Final answer:
Normal visual acuity of 20/20 indicates that at 20 feet, a person can see what someone with normal vision is expected to see. The numerator denotes test distance (20 feet), and the denominator signifies the distance a person with normal vision can read the same line of letters.
Step-by-step explanation:
When we say that normal visual acuity is 20/20, we are referring to a standard of vision measured using a Snellen chart. Visual acuity is represented by two numbers. The numerator (the first number) refers to the distance in feet at which the test is conducted - usually 20 feet. The denominator (the second number) indicates the distance at which a person with normal vision could see the same line of letters that the person being tested can see at 20 feet. Therefore, having a 20/20 vision means you can see at 20 feet what a person with normal vision should see at that distance. If someone has 20/60 vision, the smallest letters they can see at 20 feet can be seen by a person with normal acuity at 60 feet away.