ILM peeling has been the main surgical approach for treating MH since its introduction in 1991 . The surgery aims to relieve tractional forces responsible for the hole development and trigger reparative gliosis using the Müller cells [25, 26]. Although the MH closure rates can reach up to 90% with the standard surgical procedure, some cases (e.g., large, chronic, or myopic MHs) are more challenging and display a worsened prognosis [9–11]. Michalewska et al. first presented the inverted ILM flap technique for the treatment of large idiopathic MHs (diameter > 400 µm) and myopic MHs [12, 27]. The exact mechanism behind the improved anatomical and functional results remains unclear. One theory is that the inverted ILM flap provides a smooth and gap-free natural scaffold for glial cells and photoreceptors towards the fovea [12, 20]. Another proposes that the ILM acts as a barrier preventing the entry of fluid from the vitreous cavity into the MH . Moreover, the activated Müller cells secrete neurotrophic and growth factors on the surface of the ILM, which may promote the survival of retinal neurons and photoreceptors cells and may contribute to the closure of the MH . In her first description of this technique, Michalewska et al. reported an anatomical success rate of 98%. In addition, the post-operative BCVA was significantly higher in the inverted flap group compared to the standard surgery group (p = 0.001). However, despite its advantages, the appearance of dark striae on autofluorescence imaging in areas of previous ILM peeling has been reported by several authors . These striae correspond to the swelling of the inner retinal layers, which is followed by the formation of small dimples in the retinal nerve fiber layer (RNFL). Various modifications of the original IFT, such as filling the hole with a folded ILM, a free ILM flap, and a pedicle ILM transposition flap, have been reported to minimize the surgical trauma and maximize the hole closure rates [30–32].
Michalewska et al. subsequently introduced the novel technique of the temporal inverted ILM flap, which included peeling off the ILM only from the temporal side of the fovea and inverting the flap nasally to cover MH. In their study, they compared the MH closure rates between the classic IFT (n = 43) and the temporal IFT, and they reported that the temporal inverted ILM flap technique was non-inferior to the classic inverted technique for MHs > 400 µm. In addition, the post-operative inner retinal dimplings was significantly lower in this modified technique . MH closure was reported in 93% of the patients with temporal IFT after the initial surgery in this study. A second surgery was performed in 3 patients between 1 and 7 months after the initial surgery and, a hole closure rate of 100% was achieved. Takai et al. retrospectively analysed the outcomes of temporal IFT in chronic, large, and highly myopic patients and found a 100% hole closure rate in their study . In another comparative study, Avci et al recently reported a 100% MH closure rate with temporal IFT in patients with a minimum hole diameter > 400 µm . The study showed significantly higher MH closure rates in the temporal IFT group than the conventional ILM peeling group (100% vs. 72.2%). Similar to these results, we also observed a high MH closure rate in the temporal IFT group compared to the conventional ILM peeling group in the current study. The difference between our study and these studies was that only patients with minimal MH diameter larger than 600 µm were included in the study.
Previously, three types of successful MH closures have been described: U-, V-, and W-shaped. The first type is defined as a contour similar to that of a healthy fovea; The V-shaped closure is described as the RPE covered by the retinal layers with a steep notch; The last closure is defined as the RPE covered by the retinal tissue with an irregular surface. Michalewska et al. reported that the post-operative closure type and foveal contour could influence the BCVA, and the best results were achieved in eyes with U-shaped closures . In another work using the temporal IFT, Michalewska et al. reported the rates of U-, V-, and W-shaped closures at the end of the 6 months to be 64%, 14%, and 16%, respectively . Avci et al. observed the U- and V-shaped closure rates of 80% and 20%, respectively, at 12 months after surgery. However, in the same study, the rate of U-shaped closure was reported to be only as %5 percent in the conventional ILM peeling group. In the current study, the U-, V-, and W-shaped closures were achieved in 15 (71%) eyes, 3 (14%) eyes, and 2 (5%) eyes in the temporal IFT group, respectively. In addition, similar to Avci et al.’s study, we observed a decrease in U-shaped closure rate in the conventional ILM peeling group. Thus, the higher BCVA values in the temporal IFT group can be explained by the higher rate of the U-shaped MH closure.
The post-operative structural analysis showed that patients with U-shaped closures had smaller ELM and EZ defects as well as normal retinal thickness at the end of the follow-up.[24, 35] The restoration of those structures can reportedly predict good post-operative visual outcomes. Michalewska et al. , Wakabayashi et al. , and Ramtohul et al.  reported that the integrity of ELM and EZ significantly correlated with the post-operative final BCVA. In her first description of temporal IFT, Michalewska et al. reported significantly worsened BCVA in patients with lasting ELM and EZ defects . In the current study, both the statistically significant reduction in ELM and EZ defect sizes and higher post-operative complete restoration rates of ELM and EZ contributed to the better BCVA in the temporal IFT group compared to the conventional ILM peeling group. Our study results are consistent with those of previous studies that showed that ELM and EZ are critical structural features significantly correlated with BCVA.
Several researchers have suggested that a single-layered flap provides superior morphological and functional results compared with the multilayered flap or insertion technique [30, 38]. Michalewska et al. and Avci et al. found significant visual acuity improvement in cases undergoing temporal IFT surgery [20, 34]. Similar to their results, we found significant improvement in terms of BCVA (1.07 ± 0.34 logMAR vs. 0.51 ± 0.26 logMAR) at 6 months after surgery. None of the eyes underwent deterioration in visual acuity. A challenging part in the original temporal IFT technique is the flap detachment during the fluid–air exchange. To overcome this, we applied PFCL to the flap and gently massaged it on the edges to create a proper, single-layered, and unwrinkled covering over the hole. This modification may have contributed to the good anatomical and morphological results of the current study. No serious complications were observed in the study. The retrospective design, small sample size, and the follow-up period of six months, which was relatively short for evaluating the restoration of the outer retinal layers and visual outcomes, could be considered as some of the study limitations. However, to the best of our knowledge, this is the first study comparing conventional ILM peeling vis-à-vis single-layered temporal inverted ILM flap technique for the initial treatment of idiopathic and large macular holes with a minimum diameter larger than 600 µm.
In conclusion, large MHs are challenging cases with low surgical success rates. The temporal inverted ILM flap technique is more effective than conventional ILM peeling for larger than 600 µm macular holes and improves anatomical, morphological, and functional outcomes. Recovery of the outer retinal layers significantly correlated with better final visual outcomes. Further studies with larger sample sizes and longer follow-up times are needed to evaluate this surgical technique in more detail.