Correlation between cataract and retinopathy due to lighting in F344 rats used in a long-term carcinogenicity study

Correlations between light intensity of animal room lighting and both cataract and retinopathy of rats were examined, and relationships between the cataract and the retinopathy were further investigated. Seventy-nine male rats and 106 female rats surviving to the end of a 2-yr carcinogenicity study of monosodium succinate were used in this investigation. Animals were housed in polycarbonate cages, each containing 4 rats, with wire lids and hardwood chips for bedding and with a 12-h light/dark cycle. Individual groups comprising 13 cages were inserted into 3 by 5 cage hanging type racks. Light intensity was measured at the bottom (on the bedding) of individual cages. Statistically, both the incidence of cataracts and the severity of retinopathy were closely related to light intensity. The incidence of cataracts in males was significantly higher than that in females, while no sex difference was observed for the severity of retinopathy. Meanwhile, no differences in either the incidence of cataracts or the severity of retinopathy were observed between the monosodium succinate-treated and control groups and between the right and left eyes. While the occurrences of retinopathy and cataract were strongly associated, our results indicated that retinopathy occurs more frequently than cataracts, and thus the retina appeared to be more sensitive to the effects of lighting.