Vitrectomy with or without internal limiting membrane peeling for myopic foveoschisis

Myopic foveoschisis (MF) was first described by Takano and Kishi in 1999, and is recognized as one of the major complications associated with pathological myopia [1, 2]. Many subsequent studies have demonstrated that vitrectomy with internal limiting membrane peeling (ILMP) can be effective in producing both anatomical and functional improvement in MF [3‐7]. In order to reduce postoperative macular hole (MH) formation and foveal damage, a partial ILMP technique with foveal sparing was proposed [8], but there is little evidence that this technique has better outcomes than complete ILMP [9, 10] Furthermore, more recent studies have shown similar anatomical and functional improvements can be achieved without any form of IMLP [4, 11], casting doubt on the benefits of ILMP.

In this study we retrospectively analyze the medical records of patients with MF who were treated by vitrectomy at our specialist ophthalmology department in China. Specifically, we divide the patients retrospectively into two cohorts — those who underwent ILMP and those who didn’t — and compare the two.

Ethics panel approval for this study was obtained from the Medical Ethics Committee of Chongqing Aier-Mega Eye Hospital. All methods were carried out in accordance with the tenets of the Declaration of Helsinki. We retrospectively reviewed the medical records of patients who underwent vitrectomy for MF between January 2014 and April 2018 at the Chongqing Aier-Mega Eye Hospital in Chongqing, China.

Thirty-two eyes from 32 patients with symptomatic MF were included. All the included patients had progressive visual deterioration and/or metamorphopsia, that was attributable to MF. Eyes with macular holes were not excluded unless there was associated retinal detachment clearly visible on B-ultrasound examination. All included patients had undergone surgical vitrectomy (following written informed consent) as a treatment for MF. All surgeries were performed by one experienced surgeon (J.G.). There was no prospective (preoperative) allocation of patients to groups as part of this study. The decision whether or not to perform ILMP during surgery was at the discretion of the surgical team and varied depending on the particular patient. For this study, patients were retrospectively assigned to one of two cohorts — ILMP and non-ILMP — on the basis of whether or not they had ILMP during surgery.

As part of their routine work-up, all patients had a complete ophthalmic examination, including measurement of best-corrected visual acuity (BCVA), refraction, axial length (AXL), slit-lamp examination, fundus examination and optical coherence tomography (OCT). Preoperative and postoperative BCVAs were determined as decimal visual acuity and then converted to logarithm of the minimum angle of resolution (logMAR) units for statistical analysis. We also defined an improvement or worsening in postoperative BCVA as a change of 0.2 logMAR units from baseline.

Our results demonstrate that, for the treatment of myopic foveoschisis (MF), vitrectomy without internal limiting membrane peeling (ILMP) has similar outcomes to vitrectomy with ILMP. This is consistent with previous reports [4, 11]. Indeed, within-cohort statistical analysis showed that significant visual improvement was only achieved in the no-ILMP cohort. The percentage of eyes with a significant improvement of the final BCVA was also higher in the no-ILMP cohort (90.9%) than that in the ILMP cohort (57.1%), although this difference was not statistically significant (p = 0.072). A direct between-cohort statistical comparison of BCVA improvement did not demonstrate a significant advantage of vitrectomy without ILMP, although this may be a false negative, due to the lower power of the unpaired test. A larger study, ideally prospective, is required to support a definitive conclusion on the advantage of vitrectomy without ILMP.

As MF mainly occurs in patients with pathological myopia (especially those with staphylomas), ILMP in such patients is often difficult and ILM staining is necessary. Due to its availability, indocyanine green (ICG) is widely used (including by us) to stain the ILM. Although some studies demonstrate that ICG-assisted vitrectomy combined with ILMP is safe and effective in the treatment of idiopathic macular holes and epiretinal membranes [12, 13], animal studies show that 0.05% ICG can cause neuroretinal thinning in rats and reduced mfERG responses in pigs [14, 15]. Using multifocal electroretinography, Lai and colleagues demonstrate functional changes in the macula during epiretinal membrane surgery with ICG-assisted ILMP, and show that higher concentrations of ICG (1.25 mg/ml) produce significant reductions in N1 and P1 response amplitudes compared with baseline [16]. Furthermore, Sayanagi and colleagues show that the pattern of ICG residue in severe myopia is different from those in non-myopics [17]. In eyes with patch atrophy, ILMP is so difficult that repeated staining is often required, increasing the potential retinal toxicity of ICG. We therefore suggest that ICG toxicity may (at least partly) explain why performing ILMP with vitrectomy does not improve postoperative visual acuity as much as might be expected.

There is a similar debate on the benefits and harms of ILMP in the treatment of epi-macular membranes. Opponents of ILMP show that the visual outcomes between eyes that undergo ILMP and those that do not are the same. Stripping of the ILM removes the Müller cell footplates, so it is reasonable to expect some Müller cell dysfunction. Adverse events such as eccentric para-central macular holes, macular microscotomata, and retinal dimpling have also been associated with ILMP [18]. Such adverse events may be even more common in pathological myopia, characterized by long axial length and diffuse chorioretinal atrophy. To prevent postoperative macular hole formation and possible damage to the fovea, a fovea-sparing ILMP technique has been advocated [8, 19, 20], but some studies have shown that there is no difference in postoperative visual acuity between fovea-sparing ILMP and complete ILMP [9, 10].

In the current study, two eyes in the ILMP cohort developed postoperative retinal detachment. One was associated with postoperative macular hole formation, as a result of the progression of unresolved MF. The other was caused by a posterior hole unrelated to ILMP, but which may have been caused by the surgical separation of the remaining posterior vitreous. This highlights the risks of performing suction or peeling on the residue of the posterior vitreous.

There are many limitations to our current study. It is a retrospective, non-randomized cohort study with a small number of cases. Although the average follow-up time is long enough, it may not be sufficient for some cases. We did not find a significant difference in visual acuity improvement between ILMP and no-ILMP groups, but it is possible that this was a false negative, due to the limited sample size available for this study. Our data suggest that vitrectomy without ILMP may indeed produce better outcomes than vitrectomy with ILMP, but ideally a prospective, randomized-controlled trial is required (with appropriate pre-trial power calculations and sufficient recruitment) to assess which approach is better. The same (or a separate) study should also be designed to assess the benefits and harms of ICG dye.

In conclusion, we show that vitrectomy without ILMP for MF has comparable anatomical outcomes to vitrectomy with ILMP. We also provide some evidence that visual outcomes are better without ILMP, and we highlight the potential retinal toxicity of the ICG dye commonly used in ILMP.