Snellen fraction

The Snellen fraction is a way to measure visual sharpness or clarity, commonly used in eye exams. It compares the distance a person can see clearly to the distance a standard or "normal" eye can see. For example, 20/20 vision means you see at 20 feet what a typical eye can see at that distance. If your result is 20/40, it means you need to be closer, at 20 feet, to see what a normal eye can see from 40 feet away. The first number indicates the testing distance, and the second shows the distance at which a person with normal vision can read the same line.