity and a lower average stereoacuity than expected because patients were often undercorrected for near on entrance to the study. Thus, the average stereoacuity with multifocal lenses surpassed the baseline stereoacuity measurement by approximately 30-sec arc. Overall, however, the average stereoacuity with multifocal contact lenses was not as good as either what would be expected with full binocular near correction or as measured in previous studies. This may be the result of the fact that the stereoacuity test used in this study did not have monocular cues and was therefore a more accurate representation of true stereoacuity than findings from previous studies. The loss of stereoacuity may also be the result of the near blur (20/32 low-contrast acuity) found with the multifocal contact lens. Finally, approximately 34% of our subjects wore the multifocal in a “modified monovision” format (one high add and one low add). The fitting was done according to the manufacturer’s fitting guidelines, and this technique is a relatively common practice used by practitioners with this and other bifocal and multifocal contact lenses. Although this fitting technique may not accurately assess full multifocal to monovision performance, it is a better assessment of how patients are fitted outside a research setting and how they would experience the lenses if they were fitted in an average practice. The modified monovision fitting may be the reason for the decrease in stereoacuity seen in our patients with multifocal contact lenses.

The NEI-RQL instrument was developed to measure how refractive error and vision correction affect a person’s daily living. It is known that common in-office testing such as Snellen visual acuity or stereoacuity with monocular cues fail to evaluate all aspects of visual function. In fact, Berry and coworkers found that even when patients are corrected to 20/30 or better, they still have complaints about their vision and correction. Furthermore, the means of correction plays an important role in patient satisfaction. In Berry’s survey, the frequency of positive to negative comments in those patients wearing glasses was approximately equal. With contact lenses, positive comments outweighed negative comments by two to one.

In this study, no differences were found from the NEI-RQL results for expectations, diurnal fluctuations, dependence on correction, or worry. This was an expected result, because these subscales are more pertinent to patients with ocular disease or undergoing surgery. Also, the questions about suboptimal correction were not valid for this study. These patients were instructed to wear their contact lenses as much as possible during the study. Thus, because these questions asked about the frequency of using one type of correction over another, they were not relevant to the current study.

The differences in near and distance vision were not significant, yet there was a significant drop in clarity of vision with both contact lens modalities compared with the patient’s habitual correction. The near and far vision questions ask how the patient functions on many common visual tasks such as reading and driving. Patients felt that they could function well with their contact lenses and did not have difficulty performing most visual tasks; however, the clarity of vision subscale includes more general questions about whether the patient experienced any blur or distorted vision. It is understandable that patients would experience more transient blur with contact lenses then with their habitual correction (usually reading or multifocal spectacles), especially if they were new contact lens wearers.

Likewise, it was not surprising to find an increase in symptoms with both contact lens types. The NEI-RQL symptoms questions included discomfort, dryness, tearing, itching, and soreness, all of which can be very common in new contact lens wearers. Because this study excluded patients with previous multifocal or monovision contact lens experience, over two thirds of the subjects were new wearers. It is interesting to note, however, that there were no significant differences in symptoms between the two contact lens modalities.

The differences on activity limitations as a function of correction were not significant. Contact lenses could have been expected to improve the patients’ ability to participate in recreational activities. However, even at baseline, numerous subjects scored at the maximum level, so there was not much room for improvement in this area. This is consistent with previous studies using this survey.

Contrary to older studies, there was no statistically significant increase in glare symptoms with presbyopic contact lenses. Many studies have shown that glare was a major complaint with both multifocal and monovision contact lenses. Our results showed no difference in glare symptoms for monovision, multifocal, or baseline. This could be the result of the fact that the multifocal is a newer design. Additionally, some of the earlier studies used traditional lenses that may have caused corneal edema, whereas this study used disposable lenses. Furthermore, a recent study by McDonnell found no difference in glare symptoms when comparing monovision wearers with single-vision corrected presbyopes.

It is interesting to note that the subjects were significantly happier with their appearance in contact lenses compared with their previous correction. Both multifocal and monovision scored over 30 points higher than baseline on the appearance subscale—a large difference on a 100-point scale.

There was a trend toward higher overall satisfaction with multifocal contact lenses compared with either monovision contact lenses or the previous correction. Unfortunately, with this sample size, it was not possible to achieve statistical significance. The final study outcome, lens preference, speaks to the same question. Patients were asked to choose which presbyopic contact lens modality they preferred—multifocal or monovision. Because eligible patients could not have had prior experience with either lens modality before entering the study, there is no evidence to suggest their responses were biased by previous events.

Comparing both the objective and subjective results, there was only one test in which multifocal contact lenses were significantly superior to monovision: stereoacuity. Patients had better stereoacuity with multifocal contact lenses than with monovision, in some cases even better than what they were accustomed to with their previous correction. The importance of the loss of stereoacuity is often downplayed. Previous authors have claimed that studies have failed to show a subjective impairment related to the decreased depth perception and that patients do not complain of a loss of stereoacuity. However, the loss of depth perception may play a larger role in the success or failure of monovision than once thought. More recent examinations of monovision found that failed monovision wearers had larger losses of distance and near stereoacuity than successful monovision patients. Du Toit also established that the loss of near stereoacuity was greater in an unsuccessful group of monovision patients than in her successful group.

Patients may not realize that it is a loss of stereoacuity that causes difficulties with task performance and visual function, and the average patient may not have an adequate enough understanding of stereoacuity to volunteer such information. However, Papas found that when patients were given the opportunity to wear both monovision and bifocals and were asked if they noticed difficulty judging distances, 43% reported difficulty with monovision but only 5% reported difficulty with bifocals.

After trying the Bausch & Lomb SofLens Multifocal and SofLens 59 monovision contact lenses in close succession to allow for a true comparison, patients preferred multifocal lenses three to one over monovision. The reason patients prefer the multifocal contact lens is most likely because the multifocal provided comparable visual acuity without compromising stereoacuity to the same degree as monovision.

Conclusion

The majority of our patients preferred multifocals to monovision, most likely because the Bausch & Lomb SofLens Multifocal provides excellent visual acuity without compromising stereoacuity to the same degree as monovision.

Post-laser in-situ keratomileusis ectasia: current understanding and future directions.

2006-09-16T21:23:00.000-07:00

Introduction

Corneal ectasia remains one of the most insidious complications after laser in situ keratomileusis (LASIK). Since the first reports by Seiler and colleagues in 1998, fewer than 150 cases have been reported in the ophthalmic literature, although this number is likely an underrepresentation of the actual incidence. Thus, while rare, post-LASIK ectasia can have dramatic consequences and in some instances require corneal transplantation for visual rehabilitation.

