What does the numerator stand for in the 20/20 notation?

In the 20/20 notation used to express visual acuity, the numerator indicates the distance from the patient's eyes to the chart, which is typically standardized at 20 feet in the United States. This means that when an individual has 20/20 vision, they can see at 20 feet what a person with normal vision can also see at that same distance. This standardized measurement allows for a consistent understanding of visual capability across different individuals and settings.

The other options do not accurately describe the role of the numerator in this notation. The concept of "further distance" or "closest distance" does not apply to the numerator of the 20/20 ratio, as it strictly refers to the testing distance.