Definition
A visual disturbance in which a single object is perceived as two overlapping or side-by-side images, caused by the eyes failing to align properly on the same point. In aviation, diplopia can result from hypoxia, decompression sickness affecting the central nervous system, fatigue, or certain medications.
Plain English
Double vision. You look at one thing and see two of it because your eyes aren't pointing at exactly the same spot.
Context Anchor
Seen in lists of possible altitude-induced decompression sickness symptoms after flight at high altitude or after a rapid pressure change.
Derivation
From the Greek 'diplous' meaning 'double' and 'ops' meaning 'eye.' Literally 'double-eye' — a useful anchor because the symptom is exactly that: seeing double.
Why Pilots Care
It degrades depth perception and visual clarity, creating an immediate safety risk during flight.
Intuition Check
Diplopia does not mean ordinary blurry vision. Blurry vision makes one image unclear; diplopia means one object appears as two images.
Example Sentence 1
After climbing above 18,000 feet without supplemental oxygen, the pilot reported diplopia and immediately began a descent.
Example Sentence 2
Diplopia appeared as one of several symptoms after the unpressurized flight above 18,000 feet.