Due to not only the visual and medical but also the medico-legal ramifications of post-LASIK ectasia, seven members of the American Academy of Ophthalmology, International Society of Refractive Surgery, and the American Society of Cataract and Refractive Surgery have rendered a consensus opinion paper to summarize current knowledge on the subject.

Eliminating this complication altogether may prove difficult. Increased understanding of the alterations in corneal biomechanics after LASIK, improved recognition of risk factors for post-LASIK ectasia, and improved management strategies, however, can considerably reduce both the incidence and the severity of this potentially significant complication.

Incidence and etiology

Corneal ectasia after LASIK is a progressive corneal steepening, usually inferiorly, with an increase in myopia and astigmatism, loss of uncorrected visual acuity, and often loss of best-corrected visual acuity that can present days to years after LASIK. The actual incidence remains undetermined, and no good data support firm predictions; previous estimates, however, have ranged from 0.04% to 0.2% to 0.6%. Among members of the International Society of Refractive Surgery (ISRS) of the American Academy of Ophthalmology (AAO) responding to the practice patterns survey in 2004, more than 50% had at least one case of ectasia develop in their practice. Approximately 50% of cases present within the first 12 months, but late onset ectasia can also occur.

Corneal refractive surgery by definition alters the effective shape, thickness, curvature, and tensile strength of the cornea. Chang and Stulting found that intraocular pressure reductions after LASIK were directly correlated with increasing refractive correction, with an independent effect of flap creation, signifying that the lamellar flap does not contribute to the tensile strength of the post-LASIK cornea. Andreassen and colleagues found the elastic modulus of the keratoconic cornea to be 1.6–2.5 (average 2.1) times less than that of a normal cornea. Post-LASIK ectasia may mimic this altered corneal elastic modulus.

The specific mechanisms resulting in extreme corneal shape alterations manifesting as post-LASIK ectasia remain undetermined, although complex biomechanical modeling that takes into account factors such as corneal ‘plasticity’ and ‘viscoelasticity’ and corneal parameters such as Young's modulus, Poisson's ratio, and curvature radius, among others, may provide insight in the future.

Risk factors

LASIK inevitably reduces the tensile strength of the cornea. Among the first four reported post-LASIK ectasia cases, all had greater than 10 diopters of myopia preoperatively and less than 250 µm residual stromal bed thickness (RSB) postoperatively, and two patients had forme fruste keratoconus. Extrapolating from Andreassen's data, Seiler postulated that reduction in the load-bearing portion of a normal cornea from 525 to 250 µm (a factor of 2.1) might simulate the elasticity of a cornea with keratoconus, and predispose to developing ectasia. This value also coincides with Barraquer's early recommendation that a RSB of at least 250–300 µm be maintained to prevent corneal ectasia after myopic keratomileusis. Pallikaris and colleagues also reported a large series of patients with myopia greater than 10 diopters that developed post-LASIK ectasia with variable RSB.

A population of post-LASIK ectasia patients was compared with a general post-LASIK control population and a post-LASIK control population with high myopia preoperatively (greater than -8 diopters). This study confirmed earlier suspicions and found a significant difference between control populations and post-LASIK ectasia patients, with ectasia patients having higher myopia preoperatively and low RSB postoperatively – usually less than 225 µm. Additionally, 88% of ectasia cases had forme fruste keratoconus preoperatively as defined by Rabinowitz and McDonnell, compared with 2–4% of control cases. Additionally, multiple postoperative LASIK enhancements have also been correlated with postoperative ectasia. These findings were further supported by subsequent reports on the characteristics of post-LASIK ectasia. Binder provides comprehensive analysis of features of reported ectasia cases through 2003.

High myopia

It follows logically that patients with high myopia will have lower residual stromal beds after appropriate tissue ablation than their counterparts with less myopia; thus, it remains possible that high myopia simply predisposes to a thinner RSB rather than independently increasing the risk for developing ectasia. Some of the patients with post-LASIK ectasia reported by Pallikaris and colleagues, however, had theoretically adequate RSB (more than 250 µm) despite treatments for high myopia.

Low residual stromal bed thickness

Factors contributing to low postoperative RSB in addition to high myopia include excessive flap thickness and deeper than expected stromal ablations. There can be significant variability in the measurement of corneal thickness, flap thickness, and ablation depth measurements. While most of the microkeratome plate markings overestimate average actual flap thickness, flap thickness can vary widely and excessively thick flaps still occur. Additionally, previous studies have found that actual ablation depth is usually greater than estimated ablation depth. Among surveyed members of the ISRS/AAO, only 31% currently routinely measure flap or RSB intraoperatively.

Multiple enhancements

Multiple enhancements have also been correlated with ectasia; it remains difficult, however, to determine whether multiple enhancements are a contributing cause of ectasia in ways other than simple residual stromal bed reduction, and whether multiple enhancements stimulate ectasia by RSB reduction or whether they are simply performed more frequently in these cases in response to the progressive myopic shift associated with ectasia. Previous studies have demonstrated significant inconsistencies between RSB estimations by various direct and indirect calculations and highlight the value of directly measuring RSB via intraoperative pachymetry measurements.

Topographic abnormalities

Most authors recognize preoperative topographic abnormalities as uniquely indicative of increased risk for post-LASIK ectasia; the definition of ‘abnormal’, however, remains a source of great debate. Forme fruste keratoconus as defined by the Rabinowitz criteria is a risk factor for post-LASIK ectasia. Pellucid marginal corneal degeneration suspects are also at increased risk. Rao and colleagues reported that preoperative posterior float elevations greater than 40 µm may signify increased ectasia risk. Based on extensive review of the literature, the members of the AAO/ISRS/American Society of Cataract and Refractive Surgery (ASCRS) joint committee now recommend avoiding LASIK in patients with asymmetric inferior corneal steepening or asymmetric bowtie patterns with skewed steep radial axes above and below the horizontal meridian.

Ambrosio and colleagues found that approximately 1% of refractive surgery candidates were excluded due to abnormal topographies, including keratoconus, keratoconus suspect, and pellucid marginal corneal degeneration. The risk profile for more subtle topographic abnormalities, including asymmetric bowtie and mild inferior steepening patterns, however, remains unclear. Varsanno and colleagues and Kanpolat and colleagues both independently found that up to one-third of patients presenting for refractive surgery do so with an asymmetric bowtie topographic pattern.

