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Understanding Visual Acuity


We've all heard the expressions twenty-twenty vision and visual acuity. As common as these terms may be, do people actually grasp what they mean?

The term 20/20 refers to the clarity and sharpness of sight from 20 feet away. If you've been told you have 20/20 vision, that basically means that from a distance of twenty feet you're able to accurately see what normal-sighted people can see from that distance. Alternatively, 20/100 vision would indicate that to see what most people can see from 100 feet, you would have to stand only 20 feet away. Obviously, if this was the case, it would mean that you would be pretty near sighted.

Both eyes are examined one after the other. When you're asked to read the letters on the eye chart aloud, the smallest row that you are able to read properly indicates the visual acuity in the eye that's being tested.

20/20 vision doesn't necessarily mean that your eyesight is flawless, because, after all, it only assesses how good your eyesight is at a distance. There are other really crucial vision skills; your ability to focus on objects that are close by, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision - these are all extremely important to your general vision. Also, someone with 20/20 vision can have unhealthy eyes. People with damage to the nerves inside their eyes due to diabetes, high blood pressure, glaucoma, or other diseases are still able to have 20/20 vision. This is why an optometrist always performs a comprehensive eye exam, and not just a plain eye chart examination.

When you're having your next eye exam, you'll know what we're looking for when we ask you to read aloud from an eye chart!