Visual-deficit following long-term continuous light exposure

Abstract

Extensive retinal degeneration without significant visual deficit has been shown to follow long-term continuous light (CL) exposure of albino rats. The present study attempted to determine if vision was affected with the CL exposure extended beyond that necessary for complete degeneration of the rod cells. Performance of a light-dark discrimination task tested visual function in albino rats after 400 1x CL exposure. Microscopic examination of all retinas assessed rod cell density. Performance decrements and retinas without rod cells appeared after 90 days CL exposure. Five animals without rod cells accurately performed the discrimination task (84–99% correct.) No rod cells were found in retinas CL exposed more than 130 days. Animals CL exposed for 130–216 days showed a progressive performance decrement with exposure. Five animals trained early in a 120–150-day CL exposure period maintained high performance levels ( 96.8%) . Lower performance levels ( 75.6%) were obtained by animals trained after 120 days CL exposure. These results verify previous findings that rats could perform light-dark discriminations without rod cells. It was concluded that cells supporting visual function in the absence of rod cells were subject to functional deficits after long-term CL exposure. It was predicted that exposure to CL of sufficient intensity and duration would result in blindness. A process of generalization was proposed in which learning with intact rod cells generalized to other cell types to account for the maintained high performance levels of animals trained at the beginning of long-term CL exposure.