Retinal light perception and biological rhythms: The role of light in sleep and mood from an ophthalmic perspective (Review)
Abstract
Light is the paramount environmental signal for the entrainment of endogenous circadian rhythms. Its non-visual effects, mediated by the retina, exert a profound control over human sleep, mood and systemic physiological homeostasis. Beyond its canonical function in image formation, the retina operates as a primary irradiance detector through a specialized class of neurons, the intrinsically photosensitive retinal ganglion cells (ipRGCs), which utilize the photopigment melanopsin. These cells convey environmental light information directly to the suprachiasmatic nucleus (SCN), the brain's master circadian pacemaker, thereby synchronizing the body's internal timekeeping with the external solar cycle. Compelling evidence demonstrates that the spectral quality of light, particularly within the short-wavelength blue range, potently modulates neuroendocrine and neural systems via the ipRGC pathway, governing melatonin synthesis, the architecture of the sleep-wake cycle and affective regulation. The modern light environment, characterized by ubiquitous artificial light at night and pathological states of light perception resulting from ophthalmic diseases such as glaucoma and retinal degenerations, can severely disrupt this synchronization. The consequent circadian misalignment is a significant etiological factor in sleep disorders, depressive symptoms and other systemic morbidities. The retina's integral position within the light-rhythm-behavior axis is thus a critical nexus…
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