night blindness

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night blindness

night blindness inability to see normally in subdued light. It is usually a result of vitamin A deficiency. The rod cells, one of two light-sensitive areas of the retina of the eye , are impaired in their capacity to produce a chemical compound called rhodopsin, or visual purple, that is necessary for the perception of objects in dim light. Consequently, the visual threshold, or the minimum intensity of light necessary for sight, is greatly increased. Folk medicine has long recognized the role of the ingestion of liver in alleviating the condition, but it was not until the first quarter of the 20th cent. that vitamin A was identified as the crucial element. Treatment of night blindness consists of the oral or intravenous administration of vitamin A.

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night blindness

The Oxford Pocket Dictionary of Current English | 2009 | © The Oxford Pocket Dictionary of Current English 2009, originally published by Oxford University Press 2009. (Hide copyright information) Copyright

night blind·ness • n. less technical term for nyctalopia.

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night blindness

A Dictionary of Food and Nutrition | 2005 | | Â© A Dictionary of Food and Nutrition 2005, originally published by Oxford University Press 2005. (Hide copyright information) Copyright

night blindness Nyctalopia. Inability to see in dim light as a result of vitamin A deficiency. See also dark adaptation; vision.

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DAVID A. BENDER. "night blindness." A Dictionary of Food and Nutrition. 2005. Encyclopedia.com. 21 Dec. 2009 <http://www.encyclopedia.com>.

DAVID A. BENDER. "night blindness." A Dictionary of Food and Nutrition. 2005. Encyclopedia.com. (December 21, 2009). http://www.encyclopedia.com/doc/1O39-nightblindness.html

DAVID A. BENDER. "night blindness." A Dictionary of Food and Nutrition. 2005. Retrieved December 21, 2009 from Encyclopedia.com: http://www.encyclopedia.com/doc/1O39-nightblindness.html

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