Miosis

Not to be confused with meiosis, mitosis, or myositis.

Miosis
Classification and external resources
Slight miosis of the left eye (there is also concurrent partial ptosis on the left, most likely part of Horner's syndrome)
ICD-10	H57.0
ICD-9	379.42
DiseasesDB	8243
MeSH	D015877

Miosis (or myosis, from Ancient Greek μύειν, mūein, "to close the eyes") is the constriction of the pupil of the eye to two millimeters or less.^[1] The pupillary response (enlargement or reduction of the pupil) is a normal response to changes in light levels, but changes in pupil size can also be associated with certain pathological conditions, microwave radiation exposure^{[citation needed]}, and certain drugs, especially opioids. Parasympathetic stimulation of the iris sphincter muscle (pupillary sphincter muscle) decreases the pupillary aperture (size of the pupil). This constriction is referred to as miosis.

The opposite condition, mydriasis, is the dilation of the pupil.

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 ganglion cells have three functions: 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

Causes

Age

Diseases

• Horner syndrome (a set of abnormalities in the nervous supply of the face due to damage to the sympathetic nervous system).
• Hemorrhage into pons (intracranial hemorrhage)
• Cluster Headaches with ptosis
• Iridocyclitis
• Fatal familial insomnia

Drugs

• Opioids such as fentanyl, morphine, heroin and methadone (the notable exception being demerol)
• Antipsychotics, including haloperidol, thorazine, olanzapine, quetiapine and others
• Cholinergic agents such as acetylcholine
• Some cancer chemotherapy drugs, including camptothecin derivatives
• Mirtazapine, a noradrenergic and specific serotonergic antidepressant (NaSSA)
• Trazodone
• Some MAO Inhibitors.
• In some rare cases, when exposed to mustard gas.
• Organophosphates

Miotics

A miotic substance causes the constriction of the pupil of the eye (or miosis). It is the opposite of a mydriatic substance, which causes dilation of the pupil.

See also

• Adie syndrome
• Anisocoria
• Cycloplegia
• Marcus Gunn pupil
• Mydriasis
• Parinaud's syndrome
• Syphilis

References

1. ^ Seidel, Henry M.; Jane W. Ball, Joyce E. Dains, G. William Benedict (2006-03-29). Mosby's Guide to Physical Examination. Mosby. ISBN 0323035736, 9780323035736. 

External links

• FP Notebook
• -1254817782 at GPnotebook

This medical sign article is a stub. You can help Wikipedia by expanding it.v · Categories: Diseases of the eye and adnexa Medical sign stubs Wikimedia Foundation. 2010. Игры ⚽ Поможем написать курсовую Broadway Bridge (Portland) I Know Where I'm Going Look at other dictionaries: miosis — f. oftalm. Estenocoria. Medical Dictionary. 2011. miosis 1. contracci …   Diccionario médico miosis — (plural miosis) sustantivo femenino 1. Área: medicina Contracción anormal y permanente de la pupila del ojo …   Diccionario Salamanca de la Lengua Española Miosis — (Rhet.), so v.w. Meiosis …   Pierer's Universal-Lexikon Miōsis — (Meiosis, griech.), Verkleinerung, besonders als rhetorische Figur, im Gegensatz zu Hyperbel (s. d.). In der Pathologie: abnorme dauernde Verengerung der Pupille, kommt bei Gehirnleiden durch Reizung der betreffenden Nerven oder durch Lähmung von …   Meyers Großes Konversations-Lexikon Miosis — Miōsis (grch.), Verengerung der Pupille (s.d.) …   Kleines Konversations-Lexikon miosis — (n.) 1819, from Gk. myein to shut (the eyes) + OSIS (Cf. osis). Greek myein is perhaps originally to close the lips, from PIE *meue to be silent (see MUTE (Cf. mute) (adj.)). Related: Miotic …   Etymology dictionary miosis — (Del gr. μύειν, guiñar los ojos, y sis). f. Med. Contracción permanente de la pupila del ojo …   Diccionario de la lengua española miosis — [mī ō′sis] n. pl. mioses [mī ō′sēz΄] [ModL < Gr myein, to close (< IE base * mu : see MUTE) + OSIS] contraction of the pupil of the eye miotic [mīät′ik] adj., n …   English World dictionary Miosis — Para la división celular, véase Meiosis y Mitosis. Miosis Miosis del ojo izquierdo, véase la diferencia de apertura de la pupila en ambos ojos. Clasificación y recursos externos …   Wikipedia Español Miosis — Klassifikation nach ICD 10 H57.0 Pupillenfunktionsstörungen …   Deutsch Wikipedia 18+ © Academic, 2000-2024 Contact us: Technical Support, Advertising Dictionaries export, created on PHP, Joomla, Drupal, WordPress, MODx. Mark and share Search through all dictionaries Translate… Search Internet Share the article and excerpts Direct link … Do a right-click on the link above and select “Copy Link”