Causes
The etiology of Non-24 is unknown in sighted individuals. However, chronotherapy has been known to cause it in humans. "Studies in animals suggest that a hypernyctohemeral syndrome could occur as a physiologic aftereffect of lengthening the sleep-wake cycle with chronotherapy.". According to the American Academy of Sleep Medicine (AASM): "Patients with free-running (FRD) rhythms are thought to reflect a failure of entrainment".
In the blind without any light sensitivity, the brain is not cued to reset the circadian clock to a 24-hour sleep-wake cycle.
Read more about this topic: Non-24-hour Sleep-wake Disorder