Mydriasis - wikipedia Mydriasis Mydriasis Pupil dilated for examination by ophthalmologist Classification and external resources Specialty Ophthalmology ICD - 10 H57. 0 ICD - 9 - CM 379.43 OMIM 159420 159410 106240 DiseasesDB 8603 MeSH D015878 ( edit on Wikidata ) Mydriasis ( / mɪˈdraɪ. əsɪs / ) is the dilation of the pupil, usually having a non-physiological cause, or sometimes a physiological pupillary response. Non-physiological causes of mydriasis include disease, trauma, or the use of drugs. Normally, as part of the pupillary light reflex, the pupil dilates in the dark and constricts in the light to respectively improve vividity at night and to protect the retina from sunlight damage during the day. A mydriatic pupil will remain excessively large even in a bright environment. The excitation of the radial fibres of the iris which increases the pupillary aperture is referred to as a mydriasis. More generally, mydriasis also refers to the natural dilation of pupils, for instance in low light conditions or under sympathetic stimulation. An informal term for mydriasis is blown pupil, and is used by medical providers. It is usually used to refer to a fixed, unilateral mydriasis, which could be a symptom of raised intracranial pressure. The opposite, constriction of the pupil, is referred to as miosis. Both mydriasis and miosis can be physiological. Anisocoria is the condition of one pupil being more dilated than the other. Contents 1 Mechanism 1.1 Effects 1.2 Autonomic neuropathy 1.3 Traumatic 1.4 Drugs 1.5 Mydriatics 2 See also 3 Notes 4 References Mechanism This section needs additional citations for verification. Please help improve this article by adding citations to reliable sources. Unsourced material may be challenged and removed. ( August 2014 ) There are two types of muscle that control the size of the iris : the iris sphincter, composed of circularly arranged muscle fibers, and the iris dilator, composed of radially arranged muscle fibers. The sphincter is innervated by ( signaled by nerves of ) the parasympathetic nervous system ; the dilator by the sympathetic nervous system. Sympathetic stimulation of the adrenergic receptors causes the contraction of the radial muscle and subsequent dilation of the pupil. Conversely, parasympathetic stimulation causes contraction of the circular muscle and constriction of the pupil. 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 normally constricts the pupil ) or overactivity of the sympathetic nervous system ( SNS ). Effects Natural release of the hormone oxytocin can cause mild to moderate mydriasis. Autonomic neuropathy Parasympathetic fibers travel with cranial nerve III, the oculomotor nerve, to innervate the circular layer of muscle of the eye ( sphincter pupillae ). Damage to this nerve typically manifests itself as mydriasis, because the sympathetic supply to the pupil, which causes mydriasis, remains unaffected, and therefore unopposed. Multiple central nervous system disorders e.g. epilepsy, stroke, and impending brain herniation are known to lead to temporal mydriasis as well. A brain catastrophe, or a rapidly increasing brain mass, can cause compression of the oculomotor nerve. 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 the normal pupillary light reflex. Drugs Tropicamide is used as a mydriastic agent during cataract surgery. Anticholinergics such as atropine, hyoscyamine, and scopolamine antagonize the muscarinic acetylcholine receptors in the eye. By blocking these receptors, the pupils are no longer capable of constriction and dilation results. Such alkaloids present in many plants of the family Solanaceae may also induce mydriasis when used The neurotransmitter norepinephrine regulates many physiological processes in the body and brain. One of them is the autonomic constriction and contraction of certain muscles. The psychoactive drug cocaine potently inhibits the normal reuptake of norepinephrine into presynaptic nerve terminals, resulting in an increased level of extracellular norepinephrine. Amphetamines also potently release and prevent the reuptake of norepinephrine. The released norepinephrine then proceeds to bind to adrenergic receptors, and the biological effects of norepinephrine finally occur. When a solution of cocaine is dropped into the eye, this process takes place and the end result is dilation of the pupil. Cocaine itself is not typically used for this task, however. Any potent norepinephrine reuptake inhibitor or release agent should be capable of such an effect. Opiates such as morphine and heroin do not cause pupil dilation. Instead they cause miosis ( pupil contraction ). Mydriasis occasionally occurs during opiate rebound and withdrawal. Mydriatics Pupil dilated using the anticholinergic drug tropicamide. A mydriatic is an agent that 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 ). Phenylephrine ( e.g. Cyclomydril ) is used if strong mydriasis is needed for a surgical intervention. One effect of administration of a mydriatic is intolerance to bright light ( photophobia ). Purposefully - induced mydriasis via mydriatics is also used as a diagnostic test for Horner 's syndrome. See also Miosis Anisocoria