Ultrastructure of the vitreoretinal interface following removal of the internal limiting membrane using indocyanine green

We read with interest the article by Nakamura and coworkers about their experimental approach of internal limiting membrane (ILM) peeling in primates. We appreciate the effort undertaken by the authors in performing macular surgery in an animal model like this, as well as the critical discussion of the results, and we congratulate Nakamura and colleagues on their work. To our knowledge, this is the first time that ILM peeling has been performed in an animal model, although many questions in macular surgery are still unanswered, and a valid model of ILM peeling is needed. We have been searching for an animal model of staining and peeling of the vitreomacular interface in order to correlate our clinical and ultrastructural findings of macular surgery and our experimental findings in human donor eyes, with results obtained from an experimental setting in vivo. We performed ILM peeling in the cat model, which has provided essential data on retinal detachment for years, and which is known for the validity of the results in terms of comparability with the human retina. We found that the cat macula does not perform like the human macula on attempted ILM peeling. Attempted removal of the ILM did not result like a clean plane of separation as is the case clinically in humans but resulted in small fragments of retinal tissue being avulsed with associated localised intraretinal bleeding. These hemorrhages were not caused by direct trauma to the retina but occurred when tangential traction was applied to the macula during ILM removal (data submitted). The continuity of ILM and Müller cells in 19-month-old cats appeared to be too firm to allow a selective separation of the ILM from the retina. Intraoperatively, we used Trypan blue, which resulted in a faint blue staining of the ILM, and from a surgical point of view, peeling of the ILM should have been feasible. We avoided using indocyanine green (ICG) in these eyes, as we were aware of untoward effects that had been attributed to the dye in human macular surgery and in experimental settings after death. Staining of the cat ILM with ICG (without peeling) resulted in the same ultrastructural findings as reported in an experimental setting in human donor eyes. There were circumscribed detachments of the ILM after application of the dye to the vitreomacular interface, and retinal debris was present at the retinal side of the ILM as a result of disruption of Müller cell endfeet. When ICG and light was applied to the macula, the ILM was lost, and the inner retinal layers were grossly disorganized. Nakamura and colleagues show tearing of Müller cells and total loss of Müller cell endfeet with subsequent exposure of the nerve fiber layer to the vitreous fluid in the peeled area (see Fig. 2 there in). These findings are similar to previous clinicopathological work of our group, which demonstrated ruptured Müller cell endfeet on the retinal side of the ILM after ICG-assisted ILM removal. We did not find these retinal elements in a series of 93 surgical specimens following ILM removal without the use of ICG (unpublished data). In that series, there were only small fragments of Müller cell membrane adherent to the undulations