Changes in the aging rat retina.

To characterize aging as a factor responsible for structural changes, the retinae of 47 Wistar-derived albino rats and 50 pigmented rats of the Norway and BDE (Han) strains between the ages of 1 and 36 months were examined by light and electron microscopy and analyzed for changes in cell densities. In all 3 rats strains there was an overall decline in nuclear densities of outer layer nuclei by 38-50% and inner layer nuclei by 27-33% between the ages of 1 and 27 months. Over the same age range, the ganglion cell loss was comparable to the decline in the inner nuclear layer. Neuronal cell death occurred at all ages and was more pronounced in albino rats. Moreover, in albino rats, cones were more resistant than rods to destruction by age and ambient light. As age-related ultrastructural changes in the retinal pigment epithelium (RPE) (1) a substantial accumulation of lipofuscin; (2) an apparent thickening of the basement membrane; (3) greatly enlarged and pleomorphic basal infoldings, and (4) shorter apical microvilli were encountered. Besides mature stage IV melanosomes 27-month-old BDE (Han) and 36-month-old Norway rats also revealed stage III melanosomes. Tyrosinase activity in peripheral RPE cells could be demonstrated in Norway rats up to 12 months old and BDE (Han) rats up to 24 months old. Characteristics of RPE cells in old rats of these two pigmented strains were also melanolysosomes, melanophagolysosomes and melanolipofuscin granules. Age-related changes in retinal vessels were found in the superficial and deep capillary network and consisted of a 2- to 3-fold increase in thickness of the capillary basement membrane.