Slit-lamp assessment of onset of cataracts in black-eyed, black-hooded retinal dystrophic rats.
Various types of hereditary retinal degeneration have associated posterior subcapsular cataract (PSC). It has been claimed that in the Royal College of Surgeons (RCS) rat model of hereditary retinal dystrophy, the cataract is manifested unpredictably and does not display Mendelian inheritance. It ws shown previously, however, that 100% of pink-eyed retinal dystrophic RCS rats had an onset of bilateral PSC at 7 to 8 weeks of postnatal age, and by 9 to 11 months, 23% of the animals had cataracts visible to the unaided eye. The congenic black-eyed retinal dystrophic RCS rat, however, is a better model for the generally more pigmented human eye. In the present work, it was found that 100% of black-eyed RCS rats had bilateral slit-lamp-detectable PSC beginning at 8 weeks of postnatal age, just as the pink-eyed rats did, despite the fact that dark-eye pigmentation is associated with a 10- to 35-day delay in the rate of degeneration in retinal areas other than the peripheral part of the inferior hemisphere. A higher incidence of mature cataracts in pink-eyed rats (23%) as compared with black-eyed rats (3%) suggests that the amount or intensity of light reaching the lens, retina, and pigmented epithelium may influence maturation of the cataract. However, if light is important in initiating the PSC, its influence was not decreased by dark pigmentation of the eye. RCS rats may be a model for an early onset type of human autosomal recessive retinal degeneration having a constant association of PSC.