Sleep and circadian rhythms in the blind

In the majority of totally blind individuals, the biological clock is no longer synchronized, or entrained, by the light/dark cycle. Despite exposure to regular social cues, meal times and sleep/wake schedules, the circadian phase (timing) of biological events in these individuals continues to drift to a progressively later (or, rarely, earlier) hour. As a result, these individuals suffer from periodic bouts of nighttime insomnia and daytime hypersomnolence, as the circadian sleep propensity rhythm moves in and out of synchrony with the 24-hour day. Recently, oral melatonin has been shown to be highly effective in resetting the biological clock in these individuals.¹