The first part of the study is observational, in which the body clock rhythms of blind individuals are assessed for variability in patterns across subjects. The second part of the study involves a melatonin treatment (0.025-20 mg). The dose for each subject will be determined by the previous, observational data collected on the specifics of their individual body clock. The purpose of the intervention is to find an optimized dosing regimen and administration time to synchronize the body clocks of blind individuals, that seem to operate independent of the 24-hour environmental light/dark cycle, to the 24-hour day.