Eye chart

Eye chart

__NOTOC__Infobox Laboratory equipment
name = Eye chart


caption = Typical Snellen chart used for visual acuity testing.
acronym =
other_names =
uses = Vision testing
inventor =
manufacturer =
model =
related = Snellen chart Landolt C Lea test Tibetan eye chartAn eye chart is a chart used to measure visual acuity. Types of eye charts include the Snellen chart, Landolt C, and the Lea test.

Procedure

Charts usually display several rows of optotypes (test symbols), each row in a different size. The person is asked to identify the numbers or letters on the chart, usually starting with large rows and continuing to smaller rows until the optotypes cannot be reliably identified anymore.

Technically speaking, testing visual acuity with an eye chart is a psychophysical measurement that attempts to determine a sensory threshold (see also "psychometric function").

Variations

Charts are available for very young children or illiterate adults that do not require letter recognition. One version uses simple pictures or patterns. Others are printed with the block letter "E" turned in different orientations, the so called [http://pediatrics.about.com/cs/pediatricadvice/a/vision_scrning_2.htm Tumbling E] . The patient simply indicates which direction each "E" is facing. The Landolt C chart is similar: rows have circles with different segments missing, and the test-taker describes where each broken piece is located. The last two kinds of charts also reduce the possibility of patient guessing the images.

Alternatives

Computer-based semi-automatic alternatives to the eye chart have been developed (e.g. [http://www.augen.uniklinik-freiburg.de/mit/bach/fract_universal/index.html] ), but are not very common. They have several potential advantages, such as a more precise measurement and less examiner-induced bias. Some of them are also well suited for children since they resemble a video game.


Wikimedia Foundation. 2010.

Игры ⚽ Нужна курсовая?

Look at other dictionaries:

  • eye chart — n a chart that is read at a fixed distance for purposes of testing sight esp one with rows of letters or objects of decreasing size …   Medical dictionary

  • eye chart — eye′ chart n. cvb oph a chart for testing vision, usu. containing letters in rows of decreasing size to be read at a fixed distance • Etymology: 1940–45 …   From formal English to slang

  • eye chart — n. a chart used to test vision from a specified distance: it consists typically of rows of letters of decreasing size …   English World dictionary

  • eye chart — noun a chart that is read from a fixed distance; used as a test of vision • Hypernyms: ↑chart * * * noun : a chart that is read at a fixed distance for purposes of testing sight ; especially : one with rows of letters or objects of decreasing… …   Useful english dictionary

  • eye chart — noun a sign or poster showing letters or symbols in progressively smaller lines of type, used to test distance vision The doctor said I needed glasses after I failed to read past the fourth line on the eye chart …   Wiktionary

  • 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

  • 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

  • eye chart — noun Date: 1943 a chart read at a fixed distance for purposes of testing sight; especially one with rows of letters or objects of decreasing size …   New Collegiate Dictionary

  • eye chart — Ophthalm. a chart for testing vision, typically containing letters, symbols, or pictures in rows of decreasing size that are to be read or identified at a fixed distance. [1940 45] * * * …   Universalium

  • Tibetan eye chart — The Tibetan eye chart is a tool created by Tibetan monks. According to them, it can be used to train the muscles and nerves of the optical system, correcting visual problems.Fact|date=March 2008ee also*Bates Method *Eye chart External links *… …   Wikipedia

Share the article and excerpts

Direct link
… Do a right-click on the link above
and select “Copy Link”