Internal limiting membrane ablation in pig eyes with the Er : YAG laser under perfluorodecalin

Purpose: The aim of our study was to evaluate the in vivo feasibility of no n-contact Er:YAG laser ablation of the internal limiting membrane (ILM), wh ich is recommended for the treatment of macular holes. Method: Vitrectomy w as 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 mum, pulse length 250 mus, repetition rate 1.7 Hz, radiant ex posure 0.6-2.05 J/cm(2)). The eyes were enucleated either immediately (11 e yes, group 1) or 2 weeks after laser therapy (5 eyes, group 2). Furthermore , in one additional pig eye the retina was carefully treated with microforc eps after vitrectomy to assess the damage produced by conventional techniqu es 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 an d no posterior vitreous detachment was present histologically. Group 2: Fou r eyes (problems with fixation in one eye) could be examined. The ILM was e ither 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 neith er been intraoperative whitening or hemorrhage nor histologically visible p osterior vitreous detachment. In both groups, the nerve fiber layer in trea ted areas was thicker than in adjacent untreated retina. In one eye the ret ina was gently manipulated with microforceps in an attempt to perform ILM p eeling. This led to damage to all layers of the retina. Conclusions: Remova l 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 indic ator of ablation depth. In any case, any damage to the retina was lesser th an that produced by microforceps.