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.
Plain English
The clear front window of the eye. Light enters here first, and the curved shape starts the job of focusing what you see.
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.
Analogy
Think of the cornea like a clean windshield in front of your eye. If it is clear and smooth, light comes through cleanly; if it is scratched or dry, lights can look smeared or blurry.
Intuition Check
Do not confuse the cornea with the lens. The cornea is the clear outside front surface of the eye; the lens is deeper inside the eye.
Example Sentence 1
Light from the runway lights passes through the cornea before reaching the retina, where the image is actually sensed.
Example Sentence 2
Dry air in the cockpit can cause the cornea to lose moisture, slightly blurring vision until the pilot blinks or uses artificial tears.