What does it mean when a persons visual acuity is 20/20?
In the common notation that looks like a fraction (for example, 20/20 or 20/200), the denominator or lower number refers to the furthest distance at which a person with normal vision could see a specific visual target. The top number or numerator is the furthest distance at which the person whose visual acuity is being tested can see that same target. So, a person with 20/20 vision can see the detail of a target at a distance of 20 feet (numerator), which is the same distance that a person with normal visual acuity could see that target (denominator). A visual acuity of 20/200 implies that the person cannot see the detail of a target beyond a distance of 20 feet, while a person with normal vision could make out the detail of that same target at a distance of 200 feet.
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