It's likely that you have run into the terms visual acuity and twenty-twenty vision. As common as these terms may be, do you actually know their meaning? Understanding them will help you appreciate how an eye specialist evaluates your eyes when you have an eye exam.
20/20 actually refers to the accuracy of eyesight from 20 feet away. If you've been told you have 20/20 vision, it means that from 20 feet away you can see that which normal-sighted people can see from that distance. Did you know that 20/20 isn't the best possible visual acuity? The truth is, a considerable number of people have eyesight better than 20/20; for example, vision that measures 20/15, so what they could see at 20 feet, a person with normal vision might only be able to discriminate from 15 feet.
Your eyes are examined separately. When you're asked to look at the eye chart and read out the letters, the smallest row that you can read accurately determines the visual acuity of the eye that's being examined.
But 20/20 vision doesn't necessarily mean that your eyesight is totally free of flaws, because it only indicates how well you see at a distance. There are several other vital vision skills; being able to focus on close objects, contrast sensitivity, peripheral awareness, depth perception, eye coordination and color vision - these are all extremely important to your overall eyesight. And actually, a patient with 20/20 vision can certainly still have unhealthy eyes. Even people who have damage to the nerves within their eyes from diabetes, high blood pressure, glaucoma, or numerous other diseases can still have 20/20 vision without glasses. And because of this, your optometrist should always perform a comprehensive eye exam, and not just a regular eye chart test.
During your next eye exam, you'll know what we're looking for when we ask you to read letters from an eye chart!