The retinal circadian clock: Retinal health and retinal disorders

Abstract

Circadian clocks are molecular pacemakers that regulate various behavioral and physiological processes according to the 24-hour light/dark cycle. Ocular clocks, which were first identified in the retina of the eye, have also been determined in the cornea, the retinal pigment epithelium (RPE), and the ciliary body. The retina represents a complex structure consisting of three layers and containing various cell types. Many studies have been conducted to determine which cell types in the retina have real clock properties. As a result of these studies, it has been determined that inner retinal neurons, as well as photoreceptors, also exhibit clock properties. However, clock properties are thought to be widely distributed among different retinal cell types. In mammals, only the cornea and retina maintain direct light-dependent phase regulation, which distinguishes the retina and probably other ocular clocks from peripheral oscillators, the phases of which depend on the rate-determining characteristics of the suprachiasmatic nuclei (SCN), the hypothalamic central brain clock. Dopamine and melatonin are used as light-and dark-adapting neuromodulators, respectively, by retinal circadian regulation in mammals and non-mammalian vertebrates, and the circadian phase can be regulated by light in an indirect manner via dopamine signaling. Circadian clocks in the eye are crucial for optimal visual function, in which they are involved in fine-tuning visual sensitivity. The disrupted circadian rhythm in the retina through genetic or environmental stressors produces a state of circadian deviation associated with the development of different diseases, e.g., glaucoma, myopia, and RPE degeneration. The protective activity of molecules produced by the circadian rhythm in the retina against retinal inflammation, angiogenesis, apoptosis, and oxidative stress has been determined. This chapter presents the current knowledge about the retinal circadian clock, its molecular mechanism, and its potential role in eye diseases. © 2024 Nova Science Publishers, Inc. All rights reserved.