Ectasia without risk factors

Although most reported cases have at least one of the aforementioned risk factors, there are reports of post-LASIK ectasia developing in patients without risk factors, and of patients developing ectasia after surface ablation.

Risk factors summary

At this time, currently recognized risk factors for the development of post-LASIK ectasia include keratoconus, high myopia, low RSB (probably less than 225–250 µm) resulting from excessive ablation relative to preoperative corneal thickness for high myopia or thicker than expected lamellar flap creation, and preoperative topographic abnormalities, including forme fruste keratoconus and pellucid marginal corneal degeneration.

As discussed eloquently by the AAO/ISRS/ASCRS joint committee, however, no single risk factor or defined combination of risk factors stands alone as an absolute predictor of post-LASIK ectasia occurrence. Ectasia can certainly also occur in patients without any recognized risk factors.

Management

Post-LASIK ectasia management includes first and foremost prevention of its occurrence, which requires recognition of the problem, identifying and refining known risk factors, and utilizing alternative treatment strategies in high-risk patients. When ectasia occurs, prior to performing corneal transplantation, a variety of treatments are available currently, including intraocular pressure reduction, rigid gas permeable contact lenses, and intracorneal ring segments.
Hiatt and colleagues recently reported a case of early ectasia reversed by intraocular pressure (IOP) reduction. The authors postulate that there exists a ‘window of opportunity’ very early in the development of ectasia when IOP lowering may be beneficial, whereas they report no success in reversing long-standing post-LASIK ectasia with IOP management. The full effect of IOP management on post-LASIK ectasia remains to be determined.

When ectasia becomes manifest, rigid gas permeable contact lenses are usually necessary and frequently sufficient for visual rehabilitation. Fitting strategies for post-LASIK ectasia are often similar to those for keratoconic eyes. Various specific lens styles can be used, including standard aspheric, multicurve, or reverse-geometry lenses either alone or in combination with high oxygen-transmissible soft lenses in a piggyback lens system to improve comfort. The specific fitting parameters should be customized to each case, as post-LASIK ectatic corneas may present quite dissimilarly.

Recently, intracorneal ring segments (Intacs; Addition Technology Inc., Sunnyvale, California, USA) have been approved for use in keratoconus, and some promising results have been reported when used off-label for post-LASIK ectasia. Techniques reported have varied in terms of wound location and the size, symmetry, and number of Intacs placed. Some surgeons have placed symmetric thickness Intacs segments in the same manner as for low myopic correction, with the wound in the 180° meridian, while other surgeons have used both symmetric and asymmetric segments, with a thicker segment inferiorly, with standard wound placement. Alio and colleagues reported success with placement of symmetric thickness segments with the wound location in the steep corneal meridian. Pokroy and colleagues reported success with single Intacs segment implantation placed inferiorly. While the early results for Intacs appear promising, few longitudinal follow-up data exist; thus the long-term utility of this procedure for post-LASIK ectasia also remains to be determined.

Future directions: recognition and prevention

When potential at-risk patients present for surgery, especially those with high myopia, thinner corneas, or subtle topographic abnormalities, novel screening approaches and surgical options other than LASIK, including surface ablation and phakic intraocular lens implantation, should be explored.

Utilizing alternative treatment strategies for at-risk patients

Once a LASIK flap has been created, collagen fibers anterior to the flap contribute little if anything to the overall tensile strength of the cornea. The posterior stroma also appears more vulnerable to biomechanical weakening than the anterior stroma. For these reasons, surface ablation techniques including photorefractive keratectomy, laser subepithelial keratomileusis, and epi-LASIK, may be more suitable for borderline candidates, especially those with thinner corneas or mild topographic irregularities.

Phakic intraocular lens implantation avoids altering a potentially unstable cornea for highly myopic at-risk patients, and these lenses have recently shown promising results in keratoconic eyes and may also be applicable to some of the at-risk patients presenting for LASIK.

Utilizing new technology to identify abnormal corneas

Some studies suggest that patients developing ectasia without risk factors may be younger or have surgery prior to manifesting latent topographic abnormalities, as evidenced by a case in which bilateral corneal ectasia developed after unilateral LASIK. This suggests that current screening approaches rely on relatively late indicators of reduced corneal integrity, namely topographic evidence of corneal weakness. Newer techniques, including corneal interferometry, corneal hysteresis measurements, and dynamic corneal imaging may allow identification of at-risk patients with normal topographies but reduced biomechanical integrity preoperatively.

Avoiding retreatment in corneas with low residual stromal bed thickness

As corneal thickness measurements taken months after initial LASIK usually overestimate RSB thickness at the time of LASIK retreatment, accurate assessment of actual RSB is critical to avoid excessive ablation of the posterior stroma. This can be avoided by utilizing intraoperative pachymetry measurements prior to laser ablation, or by utilizing confocal microscopy prior to enhancement, as the confocal microscope can accurately measure RSB thickness without ever lifting the flap.

Future directions: management and reversal

In addition to the aforementioned treatment strategies, corneal collagen cross-linking may improve the course of post-LASIK ectasia. Using riboflavin as a photosensitizer followed by ultraviolet-A exposure, Wollensak and colleagues found that collagen cross-linking halted the progression of ectasia in keratoconus patients and in many cases reversed the process, as evidenced by a reduction in corneal steepening and refractive error. Future work will examine the safety and efficacy of this approach for post-LASIK ectasia patients.

Conclusion

Current evidence suggests that, although cases of post-LASIK ectasia will likely continue to infrequently occur, there should not be an impending ‘ectasia epidemic’. In fact, as methods for identifying at-risk patients improve and alternative treatment strategies are employed, the incidence should significantly decrease. This decrease will be facilitated by improved preoperative patient evaluation utilizing advanced topographic analysis and corneal elasticity measurements. Measurement of intraoperative pachymetry should become routine to avoid treatment after inadvertent thick flap creation. Alternative surgical options, including surface ablation and phakic intraocular lenses, should be considered for at-risk patients. When ectasia initially occurs, effective treatment strategies including intraocular pressure reduction and collagen cross-linking may be able to reverse ectasia. When ectasia becomes manifest, rigid gas permeable contact lenses and intracorneal ring segments may both be utilized as effective first-line treatments for visual rehabilitation. Thus, with time, the need for corneal transplantation for post-LASIK ectasia should significantly diminish.

Screening for Myopia and Refractive Errors Using LogMAR Visual Acuity by Optometrists and a Simplified Visual Acuity Chart by Nurses.

