Circadian rhythm disorders in the blind.

Non-24-h sleep-wake disorder in blind patients without light perception is an orphan circadian rhythm sleep-wake disorder and is extremely rare in sighted people. Non-24-h sleep-wake disorder is characterized by insomnia and daytime sleepiness alternating with asymptomatic episodes. The frequency of symptomatic periods depends on the daily desynchronization of endogenous circadian pattern of each patient. Diagnosis requires anamnesis, a sleep diary, and actigraphy, if possible; in addition, repeated 24-h measures of circadian markers such as melatonin secretion are also required. Treatment consists of sleep hygiene, behavioral therapy, and melatonin/melatonin agonist administration. Melatonin treatment should start when the circadian rhythm of the patient is in phase with the solar cycle. Efficacy of treatment may be evident after weeks even months from the beginning. There is often a relapse when the medication is stopped.