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

PURPOSE: To determine whether the degenerating photoreceptors in nervous (nr/nr) and Purkinje cell degeneration (pcd/pcd) mutant mice are more susceptible to the damaging effects of constant light than those in age-matched normal mice.

METHODS

Beginning at two ages for each mutant, albino nr/nr and pcd/pcd mice were placed into constant fluorescent light at an illuminance of 115 foot-candles to 130 foot-candles for a period of 1 week. Age-matched (usually littermate) normal (+/-) mice were exposed at the same time. The degree of photoreceptor cell loss was quantified histologically by obtaining a mean outer nuclear layer thickness for each animal. The light-exposed mice were compared with age-matched mutant and normal mice that were maintained in cyclic 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 to patients with inherited or age-related photoreceptor degenerations. The present data add to other experimental evidence suggesting that photoreceptors already undergoing inherited or other forms of degeneration may be particularly susceptible to the damaging effects of excessive light.