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Focusing on Visual Acuity


You have most likely run into the expressions 20/20 vision and visual acuity. As frequently used as these terms are, do most people actually know what they mean?

20/20 refers to the sharpness of eyesight measured at a distance of 20 feet. When you have 20/20 eyesight, that means that from 20 feet away you can clearly see what should be seen from that distance. So, 20/100 eyesight 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, you would be very near sighted.

Both eyes are examined one after the other. During the part when you're asked to read the letters on the eye chart, the smallest row that you can read accurately determines the visual acuity of the eye that's being evaluated.

But 20/20 vision actually doesn't mean your vision is perfect, and that's because it only indicates your clarity of vision at a distance. There are several other important vision skills; being able to focus on objects that are close by, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision - these are aspects of healthy vision. Furthermore, a patient with 20/20 vision can have unhealthy eyes. Even those who have suffered damage to the retina as a result of diabetes, high blood pressure, glaucoma, or a range of other diseases can still have 20/20 vision. For this reason, your eye care professional will always carry out a comprehensive eye exam, and not just a simple visual acuity exam.

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