Turn Off the Lights

By Christine Gorman

If your kids are under two, turn off all the lights in the room when you put them to bed at night. Don't even leave a night light on, unless you want to increase significantly the chances that your children will grow up nearsighted and have to wear glasses for the rest of their lives. That's the advice issued last week by a group of researchers from the University of Pennsylvania. As someone who has needed glasses since fifth grade, I couldn't believe my eyes when I read their report in the current issue of Nature. It seemed like yet another alarming scientific study that raises more questions than it answers.

So I called Dr. Richard Stone, a pediatric ophthalmologist and one of the authors of the report. Practically the first words out of his mouth were, "We didn't prove anything." Then he went on to explain what he and his colleagues had found. They were following up a clue from the poultry industry, which has long known that baby chicks grow faster if you leave the lights on 24 hours a day. It turns out that their eyeballs grow longer as well--and long eyeballs is a pretty good description of what causes nearsightedness, also called myopia, in humans.

Almost as a lark, the investigators decided to ask the parents of 479 of their patients about the nighttime lighting in their children's bedrooms. It was a shot in the dark, but what they found was truly eye opening. While 10% of the kids who slept in darkness before age two later became nearsighted, the figure rose to 34% among those who slept with a night light, and an astonishing 55%--nearly a fivefold increase--among those who slept with the room lights on. It may be that eyes need a period of darkness to develop properly. Bedroom lighting didn't seem to make a difference after age two, when kids' eyes are no longer developing as rapidly.

The most important thing to keep in mind with observational studies like this is that they are the scientific equivalent of gossip. Subjects A and B show up together, which may be significant but is more likely to be an innocent coincidence. In this study, for example, the investigators didn't take into account whether the parents were nearsighted. That could explain a lot right there, since at least some aspects of myopia are inherited. Or perhaps nearsighted parents, are, for whatever reason, more likely to leave the lights on at night.

It could take an additional 20 years to sort out all the scientific issues, which won't do you much good if there's a baby in your life right now. Since the proposed remedy isn't at all onerous, however, and since most kids don't develop a fear of the dark until after age two, it seems reasonable to turn the lights out in your infant's room.

Don't go overboard, though. There's nothing wrong with flipping a light on in the middle of the night to change a diaper or comfort a crying infant. And don't change your daytime routine; children need plenty of daylight to thrive.

There's no point in feeling guilty if your children slept with the lights on as infants. "This is not something that anyone would have predicted," Stone says. Furthermore, as I and about 65 million other Americans can attest, being nearsighted is no big deal. True, we're at a slightly greater risk of developing glaucoma and detached retinas, but for most of us, nearsightedness is a minor inconvenience. Besides, I think glasses are kind of cool.

For more on nearsightedness, visit our website at time.com/personal You can e-mail Christine at gorman@time.com