Plain English Meaning

An eye condition where the front of the eye isn't shaped quite right, so things look blurry or stretched. It often gets worse in dim light, which matters at night.

Full Definition

A vision defect in which the cornea or lens of the eye is not perfectly curved, causing light entering the eye to focus unevenly on the retina. The result is blurred or distorted vision at certain distances or in certain directions, which can be more pronounced in low light such as night flying.

Context Anchor

Seen in night vision discussions because it can make lights, runway markings, and distant objects harder to see clearly during night flying.

Derivation

From Greek 'a-' (without) and 'stigma' (a point or spot). Literally 'without a point' — meaning light rays don't converge to a single sharp focus point on the retina.