Everyone has run into the terms visual acuity and twenty-twenty vision. As frequently used as these terms are, do people actually know what they mean?
20/20 vision actually refers to the clarity and sharpness of eyesight measured at a distance of 20 feet. If you have 20/20 eyesight, it means that from a distance of 20 feet you can see that which should be seen from that distance. So, 20/100 vision would indicate that to see what most people can see from 100 feet, you would have to stand only 20 feet away. Obviously, if this was the situation, you would be extremely near sighted.
Your eyes are tested separately. When you're asked to read the letters on the eye chart aloud, the smallest row that you are able to read without error indicates the visual acuity of the eye that's being tested.
It's important to recognize that 20/20 eyesight doesn't always mean that your eyesight is perfect, because it can only judge your clarity of vision at a distance. There are several other necessary components to seeing clearly; the ability to focus on close objects, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision – these are aspects of good vision. And actually, someone with 20/20 vision can have eye problems. Even those who have suffered damage to the retina due to diabetes, high blood pressure, glaucoma, or numerous other diseases can still have 20/20 vision without glasses. For this reason, an eye care professional always conducts a comprehensive eye exam, rather than just a simple eye chart examination.
The next time you find yourself at an eye exam, you'll know exactly why you're being told to read letters from the eye chart, and more!