di·​op·​ter | \ dī-ˈäp-tər How to pronounce diopter (audio) , ˈdī-ˌäp- \

Definition of diopter

: a unit of measurement of the refractive power of lenses equal to the reciprocal of the focal length in meters

Examples of diopter in a Sentence

Recent Examples on the Web Monoyer invented the diopter, a unit of measurement that determines the distance someone must be from a text to read it. Brett Molina, USA TODAY, 9 May 2017 Perhaps the glasses’ increasing diopters told a narrative. The Washington Post, The Mercury News, 13 Mar. 2017

These example sentences are selected automatically from various online news sources to reflect current usage of the word 'diopter.' Views expressed in the examples do not represent the opinion of Merriam-Webster or its editors. Send us feedback.

First Known Use of diopter

circa 1864, in the meaning defined above

History and Etymology for diopter

diopter (an optical instrument), from Middle French dioptre, from Latin dioptra, from Greek, from dia- + opsesthai to be going to see — more at optic

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Time Traveler for diopter

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The first known use of diopter was circa 1864

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Cite this Entry

“Diopter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diopter. Accessed 30 Jun. 2022.

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More Definitions for diopter


variants: or chiefly British dioptre \ dī-​ˈäp-​tər, ˈdī-​ˌäp-​ How to pronounce diopter (audio) \

Medical Definition of diopter

: a unit of measurement of the refractive power of a lens equal to the reciprocal of the focal length in meters

More from Merriam-Webster on diopter

Britannica.com: Encyclopedia article about diopter


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