Red eye
Exam Tips
- In OSCEs, document visual acuity early in every red-eye case before giving drops unless immediate chemical irrigation is required.
- Pain + photophobia + reduced vision + ciliary flush should be treated as sight-threatening until proven otherwise.
- A contact lens wearer with painful unilateral red eye is keratitis until excluded; same-day ophthalmology referral is expected.
- Do not palpate the globe if perforation is possible; protect eye and refer urgently.
- Topical steroid or topical anaesthetic prescriptions for undiagnosed red eye are unsafe in primary care.
- Differentiate episcleritis (often mild discomfort, sectoral redness, normal vision) from scleritis (deep severe pain, possible visual reduction).
- Subconjunctival haemorrhage is usually painless with normal vision and pupils; check blood pressure and anticoagulant history.
- Image reference: see standard ophthalmology textbook figure showing conjunctival injection vs ciliary flush and a slit-lamp image of corneal fluorescein staining.
Definition
Red eye is conjunctival, episcleral, scleral, or ciliary vessel injection that presents as ocular redness and may reflect anything from self-limiting conjunctivitis to immediately sight-threatening pathology. In UK clinical practice it is treated as a syndrome rather than a single diagnosis, with urgent triage driven by visual change, pain severity, photophobia, corneal involvement, trauma history, and pupil abnormalities.
Pathophysiology
Ocular redness occurs through vasodilatation and inflammatory hyperaemia of superficial or deep ocular vessels. Superficial conjunctival inflammation (for example viral/allergic conjunctivitis) typically causes diffuse injection with relatively preserved vision, whereas deeper inflammation (anterior uveitis, scleritis) and corneal or angle pathology produce ciliary/perilimbal injection, pain, and higher risk of visual loss. Acute angle-closure glaucoma arises from sudden obstruction of aqueous outflow causing rapid intraocular pressure rise, corneal oedema, iris ischaemia, and optic nerve risk. Corneal ulceration (especially in contact lens wearers) reflects epithelial breach with microbial invasion and stromal inflammation, which can progress to thinning and perforation. Chemical burns (notably alkali) penetrate ocular tissues rapidly via saponification, causing ongoing surface and limbal stem-cell damage even after initial exposure.
Risk Factors
- Contact lens wear (especially overnight use or poor lens hygiene)
- Recent ocular trauma, high-velocity metal/glass injury, or foreign body exposure
- Chemical exposure (alkali burns are particularly destructive)
- Recent intraocular surgery (risk of post-operative endophthalmitis)
- Autoimmune/inflammatory disease (for example ankylosing spondylitis, rheumatoid arthritis, SLE)
- Atopy/allergic disease
- Use of pupil-dilating or antimuscarinic drugs that can precipitate angle closure (for example phenylephrine eye drops, tricyclic antidepressants)
- Neonatal age (first 28 days) for ophthalmia neonatorum
- Hypertension or anticoagulant therapy in subconjunctival haemorrhage
Clinical Features
Symptoms
- Redness (unilateral or bilateral) with onset and duration pattern
- Eye pain (mild irritation to severe deep pain)
- Photophobia
- Blurred vision or reduced acuity
- Foreign body sensation or grittiness
- Discharge (watery, mucoid, or purulent)
- Itch (suggests allergic conjunctivitis)
- Headache, haloes around lights, nausea/vomiting (suggest acute angle closure)
Signs
- Reduced visual acuity on Snellen testing
- Pattern of injection: diffuse conjunctival vs ciliary/perilimbal flush
- Corneal fluorescein uptake (abrasion/ulcer) or corneal haze
- Pupil abnormality (fixed mid-dilated pupil in acute glaucoma; small/irregular pupil in uveitis)
- Pain on pupillary constriction (ciliary spasm/uveitis)
- Unequal or distorted pupils, RAPD, or abnormal light reflexes
- Hyphaema or hypopyon in anterior chamber
- Localized sharply demarcated subconjunctival haemorrhage with normal vision/pupil
- Eyelid swelling or retained subtarsal foreign body after upper lid eversion
Investigations
Management
Lifestyle Modifications
- Treat as an ocular triage problem first: same-day emergency eye referral for reduced vision, moderate-severe pain, photophobia, ciliary flush, corneal staining/ulcer, abnormal pupils, hypopyon/hyphaema, chemical injury, penetrating/high-velocity trauma, neonatal conjunctivitis, contact lens-related painful red eye, or suspected endophthalmitis
- Stop contact lens wear immediately; keep lenses/case for possible culture and do not restart until symptom resolution and specialist review if keratitis suspected
- Immediate copious irrigation for chemical injury before/while arranging urgent transfer
- Avoid eye rubbing and share infection-control advice (hand hygiene, avoid sharing towels) for conjunctivitis
- Do not patch an infected eye and avoid driving if vision is impaired
Pharmacological Treatment
Lubricants for dry eye/irritative symptoms
- Hypromellose 0.3% eye drops, 1 drop 3-4 times daily as needed
- Carbomer 0.2% gel, 1 drop up to 4 times daily
Useful for mild non-infective irritation; preservative-free preparations preferred with frequent dosing or contact lens intolerance.
