It's safe to say that everyone has come across the terms visual acuity and 20/20 vision. Yet, do people know what these terms really mean? When you understand them, you will know why an optometrist needs to assess more than just how well you read from an eye chart.
20/20 actually refers to the sharpness of your eyesight from 20 feet away. If you have 20/20 vision, that means that from twenty feet away you're able to accurately see that which normal-sighted people can see from that distance. So, 20/100 vision indicates that you would need to be as near as 20 feet away to see what a person with normal vision would see from 100 feet away.
Each of your eyes is examined separately. When you're asked to read the letters on the eye chart, the smallest letters you can clearly see determine the visual acuity in the eye being examined.
However 20/20 vision doesn't always mean your vision is perfect, and that's because it can only judge your distance vision. There are lots of equally vital vision skills; being able to focus on close objects, contrast sensitivity, peripheral awareness, depth perception, eye coordination and color vision - these are aspects of good vision. Furthermore, a person who has 20/20 vision can still have unhealthy eyes. Even those who have suffered damage to the retina from diabetes, high blood pressure, glaucoma, or a range of other conditions are still able to have 20/20 vision. This is why your eye care professional should always perform a comprehensive eye exam, and not just a simple eye chart examination.
During your next eye exam, you'll understand why you're being told to read letters off an eye chart, and more!