WEDNESDAY, May 23, 2001 (HealthDayNews) -- A couple of years ago, researchers in Pennsylvania stunned parents by suggesting that night lights could lead to nearsightedness in kids. But now, a new study supports a growing body of research that says absolute darkness isn't an absolute necessity.
There is one big caveat: The researchers in the latest study examined monkeys, not humans. But even if your child doesn't belong in the zoo, the results are encouraging, says study co-author Dolores Bradley, a research associate at Emory University's Yerkes Regional Primate Research Center.
"Parents shouldn't be afraid that leaving a light on in their children's room will make them myopic," she says.
The first night light study, which came out in 1999, suggested that children who sleep with a light on -- even a tiny one -- are five times more likely to develop myopia, which is also known as nearsightedness and is caused by elongated eyeballs. Myopic people have trouble with distance vision, and advanced cases can even rob them of the ability to read without glasses or contacts.
Researchers in the first study were inspired to probe lighting because the eyes of chickens grow abnormally when they are continually exposed to light.
But their findings were attacked by critics who said the study didn't account for the fact that myopic parents are much more likely to have myopic children.
Two later studies then found no connection between night light use and myopia.
In the newest study, researchers kept lights on around the clock in the cages of nine monkeys. "They were bottle-fed and in a group cage, running around, playing with each other, playing with staff, doing what monkeys do," Bradley says.
Monkeys' eyes are similar to those of humans, she notes, adding that scientists can induce physical nearsightedness in the monkeys by giving them special out-of-focus goggles.
That's because myopia in monkeys does not happen naturally, she says.
"Left to their own devices, there's nothing in their environment or genetics to induce myopia," she adds.
During her study, she says, the monkeys' sleep cycles did go out of whack because of the constant daylight, but their vision was unchanged.
Bradley points out that, because of ethical concerns, it would be impossible to test human babies in continual light during their infancy. But because monkeys closely resemble humans, the results should put parents at ease, she adds.
Not so fast, says Dr. Richard A. Stone, the senior author of the controversial study that started the debate.
Stone, a professor of ophthalmology at the University of Pennsylvania School of Medicine, points out that some of the monkeys in the new study did, in fact, develop sight problems. Also, the monkeys were very young at the end of the study, he notes, which suggests that they could develop problems later on.
"The issue is light and dark, not night lights," he says. "There's a tremendous increase in myopia worldwide, and the question is: What is going on? It had to be an environmental thing."
Other research suggests that a cycle of light and dark is necessary for proper eye growth, he adds. "It seems that eyes develop better with a daily period of darkness," he says. "We don't know how dark it has to be, or [for] how long."
What To Do
The research seems to suggest that night lights are not a risk to young children's sight. If you want to be on the safe side, though, keep your kids' rooms dark and bring along a flashlight when you check on them.
You can learn more about nearsightedness from this fact sheet created by the Washington Association of Optometric Physicians.
Learn about how your eyes work, at the Bausch & Lomb company.