Prevention of cataracts in pink-eyed RCS rats by dark rearing

Royal College of Surgeons rats have hereditary retinal degeneration and associated posterior subcapsular opacities (PSO) of the lens, detectable by slitlamp at 7-8 postnatal weeks in both pink- and black-eyed rats. The retinal degeneration is intensified by light, especially in pink-eyed rats. A fourth of pink-eyed rats developed mature cataracts by 9-12 months of age, but black-eyed rats whose retinas are protected from light by pigmented irises and pigment epithelium rarely have mature cataracts (3% or less), indicating light may be a factor in cataractogenesis. Prior work had shown that dark rearing reduced the rate of retinal degeneration in pink- but not black-eyed rats, but cataracts were not studied. In the present work, pregnant pink-eyed females were placed in a darkroom 1 week before parturition. Pups were removed over intervals at 20-85 postnatal days for: (a) microscopic study of fresh lenses and of fixed, stained retina and lens, and (b) counts of cells mm^-2 of the web-like vitreous cortex after it had been dissected free. The macrophage-like cells are a quantitative index of immune reaction to retinal damage. At 50-53 postnatal days, in pink-eyed cyclic light reared RCS, the mean number of macrophages was 4·6-fold that in congenic controls, but in those that were dark reared it was only 1·4-fold. This was less than the increase in cyclic light reared black-eyed RCS (2·3-fold that in congenic black-eyed controls). Total absence of light reduced retinal degeneration and the number of macrophages, and prevented PSO detectable microscopically. The results show that light is essential for initiation of the RCS cataract. This is consistent with the hypothesis that the lens is damaged by light-initiated toxic lipid peroxidation products and that these can be prevented by dark rearing.