Changes in absolute threshold with light-induced retinal damage

Albino rats were trained on a mixed signalled reinforcement procedure designed to yield repeated absolute visual thresholds within each session. After threshold stability animals were exposed 12 hours per night to 1000 lux of light froma cool-white fluorescent source. Log threshold rose as an approximate linear function of exposure time to a maximum of 2.0 log units above baseline after 36 cumulative hours of exposure. Light and electron microscopic analysis of the irradiated retinas revealed vesiculated photoreceptor outer segments, with varying degrees of vacuolation of the inner segments and pyknosis of photoreceptor nuclei depending on exposure time. The various combinations of retinal pathology suggests that damage to photoreceptor outer segments and inner segments interact to jointly affect psychophysical thresholds in light-induced retinal damage.