Non-24-hour sleep-wake rhythm disorder in sighted and blind patients

Non-24-hour sleep-wake rhythm disorder (N24SWD) is a cyclic debilitating circadian rhythm sleep disorder characterized by an inability to sleep on a 24-hour schedule. Individuals isolated from a 24-hour light-dark cycle exhibit sleep-wake cycles different from 24 hours. Relatively rare in sighted patients, it may be associated with delayed sleep-wake rhythm disorder or psychiatric disorders. It is more common in totally blind individuals owing to the lack of light information reaching the circadian pacemaker in the hypothalamus. We review the clinical characteristics of patients with N24SWD, discuss the biological mechanisms that may underlie its development, and describe treatment strategies