The Red Eye Challenge

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.

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.

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

1. severe eye pain (unrelieved by topical anesthetics)
2. impaired vision
3. poorly reactive pupils
4. abnormal slit lamp examination +/- abnormal intra-ocular pressure

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

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

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

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

Severe eye aching

Prominent photophobia

Impaired vision

Cloudy cornea

Corneal opacification

Circumcorneal conjunctival injection

Cloudy anterior chamber

Pain on eyeball palpation

Proptosis

Impaired, or painful, extraocular eye movements

Fever, toxic appearance

Hyperpurulent discharge from an “angry” eye

Prominent nausea and vomiting

Small, irregular, poorly-reactive pupil

Fixed mid-dilated pupil

Increased intra-ocular pressure

History of connective tissue disease, or granulomatous disease

• 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]