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Digital Supplement | Sponsored by Alcon

The Evidence: A Clinical Perspective on the HORIZON Trial


It has been a little over a decade since the first standardized definition of micro-invasive glaucoma surgery (MIGS) was introduced.1 In that time, ophthalmology has seen the release of various devices and surgical techniques within the category that have transformed how glaucoma patients are managed. Taken together, it is fair to say that the introduction of MIGS has revolutionized what we are capable of doing on behalf of our patients; clinical trial data from major studies continue to demonstrate repeatable and predictable IOP responses after MIGS procedures with demonstrated safety. Clinical trials, like the HORIZON trial, show us that MIGS devices are also associated with a greater ability to reduce or eliminate medication burden and achieve long-term IOP stability.2-4

It is always relevant to ask to what degree clinical trial data might apply to one’s clinical practice. Are the findings limited to the particular study population, or do they represent what you might find in the real world? Data from a well-designed and executed prospective clinical trial conducted within a highly representative population with sufficient enrollment might aid in our interpretation as we attempt to guide our practices by the available evidence. We should also look at MIGS device studies not only for whether they demonstrate statistical significance in favor of one group or the other, but whether those outcomes are truly clinically meaningful.

The HORIZON trial, in which the Hydrus Microstent (Alcon LLC; Fort Worth, TX; USA) plus cataract surgery (CS) was compared to CS alone, may be such a clinical trial from which our field can learn to further improve outcomes for patients with primary open-angle glaucoma (POAG). After 2 years, this pivotal trial led to US FDA approval after it met its primary endpoint in demonstrating a greater percentage of patients achieving a 20% or more reduction in IOP compared to CS alone.2 The trial sponsor had the great foresight to plan patient enrollment for 5-year follow-up, and in the subsequent years of the study of the device, the long-term safety and efficacy were confirmed.3,4

The study shows us the very real impact we can potentially have in our patients’ lives. MIGS has allowed us to surgically intervene earlier in the disease continuum, addressing the anatomy of the aqueous drainage pathway to accomplish long-term control of the only known, modifiable, risk factor to prevent progression. These facts are extremely meaningful when sitting with the individual patient explaining the options available for addressing elevated IOP in patients with mild-to-moderate POAG.

I sat down with two of my trusted colleagues, Brian Flowers, MD, and Pradeep Ramulu, MD, PhD, to review this impressive data set and to talk about how we each interpret findings from HORIZON in our own clinical practices (Figure 1). The results of this collaboration are included in this supplement. As we reviewed all the evidence and talked through the nuances, it became apparent that the true benefit of MIGS versus cataract surgery was not represented in a single finding from HORIZON; rather, the additive effects of gaining control of the IOP in a way that addresses the significant medication compliance issues our patients face suggests we are doing something fundamental to address the disease course. The evidence makes the difference as we expand MIGS devices and shape our decision-making.

Figure 1. From left to right, Drs. Ramulu, Flowers, and Singh sit down to discuss the latest data from the HORIZON trial at AAO 2022 in Chicago.

— I. Paul Singh, MD

1. Saheb H, Ahmed II. Micro-invasive glaucoma surgery: current perspectives and future directions. Curr Opin Ophthalmol. 2012;23(2):96-104.

2. Samuelson TW, Chang DF, Marquis R, et al; HORIZON Investigators. A schlemm canal microstent for intraocular pressure reduction in primary open-angle glaucoma and cataract: The HORIZON Study. Ophthalmology. 2019;126(1):29-37.

3. Ahmed IIK, Rhee DJ, Jones J, et al; HORIZON Investigators. Three-year findings of the HORIZON Trial: a schlemm canal microstent for pressure reduction in primary open-angle glaucoma and cataract. Ophthalmology. 2021;128(6):857-865.

4. Ahmed IIK, De Francesco T, Rhee D, et al; HORIZON Investigators. Long-term outcomes from the HORIZON Randomized Trial for a schlemm’s canal microstent in combination cataract and glaucoma surgery. Ophthalmology. 2022;129(7):742-751.