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By Laird Harrison
Several new microinvasive glaucoma surgery (MIGS) devices offer promise for treating glaucoma, reported Steven Vold, MD. He pointed out that initial results are encouraging with early mean postoperative IOP using these devices generally in the mid-to-high teens.
Dr. Vold, medical director of Vold Vision, PLLC, Fayetteville, AR, began by describing the iStent inject (Glaukos), a second-generation version of the iStent. “What we’re trying to do is simplify the iStent procedure,” said Dr. Vold.
Steven Vold, MD. points out that the new MIGS devices are encouraging platforms in treating glaucoma.
Using the accompanying M-IS injector, “we can actually implant multiple devices by just simply hitting the button on the device and it will inject,” said Dr. Vold. “It will implant the device into proper position very nicely with good surgical technique.”
The iStent inject resembles a rivet in shape. The end of the rivet inserts into Schlemm’s canal, with the head in the anterior chamber allowing aqueous fluid to pass through the lumen in the middle of the device.
The injection takes only seconds, said Dr. Vold. “The design and efficiency of the procedure is impressive.” It’s so easy it might one day be offered in ophthalmology offices and could potentially be performed in a minor procedure suite, he said.
He moved next to the Ivantis Hydrus Aqueous implant. This device takes the form of a flexible scaffold composed of a biocompatible alloy of nickel and titanium, called nitinol. Its scalloped and open design allows for aqueous flow along its three-clock-hour length, targeting multiple collector channels.
“Our hope with this device is that we’re actually expanding the area of aqueous outflow,” said Dr. Vold. “What this stent does is dilate and permanently support Schlemm’s canal.”
In one preliminary clinical trial cited by Dr. Vold, the device reduced IOP from a mean of 20.3 mm Hg to about 15 mm Hg and reduced the number of medications needed. The skill set required to implant the device is similar to what is needed for the Trabectome (NeoMedix) or the iStent, Dr. Vold added.
He moved next to a discussion of devices that target the uveoscleral aqueous outflow pathway. “When I first started my residency, we thought this outflow was about 10% of our total aqueous outflow,” said Dr. Vold. “More recent studies show it’s really over 50%, which makes it a really nice target for lowering IOP.”
The exit is primarily through the sclera and choroidal blood vessels, and its highest point of resistance is the ciliary body, he said. The pressure gradient is relatively robust, with a differential between the anterior chamber and the suprachoroidal space of about 4 mm Hg, he said.
He added that its surface area is 160 times greater than the trabecular meshwork. “Theoretically, suprachoroidal devices offer superb IOP-lowering efficacy based on physiological mechanism.”
In the past, surgeons created cyclodialysis clefts with inconsistent postoperative results, he said. The new devices are designed to create a predictable, controlled cyclodialysis cleft.
The CyPass Micro-Stent (Transcend Medical) and the iStent supra (Glaukos) are both designed to release aqueous through the uveoscleral outflow pathway. Techniques for implanting these two devices are similar, said Dr. Vold.
Preliminary safety results from international experience are in line with other microinvasive glaucoma surgery (MIGS) devices, he added. “It really does appear to have a very promising future.”
Finally, Dr. Vold described two novel subconjunctival devices: the XEN Implant (AqueSys) and the MicroShunt (InnFocus).
The Xen is a gel-based implant with a bore of only 45 µm that connects the anterior chamber to the subconjunctival space, said Dr. Vold. “It’s being placed in the United States in refractory glaucoma patients,” he said. “We have participated in two FDA-approved clinical trials.”
In one study, researchers have injected it from an ab-interno approach without an antifibrotic agent, and in another with mitomycin C.
“It’s very versatile,” said Dr. Vold. “As a single implant, it delivers desired efficacy. It’s removable and potentially repeatable. And it’s certainly a less invasive procedure than what you’ll see with a trabeculectomy.”
Traditional trabeculectomy requires more dissection of Tenon’s capsule and the conjunctiva. There is significant inflammation healing response.
“We’re getting outstanding results with the pressure often in the low-to-mid teens, a tremendous drop in IOP,” said Dr. Vold about the Xen. “This is approved in Europe, and it’s really doing quite well on the market.”
The InnFocus MicroShunt works on a similar principle. It has a 70-µm lumen and is about 8.5 mm in length.
It is made out of poly (styrene-block-isobutylene-block-styrene) known as SIBS, “an incredibly noninflammatory material” used in Boston Scientific’s Taxus coronary stents.
“The concept is the less we have inflammation, the better for our patients,” said Dr. Vold. He showed slides in which the MicroShunt caused much less scarring than was caused by silicon rubber. “So clearly the type of material potentially matters,” he added.
In early clinical trials, the MicroShunt has lowered IOP into the low teens. “Again, many of these patients are getting off almost all their medication “said Dr. Vold. “These filtration blebs are posterior and lightly vascular in nature. Early postoperative data looks incredibly good.”