Meaning of “dioptre” in the English Dictionary

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"dioptre" in English

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dioptrenoun [ C ]

UK specialized US diopter /daɪˈɒp.tər/ /-ˈɑːp.tɚ/

a unit of measurement of the power of a lens, used for measuring a person's eyesight:

A typical short-sighted person in Britain is -4.5 dioptres.

(Definition of “dioptre” from the Cambridge Advanced Learner’s Dictionary & Thesaurus © Cambridge University Press)