acuity uh-KYOO-uh-tee, noun:
Acuteness of perception or vision; sharpness.


They fail to understand how a person can hold beliefs so contrary to theirs and still retain any mental acuity.
-- Charles Krauthammer, ". . . Why Bush Will Win", Washington Post, November 3, 2000

With unusual acuity, one of the wire service reporters pounced on that possibility with an insinuating question.
-- Alfred Alcorn, Murder in the Museum of Man

Monkeys, diurnal animals that have a high visual acuity -- necessary for finding food and for moving through the trees without bumping into things or missing one's hold on a branch -- have a large visual area of the neocortex.
-- Stephen Budiansky, If a Lion Could Talk

Horses tend to shy a lot because the construction of their eyes is optimized for a near 360-degree field of view, useful for spotting danger, but the price the horse pays for that is relatively poor acuity and some out-of-focus spots that can cause objects within the field of view to suddenly sail into sharp focus.
-- Stephen Budiansky, If a Lion Could Talk

Acuity comes from Latin acutus, "sharpened, pointed, acute," past participle of acuere, "to sharpen."