Effect of Intraocular Pressure Control on Visual Field Progression in the HORIZON Trial

PURPOSE: To analyze the effect of intraocular pressure (IOP) characteristics on the 5-year rate of visual field mean deviation (MD) progression in the HORIZON trial. DESIGN: Post-hoc analysis of data from a randomized clinical trial. PARTICIPANTS: Patients with glaucoma and visually significant cataract randomized to cataract surgery (CS) with or without the implant of the Hydrus Microstent (HMS). METHODS: One eye of each participant with at least 3 reliable visual fields (false positive errors ≤15%) over at least 1 year was included. We used a published Bayesian hierarchical model, designed to minimize the effect of perimetric noise and learning. We compared the mean rate of MD progression between the 2 arms and measured the effect of postoperative mean intraocular pressure (MIOP), peak washed-out intraocular pressure (WO-PIOP), mean washed-out intraocular pressure (WO-MIOP), and day-1 IOP. These IOP metrics were mean-centered and standardized (divided by their standard deviation) to allow a direct comparison of their effect. MAIN OUTCOME MEASURES: Mean rate of MD progression. RESULTS: Data from 517 eyes (352 in the CS-HMS arm) were analyzed. The MD rate was -0.55 [-0.72,-0.39] dB/year (mean [95% credible intervals]) for the CS-only arm and -0.30 [-0.38,-0.22] dB/year for the CS-HMS arm (44.6% [18.0, 64.2] reduction, P = 0.004). Increase in all IOP metrics was significantly associated with a faster MD rate. MIOP, WO-MIOP, and WO-PIOP had similar proportional effects. Day-1 IOP had a considerably smaller effect. The difference in rate between the 2 arms remained significant after adjusting for MIOP (P = 0.002) but was largely eliminated after adjusting for WO-MIOP and WO-PIOP (P = 0.396). The MD rate in the CS arm remained significantly faster than CS-HMS (P = 0.001) after removing eyes with a day-1 IOP spike (IOP > 40 mmHg or 10 mmHg above the washed-out baseline IOP). CONCLUSIONS: The MD rate was significantly slower in the CS-HMS arm in the HORIZON trial, compared to CS alone. This difference was not explained by day-1 IOP spikes or MIOP, but was largely accounted for by WO-IOP metrics. FINANCIAL DISCLOSURE(S): Proprietary or commercial disclosure may be found in the Footnotes and Disclosures at the end of this article.