| Summary: | Macular hole (MH) is a full-thickness defect in the fovea, the central part of the neurosensory retina. As the fovea is the site responsible for central vision, the main clinical manifestation of MH is central visual field defect and metamorphopsia. Descriptions of MH in the medical literature are available since the 19th century. However, these only aroused renewed interest after Kelly and Wendel had shown that surgery of pars plana vitrectomy (PPV), combined with vitreous cortex detachment and fluid–gas exchange could close MH in a significant proportion of cases, although it was assumed that the retina would be unable to heal. With time, the success rate of MH surgery gradually increased and this surgery is now one of the most successful vitreoretinal surgeries. A recent innovation was the introduction of internal limiting membrane (ILM) peeling, which leads to a reduction in tangential traction and a higher rate of closure, with less recurrence. In the last 10 years, ILM peeling during MH surgery has thus become a routine step and is nowadays performed by most retinal surgeons. With the advent of modern spectral-domain (SD) optic coherence tomography (OCT), however, one can now see abnormal structural changes to the inner retinal surface after surgery with ILM peeling, suggesting that the procedure can cause retinal damage, even though vision improves. Moreover, some clinical studies found adverse functional events that have given rise to concerns regarding the safety of ILM peeling. The purpose of the present PhD thesis was to examine anatomical and functional effects of ILM peeling in MH surgery. We conducted a prospective study in 72 patients with MH, (stages 2, 3 and 4). MH surgery consisted in PPV, ILM peeling, intraocular gas and face down position. Morphologic and functional outcomes were assessed, 3, 6 and 12 months after surgery. The results reveal the presence of microstructural alterations in the different macular layers after MH surgery with ILM peeling, when compared to pre-operative measurements. Thinning of the Ganglion Cell Layer (GCL) and Inner Plexiform Layer (IPL) on both sides of the fovea were the main structural alterations, in particular at the temporal region. In addition, nasal Internal Retinal Layer (IRL) thickening and shortening of papilo-macular distance could also be detected in cases of successful MH surgery with ILM peeling. Multifocal electroretinography (mf ERG) is a noninvasive method that analyses multiple retinal locations around macular area, and was used in this work to provide a topographic map of electrophysiological activity in central retina. Before surgery, mf ERG showed almost undetectable retinal response in foveal and parafoveal areas, in ring 1 and ring 2. After surgery, the improvement in the retinal response density of mf ERG in the same ring seems to be consequent to closure of the MH, with realignment of photoreceptor cells and glial cell activation. Resolution of the central scotoma could be attributed to anatomical repair and, in our study, we found a statistically significant increase in N1 and P1 in ring 1. This increase was dependent on the integrity of Outer Retina Layers (ORL), External Limiting Membrane (ELM) and Elipsoide Zone (EZ). To study the contribution of the peeled ILM to the outcome of MH surgery, the final position of the ILM after surgery was assessed. This analysis reveals that when the ILM flap ended buried into the hole after surgery, no realignment of external layers could be observed. In contrast, when the ILM flap remained over the hole, ELM and EZ were realigned, and vision was improved. In this study, duration of MH and ORL integrity were studied and we concluded that duration of symptoms of MH seem to relate to integrity to these layers. The ultrastructure and behavior of peeled ILM was studied by using light and transmission electron microscopy. We found that when both ILM vitreous sides are in apposition, there are signs of fibrotic activity, producing a basal membrane with collagen microfibrils between the two sides. This suggests that the two ILM surfaces may adhere, flanking the hole and establish a bridge that contributes to better hole closure after MH surgery. Based on the above findings, we conclude that ILM peeling performed in cases of FTMH surgery allows hole closure and vision improvement, even though anatomical differences as seen in OCT, reveals thinning of inner retinal layers and nasal displacement of the closed hole. Multifocal ERG revealed a functional alteration that is dependent on integrity of the ORL. Also, the position of ILM over the hole may have consequences on integrity of ORL and, consequently, BCVA.
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