Melatonin and cortisol profiles in the absence of light perception.

As light plays an important role in the synchronisation of the internal biological clock to the environmental day/night schedule, we compared the 24-h profiles of biological circadian markers in blind and normal sighted individuals. Salivary melatonin and cortisol concentrations were collected every two hours in eleven blind subjects, reporting no conscious light perception, and eleven age- and sex-matched normal sighted controls. Timing of melatonin onset and associated cortisol quiescence period confirm an increased incidence of abnormal circadian patterns in blindness. Additionally, blind subjects showed a greater overall melatonin concentration throughout the 24-h period. Cortisol profiles, including concentration and morning cortisol peaks, on the other hand, did not differ between blind and sighted individuals. These findings support previous reports of an increase in abnormal circadian rhythms and the absence of the entrainment properties of light in blindness.