Purpose: The aim of our study was to evaluate the in vivo feasibility of non-contact Er:YAG laser ablation of the internal limiting membrane (ILM), which is recommended for the treatment of macular holes.
Method: Vitrectomy was performed in 16 eyes of 15 pigs. After perfluorodecalin filling, it was attempted to remove the ILM using a free-running fiber-guided Er:YAG laser (lambda=2.94 microm, pulse length 250 micros, repetition rate 1.7 Hz, radiant exposure 0.6-2.05 J/cm2). The eyes were enucleated either immediately (11 eyes, group 1) or 2 weeks after laser therapy (5 eyes, group 2). Furthermore, in one additional pig eye the retina was carefully treated with microforceps after vitrectomy to assess the damage produced by conventional techniques of ILM peeling. All eyes were examined histologically.
Results: Group 1: Nine eyes could be examined (problems with fixation in two eyes). In four of nine eyes, the ILM was either removed or detached, in one eye there was a superficial retinal hemorrhage, and in four eyes the ILM was still intact. In the latter cases, there was no intraoperative whitening or bleeding and no posterior vitreous detachment was present histologically. Group 2: Four eyes (problems with fixation in one eye) could be examined. The ILM was either removed or detached in three eyes. In one eye there was a superficial retinal hemorrhage. In one eye the ILM was not removed and there had neither been intraoperative whitening or hemorrhage nor histologically visible posterior vitreous detachment. In both groups, the nerve fiber layer in treated areas was thicker than in adjacent untreated retina. In one eye the retina was gently manipulated with microforceps in an attempt to perform ILM peeling. This led to damage to all layers of the retina.
Conclusions: Removal of the ILM by Er:YAG laser is possible in vivo. However, the variability of the laser effects calls for further improvement such as a reliable indicator of ablation depth. In any case, any damage to the retina was lesser than that produced by microforceps.