98th Annual Meeting DOG 2000

V 180

Er:YAG laser ablation of the internal limiting membrane in pigs

P. Janknecht, T. Wesendahl, N. Feltgen, J. Wiek, B. Guessregen, B. Ott, M. Frenz

Purpose: The use of an Er:YAG laser for the intraoperative removal of epiretinal membranes or the internal limiting membrane (ILM) remains to be explored. Using our experimental data of in-vitro ablation of retinal tissue we performed intraoperative in-vivo ILM removal in pig eyes.

Method: We performed vitrectomy in 16 eyes of 15 pigs. After perfluordecaline filling, the ILM was ablated using a free-running Erbium:YAG laser and an attached ZrF4 fiber (l=2.94 µm, pulse length 250 us, repetition rate 1.7 Hz, radiant exposure 0.6 to 2.05 J/cm2). The eyes were either enucleated immediately (11 eyes, group 1) or two weeks after laser therapy (5 eyes, group 2) and thereafter examined histologically.

Results: Group 1: 9 eyes could be examined (problems with fixation in 2 eyes). In 4/9 eyes, the ILM was either removed or detached, in 1 eye there was a superficial retinal hemorrhage, and in 4 eyes the ILM was still intact. In the latter cases, there was no intraoperative whitening or bleeding. Group 2: 4 eyes (problems with fixation in 1 eye) could be examined. The ILM was either removed or detached in 3 eyes. In 1 eye there was a superficial retinal hemorrhage. In 1 eye the ILM was not removed. In this case and there had not been any intraoperative whitening nor hemorrhage.

In both groups, the nerve fiber layer in the treated area was thicker than in the adjacent retina because of edema or non-removed debris.

Conclusions: In vivo removal of the ILM by Er:YAG laser is possible. In this series the end point of the laser treatment was whitening of the superficial retina as can be seen after ILM removal by microforceps. However, experience with older animals shows that this is not a reliable clinical sign for the endpoint of laser therapy. It is perhaps necessary to use a feedback mechanism based on optical coherence tomography to exactly stop laser irradiation after removal of a defined amount of tissue.

Augenklinik der Albert-Ludwigs-Universität Freiburg