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Ophthalmology. 2019 Jan;126(1):29-37. doi: 10.1016/j.ophtha.2018.05.012. Epub 2018 Jun 23.

A Schlemm Canal Microstent for Intraocular Pressure Reduction in Primary Open-Angle Glaucoma and Cataract: The HORIZON Study.

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University of Minnesota, Minnesota Eye Consultants, Minneapolis, Minnesota. Electronic address:
Altos Eye Physicians, Los Altos, California.
Texan Eye and Keystone Research, Austin, Texas.
Ophthalmology Associates, Fort Worth, Texas.
Department of Ophthalmology, St. Thomas Hospital, London, United Kingdom.
Department of Ophthalmology, University of Toronto, Toronto, Canada.
Wilmer Eye Institute, Baltimore, Maryland.
Singapore National Eye Center, Singapore.
Moran Eye Center, University of Utah, Salt Lake City, Utah.
Stanford University, Stanford, California.



To compare cataract surgery with implantation of a Schlemm canal microstent with cataract surgery alone for the reduction of intraocular pressure (IOP) and medication use after 24 months.


Prospective, multicenter, single-masked, randomized controlled trial.


Subjects with concomitant primary open-angle glaucoma (POAG), visually significant cataract, and washed-out modified diurnal IOP (MDIOP) between 22 and 34 mmHg.


Subjects were randomized 2:1 to receive a single Hydrus Microstent (Ivantis, Inc, Irvine, CA) in the Schlemm canal or no stent after uncomplicated phacoemulsification. Comprehensive eye examinations were conducted 1 day, 1 week, and 1, 3, 6, 12, 18, and 24 months postoperatively. Medication washout and MDIOP measurement were repeated at 12 and 24 months.


The primary and secondary effectiveness end points were the proportion of subjects demonstrating a 20% or greater reduction in unmedicated MDIOP and change in mean MDIOP from baseline at 24 months, respectively. Hypotensive medication use was tracked throughout the course of follow-up. Safety measures included the frequency of surgical complications and adverse events.


A total of 369 eyes were randomized after phacoemulsification to Hydrus Microstent (HMS) and 187 to no microstent (NMS). At 24 months, unmedicated MDIOP was reduced by ≥20% in 77.3% of HMS group eyes and in 57.8% of NMS group eyes (difference = 19.5%, 95% confidence interval [CI] 11.2%-27.8%, P < 0.001). The mean reduction in 24-month unmedicated MDIOP was -7.6±4.1 mmHg (mean ± standard deviation) in the HMS group and -5.3±3.9 mmHg in the NMS group (difference = -2.3 mmHg; 95% CI, -3.0 to -1.6; P < 0.001). The mean number of medications was reduced from 1.7±0.9 at baseline to 0.3±0.8 at 24 months in the HMS group and from 1.7±0.9 to 0.7±0.9 in the NMS group (difference = -0.4 medications; P < 0.001). There were no serious ocular adverse events related to the microstent, and no significant differences in safety parameters between the 2 groups.


This 24-month multicenter randomized controlled trial demonstrated superior reduction in MDIOP and medication use among subjects with mild-to-moderate POAG who received a Schlemm canal microstent combined with phacoemulsification compared with phacoemulsification alone.

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