| Eye Chart |
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| ophthalmology | |
| ophthalmic equipment | |
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PROCEDURE Charts usually display several rows of Optotypes (test symbols), each row in a different size. The person is asked to identify the optotypes displayed 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. Others are printed with the capital block letter "E" turned in different orientations. The patient simply indicates which direction each "E" is facing. The "broken ring" 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. {Link without Title} ), 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 be suited for children since they resemble a Video Game . SEE ALSO |
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