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Comparison of mean itch scores at baseline and 16 h after treatment instillation at 3 min post-conjunctival allergen challenge (primary endpoint). Mean itch scores for alcaftadine 0.25%, olopatadine 0.2%, and placebo. *P < 0.0001 for alcaftadine and olopatadine versus placebo; **P = 0.0006 for alcaftadine versus olopatadine. P values calculated using the two-sample t test
