Key Facts

Conjunctivitis is usually benign and self-limiting but must be distinguished from sight-threatening causes of red eye. Bacterial conjunctivitis improves without treatment in 65% within 5 days.

Epidemiology

• Most common eye condition seen in primary care
• Viral conjunctivitis: most common overall; highly contagious
• Bacterial: more common in children
• Allergic: affects 15-20% of population (often with atopy)

Aetiology

• Bacterial: S. aureus, S. pneumoniae, H. influenzae, Moraxella; gonococcal (hyperacute); chlamydial (chronic)
• Viral: adenovirus (most common), herpes simplex, enterovirus
• Allergic: seasonal (pollen), perennial (house dust mite), vernal, atopic

Pathophysiology

• Infection or allergen exposure → conjunctival inflammation → vasodilation (redness), increased vascular permeability (oedema/chemosis), mucus and inflammatory cell secretion (discharge)
• Viral: lymphocytic infiltrate; often associated with conjunctival follicles
• Bacterial: neutrophilic infiltrate; purulent discharge
• Allergic: mast cell degranulation → histamine release → itch, oedema, watering

Bacterial

• Purulent/mucopurulent discharge
• Crusting of eyelids (stuck together on waking)
• Usually starts unilateral, becomes bilateral
• Mild discomfort (gritty)
• Normal vision

Viral

• Watery discharge
• Preauricular lymphadenopathy
• Often follows or accompanies URTI
• Bilateral (may start unilateral)
• Follicular reaction on eversion of lid
• Highly contagious (2-3 week course)

Allergic

• Itching (hallmark — distinguishes from infective)
• Watery discharge
• Bilateral
• Chemosis (conjunctival oedema)
• Seasonal pattern (hay fever association)
• Papillary reaction on lid eversion

Red Flags (NOT Simple Conjunctivitis)

• Reduced visual acuity
• Severe pain
• Photophobia
• Corneal involvement (opacity, ulcer)
• Contact lens wearer
• Neonatal (ophthalmia neonatorum)
• Hyperacute onset with profuse purulent discharge (gonococcal)

Bedside

• Visual acuity (must be normal in simple conjunctivitis)
• External eye examination (discharge character, lid involvement)
• Evert upper lid (follicles vs papillae)
• Fluorescein staining (exclude corneal involvement)

Bloods

• Not needed for routine conjunctivitis

Imaging

• Not needed

Special Tests

• Conjunctival swab: if gonococcal or chlamydial suspected (MC&S + NAAT)
• Slit lamp: if uncertain diagnosis or red flags
• Neonatal: urgent conjunctival swab for gonococcus and chlamydia

Non-pharmacological

• Hygiene: hand washing, avoid sharing towels; avoid rubbing eyes
• Cool compresses: allergic conjunctivitis
• Lid cleaning: warm compresses, cotton wool with cooled boiled water
• Remove contact lenses until fully resolved

Pharmacological

• Bacterial:
  • Chloramphenicol 0.5% drops QDS + 1% ointment at night for 5-7 days (first-line)
  • Fusidic acid 1% drops BD for 7 days (alternative; better adherence)
  • Most cases self-limit within 5-7 days even without antibiotics
• Gonococcal: IM ceftriaxone 500mg single dose + saline irrigation; same-day ophthalmology referral
• Chlamydial: oral azithromycin 1g single dose or doxycycline 100mg BD for 7 days; GUM referral for sexual health screening
• Viral: self-limiting (2-3 weeks); lubricant drops for comfort; no antiviral unless HSV suspected (aciclovir 3% ointment 5×/day)
• Allergic:
  • Mast cell stabiliser: sodium cromoglicate 2% QDS
  • Dual-action antihistamine/mast cell: olopatadine 0.1% BD
  • Oral antihistamine: cetirizine 10mg OD or loratadine 10mg OD
  • Avoid rubbing eyes; cold compresses
  • Short course of mild steroid drops (fluorometholone) for severe cases — specialist only

Surgical/Interventional

• Not applicable for routine conjunctivitis

Referral Criteria

• Reduced vision, severe pain, photophobia: urgent ophthalmology
• Contact lens wearer: urgent (exclude keratitis)
• Neonatal conjunctivitis: urgent ophthalmology + paediatrics
• Hyperacute purulent discharge: same-day ophthalmology (gonococcal)
• Chronic conjunctivitis not responding to treatment: ophthalmology

• Bacterial: resolves within 5-7 days; 65% resolve without antibiotics
• Viral: self-limiting in 2-3 weeks; epidemic keratoconjunctivitis may cause subepithelial infiltrates persisting months
• Allergic: chronic relapsing course; well-controlled with topical treatment
• Gonococcal: can cause corneal perforation within 24-48 hours if untreated — emergency
• Chlamydial: chronic course; trachoma (chlamydial) is the leading infectious cause of blindness worldwide

Comparison of Conjunctivitis Types