Staining and peeling of the internal limiting membrane in the cat eye

Purpose: To investigate the cat vitreomacular interface using trypan blue (TB) and indocyanine green (ICG) and to determine the validity of the cat model in terms of staining and peeling of the internal limiting membrane (ILM). Methods: Lensectomy and vitrectomy were performed in four eyes of two cats. The ILM of two eyes was stained with TB (0.15%). ILM peeling was performed in one eye. Two eyes were stained with ICG (0.5%). One eye was illuminated for 3 min. Light and transmission electron microscopy and confocal microscopy were performed. Results: Clinically, both dyes stained the cat ILM similar to human ILM. TB staining resulted in a normal ultrastructure and antigenity of the retina. ILM peeling was associated with intraretinal bleeding. There were fragments of Muller cells adherent to the retinal side of the ILM, and Muller cell endfeet were ruptured and avulsed. ICG staining of the ILM followed by illumination caused severe inner retinal damage. ICG without illumination resulted in focal ILM detachments associated with tearing of Muller cell endfeet. Conclusions: The cat can be used as a model to study the effect of TB and ICG on the central area of the cat retina, as previous results from clinical and experimental postmortem settings in human eyes were confirmed in the current study. Peeling of the ILM as a sheet as performed in human macular surgery is not feasible. Differences in the ultrastructure of the ILM and a strong adhesion of the ILM to Muller cell endfeet may account for this observation.