20/20 vision is used to indicate the clarity and sharpness of your vision measured at a distance of 20 feet. If you have 20/20 vision, you can see clearly at 20 feet what is normally seen at that distance. If you have 20/100 vision, it means that you need to be as close as 20 feet to see what a person with normal vision can see at 100 feet. Did you know that 20/20 is just a standard? Many people can actually see better than 20/20, for example 20/15.
Each eye is tested separately. When you're asked to read the letters on the eye chart during your eye exam, the smallest row that you are able to read accurately indicates your visual acuity in the eye that is being tested.
20/20 vision doesn't necessarily mean your vision is perfect as it only indicates the sharpness or clarity of vision at a distance. Other important vision skills, such as the ability to bring close objects into focus, contrast sensitivity, peripheral awareness (side vision), depth perception, focusing ability, eye coordination and color vision contribute to your overall ability to see. Also a person that has 20/20 vision may still have unhealthy eyes. People that have damage to the sensory nerves within your eyes (the retina) from glaucoma, diabetes, high blood pressure, or other diseases can still obtain 20/20 vision without glasses. This is why your optometrist always performs a comprehensive eye exam, rather than just a simple vision test.
So the next time you have a comprehensive eye exam, you'll be able to understand why we ask you to read the letters on the chart in front of you and more!