Do Night Lights Cause Myopia?

A new study, published in the journal Nature, reports that children who sleep with a night light or other artificial light in their room until the age of two have a higher incident of nearsightedness - also known as myopia -- as they get older, CBS News Health Consultant Dr. Bernadine Healy reports.

Although genetic and environmental factors are thought to affect people's vision, scientists at the University of Pennsylvania and the Children's Hospital of Philadelphia suggest in their study that too much light could prompt the eyes to grow excessively and skew their natural focus. The first two years of life are when the eyes develop most rapidly.

Nearsightedness results when the eye grows excessively and its shape is too long rather than perfectly round. This causes incoming light to converge in front of the retina instead of on it, making things appear blurry.

About 25 percent of Americans are nearsighted, and children usually discover they have myopia when they have trouble seeing a classroom blackboard. In most cases, myopia is corrected with eyeglasses.

Later in life, nearsighted people are more likely to develop macular degeneration, detached retinas, and other disorders that can lead to blindness.

The Philadelphia researchers asked the parents of 479 children who had been patients at the doctors' eye clinic to recall the lighting conditions in the youngsters' bedrooms between birth and age 2.

A total of 172 of the children slept in darkness; 10 percent developed nearsightedness. A total of 232 slept with a night light; 34 percent had become nearsighted. An additional 75 slept with a lamp on; 55 percent developed myopia.

Ophthalmologist Dr. Graham Quinn, the study's lead author, acknowledged the study does not conclusively demonstrate that low light cause myopia, but he urged parents to provide sleeping infants and toddlers with a dark bedroom -- within reason.

"We don't want parents to overreact and start putting up blackout shades," he said. "We don't want them to think they have to change a diaper in the dark, and drop their baby because they can't see what they're doing."

However, other experts dismissed the study as premature and incomplete, saying the researchers had failed to take into account obvious risk factors, such as heredity.

"There are other factors involved in childhood myopia, the most important of which is whether the parents are nearsighted or not," said myopia researcher Donald Mutti of the University of California at Berkeley.

They also said the study is flawed because the researchers relied on information supplied by parents of nearsighted children after several years. Nor did they account for other, stronger sources of light that parents cannot control, such as a streetlight shining through a bedroom window.

A more reliable approach would be to conduct controlled experiments in the illuminated and darkened bedrooms of children, then ceck their vision several years later, the experts said.

"I don't think a retrospective study based on a questionnaire is valid," said Dr. Robert Cykiert, an ophthalmologist at the New York University School of Medicine. "They're grasping at straws."

Other researchers said parents should wait for the results of follow-up research before tossing their night lights in the trash.

Mutti said: "Do what is comfortable for your children in order to get them to sleep.