Visual acuity

Visual acuity (VA) is acuteness or clearness of vision, especially form vision, which is dependent on the sharpness of the retinal focus within the eye, the sensitivity of the nervous elements, and the interpretative faculty of the brain.VA is a quantitative measure of the ability to identify black symbols on a white background at a standardized distance as the size of the symbols is varied. The VA represents the smallest size that can be reliably identified. VA is the most common clinical measurement of visual function. The well-known phrase "20-20 vision" refers to the distance in feet that objects separated by an angle of 1 arc minute can be distinguished as separate objects. The metric equivalent is 6-6 vision.
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Visual acuity n. Sharpness of vision, especially as tested with a Snellen chart. Normal visual acuity based on the Snellen chart is 20/20. [more]Visual acuity - Community and Resources

Noun
1. sharpness of vision; the visual ability to resolve fine detail (usually measured by a Snellen chart)
(synonym) acuity, sharp-sightedness
(hypernym) sight, vision, visual sense, visual modality
(hyponym) oxyopia

level of clarity, distinction, or sharpness.

ACUTEZZA VISIVA