Acuteness of vision or perception; keenness.(noun)
American Heritage(R) Dictionary of the English Language, Fifth Edition. Copyright (c) 2011 by Houghton Mifflin Harcourt Publishing Company. Published by Houghton Mifflin Harcourt Publishing Company. All rights reserved.
Use "acuity" in a sentence
"AGENT ORANGE, annoyed: Your visual acuity is uncanny."
"Terry Pratchett, who has early-onset Alzheimer's (and whose mental acuity is still fine) has written a stirring editorial on the need to legalize suicide in the UK."
"She just turned 90, and her mental acuity is better than most people half her age."