Implantation of a trabecular bypass microstent (iStent GTS-100 Trabecular Micro-Bypass Stent, Glaukos Corp.) effectively lowered IOP and dramatically decreased anti-glaucoma medication use among 48 subjects in a prospective, 24-month, multicenter evaluation. The stent bypasses the blocked trabecular meshwork to allow aqueous fluid to move into the Schlemm's canal area and then out through collector channels.
"Implantation of the study stent effectively lowered IOP without conjunctival incisions or complications traditionally associated with filtering procedures and subconjunctival drainage tubes," said E. Randy Craven, MD, at the annual meeting of the American Society of Cataract and Refractive Surgery. The stent also reduced reliance on topical ocular hypotensive agents throughout a 12-month follow-up, he said.
Dr. Craven, one of the founders of Glaucoma and Cataract Consultants of Colorado, Littleton, and an associate clinical professor of ophthalmology at the University of Colorado School of Medicine, Denver, said many new therapies are targeting reduction of IOP without creating a filtering bleb.
"This procedure bypasses the trabecular meshwork to access Schlemm's canal and presents a way to get aqueous fluid into the Schlemm's canal area and then out through the collector channels," he said.
Dr. Craven and colleagues conducted a prospective, 24-month, multicenter, multi-country evaluation of 59 subjects with uncontrolled primary open-angle glaucoma (POAG) and cataract. The subjects underwent clear cornea phacoemulsification cataract extraction, followed by ab interno gonioscopically guided implantation of the trabecular micro-bypass stent. To be included in the study, subjects must have had a baseline IOP of >18 mm Hg on at least two preoperative visits and be taking at least one anti-glaucoma medication.
Most of the subjects were female (66.1%), and the vast majority (98.3%) were Caucasian. Mean age was 74.6 years (range, 28 to 87 years). Baseline mean IOP was 21.5 mm Hg, and baseline mean number of glaucoma medications was 1.7. In terms of ophthalmic history, 16.9% of the patients had pseudoexfoliation, 15.2% had macular degeneration, 8.5% had pigment dispersion syndrome, and 6.8% had undergone prior argon laser trabeculoplasty.
Eleven subjects were removed from the per-protocol analysis based on inclusion/exclusion criteria, leaving a total of 48 subjects in the per-protocol population. This changed the baseline mean IOP to 21.9 mm Hg and the baseline mean number of medications to 1.6.
IOP, drug burden reductions
On day 1 after the implantation of the stent, IOP dropped from a mean of 21.9 mm Hg to a mean of 17.6 mm Hg (p < 0.001). This improvement persisted out to 12 months, when mean IOP was 17.4 mm Hg. The stent also provided a significant reduction in drug burden, from a mean of 1.6 preoperatively to 0.4 at 12 months (p < 0.001). Half of the patients (50%) had an IOP of less than 18 mm Hg at 12 months with no medications.
The most common adverse events were stent lumen obstruction (seven of 59 subjects) and stent-iris touch (six subjects). Other adverse events were trabeculectomy (three), inability to implant stent (two), explanting of malpositioned stent with replacement (two), repositioning malpositioned stent (one), postoperative anterior chamber collapse (one), vitrectomy at the time of cataract surgery (one), and incorrect laterally implanted stent (one).
In describing the surgical technique to implant this stent, Dr. Craven said the idea is to visualize the trabecular meshwork then place the stent through the trabecular meshwork into Schlemm's canal, thus providing a trabecular bypass.
"It's easy to visualize the trabecular meshwork with moderately high magnification, and when you push the stent down into it, you'll see a reflux of blood come out once you've gone into Schlemm's canal," he said. "That helps you identify that you're in the right place."
Once the stent has been placed, Dr. Craven said, he uses irrigation and aspiration to clean up any blood products around it, and then he gently nudges the tip of the device to make sure it is well-seated in the trabecular meshwork.
"This stent provides me a way of bypassing where the glaucoma supposedly occurs, which is a blocked trabecular meshwork," Dr. Craven said. "The promising technique with this stent allowed us to work with the combination cataract and glaucoma procedure, allowed us to have a reduced drug burden, maintained IOP reduction at a year out, and did so without creating a filtering bleb."