TUESDAY, June 21 (HealthDay News) -- Here's yet another reason to breast-feed babies: a new study finds it may reduce a child's likelihood of growing up to need eyeglasses.

Researchers who compared a group of breast-fed infants with formula-fed babies found that breast-fed infants were a bit less likely to be nearsighted at ages 10 to 12.

"It may have to do with some constituents in breast milk, but we can't be sure," said Dr. Richard Stone, an ophthalmologist at the University of Pennsylvania and a co-author of a research letter on the study in the June 22/29 issue of the Journal of the American Medical Association.

Stone and his colleagues, led by Dr. Yap-Seng Chong of the National University of Singapore, evaluated 797 Singapore children at ages 10 to 12, including 418 who had been exclusively breast-fed and 379 who had not been.

While 62 percent of the breast-fed children had myopia, or nearsightedness, 69 percent of those not breast-fed did. "It's really a modest effect," Stone said.

Even after the researchers controlled for factors such as the parents' nearsightedness, maternal age at delivery and birth weight, the association still held.

In developed countries, nearsightedness is the leading cause of visual impairment, the authors noted, and in the United States, more than 30 million adults are nearsighted. The prevalence of myopia has been increasing among urban Asian children, they added.

While the study is believed to be the first to observe an association between breast-feeding and myopia, other studies have found that breast-feeding is good for the development of children's eyes and is associated with better school performance by children.

Several of these studies have been conducted by scientists at the Retina Foundation of the Southwest in Dallas, Texas.

Dennis Hoffman, director of the visual biochemistry laboratory at the foundation said the new study findings are consistent with those done by his group.

"We've shown that breast-fed infants have improved visual maturation at one and a half years, compared to those fed formula," he added.

Stone and his colleagues speculate that a substance in breast milk, docosahexaenoic acid or DHA, may underlie the decreased risk of myopia. DHA is a fatty acid crucial for the growth and functional brain development in infants and it's also required for maintenance of normal brain functioning in adults.

It is also important, the study authors noted, for the development of photoreceptor cells in the retina, which play a major role in whether children become nearsighted.

The retina lines the inner eyeball and is connected by the optic nerve to the brain. The eye's lens focuses light on the retina, which then converts this light into signals sent to the brain. In nearsightedness, the eyeball is too long and light rays focus in front of the retina, rather than on it, causing the person to be able to see objects up close but not at a distance.

While the effect of breast-feeding on nearsightedness was modest, "on this basis, it seems sensible to breast-feed," said Stone, citing the numerous other benefits attributed to the practice.

More information:

To learn more about breastfeeding, visit the American Academy of Pediatrics.