Conjunctivitis
A superficial red, gritty, itchy or discharging eye caused by infection, allergy or irritation; preserved vision and a comfortable cornea support the diagnosis, while pain, photophobia, reduced vision, contact-lens use or neonatal disease needs urgent escalation.
Definition
Conjunctivitis is inflammation of the conjunctiva causing a red, gritty, itchy or discharging eye. It is commonly infective, allergic or irritant and usually benign, but red-eye red flags must be excluded.
Epidemiology
Common in primary care and community eye services. Viral disease often follows a respiratory infection and is contagious; bacterial disease is common in children; allergic disease is common with atopy and seasonal exposure. Neonatal conjunctivitis and contact-lens-associated red eye are distinct higher-risk presentations.
Pathophysiology
Infective, allergic or irritant stimuli dilate superficial conjunctival vessels and produce inflammatory discharge. Viral disease is often watery, bacterial disease may be purulent and allergic disease is itch-dominant with chemosis. Corneal, anterior-chamber or optic-nerve involvement produces pain, photophobia or vision change and moves the patient into a different urgent pathway.
First principles
Conjunctivitis is superficial inflammation, so sight should be preserved
Inflammation of the conjunctiva causes diffuse redness, grittiness and discharge without primarily involving the cornea, anterior chamber or optic nerve. Visual acuity should be essentially preserved and the pupil should react normally. Pain, photophobia or reduced vision should therefore prompt reconsideration of the diagnosis.1,2,3
The discharge and associated symptoms suggest the cause but do not prove it
Watery discharge and a preceding respiratory illness favour viral disease; sticky purulent discharge favours bacterial disease; itch and bilateral watery symptoms favour allergy. These patterns overlap, so the red-eye safety examination is more important than treating discharge colour as a stand-alone diagnostic test.1,2,4
The highest-risk groups are not routine conjunctivitis
A painful red eye in a contact-lens wearer may be microbial keratitis, while a neonate with a red sticky eye may have gonococcal or chlamydial ophthalmia. Corneal involvement, severe pain, photophobia or visual change can threaten sight and need urgent eye assessment.1,3,4
Treatment is cause-specific and antibiotics are not universal
Most viral conjunctivitis is self-limiting and does not respond to antibiotics. Bacterial disease may be managed with hygiene alone or topical antibiotic treatment when clinically appropriate; allergic disease needs allergen avoidance and anti-allergy treatment. Topical steroid drops should not be started in an undifferentiated red eye without specialist direction.1,2,5
Presentation
Diffuse red eye with grittiness, watery or sticky discharge and mild irritation, often bilateral in viral or allergic disease. Simple conjunctivitis should not cause marked pain, photophobia or reduced vision.1,2,3
Cardinal features
- Diffuse conjunctival redness
- Gritty or foreign-body sensation
- Watery discharge in viral or allergic disease
- Sticky or purulent discharge in bacterial disease
- Itch as the dominant symptom in allergic disease
- Preserved visual acuity and normal pupil reaction
Red flags
- Eye pain, photophobia or reduced or distorted vision
- Corneal opacity, ulcer, staining defect or marked circumcorneal injection
- Red eye in a contact-lens wearer
- A neonate or baby under 30 days with a red sticky eye
- Very severe unilateral redness, proptosis, restricted eye movements or systemic illness
- Symptoms not clearing as expected or recurrent unexplained disease
Investigations
Visual acuity, pupils and red-eye examination
Conjunctivitis is a clinical diagnosis, but documenting visual acuity, pupil reaction, pattern of injection, discharge, eyelids and pain identifies features inconsistent with an uncomplicated superficial process.
Expected finding: Essentially preserved acuity, a reactive pupil, diffuse conjunctival injection and no severe corneal or anterior-chamber signs.
1,2,3Fluorescein examination when pain, photophobia or corneal disease is possible
Fluorescein can reveal an abrasion, epithelial defect, dendritic pattern or corneal ulcer. A positive or concerning result changes the pathway to urgent eye assessment rather than routine conjunctivitis care.
Expected finding: No significant corneal staining in uncomplicated conjunctivitis.
1,4Contact-lens, neonatal and sexual-health assessment
Ask about contact lenses, lens hygiene, recent sexual exposure, neonatal age, birth history and maternal infection risk. These contexts increase the risk of microbial keratitis or gonococcal/chlamydial ophthalmia and require a different pathway.
Expected finding: No high-risk context in uncomplicated disease; a positive context triggers urgent specialist or sexual-health assessment.
1,3Conjunctival swab or targeted microbiology in selected cases
Do not swab routine mild disease. Consider microbiology or specialist testing for severe, recurrent, neonatal, sexually transmitted, atypical or treatment-resistant disease, when the result will change treatment or public-health action.
Expected finding: Routine cases need no microbiological confirmation; selected cases may identify a bacterial or viral cause.
