Final answer:
The most common test for measuring visual acuity is the Snellen chart, which displays standard Roman letters in various sizes and is read from a distance of 20 feet.
Step-by-step explanation:
The most common test for measuring visual acuity is the Snellen chart. This chart displays standard Roman letters in various sizes, and the person being tested is asked to read the letters from a distance of 20 feet. The Snellen chart provides a rough estimate of a person's visual acuity based on the smallest letters they can see at that distance. For example, if a person has 20/60 vision, it means that they can see the same letters that a person with normal vision can see from 60 feet away.