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Abstract

We thank Dr Haritoglou et al for their interest in our article. It is interesting that Haritoglou et al did not observe cases of the appearance of a dissociated optic nerve fiber layer (DONFL) in their prospective investigation on internal limiting membrane (ILM) peeling for macular hole repair in 105 patients. However, they did report cases of paracentral scotomata and nerve fiber layer defects after the ILM peeling for macular hole repair.1Haritoglou C. Gass C.A. Schaumberger M. et al.Macular changes after peeling of the internal limiting membrane in macular hole surgery.Am J Ophthalmol. 2001; 132: 363-368Abstract Full Text Full Text PDF PubMed Scopus (203) Google Scholar, 2Haritoglou C. Gass C.A. Schaumberger M. et al.Long-term follow-up after macular hole surgery with internal limiting membrane peeling.Am J Ophthalmol. 2002; 134: 661-666Abstract Full Text Full Text PDF PubMed Scopus (178) Google Scholar In our series, we could not find such paracentral scotomas using microperimetry (spot size equivalent to Goldmann I; brightness, −15 decibels; background intensity, 10 candelas per square meter) with a scanning laser ophthalmoscope (Rodenstock Inc., Munich, Germany). The differences in the number of cases of DONFL may be due to how the ILM was peeled and the size of the ILM peeled. The area of ILM removed was intended to be 1 disc diameter around the macular hole in Haritoglou et al’s cases, and it was about 2 to 3 disc diameters in our cases. Because the thickness of the nerve fiber layer is greater in the peripheral macula than near the fovea, and because the DONFL is a focal dehiscence of the optic nerve fiber layer, we suggest that the larger the area of ILM that is peeled, the more likely that a DONFL will be observed. However, we have not evaluated this relationship quantitatively in our cases. The differences also may be due to differences in the fundus color due to racial differences. It is probably easier to detect a DONFL in highly pigmented Japanese than in the patients in Haritoglou et al’s case series. In addition, we noted that it was easier to detect a DONFL with the argon blue laser of the scanning laser ophthalmoscope than red-free fundus photographs, and the incidence of DONFL may have increased if Haritoglou et al had used an argon blue laser. But even in our cases, the ILM was peeled by the same method in all cases, but only about a half of the cases had DONFL. Thus, it is difficult to determine the exact factor that caused the differences. We did not perform histological studies in this study. However, in an earlier study in which we peeled the ILM for macular hole surgery using the same method as this study,3Asami T. Terasaki H. Kachi S. et al.Ultrastructure of internal limiting membrane removed during plasmin-assisted vitrectomy from eyes with diabetic macular edema.Ophthalmology. 2004; 111: 231-237Abstract Full Text Full Text PDF PubMed Scopus (62) Google Scholar morphological analysis of the peeled ILM was done by electron microscopy. In those cases, we did not find any torn nerve fibers on the ILM as Haritoglou et al reported. Therefore, we agree with Haritoglou et al that a tearing of the nerve fibers did not cause these changes directly. In our cases, the incidence of a DONFL in cases of ILM staining by indocyanine green did not significantly differ from that without staining. Because similar results have been reported in another study,4Mitamura Y. Ohtsuka K. Relationship of dissociated optic nerve fiber layer appearance to internal limiting membrane peeling.Ophthalmology. 2005; 112: 1766-1770Abstract Full Text Full Text PDF PubMed Scopus (103) Google Scholar indocyanine green probably did not affect the incidence of DONFL. As Haritoglou et al suggest, we also feel a difference between a stained and an unstained ILM during ILM peeling. Thus, indocyanine green may affect the properties of the ILM, but further study is needed.