A person with 20/15 vision can see an object from 20 feet away with the same acuity as a normal person would at 15 feet away. Technically, then, a person with 20/15 vision has better than perfect vision.
In the vision formula, the eyesight of the individual in question comes first. For example, someone who had 20/100 vision could see an object from 20 feet away with the same clarity as a normal person would at 100 feet away. Legally blind individuals have 20/200 vision. This formula is useful in helping eye doctors to diagnose the vision of an individual.