Everyone has stumbled upon the terms visual acuity and 20/20 vision. But what do these terms actually mean?
20/20 is used to indicate the accuracy of sight from 20 feet away. If you've been told you have 20/20 vision, that means that from twenty feet away you can see what should be seen from that distance. And did you know that 20/20 is really just a standard measurement? Many people have eyesight better than 20/20; for instance, some people have 20/15 vision, so what they could see at 20 feet, a person with normal vision might only be able to discriminate at 15 feet.
Each of your eyes is tested separately. When the optometrist asks you to read the letters on the eye chart aloud, the smallest letters you can properly see determine the visual acuity in the eye that's being examined.
It's important to recognize that 20/20 vision doesn't always mean that your eyesight is flawless, because, after all, it only assesses your distance vision. There are other really vital vision skills; the ability to focus on close objects, contrast sensitivity, peripheral awareness, depth perception, eye coordination and color vision – these are all very important to your general vision. And actually, someone with 20/20 vision may have plenty of other eye-related health problems. Even people who have damage to the retina as a result of diabetes, high blood pressure, glaucoma, or a range of other conditions might 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.
The next time you find yourself at an eye exam, you'll know exactly why you're being told to read letters from the eye chart, and more!