We've all come across the expressions twenty-twenty vision and visual acuity. Still though, what do these terms truly mean? When you understand these terms, you will know why an eye care professional needs to assess more than just how well you read an eye chart.
20/20 indicates the clarity of eyesight from 20 feet away. If you have 20/20 eyesight, that means that from a distance of twenty feet you can clearly see that which normal-sighted people can see from that distance. You may not know this, but 20/20 vision isn't the best possible visual acuity. Actually, a lot of people can even see better than 20/20; for example, some people have 20/15 vision, so what they could see at 20 feet, a person with normal vision might only be able to discriminate from 15 feet.
Each one of your eyes is tested separately. During the part when you're asked to read the letters on the eye chart aloud, the smallest row that you can read clearly determines the visual acuity of the eye being evaluated.
It's important to recognize that 20/20 eyesight actually doesn't mean your vision is perfect, because, after all, it only determines your distance vision. Other vital sight skills; your ability to focus on close objects, contrast sensitivity, peripheral vision, eye coordination, depth perception and color vision - these are aspects of healthy vision. Also, a patient who has 20/20 vision can have plenty of other eye-related health problems. Even those who have suffered damage to the retina due to diabetes, high blood pressure, glaucoma, or numerous other diseases might still have 20/20 vision. And because of this, an eye care professional should always conduct a comprehensive eye exam, as opposed to just a regular eye chart test.
The next time you find yourself having an eye test at the optometrist, you'll know exactly why we're asking you to read letters from the eye chart, and more!