2006-09-13T09:13:00.000-07:00

Refractive errors (e.g., myopia, hyperopia, and astigmatism) are important vision disorders requiring screening in children and adults. Although screening using a visual acuity chart is the most practical method to detect refractive errors, the methods and thresholds of screening have not been universally accepted. Early detection of refractive errors in children allows timely intervention in the form of spectacle correction.

For the purpose of screening elementary schoolchildren, two types of visual acuity charts have been most commonly used. The first type, the non-logarithm of the minimum angle of resolution (MAR) type of visual acuity chart, uses lines of English alphabets, with no universally accepted number of letters per line or standardized number of lines per chart, and has acuity values recorded as a Snellen notation (a fraction) or as a decimal. The second type, from the Early Treatment Diabetic Retinopathy Study (ETDRS), is a letter-counting type of visual acuity chart, which not only has a standardized number of lines and letters per line but also is able to discriminate finer levels of visual acuity and document minimum resolution acuity in a logarithmic scale (logMAR), which facilitates algebraic operations for compiling statistics.

Despite the shortcomings of using the non-logMAR visual acuity chart and the advantages of the second type of visual acuity chart, screening traditionally has been performed in many studies using simplified visual acuity charts based on Snellen fractions. Various studies using a “Snellen” chart for screening in children have been reported in the U.S., Western Australia, Denmark, Oman, and England using an equivalent of “6/12 or worse” criterion without previous justification of this threshold. For methodological reasons discussed elsewhere, these previous studies were also unable to determine the actual sensitivity and specificity of screening. In contrast, in many scientific studies, especially clinical trials, in which visual acuity and its changes were important endpoints, visual acuity has been measured using an ETDRS type chart and documented in logMAR format. The optimal logMAR visual acuity threshold for screening referral recently has been reported.

In Singapore, a multilingual society with a high rate of English literacy, simple 7-line visual acuity charts with English alphabets have been used for many years to screen for eye problems in schools. Children with visual acuity of “6/12 or worse” are referred for further assessment. The accuracy of screening using the non-logMAR type chart compared with the ETDRS chart has not yet been evaluated in a large study involving schoolchildren.

The objective of this study was to compare the sensitivity and specificity of a method of screening using a simple 7-line acuity chart with a more exacting method using the ETDRS chart for the purpose of screening for refractive errors in Singapore schoolchildren. As a secondary objective, the study aimed to estimate the best cutoff values for the detection of refractive errors.

DISCUSSION

The two main findings in this study were the optimal referral thresholds for the two methods of measurement of visual acuity and the greater relative accuracy of the logMAR visual acuity measurement by optometrists to correctly predict cases of myopia and any refractive errors in children.

Bearing in mind that different types of professionals were used for the visual acuity measurements, this study showed that the optimal threshold level for using the visual acuity chart to screen for myopia is similar between the ETDRS and the simplified screening charts. In the case of the prediction of any refractive errors, the optimal threshold for referring cases on the logMAR visual acuity appears to be lower than the case for the simplified acuity charts. Nevertheless, it would appear from the data that the intuitive threshold of 6/12 used in screening seems to be the optimal level.

The determination of the optimal threshold in this study assumes the sensitivity and specificity of screening to be equally important. In populations with different prevalences of myopia and refractive errors, this assumption may not be valid. In populations with low prevalences of myopia, for example, it may be preferable to adopt a more specific test that may result in fewer false-positive referrals.

The ROC curve for the ETDRS chart was higher than the simplified visual acuity screening chart. This implied that for any threshold on the simplified chart as used by nurses, there would exist a superior threshold using the logMAR chart by optometrists in terms of sensitivity and specificity for the detection of refractive errors. This superior accuracy of the logMAR has never been demonstrated in any previous study. For given levels of sensitivity, the specificity values of the ETDRS method were superior. At the 91% sensitivity level, the specificity is about 88% for the ETDRS and 83.5% for the method using the simplified screening chart. Although the superiority of the ETDRS method is clear, economic considerations will dictate whether this level of benefit warrants a switch in real screening scenarios.

Camparini et al. have shown that a fast ETDRS threshold testing method to measure logMAR visual acuity is valid compared with the full threshold testing method. In this article, we have taken this one step further to show that in a school population, which is a common target for screening for refractive errors, the logMAR visual acuity test, using this fast threshold algorithm, performed superiorly by optometrists compared with the current standard of visual acuity screening as performed by school nurses.

What are the possible reasons for this relative superiority in the case of screening with logMAR visual acuity measurement by optometrists? Besides the issues of standardized letter sizes and spacing, this study used the line-by-line scoring with the simplified screening visual acuity chart, a common practice with this type of visual acuity chart. In contrast, letter-by-letter scoring was performed using the ETDRS charts. Letter-by-letter scoring has been shown to result in improved test-retest variability than is permitted by line-by-line scoring. In this particular study, the testing of the children was performed by different testers for the two different types of visual acuity charts. It may be that optometrists could perform the testing procedure more rigorously than nurses. In the case of the simplified screening visual acuity charts, there is a possibility of some children artificially obtaining better than real visual acuity in the left eyes from the effect of memorizing the letters while reading with the right eyes.

The mean difference between the logMAR visual acuity compared with the simplified screening acuity was significantly different from zero. This suggests that visual acuities measured on the simplified charts have a tendency to be worse. A systematic difference exists despite the presence of a good correlation, which measures degree of association but not agreement.

The strengths of this study include a large sample size drawn from a population, uniformity of assessment, and objectivity of autorefraction. The use of cycloplegia excluded pseudomyopia or accommodative spasm.

Economic and logistic considerations, important in screening tests, have not been considered in this article. Initial impression of the testing indicated that the time required for measuring visual acuities with the logMAR method was slightly longer than that for the simplified screening acuity charts (unpublished data).

The study sample was not randomly selected from the school population of Singapore. The method of sampling was an issue in this study. The sensitivity and specificity profile may change with differing disease prevalences in different schools. Berkson’s fallacy dictates that in a sample obtained from high-risk and low-risk populations, a biased sensitivity estimate is obtained in the high-risk population and a biased specificity estimate is obtained in the low-risk population. These limitations of the study make it more difficult to generalize our findings to other populations.

A further limitation of the study is the time interval between the two methods of visual acuity assessment; in a period of up to 4 months, it is possible that some of the subjects may have had progression of their refractive errors (in particular, myopia). The direction of bias introduced is uncertain. To evaluate the possible effect of bias, the adjusted scores ([kappa]) for sensitivity and specificity also were calculated. The result, once again, favors the logMAR visual acuity measurement.

