Acutely Red And Painful Eye

This is a common reason for an urgent surgery appointment. If a visit request is made, try to negotiate consultation in surgery, where optimal examination conditions and equipment are to hand. Carefully examine to assess acuity, state of the cornea and pupillary reflexes.

Published: 2nd August 2022 | Updated: 15th August 2022

Differential diagnosis

Common Diagnoses

  • Acute Conjunctivitis (Allergic or Infective)
  • Acute Iritis
  • Acute Glaucoma
  • Keratitis/Corneal Ulcer
  • Corneal Abrasion or Superficial Foreign Body (FB)

Occasional Diagnoses

  • Episcleritis
  • Scleritis
  • Keratoconjunctivitis Sicca
  • Trauma: Contusion and Penetrating Wound, Burns (Arc Eye and Chemical)
  • Orbital Cellulitis

Rare Diagnoses

  • Carotico-Cavernous Fistula (Rupture of Carotid Aneurysm)
  • Gout (Urate Deposits in Conjunctiva or Sclera)
  • Granulomatous Disorders: TB, Sarcoid, Toxoplasmosis
  • Onchocerciasis (Transmitted by Simulium Black Fly in Africa)
  • Tumour: Primary Eye Tumour, Invasion from Nasopharyngeal Tumour

Ready reckoner

Key distinguishing features of the most common diagnoses

Conjunctivitis IritisGlaucomaKeratitis/Ulcer Abrasion/FB
Visual DisturbanceNoYesYesPossiblePossible
Circumcorneal InjectionNoYesPossiblePossibleNo
Poor Pupil ReflexNoYesYesNoPossible
Hazy CorneaNoPossibleYesPossibleNo

Possible investigations

  • In practice, the problem is either easily treated by the GP (e.g. conjunctivitis or foreign body) or usually requires urgent referral. The GP’s role in investigating the painful red eye is therefore very limited.
  • Swab of discharge for microbiology: Very occasionally helpful in conjunctivitis not settling with usual treatment.
  • Blood: Raised WCC and ESR/CRP may support diagnosis of inflammatory disorders. Rheumatoid factor in suspected rheumatoid arthritis (RA); HLA-B27 usually positive in ankylosing spondylitis. The latter investigations would normally be performed at leisure rather than in the acute situation, when an underlying collagen disease is suspected (e.g. iritis).
  • Intraocular pressure measurement is essential if acute glaucoma is suspected. Usually done by a specialist.

Top Tips

  • If in serious doubt about the diagnosis, refer for urgent assessment – this is one scenario where a delay in treatment can have devastating consequences.
  • Don’t rely on the patient’s subjective assessment of blurring of vision – check the visual acuity.
  • Remember to evert the upper lid to check for a concealed foreign body.
  • Review the patient 24–48 hours after removing a foreign body to ensure that the cornea has healed.

Red Flags

  • Never use mydriatics when examining the red eye: You may precipitate acute glaucoma.
  • Bilateral red eye is usually caused by conjunctivitis. If unilateral, consider other causes.
  • Failure to recognise herpetic corneal ulcer or acute glaucoma may lead to permanent visual loss. If in doubt, refer for urgent specialist opinion.
  • Never instil steroid drops unless you are absolutely sure you are managing the problem correctly and have excluded herpetic ulceration.
  • Take a careful history when dealing with foreign bodies. Any possibility of a high-speed impact (e.g. grinding metal) requires urgent specialist assessment to exclude intraocular foreign body.
  • Contact lens wearers are at risk of a number of significant ocular problems – refer any unilateral red eye in a contact lens wearer for same day specialist assessment.
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Website disclaimer

Pulse Reference is based on the best-selling book Symptom Sorter.

The experts behind Pulse Reference are Dr Keith Hopcroft who is the co-author of Symptom Sorter, a GP in Essex and Pulse’s editorial advisor and Dr Poppy Freeman, a GP in Camden and also a clinical advisor to Pulse.

This website is for clinical guidance only and cannot give definitive diagnostic information. Practitioners should work within the limits of their individual professional practice, seek guidance when necessary and refer appropriately.