Final answer:
The nurse typically places the client 20 feet away from the Snellen chart when testing for visual acuity, as this is the standard testing distance to evaluate the smallest letters that a person with normal vision should be able to see, which subtend 5 minutes of an arc.
Step-by-step explanation:
When testing for visual acuity, a nurse typically positions the client at a distance where the smallest letters that a person with normal acuity should be able to read are designed to be seen. This distance is most commonly 20 feet, which corresponds to the top number in the visual acuity measurement (e.g., 20/20, 20/40, etc.). The Snellen chart is used during this test, presenting rows of standard Roman letters that decrease in size. The letters on this chart correspond to specific visual angles; for instance, the line of letters that a person with normal vision should be able to read at 20 feet subtends 5 minutes of an arc. When using the Snellen chart, the person being tested is asked to read the smallest line of letters they can see from a 20-foot distance. An example provided is that of a 20/60 vision, meaning that what an individual can see clearly at 20 feet, a person with normal vision can see at 60 feet, indicating impaired acuity.