The effects of prolonged dark exposure on visual thresholds in young and adult rats.

A comparison of electroretinogram (ERG) thresholds measured on rats reared in continuous darkness and under cyclic lighting conditions shows that by 30 days of age the dark-reared animals have achieved significantly lower thresholds than the animals reared under cyclic illumination. Ten days of continuous dark exposure produces this same increase in sensitivity in adult rats reared in cyclic lighting. These changes in sensitivity appear to reflect structural changes occurring within the rod outer segments.