We've all heard the expressions visual acuity and twenty-twenty vision. As frequently used as these terms are, do most people really know what they mean?
The term 20/20 vision refers to the clarity of your eyesight from 20 feet away. If you've been told you have 20/20 vision, that basically means that from a distance of twenty feet you are able to accurately see that which should be seen from that distance. You may not know this, but 20/20 vision isn't the best possible visual acuity. Actually, a considerable number of people can even see better than 20/20; for example, vision that measures 20/15, so what they would be able to see at 20 feet, a person with normal vision would only be able to discriminate as close as 15 feet.
Both eyes are examined one after the other. When your optometrist instructs you to read the letters on the eye chart, the smallest row that you are able to read without error indicates the visual acuity of the eye being evaluated.
However 20/20 vision actually doesn't mean that your eyesight is flawless, because, after all, it can only judge how well you see at a distance. There are lots of equally vital vision skills; your ability to focus on close objects, contrast sensitivity, peripheral awareness, depth perception, eye coordination and color vision - these are all extremely important to your general eyesight. And actually, a person with 20/20 vision can have unhealthy eyes. People with damage to the retina from glaucoma, diabetes, high blood pressure, or a range of other conditions can still have 20/20 vision, without the help of glasses. For this reason, your eye care professional should always conduct a comprehensive eye exam, rather than just a plain eye chart examination.
When you're having your next eye exam, you'll understand why we're asking you to read letters from the eye chart, and more!