For now, we conclude that the advantage of using the ETDRS method for screening for refractive errors is at least of statistical significance. This advantage may be related to the nature of the visual acuity chart or to the different background of the screeners. Should the cost-effectiveness of screening be equivalent for the two methods of determining visual acuity, the logMAR method of screening is preferred for detection of myopia or any refractive errors in a population like Singapore, where there is a relatively high prevalence of refractive errors, particularly myopia.

A deficit in visits to the optometrist by preschool age children: implications for vision screening.

2006-09-07T20:09:00.000-07:00

Vision screening in children is aimed primarily at detecting non-strabismic amblyopia (other forms of vision defect are generally evident to parents). Such non-strabismic amblyopia occurs mostly as a result of uncorrected refractive errors. In the December 2003 report by the Child Health Sub-group it was recommended that all 4-5 year olds should receive vision screening.

The Health For All Children 4 (HFAC4, 2003) “Hall Report” and the Children’s Eye Health Working Party guidelines similarly suggest vision screening should be undertaken in all 4–5 year olds. This advice is in accord with the results of the first randomised controlled trial of treatment for amblyopia, which found that treatment of moderate amblyopia (acuity 6/36-6/18) in preschool aged children was effective. However, currently the coverage of vision screening is patchy, and numbers of specialist screening personnel may be insufficient to meet demand if the recommendation to screen all 4-5 year olds were to be implemented. In districts where vision screening is not carried out, optometrists might act as an important safety net by providing an additional route for referral of non-strabismic amblyopes.

METHODS

As part of an investigation into the genetics of myopia, we investigated the age distribution of individuals attending for a sight test at 19 optometry practices in northern England during the period January 2000–December 2001. For subjects attending more than once, only the most recent visit was recorded. Of the 90 884 attendees, age was known for 90 750. None of the optometry practices operated in a manner that would be expected to discourage the attendance of children. The age distribution of this optometric cohort was compared with data from the census of England and Wales, conducted in 2000.

RESULTS

Although the optometry practices were not selected according to defined epidemiological sampling criteria, the high similarity in the age distribution of the two datasets after the age of 10 suggests the optometry attendees are generally representative of the UK population. However, there was a clear deficit in visits to optometrists in the preschool age group, which was highly significant. Attendance to optometrists appeared to increase linearly until about age 11 when it reached adult levels. Our analysis suggests that only ~7% of children aged 0-5 years visit an optometrist (1.48% of visits in the optometric cohort were for infants aged 0-5 years, and there were 16.6 million sight tests carried out in Great Britain in total, in the year 2000, suggesting 246 000 tests on the 3.7 million infants in this age group). Because infants in whom a refractive error has been detected are likely to visit their optometrist each subsequent year, this figure must be an overestimate of the proportion attending for the first time—that is, in a screening context.

COMMENT

The fact that a visit to the optometrist is such an exception to the rule at this age underlines the importance of vision screening programmes, and suggests that every effort should be made to implement a comprehensive system of screening at age 4-5 in order to detect children likely to benefit from early treatment for amblyopia. However, where such programmes are not in place, we suggest that encouraging children to visit an optometrist should help in the early referral of non-strabismic amblyopes.

Survey of Contact Lens-Wearing Habits and Attitudes Toward Methods of Refractive Correction: 2002 versus 2004.

2006-08-27T10:01:00.000-07:00

There is no one method for correction of refractive error that is either appropriate for or appealing to all patients. Some patients and practitioners choose spectacles as the best choice, whereas contact lenses or refractive surgery is the correction of choice in other circumstances.

To add further complexity, with the numerous technologic advances in contact lens materials and manufacturing, some patients may now wear lenses for 1 day and discard them, whereas others wear them for a month. The majority of patients use their lenses for 1 to 4 weeks before replacement, although some keep lenses for a year or more on a conventional replacement schedule. Another use dimension that offers flexibility (or confusion) is in the lens-wearing schedule; patients may wear lenses only while awake; or may sleep in lenses a few nights a week, for an entire week, or for 30 continuous nights, depending on lens type and practitioner recommendation. The overnight wear factor is of particular interest because it has been cited as a factor for the success of lens wear and, conversely, in the development of complications such as corneal infections. Researchers in the contact lens field have strived to learn how patients regard their contact lenses and about their patterns of use to improve patient success with contact lenses.

A survey conducted at the Contact Lens and Primary Care Clinics of Indiana University during the spring of 2002 showed that contact lens patients and spectacle wearers alike were less interested in 7-day extended overnight wear (EW) and 30-day continuous overnight wear (CW) contact lenses than laser in situ keratomileusis (LASIK) or orthokeratology (OK) when the treatments were described in a hypothetical model in which cost was not a factor. At the time of that survey, in the United States, 30-day CW wear silicone hydrogel lenses had been only recently made available and 7-day EW lenses remained relatively unchanged for over a decade in terms of materials, lens designs, and prescribed replacement schedules.

Early in this decade, there was an increase in the amount of direct advertising for LASIK, thus, patients in eye care offices very likely had less information about overnight wear of contact lenses than they had received about LASIK. Whether the patients would actually choose LASIK more than overnight wear of CW or EW contact lenses when the real-world factors of differences in cost, predictability, reversibility, and vision quality were incorporated is impossible to determine. It is possible, however, to measure whether there have been any significant changes in the degree of interest in or use of overnight wear with contact lenses after the introduction of new contact lens technology in the past few years by surveying two groups of patients presenting for eye care in 2002 and 2004.

Not surprisingly, the 2002 survey showed that current use of contact lenses was associated with more positive attitudes toward all nonspectacle methods of refractive correction. The survey also showed that gender had a significant influence on the reported amount of overnight contact lens wear at that time, with significantly more males reporting overnight wear of contact lenses. Men in that survey also indicated a significantly higher opinion about the health and safety of and interest in 7- and 30-day overnight wear lenses compared with women. Patients with a high amount of refractive error were not found to have any different attitudes and preferences for refractive error correction in that study compared with those with lower refractive errors.

Measuring patient attitudes and satisfaction with medical treatments is important because the patients' degree of satisfaction has been shown to correlate with utilization of healthcare. If patients have positive attitudes and a high level of satisfaction, they are more likely to use or continue use of medication, a device, or service provider. Measurement of attitudes among patients who do not use a particular refractive treatment can help practitioners understand whether patients have a realistic understanding and expectation of that treatment.

