Most Common Cause of Conjunctivitis
Viral conjunctivitis is the most common overall cause of infectious conjunctivitis, accounting for approximately 80% of all acute conjunctivitis cases. 1
Types of Conjunctivitis by Frequency
Viral conjunctivitis: Most common (80% of acute cases)
- Primarily caused by adenoviruses
- Other viral causes include enterovirus and herpes viruses
- Highly contagious and easily transmitted
Bacterial conjunctivitis: Second most common infectious cause 2
- More common in children than adults
- Usually self-limiting but can be treated with antibiotics
Allergic conjunctivitis: Affects up to 40% of the population, though only a small proportion seek medical attention 2
Other causes:
- Mechanical/irritative/toxic conjunctivitis
- Dry eye-related conjunctivitis
- Contact lens-related conjunctivitis
- Medication-induced conjunctivitis
Clinical Differentiation Between Types
Viral Conjunctivitis
- Watery discharge
- Bilateral presentation (often starts in one eye, spreads to the other)
- Preauricular lymphadenopathy may be present
- Associated with upper respiratory symptoms
- Self-limiting course (1-2 weeks)
Bacterial Conjunctivitis
- Mucopurulent discharge
- Eyelids often matted shut upon waking
- Less itching compared to allergic conjunctivitis
- Can be unilateral or bilateral
Allergic Conjunctivitis
- Intense itching (most consistent symptom)
- Bilateral presentation
- Seasonal patterns may be present
- Watery discharge
- Often associated with allergic rhinitis
Diagnostic Pearls
No single sign or symptom can accurately differentiate viral from bacterial conjunctivitis 3. However, the American Academy of Ophthalmology notes that discharge assessment can help differentiate:
- Purulent/mucopurulent discharge suggests bacterial etiology
- Watery discharge suggests viral etiology 4
Management Considerations
While most cases of conjunctivitis are self-limiting, proper diagnosis is important for:
- Preventing complications
- Reducing transmission of infectious forms
- Providing symptomatic relief
- Allowing earlier return to work/school
Common Pitfalls to Avoid
- Misdiagnosing viral conjunctivitis as bacterial, leading to unnecessary antibiotic use
- Failing to recognize more serious forms of conjunctivitis that require specific treatment (e.g., gonococcal, chlamydial)
- Using topical corticosteroids without ophthalmologic consultation, which can worsen certain infections, particularly herpes simplex virus 4
- Neglecting strict hygiene measures to prevent transmission of infectious conjunctivitis
Understanding that viral conjunctivitis is the most common cause helps guide appropriate management and reduces unnecessary antibiotic use in clinical practice.