What does the numerator represent in the 20/20 visual acuity notation?

In the 20/20 visual acuity notation, the numerator indicates the distance from the patient's eyes to the chart. Typically, visual acuity is measured at a distance of 20 feet in the United States, which is why the numerator is set at 20. This means that a person with 20/20 vision can see at 20 feet what a person with normal vision can see at that same distance.

This understanding is crucial in assessing a person's visual capability compared to a standard or normative value. For instance, if someone has a visual acuity of 20/40, it means they must be at 20 feet to see what a person with normal vision can see at 40 feet, indicating lower visual acuity.