For Glaucoma, Microstent May Offer Alternative to Medication

CHICAGO — An intracanalicular microstent achieved significant and sustained lowering of intraocular pressure (IOP) in patients with primary open-angle glaucoma, according to 12-month data from an international trial reported at the American Academy of Ophthalmology (AAO) 2012 Annual Meeting.

"The Hydrus Microstent [Ivantis, Inc, Irvine, California] minimally invasive glaucoma surgery [MIGS] procedure provides safe and effective IOP reduction using an ab interno surgical approach," said Thomas W. Samuelson, MD, of Minnesota Eye Consultants in Minneapolis.

"Significant reductions in IOP and medication use were observed from baseline levels through 12 months, when the device was used alone or in combination with cataract surgery," he reported. "We saw no device migration or perforation, and no serious complications."

The Hydrus device increases outflow facility by bypassing the trabecular meshwork and dilating Schlemm's canal to increase circumferential flow. The implant is composed of nitinol (a nickel-titanium alloy) and has a nonluminal, open design to improve the flow of aqueous humor into the canal and gain better access to collector channels within the canal, Dr. Samuelson explained.

The study included 69 patients with glaucoma, with or without cataracts, with IOP ? 26 mm Hg and who were currently on up to 4 glaucoma medications.

In the 40 patients having Hydrus surgery alone, mean IOP was 21.6 mm Hg at baseline and dropped to 17.9 mm Hg 12 months after device implantation (P < .05). Mean number of glaucoma medications was reduced from 1.7 to 0.3, Dr. Samuelson reported.

Transient hyphema was the most common adverse event, which occurred in 17% of patients and was transient (< 7 days) in 15%. Four patients developed peripheral anterior synechia, 1 had a corneal complication, 2 had IOP > 10 mm Hg over baseline, and 1 had some vision loss.

Hydrus Plus Phaco

"MIGS outcomes are often reported in conjunction with cataract extraction, which is known to lower IOP itself, so the contribution of the device itself is not well understood. The study examined the effect of the Schlemm's canal microstent on IOP reduction," he said. Phacoemulsification was completed prior to device implant.

In the 29 patients who received both glaucoma stenting and cataract surgery, mean IOP decreased by 4.2 mm Hg, from 21.1 mm Hg at baseline to 16.9 mm Hg at 12 months, a 22% reduction. The number of medications was reduced by 2.1 medications per patient, Dr. Samuelson reported — a 95% reduction.

"At 12 months, 26 of 29 patients were entirely medication free," Dr. Samuelson noted.

A preoperative and 12-month medication washout was instituted to determine the IOP-lowering effect of the device alone. In the washout analysis, change in IOP was from 25.5 mm Hg at baseline to 16.9 mm Hg at 12 months, a 33% reduction. A 20% drop in IOP was achieved by 85% of patients, he stated in his presentation.

There was 1 case of mild iris damage but no other surgical complications in this cohort. There were no reports of hypotony, endophthalmitis or shallow anterior chamber; 3 patients developed a small area of peripheral anterior synechia.

Dr. Samuelson said the median pressures and medication-free distribution "suggests stability from 1 to 18 months post-operatively" with the Hydrus Microstent, and noted that 5 randomized controlled trials are now under way in the United States and elsewhere.

Microstents May Be Best Suited for Mild/Moderate Cases Only

Putting the Hydrus and other microstents into perspective were Robert L. Stamper, MD, professor of clinical ophthalmology and director of the Glaucoma Service at the University of California, San Francisco, and Peter Andreas Netland, MD, PhD, the DuPont Guerry III Professor and chair of the Department of Ophthalmology at the University of Virginia, Charlottesville.

Dr. Stamper noted that the Hydrus is 1 of several stents implanted in Schlemm's canal and is slightly larger than the currently approved iStent. "The shape is such that it presumably preserves access to the collector channels that go through the outer wall of Schlemm's canal, so theoretically it should have a little better IOP response," he said. He added that the device must be threaded across a longer course, "but once you find the right way, it goes easily."

He suggested that 4-mm IOP-lowering "is not exactly spectacular," but, on the other hand, "going from 2 medications to almost none is impressive."

Dr. Netland agreed, noting that the microstents under evaluation "hit IOP in the mid-teens, and this has got to improve. The typical glaucoma patient we see has advanced cupping, and this is not the solution for these patients, whose target pressures are 10 or 12 mm Hg."

This means that microstents may not be the solution for advanced glaucoma, Dr. Stamper continued, but suggested, "if we find a surgical procedure that is safe, relatively quick to do and gets pressure down to the mid-teens, we may expand the indications for surgery in earlier glaucoma, particularly given what we know about poor adherence and cost of medical therapy. These patients may be nicely controlled with pressures of 15 to 17 mm Hg," he said.

Randomized, controlled, comparative studies will be important in the pursuit of "this interesting concept," Dr. Stamper emphasized.

Dr. Samuelson is an investigator for and consultant to Ivantis, Inc, which manufactures the device. Dr. Stamper disclosed financial relationships with Alcon Laboratories, iScience, SightSciences, and Transcend, Inc. Dr. Netland disclosed relationships with Alcon Surgical and Solx.

American Academy of Ophthalmology (AAO) 2012 Annual Meeting: Abstract PA098. Presented November 13, 2012.