Generation by visible light of labile free radicals in the melanin granules of the eye.

The melanin granules of the eye generate a free radical when irradiated with visible light under approximately physiological conditions. The rapid generation in light and decay in dark of the free radical as indicated by electron spin resonance studies, coupled with the anatomical proximity of the melanin granules to the rods and cones of the eye, suggest that these granules may play an important role in the visual process. The investigation of this free radical offers a possible approach to connect the photochemical events in the eye with the subsequent electrophysiological events in the nerve.