Definition
A transparent, flexible structure inside the eye that sits behind the pupil and focuses incoming light onto the retina by changing its shape.
Plain English
The clear part inside your eye, just behind the coloured ring, that bends light so the picture lands sharply at the back of the eye. It flexes thicker or thinner to focus on things near or far.
Context Anchor
Seen in night vision discussions when the FAA explains how the eye receives and focuses light.
Derivation
From the Latin word for lentil, because a glass lens shaped like a lentil bean was the first kind made. The eye's lens has the same rounded shape, which is why it shares the name.
Why Pilots Care
At night, the lens has to work harder to focus, and its ability to flex decreases with age. Understanding this helps explain why night vision changes over a pilot's career and why focus can feel slower in low light.
Analogy
A camera lens helps bring a picture into focus. The eye’s lens does a similar job, but it is a living part of the eye that can change shape.
Intuition Check
Do not think of “lens” here as eyeglasses or a camera part. In this FAA context, it means the natural focusing part inside the eye.
Example Sentence 1
As pilots age, the lens of the eye becomes less flexible, which can make it harder to shift focus quickly between the instrument panel and the runway.
Example Sentence 2
When the cockpit is dimly lit the lens adjusts its curvature to keep instrument markings sharp without straining vision.