Mydriasis

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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

Overview

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.

Pathophysiology

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

Common Causes

• 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

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

• 3rd cranial nerve disorder
• Acute closed angle glaucoma
• Adie's tonic pupil
• Adregenic agents
• Amphetamines
• Antihistamines
• Antipsychotic agents
• Apraclonidine
• Atropine
• Autonomic seizure
• Benign episodic mydriasis
• Brain death
• Cerebral oedema
• Chlorpheniramine
• Chlorpromazine
• Cinnarizine
• Cocaine
• Coma
• Congenital mydriasis
• 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
• Pourfour du petit syndrome
• Prochlorperazine
• Psychedelic mushrooms
• Raised intracranial pressure
• Seizures
• Serotonin syndrome
• Sibutramine
• Systemic anticholinergics
• Tetrahydrozoline
• Third nerve palsy
• Trauma
• Tricyclic antidepressants
• Tropicamide
• Weber syndrome

Diagnostic Findings

History and Symptoms

• Complete history with special attention to:

• Neurologic
• Ophthalmologic
• Otolaryngologic

Eyes

• 
  Pupil dilated using anaesthetic and muscle relaxant
• 
  Pupillary response

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

MRI

• MRI to check for third cranial nerve palsy

Treatment

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

Related Chapters

• Miosis
• Anisocoria