Purpose To evaluate the efficacy and safety of the Ultrasonic Circular Cyclo Coagulation (UC3) procedure in patients with primary open-angle glaucoma (POAG). Methods Prospective multicenter clinical trial. 42 eyes of 42 patients with POAG, intraocular pressure (IOP) > 21 mmHg, an average of 1.65 failed previous surgeries and an average of 3.2 hypotensive medications were insonified with a probe comprising 6 piezoelectric transducers. 18 patients (group 1) were treated with a 4 seconds exposure time for each shot and 24 patients (group 2) with a 6 seconds exposure time. Follow-up visits were performed at 1 day, 1 week, 1, 2, 3, 6 and 12 months after Results IOP was significantly reduced in both groups (p20%) was achieved in 12 of 18 (67%) ...