Red Eye (General Approach)

🔍 When to Suspect

Any patient presenting with redness of the conjunctiva or sclera; the key is to differentiate benign conditions from sight-threatening emergencies through careful history and examination

From the full topic in The Ocean Library: Red Eye (General Approach)

🧭 When to suspect

"Red eye" is a presenting symptom, not a diagnosis. The clinical task in primary care is to separate the common, benign, self-limiting causes – infective and allergic conjunctivitis, subconjunctival haemorrhage, episcleritis – from the small number of sight-threatening emergencies: acute angle-closure glaucoma, microbial keratitis, anterior uveitis, scleritis, and penetrating or chemical injury.

Two screening questions do most of the diagnostic work: is the eye painful? and is vision affected? A painless eye with normal acuity is almost always benign; pain, photophobia, reduced vision, or contact-lens wear should raise concern. Visual acuity (VA) is the vital sign of the eye – document it in both eyes at every red-eye consultation, as it is the single best discriminator between surface irritation and serious intraocular disease.

Likely cause	Pain	Vision	Key distinguishing feature
Infective conjunctivitis	Gritty, no true pain	Normal	Diffuse redness with discharge (purulent → bacterial; watery → viral); often bilateral or sequential
Allergic conjunctivitis	Itch, no pain	Normal	Bilateral, itch-dominant, watery, stringy mucus; history of atopy
Subconjunctival haemorrhage	None	Normal	Flat, bright-red patch with a defined edge; white sclera elsewhere; no discharge
Episcleritis	Mild ache or none	Normal	Sectoral redness; vessels blanch with topical phenylephrine
Scleritis	Severe, deep, boring; wakes from sleep	May reduce	Violaceous deep redness that does not blanch; associated systemic autoimmune disease
Anterior uveitis (iritis)	Aching, photophobia	Blurred / reduced	Circumlimbal (ciliary) flush; small or irregular pupil
Microbial keratitis	Painful, foreign-body sensation	Reduced	Contact-lens wearer; corneal white spot or opacity; fluorescein-staining defect
Acute angle-closure glaucoma (AACG)	Severe, with headache, nausea, vomiting	Markedly reduced; haloes around lights	Fixed mid-dilated oval pupil; hazy cornea; hard, tender globe
Herpes zoster ophthalmicus (HZO)	Pain, dysaesthesia	Variable	Unilateral V1 vesicular rash; Hutchinson's sign (lesion on the nose tip)

Source: NICE · College of Optometrists

---