Everyone has run into the terms visual acuity and twenty-twenty vision. Still though, do people understand what these terms actually mean?
20/20 indicates the sharpness of vision measured at a distance of 20 feet. When you have 20/20 eyesight, that basically means that from twenty feet away you're able to accurately see what is normally seen from that distance. To give an extreme example, 20/100 vision would indicate that to see what most people can see from 100 feet, you would have be as close as 20 feet away. Obviously, in this scenario, it would mean that you would be extremely near sighted.
Each eye is evaluated separately. When the optometrist instructs you to read the letters on the eye chart aloud, the smallest row that you are able to read properly indicates the visual acuity in the eye that's being examined.
However 20/20 vision actually doesn't mean your vision is perfect, because it can only judge your distance vision. Other necessary sight skills; the ability to focus on objects that are close by, contrast sensitivity, peripheral awareness, eye coordination, depth perception and color vision – these are aspects of healthy vision. And actually, a person with 20/20 vision can have unhealthy eyes. Even people who have damage to the retina as a result of glaucoma, diabetes, high blood pressure, or other diseases might still have 20/20 vision without glasses. For this reason, an eye care professional will always carry out a comprehensive eye exam, as opposed to just a simple eye chart examination.
The next time you have a comprehensive eye exam, you'll understand what we're looking for when we ask you to read aloud from an eye chart!