Cataract Surgery Alone or With the Hydrus Microstent?

Shuchi B. Patel, MD


November 09, 2021

Study Summary

The HORIZON trial, which compared cataract surgery alone with cataract surgery in conjunction with implantation of the Hydrus Microstent (Ivantis, Inc; Irvine, California), concluded at 3 years that the combination surgery was more effective at intraocular pressure (IOP) lowering. Furthermore, the study concluded that placement of the Microstent reduced the mean number of medications needed as well as the risk for further incisional surgeries over 3 years.

A total of 556 eyes were included, with eyes randomly assigned 2:1 to either receive the stent or not. The statistically significant findings were that 73% of patients in the Microstent group were medication free compared with 48% in the cataract surgery–alone group. Yet, the mean IOP was similar in both groups at about 17 mm Hg. More medication was required in the cataract surgery–alone group, however, with a mean of 0.8 ± 1.0, while the stent group's mean medication was 0.4 ± 0.8.

There were no procedure- or device-related adverse events or significant loss of corneal endothelial cells. Thus, the data from the HORIZON trial 3-year results suggest that combining Schlemm canal Microstent insertion with cataract surgery in patients with mild to moderate open-angle glaucoma is an effective way to lower IOP with less medication dependence while also potentially reducing the risk of requiring further incisional surgery.


The HORIZON study 3-year results are important for the understanding of long-term effects on IOP with minimally invasive glaucoma surgery (MIGS) procedures. Previous studies on different MIGS procedures, such as the iStent (Glaukos Corporation; San Clemente, California), have shown reduced effectiveness in IOP reduction over time — ie, from 1 year to 2 years postoperatively. Similarly, other MIGS procedures have shown side effects over time, such as loss of corneal endothelial cells. Therefore, long-term safety and efficacy assessment is critical.

This study showed favorable results for implanting the Hydrus Microstent with no serious adverse events. The mean central endothelial cell loss was not statistically significant at any time point between the two groups. However, the loss of 30% or greater endothelial cells was observed at a greater frequency in the Microstent group: 17.3% of eyes at 3 months vs 9.4% of eyes in the cataract surgery–alone group. The percentage of eyes with loss did decrease at 3 years in the Microstent group, with 14.2% of eyes with 30% loss, but increased to 10.0% in the cataract surgery–alone group. This seems to suggest that there is an undeniable initial increase in loss of cells, probably due to the added surgical time and manipulation with insertion of the device, but there is no progressive loss due to the positioning or presence of the device. Thus, in my opinion, the device is safe for implantation without increased risk for progressive endothelial damage. But the initial increase in loss of endothelial cells should be noted — and implantation of the device should be done with caution — in patients with a preexisting increased risk for corneal decompensation.

Another point of note from this study is that the mean IOP in both groups postoperatively was almost the same: 16.7 ± 3.1 mm Hg in the Microstent group and 17.0 ± 3.0 mm Hg in the cataract surgery–alone group, with the difference not reaching statistical significance. The number of patients who maintained this IOP medication-free, however, was statistically significantly higher in the Microstent group, and the mean medication usage was lower in the Microstent group. The study confirmed what may seem a logical conclusion: that eyes receiving one preoperative medication are more likely to remain medication-free compared with eyes receiving two or more preoperative medications. Thus, even though there was a reduction in overall medication usage, to me it is important to note during my preoperative counseling to patients the realistic chance that the patient will be medication-free. Reduction of medication burden is very helpful to many patients, especially those that may be having side effects from certain topical IOP-lowering agents; but to many patients, using a combination drop such as dorzolamide/timolol vs dorzolamide alone is not different, and they may not feel a significant benefit from the additional insertion of a stent. Thus, setting realistic expectations is important with patients, and understanding a patient's goals will aid in deciding whether adding a Microstent to cataract surgery will help achieve the desired outcome. After analyzing the results of this study, it seems that it may be more beneficial to implant a Microstent in patients with mild glaucoma who are taking only one medication so that there is a greater possibility of being medication free.

That being said, the study concluded that the cumulative probability of incisional surgery was lower in the Microstent group compared with the cataract surgery–alone group. Given that the preoperative baseline findings and the postoperative mean IOP were similar in both groups, one possible reason for a higher proportion of patients requiring incisional surgery in the cataract surgery–alone group may be the higher number of medications needed to achieve the goal IOP. Adherence to and long-term compliance with a more complicated medication regimen is known to be challenging. Thus, daily fluctuation in IOP in patients on multiple medications may lead to visual-field loss progression. In addition, even with good compliance, circadian fluctuation in IOP is always more significant in patients with medication usage vs those who have had surgical or laser intervention. This may also account for greater progression of visual-field defects, leading to more candidates for incisional surgery in the cataract surgery–alone group.

Thus, with that information, addition of the Microstent may be beneficial not only in patients with mild glaucoma who are taking one medication (to allow the patient to be medication-free) but also in those with moderate glaucoma who are taking multiple medications (to reduce the risk for future incisional surgery).

I am looking forward to adding Microstent to the MIGS offerings for my patients. In patients who are deemed appropriate candidates from the standpoint of open-angle, mild-to-moderate glaucoma and a healthy cornea, implantation of a Microstent in conjunction with cataract surgery appears to be safe. The reduction in medication burden and the possibility of being medication-free greatly improves quality of life, while the reduced risk for progression of visual-field defects and need for incisional surgery are added long-term benefits. After determining good surgical candidates for Microstent implantation and understanding the goals of the patient and of the intervention, the Microstent will add to the options that patients have to improve their quality of life and vision.

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