RESUMO
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 maximal 36 month were examined by light and electronmicroscopy and analysed for changes in cell densities. In all 3 rat 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. Age-related ultrastructural changes in the retinal pigment epithelial cells (RPE) were in both pigmented strains: (1) a substantial accumulation of lipofuscin, (2) an apparent thickening of the basement membrane and (3) absent or greatly enlarged pleomorphic basal infoldings. In up to 27-month old BDE (Han) and 36-month old Norway rats besides mature stage IV-melanosomes also stage III-melanosomes can be observed. Characteristic of RPE-cells in old rats of these two strains were also compound granules and compound melanosomes. In peripheral RPE-cells of albino rats premelanosomes can be sporadically detected up to 31 months of age. Age-related changes in retinal vessels were found in the superficial and deep capillary network. The only finding was a 2-3 fold increase in thickness of the capillary basement membrane.