Diopter
/ˈdaɪ.ɒp.tər/noun
A unit of optical power equal to the reciprocal of focal length in meters, used for lenses and vision correction.
Did you know?Diopter ultimately comes from Greek optical terminology built on the verb *diopteuein*, meaning to see through or inspect, so the word’s history is tied to the ancient science of piercing appearances.
Etymological Timeline
Ancient Greek
Greek
διόπτρα (dioptra)
“An instrument for sighting or looking through; a surveying and astronomical device.”
Late Greek
Greek
διόπτης (dioptēs)
“One who sees through or examines carefully.”
Medieval Latin
Latin
dioptra
“A sighting instrument used in surveying and astronomy.”
17th Century
English
diopter
“A lens or optical instrument, especially in scientific contexts.”
19th Century
English
diopter
“A unit of optical power for lenses and corrective optics.”