You have most likely stumbled upon the terms visual acuity and 20/20 vision. As frequently used as these terms may be, do you actually know their meaning? Understanding these terms will enlighten you as to how an optometrist assesses your vision in an eye exam.
The term 20/20 vision indicates the accuracy of sight from 20 feet away. When you have 20/20 vision, that basically means that from twenty feet away you're able to accurately see what normal-sighted people can see from that distance. Alternatively, 20/100 vision would indicate that you'd need to be as near as 20 feet away to see what a normal-sighted person is able to see from 100 feet away. Obviously, in this scenario, it would mean that you would be very near sighted.
Both eyes are tested one after another. During the part when you're asked to read the letters on the eye chart, the smallest letters you can properly see determine the visual acuity of the eye being evaluated.
It's important to recognize that 20/20 vision doesn't necessarily mean your vision is perfect, because, after all, it can only judge how clearly you see at a distance. There are lots of equally necessary components to seeing well; being able to focus on close objects, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision - these are aspects of good vision. More importantly, a patient with 20/20 vision can have eye problems. Even those who have suffered damage to the retina as a result of glaucoma, diabetes, high blood pressure, or a range of other conditions might still have 20/20 vision. This is why your eye care professional will always carry out a comprehensive eye exam, rather than just a simple eye chart test.
The next time you find yourself at an eye exam, you'll understand what we're looking for when we ask you to read letters aloud from an eye chart!