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Probability diagnosis


  • bacterial

  • adenovirus

  • allergic

Serious disorders not to be missed

Acute glaucoma


  • acute iritis

  • choroiditis

Corneal ulcer

Corneal injury: abrasion/foreign body

Herpes simplex keratitis

Microbial keratitis (e.g. fungal, amoeba, bacterial)

Herpes zoster ophthalmicus

Penetrating injury


Orbital cellulitis

Pitfalls (often missed)


Foreign body (esp. IOFB)


Ultraviolet light ‘keratitis’



  • cavernous sinus arteriovenous fistula

  • primary tumour of eye

Masquerades checklist

Drugs (hypersensitivity)

Thyroid disorder (hyperthyroidism)

Key history

The five essentials of the history are:

  • history of trauma, especially as indicator of intraocular foreign body (IOFB)

  • vision

  • the degree and type of discomfort

  • presence of discharge

  • presence of photophobia.

Consider association with spondyloarthropathies.

Key examination

When examining the unilateral red eye keep the following diagnoses in mind:

  • trauma

  • foreign body, including IOFB

  • corneal ulcer

  • iritis (uveitis)

  • viral conjunctivitis (commonest type)

  • acute glaucoma

The four essentials of the examination are:

  • testing and recording vision

  • meticulous inspection under magnification (slit lamp is ideal)

  • testing the pupils

  • testing ocular tension

Key investigations

  • May include swab of discharge for MC, visual acuity


  • HLAB27

  • Consider specialist referral

Diagnostic tips

  • A purulent discharge indicates bacterial conjunctivitis.

  • A clear or mucus discharge indicates viral or allergic conjunctivitis.

  • Be alert for the unilateral red eye: think beyond the conjunctivitis trio. It may be a corneal ulcer, keratitis, foreign body, trauma, uveitis or acute glaucoma.

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