eye chart
An eye chart is a standardized test used to measure a person's visual acuity. Consists of a table of characters of decreasing size, usually from the top down. The test taker then identifies the characters until they become too small for them to do so.
Common in Japan is the Landolt C test, where the chart contains circles with small gaps and the subject has to determine on which side the gap lies. Eye charts that use Latin letters, such as the Snellen chart or LogMAR chart", are common in countries that use the Latin alphabet.
Visual acuity is measured by two numbers, where the first number is the distance the subject needs to read something and the second number is the distance a normal person needs. In America, it is standard for the first number to be 20 (feet), with 20/20 being normal vision. In Japan and countries that use the metric system, the standard is 6 (meters), with normal vision being 6/6.