Microstent Keeps Intraocular Pressure Low


In glaucoma patients, the implantation of an intracanalicular microstent (Hydrus, Ivantis) maintains low intraocular pressure for 2 years and reduces the need for medication, a new study has shown.

This is the first randomized controlled trial of a microinvasive glaucoma surgery device using a washout period to separate the effects of drugs from surgery, said Thomas Samuelson, MD, an ophthalmologist in Minneapolis.

Dr Samuelson presented the findings here at the American Glaucoma Society 2015 Annual Meeting.

Microstents are an alternative to trabeculectomy because the implantation is less invasive, and they are an alternative to medication because they eliminate issues related to allergies and convenience.

The stent used in the study — which is composed of nitinol, a nickel–titanium alloy — bypasses the trabecular meshwork and scaffolds and dilates Schlemm’s canal. Its open windows are intended to prevent the obstruction of collector channels and improve the flow of aqueous humor into the canal.

To study the effect of the stent on intraocular pressure, the researchers recruited patients with primary open-angle glaucoma, pseudoexfoliative glaucoma, or pigment dispersion glaucoma from seven sites in Europe.

Fifty eyes were randomly assigned to stent implantation during cataract surgery, and 50 eyes, which served as the control group, were randomly assigned to cataract surgery alone.

All patients discontinued their hypotensive medications during washout periods before surgery, 12 months after surgery, and 24 months after surgery so that intraocular pressure could be assessed without the influence of topical hypotensive medications.

Intraocular pressure and the need for medication decreased after surgery in both groups. In the stent group, the reductions were maintained at 24 months. In the control group, however, pressure and medication use increased after 12 months.

At 24 months, intraocular pressure was significantly better in the stent group than the control group (P = .0093).

A reduction in intraocular pressure of at least 20% was achieved by more patients in the stent group than in the control group at 12 months (88% vs 74%) and at 24 months (80% vs 46%; P = .0008).

At 24 months, more patients in the stent group than in the control group were receiving no hypotensive medications (73% vs 38%).

Table. Intraocular Pressure During the Study Period

Intraocular Pressure Stent Group (mm Hg) Control Group (mm Hg)
Before washout 18.6 18.9
At baseline washout 26.6 26.3
At 12-month washout 17.4 16.6
At 24-month washout 19.2 16.9

 

There were few surgical complications. The most common adverse events were focal peri-stent peripheral anterior synechiae or adhesion, which occurred in 15 eyes in the stent group and two in the control group.

After the presentation, session moderator Janet Serle, from Mount Sinai Hospital in New York City, asked Dr Samuelson about the learning curve for this particular stent, compared with other stents.

“One thing that’s a little bit different is that you have to maintain your very good view and the patient can’t have any saccades throughout the deployment process,” Dr Samuelson explained.

And the Hydrus tracks well within Schlemm’s canal, “so there’s really no doubt whether you’re in the canal or not; there’s no guessing. If it doesn’t track, you know something has gone awry,” he said.

In general, however, the learning curve is “fairly similar” to the other canal-based devices and to the Glaukos iStent, Dr Samuelson reported.

Dr Serle also wanted to know whether stent patients could achieve intraocular pressure from 10 to 12 mm Hg without the use of medication.

The prospect of such low pressure is doubtful without medication, Dr Samuelson said. “But I think with the mixed procedures and the good pharma we have, we could start to achieve levels in the low teens.”

A panelist at the session, Paul Palmberg, MD, from the University of Miami, asked if there really were no cases of hypotony or other serious adverse events. Dr Samuelson confirmed that there were not.

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