1,3Management
| Step | Detail | Source |
|---|---|---|
| Triage the red eye before treating conjunctivitis | Arrange urgent eye assessment for pain, photophobia, reduced or distorted vision, corneal opacity or staining, marked circumcorneal injection, severe unilateral redness, proptosis or restricted eye movements. A red eye in a contact-lens wearer should be treated as possible microbial keratitis until assessed, not as routine conjunctivitis.1,3,4 | NICE CKS, infective conjunctivitis; NHS conjunctivitis safety-netting; Moorfields Eye Hospital |
| Use conservative care and hygiene for most uncomplicated cases | Clean crusts gently with clean water and a separate pad for each eye, use a cool compress for discomfort, wash hands regularly, avoid rubbing and do not share towels, pillows or eye drops. Do not wear contact lenses until the eyes are better. Routine exclusion from school or work is not required unless the person is very unwell.3,4 | NHS conjunctivitis and Moorfields Eye Hospital infective conjunctivitis advice |
| Manage suspected bacterial conjunctivitis proportionately | Most uncomplicated bacterial conjunctivitis is self-limiting. Consider a topical antibiotic such as chloramphenicol when the clinical picture, duration, severity, age and risk of spread make treatment appropriate; use the current BNF for formulation, contraindications and dosing. Do not use topical antibiotics to treat viral or allergic disease, and do not let them delay urgent contact-lens or neonatal assessment.1,5 | NICE CKS, infective conjunctivitis, and BNF chloramphenicol |
| Treat viral conjunctivitis with support and infection control | Viral conjunctivitis usually needs supportive care rather than antibiotics. Explain that symptoms can persist beyond the first few days, reinforce hand and linen hygiene, avoid shared towels and contact lenses, and reassess if pain, photophobia, visual change or corneal symptoms develop because adenoviral disease can involve the cornea.1,3,4 | NICE CKS, infective conjunctivitis; NHS and Moorfields Eye Hospital |
| Treat allergic conjunctivitis by reducing exposure and controlling itch | Reduce or avoid the trigger, use cool compresses and consider a topical antihistamine or mast-cell stabiliser such as ketotifen or sodium cromoglicate according to the BNF and the person's age, pregnancy and contact-lens circumstances. Avoid rubbing the eyes. Seek specialist advice before steroid eye drops.2,6,7 | NICE CKS, allergic conjunctivitis, and BNF anti-allergy eye-drop pages |
| Escalate neonatal and sexually transmitted conjunctivitis | A neonate or baby under 30 days with a red sticky eye needs urgent assessment. Consider gonococcal or chlamydial ophthalmia and arrange specialist, microbiology and sexual-health pathways because topical treatment alone may be inadequate and corneal damage can occur.3,1 | NHS conjunctivitis and NICE CKS infective conjunctivitis |
| Protect contact-lens wearers from microbial keratitis | Remove the lens, do not reinsert it and arrange urgent eye assessment for a red or painful contact-lens eye, especially with photophobia, reduced vision or a corneal spot. Do not simply issue routine chloramphenicol and delay examination; lens-associated keratitis can progress rapidly.1,4,5 | NICE CKS infective conjunctivitis and Moorfields Eye Hospital |
| Review if symptoms do not resolve or the diagnosis is uncertain | Arrange reassessment if symptoms have not cleared within 7 days, are worsening, recur frequently or do not fit the expected cause. Recheck acuity and cornea and consider keratitis, uveitis, glaucoma, nasolacrimal disease, chlamydial infection, blepharitis or another inflammatory cause.3,1,2 | NHS conjunctivitis and NICE CKS conjunctivitis guidance |
Illustrations
Differentials
Microbial keratitis or corneal ulcer
Pain, photophobia, reduced vision, contact-lens use or a corneal staining defect.
Anterior uveitis
Photophobia, ciliary injection, small or irregular pupil and anterior-chamber inflammation.
Acute angle-closure glaucoma
Severe pain, haloes, hazy cornea, fixed mid-dilated pupil and raised IOP.
Scleritis or episcleritis
Deep or sectoral scleral redness, with scleritis causing significant pain.
Subconjunctival haemorrhage
Painless flat red patch without discharge or visual change.
Complications
- Adenoviral keratoconjunctivitis with corneal involvement
- Contact-lens-associated microbial keratitis and corneal ulcer
- Neonatal gonococcal or chlamydial ophthalmia with corneal damage
- Chronic or recurrent allergic ocular inflammation
- Missed uveitis, glaucoma or other sight-threatening red-eye disease
Prognosis
Most uncomplicated cases resolve with hygiene and supportive or cause-specific treatment. Viral disease may persist for more than a few days, while corneal, neonatal and contact-lens complications can threaten vision and require urgent specialist care.
Guidelines
- Conjunctivitis infective (NICE CKS) (NICE)
- Conjunctivitis allergic (NICE CKS) (NICE)
- Conjunctivitis (NHS, 2024)
References
Evidence checked: 2026-08-03
This page is exam revision material, not medical advice, and must not be used for patient care. Always check drug doses against the BNF and current guidance. Full disclaimer.