Sleep in the blind
The brain has evolved over hundreds of millions of years to use light to determine daytime, the time for a wake, and nighttime, the time for sleep. In the blind, the eyes typically cannot transmit enough light to the brain to synch the brain with the external light environment. However, all of us have internal rhythms, generally lasting longer than 24 hours. In sighted individuals, light resets these circadian rhythms to 24 hours- hence we feel alert at certain times of the day and sleep at others. In the blind, these circadian rhythms run without external regulations. Thus, in the blind, wakefulness and sleepiness occur at different times each day, gradually delaying.
Such free-running circadian rhythms provide an often underappreciated challenge to the lives of the blind. Blind people have very high rates of sleepiness during the day and trouble sleeping at night. Sleepiness and insomnia may impair job function. Sleep problems compound the many challenges of lacking sight.
Currently, treatment for sleep disturbances in the blind has variable effectiveness. Evening melatonin may be beneficial in some. Regular wake and meal times may help settle the circadian rhythm. Screening for other sleep disorders- especially sleep apnea- may be beneficial, especially in those who have lost sight as a result of diabetes, which often co-occurs with sleep apnea. Sleep physicians can help guide these treatments. Vigorous science may lead to improved pharmaceutical treatments over the next few years.