Now is an excellent time to have your child's vision checked. Don't be too quick to say, "My child's vision is fine: 20/20!" In many cases that is not enough.

The Snellen chart, the instrument most frequently used to test eyesight, often gives people a false sense of security about their vision. It measures only acuity -- and that at a distance of 20 feet. How much does your child read at that distance?

The National Center for Health Statistics estimates that about 25 percent of children enter school with vision problems that can impede their school progress. Almost 50 percent of children with learning difficulties have vision problems, and up to 94 percent of children with reading problems have reduced visual skills.

Why does the Snellen chart leave some of these problems undetected? Vision involves much more than the sharpness of an image. It involves focusing -- and refocusing as attention shifts between far and near (as when copying from the board). It involves binocularity, the two eyes working together to capture accurate pictures of our world and of the printed page. Vision also involves perception, the brain's interpretation of the images taken in by the eyes.

Many people believe that vision should be checked by an ophthalmologist, the person with the highest credentials. While it is true that an ophthalmologist is an M.D., he or she has spent about the same amount of time studying the anatomy, functions, and diseases of the eye as an optometrist has spent studying vision alone. To check my child's vision I would seek an optometrist, specifically a "developmental" or "behavioral" optometrist. Not only will the vision exam be more thorough, but the developmental optometrist may prescribe a course of "vision therapy" to remedy problems.

Often we take vision for granted and do not think of it as a learned behavior. Because it is learned, however, through practice we can improve it. Experts speculate that the frequency of vision problems may be increasing because with television, video games, and computers, children today do not use their eyes in as many different ways as children did formerly; overall the vision of children entering school is less developed than it was a few decades ago.

What symptoms might indicate a vision problem? Any time a bright person struggles with reading, further investigation is warranted. Consider these specific questions in relation to yourself as well as in relation to your children or students. Answering yes to even a few of the questions justifies further examination. Do not discount a "yes" even if it is limited to special circumstances, such as fatigue.

Do you (or does the child) . . .