Everyone has come across the expressions 20/20 vision and visual acuity. As common as these terms are, do people actually know what they mean? Really understanding what they imply will give you insight into how your eye specialist evaluates your eyes when you have an eye exam.
20/20 vision refers to the clarity of your eyesight from 20 feet away. If you have 20/20 vision, that means that from 20 feet away you can clearly see what should be seen from that distance. Did you know that 20/20 is just a standard measurement? Many people can even see better than 20/20; for instance, 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.
Each one of your eyes is tested separately. When your optometrist instructs you to read the letters on the eye chart, the smallest row that you are able to read accurately indicates the visual acuity in the eye that's being examined.
20/20 vision actually doesn't mean your vision is perfect, because it only assesses how good your eyesight is at a distance. Other crucial vision skills; the ability to focus on objects that are close by, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision – these are all extremely important to your general eyesight. More importantly, someone with 20/20 vision can certainly have eye problems. Even those who have suffered damage to the sensory nerves inside their eyes due to diabetes, high blood pressure, glaucoma, or a range of other diseases might still have 20/20 vision, without the help of glasses. For this reason, an optometrist should always conduct a comprehensive eye exam, and not just a simple eye chart examination.
During your next eye exam, you'll know exactly why you're asked to read letters off an eye chart, and more!