Chart, Snellen's


Chart, Snellen's
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 letters on Snellen's chart are, not surprisingly, called Snellen's test type. Each block letter is quite scientific in design (so that at the appropriate distance the 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.

Look at other dictionaries:

  • Eye chart, Snellen's — 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 — A Snellen chart is an eye chart used by eye care professionals and others to measure visual acuity. Snellen charts are named after the Dutch ophthalmologist Herman Snellen who developed the chart in 1862.DescriptionThe traditional Snellen chart… …   Wikipedia

  • 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'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'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… …   Medical dictionary

  • Snellen chart — the commonest chart used for testing sharpness of distant vision (see visual acuity). It consists of rows of capital letters, called test types, the letters of each row becoming smaller down the chart. The large letter at the top is of such a… …   The new mediacal dictionary

  • 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

  • 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

  • Snellen fraction —    a ratio (such as 20/20 or 20/100) measuring the acuity (sharpness) of a person s eyesight for objects at a distance. The denominator (number after the slash) is the distance at which the detail of a letter on a standard test chart would… …   Dictionary of units of measurement

  • Snellen — noun Dutch ophthalmologist who introduced the Snellen chart to study visual acuity (1834 1908) • Syn: ↑Hermann Snellen • Instance Hypernyms: ↑ophthalmologist, ↑eye doctor, ↑oculist …   Useful english dictionary


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