About This Page
This is a clinician-written, evidence-based summary aligned to the 2026 MLA Content Map. It is intended for medical students and junior doctors preparing for the UKMLA. Always cross-reference with NICE guidance, local protocols, and clinical judgement.
Key points
- Commonest cause of red eye in primary care — usually benign and self-limiting
- Bacterial: purulent discharge, sticky lids — most resolve in 5–7 days without treatment
- Viral: watery discharge, bilateral, URTI association — highly contagious
- Allergic: bilateral itching, watery/stringy discharge, chemosis — antihistamine drops
- Normal pupil and normal VA distinguish from serious red eye causes
Overview
Conjunctivitis is inflammation of the conjunctiva. Bacterial conjunctivitis is caused by Staphylococcus aureus, Streptococcus pneumoniae, or Haemophilus influenzae. Viral conjunctivitis is predominantly adenoviral and highly contagious. Allergic conjunctivitis is IgE-mediated. Chlamydial conjunctivitis should be suspected in sexually active young adults with chronic follicular conjunctivitis unresponsive to standard treatment.
Epidemiology
Accounts for approximately 1–2% of GP consultations. Bacterial conjunctivitis is more common in children. Allergic conjunctivitis affects ~15–20% of the population and is associated with atopy (eczema, asthma, allergic rhinitis).
Clinical Features
Symptoms
Red eye — diffuse conjunctival injection
Discharge: purulent (bacterial), watery (viral), watery/stringy (allergic)
Intense ITCHING — hallmark of allergic conjunctivitis
Eyelids stuck together on waking (bacterial)
Significant pain, photophobia, or reduced VA — suggests alternative diagnosis
Signs
Diffuse conjunctival injection
Normal pupil and normal visual acuity
Preauricular lymphadenopathy (viral)
Chemosis (allergic)
Corneal fluorescein staining — suggests keratitis, NOT conjunctivitis
Investigations
First-line
Clinical diagnosisBased on history and examination in most cases
Visual acuityShould be NORMAL — reduced VA requires urgent assessment
Fluorescein stainingExclude corneal involvement
Second-line
Conjunctival swabIf severe, recurrent, or neonatal
Chlamydia NAATIf chronic follicular conjunctivitis in sexually active adult
Specialist
Slit-lamp examinationIf concerned about keratitis or uveitis
1
Bacterial
- Most self-limiting in 5–7 days
- If not settling: chloramphenicol 0.5% drops QDS for 5 days (OTC for ≥2 years)
- Contact lens wearers: stop lenses, urgent referral if corneal involvement
2
Viral
- Self-limiting in 1–2 weeks
- Supportive: cool compresses, lubricating drops
- Antibiotics NOT effective
- Advise hand hygiene — highly contagious
3
Allergic
- Allergen avoidance, cold compresses, artificial tears
- Topical antihistamine: azelastine or olopatadine drops BD
- Topical mast cell stabiliser: sodium cromoglicate QDS
- Oral antihistamine if associated rhinitis
Complications
- Bacterial keratitis: Risk with contact lens wear
- Epidemic keratoconjunctivitis: Severe adenoviral with corneal infiltrates
- Neonatal ophthalmia: Gonococcal (day 2–5, hyperacute) or chlamydial (day 5–14)
UKMLA Exam Tips
- 1Conjunctivitis = diffuse redness + NORMAL pupil + NORMAL VA + discharge
- 2Purulent = bacterial. Watery + preauricular node = viral. Bilateral itching = allergic
- 3Red flags: reduced VA, photophobia, severe pain, abnormal pupil, corneal opacity, contact lens wearer
- 4Neonatal: day 2–5 = gonococcal (IV cefotaxime); day 5–14 = chlamydial (oral erythromycin)
- 5Contact lens wearer + painful red eye = KERATITIS until proven otherwise
practicetest your knowledge on ConjunctivitisApply what you've learnt with UKMLA-style questions from the iatroX Q-Bank — Ophthalmology and beyond.
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