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L Jay Katz,1 Carl Erb,2 Amadeu Carceller Guillamet,3 Antonio M Fea,4 Lilit Voskanyan,5 Jane Ellen Giamporcaro,6 Dana M Hornbeak6 1Glaucoma Service, Wills Eye Hospital, Philadelphia, PA, USA; 2Glaucoma Service, Eye Clinic Wittenbergplatz, Berlin, Germany; 3Department of Ophthalmology, Hospital Quirón, Barcelona, Spain; 4Department of Surgical Sciences, University of Torino, Torino, Italy; 5Glaucoma Service, S.V.Malayan Ophthalmology Centre, Yerevan, Armenia; 6Department of Clinical Research and Medical Affairs, Glaukos Corporation, San Clemente, CA, USA Purpose: Evaluate long-term outcomes after one, two, or three trabecular micro-bypass stents implanted in a standalone procedure in eyes with open-angle glaucoma taking ocular hypotensive medication.Patients and methods: Prospective randomized ongoing study of 119 subjects (109 with 42-month follow-up) with open-angle glaucoma, preoperative intraocular pressure (IOP) 18–30 mmHg on one to three glaucoma medications, and unmedicated (post-washout) IOP 22–38 mmHg. Subjects were randomized to receive one (n=38), two (n=41), or three (n=40) iStent trabecular micro-bypass stents in a standalone procedure. Postoperatively, IOP was measured with medication and annually following washout. Data included IOP, medications, gonioscopy, pachymetry, visual field, visual acuity, adverse events, and slit-lamp and fundus examinations.Results: Preoperative mean medicated IOP was 19.8±1.3 mmHg on 1.71 medications in one-stent eyes, 20.1±1.6 mmHg on 1.76 medications in two-stent eyes, and 20.4±1.8 mmHg on 1.53 medications in three-stent eyes. Post-washout IOP prior to stent implantation was 25.0±1.2, 25.0±1.7, and 25.1±1.9 mmHg in the three groups, respectively. Postoperatively, Month 42 medicated IOP was 15.0±2.8, 15.7±1.0 and 14.8±1.3 mmHg in the three groups, and post-washout IOP (Months 36–37) was 17.4±0.9, 15.8±1.1 and 14.2±1.5 mmHg, respectively. IOP reduction ≥20% without medication was achieved in 89%, 90%, and 92% of one-, two-, and three-stent eyes, respectively, at Month 12; and in 61%, 91%, and 91% of eyes, respectively, at Month 42. The need for additional medication remained consistent at Months 12 and 42 in multi-stent eyes (four two-stent eyes and three three-stent eyes at both time points), whereas it increased in single-stent eyes (four eyes at Month 12 versus 18 eyes at Month 42). Safety parameters were favorable in all groups.Conclusion: The standalone implantation of either single or multiple iStent® device(s) produced safe, clinically meaningful IOP and medication reductions through 42 months postoperatively, with incrementally greater and more sustained reductions in multi-stent eyes. Keywords: microinvasive glaucoma surgery/MIGS, iStent, surgery, standalone, multiple