Final answer:
The Snellen chart is used to test visual acuity(option d) by having the person read letters of decreasing size from 20 feet away, determining the smallest line of letters they can read, and translating that into a measure like 20/20 or 20/40 vision.
Step-by-step explanation:
Function of a Snellen Chart
The Snellen chart is used to test the sharpness of vision, which is known as visual acuity. This chart presents a standardized arrangement of letters in decreasing size, with the goal being to determine the smallest line of letters that a person can read from a distance of 20 feet. The famous 20/20 vision implies that the smallest letters a person can see at 20 feet are the same size as those a normal person would be able to see at 20 feet. Other lines on the chart represent the equivalent visual acuity at greater distances, such as 20/40 or 20/60, indicating a decrease in visual acuity. The Snellen chart does not assess visual fields, measure the cornea, or examine the various layers of the eye; these are different visual tests.
Visual fields
are generally tested by an examiner who establishes the boundaries of peripheral vision. Checking the cornea or examining the various layers of the eye requires other ophthalmic instruments and procedures.