Increased susceptibility to constant light in nr and pcd mice with inherited retinal degenerations

PURPOSE. To determine whether the degenerating photoreceptors in nervous (n r/nr) and Purkinje cell degeneration (pcd/pcd) mutant mice are more suscept ible to the damaging effects of constant Light than those in age-matched no rmal mice. METHODS. Beginning at two ages for each mutant, albino nr/nr and pcd/pcd mi ce were placed into constant fluorescent light at an illuminance of 115 foo t-candles to 130 foot-candles for a period of 1 week. Age-matched (usually littermate) normal (+/-) mite were exposed at the same time. The degree of photoreceptor cell loss was quantified histologically by obtaining a mean o uter nuclear layer thickness for each animal. The light-exposed mice were c ompared with age-matched mutant and normal mice that were maintained in cyc lic light. RESULTS. The homozygous mutants at each age showed a significantly greater loss of photoreceptor cells caused by constant light exposure than did the normal +/- mice in the same period of light exposure. The nr/nr and pcd/pcd mutants lost two to three times the number of photoreceptor cells than did the +/- mice during the constant light exposure. CONCLUSIONS. It has long been thought that excessive light may be harmful t o patients with inherited or age-related photoreceptor degenerations. The p resent data add to other experimental evidence suggesting that photorecepto rs already undergoing inherited or other forms of degeneration may be parti cularly susceptible to the damaging effects of excessive light.