Role of Melatonin in Human Eye Physiology and Its Implications for Ophthalmic Diseases Treatment (Review)

Abstract

Melatonin is a hormone of the epiphysis and a regulator of circadian rhythms of living organisms, which affects a number of important physiological processes. Melatonin synthesis has also been found in other organs, in particular in various structural systems of the eyeball. A number of studies demonstrate that melatonin plays an important role in a variety of biochemical and physiological processes that ensure functioning of visual analyzer. This review provides information on the synthesis of melatonin, its secretion and metabolism, considers key information about melatonin receptors (MT1, MT2 and MT3), their localization in various eye’s structures, and their affinity to melatonin. Over the last years, researchers’ attention has been drawn to the therapeutic properties of melatonin, relevant for treatment of age-related diseases. The aggressive effects of solar radiation and environmental toxicants expose the organ of vision to oxidative attacks. A large amount of evidence has been accumulated of the participation of oxidative stress in the development of many eye diseases, resulting in an imbalance between the generation of reactive oxygen species and the expression of antioxidant enzymes. Melatonin, which has antioxidant and anti-inflammatory properties and regulates mitochondrial functions, can be a powerful tool to counter age-related changes. Globally, the number of people of all ages with visual impairment is estimated at 285 million. Cataract and age-related macular degeneration (AMD) are the leading causes of vision loss around the world. AMD and cataracts often coexist in patients, so there is a concern that age-related cataract surgery increases the risk of morbidity and progression of AMD. The pathogenesis of both cataracts and AMD is still unclear, although a number of theories have been put forward, including oxidative stress, age-related changes, inflammatory processes, etc. Analysis of modern domestic and foreign literature shows good perspectives of using melatonin as preventive and therapeutic agent in the treatment of ophthalmic diseases of various origins.