Light-induced variations of retinal sensitivity in rats

Purpose. ERG responses were measured as a function of Ganzfeld luminance to evaluate functional damage induced by light on rat retinas. Methods. Wistar rats were exposed to a fluorescent light of 1700 lux for 12 h, 24 h, 48 h and 72 h. We recorded ERGs before and one night after exposure, then 3, 8, 15, 22 and 29 days later. The b- and PIII-wave amplitudes were plotted against luminance for each group at each recovery time. Results. The retinal damage induced by a pupillary illuminance of 1700 lux ranged from low to severe as exposure duration increased from 12 h to 72 h, respectively. We observed an effect immediately after light exposure but no improvement during the recovery period. The b- wave amplitude was reduced by 40, 60, 80 and 90 percent after 12, 24, 48 and 72 h of light exposure, respectively; the pill-wave amplitude was reduced by 30, 40, 70 and 90 percent after these respective exposures. The Ganzfeld luminance eliciting a 50 mu V b-wave amplitude increased significantly with exposure duration, but the luminance eliciting the maximal b-wave amplitude was not dependent on this duration. Hence we suggest that the ERG decrease is due to a reduction in photoreceptor number. Conclusions. We present a full analysis of the electrophysiological parameters recorded from light-exposed or nonexposed rats. This model is a useful tool to study in vivo retinal degeneration.