Melatonin in the eye: implications for glaucoma.

Melatonin synthesis occurs in the retina of most animals as well as in humans. Circadian oscillators that control retinal melatonin synthesis have been identified in the eyes of different animal species. The presence of melatonin receptors is demonstrable by immunocytochemical studies of ocular tissues. These receptors may have different functional roles in different parts of the eye. In view that melatonin is a potent antioxidant molecule, it can be effective in scavenging free radicals that are generated in ocular tissues. By this mechanism melatonin could protect the ocular tissues against disorders like glaucoma, age-related macular degeneration, retinopathy of prematurity, photo-keratitis and cataracts. Although an increased intraocular pressure is an important risk factor in glaucoma, other concomitant phenomena like increased glutamate levels, altered nitric oxide metabolism and increased free radical generation seem to play a significant role in its pathogenesis. Data are discussed indicating that melatonin, being an efficient antioxidant with antinitridergic properties, has a promising role in the treatment and management of glaucoma.