The Red Eye Challenge

aka Ophthalmology Befuddler 002

Things are humming along nicely in the ‘Fast track’ area of the emergency department. You check the triage note of the next patient – RED EYE is written capitals.


Q1. There are many causes of ‘red eye’ — how can they broken down as an approach to diagnosis and management?
Answer and interpretation

Of course there are myriad ways of doing this. I like Jeff Mann’s approach — he has a simple way of breaking the causes down into 3 groups:

  • extra-ocular causes: (e.g. orbital cellulitis, cavernous sinus thrombosis, carotid-cavernous fistula, cluster headache)
  • external eye disease: (e.g. eye lid and conjunctival disease)
  • 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:

  • Painless —  is there diffuse or localised redness?
  • Painful?

The next step is to consider which structures are abnormal:

  • Lid, conjunctiva, cornea, sclera, or anterior chamber?

This approach gets you off to a good start in narrowing down the causes of a red eye.

Q2. What are the causes of a painless red eye?
Answer and interpretation

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

  • diffuseusually this is an eyelid abnormality as most cases of conjunctivitis are painful: e.g. blepharitis, ectropion, trichiasis, entropion, eyelid lesion (e.g. tumour, stye)
  • localisede.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.

Q3. What are the causes of a painful red eye?
Answer and interpretation

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

Q4. What 4 features usually suggest an internal cause of a red eye?
Answer and interpretation
  1. severe eye pain (unrelieved by topical anesthetics)
  2. impaired vision
  3. poorly reactive pupils
  4. abnormal slit lamp examination +/- abnormal intra-ocular pressure

Q5. What 6 features on history and exam suggest an external cause for red eye?
Answer and interpretation
  1. pain sensation is usually itching, gritty, scratching, or burning (not a deep-seated ache)
  2. pain is significantly improved by topical anesthetics
  3. eye discharge is common: (watery, mucoid or purulent depending on etiology)
  4. photophobia and blepharospasm may be present
  5. visual acuity is usually normal or near-normal (there may be some blurriness)
  6. preauricular lymphadenopathy may be present. e.g. viral or chlamydial conjunctivitis

Q6. What 7 features on exam should be present if the cause of a red eye is not serious?
Answer and Interpretation
  1. cornea clear
  2. anterior chamber clear
  3. pupils normal in size and reactivity
  4. visual acuity normal or near-normal
  5. extraocular eye movements normal
  6. proptosis absent
  7. eyeball is not tender on palpation

Q7. What is the likely diagnosis of a red eye in a middle-aged woman with the following findings?
Quick Quiz…

Mid-dilated unreactive pupil, steamy cornea, peri-orbital pain, nausea/vomiting and increased intra-ocular pressure


angle closure glaucoma

Small irregular pupil, deep-seated eye pain that is worse on eye movement and accommodation, consensual photophobia and positive slit lamp signs of flare and cells



Deep-seated eye pain that is worse at rest and at night, pain on palpation of the eye and violaceous appearance of the sclera



Proptosis, congested chemosis, painful external ophthalmoplegia, and visual loss with a relative afferent pupillary defect


orbital cellulitis or cavernous sinus venous thrombosis

Q9. What potentially serious causes of a red eye are suggested by the following features on history or examination?
Quick Quiz…

Severe eye aching


Iritis, keratitis, acute angle-closure glaucoma, scleritis, orbital cellulitis, cavernous sinus thrombosis (CST)

Prominent photophobia


Iritis, keratitis

Impaired vision


Iritis, keratitis, acute angle-closure glaucoma, orbital cellulitis, CST

Cloudy cornea


Keratitis, acute angle-closure glaucoma

Corneal opacification


Keratitis – chemical or infectious

Circumcorneal conjunctival injection


Iritis, keratitis

Cloudy anterior chamber



Pain on eyeball palpation


Scleritis (+++), orbital cellulitis, CST



Orbital cellulitis, CST, posterior scleritis

Impaired, or painful, extraocular eye movements


Orbital cellulitis

Fever, toxic appearance


Orbital cellulitis (+), CST (++)

Hyperpurulent discharge from an “angry” eye


Gonococcal conjunctivitis/endophthalmitis

Prominent nausea and vomiting


Acute angle-closure glaucoma

Small, irregular, poorly-reactive pupil



Fixed mid-dilated pupil


Acute angle-closure glaucoma

Increased intra-ocular pressure


Acute angle-closure glaucoma, iritis (secondary complication)

History of connective tissue disease, or granulomatous disease


Iritis, scleritis

  • Mahmood AR, Narang AT. Diagnosis and management of the acute red eye. Emerg Med Clin North Am. 2008 Feb;26(1):35-55, vi. PMID: 18249256.
  • NSW Statewide Opthalmology Service. Eye Emergency Manual — An illustrated Guide. [Free PDF]

Ophthalmology Befuddler 700


Ophthalmology Befuddler





On Twitter, he is @precordialthump.

| INTENSIVE | RAGE | Resuscitology | SMACC

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