Snellenn.
/ˈsnɛlən/ Ophthalmology.
Used attributively and in the possessive to designate: (a) a scale of similar square-serifed typefaces of different sizes, all subtending the same angle at different rated distances, proposed by Snellen in 1862 (in his Échelle Typographique) and used to print test cards which are presented at known distances to ophthalmic patients who are asked to read out as many lines as they can; (also) the letters, test cards, etc., associated with this scale; (b) a fraction which expresses a patient's visual acuity as the actual reading distance over the rated distance of the smallest Snellen letters read. Snellen's metroscope, an instrument for ophthalmostatometric research.
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the world > health and disease > healing > ophthalmology or optometry > [adjective] > kinds of eye-test
Snellen1864
Jaeger1869
pseudoisochromatic1879
the world > physical sensation > sight and vision > types of vision > [adjective] > normal or correct > Snellen fraction
Snellen1912
1864 T. Longmore Man. Instructions Defective Vision in Soldiers ii. 10 The emmetropic eye can read Snellen's types at any of the indicated distances.
1866 H. W. Williams Rec. Adv. Ophthalm. Sci. 29 Two other series have been added as reading tests... Both of these are almost perfectly accurate in their gradations of sizes,—and correspond, the first with the same numbers of Snellen's scale, the second with those of Jaeger's test.
1912 L. Laurance Visual Optics iv. 73 The visual acuity, as expressed by a Snellen fraction, varies..with the health of the person.
1934 C. S. Price Improvem. Sight by Nat. Methods ii. 21 The large cards or charts bearing a series of sizes in the types are conveniently known as ‘Snellen Charts’.
1960 N. Bier Correction Subnormal Vision i. 4 A person with visual acuity of 6/60 Snellen or better should not ordinarily be regarded as blind.
1971 Jrnl. Gen. Psychol. 84 85 He measured visual acuity, using Snellen letters at 10 meters.
This entry has not yet been fully updated (first published 1986; most recently modified version published online March 2022).
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n.1864