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Understanding Visual Acuity


It’s likely that you have come across the expressions visual acuity and twenty-twenty vision. As frequently used as these terms may be, do most people really grasp what they mean? Really understanding them will help you appreciate how your eye care professional evaluates your vision during an eye exam.

The term 20/20 vision is used to indicate the accuracy of your vision from 20 feet away. When you have 20/20 vision, that basically means that from a distance of twenty feet you are able to properly see that which is normally seen from that distance. 20/20 vision is just a standard measurement. A large number of people can even see better than 20/20; for instance, some people have 20/15 vision, so what they could see at 20 feet, a person with normal vision would only be able to discriminate at 15 feet.

Your eyes are examined separately. When the optometrist instructs you to read the letters on the eye chart, the smallest row that you are able to read clearly indicates the visual acuity of the eye that’s being examined.

But 20/20 eyesight doesn’t necessarily mean you have perfect vision, and that’s because it can only judge how good your vision is at a distance. Other crucial vision skills; the ability to focus on objects in your immediate surroundings, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision – these are aspects of healthy vision. More importantly, a patient who has 20/20 vision can certainly have unhealthy eyes. Even those who have suffered damage to the retina as a result of diabetes, high blood pressure, glaucoma, or numerous other conditions might still have 20/20 vision without glasses. And because of this, an optometrist should always conduct a comprehensive eye exam, rather than just a simple eye chart exam.

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