Key Facts

The acute red eye requires structured assessment to distinguish between common benign causes and sight-threatening emergencies needing urgent ophthalmology referral.

Epidemiology

• One of the most common reasons for GP and A&E ophthalmic consultations
• Conjunctivitis accounts for ~35% of all red eye presentations
• Subconjunctival haemorrhage: very common, benign
• Sight-threatening causes (AACG, keratitis, scleritis, uveitis): ~10-15% of presentations

Aetiology

• Infective: bacterial/viral conjunctivitis, keratitis (bacterial, viral, fungal, Acanthamoeba)
• Inflammatory: anterior uveitis, scleritis, episcleritis
• Vascular: subconjunctival haemorrhage
• Pressure-related: acute angle-closure glaucoma
• Allergic: allergic conjunctivitis
• Traumatic: corneal abrasion, foreign body, chemical burn

Pathophysiology

• Conjunctival injection: dilation of superficial conjunctival vessels; moves with conjunctiva
• Ciliary flush: dilation of deep ciliary vessels around the limbus (circumcorneal); does NOT move with conjunctiva; indicates deeper inflammation (uveitis, keratitis, AACG)
• The distinction between conjunctival and ciliary injection is the most important clinical sign in acute red eye assessment

Key Features by Diagnosis

• Conjunctivitis: gritty, discharge (purulent if bacterial, watery if viral), normal vision, no photophobia
• Anterior uveitis: deep aching pain, photophobia, ciliary flush, miosis, reduced vision, cells/flare
• AACG: severe pain, nausea/vomiting, haloes around lights, semi-dilated fixed pupil, hazy cornea, rock-hard eye
• Keratitis: pain, photophobia, watering, reduced vision, corneal opacity, fluorescein uptake
• Scleritis: deep boring pain (may wake from sleep), violaceous hue, tender globe, may have systemic disease (RA, GPA)
• Episcleritis: mild discomfort, sectoral redness, benign, self-limiting
• Subconjunctival haemorrhage: bright red, painless, no visual change, resolves spontaneously

Red Flags (Urgent Ophthalmology Referral)

• Reduced visual acuity
• Severe pain
• Photophobia
• Ciliary flush (circumcorneal injection)
• Corneal opacity or ulceration
• Fixed or semi-dilated pupil
• History of trauma or chemical exposure
• Contact lens wearer with red painful eye

Bedside

• Visual acuity (Snellen chart): essential in every red eye assessment
• Pupil examination: size, shape, reactivity (RAPD)
• Pen torch examination: corneal clarity, anterior chamber depth, pupil
• Fluorescein staining + blue light: corneal epithelial defects (dendritic ulcer in HSV, corneal ulcer)
• IOP measurement (tonometry): if available; essential if AACG suspected

Bloods

• Not routinely needed for acute red eye
• If uveitis: consider FBC, ESR/CRP, HLA-B27, syphilis serology, ACE level (sarcoidosis), CXR
• If scleritis: autoimmune screen (RF, anti-CCP, ANCA)

Imaging

• Not usually required
• CXR: if sarcoidosis suspected (uveitis)

Special Tests

• Slit lamp examination (ophthalmology): detailed anterior segment assessment, cells/flare, IOP
• Corneal scrape: for culture in suspected microbial keratitis
• B-scan ultrasound: if posterior scleritis suspected

Non-pharmacological

• Thorough history and examination to differentiate cause
• Visual acuity measurement in all cases
• Do NOT patch a potentially infected eye

Pharmacological

• Bacterial conjunctivitis: chloramphenicol 0.5% drops QDS (or fusidic acid BD) for 5-7 days; often self-limiting
• Viral conjunctivitis: self-limiting; lubricant drops; hygiene advice
• Allergic conjunctivitis: sodium cromoglicate drops QDS; antihistamine drops (olopatadine); oral antihistamine
• Anterior uveitis: SPECIALIST — topical steroids (dexamethasone 0.1% drops), cycloplegic (cyclopentolate 1% drops) to prevent posterior synechiae
• AACG: EMERGENCY — pilocarpine 2% drops, timolol 0.5% drops, IV acetazolamide 500mg, analgesia + antiemetic; definitive: YAG laser iridotomy
• Keratitis: SPECIALIST — intensive topical antibiotics (fortified gentamicin + cefuroxime hourly); no steroids until infection controlled
• Scleritis: SPECIALIST — oral NSAIDs (flurbiprofen 100mg TDS); severe: systemic immunosuppression
• NEVER prescribe topical steroids in primary care

Surgical/Interventional

• AACG: YAG laser peripheral iridotomy (definitive; both eyes)
• Corneal transplant: for severe keratitis with perforation

Referral Criteria

• Same-day/emergency ophthalmology: reduced vision, severe pain, AACG, suspected keratitis, hypopyon, penetrating injury, chemical burn
• Urgent (24-48h): anterior uveitis, scleritis
• Routine: recurrent episcleritis, chronic conjunctivitis not responding to treatment

• Conjunctivitis: self-limiting in most cases; full recovery
• Anterior uveitis: good prognosis with prompt treatment; recurrence in 50%
• AACG: sight-threatening if untreated; good outcome with prompt treatment
• Microbial keratitis: corneal scarring may reduce vision permanently; contact lens-related has better prognosis than Acanthamoeba
• Scleritis: requires systemic treatment; may indicate serious underlying disease

Acute Red Eye — Emergency vs Non-Emergency