World Library  
Flag as Inappropriate
Email this Article


Article Id: WHEBN0000949670
Reproduction Date:

Title: Miosis  
Author: World Heritage Encyclopedia
Language: English
Subject: Mydriasis, Pilocarpine, Pupillary response, Ectopia lentis, Argyll Robertson pupil
Collection: Diseases of the Eye and Adnexa
Publisher: World Heritage Encyclopedia


Miosis due to opiate use
Classification and external resources
ICD-10 H57.0
ICD-9-CM 379.42
DiseasesDB 8243
MeSH D015877

Miosis (or myosis, from Ancient Greek μύειν, mūein, "to close the eyes") is a term with various definitions, which generally include constriction of the pupil.

The opposite condition, mydriasis, is the dilation of the pupil. Anisocoria is the condition of one pupil being more dilated than the other.


  • Definitions 1
  • Physiology of the photomotor reflex 2
  • Causes 3
    • Age 3.1
    • Diseases 3.2
    • Drugs 3.3
  • See also 4
  • References 5
  • External links 6


Definitions of miosis include:

  • Constriction of the pupil that is excessive,[1] relative to the amount of light the pupil receives
  • Constriction of the pupil to a diameter of less than two millimeters[2][3]
  • Constriction of the pupil with causes including both abnormal and physiological ones.[4]
  • Pupillary constriction by abnormal causes.[5]

Physiology of the photomotor reflex

Light entering the eye strikes three different photoreceptors in the retina: the familiar rods and cones used in image forming and the more newly discovered photosensitive ganglion cells. The ganglion cells give information about ambient light levels, and react sluggishly compared to the rods and cones. Signals from photosensitive ganglion cells have multiple functions including acute suppression of the hormone melatonin, entrainment of the body's circadian rhythms and regulation of the size of the pupil.

The retinal photoceptors convert light stimuli into electric impulses. Nerves involved in the resizing of the pupil connect to the pretectal nucleus of the high midbrain, bypassing the lateral geniculate nucleus and the primary visual cortex. From the pretectal nucleus neurons send axons to neurons of the Edinger-Westphal nucleus whose visceromotor axons run along both the left and right oculomotor nerves. Visceromotor nerve axons (which constitute a portion of cranial nerve III, along with the somatomotor portion derived from the Edinger-Westphal nucleus) synapse on ciliary ganglion neurons, whose parasympathetic axons innervate the iris sphincter muscle, producing miosis. This occurs because sympathetic activity from the ciliary ganglion is lost thus parasympathetics are not inhibited. Image



  • senile miosis (a reduction in the size of a person's pupil in old age)



See also


  1. ^ Farlex medical dictionary citing:
  2. ^ Seidel, Henry M.; Jane W. Ball; Joyce E. Dains; G. William Benedict (2006-03-29). Mosby's Guide to Physical Examination. Mosby.  
  3. ^ Farlex medical dictionary citing: Millodot: Dictionary of Optometry and Visual Science, 7th edition.
  4. ^ Farlex medical dictionary citing: The American Heritage Medical Dictionary. Copyright 2007
  5. ^ Farlex medical dictionary citing: Mosby's Medical Dictionary, 8th edition.

External links

This article was sourced from Creative Commons Attribution-ShareAlike License; additional terms may apply. World Heritage Encyclopedia content is assembled from numerous content providers, Open Access Publishing, and in compliance with The Fair Access to Science and Technology Research Act (FASTR), Wikimedia Foundation, Inc., Public Library of Science, The Encyclopedia of Life, Open Book Publishers (OBP), PubMed, U.S. National Library of Medicine, National Center for Biotechnology Information, U.S. National Library of Medicine, National Institutes of Health (NIH), U.S. Department of Health & Human Services, and, which sources content from all federal, state, local, tribal, and territorial government publication portals (.gov, .mil, .edu). Funding for and content contributors is made possible from the U.S. Congress, E-Government Act of 2002.
Crowd sourced content that is contributed to World Heritage Encyclopedia is peer reviewed and edited by our editorial staff to ensure quality scholarly research articles.
By using this site, you agree to the Terms of Use and Privacy Policy. World Heritage Encyclopedia™ is a registered trademark of the World Public Library Association, a non-profit organization.

Copyright © World Library Foundation. All rights reserved. eBooks from Project Gutenberg are sponsored by the World Library Foundation,
a 501c(4) Member's Support Non-Profit Organization, and is NOT affiliated with any governmental agency or department.