Everyone has run into the terms visual acuity and 20/20 vision. As common as these terms may be, do you actually grasp what they mean?
The term 20/20 indicates the clarity and sharpness of your vision from 20 feet away. When you have 20/20 eyesight, it means that from twenty feet away you're able to clearly see that which is normally seen from that distance. Alternatively, 20/100 vision indicates that to see what most people can see from 100 feet, you would have be as close as 20 feet away. Obviously, if this was the situation, it would mean that you would be pretty near sighted.
Each eye is tested on its own. When you're asked to read the letters on the eye chart aloud, the smallest letters you can properly see determine the visual acuity of the eye that's being tested.
20/20 sight doesn't necessarily mean that your eyesight is flawless, because, after all, it only assesses your distance vision. There are several other crucial vision skills; being able to focus on close objects, contrast sensitivity, peripheral awareness, eye coordination, depth perception and color vision - these are all extremely important to your overall vision. More importantly, a person with 20/20 vision can certainly still have unhealthy eyes. Even people who have damage to the retina as a result of diabetes, high blood pressure, glaucoma, or other diseases are still able to have 20/20 vision without needing to wear eye glasses. For this reason, an optometrist will always carry out a comprehensive eye exam, and not just a plain visual acuity examination.
So the next time you book yourself in for a comprehensive eye exam, you'll know exactly why you need to read letters from the eye chart, and more!