What is allergic conjunctivitis and how is it treated?

Allergic Conjunctivitis: Definition and Clinical Significance

Allergic conjunctivitis is an inflammatory response of the conjunctiva triggered by allergen exposure, characterized primarily by ocular itching, and is best treated with dual-action antihistamine/mast cell stabilizers for most cases, with corticosteroids reserved for severe forms.1, 2

Definition and Classification

Allergic conjunctivitis is not a single entity but rather a group of related conditions affecting the ocular surface, typically associated with type 1 hypersensitivity reactions. It can be classified into:

1. Acute forms:

   • Seasonal allergic conjunctivitis (SAC)
   • Perennial allergic conjunctivitis (PAC)/Chronic allergic conjunctivitis (CAC)

2. Chronic forms:

   • Vernal keratoconjunctivitis (VKC)
   • Atopic keratoconjunctivitis (AKC)
   • Giant papillary conjunctivitis (GPC)3

Clinical Presentation

The hallmark symptoms and signs include:

• Itching - the most consistent and characteristic symptom1, 2
• Redness of the conjunctiva
• Tearing
• Eyelid swelling
• Photophobia (in severe cases)
• Mattering and adherence of eyelids (less common than in bacterial conjunctivitis)1

In severe chronic forms, patients may experience extreme discomfort and potential damage to the ocular surface3.

Epidemiology and Significance

• Allergic conjunctivitis affects up to 40% of the population, though only a fraction seek medical attention1
• It significantly impacts quality of life through:
  • Discomfort and visual disturbance
  • School/work absenteeism
  • Reduced productivity
  • Potential for ocular surface damage in severe chronic forms3

Diagnostic Approach

Diagnosis is primarily clinical, based on:

• Characteristic itching (the most reliable symptom)
• Seasonal patterns (for SAC)
• Associated allergic conditions (e.g., rhinitis)
• Lack of purulent discharge (distinguishes from bacterial conjunctivitis)

Confirmatory testing may include:

• Skin testing (most reliable diagnostic method for CAC)4
• Serum IgE levels (elevated in only ~30% of CAC cases)
• Tear IgE levels (pathological in >50% of CAC cases)4
• Conjunctival allergen provocation test (when standard allergy testing is inconclusive)2

Treatment Algorithm

1. First-line approaches:

   • Allergen avoidance and environmental modifications
   • Artificial tears/lacrimal substitutes
   • Cold compresses
   • Protection of the ocular surface2

2. Second-line pharmacotherapy:

   • Dual-action antihistamine/mast cell stabilizers (preferred for most cases)
   • Single-dose formulations or preservative-free preparations are preferable2

3. Third-line options for severe or refractory cases:

   • Topical corticosteroids (short-term use for acute exacerbations)
     • Newer C-20 ester corticosteroids like loteprednol etabonate offer improved safety profiles with reduced risk of IOP elevation and cataract formation5
   • Cyclosporine (disease-modifying treatment for severe chronic forms)2

Clinical Pearls and Pitfalls

• Differential diagnosis pitfalls: Always consider dry eye syndrome, which can present with similar symptoms and may coexist with allergic conjunctivitis2

• Treatment pitfalls: Avoid prolonged use of traditional corticosteroids due to risks of cataracts, glaucoma, and other ocular complications3, 5

• Special populations: Conjunctivitis in contact lens wearers requires particular attention as it may represent giant papillary conjunctivitis or complicate existing allergic conjunctivitis1, 4

• Non-specific triggers: Astigmatism, heterophoria, photosensitization, local infections, and trauma may exacerbate allergic conjunctivitis symptoms in predisposed individuals4

• Monitoring: Patients with chronic forms (VKC, AKC) require specialized ophthalmological follow-up due to potential for corneal involvement and vision-threatening complications2