Many people don't see well.

Vision screening of a broad sample of people in the United States ages 12 and older finds that 6.4 percent of them have substandard vision. That extrapolates to roughly 14 million people nationwide, National Institutes of Health (NIH) researchers report in the May 10 Journal of the American Medical Association.

Using mobile testing facilities throughout the country; scientists randomly offered people free vision tests. Some participants wore glasses or contact lenses; some didn't. Overall, 13,265 people completed the test.

Participants "failed" the exam if they had vision of 20/50 or worse in both eyes, whether or not they took the exam using corrective lenses. Of those who flunked, 83 percent could achieve good visual acuity by getting lenses for the first time or by replacing an out-of-date prescription, says study coauthor Mary Frances Cotch, an epidemiologist at NIH in Bethesda. Md.

Minorities, teenagers, and people without health insurance were more likely than others to have poor sight that wasn't being corrected, the researchers report.

"We recommend that health care professionals talk to their patients about eye health and encourage people to return for periodic eye exams," Cotch says. --N.S.