What is allergic conjunctivitis?

Allergic Conjunctivitis

Allergic conjunctivitis is an IgE-mediated inflammatory condition of the conjunctiva characterized primarily by itching, redness, swelling of the eyelids, and tearing. 1 It represents a subtype of non-infectious conjunctivitis that can present as acute, intermittent, or chronic inflammation, most frequently triggered by airborne allergens.

Clinical Presentation

The hallmark symptoms and signs include:

• Itching (the most characteristic symptom)
• Redness of the conjunctiva ("red eye")
• Chemosis (conjunctival swelling)
• Eyelid swelling
• Tearing
• Often associated with allergic rhinitis 2, 1

Classification

Allergic conjunctivitis can be classified into several forms:

1. Seasonal allergic conjunctivitis (SAC) - also known as hay fever conjunctivitis
2. Perennial/Chronic allergic conjunctivitis (PAC/CAC) - most common in Northern Europe, particularly in urban areas
3. Atopic conjunctivitis
4. Vernal conjunctivitis
5. Upper limbal (kerato-) conjunctivitis
6. Conjunctivitis associated with oculomucocutaneous syndromes 1

Each form has distinctive clinical features, causative agents, and treatment approaches.

Pathophysiology

The underlying mechanism involves:

• IgE-mediated mast cell activation upon allergen exposure
• Release of histamine and other inflammatory mediators
• Early phase reaction (minutes after exposure) causing immediate symptoms
• Late phase reaction involving recruitment of inflammatory cells that sustain prolonged inflammation 3, 4

Common Triggers

• Airborne allergens (pollen, dust, mold)
• House dust mites (particularly in chronic forms)
• Animal dander (especially cats and dogs)
• Topical and systemic drugs
• Cosmetics 2, 1

Diagnostic Considerations

Diagnosis primarily relies on:

• Clinical evaluation of symptoms and signs
• Skin testing (most reliable diagnostic method, particularly for house dust/mite allergies)
• Serum IgE levels (elevated in only about 30% of cases)
• Tear IgE levels (pathological in over 50% of cases) 2

Important Clinical Pearls

1. Non-specific factors may predispose or exacerbate allergic conjunctivitis:

   • Contact lens intolerance
   • Local infections
   • Eye trauma
   • Astigmatism
   • Heterophoria
   • Photosensitization 2

2. These non-specific factors may explain:

   • Unilateral presentations
   • Association with other forms of chronic conjunctivitis 2

3. Slit-lamp examination often reveals non-specific findings that may overlap with other conjunctival allergies (papillary, follicular, or atrophic changes) 2

Management Approach

The management of allergic conjunctivitis follows a stepwise approach:

1. Allergen avoidance - elimination of the offending allergen is the first-line treatment 2

2. Pharmacological therapy:

   • Artificial tears
   • Antihistamines (topical and oral)
   • Mast cell stabilizers (e.g., nedocromil sodium)
   • Dual-action agents (antihistamine/mast cell stabilizers like ketotifen, epinastine, and olopatadine)
   • NSAIDs
   • Corticosteroids (for severe cases) 3, 5

3. Immunotherapy - specific desensitization to allergens like house dust or mites can be effective for long-term management 2

4. Advanced therapies - for severe forms:

   • Immunomodulators (cyclosporine A and tacrolimus) have shown promising results in severe cases like atopic and vernal keratoconjunctivitis 3
   • Modified corticosteroids with improved safety profiles (e.g., loteprednol etabonate) 5

Treatment Considerations

When using corticosteroids:

• Traditional corticosteroids effectively relieve inflammation but have significant ocular and systemic side effects
• Modified corticosteroids like loteprednol etabonate (C-20 ester corticosteroid) offer similar efficacy with improved safety profiles
• These modified agents are less likely to elevate intraocular pressure or form cataracts 5

Clinical Pitfalls to Avoid

1. Failing to distinguish between infectious and allergic conjunctivitis
2. Overlooking associated non-specific factors that may exacerbate symptoms
3. Prolonged use of traditional corticosteroids without monitoring for side effects
4. Not addressing underlying allergic triggers
5. Neglecting to treat associated allergic conditions (e.g., allergic rhinitis)