Measurement of attitudes among patients who have previously undergone a procedure more directly measures satisfaction with the procedure. Sequential surveys of practitioners' prescribing habits and preferred treatment methods have been used to assess the clinical community's uptake of newly introduced treatment paradigms. The current study was conducted in a noncorporate, neutral clinical setting among patients who were seeking eye care on that day, making them a particularly appropriate group to survey.

The purpose of this study was to assess the lens-wearing patterns and patient attitudes toward six methods of refractive error correction and track changes over time. Sequential surveys in the same clinical setting were conducted approximately 2 years apart to determine whether there shift in use patterns and attitudes had occurred over time, taking patient age and gender into account.

DISCUSSION

Patients who are seeking options for correction of their refractive error in the new century have a vast array of information sources to draw on. As stated by Ursula Vogt, MD, in the 2003 Kersley Lecture at the International Medical Contact Lens Symposium regarding information sources for patients, “They may look on the Internet, even buy their contact lenses there, but then they turn to you (practitioner) for guidance.” However, before they turn to an eye care practitioner, patients will have received abundant, often sound yet conflicting information that is difficult for them to dissect as it relates to their individual refractive and ocular condition.

Fortunately, unlike patients, clinicians are trained to recognize the complex factors that contribute to suitability for the various methods of refractive correction, the patient's age and refractive error, the condition of their ocular surface, and pupil size to name just a few.

Refractive surgery practices have widely adopted the use of educational seminars and direct advertising to communicate the benefit of LASIK to potential patients. Regardless of the method of initially reaching potential patients, a recent study of the rejection rate among patients screened for LASIK concluded that 13% of patients were rejected from surgery, regardless of whether they were screened by telephone or an educational seminar before they presented for examination.

Most of the rejections were the result of the presence of cataract or for a lack of acceptance or understanding of presbyopia; two concepts that are somewhat difficult for patients to grasp on their own and are of particular importance to patients above age 40. That study and others concluded that the most important element in the process of assisting patients in the right choice of refractive error correction was for a “qualified eye care professional to examine the patient in a thorough and critical manner” and that the patient is rather ill-equipped to self-diagnose their own suitability for a refractive surgical procedure.

Eye care patients' negative attitudes about EW contact lenses have been forged for many years by conscientious practitioners who were informing patients of the increase in risk of corneal infections from low dK hydrogel lenses. That cautious message was appropriate to reflect the clinical knowledge available at the time. Recent direct advertising to patients about CW silicone hydrogel lenses has attempted to reintroduce the patient to benefits that new lens technology offers that was lacking in the earlier contact lens materials. The specific change in attitudes toward the health and safety of 7 and 30 days overnight contact lens wear among women (especially those under age 30) in our recent survey could be the result of targeted messages in magazines and advertising aimed at young women. The change in use of EW, however, was significantly greater even when controlling for the change in age of the surveyed population. Interestingly, the distribution of lens replacement schedules did not change during the period between surveys.

Although serious infections have been reported with silicone hydrogel lenses, the rate of infections or risk factors with CW silicone hydrogel lenses is as yet not established as it was with low oxygen transmission lenses. The case series have thus far implicated pathogens already known to also be associated with infections with low transmissibility lenses, but the number of cases have not been high enough to establish any difference in the rate of infections. Postmarket studies will be required to provide that information for CW silicone hydrogel lenses. On the positive note, clinical studies abound that have shown an improvement in corneal and ocular surface physiology resulting from higher oxygen from silicone hydrogel lenses.

The patients in this study did not report any significant shift in their attitudes toward OK over the 2-year period. At the time of our previous survey, modern OK was in early stages of reintroduction to the ophthalmic community as a method for refractive correction, with overall promising early clinical and technical results. Because that time a number of reports of corneal ulceration associated with OK have emerged, primarily from China and the United States. There is always a possibility that infectious complications are induced by local factors; the safety and quality of the air and water supply in China may be important factors in these events along with the higher use rate of OK associated with the epidemic of myopia. The U.S. case series, however, also included two cases that were presumed infectious. Over the next few years, because OK is more widely used, clinicians will be better able to verify the safety of the corneal reshaping modality.

Our study shows that significantly fewer subjects over age 30 in the recent survey reported a high degree of interest in LASIK. Perhaps the problematic outcomes with monovision or uncorrected presbyopia have patients aware that older patients may have more difficulty with LASIK, are more likely to need retreatment, or to be rejected as candidates for the treatment. Hill found that of 200 consecutively surveyed LASIK patients (mean age 38 years), 24.5% required reading glasses at least some of the time after their LASIK procedure, notwithstanding their overall satisfaction with the procedure.

From another point of view, the proportion of refractive surgery practitioners who would wait rather than conduct a refractive surgery procedure rose dramatically with increasing patient age and degree of hyperopia in hypothetical models in a recent survey. Although the patient populations for LASIK are older than the typical contact lens wearer, presbyopia remains a complicating factor in the success of LASIK. Our survey shows that at least older female patients may be becoming aware of some complications of presbyopia (higher rate of second procedures or “enhancements”) and LASIK and that this may be dampening their enthusiasm for the procedure. In a very recent manuscript, Miranda and Krueger state that “Despite this growth (in LASIK) presbyopia remains a challenge for refractive surgery.”

The diminished size of the 2004 survey may have hampered our ability to show changes that may be occurring in attitudes or contact lens-wearing habits. For that reason, the proportion of wearers who responded from each survey is shown in the figures, allowing the reader to interpret the findings beyond the restriction of smaller sample size in some of the variables. A global statement about the degree to which the later study limits the statistical power is not possible, because the number of respondents changes with each variable investigated.

Generally, in cases in which we found nonsignificant changes by statistical analysis, the trend was insufficient to overcome the smaller sample size in the later survey. Ideally, this study would have been conducted with a sample of equivalent size in the 2004 survey. In addition, some small proportion of those surveyed might appear in both surveys, although this information was not collected at the 2004 survey.

CONCLUSION

The factors that influence patient attitudes toward new technologies that correct refractive error are manifold. Patients today must sift through information that comes to them through advertising, Internet information, government publications, messages prepared by provider organizations, lay magazines, and television news each day to determine what they think of the safety or suitability of contact lenses or refractive surgery.

Regardless of all these influences, this study found that patients, particularly females, have more positive attitudes to overnight wear of lenses compared with 2 years ago and that the enthusiasm of older patients has dampened toward LASIK. Eye care providers remain the most trusted source of recommendation and information and, as such, are burdened with the responsibility to keep abreast of the latest information regarding the safety, effectiveness, and suitability of new and established methods of refractive correction to best serve their diverse patient base.

