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Experimental light damage increases lipofuscin in the retinal pigment epithelium of Japanese quail (Coturnix coturnix japonica).

Lipofuscin accumulation in the retinal pigment epithelium (RPE) of Japanese quail was investigated in normal and light-damaged animals at 4 months and 12 months of age following a single, 18-hr light-damaging exposure (3000-3200 lx) evaluated 6 weeks postexposure. Quail in a second experimental group light-damaged at 4 months of age were exposed to a second, identical light-damaging exposure at 12 months of age. RPE lipofuscin was quantitatively assessed in three ways: (1) total lipofuscin, expressed as a percentage of the basal RPE cell area, (2) mean number of lipofuscin granules per RPE cell, and (3) mean area of lipofuscin granules. At 12 months of age, control female RPE cells showed substantially more lipofuscin than did males. Animals that received a single damaging light-exposure showed no significant differences in lipofuscin at either age when compared with controls, and none were observed between males and females. However, in the double light-exposure condition, both total lipofuscin and the number of lipofuscin granules were significantly higher in females compared to controls and also, when compared with animals in the single light-exposure condition. Mean lipofuscin granule size decreased in females in the double light-exposure condition when compared with control values. Histopathological evaluation of photoreceptor outer segments and outer nuclear layer indicated that double-exposed, 12-month-old females showed the most severe effects, including a substantial decrease (70%) in rod photoreceptor densities. However, only a small change was observed in cone densities for either sex (12-15%) in this condition. Overall, a strong, negative correlation (r = -0.78) was obtained between total lipofuscin and average rod density across age, sex, control and experimental conditions. A somewhat greater correlation (r = -0.82) was obtained for females, alone. These results suggest that rods, when severely damaged by light exposure, contribute to increased RPE lipofuscin. Age, sex and light-exposure history appear to be critical variables that can influence both the amount of lipofuscin present in RPE cells as well as the relative vulnerability of rod and cone photoreceptors to cumulative light-exposure damage. These results have implications for the development of a variety of age-related changes and diseases of the outer retina, including age-related macular degeneration.