Novel microshunt providing dramatic and stable IOP control

TAKE HOME:

An investigational glaucoma device that shunts aqueous from the anterior chamber to a subconjunctival/sub-Tenon’s pouch is being evaluated in a prospective study of 35 eyes operated on at two centers.

By Cheryl Guttman Krader; Reviewed by Richard K. Parrish II, MD

A novel, investigational glaucoma device that shunts aqueous from the anterior chamber to a subconjunctival/sub-Tenon’s pouch (InnFocus MicroShunt [previously known as the MIDI arrow], InnFocus Inc.) is demonstrating very promising results in eyes for up to 2 years in an international prospective study.

“Because this device establishes an outflow path for aqueous into the subconjunctival/sub-Tenon’s space, it has the potential to provide dramatic lowering of IOP,” said Richard K. Parrish II, MD, professor of ophthalmology, Bascom Palmer Eye Institute, University of Miami Miller School of Medicine, Miami. “And, based on its material and design, rates of postoperative hypotony and problems-such as leakage around the device, blockage, erosion, and migration-are low.”

More in Special Report: Study-Visual field loss impacts driving performance

Study findings

Dr. Parrish presented outcomes from a series of 35 eyes with primary open-angle glaucoma (POAG) operated on by Juan Batlle, MD, Santo Domingo, Dominican Republic, and Isabelle Riss, MD, Bordeaux, France. All eyes had a failed response to maximum tolerated medication. Twelve eyes underwent simultaneous cataract surgery, and the other 23 eyes, of which 7 were already pseudophakic, received the microshunt alone. About two-thirds of the patients had at least some Afro-Caribbean, Hispanic, or Arawak Indian heritage with the remainder being Caucasian.

NEXT: Page 2 + Photo

Baseline IOP ranged from 18 to 38 mm Hg, with a mean of 23.8 ± 5.3 mm Hg. Patients were being treated with an average of 2.8 IOP-lowering medications daily.

Data from 22 eyes seen at 2 years show that IOP control remained stable over time. Mean IOP was 11.3 ± 3.2 mm Hg (–55% from baseline), and patients were using an average of 0.3 medications per day. However, 89% of patients were taking no glaucoma medications, and 91% of eyes met criteria for qualified success (IOP < 21 mm Hg with medications plus a 20% drop from baseline).

Not surprisingly, IOP in patients who underwent combined cataract/shunt surgery were 1 to 2 mm Hg lower on average in the first year compared with the subgroup that had only the MicroShunt procedure. However, by year 2, the IOPs were similar in the two cohorts.

Further reading: Near, intermediate vision with inlay maintained over the long-term

All eyes had diffuse blebs except two that did not have discernable blebs, but had IOPs that were stable in the low teens.

There have been few device-related complications, and no patients developed any sight-threatening or persistent adverse events.

Adverse events that occurred in the study eyes included five cases of hypotony (IOP <5 mm Hg after day 1) (14%) that was transient and resolved spontaneously in all cases. Other adverse events were IOP elevation requiring bleb needling (14%), hyphema (14%), corneal edema (11%), choroidal effusion or detachment (6%), and transient tube obstruction by iris, blood, or fibrin (3%).

NEXT: Device material, procedure

Device material, procedure

The device used in the study reported by Dr. Parrish represents a fourth iteration using the inert biomaterial known as SIBS [poly(styrene-block-isobutlylene-block-styrene)].

“This biomaterial is thin and soft, which allows it to conform to the curvature of the eye, the lumen dimensions have been modified to prevent blockage and hypotony, and the fins on the device prevent its migration and leakage around the outside of the tube,” Dr. Parrish explained.

The implantation procedure involves creation of a 6- to 8-mm deep fornix-based subconjunctival/sub-Tenons capsule flap over one quadrant. Using soaked LASIK shields, mitomycin-C (0.2 to 0.4 mg/ml) is placed into the pouch for 2 to 3 minutes and then rinsed out with balanced salt solution.

Next, a half-thickness scleral pocket measuring about 1 × 1 mm is made 3 mm from the limbus with a flat, long-angled knife blade. Then, a 27-gauge needle is advanced through the scleral pocket into the anterior chamber, bisecting the angle between the iris and cornea. The microshunt is inserted through the needle tract using a Kelman or jewelers forceps and fixed into position by wedging its 1.1-mm wingspan fins in the 1-mm wide scleral pocket.

After the surgeon confirms aqueous flow through the device, its distal end is tucked under the flap and then the conjunctiva is closed.

“These results from long-term follow-up in a small series of eyes are encouraging in suggesting that the [microshunt] may be able to achieve its goal of providing a safe, effective, easy to perform, and cost-effective surgical treatment for early-stage to trabeculectomy-stage patients with POAG,” Dr. Parrish said. “We look forward to the results from an ongoing FDA-authorized multicenter, randomized, masked study in the United States that is comparing the [device] with MMC to trabeculectomy with MMC.”

Richard K. Parrish II, MD

E: rparrish@med.miami.edu

Dr. Parrish serves on the scientific advisory board of InnFocus and is compensated for these activities.