You've probably heard the expressions twenty-twenty vision and visual acuity. Yet, do people understand what these terms really mean? When you understand what they imply, you will get why your optometrist asks you to do more than simply read an eye chart.
The term 20/20 vision refers to the sharpness of your eyesight from 20 feet away. If you've been told you have 20/20 vision, it means that from 20 feet away you can see that which is normally seen from that distance. To give an extreme example, 20/100 eyesight indicates that to see what most people can see from 100 feet, you would have be as close as 20 feet away. Obviously, if this was the situation, you would be pretty near sighted.
Your eyes are tested separately. When your optometrist asks you to correctly read letters from the eye chart, the smallest row that you can read accurately indicates the visual acuity of the eye that's being examined.
It's important to recognize that 20/20 vision actually doesn't mean you have perfect vision, and that's because it can only judge your clarity of vision at a distance. Other crucial sight skills; being able to focus on objects in your immediate surroundings, contrast sensitivity, peripheral awareness, depth perception, eye coordination and color vision - these are all very important to your general vision. And actually, a patient who has 20/20 vision can have plenty of other eye-related health problems. Even people who have damage to the nerves inside their eyes from glaucoma, diabetes, high blood pressure, or other conditions can still have 20/20 vision without needing to wear eye glasses. And because of this, your eye care professional always performs a comprehensive eye exam, and not just a simple visual acuity exam.
So the next time you book yourself in for a comprehensive eye exam, you'll understand what we're looking for when we ask you to read from an eye chart!