di·​op·​ter dī-ˈäp-tər How to pronounce diopter (audio)
: 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 Current Clinical Trials and Outcomes Clinical trials have started on the effectiveness of spiral diopter lenses for correcting presbyopia. William A. Haseltine, Forbes, 26 Feb. 2024 Most of the visual effects, in terms of the clairvoyance, were done in camera with me and a diopter, making a lot of noise and smashing glass against glass and a flashlight. Simon Thompson, Forbes, 13 Feb. 2024 While keeping the left side covered, rotate the diopter dial on the right eyecup until the image is in focus. Katherine Alex Beaven, Travel + Leisure, 17 Jan. 2024 Ophthalmologists measure this distortion in diopters, which refer to the strength of the lens required to bring someone’s vision back to normal. Amit Katwala, WIRED, 22 Aug. 2023 Take note of different arm heights, the number of nose bridges included, and whether or not there is built-in diopter tuning for nearsightedness. Hunter Fenollol, Popular Mechanics, 20 June 2023 The non-locking diopter is a tad too loose, and the finish is a little slick—both minor quibbles. Dave Hurteau, Field & Stream, 10 May 2023 With the exception of a slightly loose, non-locking diopter dial, everything feels smooth and positive and well-finished. Dave Hurteau, Field & Stream, 10 May 2023 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

These examples are programmatically compiled from various online sources to illustrate current usage of the word 'diopter.' Any opinions expressed in the examples do not represent those of Merriam-Webster or its editors. Send us feedback about these examples.

Word History


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

First Known Use

circa 1864, in the meaning defined above

Time Traveler
The first known use of diopter was circa 1864

Dictionary Entries Near diopter

Cite this Entry

“Diopter.” Merriam-Webster.com Dictionary, Merriam-Webster, https://www.merriam-webster.com/dictionary/diopter. Accessed 22 May. 2024.

Medical Definition


variants or chiefly British dioptre
: a unit of measurement of the refractive power of a lens equal to the reciprocal of the focal length in meters

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