You've probably stumbled upon the terms 20/20 vision and visual acuity. Still though, what do these terms actually mean? Having a proper understanding of what they imply will give you insight into how your optometrist evaluates your vision during an eye exam.
20/20 is used to indicate the clarity of vision from 20 feet away. When you have 20/20 eyesight, that basically means that from a distance of twenty feet you can see what normal-sighted people can see from that distance. And did you know that 20/20 is really just a standard measurement? A large number of people can even see better than 20/20; for example, vision that measures 20/15, so what they would be able to see at 20 feet, a person with normal vision would only be able to discriminate as close as 15 feet.
Your eyes are examined separately. During the part when you're asked to correctly read letters from the eye chart, the smallest letters you can properly read determine the visual acuity of the eye that's being evaluated.
It's important to recognize that 20/20 vision doesn't necessarily mean your vision is perfect, because it only assesses your clarity of vision at a distance. There are other really crucial vision skills; your 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 with 20/20 vision may have unhealthy eyes. People with damage to the nerves within their eyes from diabetes, high blood pressure, glaucoma, or numerous other conditions can still have 20/20 vision without glasses. And because of this, your optometrist should always perform a comprehensive eye exam, rather than just a plain visual acuity exam.
The next time you find yourself having an eye test at the optometrist, you'll know what we're testing for when we ask you to read aloud from an eye chart!