Studies of the pathogenic mechanisms of light on rat retina.

Abstract

The effects of low-intensity light on the rat retina was investigated by light, transmission and scanning electron microscopy. The earliest signs of light damage were observed in the retinal pigment epithelium (RPE) of albino rats after 24 h of exposure to 35 footcandles of fluorescent light at room temparature (24 °C). These changes included an increase in the electron density of the cytoplasmic matrix, modifications of the endoplasmic reticulum, changes in the number and distribution of lysosomes and changes in the number and size of apical processes and their population of inclusions. Newly phagocytized outer segments were not seen in the RPE whereas large numbers of condensed lamellated inclusions had accumulated. This suggested that damaged RPE is unable to phagocytize outer segments and to digest previously phagocytized outer segments as a result of changes in the endoplasmic reticulum and the phagolysosomal system. Pigmented rats were more resistant to light damage than albino rats; when exposed to the same continuous low-intensity light of 35 footcandles for 4 weeks, pigmented rats developed remarkable alterations in the RPE without any morphological changes in the photoreceptor cells or their outer segments. The initial site of light damage was apparently in the RPE. The early extensive changes in RPE indicated the disruption of normal metabolic activities in the RPE; the subsequent alterations of the RPE-photoreceptor metabolic equilibrium is probably the initial step of photic retinal damage induced by low-intensity light.