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Editor-In-Chief: C. Michael Gibson, M.S., M.D. [1] Associate Editor(s)-in-Chief: Luke Rusowicz-Orazem, B.S.

Synonyms and keywords: Pupillary dilation; dilated pupil


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.


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).


Common Causes

Causes by Organ System

Cardiovascular No underlying causes
Chemical/Poisoning No underlying causes
Dental No underlying causes
Dermatologic No underlying causes
Drug Side Effect Adregenic agents, Amphetamines, Antihistamines, Antipsychotic agents, Apraclonidine, Atropine, Chlorpheniramine, Chlorpromazine, Cinnarizine, Cocaine, Cyclopentolate, Diphenhydramine, Dipivefrin, Disopyramide, Dopram injection, Doxapram hydrochloride, Hallucinogens, Hexamethonium, Hydroxyzine, Lachesine, Levomepromazine, Lysergic acid diethylamide, Mdma, Mescaline, Naphazoline, Noradrenaline, Opiate, Oxcarbazepine, Perazine, Phenelzine, Phenylephrine, Pipothiazine, Pizotifen, Prochlorperazine, Psychedelic mushrooms, Sibutramine, Systemic anticholinergics, Tetrahydrozoline, Tricyclic antidepressants, Tropicamide
Ear Nose Throat No underlying causes
Endocrine No underlying causes
Environmental No underlying causes
Gastroenterologic No underlying causes
Genetic No underlying causes
Hematologic No underlying causes
Iatrogenic No underlying causes
Infectious Disease No underlying causes
Musculoskeletal/Orthopedic No underlying causes
Neurologic 3rd cranial nerve disorder, Adie's tonic pupil, Autonomic seizure, Brain death, Cerebral oedema, Coma, Raised intracranial pressure, Seizures, Serotonin syndrome, Third nerve palsy, Weber syndrome
Nutritional/Metabolic No underlying causes
Obstetric/Gynecologic No underlying causes
Oncologic No underlying causes
Ophthalmologic Acute closed angle glaucoma, Adie's tonic pupil, Benign episodic mydriasis, Pourfour du petit syndrome
Overdose/Toxicity No underlying causes
Psychiatric No underlying causes
Pulmonary No underlying causes
Renal/Electrolyte No underlying causes
Rheumatology/Immunology/Allergy No underlying causes
Sexual No underlying causes
Trauma Coma, Trauma
Urologic No underlying causes
Miscellaneous No underlying causes

Causes in Alphabetical Order

Causes in Alphabetical Order

Diagnostic Findings

History and Symptoms

  • Complete history with special attention to:
  • Neurologic
  • Ophthalmologic
  • Otolaryngologic

Physical Examination


  • Pupil size (light & dark)
  • Pupil response to light and convergence
  • Lid position



Medical Therapy

  • Adie's pupil - Pilcarpine .125% BID-QID
  • Migraines - pain meds, antidepressants, anticonvulsants, beta blockers, calcium channel blockers

Primary Prevention

  • Remove causative medication
  • Sunglasses to decrease light sensitivity

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