Allergic conjunctivitis results from IgE-mediated hypersensitivity to airborne allergens — pollen (seasonal), dust mites, pet dander, and mold (perennial). The conjunctiva releases histamine and other mediators causing intense itching, redness, tearing, and swelling. Eye allergies frequently coexist with allergic rhinitis.

Allergic conjunctivitis causes intense itching — the hallmark distinguishing feature — with watery, bilateral redness and often associated nasal allergy symptoms. Infectious conjunctivitis may cause discharge (bacterial) or watery redness following a cold (viral) — but itching is typically mild or absent. A clinical evaluation distinguishes these.

Topical antihistamine/mast cell stabilizer drops — olopatadine (Pataday), ketotifen (Zaditor) — are the most effective and practical first-line treatment for allergic conjunctivitis. They provide rapid itch relief and prevent mediator release. Daily use during allergy season is more effective than as-needed use alone.

Oral antihistamines reduce systemic allergic response and provide modest improvement in eye symptoms. However, they can worsen dry eye by reducing tear production — topical eye drops are generally preferred for ocular-predominant symptoms. Combining both approaches is reasonable when nasal symptoms are also significant.

Topical antihistamine drops are very well tolerated — mild stinging on instillation is the most common complaint. Topical decongestant drops (tetrahydrozoline/Visine) cause rebound redness with regular use and are not recommended. Topical corticosteroid drops are effective but require monitoring for elevated eye pressure and cataract formation with prolonged use. Eye Allergies visit What to expect from a Eye Allergies visit