ABSTRACT: BACKGROUND:Symptom relief for the duration of 24 hours after treatment would benefit patients with allergic conjunctivitis. OBJECTIVE:To compare the safety and efficacy of olopatadine 0.77% with vehicle or olopatadine 0.2% in patients with allergic conjunctivitis in a conjunctival allergen-challenge clinical study. PATIENTS AND METHODS:In this Phase III, multicenter, double-masked, parallel-group, randomized trial, patients with allergic conjunctivitis received olopatadine 0.77%, its vehicle, or olopatadine 0.2%, administered once at visits 3A (day 0), 4A (day 14 ±2), and 5 (day 21 +3). Allergic conjunctivitis-associated sign and symptom assessments included ocular itching, conjunctival redness, total redness, chemosis, and tearing scores. Adverse events and ocular safety parameters were also assessed. RESULTS:A total of 202 qualifying patients were randomized. Olopatadine 0.77% was superior (P<0.001) to vehicle for treatment of ocular itching at 3, 5, and 7 minutes postchallenge at onset of action and 16- and 24-hour duration of action. Conjunctival redness mean scores were significantly lower for olopatadine 0.77% versus vehicle at all three post-conjunctival allergen-challenge time points: onset (-1.52 to -1.48; P<0.001), 16 hours (-1.50 to -1.38; P<0.01), and 24 hours (-1.58 to -1.38; P<0.05). At 24 hours, olopatadine 0.77% was superior to olopatadine 0.2% at all three postchallenge time points for ocular itching (P<0.05), conjunctival redness (P<0.05), and total redness (P<0.05). No clinically relevant differences in safety parameters or adverse events were observed between the treatment groups. CONCLUSION:Olopatadine 0.77% is superior to both its vehicle and olopatadine 0.2% for the treatment of allergen-mediated ocular itching and conjunctival redness. Ocular itching symptom relief is maintained over 24 hours, supporting once-daily dosing and demonstrating a comparable safety profile to olopatadine 0.2%.