miosis

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 a term with various definitions, which generally include constriction of the pupil.

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

Definitions

Definitions of miosis include:

• Constriction of the pupil that is excessive,^[1] which may potentially be interpreted as being relative to what would be expected by 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 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. ^ Farlex medical dictionary citing:
   • Miller-Keane Encyclopedia and Dictionary of Medicine, Nursing, and Allied Health, Seventh Edition.
   • Saunders Comprehensive Veterinary Dictionary, 3 ed.
2. ^ 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. 
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

• FP Notebook
• -1254817782 at GPnotebook

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