How do you differentiate and treat allergic vs viral conjunctivitis?

Differentiating and Treating Allergic vs Viral Conjunctivitis

Allergic conjunctivitis is distinguished by itching as the most consistent symptom, bilateral presentation, and watery discharge with mild mucous component, while viral conjunctivitis presents with abrupt onset, initially unilateral becoming bilateral within days, watery discharge, follicular reaction on inferior tarsal conjunctiva, and preauricular lymphadenopathy. 1, 2

Key Diagnostic Features

Allergic Conjunctivitis

• Itching is the hallmark symptom that most reliably differentiates allergic from infectious causes 1, 3
• Bilateral presentation from onset with eyelid edema and periorbital hyperpigmentation 1, 2
• Watery discharge with mild mucous component (not purulent) 1, 2
• Papillary reaction on tarsal conjunctiva (not follicular) 2
• Affects up to 40% of the population 1, 3
• History of atopy, seasonal patterns, or exposure to known allergens 4

Viral Conjunctivitis

• Abrupt onset, starting unilateral but becoming sequentially bilateral within days 1, 2
• Watery discharge without significant mucous or purulent component 2, 5
• Follicular reaction on inferior tarsal conjunctiva (key physical finding) 1, 2
• Preauricular lymphadenopathy present 2
• Potential subconjunctival hemorrhages 2
• Often associated with concurrent upper respiratory infection 5
• Self-limited with improvement within 5-14 days 2

Critical Differentiating Algorithm

Step 1: Assess for itching

• If prominent itching present → strongly suggests allergic conjunctivitis 1, 3
• If itching absent → consider viral or bacterial causes 3

Step 2: Evaluate discharge character

• Watery discharge → viral or allergic 2, 5
• Mucopurulent discharge with matted eyelids on waking → bacterial 1, 2

Step 3: Examine tarsal conjunctiva

• Follicular reaction (small, dome-shaped elevations) → viral 1, 2
• Papillary reaction (flat-topped elevations) → allergic or bacterial 2

Step 4: Check laterality at onset

• Initially unilateral becoming bilateral → viral 1, 2
• Bilateral from onset → allergic 1, 2

Step 5: Palpate preauricular lymph nodes

• Enlarged preauricular lymph node → viral 2
• Absent lymphadenopathy → allergic or bacterial 2

Treatment Approach

Allergic Conjunctivitis Treatment

Topical antihistamines with mast cell-stabilizing activity are the treatment of choice 1, 5

• First-line: Second-generation topical H1-receptor antagonists with mast cell stabilizing properties 6
• Simple measures: wearing sunglasses as allergen barrier, cold compresses, refrigerated artificial tears, avoiding eye rubbing, and allergen avoidance 6
• Hypoallergenic bedding, eyelid cleansers to remove allergens, frequent clothes washing, and showering before bedtime 6
• Avoid chronic vasoconstrictor agents due to rebound vasodilation 6
• For severe cases: brief 1-2 week course of topical corticosteroids with low side effect profile 6
• Avoid punctal plugs as they prevent flushing of allergens and inflammatory mediators 6
• Oral antihistamines may worsen symptoms by inducing dry eye 6

Viral Conjunctivitis Treatment

Viral conjunctivitis is self-limited and requires only supportive care with artificial tears, cold compresses, and antihistamine eye drops for symptomatic relief 1, 5

• Artificial tears for symptomatic relief 5
• Cold compresses 5
• Topical antihistamines for comfort (not curative) 5
• Patient education about high contagiousness and strict hand hygiene is essential 1
• Infected individuals should wash hands frequently, use separate towels, and avoid close contact during contagious period 6
• Indiscriminate use of topical antibiotics or corticosteroids should be avoided 6, 1
• Corticosteroids can potentially prolong adenoviral infections 6

Critical Red Flags Requiring Immediate Ophthalmology Referral

Refer immediately for:

• Visual loss or decreased vision 1, 5
• Moderate or severe pain 1, 5
• Severe purulent discharge 1
• Corneal involvement 1
• Conjunctival scarring 1
• Lack of response to therapy 1
• History of HSV eye disease 1, 5
• Immunocompromised state 1, 5
• Recent ocular surgery 1, 5
• Vesicular rash on eyelids or nose 1, 5

Common Pitfalls to Avoid

• Do not prescribe antibiotics for viral conjunctivitis - they provide no benefit and may cause toxicity 6, 1
• Do not use corticosteroids empirically - they can prolong viral infections and worsen HSV infections 6
• Failing to recognize that dry eye and blepharitis are the most frequent causes of conjunctival inflammation may lead to inadequate treatment 1, 2
• Chronic and/or recalcitrant conjunctivitis may indicate underlying malignancy and requires further evaluation 1
• Unless absolutely necessary, defer IOP measurement for patients with acute conjunctivitis to prevent transmission 6