Ophthalmic Mast Cell Stabilizer/Antihistamines For Seasonal Allergic Conjunctivitis

MCS/AHs do not cause rebound congestion with prolonged use (> 3 days), unlike first-line antihistamine/decongestion products. Ophthalmic MCS/AHs block histamine-1 receptors and inhibit the release of histamine from mast cells. Histamine receptor blockage occurs instantly, but preventing mast cell degranulation may take up to 2-4 weeks. This dual approach decreases the signs and symptoms of AC, such as redness, mucus production, tearing, and itching. Alleviation of AC by medication is assessed with the conjunctival allergen challenge test (CAC). In the CAC, an allergen is placed into the eye, and itch scores (0-4) are reported every 30 seconds for 20 minutes. The CAC allows for a quantifiable subjective measurement of itching response when a known amount of allergen is applied to the conjunctiva.