Circadian Rhythms and the Blind Many blind people have desynchronized circadian rhythms because they’re unable to detect the sunlight that normally sets the body’s internal biological clock, the SCN. Like sighted people deprived of all environmental time cues, blind people can experience desynchronized melatonin, body temperature, and sleep–wake circadian cycles. Consequently, about 60 percent of blind people suffer from recurring bouts of insomnia and other sleep problems (Arendt & others, 2005; Mistlberger & Skene, 2005).
Kieran Doherty/Reuters/Corbis