Thirty Years in an Urban Low Vision Clinic: Changes in Prescribing Habits of Low Vision Practitioners.

2006-08-24T07:56:00.000-07:00

The low vision clinic at Moorfields Eye Hospital in London was established in its current form in 1969 and has grown to become one of the world's largest low vision centers, caring for over 2500 patients each year. A key element of the service provision in the clinic is the prescription of optical low vision devices (LVDs), which are issued on a permanent loan system from the hospital. Since the clinic was inaugurated, LVDs have become more sophisticated, most notably with the introduction of the closed-circuit TV system (CCTV; first used at Moorfields Eye Hospital in 1970) and the recent availability of LED illumination for hand and stand magnifiers (available in the United Kingdom since the late 1990s).

Meticulous records of patient attendances have been kept since the early 1970s in a summary format additional to the patient notes. This summary ledger incorporates the name, hospital number, sex, date of birth, and principal diagnosis of every patient assessed in the low vision clinic; the type or types of LVDs prescribed; and the planned follow up for each patient. In addition, it records whether the visit is a first attendance or a repeat attendance.

Wolffsohn and Cochrane examined the changes in diagnosis and demographics in a low vision clinic in Kooyong, Australia, over a similar length of time. As expected, their paper reported an increase in the number of patients with age-related macular degeneration (AMD), as well as a general aging of the clinic population from 1972 to 1996. By 1998, 13% of patients seen were under 60 years old, with only 4% being under the age of 30. Wolffsohn and colleagues did not measure changes in LVD prescription over time, but in a prospective study in 1998, they found that nearly 60% of patients were prescribed at least one low vision device. The most frequently prescribed devices were illuminated stand magnifiers, bright field magnifiers, and illuminated hand magnifiers.

The type of low vision devices prescribed appears to vary between clinics. Unlike the Kooyong Center described by Wolffsohn (based on data collected in 1998), an analysis of patients seen in 1995 and 1996 by Scott and colleagues reported a large proportion of patients being prescribed spectacle magnifiers and spectacle-mounted telescopes. In contrast, more high addition spectacles were prescribed in a Dutch clinic in 1989 to 1990. These differences do not appear to be the result of changes over time, because all of these analyses were of prescribing habits within a period of 8 years. Furthermore, these differences are not exclusively the result of the country within which the clinic is located. For example, in one clinic in the United Kingdom, the most frequently prescribed devices were illuminated stand magnifiers, illuminated hand magnifiers, and nonilluminated hand magnifiers, whereas in another British clinic, far more spectacle additions and telescopes were used. No studies have been published to date that compare changes in low vision device prescription over time.

The present study retrospectively analyzed the data from the summary ledger for all patients who attended the low vision clinic in 1 month in each of 7 years between 1973 and 2003, with particular reference to the type of low vision devices prescribed.

DISCUSSION

This study has presented longitudinal results of changes in the clinic population and the devices prescribed for patients attending a large state-funded low vision clinic in central London between 1973 and 2003. It is not intended to present a standard of LVD prescription, but merely to provide a historical perspective on the types of low vision devices prescribed in this center. Although we admit that the results presented here may not be surprising to experienced low vision practitioners, we believe that this study is the first to identify changes in low vision prescribing habits over the last 30 years.

Contrary to expectation, the median age of patients in this clinic did not systematically change over the past 30 years, despite the median age of the U.K. population rising by 4 years over this time. This may be, in part, the result of the relatively young age of London's inhabitants compared with the United Kingdom as a whole; London has fewer people over the age of 65 than the rest of the United Kingdom, and there is a net migration of older adults away from London. Furthermore, a number of specialist pediatric ophthalmology and inherited eye disease clinics at Moorfields attract referrals from across the United Kingdom, causing younger patients from outside London to be overrepresented in the low vision clinic. For these reasons, our low vision clinic has a lower median age and has a lower proportion of patients with AMD than other clinics.

The most frequently prescribed LVD in the Moorfields Clinic in each sampled month was the nonilluminated hand magnifier, which accounted for 19% of all devices prescribed. The availability of illuminated hand magnifiers (in particular those with LED illumination) has contributed to the rise in the number of hand magnifiers issued, yet nonilluminated hand magnifiers still represent the bulk of the devices issued. The frequent use of hand and stand magnifiers in our clinic is similar to that reported elsewhere in the United Kingdom and in Australia.

Spectacle-mounted telescopes are prescribed less frequently in the Moorfields Clinic than in some other centers, and the proportion of spectacle-mounted devices prescribed is falling. As a publicly funded clinic, Moorfields Eye Hospital does have financial restrictions. These pecuniary considerations may contribute to the relatively low numbers of spectacle-mounted devices prescribed; a near spectacle-mounted telescope costs approximately 10 times as much as a nonilluminated hand magnifier.

From the results of a telephone survey, D'Allura and colleagues found that only two thirds of patients who were dispensed with telescopic devices were using them some months later, whereas 89% of those with more simple magnifiers were still using them. It is possible that similar experiences may have been noted by practitioners in the low vision clinic at Moorfields, leading to a reduction in the number of devices prescribed.

The hospital does not supply CCTV systems for patients, hence their absence from the data presented. However, CCTVs are demonstrated in the low vision clinic and patients are given suppliers' information. In addition, schoolchildren have CCTVs supplied by their local education authority. The increased use of CCTVs between 1973 and 2003 may have contributed to the decline in the prescription of spectacle-mounted magnifiers over this time; for patients without a CCTV, the primary requirement of a low vision aid may be to read correspondence, whereas if the patient owns a CCTV for this task, they may require an optical LVD only for use outside the house. An illuminated hand magnifier would generally be more appropriate than a spectacle-mounted device for this purpose. Unfortunately, data on CCTV ownership were not available for analysis.

The two most noticeable changes in LVD prescription evident from this review of 30 years' worth of data are the increase in prescription of the bright field magnifier and the increased use of illuminated hand magnifiers. Although glass “dome” magnifiers have been available for many years, the lighter acrylic bright field magnifier has been manufactured in the United Kingdom since the mid 1980s (Edward Marcus, Low Vision Devices, UK, personal communication, 2004). These magnifiers are now responsible for nearly one fourth of all near low vision devices issued to new patients in this clinic.

Similarly, although illuminated hand magnifiers have been available for many years (they are reported in Faye's textbook from 1984), they have been prescribed in this clinic only since the early 1990s after the introduction of illuminated hand magnifiers with a greater range of magnification. Illuminated devices now account for 40% of all hand magnifiers issued. The recent introduction of LED illumination for hand and stand magnifiers has reduced the number of magnifiers being prescribed with conventional tungsten bulbs.

