ARTICLE Results from the United States cohort of the HORIZON trial of a Schlemm canal microstent to reduce intraocular pressure in primary open-angle glaucoma Jason Jones, MD, Douglas D. Koch, MD, Steven Vold, MD, Cathleen McCabe, MD, Douglas Rhee, MD, Richard Lewis, MD, Stephen Smith, MD, Quang H. Nguyen, MD, Thomas W. Samuelson, MD, for the HORIZON U.S. investigators Purpose: To assess the safety and effectiveness of Schlemm ca- nal stenting for reducing intraocular pressure (IOP) in combination with cataract surgery in the United States cohort of the HORIZON study. Setting: Twenty-six clinical sites in the U.S. Design: Prospective clinical trial. Methods: Eyes with mild to moderate primary open-angle glaucoma (POAG) on 1 to 4 medications, significant cataract, and an unmedicated diurnal IOP between 22 mm Hg and 34 mm Hg after medication washout were randomized 2:1 to receive the Hydrus microstent or no further treatment after successful cataract surgery. Patients were followed for 24 months. Medication washout and diurnal IOP measurements were repeated at 12 months and 24 months. Results: Two hundred nineteen eyes were randomized to micro- stent implantation and 112 patients to phacoemulsification only. At 24 months, the diurnal IOP was reduced by 20.0% or more in a greater proportion of eyes in the microstent group (78.5% versus 54.5%; P < .001). The mean change in the number of medications was 1.2 G 0.9 (SD) in the microstent group and 0.8 G 1.1 in the phaco-only group (P < .001), and 78.5% of eyes and 39.2% of eyes, respectively, were medication free (difference 38.8%; P < .001). Conclusions: Implantation of a Schlemm canal microstent after phacoemulsification significantly reduced diurnal IOP and medica- tion use compared with phacoemulsification only in patients with mild to moderately severe POAG. The combination procedure was equivalent to cataract surgery alone in terms of visual acuity outcomes and the rate of adverse ocular events. J Cataract Refract Surg 2019; -:-–- Q 2019 Published by Elsevier Inc. on behalf of ASCRS and ESCRS C ataract, open-angle glaucoma (OAG), and age- related macular degeneration are among the most commonly diagnosed ocular disorders in the United States, 1 and cataract surgery is one of the most common surgical procedures. 2 Up to 1 in 6 patients with OAG become bilaterally blind. 3 The only proven way to prevent vision loss is to reduce intraocular pressure (IOP). 4 Traditional approaches to reducing IOP include medical therapy, laser treatments, and surgery. 5 Recently, two large-scale multicenter randomized clinical trials 6,7 found that microinvasive glaucoma surgery (MIGS) de- vices combined with cataract surgery significantly reduced IOP and sustained the effect for at least 2 years, providing another therapeutic option for the glaucoma patient. The most recent of these trials, the HORIZON study, 7 evaluated the Hydrus microstent (Ivantis, Inc.) in combina- tion with cataract surgery in 556 eyes treated at 38 interna- tional centers. The study showed significant decreases in IOP and medication use in eyes randomized to device treat- ment. The HORIZON United States subgroup reflects the Submitted: November 20, 2018 | Final revision submitted: March 15, 2019 | Accepted: March 26, 2019 From the Jones Eye Clinic (Jones), Sioux City, Iowa, the Cullen Eye Institute (Koch), Baylor College of Medicine, Houston, Texas, Vold Vision (Vold), Fayetteville, Arkansas, Eye Associates (McCabe), Sarasota, Florida, University Hospitals (Rhee), Case Western Reserve University, Cleveland, Ohio, Sacramento Eye Consultants (Lewis), California, Eye Associates of Fort Myers (Smith), Florida, Scripps Clinic (Nguyen), La Jolla, California, and Minnesota Eye Consultants (Samuelson), Minneapolis, Minnesota, USA. Supported by Ivantis, Inc., Irvine, California, USA. Presented at the ASCRSASOA Annual Meeting, Washington, DC, USA, April 2018. Corresponding author: Jason Jones, MD, Jones Eye Clinic, 4405 Hamilton Blvd, Sioux City, IA 51104, USA. Email: jasonjonesmd@mac.com. Q 2019 Published by Elsevier Inc. on behalf of ASCRS and ESCRS. 0886-3350/$ - see frontmatter https://doi.org/10.1016/j.jcrs.2019.03.024 1