sleep foundation

Non 24 Sleep Wake Disorder

The National Sleep Foundation

Medically Reviewed by

The National Sleep Foundation

Written by

The National Sleep Foundation

Although the majority of people with Non 24-Hour Sleep Wake Disorder (Non-24) are blind, it also occurs in a small number of sighted individuals. As many as half to three-quarters of totally blind patients (i.e., having no light perception) are considered to have Non-24, representing approximately 65 to 95 thousand Americans. The number of sighted people with Non-24 is unknown.

Most blind people have some light perception. As a result, their circadian rhythms are synchronized to a 24-hour day-night cycle, as in the sighted. However, it has been estimated that of the 1.3 million blind people in the United States, 10% have no light perception. These totally blind individuals are at the greatest risk for Non-24.

Non-24 is common in totally blind people due to a lack of light entering the eyes. Photoreceptors in the retina normally signal the brain and regulate the 24-hour day-night cycle. For a totally blind individual with Non-24, their inability to perceive light prevents the synchronization of their internal body clock to the day-night cycle. As a result, the internal body clock defaults to a non-24 hour cycle, causing fluctuating periods of good sleep followed by periods of poor sleep and excessive daytime sleepiness.

The exact cause of Non-24 in sighted people is unknown. But, it is believed to be caused by neurological factors.

Sighted vs. Blind