The importance of ensuring adequate lighting for patients with low vision cannot be underestimated; it has been shown that when reading at home, patients use on average one seventh of the illumination present in the hospital consulting room where devices were demonstrated and that visual acuity is adversely affected by this reduction in lighting.

Although the optimum method for improving lighting is to adapt the light sources in patients' homes, providing illuminated task magnifiers in the clinic will also ameliorate the effects of poor home lighting.

Although the summary ledger is in general well-maintained and legibly written, we concede that there may be errors and omissions within the document. However, there is no evidence that such omissions would be systematic; if anything, they would have caused random undersampling of the data. The fluctuation in the proportion of patients being issued a low vision device may be caused by differences in the prescribing habits of individual staff. However the large number of staff employed by the optometry department should minimize the effect of bias of an individual clinician; in June 2003, for example, 27 different optometrists saw patients in the low vision clinic. The turnover of staff in this clinic is reasonably low; at least three optometrists made entries in the LVA ledger in every year of the study.

The low vision clinic at Moorfields has always been an optometrist-led service; although the authors welcome the move toward multidisciplinary low vision clinics whereby each patient is assessed by a range of low vision professionals, the clinic structure at Moorfields remained unchanged over the 30 years of this study. Although the present study has only sampled the LVA ledger at 5-year intervals, this was deemed necessary in view of the very large number of patients assessed in the Moorfields low vision clinic.

We believe the ledger analyzed in this article to be the largest record of low vision clinic attendances in the world; on current trends, the 100,000th entry on the LVA ledger will be made at some point in mid 2005.

Outcomes of referrals by community optometrists to a hospital glaucoma service.

2006-08-21T10:51:00.000-07:00

Partly in response to the increasing burden on the hospital eye service resulting from demographic changes, major modifications to the way glaucoma detection and care are carried out in the United Kingdom are likely in the near future. Government plans envisage a significant proportion of clinical glaucoma management being transferred from hospital to primary care.

Central to the new system will be the development of a cadre of specialist optometrists, who, it is proposed, will assume much of the work of screening and initial management of referrals for suspected glaucoma currently carried out by ophthalmologists.

In light of these impending developments in service provision, we examined the outcomes of glaucoma referrals to our unit under the current system. Our principal aim was the provision of feedback to local referral sources, comparing our own data with previously published results. Given the large number of referrals surveyed, the information furnished should also be of interest to a geographically and professionally wider audience, aiding planning and resource allocation and providing a baseline against which the effectiveness of any novel system can be compared.

DISCUSSION

Differences between surveys are evident across a range of parameters including diagnostic definitions and classification systems, methods of data collection, referral sources and population demographics. Some studies included only a small number of patients, and have been criticised for the resultant limited statistical legitimacy. It is important to emphasise in this context that our own reported diagnostic outcomes are based exclusively on the information available at the initial consultation. This should also be borne in mind when considering our figures for the initiation of treatment.

Our confirmed glaucoma rate of just over 20% is similar to the 17% rate found in the Edinburgh study of 271 patients seen over 6 months from 1993 to 7 and the 22% found by Harrison et al and Theodossiades and Murdoch. The diagnosis of NTG is complicated by considerations such as diurnal IOP variation. Theodossiades and colleagues specifically excluded NTG as a category distinct from open angle glaucoma in their study of referrals as it was thought that the diagnosis could not be made authoritatively following a single clinic appointment. Based on the IOP at the initial hospital examination, approximately one third (31%) of our confirmed glaucomas fell within the NTG group, a similar rate to the 33% reported by the Edinburgh study.

Our OHT rate was just under 30%. There has been substantial variation in reported rates, which in recent studies range from 14% to 42%. Not all published studies have included OHT as a distinct diagnostic category, including the largest before our own, which grouped patients with OHT and glaucoma suspects together in the category “uncertain, follow up required.” We found a glaucoma suspect rate of 5.0%. Half of the studies reviewed did not have an explicit “glaucoma suspect” grouping, and valid comparison with other published data is particularly difficult with respect to this category, which, almost by definition, may be prone to a higher degree of subjectivity.

Treatment to reduce IOP was instituted for 458 patients (18.3% of referrals), mainly for glaucoma. A minority of those treated had OHT or were glaucoma suspects. While some previous surveys detail the proportion of patients with OHT commenced on treatment, none has reported the number of treated confirmed glaucoma patients. Some of our patients are likely to have been treated subsequent to the first consultation upon which the presented findings are based. This may apply particularly to patients with NTG, for whom treatment is often withheld pending evidence of progression; in our survey, 79% (276/350) of those with glaucoma featuring elevated IOP were treated at the first visit, but only 54% (87/160) of those with NTG.

A total of 1148 (45.8%) patients were discharged from ophthalmological review, the majority of whom had no evidence of glaucoma; some had OHT but were considered to be at extremely low risk of developing glaucoma, and others had pathology which did not require further ophthalmological intervention at the time of assessment. Four patients with glaucoma (including three with NTG) and one glaucoma suspect were discharged, as their life expectancy was considered low in comparison with the risk of visually significant glaucomatous progression.

In the only other study reporting a specific figure for patients who were discharged, 30% required no follow up. By no means will every referral have been made in the belief that the patient definitely had glaucoma. This has been studied by Tuck, who found that 74% of the patients referred by an optometrist with “almost definite” glaucoma were confirmed as having the condition, compared with only 21% of “possible” glaucomas. Community optometrists are under considerable pressure to detect every case of sight threatening disease, with a missed diagnosis having potentially serious ramifications for the responsible practitioner.

In contrast, little disadvantage results from a false positive referral. Many patients will have been referred in the belief that they had OHT rather than glaucoma and that only monitoring was required. Under the present system there may be no alternative in these circumstances to a request for appraisal by the hospital eye service, but these patients may in the future be managed in the community by a specialist optometrist. Henson et al have reported a cost effective 40% reduction in new glaucoma referrals to Manchester Royal Eye Hospital from a scheme involving initial assessment by specially trained community optometrists, although figures for diagnostic accuracy have not yet been published.

In conclusion, this study is the largest survey to determine the outcomes resulting from optometric referrals for suspected glaucoma to a specialist hospital eye clinic. It is hoped that planned changes to the system of referral for suspected glaucoma in the United Kingdom will lead to a substantial decrease in the number of false positives reaching the hospital eye service, without a commensurate increase in false negatives.