Importance: Treatment of acquired blepharoptosis (ptosis) is currently limited to surgical intervention., Objective: To examine the efficacy and safety of oxymetazoline hydrochloride, 0.1%, ophthalmic solution (oxymetazoline, 0.1%) in participants with acquired ptosis., Design, Setting, and Participants: This pooled analysis of 2 randomized, double-masked, placebo-controlled, multicenter phase 3 clinical trials included participants 9 years and older with acquired ptosis and superior visual field deficit. The 2 studies were conducted across 16 and 27 sites in the United States. Patients were enrolled from May 2015 to April 2019. Analyses for the individual trials were initiated after database lock and completed on September 6, 2017, and May 16, 2019. Pooled analysis was completed on August 25, 2019., Interventions: Participants (randomized 2:1) received oxymetazoline, 0.1%, or vehicle, self-administered as a single drop per eye, once daily, for 42 days., Main Outcomes and Measures: The primary efficacy end point was change from baseline in the number of points seen on the Leicester Peripheral Field Test, a test to detect superior visual field deficits due to ptosis, on days 1 (6 hours after instillation) and 14 (2 hours after instillation). The secondary end point, change from baseline in marginal reflex distance 1, was assessed at the same time points., Results: In total, 304 participants were enrolled (mean [SD] age, 63.8 [13.8] years; 222 women [73%]). Overall, 97.5% (198 of 203) of participants receiving oxymetazoline, 0.1%, and 97.0% (98 of 101) of participants receiving vehicle completed the studies. Oxymetazoline, 0.1%, was associated with a significant increase in the mean (SD) number of points seen on the Leicester Peripheral Field Test vs vehicle (day 1: 5.9 [6.4] vs 1.8 [4.1]; mean difference, 4.07 [95% CI, 2.74-5.39]; P < .001; day 14: 7.1 [5.9] vs 2.4 [5.5]; mean difference, 4.74 [95% CI, 3.43-6.04]; P < .001). Oxymetazoline, 0.1%, also was associated with a significant increase in marginal reflex distance 1 from baseline (mean [SD]: day 1: 0.96 [0.89] mm vs 0.50 [0.81] mm; mean difference, 0.47 mm [95% CI, 0.27-0.67]; P < .001; day 14: 1.16 [0.87] mm vs 0.50 [0.80] mm; mean difference, 0.67 mm [95% CI, 0.46-0.88]; P < .001). Treatment-emergent adverse events (TEAEs) occurred in 31.0% (63 of 203) of participants receiving oxymetazoline, 0.1%, and 35.6% (36 of 101) of participants receiving vehicle. Among participants receiving oxymetazoline, 0.1%, with a TEAE, 81% (51 of 63) had a maximum TEAE intensity of mild, and 62% (39 of 63) had no TEAE suspected of being treatment related., Conclusions and Relevance: Oxymetazoline, 0.1%, was associated with positive outcomes and was well tolerated in phase 3 trials after instillation at days 1 and 14, demonstrating its potential promise for the treatment of acquired ptosis, although further study is needed to elucidate the clinical relevance of these findings beyond 6 weeks.