Sleep Tight, Little Baby, Sleep Without a Light

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What could be more reassuring to a young child than going to sleep with a light on? A new study to be published Thursday in the journal Nature suggests the common practice may not be such a good idea. Research from the University of Pennsylvania Medical Center and the Children's Hospital of Phildelphia indicates that children who regularly sleep with the light on before they reach the age of two exhibit a higher rate of developing myopia, or nearsightedness, later in life. In fact, says the team, the more intense the light, the greater the chance of myopia. Of children who had slept with a night light before the age of two, 34 percent became myopic; of those who had slumbered under a room light, the figure rose to 55 percent. Meanwhile, only 10 percent of those who had slept in the dark as infants were later reported as nearsighted.

So what should parents do? First thing, says TIME medical columnist Christine Gorman, is to stay calm. "Don’t panic over the study," she says. While the research may ultimately shed light on the importance of darkness during sleep, for the moment "this is just an observational study," says Gorman, "and observational studies are famous for falling apart upon further investigation." The scientists wanted to conduct "quick and dirty" research, says Gorman, to learn if nighttime lighting was worth looking into as a source of increasing levels of myopia. They didn’t impose some key controls on the research, such as whether the children in the study had nearsighted parents. In the meantime, considering it’s not much of a hardship to switch off the lights, obviously it would seem prudent to let a child under two sleep in the dark. At the same time, it makes sense not to get obsessive about it: "This doesn’t mean you have to change the diaper in the dark," says Gorman. As for those with older children who’ve already slept in lighted rooms, "don’t worry and don’t feel guilty about it," she says. The results of the study are not yet proven, and for most people myopia is mostly an inconvenience that can be corrected by glasses or contact lenses.