Cover Story

Micro-stents progressively defining their role in glaucoma management

Hydrus

The Hydrus is a crescent-shaped device made of nitinol, a highly biocompatible material used for vascular stents. It is implanted into Schlemm’s canal using an injector through a small incision of less than 2 mm.

This novel 8-mm device stents and dilates the canal, providing a greater possibility that multiple collector channels are within the surgical watershed zone, Samuelson said.

The distal end of the Hydrus is advanced through the trabecular meshwork and then into Schlemm’s canal, allowing the aqueous humor to enter the eye at its end and leave the implant through oval-shaped holes into the canal. Studies are testing the effects of the Hydrus in patients with mild-to-moderate glaucoma, relatively high pressure and visual field defects.

“The limitation in IOP decrease is still the episcleral venous pressure, but you are opening up a wider section of Schlemm’s canal, potentially gaining access to more collection channels. Potentially, the long-term efficacy could be higher,” Feijoo said.

The Hydrus has the CE mark in Europe, and Ivantis is active in providing scientific evidence of the safety and efficacy of the device.

Xen

The Xen implant is a small tube made of soft, collagen-derived gelatin that conforms to the ocular tissue, minimizing tissue reaction. It is inserted ab interno with a 27-gauge needle injector through a sub-2-mm incision in clear cornea to connect the anterior chamber to the sclera and episcleral surface. It has evolved through three generations: Xen, Xen mini and Xen nano. Xen has been granted the CE mark in Europe.

“It is a procedure that is generally more potent than other micro-stents like those going in the canal. There are more requirements for postoperative assessment, but one of the benefits is that it can be titrated and modified after surgery,” Ahmed said.

The creation of a bleb is typically seen and is a good sign of success.

“These blebs are more posterior and diffused than in traditional filtration procedures. Some steps are required to keep them healthy, including topical medications and wound-healing therapies with mitomycin C in the early postop. If bleb healing is excessive, it can be titrated by a needling procedure to lower the pressure, but this is not required in the majority of cases,” Ahmed said.

The mechanism of action of the Xen allows for a target pressure in the low teens, which makes it suitable for more advanced glaucoma stages. Although it can be used in combination with cataract surgery, its efficacy is equal, if not greater, as a standalone procedure, according to Ahmed.

“It’s the use of MMC that can make the difference. Without MMC, we can aim for IOP in the mid-teens, with little use of medications. With MMC, we lower the pressure more,” he said.

InnFocus

The InnFocus MicroShunt is a micro-tube made of a biomaterial called SIBS, which is used in coronary stents. It is soft and flexible and conforms to the eye.

In a clinical trial, Juan Batlle, MD, successfully implanted the InnFocus MicroShunt in more than 20 mixed-race patients with a genetic predisposition for tissue reaction.

“There was very little postoperative bleeding or inflammation, and the eyes remained quiet throughout the follow-up. The material is very inert, and surgery does not involve dissection of the sclera or iridectomy. The elimination of iridectomy might reduce the risk of inducing cataract,” Paul Palmberg, MD, PhD, who examined several of the patients at their 2-year postoperative visit and graded the bleb photos for an upcoming publication, said.

“Surgery is quite easy,” he said. “One simply opens the conjunctiva, applies MMC and rinses, makes a needle track, inserts the tube and closes. It takes about 15 minutes instead of 30 to 45 minutes for a trabeculectomy with MMC. Virtually no postoperative care is required.”