The vision test is one of the simplest yet most important components of the eye exam.
In order for eye results to be compared, it's always performed at a standard distance of twenty feet. The charts are standard and doctors around the world use the same basic format.
Each line of the eye chart is assigned a notation in the form of a fraction that represents your visual acuity. The numerator is the distance in feet the patient is from the eye chart. The denominator represents the distance an eye with "normal" vision can read the same line. Interpreting the numbers is simple. If you can read the 20/40 line, you're able to see at 20 feet what a normal eye could see at 40. And if your vision is 20/15, you're above average because you can see and object from 20 feet that a normal eye sees at 16.