Chorioretinal diffusion processes following pigment epithelial degeneration.

We studied the effect of sodium iodate-induced pigment epithelial degeneration on chorioretinal diffusion processes. Rabbits received two intravenous injections of sodium iodate at the retinotoxic dose of 22.5 mg. per kilogram over a six- to eight-hour period. Combined horseradish peroxidase tracing technique and electron microscopy were used to compare diffusion processes over a five-week period. Ultrastructural examination of retina twenty-four hours after iodate administration revealed pigment epithelial degeneration, accompanied by disruption of junctional complexes (zonulae occludentes). Peroxidase molecules were found in areas of greater cytoplasmic degeneration and in intercellular spaces up to the level of the external limiting membrane. Ultrastructural observations at later stages revealed similar findings except in the case of Muller cells, 20 per cent of which showed cytoplasmic degeneration and peroxidase uptake. The diffusion barrier was not re-established as the replacement cells did not rebuild zonulae occludentes.