Schlemm canal microstent implantation associated with long-term reduction in intraocular pressure and need for additional surgeries

1. Among patients with primary open angle glaucoma and cataract, implantation of a Schlemm canal microstent in addition to cataract surgery is more effective at lowering intraocular pressure with fewer medications at three years compared with cataract surgery alone.

2. Patients who underwent both microstent placement and cataract surgery were significantly less likely to require a further intraocular pressure-lowering surgery at three years.

Evidence Rating Level: 1 (Excellent)

Study Rundown: Two of the most diagnosed ocular disorders in the U.S. are age-related cataract and glaucoma. Multiple randomized studies have demonstrated how minimally invasive glaucoma surgery (MIGS) implants placed in Schlemm’s canal in addition to cataract surgery lowers intraocular pressure (IOP) and medication use compared with cataract surgery alone for patients with primary open angle glaucoma (POAG) and cataract. Evidence for efficacy beyond two years, though, is lacking. This study reports on three-year outcomes of the HORIZON study, a 2019 randomized controlled trial comparing cataract surgery with implantation of a Schlemm canal Hydrus^® Microstent (HMS cohort) with cataract surgery alone (CS cohort) for the reduction IOP and medication use after 24 months.

Primary outcomes included, among others, IOP, medication use, rate of reoperation, and adverse events. A total of 556 patients were included. At three years, there was no significant difference in IOP between the HMS and CS cohorts. The number of glaucoma medications as well as medication-free eyes, however, was significantly lower in the HMS cohort; furthermore, the HMS cohort had a greater number of eyes with IOP ≤ 18 mmHg without the use of medications as well as a greater proportion of IOP reduction of at least 20, 30, or 40 percent compared with the CS cohort. Kaplan-Meier time to event analysis revealed a significant increase in the risk of incisional surgery among the CS cohort; indeed, the cumulative probability of surgery was 3.9% in the CS cohort and 0.6% in the HMS cohort. Overall, there were very few adverse events in both cohorts between years two and three.

Strengths of this study include the randomized design as well as large sample size. Limitations include not repeating medication washout after two years; thus, IOP reduction attributed to the microstent alone at three years is indirect. In all, this study suggests that cataract surgery and microstent implantation compared with cataract surgery alone is associated with a long-term reduction in IOP and medication usage, as well as the need for additional IOP-lowering procedures.

Click here to read the study in Ophthalmology

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

In-depth [randomized controlled trial]: 369 patients were randomized to the HMS cohort and 187 to the CS cohort. IOP between the HMS and CS cohorts did not differ significantly at three years (16.7±3.1 vs. 17.0±3.4, p = 0.85). However, compared with the CS cohort, patients in the HMS cohort were at three years on significantly fewer glaucoma medications (0.4±0.8 vs. 0.8±1.0, p < 0.001) and significantly more likely to be medication free (73% vs. 48%, p < 0.001). They were also significantly more likely to have an IOP ≤ 18 mmHg (56.2% vs. 34.6%, p < 0.001). Importantly, the cumulative probability of incisional glaucoma surgery was significantly lower in the HMS cohort compared with the CS cohort (HR 0.156, 95% CI 0.031 to 0.773, p = 0.02). Although incidence was low in both cohorts, IOP-lowering surgery is a dramatic escalation in management and carries with it serious risk. Thus, the lower incidence seen in the HMS cohort likely has significant impact on future wellbeing.

Image: PD

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