How Does the Circadian Rhythm Function in Blind People Who Have No Light Perception?

Circadian rhythms in the body affect physiological functions and behaviors and therefore have important roles on health.These rhythms mainly regulate important physiological processes such as the sleep-wake cycle, autonomic activity, endocrine function and immune system.Regarding biological rhythm, the master structure is the suprachiasmatic nucleus (SCN) in the hypothalamus.Furthermore, many circadian oscillators are present in the central nervous system and peripheral body tissues.These oscillators exhibit their function under the coordination of SCN for the functional integrity of the circadian rhythms.Daily retinal light-dependent stimuli are essential for the rhythm of day and night and the synchronization of circadian clocks.In this synchronization, melatonin hormone has a major role as an endocrine factor.The expression of melatonin is regulated by light signals reaching to the SCN.In many blind people without light perception, circadian rhythm synchronization is impaired due to the inability of the SCN to receive light information.In such cases, serious sleep disorders can be seen.This condition is called non-24-Sleep-Wake Rhythm Disorder.This disorder can be treated with behavioral therapy and medial therapy.Moreover, melatonin or its agonists are used in medical treatment.