Abstract
Adult male rats were exposed to intense light at a body temperature of about 39°C for 2 half-hour periods with an interval of 2 hr in the dark. Under these standardized conditions, this treatment caused a highly reproducible degeneration of all the epithelial cells and all the visual cells. The histochemically demonstrable changes in the lipid pattern were examined at different time intervals. The outer segments of the visual cells in the normal rat retina are characterized by a strong reaction to phospholipids and a moderate reaction with the modified PAS method. They show less intense reactions with other histochemical lipid methods. The light-induced degeneration of the epithelial and rod cells occurs in three distinct stages. During the first phase, lasting about 2 days, there is rapidly progressive structural disintegration and edema in the scleral half of the retina, without any significant change in the lipid pattern. During the second phase, characterized by phagocytosis and removal of debris from the retina, there are no qualitative changes in the histochemical lipid pattern, although the intensities of the lipid reactions rapidly diminish. Most of the lipid material is removed during the first days of the second stage. Almost no reacting lipids are present during the third reparative stage. Eventually, the retina consists only of the five vitreous layers separated from the choroid by a single cell layer. There is good correlation between the histochemical and biochemical lipid patterns of the outer segments of the photoreceptor cells. The changes in the histochemical lipid pattern in the light-damaged retina are different from those occurring during Wallerian degeneration in spite of the ultrastructural similarities between the outer segments of photoreceptor cells and the myelin. Debris is removed by phagocytizing cells in the same manner in both of these damaged tissues, but the process is much more rapid in the light-damaged retina.
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