Understanding 20/20 Vision and Visual Acuity
It's safe to assume that you've run into the expressions visual acuity and 20/20 vision. But do people know what these terms really mean?
The term 20/20 vision indicates the clarity and sharpness of sight from 20 feet away. If you have 20/20 eyesight, that basically means that from twenty feet away you can see that which is normally seen from that distance. Did you know that 20/20 is just a standard measurement? Many people can even see better than 20/20; for instance, vision that measures 20/15, so what they could see at 20 feet, a person with normal vision might only be able to discriminate at 15 feet.
Both eyes are examined one after the other. During the part when you're asked to read the letters on the eye chart aloud, the smallest letters you can clearly see determine the visual acuity of the eye that's being evaluated.
But 20/20 sight actually doesn't mean that your eyesight is perfect, because it only assesses how accurately you see at a distance. There are several other important components to seeing properly; the ability to focus on objects that are close by, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision - these also contribute to your overall vision. And actually, a patient who has 20/20 vision can have unhealthy eyes. Those with damage to the nerves inside their eyes as a result of diabetes, high blood pressure, glaucoma, or a range of other diseases might still have 20/20 vision without glasses. For this reason, your eye care professional will always carry out a comprehensive eye exam, as opposed to just a plain eye chart examination.
The next time you find yourself having an eye test at the optometrist, you'll understand why you need to read letters off an eye chart, and more!