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.
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