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[toh-sis] /ˈtoʊ sɪs/
noun, Pathology
a drooping of the upper eyelid.
prolapse or drooping of any organ.
1735-45; < New Latin < Greek ptṓsis a falling
Related forms
[toh-tik] /ˈtoʊ tɪk/ (Show IPA),
adjective Unabridged
Based on the Random House Dictionary, © Random House, Inc. 2015.
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British Dictionary definitions for ptosis


noun (pl) ptoses (ˈtəʊsiːz)
prolapse or drooping of a part, esp the eyelid
Derived Forms
ptotic (ˈtɒtɪk) adjective
Word Origin
C18: from Greek: a falling
Collins English Dictionary - Complete & Unabridged 2012 Digital Edition
© William Collins Sons & Co. Ltd. 1979, 1986 © HarperCollins
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Word Origin and History for ptosis

1743, from Greek ptosis, literally "falling, a fall," also "the case of a noun," nominal derivative of piptein "to fall" (see symptom). In English, especially of the eyelid. Related: Ptotic.

Online Etymology Dictionary, © 2010 Douglas Harper
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ptosis in Medicine

ptosis pto·sis (tō'sĭs)
n. pl. pto·ses (-sēz)
Abnormal lowering or drooping of an organ or a part, especially a drooping of the upper eyelid caused by muscle weakness or paralysis.

The American Heritage® Stedman's Medical Dictionary
Copyright © 2002, 2001, 1995 by Houghton Mifflin Company. Published by Houghton Mifflin Company.
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Encyclopedia Article for ptosis


drooping of the upper eyelid. The condition may be congenital or acquired and can cause significant obscuration of vision. In congenital ptosis the muscle that elevates the lid, called the levator palpebrae superioris, is usually absent or imperfectly developed. If severe and not corrected in a timely manner, congenital ptosis can lead to amblyopia and permanent vision loss. Congenital palsy of the third (oculomotor) cranial nerve (which normally stimulates elevation of the upper lid) is a more rare cause of congenital ptosis.

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Encyclopedia Britannica, 2008. Encyclopedia Britannica Online.
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