Mydriasis
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| Mydriasis Classification and external resources | |
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| An abnormally dilated pupil. | |
| ICD-10 | H57.0 |
| ICD-9 | 379.43 |
| OMIM | 159420 159410 106240 |
| DiseasesDB | 8603 |
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Ongoing Trials on Mydriasis at Clinical Trials.gov Clinical Trials on Mydriasis at Google
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US National Guidelines Clearinghouse on Mydriasis
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Mydriasis is an excessive dilation of the pupil due to disease, trauma or drugs. Normally, the pupil dilates in the dark and constricts in the light. A mydriatic pupil will remain excessively large, even in a bright environment. Sometimes colloquially referred to as a "blown pupil."
The opposite, constriction of the pupil, is called miosis.
Mechanism
There are two types of muscle that control the size of the iris: circular muscle and radial muscle. The former is innervated by the parasympathetic nervous system, the latter by the sympathetic nervous system. Sympathetic stimulation of α1 adrenergic receptors causes the contraction of the radial muscle, and subsequent dilation of the pupil. Conversely, parasympathetic stimulation cause contraction of the circular muscle and constriction of the iris.
The mechanism of mydriasis depends on the agent being used. It usually involves either a disruption of the parasympathetic nerve supply to the eye (which causes contraction of the pupil), or over activity of the sympathetic nervous system (SNS).
Causes
Non Pathological
Mydriasis can be congenital.
Pathological
The parasympathetic nervous supply which causes constriction of the pupil, or miosis, is supplied by cranial nerve III, the oculomotor nerve. Damage to this nerve typically manifests itself as mydriasis, because the sympathetic supply to the pupil which causes mydriasis remains unaffected, and therefore unopposed.
Traumatic
In cases of head injury or orbit trauma (eye injury), the iris sphincter (the muscle responsible for closing the pupil) or the nerves controlling it can be damaged, reducing or eliminating reactivity to light.
Drugs
Atropine blocks muscarinic acetylcholine receptors. Acetylcholine (ACh) is the neurotransmitter of the parasympathetic nervous system and blocking its action means the pupil cannot constrict.
Cocaine inhibits the reuptake of noradrenaline (norepinephrine) within a nerve synapse. When a solution of cocaine is dropped into the eye, noradrenaline is no longer reabsorbed by neurons, and its levels increase. Noradrenaline, the neurotransmitter for the SNS, causes dilation of the pupil. Mydriasis is used as a diagnostic test for Horner's Syndrome, in which it is initiated using a similar mechanism, though cocaine is not usually used in this procedure. Many other drugs such as amphetamines and psychedelic drugs (LSD, psychedelic mushrooms, mescaline, and MDMA) are also known to cause mydriasis.
Opiate withdrawal can cause dilated pupils in some people. [1]
Antihistamines and tricyclic antidepressants may cause mydriasis.
Mydriatic drops
A mydriatic is an agent which induces dilation of the pupil. Drugs such as tropicamide are used in medicine to permit examination of the retina and other deep structures of the eye, and also to reduce painful ciliary muscle spasm (see cycloplegia). One effect of administration of a mydriatic is intolerance to bright light.
Physiological Response Indicating Interest
Pupillary response may also indicate interest in the subject of attention or sexual stimulation.[1]
Diagnostic Findings
 Pupil dilated using anaesthetic and muscle relaxant |
 Pupillary response |
References
See also
WikiDoc Research Resources for Mydriasis | |
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| Articles on Mydriasis | Most recent articles on Mydriasis • Most cited articles on Mydriasis • Review articles on Mydriasis • Articles on Mydriasis in N Eng J Med, Lancet, BMJ |
| Media (Slides, Video, Images, MP3) on Mydriasis | Powerpoint slides on Mydriasis • Images of Mydriasis • Photos of Mydriasis • Podcasts & MP3s on Mydriasis • Videos on Mydriasis |
| Evidence Based Medicine Regarding Mydriasis | Cochrane Collaboration on Mydriasis • Bandolier on Mydriasis • TRIP on Mydriasis |
| Cost Effectiveness of Mydriasis | Cost Effectiveness of Mydriasis |
| Clinical Trials Involving Mydriasis | Ongoing Trials on Mydriasis at Clinical Trials.gov • Trial results on Mydriasis • Clinical Trials on Mydriasis at Google |
| Guidelines / Policies / Government Resources (FDA/CDC) Regarding Mydriasis | US National Guidelines Clearinghouse on Mydriasis • NICE Guidance on Mydriasis • NHS PRODIGY Guidance • FDA on Mydriasis • CDC on Mydriasis |
| Textbook Information on Mydriasis | Books and Textbook Information on Mydriasis |
| Pharmacology Resources on Mydriasis | Dosing of Mydriasis • Drug interactions with Mydriasis • Side effects of Mydriasis • Allergic reactions to Mydriasis • Overdose information on Mydriasis • Carcinogenicity information on Mydriasis • Mydriasis in pregnancy • Pharmacokinetics of Mydriasis • |
| Genetics, Pharmacogenomics, and Proteinomics of Mydriasis | Genetics of Mydriasis • Pharmacogenomics of Mydriasis • Proteomics of Mydriasis |
| Newstories on Mydriasis | Mydriasis in the news • Be alerted to news on Mydriasis • News trends on Mydriasis |
| Commentary on Mydriasis | Blogs on Mydriasis |
| Patient Resources on Mydriasis | Patient resources on Mydriasis • Discussion groups on Mydriasis • Patient Handouts on Mydriasis • Directions to Hospitals Treating Mydriasis • Risk calculators and risk factors for Mydriasis |
| Healthcare Provider Resources on Mydriasis | Symptoms of Mydriasis • Causes & Risk Factors for Mydriasis • Diagnostic studies for Mydriasis • Treatment of Mydriasis |
| Continuing Medical Education (CME) Programs on Mydriasis | CME Programs on Mydriasis |
| International Resources on Mydriasis | Mydriasis en Espanol • Mydriasis en Francais |
| Business Resources on Mydriasis | Mydriasis in the Marketplace • Patents on Mydriasis |
| Informatics Resources on Mydriasis | List of terms related to Mydriasis |
de:Mydriasisfr:Mydriase it:Midriasi ja:散瞳sv:Mydriasis
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Acknowledgement and Attribution Regarding Sources of Content
Some of the initial content on this page may be incorporated in part from copyleft sources in the public domain including wikis such as Wikipedia and AskDrWiki. Drug information for patients came from the The National Library of Medicine. Infectious disease information may have come from the Centers for Disease Control (CDC). Differential Diagnoses are drawn from clinicians as well as an amalgamation of 3 sources: 1.The Disease Database; 2. Kahan, Scott, Smith, Ellen G. In A Page: Signs and Symptoms. Malden, Massachusetts: Blackwell Publishing, 2004:3; 3. Sailer, Christian, Wasner, Susanne. Differential Diagnosis Pocket. Hermosa Beach, CA: Borm Bruckmeir Publishing LLC, 2002:7 .
