Red eye DDx


Red eye is a catch all term for the inflamed or injected external appearance of the eye, for which there are many causes.

I like Jeff Mann’s approach to red eye — he breaks the causes down into 3 groups:

  1. extra-ocular causes (e.g. orbital cellulitis, cavernous sinus thrombosis, carotid-cavernous fistula, cluster headache)
  2. external eye disease (e.g. eye lid and conjunctival disease)
  3. internal eye disease (e.g. iritis, glaucoma)

Once an extra-ocular cause is excluded (this will be discussed in a later post), a helpful approach is to divide up the causes of red eye as follows:

  1. Painless —  is there diffuse or localised redness?
  2. Painful?

The next step is to consider which structures are abnormal: Lid, conjunctiva, cornea, sclera, or anterior chamber?


Painless red eye

These can be classified according to whether the redness is diffuse or localised.

  • diffuse
    • usually this is an eyelid abnormality as most cases of conjunctivitis are painful: e.g. blepharitis, ectropion, trichiasis, entropion, eyelid lesion (e.g. tumour, stye)
  • localised
    • e.g. pterygium, corneal foreign body, ocular trauma, subconjunctival hemorrhage

If you’re stuck for a differential diagnosis, fall back on working through the anatomical components of the eye and running through a pathophysiological sieve.

Painful red eye

These can be classified according which structure is abnormal:

  • abnormal cornea
    • e.g. herpes simplex keratitis, corneal ulcer, marginal keratitis, corneal abrasion,
  • abnormal eyelid
    • e.g. chalazion/ stye, acute blepharitis, herpes zoster ophthalmicus
  • diffuse conjunctival injection
    • e.g. viral conjunctivitis, allergic conjunctivitis, bacterial conjunctivitis, dry eyes, acute glaucoma
  • ciliary injection/ scleral involvement
    • e.g. scleritis
  • anterior chamber involvement
    • e.g. acute anterior uveitis (iritis), hypopyon, hyphema

References and Links


CCC 700 6

Critical Care


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, 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.

| INTENSIVE | RAGE | Resuscitology | SMACC

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