Sleep structure in blindness is influenced by circadian desynchrony

We examined the structure, duration and quality of sleep, including non-rapid eye movement sleep and rapid eye movement sleep, in 11 blind individuals without conscious light perception and 11 age- and sex-matched sighted controls. Because blindness is associated with a greater incidence of free-running circadian rhythms, we controlled for circadian phase by a measure of melatonin onset timing. When circadian rhythm was entrained and melatonin onset occurred at normal times, sleep structure did not differ between blind and sighted individuals. On the other hand, an abnormal timing of the circadian phase, including delayed, shifted and unclassifiable melatonin onsets, led to larger rapid eye movement sleep latencies and increased wake times. No differences were observed for stages of non-rapid eye movement sleep, either between congenital and late blind and sighted individuals, or across the different circadian phases. Moreover, abnormal circadian phases were more common in the blind (n = 5) than the sighted (n = 2) sample. Our findings suggest that the sleep structure of blind individuals depends on entrainment of circadian phase, rather than on the absence of vision.