Notes References Jump up ^ Mydriasis in Farlex medical dictionary. In turn citing : The American Heritage Medical Dictionary ( 2007 ) Mosby 's Dental Dictionary, 2nd edition. Jump up ^ Mydriasis in Farlex medical dictionary. In turn citing : Mosby 's Medical Dictionary, 8th edition. Jump up ^ `` Traumatic Brain Injury ''. American Association of Neurological Surgeons. Retrieved 27 March 2012. Jump up ^ Saenz - de-Viteri, Manuel ; Gonzalez - Salinas, Roberto ; Guarnieri, Adriano ; Guiaro - Navarro, María Concepción ( 2016 ). `` Patient considerations in cataract surgery -- the role of combined therapy using phenylephrine and ketorolac ''. Patient Preference and Adherence. Volume 10 : 1795 -- 1801. ISSN 1177 - 889X. doi : 10.2147 / PPA. S90468. Jump up ^ http://www.nd.gov.hk/chapter_4b2_eng.pdf Jump up ^ `` Cyclomydril - FDA prescribing information, side effects and uses ''. Jump up ^ `` Common eye diseases and their management '', Galloway / Amoako / Browning, Springer science 2006, 3rd edition, p196 Diseases of the human eye ( H00 -- H59 360 -- 379 ) Adnexa Eyelid Inflammation Stye Chalazion Blepharitis Entropion Ectropion Lagophthalmos Blepharochalasis Ptosis Blepharophimosis Xanthelasma Eyelash Trichiasis Madarosis Lacrimal apparatus Dacryoadenitis Epiphora Dacryocystitis Xerophthalmia Orbit Exophthalmos Enophthalmos Orbital cellulitis Orbital lymphoma Periorbital cellulitis Conjunctiva Conjunctivitis allergic Pterygium Pinguecula Subconjunctival hemorrhage Globe Fibrous tunic Sclera Scleritis Episcleritis Cornea Keratitis herpetic acanthamoebic fungal Corneal ulcer Photokeratitis Thygeson 's superficial punctate keratopathy Corneal dystrophy Fuchs ' Meesmann Corneal ectasia Keratoconus Pellucid marginal degeneration Keratoglobus Terrien 's marginal degeneration Post-LASIK ectasia Keratoconjunctivitis sicca Corneal neovascularization Kayser -- Fleischer ring Haab 's striae Arcus senilis Band keratopathy Vascular tunic Iris Ciliary body Uveitis Intermediate uveitis Hyphema Rubeosis iridis Persistent pupillary membrane Iridodialysis Synechia Choroid Choroideremia Choroiditis Chorioretinitis Lens Cataract Congenital cataract Childhood cataract Aphakia Ectopia lentis Retina Retinitis Chorioretinitis Cytomegalovirus retinitis Retinal detachment Retinoschisis Ocular ischemic syndrome / Central retinal vein occlusion Central retinal artery occlusion Retinopathy diabetic hypertensive Purtscher 's of prematurity Bietti 's crystalline dystrophy Coats ' disease Macular degeneration Retinitis pigmentosa Retinal haemorrhage Central serous retinopathy Macular edema Epiretinal membrane ( Macular pucker ) Vitelliform macular dystrophy Leber 's congenital amaurosis Birdshot chorioretinopathy Other Glaucoma / Ocular hypertension / Primary juvenile glaucoma Floater Leber 's hereditary optic neuropathy Red eye Globe rupture Keratomycosis Phthisis bulbi Persistent fetal vasculature / Persistent hyperplastic primary vitreous Persistent tunica vasculosa lentis Familial exudative vitreoretinopathy Pathways Optic nerve Optic disc Optic neuritis optic papillitis Papilledema Foster Kennedy syndrome Optic atrophy Optic disc drusen Optic neuropathy Ischemic anterior ( AION ) posterior ( PION ) Kjer 's Leber 's hereditary Toxic and nutritional Strabismus Extraocular muscles Binocular vision Accommodation Paralytic strabismus Ophthalmoparesis Chronic progressive external ophthalmoplegia Kearns -- Sayre syndrome palsies Oculomotor ( III ) Fourth - nerve ( IV ) Sixth - nerve ( VI ) Other strabismus Esotropia / Exotropia Hypertropia Heterophoria Esophoria Exophoria Cyclotropia Brown 's syndrome Duane syndrome Other binocular Conjugate gaze palsy Convergence insufficiency Internuclear ophthalmoplegia One and a half syndrome Refraction Refractive error Hyperopia Myopia Astigmatism Anisometropia / Aniseikonia Presbyopia Vision disorders Blindness Amblyopia Leber 's congenital amaurosis Diplopia Scotoma Color blindness Achromatopsia Dichromacy Monochromacy Nyctalopia Oguchi disease Blindness / Vision loss / Visual impairment Anopsia Hemianopsia binasal bitemporal homonymous Quadrantanopia subjective Asthenopia Hemeralopia Photophobia Scintillating scotoma Pupil Anisocoria Argyll Robertson pupil Marcus Gunn pupil Adie syndrome Miosis Mydriasis Cycloplegia Parinaud 's syndrome Other Nystagmus Childhood blindness Infections Trachoma Onchocerciasis Retrieved from `` https://en.wikipedia.org/w/index.php?title=Mydriasis&oldid=794149156 '' Categories : Medical signs Ophthalmology Hidden categories : Articles needing additional references from August 2014 All articles needing additional references All articles with unsourced statements Articles with unsourced statements from April 2017 Articles with unsourced statements from January 2013 Talk Contents About Wikipedia Català Dansk Deutsch Español فارسی Français Hrvatski Italiano Nederlands 日本 語 Norsk Polski Português Română Русский Slovenščina Српски / srpski Srpskohrvatski / српскохрватски Svenska ไทย Українська 中文 Edit links This page was last edited on 6 August 2017, at 04 : 46. 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Question: an agent that causes the pupil to dilate is called
Answer: Mydriasis