The effects of dim cyclic light on pigment epithelial function in the albino rat

Most pathologies of the outer retina include physiological and morphological changes in the pigment epithelium. The question of pigment epithelial involvement in retinal light damage caused by low intensities of light is still unresolved. In the present study, we investigated the effects of low intensity cyclic light on pigment epithelial function in albino rats. The functioning of the pigment epithelium was assessed electrophysiologically from d.c. recordings of ERG c-waves and sodium azide induced changes in the resting potential. Responses obtained from albino rats raised under low intensity cyclic light (0.63 ft cd. 12:12 L:D) were compared to those obtained from albino rats raised under minimal light exposure conditions (dark-reared) and pigmented rats housed under low intensity cyclic light. We report, for the first time, that albino rats raised from birth under low intensity cyclic light possess c-waves. Their responses were comparable in amplitude and latency to those recorded from pigmented rats housed under similar conditions, but were significantly smaller than those recorded from dark-reared albino rats. The reduction in the amplitudes of the c-waves recorded from cyclic light-reared albino rats was probably not due to retinal light damage. Comparisons of the amplitudes and latencies of ERG b-waves recorded from cyclic light-reared and dark-reared albino rats did not suggest that the retinas of the cyclic light-reared albino rats had been damaged by light. Light microscopic examination of these retinas also provided no evidence for light damage. The transient, positive potential changes recorded from cyclic light-reared albino rats in response to bolus injections of sodium azide were significantly smaller than those recorded from either dark-reared albino rats or pigmented rats housed under low intensity cyclic light. The results of these experiments suggest that the pigment epithelium of albino rats is functionally altered by extremely low intensities of cyclic light.