Final answer:
The correct distance for a patient undergoing a test with a Snellen chart is 20 feet away from the chart. This standard measure ensures that the visual acuity can be accurately assessed.
Step-by-step explanation:
When performing visual acuity testing using a Snellen chart, the correct statement is that the patient stands 20 feet away from the chart. This standardized distance is part of the definition of the Snellen chart and corresponds to the standard measurement in visual acuity testing where the smallest letters that a person with normal vision should be able to read at that distance subtend a visual angle of 5 minutes of an arc. Larger letters are used for lines representing lower visual acuities, like 20/200 vision, which means a person with normal vision can read these letters from 200 feet away.