Plain English Meaning
The clear front window of the eye. Light enters here first, and the curved shape starts the job of focusing what you see.
Full Definition
The cornea is the clear, dome-shaped front surface of the eye that covers the iris and pupil. It is the eye's first optical element, doing most of the bending (refraction) of incoming light before that light passes through the lens to be focused on the retina.
Context Anchor
Seen in night vision discussions when the FAA explains how the eye receives and focuses light.
Derivation
From the Latin cornea, meaning 'horny,' because early anatomists thought the tough, transparent front of the eye resembled thin horn. Knowing this helps remember that the cornea is firm and protective, not soft like the inside of the eye.
Why Pilots Care
The cornea is the first surface light strikes; any irregularity or dryness reduces how much light reaches the retina, directly affecting night vision.