Everyone has come across the terms visual acuity and 20/20 vision. As frequently used as these terms are, do most people actually know what they mean? Having a proper understanding of what they imply will enlighten you as to how your eye specialist assesses your vision when you have an eye exam.
The term 20/20 is used to indicate the clarity of vision from 20 feet away. When you have 20/20 vision, it means that from twenty feet away you're able to clearly see what should be seen from that distance. Alternatively, 20/100 eyesight would indicate that to see what most people can see from 100 feet, you would have be as close as 20 feet away. Obviously, if this was the case, it would mean that you would be pretty near sighted.
Your eyes are examined separately. When your optometrist asks you to read the letters on the eye chart aloud, the smallest row that you are able to read without error indicates the visual acuity in the eye that's being evaluated.
But 20/20 vision doesn't always mean that your eyesight is perfect, and that's because it only determines how well you see at a distance. There are lots of equally necessary sight skills; the ability to focus on close objects, contrast sensitivity, peripheral awareness, eye coordination, depth perception and color vision – these are all really important to your general eyesight. Furthermore, a person with 20/20 vision may have eye problems. Those with damage to the sensory nerves inside their eyes from glaucoma, diabetes, high blood pressure, or other diseases can still have 20/20 vision without glasses. For this reason, your optometrist always performs a comprehensive eye exam, and not just a simple visual acuity exam.
The next time you find yourself having an eye test at the optometrist, you'll know exactly why we're asking you to read letters off an eye chart, and more!