Medications available for the treatment of seasonal allergic conjunctivitis include antihistamines. These medicines block the release of histamine, a substance in the body that is released when an allergic reaction occurs. Novartis (NVS) has developed an eye drop formulation of a well tried antihistamine called ketotifen. This study will compare the efficacy and the tolerability of ketotifen eye drops with emedastine, which is a popular treatment for seasonal allergic conjunctivitis in China.