Solar radiation and age-related macular degeneration.

Age-related macular degeneration (AMD) involves a progressive impairment of the outer layers in the center of the retina. Experimental studies have demonstrated that bright light preferentially damages precisely the region that degenerates in AMD. The evidence that solar radiation is responsible for some of the deteriorative changes that lead to AMD is examined in this review. In the primate eye, the high-energy portion of the solar spectrum is most hazardous to retinal molecules, with damaging effects increasing as photon energy rises. This action spectrum is explicable by the quantum laws which describe the interaction of radiation with matter. High-energy visible and ultraviolet photons can produce molecular damage by a photochemical mechanism. The lesion is exacerbated by oxygen, which initiates free-radical chain reactions (photodynamic effects). Melanin exerts a protective effect against damage from sunlight. In the human retina, documented lesions from solar radiation range from the acute effects of sun-gazing to injuries resulting from prolonged periods of exposure in brightly illuminated environments. The damage occurs in the same region that degenerates in AMD. A cataractous lens and ocular melanin both protect the retina against AMD, as predicted by the radiation hypothesis. Identification of an environmental factor that evidently plays a role in the etiology of AMD provides the basis for a program of preventive medicine.