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 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:

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  • 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

  • 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

  • test type — noun : any of the printed letters or characters on an eye chart a typeface carefully chosen for use as test type …   Useful english dictionary

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