It's safe to say that everyone has run into the terms twenty-twenty vision and visual acuity. As frequently used as these terms are, do you really grasp what they mean?
20/20 vision is used to indicate the clarity and sharpness of vision from 20 feet away. When you have 20/20 eyesight, that means that from a distance of 20 feet you are able to properly see what is normally seen from that distance. Alternatively, 20/100 vision would indicate that you would need to be as close as 20 feet away to see what a person with normal vision can see from 100 feet away. Obviously, if this was the situation, it would mean that you would be very near sighted.
Each one of your eyes is examined separately. When the optometrist asks you to correctly read letters from the eye chart, the smallest row that you can read without error indicates the visual acuity in the eye being evaluated.
20/20 eyesight doesn't necessarily mean your vision is perfect, because it can only judge your distance vision. There are other really important components to seeing clearly; the ability to focus on objects in your immediate surroundings, contrast sensitivity, peripheral awareness, eye coordination, depth perception and color vision - these all contribute to your overall ability to see. And actually, a patient with 20/20 vision can certainly have unhealthy eyes. People with damage to the sensory nerves within their eyes as a result of glaucoma, diabetes, high blood pressure, or numerous other conditions might still have 20/20 vision without needing to wear eye glasses. And because of this, your eye care professional will always carry out a comprehensive eye exam, rather than just a regular visual acuity exam.
So the next time you book yourself in for a comprehensive eye exam, you'll know what we're testing for when we ask you to read letters from an eye chart!