Time-course changes of tear breakup time (BUT). In the 0.1% LMWHA, 0.3% LMWHA, DQ, and EDES+/Treatment− groups, tear BUT significantly decreased after exposure to EDES. In contrast, in the HMWHA and EDES−/Treatment− groups, there were no significant changes after exposure to EDES. Tear BUT in the HMWHA after exposure to EDES was significantly longer than 0.1% LMWHA, 0.3% LMWHA, DQ, and EDES+/Treatment− groups. * and ** represent p < 0.05 and p < 0.001, respectively. LMWHA, low molecular weight hyaluronic acid (HA); DQ, diquafosol sodium; HMWHA, high molecular weight HA; EDES, environmental dry eye stress.