We've all heard the terms visual acuity and twenty-twenty vision. As common as these terms are, do people really grasp their meaning? When you really understand what they imply, you will see why an eye doctor asks to assess more than just how well you read from an eye chart.
The term 20/20 indicates the sharpness of sight from 20 feet away. When you have 20/20 vision, that means that from a distance of 20 feet you can see what should be seen from that distance. Did you know that 20/20 is just a standard measurement? A large number of people have eyesight better than 20/20; for example, some people have 20/15 vision, so what they would be able to see at 20 feet, a person with normal vision would only be able to discriminate at 15 feet.
Both eyes are examined one after the other. During the part when you're asked to look at the eye chart and read out the letters, the smallest letters you can properly read determine the visual acuity in the eye that's being evaluated.
It's important to recognize that 20/20 sight doesn't necessarily mean your vision is perfect, and that's because it only assesses how well you see at a distance. There are lots of equally necessary vision skills; your ability to focus on objects in your immediate surroundings, 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 may have unhealthy eyes. Even those who have suffered damage to the sensory nerves inside their eyes as a result of glaucoma, diabetes, high blood pressure, or other conditions are still able to have 20/20 vision, without the help of glasses. For this reason, your optometrist always conducts a comprehensive eye exam, rather than just a regular visual acuity examination.
During your next eye exam, you'll understand what we're looking for when we ask you to read aloud from an eye chart!