• synonyms


[mi-drahy-uh-sis, mahy-]
noun Medicine/Medical.
  1. excessive dilatation of the pupil of the eye, as the result of disease, drugs, or the like.
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Compare miosis.

Origin of mydriasis

1650–60; < Latin mydriāsis < Greek mydríāsis
Dictionary.com Unabridged Based on the Random House Unabridged Dictionary, © Random House, Inc. 2018

Examples from the Web for mydriasis

Historical Examples

  • Mydriasis does not always occur, and when it does, is much less than with cocaine.

    Merck's 1899 Manual

    Merck &amp; Co.

  • Visual acuteness on both sides 5/12, the left slightly better than the right; emmetropia in mydriasis by atropine.

  • Mydriasis, mi-drī′a-sis, n. morbid dilatation of the pupil of the eye.

  • At the same time there is a certain amount of mydriasis, but this is less pronounced than that produced by atropine.

British Dictionary definitions for mydriasis


  1. abnormal dilation of the pupil of the eye, produced by drugs, coma, etc
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Word Origin

C17: via Late Latin from Greek; origin obscure
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition © William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins Publishers 1998, 2000, 2003, 2005, 2006, 2007, 2009, 2012

mydriasis in Medicine


  1. Prolonged abnormal dilation of the pupil of the eye induced by a drug or caused by disease.
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The American Heritage® Stedman's Medical Dictionary Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.