Author: Claude (AI), from PubMed abstracts · Reviewed by: Dr Mina Abdelmseih · Reviewed: 2026-11-15 · Review due: 2027-11-15

Educational content only. Not personalised medical advice. Clinical decisions remain the responsibility of the treating clinician.

The red eye: triage

Red eye is one of the main reasons for urgent consultation in primary care and eye emergency services; most causes are benign, but not every red eye is conjunctivitis [S11]. The task at first contact is to recognise the warning signs of sight- or life-threatening disease, such as keratitis, uveitis, glaucoma, scleritis, trauma, orbital cellulitis and cavernous sinus thrombosis, and refer them promptly [S2] [S11].

Key points - Measure visual acuity and examine the pupils in every red eye [S4]. - Photophobia and anisocoria (smaller pupil in the red eye) are among the most useful bedside signs of serious eye disease [S5]. - Contact lens wearers with a red eye may have early microbial keratitis, which can look subtle at first [S12]. - Acute infective conjunctivitis is usually self-limiting; antibiotics give only a small benefit, so a delayed or no-antibiotic approach is reasonable [S1] [S3]. - No single sign reliably separates viral from bacterial conjunctivitis [S8].

Evidence last checked: 2026-10-17 (PubMed abstracts).

Red flags

Refer urgently if any of these are present [S2]: - Vision loss. - Severe pain not relieved by topical anaesthetic. - Copious purulent discharge. - Corneal involvement. - Traumatic eye injury or chemical exposure [S2] [S4]. - Recent eye surgery. - Distorted pupil. - Herpes infection or recurrent infections. - A need for topical steroids.

Additional findings that point to serious disease: - Photophobia elicited by direct light (LR 8.3), indirect light (LR 28.8) or the finger-to-nose convergence test (LR 21.4) [S5]. - Anisocoria with the smaller pupil in the red eye and a difference of more than 1 mm (LR 6.5) [S5]. - Contact lens wear with a red, painful eye [S12]. - Features of extraocular disease such as orbital cellulitis or cavernous sinus thrombosis, which are systemically severe [S11].

Recognise it

• Common causes: conjunctivitis (the most common), blepharitis, corneal abrasion, foreign body, subconjunctival haemorrhage, keratitis, iritis, glaucoma, chemical burn and scleritis [S2].
• Groups by seriousness: ocular surface disease (generally benign), intraocular disease such as uveitis, glaucoma, scleritis and trauma (ophthalmically severe), and extraocular disease such as orbital cellulitis and cavernous sinus thrombosis (systemically severe) [S11].
• Conjunctivitis: viral, bacterial or allergic; it is usually self-limiting but symptoms can last up to three weeks [S10]. Bacterial conjunctivitis was more common in children (71% vs 16% viral), and viral more common in adults (78% vs 16% bacterial), on limited evidence [S8].

Confirm it

• Basic examination: visual acuity, pupils, visual fields, penlight or slit-lamp examination of the anterior segment and direct fundoscopy [S4]. The cause is diagnosed through a detailed history and careful examination [S2].
• Bedside clues for conjunctivitis type:
• Favour viral: pharyngitis (LR+ 5.4 to 9.9), preauricular lymphadenopathy, contact with another person with red eye [S8].
• Favour bacterial: mucopurulent discharge (LR+ 2.1), otitis media [S8]; complete conjunctival redness obscuring tarsal vessels (LR 4.6), observed purulent discharge (LR 3.9) and both eyes matted in the morning (LR 3.6) [S5].
• Against bacterial: no redness visible from 20 feet (LR 0.2) and no morning gluing of either eye (LR 0.3) [S5].
• Swabs: because clinical diagnosis is difficult, a swab for PCR and culture can help confirm the cause [S10].

Manage it

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Tier A (primary care / no specialist)

1. Screen every patient against the red flags above; red flags are especially valuable where investigations are minimal [S7].
2. Simple conjunctivitis: manage conservatively. Prescribe antibiotics after a delay if symptoms do not improve within 3 days, or not at all, as recommended in [S1]. In an individual patient data meta-analysis of 3 trials (622 patients), 80% given antibiotics and 74% of controls were cured at day 7; benefit was small and seen mainly with purulent discharge or mild redness [S3].
3. Give written information on the self-limiting course; this was the most effective way to manage the condition and improve satisfaction [S1].
4. Contact lens wearer with suspected bacterial keratitis and no confirmed timely ophthalmology review: frequent topical fluoroquinolone may be needed, because commonly used antibiotics may not cover the cornea adequately [S12]. Doses are not given in the abstract; follow local formularies.
5. Trauma and chemicals: irrigate chemical injuries immediately; cover a suspected globe injury with a metal shield and refer [S4].

Tier B (general eye clinic)

• Examine the anterior segment with the slit lamp to identify keratitis, uveitis, glaucoma or scleritis [S4] [S11].
• Treatment follows the underlying cause [S2].

Tier C (specialist centre)

• Not specifically addressed by these sources; see the condition-specific articles in this library.

Refer when

Pitfalls

• Labelling every red eye as conjunctivitis [S11].
• Skipping visual acuity and the pupil check [S4] [S5].
• Missing early keratitis in contact lens wearers [S12].
• Routine antibiotics for conjunctivitis may delay diagnosis of other serious red eye conditions [S1].
• Overconfidence: many emergency department foundation doctors lack confidence with fundoscopy and the slit lamp; formal eye training in emergency departments was considered inadequate [S9].

Evidence notes

• The red-flag list for referral is expert opinion from narrative reviews [S2] [S11]; only the bedside-sign likelihood ratios come from systematic reviews [S5] [S8], and some confidence intervals are very wide (photophobia to indirect light: LR 28.8, 95% CI 1.8 to 459) [S5].
• Prevalence of viral versus bacterial conjunctivitis in adults comes from a single study [S8].
• Not covered by these sources: adenoviral outbreak control, neonatal conjunctivitis, allergic conjunctivitis treatment and specific drug doses.

Related articles

• Acute Primary Angle Closure
• Bacterial keratitis
• Anterior Uveitis
• Scleritis

References

See the numbered source list below. Each marker [S#] links to its PubMed and DOI record.