Final answer:
A Snellen chart is used to measure visual acuity, providing a rough generalization of a person’s sight based on the smallest letters they can read at a specific distance.
Step-by-step explanation:
Visual acuity measures a person's sight at specific distances using a Snellen chart. The Snellen chart presents a standardized arrangement of letters in decreasing size, providing a rough generalization of a person's visual acuity. Those with 20/60 vision can see at 20 feet what a person with normal acuity can see at 60 feet. The chart is used to determine the smallest letters a person can read at a certain distance, indicative of their visual acuity. In contrast, an ophthalmoscope is used for physical inspection of the optic disk and not for measuring visual acuity.