Purpose: To compare the efficacy and safety of PreserFlo™,MicroShunt (Santen, Osaka, Japan) combined with phacoemulsification to PreserFlo™,MicroShunt as a standalone procedure in eyes with moderate to advanced open-angle glaucoma. Methods: In an observatory, prospective, clinical study, 30 patients (30 eyes) with moderate to advanced angle glaucoma were allocated to either PreserFlo ™, MicroShunt combined with phacoemulsification (15 eyes,Group A) or PreserFlo™,MicroShunt as a standalone procedure (15 eyes,Group B). The follow-up time of the study was 12 months. Results: Average intraocular pressure (IOP) at 12 months was 11. 62 ±,1. 6 mmHg in Group A and 13. 8 ±,3. 6 mmHg in Group B, which was significantly lower than baseline IOP (Group A: 23. 47 ±,8. 99 mmHg, P < 0. 001,Group B: 23. 4 ±,8. 68 mmHg, P < 0. 001). The absolute reduction of IOP within the 12 postoperative months was not significantly different between the two groups (P = 0. 056). The number of the topical medications that were administered 12 months after ocular surgery was 0 in Group A and 0. 6 ±,0. 8 in Group B, compared to 3. 13 ±,1. 02 in Group A (P < 0. 001) and 2. 4 ±,1. 45 in Group B (P = 0. 004) at baseline. Phacoemulsification combined with PreserFlo™,MicroShunt significantly reduced the number of antiglaucoma agents after 12 months compared to the standalone procedure (P = 0. 026). One eye in Group A was referred for bleb revision due to bleb fibrosis and a consequent acute postoperative rise in IOP. One eye in Group A required transscleral cyclophotocoagulation with MicroPulse ®, laser. One bleb revision was also necessary in Group B at the 4 th postoperative week. Endothelial cell density did not significantly change over 12 months in either group (Group A: baseline, 2017. 3 ±,346. 8 cells/mm 2, 12 months, 1968. 5 ±,385. 6 cells/mm 2, P = 0. 38,Group B: baseline, 2134. 1 ±,382. 6 cells/mm 2, 12 months, 2094. 4 ±,373. 3 cells/mm 2, P = 0. 42). The PreserFlo™,MicroShunt combined with phacoemulsification produced higher absolute success rates after 12 months in patients with moderate to advanced open-angle glaucoma than the PreserFlo™,MicroShunt as standalone procedure (Group A: 80% and Group B: 60%, P = 0. 022). Conclusions: In eyes with moderate to advanced open-angle glaucoma, PreserFlo™,MicroShunt with or without phacoemulsification is effective in reducing IOP and the number of the antiglaucoma agents with a very small incidence of complications and subsequent glaucoma surgeries. However, adding phacoemulsification to PreserFlo™,MicroShunt successfully reduces IOP without the need for ongoing topical medications as are needed after the standalone procedure.