Effect of a Schlemm's Canal Microstent on Early Postoperative Intraocular Pressure after Cataract Surgery: An Analysis of the HORIZON Randomized Controlled Trial

Purpose: To compare early postoperative intraocular pressure (IOP) in patients who underwent cataract surgery alone with those who underwent cataract surgery combined with implantation of a Hydrus Microstent (HMS) (Ivantis, Irvine, CA). Design: Subanalysis of data from the randomized controlled HORIZON trial, a multicenter trial including 26 US and 12 international sites. Participants: Participants with mild/moderate primary open-angle glaucoma (POAG) and visually significant cataract with mean modified diurnal IOP between 22 and 34 mmHg after washout of IOP-lowering medications. Methods: A total of 556 subjects were randomized in a 2:1 ratio to undergo cataract surgery with placement of the HMS versus cataract surgery alone (no microstent [NMS]). All eyes were washed out of IOP-lowering medications before surgery and remained unmedicated until surgery. No IOP-lowering prophylaxis was used postoperatively. Comprehensive eye examination including measurement of intraocular pressure was conducted on postoperative day (POD) 1, week 1, and month 1. Main Outcome Measures: Postoperative IOP >40 mmHg was analyzed as the primary outcome. Incidence of IOP increase >10 mmHg above baseline, unmedicated IOP, and mean IOP were analyzed as secondary outcomes. Results: A total of 369 eyes were randomized to the HMS group, and 187 eyes were randomized to cataract surgery alone. The HMS and NMS groups did not differ with respect to baseline demographic or ocular characteristics. On POD1, the incidence of IOP spike >40 mmHg was significantly higher at 14.4% in the NMS group compared with 1.4% in the HMS group (P < 0.001). The incidence of IOP increase ≥10 mmHg relative to baseline on POD1 was also significantly higher in the NMS group than in the HMS group (22.5% vs. 3.0%, P < 0.001). IOP in the NMS group was significantly higher than in the HMS group (27.6 vs. 17.0 mmHg, P < 0.001). In multivariable logistic regression analysis, higher baseline IOP predicted higher odds of POD1 IOP spike >40 mmHg, whereas the presence of HMS was associated with a lower likelihood of postoperative IOP spike. Conclusions: The addition of an HMS at the time of cataract surgery lowered the risk of markedly elevated IOP in the early postoperative period in patients with glaucoma.