Red Eye: Triage & Differential Diagnosis
Separate uncomplicated surface irritation from urgent corneal, intraocular and orbital disease.
Quick revision ↓ Medical Dictionary
01A red eye is a sign
Ask about pain, discharge, itch, photophobia, reduced vision, contact lenses and recent surgery or injury. Measure acuity and compare eyes. Severe pain, light sensitivity or reduced vision should prevent casual labelling as conjunctivitis. The degree of visible redness alone is an unreliable guide to the severity of the underlying problem.
02Surface patterns
Itch with bilateral watering suggests allergy, while discharge and gritty discomfort may accompany conjunctivitis. A sharply demarcated subconjunctival bleed may look dramatic despite preserved vision and little discomfort. These patterns guide a differential, not an automatic diagnosis. Trauma, recurrent bleeding or systemic concerns may require additional assessment even when the surface appearance seems familiar.
03Corneal and intraocular clues
A focal corneal opacity, epithelial defect, ciliary injection or abnormal pupil increases concern for deeper disease. Keratitis, anterior uveitis and acute angle closure may all cause a painful red eye. Appropriate examination and urgent ophthalmic review distinguish them. Do not start unsupervised steroid drops in an undiagnosed red eye because infection may worsen.
04Context changes risk
Contact-lens wear increases concern for microbial keratitis, and recent ocular surgery raises concern for postoperative infection. A newborn with marked discharge needs urgent assessment. Fever, proptosis or painful restricted eye movements suggests orbital involvement. Ask these contextual questions early rather than waiting until routine surface treatment has failed.
05Choose a safe pathway
Minor surface disease may be managed through an appropriate local pathway with review advice, but red flags need urgent specialist assessment. Document vision, pain, pupil findings and any corneal abnormality. Explain that increasing pain, photophobia or reduced vision requires prompt reassessment. A short period of symptom improvement does not remove the need to evaluate persistent warning signs.
High-Yield Revision
- Check vision in a red eye.
- Contact lenses and recent surgery raise the stakes.
- Avoid empirical steroid drops without a diagnosis and supervision.
Common Pitfalls
- Diagnosing conjunctivitis from redness alone.
- Using the amount of redness as a severity score.
References & Further Reading
Read the relevant guideline sections alongside these original clinical teaching cases. Local pathways, available services and individual patient factors determine care.
Reference review: 28 September 2026. Consult current local protocols for prescribing, procedures and escalation.