Myopia link to night lights doubted

Last year, researchers in Philadelphia reported a correlation between use of night lights in an infant’s room and an increased incidence of nearsightedness later—and wondered whether the former might trigger the latter (SN: 5/29/99, p. 351).

Two studies reported in the March 9 Nature cast doubt on a causal link. Rather, they suggest that parental nearsightedness, or myopia, may actually play a stronger role in predicting a child’s myopia than use of night lights does.

Karla Zadnik, an optometrist at Ohio State University in Columbus, and her colleagues studied 1,220 children, average age 10 years. They interviewed parents to ascertain the children’s sleeping conditions between birth and age 2. Whether children slept in darkness, with a night light, or in full light didn’t affect their chances of being myopic later in childhood, Zadnik says. The proportion of nearsighted youngsters in all three groups, between 17 and 22 percent, was not significantly different, the researchers report. “Ambient light has no influence [on myopia], based on our study,” Zadnik concludes.

In the other new study, a team at the New England College of Optometry in Boston also arrived at a rough figure of 20 percent for myopia in children, regardless of nursery lighting. Both studies found a correlation between nearsighted parents and the tendency to have night lights in a nursery. The Boston researchers noted that families with two myopic parents used night lights significantly more often than did those with one myopic parent or none.

Since the most common type of myopia seems to have an unidentified hereditary component, Zadnik says, the link found earlier may have arisen because “myopic parents produce myopic children and use night lights.”

The University of Pennsylvania School of Medicine researchers noted that their earlier research received widespread publicity. In the two recent studies, parents might have underreported night-light use for fear of mentioning behavior that they perceived as potentially harmful to their children, Richard A. Stone and his colleagues say in the same journal.