Definition
The sharpness of vision — the eye's ability to resolve fine detail and distinguish small objects clearly at a given distance. Visual acuity depends on the health of the eye, lighting conditions, and the part of the retina being used to view the object.
Plain English
How clearly and sharply you can see detail. Good visual acuity means you can pick out small things clearly; reduced visual acuity means objects look blurry, faint, or harder to make out.
Context Anchor
Used in night vision training when discussing how well a pilot can see detail in daylight, darkness, and low-light cockpit conditions.
Derivation
From the Latin 'acuitas', meaning sharpness or keenness, from 'acus' (needle). Combined with 'visual', it literally means 'sharpness of sight' — a useful reminder that acuity is about precision of vision, not just whether you can see.
Why Pilots Care
Good visual acuity lets pilots identify runway lights, markings, obstacles, and other traffic, especially at night when overall vision is already reduced.
Grounding Statement
At night, you may notice that something is there before you can clearly see its shape or detail.
Intuition Check
Visual acuity does not mean overall eyesight in every sense. Here it means the sharpness of detail you can see, not just whether you can detect light or motion.
Example Sentence 1
The pilot's visual acuity decreased noticeably after sunset, making it harder to read sectional chart details in the cockpit.
Example Sentence 2
Reduced visual acuity at night made it harder to judge distance to the ground until the aircraft was close.