Suspect herniation due to an intracranial mass lesion as a cause of fixed dilated pupil in an unconscious patient. A fixed dilated pupil in an awake patient is NOT due to herniation.
Pharmacologic blockade is the most common cause of a fixed dilated pupil in an otherwise normal healthy patient.
A single fixed dilated (mydriatic) pupil can be caused by:
- Pharmacological blockade– typically topical mydriatic drugs used to facilitate ophthalomological examinations.
- anticholinergic drugs: e.g. atropine, cyclopentolate and tropicamide
- alpha1-agonists: phenylephrine.
- Oculomotor nerve palsy (3rd cranial nerve)
- parasympathetic nerves are in the superficial parts of the nerve, so tend to be more vulnerable to compressivelesions and spared by vascular lesions (e.g. diabetes mellitus).
- If an acute third nerve palsy is accompanied by pupillary mydriasis an aneurysm arising from the posterior communicating artery must be excluded.
[See a Spider called Willis for an easy way to remember the components of the Circle of Willis and its relations.]
- Holmes-Adie pupil (tonic phase)
- post-traumatic iridocyclitis (e.g. direct facial trauma)
- acute closed-angle glaucoma
- ocular prosthesis – the normal pupil may be relatively constricted due to ambient light.
Chris is an Intensivist and ECMO specialist at the Alfred ICU in Melbourne. He is also a Clinical Adjunct Associate Professor at Monash University. He is a co-founder of the Australia and New Zealand Clinician Educator Network (ANZCEN) and is the Lead for the ANZCEN Clinician Educator Incubator programme. He is on the Board of Directors for the Intensive Care Foundation and is a First Part Examiner for the College of Intensive Care Medicine. He is an internationally recognised Clinician Educator with a passion for helping clinicians learn and for improving the clinical performance of individuals and collectives.
After finishing his medical degree at the University of Auckland, he continued post-graduate training in New Zealand as well as Australia’s Northern Territory, Perth and Melbourne. He has completed fellowship training in both intensive care medicine and emergency medicine, as well as post-graduate training in biochemistry, clinical toxicology, clinical epidemiology, and health professional education.
He is actively involved in in using translational simulation to improve patient care and the design of processes and systems at Alfred Health. He coordinates the Alfred ICU’s education and simulation programmes and runs the unit’s education website, INTENSIVE. He created the ‘Critically Ill Airway’ course and teaches on numerous courses around the world. He is one of the founders of the FOAM movement (Free Open-Access Medical education) and is co-creator of litfl.com, the RAGE podcast, the Resuscitology course, and the SMACC conference.
His one great achievement is being the father of three amazing children.
On Twitter, he is @precordialthump.