Twenty-twenty and Visual acuity

Twenty-twenty noun - Normal visual acuity, as measured by the ability to read charts at a distance of 20 feet.

Visual acuity and twenty-twenty are semantically related. In some cases you can use "Visual acuity" instead a noun phrase "Twenty-twenty".

Visual acuity noun - Sharpness of vision; the visual ability to resolve fine detail (usually measured by a Snellen chart).

Twenty-twenty and visual acuity are semantically related. Sometimes you can replace phrase "Twenty-twenty" with "Visual acuity", this phrases are similar.