READING in poor light, sitting too close to the TV, wearing the wrong prescription glasses and crossing your eyes — things your mother warned you would ruin your vision — are actually generally harmless. But a truly dangerous false belief is that there is nothing you can do to prevent the loss of vision.

According to Dr. Paul R. Lichter, a professor of ophthalmology and director of the Kellogg Eye Center at the University of Michigan in Ann Arbor, seeing an ophthalmologist regularly is essential, and not just to get a new pair of glasses. “In the way of preserving your sight,” he said, “it’s making sure you don’t have any hidden eye diseases.”

Dr. Lichter recommends an ophthalmologist’s examination before a child enters school, and if everything looks good at that point, then an exam every five years is enough. But it should be a thorough exam in which the doctor dilates the pupils and examines the optic nerve.