It's likely that you have heard the terms twenty-twenty vision and visual acuity. As frequently used as these terms may be, do most people actually grasp what they mean? Understanding these terms will help you appreciate how your eye care professional determines the state of your eyes during your eye exam.
20/20 vision actually refers to the sharpness of eyesight from 20 feet away. When you have 20/20 eyesight, that means that from 20 feet away you are able to clearly see what should be 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.
Each eye is evaluated separately. When your optometrist asks you to read the letters on the eye chart aloud, the smallest row that you are able to read properly determines the visual acuity in the eye being tested.
20/20 sight doesn't necessarily mean your vision is perfect, because, after all, it can only judge your distance vision. Other important components to seeing properly; being able to focus on close objects, contrast sensitivity, peripheral vision, depth perception, eye coordination and color vision - these are all really important to your overall eyesight. More importantly, a patient who has 20/20 vision can certainly have unhealthy eyes. Even people who have damage to the retina from glaucoma, diabetes, high blood pressure, or numerous other diseases are still able to have 20/20 vision. This is why your optometrist will always carry out a comprehensive eye exam, and not just a plain visual acuity examination.
The next time you find yourself at an eye exam, you'll understand why you need to read letters from the eye chart, and more!