"measurement of the range of vision; measurement of the visual powers in general," 1886, from optometer (1738), name given to an instrument for testing vision, from opto- "sight," from Greek optos "seen, visible" (from PIE root *okw- "to see") + -metry "a measuring of." Probably influenced by French optométrie.
When I made the foregoing Experiments, I designed to repeat them with more Care and Exactness, and to make some new ones of the same Sort, by means of an Instrument I had contrived for that Purpose; which from its Use in measuring the Limits of distinct Vision, and in determining with great Exactness the Strength and Weakness of Sight, may be called an Optometer. [Dr. William Porterfield, "An Essay Concerning the Motions of our Eyes, Part II," in Medical Essays and Observations, Vol. IV, Edinburgh, 1738]
word-forming element meaning "one who does or makes," also used to indicate adherence to a certain doctrine or custom, from French -iste and directly from Latin -ista (source also of Spanish, Portuguese, Italian -ista), from Greek agent-noun ending -istes, which is from -is-, ending of the stem of verbs in -izein, + agential suffix -tes.
Variant -ister (as in chorister, barrister) is from Old French -istre, on false analogy of ministre. Variant -ista is from Spanish, popularized in American English 1970s by names of Latin-American revolutionary movements.
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Definitions of optometrist
a person skilled in testing for defects of vision in order to prescribe corrective glasses;