My son received a visual acuity test at school. His results were 20/50 in both eyes. What does this mean?

C.M.

Tests of visual acuity, or sharpness, are based on a Snellen eye chart, which displays rows of letters that get progressively smaller in size. The result of the test is given as two figures, usually in a ratio of 20/X. The first number indicates how far away the patient, in this case your son, stood from the chart when he read a row of letters, usually 20 feet. The second number indicates how far away a person with "normal" vision could stand from the chart and still read the same row of letters. So, a result of 20/50 means that your son can see at 20 feet what a person with "normal" vision could see from 50 feet away. If your son's vision was "normal," his test result would be 20/20.

If people have test results in which the second number is lower than the first, their vision is better than normal. For example, someone with 20/15 vision can read a row of letters at 20 feet that a person with "normal" vision could see only if he or she stood 15 feet away. Keep in mind that test results may be different for each eye.

Given the results of his school vision test, your son should have a more complete eye exam. He may need to wear eyeglasses to improve his vision to the normal 20/20 range -- an improvement that may help him with a wide range of activities from seeing the chalkboard to playing sports.