20/20 vision means that a person can read a certain row of letters on a standard eye chart from 20 feet away. In the United States, 20/20 is widely regarded as “normal” eyesight.
What is the 20/20 line?
So-called “normal” vision is measured by whether or not you can read the 20/20 line. If you can, it means that you can accurately read the same line of block letters from a distance of 20 feet that other people with “normal” vision can read at 20 feet.
What is on the Snellen scale?
Description. The normal Snellen chart is printed with eleven lines of block letters. A person taking the test covers one eye from 6 metres or 20 feet away, and reads aloud the letters of each row, beginning at the top. The smallest row that can be read accurately indicates the visual acuity in that specific eye.
What is 6 7.5 on the Snellen scale?
For the Snellen chart, when assigning vision as the lowest line on which all letters were read correctly, all participants with vision of 6/7.5 or better could read a number-plate at 20 m, and no participant with worse than 6/36 was able to successfully read a number-plate (figure 1).