What causes conjunctivitis (pink eye)?

Causes of Conjunctivitis (Pink Eye)

Conjunctivitis is primarily caused by viral infections, followed by bacterial infections, allergic reactions, and mechanical/irritative/toxic factors, with each cause having distinctive clinical presentations and management approaches. 1

Infectious Causes

Viral Conjunctivitis

• Adenovirus is the most common cause, accounting for approximately 80% of all viral conjunctivitis cases 2
• Typically presents with watery discharge, conjunctival injection, and sometimes preauricular lymphadenopathy 1
• Other viral causes include:
  • Herpes simplex virus (HSV) - usually unilateral with possible vesicular eyelid lesions and dendritic keratitis 1
  • Varicella zoster virus (VZV) - associated with dermatomal rash and severe pain 1
  • Measles (rubeola) - bilateral conjunctivitis with maculopapular rash 1
  • Molluscum contagiosum - associated with dome-shaped umbilicated eyelid lesions 1

Bacterial Conjunctivitis

• Second most common infectious cause, particularly prevalent in children 3
• Characterized by mucopurulent discharge and mattering of eyelids 4, 5
• Common bacterial pathogens include:
  • Staphylococcus aureus 1
  • Streptococcus pneumoniae 1
  • Haemophilus influenzae 1
  • Neisseria gonorrhoeae - causes hyperacute purulent conjunctivitis requiring urgent treatment 1
  • Chlamydia trachomatis - causes inclusion conjunctivitis and trachoma 1

Non-Infectious Causes

Allergic Conjunctivitis

• Affects up to 40% of the population 4
• Types include:
  • Seasonal/perennial allergic conjunctivitis - triggered by environmental allergens like pollens and grasses 1
  • Vernal conjunctivitis - chronic, recurrent form often affecting young males with atopic history 1
  • Atopic conjunctivitis - associated with atopic dermatitis 1
• Characterized by bilateral itching, tearing, and conjunctival injection 5

Mechanical/Irritative/Toxic Causes

• Superior limbic keratoconjunctivitis (SLK) - associated with thyroid disease 1
• Contact lens-related conjunctivitis - due to mechanical irritation, chronic hypoxia, or preservatives 1
• Giant papillary conjunctivitis (GPC) - related to contact lens wear or exposed sutures 1
• Floppy eyelid syndrome - associated with obesity and sleep apnea 1
• Medication-induced/preservative-induced keratoconjunctivitis - from topical medications 1

Other Causes

• Immune-mediated conditions:
  • Ocular mucous membrane pemphigoid (OMMP) 1
  • Stevens-Johnson syndrome/toxic epidermal necrolysis 1
• Neoplastic conditions:
  • Sebaceous carcinoma 1
  • Ocular surface squamous neoplasia 1
  • Conjunctival lymphoma 1
• Deficiency diseases:
  • Plasminogen deficiency (ligneous conjunctivitis) 1

Special Considerations

Neonatal Conjunctivitis

• Requires urgent evaluation and treatment 3
• Common causes include:
  • Chemical irritation from prophylactic eye drops 6
  • Neisseria gonorrhoeae - manifests within 1-7 days after birth 1
  • Chlamydia trachomatis - manifests 5-19 days after birth 1

Contact Lens Wearers

• Always consider bacterial infection and evaluate for corneal ulcers 3
• Poor lens hygiene, prolonged wearing time, and allergenic solutions increase risk 1

Diagnostic Pearls

• No single sign or symptom accurately differentiates viral from bacterial conjunctivitis 5
• Mattering of eyelids on waking, lack of itching, and absence of prior conjunctivitis history suggest bacterial etiology 4
• Itching is the most consistent sign in allergic conjunctivitis 4
• Unilateral granulomatous follicular conjunctivitis with regional lymphadenopathy suggests Parinaud oculoglandular syndrome 1

Common Pitfalls

• Misdiagnosing sebaceous carcinoma as chronic blepharoconjunctivitis 1
• Failing to recognize herpes simplex conjunctivitis before administering corticosteroids 2
• Not considering systemic conditions that can manifest with conjunctivitis 1
• Overlooking potentially vision-threatening causes like subconjunctival hemorrhage with concurrent trauma 7

Understanding these diverse causes helps guide appropriate management strategies and prevent complications or spread of infectious conjunctivitis.