CHANGES IN THE PUPILLARY LIGHT REFLEX OF PIGMENTED ROYAL-COLLEGE OF SURGEONS RATS WITH AGE

We studied the latency and amplitude of the pupillary light reflex res ponse of the Royal College of Surgeons rat from 10 to 52 weeks of age. The responses of these dystrophic rats were diminished compared to th ose of normal, non-dystrophic rats at all ages examined. This was most marked at the dimmest light intensity studied here and for the latenc y of dystrophic animals' responses. The latency deteriorated over the course of 52 weeks, although there was some evidence of improvement be yond 36 weeks of age. The amplitude of the dystrophic animals' respons es also suggested some deterioration occurring up to 36 weeks of age, but with a substantial improvement beyond this time. In addition to th ese 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 li ght reflex at older ages, even when very few photoreceptors remain, ma y reflect compensatory events occurring in the inner retinal layers an d/or in the central connections of the pupillary light reflex pathway. We suggest that the break in the constriction phase is a reflection o f dual inputs driving the response, one of which is affected more by t he degenerative events. This study provides baseline data on the effec t of degeneration on function over time which can be used to evaluate the efficacy of repair strategies such as transplantation. (C) 1998 Ac ademic Press.