Snellen's test type
The letters on the familiar eye chart used to measure how well you see at various distances. The eye chart, known as Snellen's chart, is imprinted with block letters that line-by-line decrease in size, corresponding to the distance at which that line of letters is normally visible. The block letters, Snellen's test type, are quite scientific in design (so that at the appropriate distance each letter subtends a visual angle of 5 degrees and each component part subtends an angle of 1 minute). The chart and the letters are named for a 19th-century Dutch ophthalmologist Hermann Snellen (1834-1908) who came up with them as a test of visual acuity. Visual acuity refers to the clarity or clearness of the vision, a measure of how well a person sees. The word "acuity" comes from the Latin "acuitas" = sharpness.

Medical dictionary. 2011.

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  • Snellen test type — block letters used in testing visual acuity, so designed that the whole letter subtends, at the appropriate distance, a visual angle usually of 5 minutes, and each component part subtends an angle of 1 minute. See also Snellen chart, under chart …   Medical dictionary

  • Test, visual acuity — This test measures how well you see at various distances. It is the familiar eye chart test. The eye chart itself the usual one is called Snellen s chart is imprinted with block letters that line by line decrease in size, corresponding to the… …   Medical dictionary

  • Test, eye chart — This test measures how well you see at various distances. The eye chart itself the usual one is called Snellen s chart is imprinted with block letters that line by line decrease in size, corresponding to the distance at which that line of letters …   Medical dictionary

  • Snellen's chart — The familiar eye chart used to measure how well you see at various distances. Snellen s chart is imprinted with block letters that line by line decrease in size, corresponding to the distance at which that line of letters is normally visible. The …   Medical dictionary

  • Snellen chart — Snel·len chart snel ən n the chart used in the Snellen test with black letters of various sizes against a white background Snellen Hermann (1834 1908) Dutch ophthalmologist. Snellen was director of an eye clinic at Utrecht. In 1862 he introduced… …   Medical dictionary

  • Snellen chart etc. — Snel·len chart, etc. (snelґən) [Hermann Snellen, Dutch ophthalmologist, 1834–1908] see under chart, eye, sign, test, and test type …   Medical dictionary

  • test types — Letters of various sizes used to test visual acuity. Jaeger t. type of different sizes used for testing the acuity of near vision. point system t. a near vision test chart …   Medical dictionary

  • Acuity test, visual — This test measures how well you see at various distances. It is the familiar eye chart test. The eye chart itself the usual one is called Snellen s chart is imprinted with block letters that line by line decrease in size, corresponding to the… …   Medical dictionary

  • Visual acuity test — This test measures how well you see at various distances. It is the familiar eye chart test. The eye chart itself the usual one is called Snellen s chart is imprinted with block letters that line by line decrease in size, corresponding to the… …   Medical dictionary

  • Eye chart test — This test measures how well you see at various distances. The eye chart itself the usual one is called Snellen s chart is imprinted with block letters that line by line decrease in size, corresponding to the distance at which that line of letters …   Medical dictionary

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