Sleep cycles are based on the complex interaction between light and a person’s internal clock. Most fall into a similar eight-hour “chronotype” (personal sleep-wake pattern) that fits right in with the standard social clock on which most everyone operates. Although these rules hold true for most, there are some individuals whose behaviors lie outside of the normal societal sleep-wake cycle and can never quite synch up. These people are known to have “social jet lag” and this condition is primarily caused by a mild malfunction of their internal clocks.
But, for the visually impaired or blind, frequently the problem isn’t their internal clocks but their ability to perceive light. Being that the body’s sensitivity to light goes a long way towards releasing the proper chemicals to fall asleep and when to wake, blind people are prone to have a serious problem regulating their sleep-wake cycle.
Just how important is the ability to sense light to keeping a consistent sleep-wake schedule? Recent research shows that up to 70% of visually-impaired people suffer from a circadian rhythm disorder known as Non-24. People who suffer from Non-24 have a sleep wake-cycle that isn’t 24 hours. Although most people’s clocks do run over the standard 24 hours, light exposure helps to re-calibrate their cycle on a daily basis. For some visually-impaired individuals this reset mechanism does not exist.
When the visually impaired suffer from Non-24, they’re thrown off their sleep schedule constantly. Bedtimes may come later and later and if wake times stay the same, the person will become increasingly sleep-deprived and unable to perform their regular jobs or attend to social commitments. The result is a permanent feeling of jet lag and a sleep schedule that completely reverses every so often.
To treat this issue, patients are put on a regular dosage of synthetic versions of the hormone melatonin which works to drag forward the onset of sleep by convincing the body that it is, indeed, nighttime. As research grows, pharmaceutical companies are working on a new drug called tasimelteon. The drug, which is intended to treat Non-24 and other circadian-rhythm sleep disorders, is being developed by Washington D.C.-based Vanda Pharmaceuticals. Although the drug is yet to be made available to doctors, hopes are that it will help people regulate their sleep cycles without counteracting any medications or leaving the user feeling tired or “hung over” the next morning. Non-24 is a serious health issue and its study highlights human light dependency and how its inextricably linked to how we perceive time.