Topical antibacterial for uncomplicated acute bacterial conjunctivitis (when treatment indicated)
- Chloramphenicol 0.5% eye drops: 1 drop every 2 hours for 48 hours, then every 4 hours while awake to complete 5 days
- Chloramphenicol 1% eye ointment: 3-4 times daily (or at night as adjunct) for 5 days
Not for contact lens-associated red eye or suspected keratitis (urgent ophthalmology required). Advise to seek review if pain, photophobia, or visual reduction develops.
Allergic conjunctivitis therapy
- Sodium cromoglicate 2% eye drops, 1 drop four times daily
- Olopatadine 0.1% eye drops, 1 drop twice daily
Add oral non-sedating antihistamine if systemic allergy symptoms coexist.
Emergency treatment in suspected acute angle-closure glaucoma (specialist/emergency protocol)
- Acetazolamide 500 mg stat (oral or IV), then 250 mg four times daily
- Timolol 0.5% eye drops, 1 drop affected eye
- Pilocarpine 2% eye drops, frequent dosing after initial pressure reduction
- Apraclonidine 1% eye drops, 1 drop
Urgent ophthalmology same day; definitive laser iridotomy needed. Check contraindications: avoid beta-blocker drops in asthma/bradycardia/heart block; acetazolamide caution in sulfonamide allergy and renal impairment.
Anterior uveitis (ophthalmology-led)
- Prednisolone acetate 1% eye drops (intensive initial regimen, then taper by specialist)
- Cyclopentolate 1% eye drops up to three times daily
Topical steroids should not be started in undifferentiated red eye in primary care because they can worsen herpetic keratitis and delay diagnosis.
Microbial keratitis/corneal ulcer (ophthalmology emergency)
- Ciprofloxacin 0.3% eye drops, intensive hourly regimen initially
- Fortified topical antibiotics per culture in severe ulcer
Contact lens wearers need urgent same-day specialist care due to Pseudomonas risk; do not delay referral.
Surgical / Interventional
- Laser peripheral iridotomy for acute angle-closure glaucoma (usually both eyes, affected first)
- Corneal/superficial foreign body removal when indicated
- Primary repair of penetrating globe injury or corneal laceration
- Intravitreal tap-and-inject +/- vitrectomy for endophthalmitis
- Corneal transplantation in severe scarring/perforation sequelae
Complications
- Permanent visual impairment or blindness from delayed recognition of glaucoma, keratitis, or endophthalmitis
- Corneal scarring, thinning, or perforation after ulcerative keratitis
- Secondary glaucoma or posterior synechiae in recurrent/chronic uveitis
- Globe perforation in severe scleritis
- Orbital/intraocular spread of infection in severe bacterial disease
- Neonatal systemic complications (for example chlamydial pneumonia)
Prognosis
Prognosis depends on cause and speed of escalation. Benign causes such as viral/allergic conjunctivitis, episcleritis, and subconjunctival haemorrhage usually resolve without visual sequelae, whereas acute glaucoma, corneal ulcer, penetrating trauma, and endophthalmitis can cause rapid and irreversible sight loss if same-day specialist treatment is delayed.
Sources & References
✅NICE Guidelines(1)
- Red eye[overview]
📖Textbook References(1)
- David Randall PhD MRCP (Editor), John Booth PhD MRCP (Editor), K - Kumar and Clark's Clinical Medicine (2025, American Elsevier Publishing Co.) - libgen.li.pdf(pp. 610)[context]