You've probably heard the terms 20/20 vision and visual acuity. As common as these terms are, do people really grasp their meaning? Understanding these terms will help you appreciate how your eye care professional evaluates your vision during an eye exam.
20/20 vision refers to the sharpness of your eyesight measured at a distance of 20 feet. When you have 20/20 vision, that basically means that from twenty feet away you can see that which is normally seen from that distance. So, 20/100 vision indicates that you'd need to be as close as 20 feet away to see what a normal-sighted person is able to see from 100 feet away.
Each of your eyes is tested separately. When your optometrist asks you to read the letters on the eye chart aloud, the smallest row that you are able to read clearly indicates the visual acuity of the eye that's being evaluated.
But 20/20 eyesight doesn't necessarily mean you have perfect vision, because it only indicates your distance vision. There are several other vital vision skills; being able to focus on objects in your immediate surroundings, contrast sensitivity, peripheral vision, eye coordination, depth perception and color vision – these are all very important to your overall eyesight. Also, a person with 20/20 vision can certainly have unhealthy eyes. Those with damage to the sensory nerves within their eyes due to glaucoma, diabetes, high blood pressure, or numerous other conditions are still able to have 20/20 vision. For this reason, your optometrist should always conduct a comprehensive eye exam, rather than just a simple visual acuity examination.
The next time you find yourself at an eye exam, you'll know what we're testing for when we ask you to read from an eye chart!