It's safe to assume that you've stumbled upon the expressions visual acuity and twenty-twenty vision. Yet, what do these terms really mean? When you understand what they imply, you will see why an eye care professional asks to assess more than just how well you read from an eye chart.
The term 20/20 vision indicates the accuracy of sight measured at a distance of 20 feet. If you've been told you have 20/20 eyesight, that basically means that from twenty feet away you're able to properly see what normal-sighted people can see from that distance. So, 20/100 eyesight would indicate that you would need to be as close as 20 feet away to see what a normal-sighted person can see from 100 feet away. Obviously, if this was the situation, you would be extremely near sighted.
Both eyes are tested one after the other. When your optometrist instructs you to read the letters on the eye chart, the smallest letters you can properly see determine the visual acuity of the eye that's being evaluated.
It's important to recognize that 20/20 eyesight doesn't necessarily mean your vision is perfect, and that's because it only indicates how well you see at a distance. Other crucial sight skills; your ability to focus on close objects, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision - these are all really important to your overall eyesight. Furthermore, a person with 20/20 vision may have eye problems. Even people who have damage to the nerves within their eyes as a result of glaucoma, diabetes, high blood pressure, or numerous other conditions are still able to have 20/20 vision. And because of this, your eye care professional should always conduct a comprehensive eye exam, as opposed to just a simple eye chart examination.
During your next eye exam, you'll understand what we're testing for when we ask you to read aloud from an eye chart!