 This is a multi-center, randomized, double-masked, placebo-controlled, parallel group Phase 2b trial designed to evaluate symptoms and signs in subjects with mild to moderate dry eye disease. Eligible patients, will be treated with placebo during 2-week placebo run-in period. Subjects will then be randomly assigned in a double-masked, 1:1 ratio to either 0.017 P-321 Ophthalmic Solution or placebo TID for 28 days. This study is designed to evaluate the changes in symptoms. Safety will be assessed throughout the study by adverse events. 