Retinal damage by light in the golden hamster: an ultrastructural study inthe retinal pigment epithelium and Bruch's membrane

The mechanism of the toxicity of light on the retina remains unclear despit e a large number of investigations. The purpose of this study is to identif y and localize the ultrastructural changes and the site of the earliest dam age after intense light exposure. Nine adult Syrian golden hamsters (Mesocr icetus auratus) have been maintained under constant illumination with a hig h-pressure mercury lamp (HQJ R 80 W Deluxe, Osram, Berlin, light intensity 1000 lx) for 12 h, followed by an additional 3 h in the dark. Light damage is assessed by light and electron microscopy. Morphological evaluation reve als focal damage to the retinal pigment epithelial (RPE) cells in close pro ximity to less-affected RPE cells and normal photoreceptors. Collagen fiber s in Bruch's membrane lose their parallel orientation. Occasionally, fusion of cell membranes of neighboring rod outer segments (ROS) is also observed . Continuous, 12 h exposure of hamsters to intense light results in initial focal damage to some RPE cells, such that severely damaged RPE cells are f ound adjacent to intact RPE cells. Only slight damage to the photoreceptors is evident, suggesting that the sequence of the pathological changes resul ting from light begins with damage to the RPE cells and associated Bruch's membrane. (C) 1999 Elsevier Science S.A. All rights reserved.