Snellen test [Hermann Snellen] , a test of visual acuity using a Snellen chart. The person being tested stands 20 feet from the chart and reads as many of the symbols as possible, reading each line and proceeding downward from the top. A score is assigned in the form of a ratio, comparing the subject’s performance to that of a statistically normal subject’s performance. For example, a person who can read at 20 feet what the average person can read at this distance has 20/20 vision, whereas a person who can read at 20 feet what the average person can read at 40 feet has 20/40 vision.
