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The disorder can occur at any age, from birth onwards, and is usually associated with or follows shortly after loss of light perception or loss or removal of a person’s eyes. The type of blindness does not seem to affect the risk of developing Non-24.

In the first detailed study of Non-24 in a blind subject, researchers reported on a 28-year-old male who had a 24.9-hour rhythm in sleep, plasma cortisol, and other parameters. Even while adhering to a typical 24-hour schedule for bedtime, rise time, work, and meals, the man’s body rhythms continued to shift.

Without light awareness, the suprachiasmatic nucleus (SCN), located in the hypothalamus, is not cued each day to synchronize the circadian rhythm to the 24-hour social day, resulting in Non-24 for a majority of totally blind individuals.

Non-24 is rare among visually impaired patients who retain at least some light perception. Researchers found that even minimal light exposure can synchronize the body clock.

The impact of Non-24 on daily life is affected by the extent to which the body clock drifts. For instance, a person with a 25-hour body clock would have a 25-day cycle with two weeks of good sleep and two weeks of poor sleep. But a person with a 24.1-hour circadian rhythm would drift only six minutes per day and take 241 days, or eight months, to go around the clock. They may have four months of good sleep and four months of bad sleep, when the cycle would begin again.