Plain English Meaning
When the eye is exposed to bright light, the pupil shrinks to a smaller size to let in less light.
Full Definition
The narrowing of the pupil of the eye in response to bright light, reducing the amount of light entering the retina.
Context Anchor
Seen in night vision discussions when learning how the eye reacts to cockpit lighting, flashlights, landing lights, or other bright lights at night.
Derivation
From the Latin 'constringere,' meaning 'to draw tight' or 'to bind together.' In the eye, it describes the iris drawing the pupil tight into a smaller opening.
Why Pilots Care
Knowing how constriction works helps pilots avoid bright lights that reset night vision and delay dark adaptation.