astigmatism

astigmatism

[uh-stig-muh-tiz-uhm]
noun
1.
Also called astigmia [uh-stig-mee-uh] . Ophthalmology. a refractive error of the eye in which parallel rays of light from an external source do not converge on a single focal point on the retina.
2.
Optics. an aberration of a lens or other optical system in which the image of a point is spread out along the axis of the system.

Origin:
1840–50; astigmat(ic) + -ism

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World English Dictionary
astigmatism or astigmia (əˈstɪɡməˌtɪzəm, əˈstɪɡmɪə)
 
n
1.  a defect of a lens resulting in the formation of distorted images; caused by the curvature of the lens being different in different planes
2.  faulty vision resulting from defective curvature of the cornea or lens of the eye
 
astigmia or astigmia
 
n

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Etymonline
Word Origin & History

astigmatism
coined (in form astigmatic) 1849 by the Rev. William Whewell (17941866), Eng. polymath, from Gk. a- "without" + stigmatos gen. of stigma "a mark, spot, puncture" (see stick (v.)).
Online Etymology Dictionary, © 2010 Douglas Harper
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American Heritage
Medical Dictionary

astigmatism a·stig·ma·tism (ə-stĭg'mə-tĭz'əm)
n.
A condition in which unequal curvatures along the different meridians in one or more of the refractive surfaces of the eye cause the rays from a light source not to be focused at a single point on the retina. Also called astigmia.


as'tig·mat'ic (ās'tĭg-māt'ĭk) adj. & n.
The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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American Heritage
Science Dictionary
astigmatism   (ə-stĭg'mə-tĭz'əm)  Pronunciation Key 


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A visual defect in which the unequal curvature of one or more refractive surfaces of the eye, usually the cornea, prevents light rays from focusing clearly at a single point on the retina, resulting in blurred vision.
The American Heritage® Science Dictionary
Copyright © 2002. Published by Houghton Mifflin. All rights reserved.
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American Heritage
Cultural Dictionary
astigmatism [(uh-stig-muh-tiz-uhm)]

A condition in which the curvature of the cornea of the eye is uneven, causing a blurring of vision. Astigmatism is normally corrected by glasses.

The American Heritage® New Dictionary of Cultural Literacy, Third Edition
Copyright © 2005 by Houghton Mifflin Company.
Published by Houghton Mifflin Company. All rights reserved.
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