Microstent demonstrates stable treatment benefit compared with cataract surgery alone

Take-home message: Eyes undergoing implantation with an investigational Schlemm’s canal microstent at the time of cataract surgery achieve significantly greater IOP control than eyes having cataract surgery alone.

By Cheryl Guttman Krader; Reviewed by Thomas W. Samuelson, MD

Minneapolis-Implantation of an investigational microstent (Hydrus Microstent, Ivantis) into Schlemm’s canal at the time of cataract surgery significantly reduces IOP and medication use in eyes with open-angle glaucoma.

In addition, the device remains safe and effective with follow-up to 2 years, according to the results from a randomized, controlled clinical trial.

Known as Hydrus II, the European study enrolled 100 patients at seven centers in Europe. Patients underwent medication washout after a screening visit and then were randomly assigned after uncomplicated cataract surgery into groups to receive the microstent or no further treatment.

IOP outcomes were analyzed based on diurnal measurements taken following medication washout at baseline and after 1 and 2 years. Per protocol, medication was used systematically after surgery if IOP was >19 mm Hg.

Efficacy analyses showed highly statistically significant differences favoring the combination surgery group versus the controls for proportion of eyes with >20% IOP lowering without medication at 1 year (88% versus 74%) and at 2 years (80% versus 46%).

In addition, mean diurnal IOP without medication was significantly lower in the combination surgery versus control group at 1 year (16.6 versus 17.4 mm Hg) and at 2 years (16.9 versus 19.2 mm Hg).

There was also a highly statistically significant difference favoring the combination group compared with the controls in an analysis of proportion of eyes remaining medication-free at both 1 year (77% versus 47%) and 2 years (73% versus 38%), said Thomas W. Samuelson, MD, who is medical monitor for the trial.

“Randomized controlled trials for glaucoma devices are rare, and [the manufacturer of this device] should be congratulated for sponsoring a study of this sort that was undertaken prior to the U.S. PMA trial,” said Dr. Samuelson, adjunct associate professor of ophthalmology, University of Minnesota, Minneapolis, and attending surgeon, Minnesota Eye Consultants, Minneapolis.

“It is the first study of a microinvasive glaucoma surgery (MIGS) procedure to use a medication washout protocol to evaluate efficacy, and this microstent is the first MIGS device to demonstrate a stable treatment benefit compared with cataract surgery alone in its ability to lower IOP more than 20% from baseline at 2 years,” he added.

About the device

The microstent dilates and scaffolds Schlemm’s canal. It is made of flexible nitinol, traverses Schlemm’s canal for 8 mm, provides 3 clock hours of scaffolding, and improves access of aqueous to multiple collector channels.

It is implanted through an ab interno incision, and its efficacy for lowering IOP is thought to occur by enabling aqueous outflow facility via two routes-directly through the device’s inlet that resides in the anterior chamber and through the dilated intact inner wall of Schlemm’s canal, Dr. Samuelson explained.

Discussing the design of the Hydrus II trial, he explained that the medication washout protocol removes much of the confounding effect of medication on IOP outcomes. As expected due to the systematic, per protocol method of adding back medication, mean medicated IOP was similar in the combination surgery and control groups at baseline (26.3 and 26.6 mm Hg) and after both 1 year (16.0 and 15.8 mm Hg) and 2 years  (16.4 and 17.0 mm Hg ).

The two study groups were also similar at baseline in most other disease-related characteristics. Most eyes in both groups had primary open angle glaucoma, mean vertical cup:disc ratio averaged 0.62, and patients in both groups were on an average of 2 medications for IOP-lowering. The mean deviation was higher in the eyes undergoing cataract surgery alone than in the combination group (–8.36 versus -5.6 dB), although the pattern standard deviation was similar (5.2 versus 5.1).

“The difference in mean deviation may be explained by the cataract surgery only group having slightly denser cataracts than the combination group,” Dr. Samuelson said. “Importantly, however, the pattern deviation was the same in the two study arms.”

Favorable safety profile

Implantation of the microstent was successful in 96% of the 50 eyes.

“That is an impressive figure considering that many of the participating surgeons were doing their first cases with this device in the context of the clinical trial,” Dr. Samuelson said.

Procedure-related adverse events included 3 eyes that developed hyphema after surgery in the combination group and single cases each of corneal edema and hypotony in the control group.

Other safety data showed that the incidence of IOP spikes on the first postoperative day was lower in the eyes implanted with the microstent compared with the cataract surgery only group whether using the cut-off of IOP >30 mm Hg (12% versus 42%), >35 mm Hg (10% versus 26%), or >40 mm Hg (2% versus 10%).

“It is no surprise to see IOP >30 mm Hg in some eyes since the surgery was performed after medication washout,” Dr. Samuelson said. “However, such high IOPs were less likely in eyes that received the MIGS device.”

By 2 years, 9 eyes (18%) developed focal peripheral anterior synechiae to the device’s inlet in the anterior chamber, but the synechiae did not affect IOP-lowering efficacy. One eye in the combination group and 2 eyes having cataract surgery alone underwent glaucoma surgery. There were no cases of stent migration or need for repositioning or removal.

Thomas W. Samuelson, MD

E: twsamuelson@mneye.com

This article was adapted from Dr. Samuelson’s presentation at the 2015 meeting of the American Society of Cataract and Refractive Surgery. Dr. Samuelson is a consultant, investigator, and/or advisor for Ivantis and many companies marketing or developing MIGS procedures.