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.
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