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.
Plain English
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.
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.
Why Pilots Care
Uncorrected astigmatism reduces sharpness and contrast, making it harder to identify runway lights, terrain, or other aircraft at night when light levels are already low.
Grounding Statement
At night, astigmatism can make a single light look like a blur, streak, or small smear instead of a clean point.
Intuition Check
Astigmatism is not simply “poor night vision.” It is a focusing problem in the eye that can make night vision worse because small lights and dark surroundings demand sharper focusing.
Example Sentence 1
The pilot's astigmatism made the runway edge lights appear to streak slightly during the night approach.
Example Sentence 2
Wearing corrective lenses resolved the blur that astigmatism introduced when scanning for traffic at dusk.