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Purpose: To evaluate the safety and efficacy of 0.75% phentolamine ophthalmic solution (POS), an α-adrenergic antagonist, in reversal of pharmacologically induced mydriasis., Design: Two phase 3, multicenter, placebo-controlled, randomized, double-masked clinical trials in healthy participants., Participants: Five hundred fifty-three healthy 12- to 80-year-old participants were randomized 1:1 (MIRA 2) and 2:1 (MIRA 3) to receive either POS or placebo eye drops in both eyes., Methods: Participants received POS or placebo administered 1 hour after mydriasis, induced by instillation of either 2.5% phenylephrine, 1% tropicamide, or 1% hydroxyamphetamine / 0.25% tropicamide., Main Outcome Measures: Percent of participants returning to within 0.2 mm of baseline pupil diameter in study eye 90 minutes after POS administration. Safety measures included treatment-emergent adverse events and tolerability measures, including conjunctival hyperemia., Results: A total of 553 participants were randomized to treatment with placebo (n = 215) or POS (n = 338). A statistically significant greater percentage of participants treated with POS showed reversal of mydriasis at 90 minutes compared to placebo (MIRA 2: 48.9% vs. 6.6% [P < 0.0001]; MIRA 3: 58% vs. 6% [P < 0.0001]) and as early as 60 minutes (MIRA 2: 27.7% vs. 2.2% [P < 0.0001]; MIRA 3: 42% vs. 2% [P < 0.0001]). Between 28% and 34% of participants receiving placebo did not returned to baseline PD at 24 hours after pharmacologic dilation compared with 8% to 11% of patients treated with POS (P < 0.0001)., Conclusions: Treatment with POS reduced PD within 60 to 90 minutes, with a statistically significant time savings of 5 to 6 hours to return to baseline PD compared with placebo. One or 2 drops of POS rapidly reversed mydriasis in all participants regardless of mydriatic agent or iris color. More participants receiving POS reported a benefit in the resolution of visual symptoms caused by pharmacologically induced mydriasis compared with placebo, with statistically significant differences noted as early as 1 hour. The safety profile was favorable, with the most common adverse effects being mild transient conjunctival hyperemia (11.2%), instillation site discomfort (10.9%), and dysgeusia (3.6%)., Financial Disclosure(s): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article., (Copyright © 2024 American Academy of Ophthalmology. Published by Elsevier Inc. All rights reserved.)