Changes in the Pupillary Light Reflex of Pigmented Royal College of Surgeons Rats with Age

Abstract

We studied the latency and amplitude of the pupillary light reflex response of the Royal College of Surgeons rat from 10 to 52 weeks of age. The responses of these dystrophic rats were diminished compared to those of normal, non-dystrophic rats at all ages examined. This was most marked at the dimmest light intensity studied here and for the latency of dystrophic animals' responses. The latency deteriorated over the course of 52 weeks, although there was some evidence of improvement beyond 36 weeks of age. The amplitude of the dystrophic animals' responses also suggested some deterioration occurring up to 36 weeks of age, but with a substantial improvement beyond this time. In addition to these parameters, we also observed a break in the constriction phase of the pupillary light reflex that was unique to the dystrophic animals' responses. The frequency with which the anomaly occurred decreased in a light-dependent manner with age. The improvement of the pupillary light reflex at older ages, even when very few photoreceptors remain, may reflect compensatory events occurring in the inner retinal layers and/or in the central connections of the pupillary light reflex pathway. We suggest that the break in the constriction phase is a reflection of dual inputs driving the response, one of which is affected more by the degenerative events. This study provides baseline data on the effect of degeneration on function over time which can be used to evaluate the efficacy of repair strategies such as transplantation.