Answer :
Final answer:
The NH vision test measures an individual's visual acuity using a Snellen chart. A person with 20/60 vision can see at 20 feet what someone with normal vision can see at 60 feet. The 20/XX notation is used, where the second number varies based on the smallest line of letters readable at 20 feet.
Explanation:
The subject of the question relates to the standards for visual acuity testing, specifically within the context of the NH vision test. The NH vision test requires that an individual must be able to obtain a reading where the denominator (the second number in the 20/something notation) could be one of several different values based on the size of the letters they are able to discern at 20 feet, using the Snellen chart. This chart presents the standard Roman letters of varying sizes, where the line with letters that subtend 5 minutes of an arc at 20 feet represents the standard of normal acuity (20/20).
To have 20/60 vision, for example, would mean that the smallest line of letters that a person can read from 20 feet away could be read by a person with normal (20/20) vision from 60 feet away. The Snellen chart also includes lines representing other levels of visual acuity wherein the numerators generally remain 20 (indicative of the test distance in feet), while the denominators increase, representing the greater distance at which an individual with normal acuity could read the same line.
