Everyone has come across the expressions visual acuity and twenty-twenty vision. But what do these terms really mean?
20/20 refers to the accuracy of your eyesight from 20 feet away. If you've been told you have 20/20 vision, that basically means that from 20 feet away you are able to properly see that which is normally seen from that distance. To give an extreme example, 20/100 vision indicates that to see what most people can see from 100 feet, you would have to stand only 20 feet away.
Both eyes are examined one after the other. When the optometrist asks you to correctly read letters from the eye chart, the smallest letters you can properly read determine the visual acuity of the eye that's being tested.
20/20 eyesight actually doesn't mean your vision is perfect, because, after all, it only indicates how well you see at a distance. There are other really crucial sight skills; being able to focus on objects that are close by, contrast sensitivity, peripheral vision, eye coordination, depth perception and color vision – these all contribute to your overall vision. Also, a person who has 20/20 vision may have unhealthy eyes. People with damage to the nerves inside their eyes from glaucoma, diabetes, high blood pressure, or numerous other conditions can still have 20/20 vision, without the help of glasses. For this reason, your optometrist will always carry out a comprehensive eye exam, as opposed to just a regular eye chart examination.
When you're having your next eye exam, you'll know exactly why you need to read letters off an eye chart, and more!