Mydriasis 207737 219599992 2008-06-16T00:57:52Z Jeff Silvers 415302 /* Physiological Response Indicating Interest */ Heading capitalization. {{Unreferenced|date=December 2007}} :''"Dilated pupil" redirects here. An [[eye examination]] sometimes requires the dilation of the pupil.'' {{DiseaseDisorder infobox | Name = Mydriasis | ICD10 = {{ICD10|H|57|0|h|55}} | ICD9 = {{ICD9|379.43}} | DiseasesDB = 8603 | OMIM = 159420 | OMIM_mult = {{OMIM2|159410}} {{OMIM2|106240}} | Image = Dilated_pupils_2006.JPG | Caption = An abnormally dilated pupil. }} '''Mydriasis''' is an excessive dilation of the [[pupil]] due to [[disease]], [[Physical trauma|trauma]] or [[Psychoactive drug|drug]]s. Normally, the pupil dilates in the [[dark]] and [[constriction|constricts]] in the [[light]]. A mydriatic pupil will remain excessively large, even in a bright environment. Sometimes [[colloquial]]ly referred to as a "[[blown pupil]]." The opposite, constriction of the pupil, is called [[miosis]]. {{TOCleft}} ==Mechanism== There are two types of [[muscle]] that control the size of the [[Iris (anatomy)|iris]]: [[Iris sphincter muscle|circular]] muscle and [[Iris dilator muscle|radial]] muscle. The former is [[innervate]]d by the [[parasympathetic nervous system]], the latter by the [[sympathetic nervous system]]. Sympathetic stimulation of α1 [[adrenergic receptors]] causes the [[Muscle contraction|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). <br clear="left"/> ==Causes== ===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=== [[Image:Eye dilate.gif|thumb|250px|right|Pupillary response]] In cases of [[head injury]] or [[eye injury|orbit trauma (eye injury)]], the [[Iris sphincter muscle|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 receptor]]s. [[Acetylcholine|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 [[neuron]]s, 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 [[amphetamine]]s and [[psychedelic drug]]s ([[LSD]], [[psychedelic mushrooms]], [[mescaline]], and [[MDMA]]) are also known to cause mydriasis. <!-- Are they known to cause mydriasis using this mechanism? If not, why are they in this paragraph? Considering the distinctiveness of their effects on the body, as compared to those of cocaine, I would strongly suggest this is misplaced. --> [[Opiate]] withdrawal can cause dilated pupils in some people. <ref>http://www.nd.gov.hk/chapter_4b2_eng.pdf</ref> Opiates normally lead to miosis or the constriction of the pupils. [[Antihistamine]]s and [[tricyclic antidepressant]]s may cause mydriasis. ===Mydriatic drops=== [[Image:Dilated_pupil.gk.jpg|thumb|200px|right|Pupil dilated using [[anaesthetic]] and [[muscle relaxer|muscle relaxant]].]] 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]] [[muscle spasm|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.<ref>{{Citation | last1 = Hess | first1 = Eckhard H. | author1-link = Eckhard Hess | last2 = Polt | first2 = James M. | author2-link = James Polt | title = Pupil Size as Related to Interest Value of Visual Stimuli | journal = Science | volume = 132 | issue = 3423 | pages = 349 | date = 5 August 1960 | year = 1960 | doi = 10.1126/science.132.3423.349 }}</ref> <br clear="both"/> ==References== <references/> ==See also== *[[Miosis]] *[[Anisocoria]] {{Eye pathology}} [[Category:Medical signs]] [[Category:Ophthalmology]] [[ca:Midriàtic]] [[da:Mydriasis]] [[de:Mydriasis]] [[es:Midriasis]] [[fr:Mydriase]] [[it:Midriasi]] [[nl:Mydriasis]] [[ja:散瞳]] [[pl:Mydriasis]] [[pt:Midríase]] [[sv:Mydriasis]]