Mydriasis
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 1 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

## Causes in Alphabetical Order

## 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

## Physical Examination

## 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