What should be the main criteria for a prescription for eyeglasses? The answer, it seems, is straightforward. Put the glasses on and the world should look sharper. But your glasses should do more than that. The primary role of vision is to allow us to locate ourselves and other things in space so that we can move with speed and accuracy. Thus, our glasses should improve the way we use our vision to reach for things, navigate around obstacles, and perform hundreds of other routine tasks. Unfortunately, these skills are not tested during the standard eye exam. Most exams involve looking at an unmoving eye chart while sitting perfectly still.

This idea became clear to me while reading a recent issue of the journal, Optometry and Vision Development. This issue was devoted to the memory of the brilliant optometrist John Streff and included reprints of several articles that Dr. Streff had written. One of them called "Viewpoints: The Value of Observation" really caught my attention. In this paper, Dr. Streff described a four-year-old, far-sighted girl who was also cross-eyed. On her first visit to him, she arrived wearing a pair of glasses to treat her condition. Although the eyeglass prescription was correct as determined by the results of standard clinical tests, the spectacles may not have provided the best lenses for her. Dr. Streff noticed that when his little patient reached for something with her glasses on, she actually increased the turn of her right eye. Her lenses did not help her to use the two eyes together for a task that is greatly aided by binocular vision!