Blind People’s Eyes May Serve Purpose in Regulating Sleep
BOSTON (AP) _ Even when people are totally blind, their eyes may serve a purpose.
A study today concludes that light entering the brain through the eyes helps regulate some blind people’s sleeping patterns, even though they cannot see it.
The discovery may open up important clues about how the brain keeps time in everyone, blind or not. It also raises questions about the common practice of removing blind people’s eyes for cosmetic reasons.
Insomnia is a major problem for many blind people, who often experience something like jet lag, nodding off during the day and tossing and turning at night.
The reason for this seems clear: The brain needs exposure to sunlight to keep its internal clock running on a 24-hour schedule. Otherwise, it falls behind about a half hour each day.
A fortunate minority of blind people, however, sleep easily at the appropriate time. Now scientists think they know why: Their brains can see light, even when their eyes cannot.
The research, conducted by Dr. Charles A. Czeisler and others from Brigham and Women’s Hospital in Boston, was published in today’s issue of the New England Journal of Medicine.
It suggests that two distinct routes shuttle information from the outside world into the brain.
One pathway, which transmits visual images, fails to work in those who are totally blind. But another avenue may survive. In ways that are still unclear, it carries in the message that the sun is shining.
The existence of such dual pathways has been shown in experimental mice but, until now, not in people.
An editorial in the journal said Czeisler’s work ``convincingly demonstrates that the conclusions drawn from studies in animals hold for humans as well.″
The blind who sleep well ``have vision without sight,″ wrote Dr. Robert Y. Moore of the University of Pittsburgh.
More than 1 million Americans are considered blind, and about 10 percent of them cannot see light. Czeisler estimates that perhaps one-third of these totally blind people sleep normally because their brains perceive light.
The body’s internal clock is housed in a part of the brain called the hypothalamus, which conveys information about light to the pineal gland, another part of the brain that makes a sleep-inducing chemical called melatonin.
Without accurate information about day and night, the gland produces melatonin at the wrong time.
The researchers experimented on 11 blind patients, three of whom slept normally.
The researchers shined bright light into the volunteers’ eyes. In the three good sleepers, melatonin levels fell by two-thirds, just as it does in sighted people. However, when they covered their eyes, melatonin did not change.
By contrast, light had no effect on the poor sleepers’ melatonin levels.
Doctors often remove the eyes of totally blind people, which can look cloudy and shriveled and are prone to infection and other disorders, and replace them with artificial eyes.
Czeisler said his work suggests this may be a mistake, because blind eyes may still be keeping their owners’ internal clocks on time.
The mother of one of the people he studied had refused to let doctors take out her son’s eyes because she hoped a medical breakthrough someday would restore his sight.
``Little did she realize that she was preventing her son from being subjected to an intractable lifelong sleep disorder,″ Czeisler said.