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Trabecular micro-bypass stent plus cataract surgery controls IOP at 2 years
The combination procedure also has a favorable long-term safety profile.
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Implantation of a small trabecular micro-bypass stent combined with cataract surgery provided significantly better IOP control, even without IOP-lowering medication, than cataract surgery alone, according to a study.
The study included 116 patients who were implanted with the iStent (Glaukos) and 123 patients randomized to cataract surgery only (control group). Mean IOP remained stable between 12 months and 24 months (17 mm Hg and 17.1 mm Hg, respectively) in the stent group, but rose (from 17 mm Hg to 17.8 mm Hg) in the control group.
“I was very happy to see that the mean IOP and medication burden for the iStent group remained stable at 2 years and that the safety profile of the iStent procedure remains impeccable. These clinical results are similar to my own favorable surgical and clinical experience using the iStent device,” study co-author E. Randy Craven, MD, said.
The study demonstrates that a single iStent achieves a sustained target IOP of less than 18 mm Hg. Emerging data from Ahmed and the MIGS Surgical Charter Group show that multiple iStent implantation in combined cataract procedures and in phakic or pseudophakic eyes can achieve sustained target IOP of 15 mm Hg or lower, Craven said.
Patients who achieve substantial IOP reduction on the first postoperative day seem to maintain long-term pressure control with a single device, he said.
E. Randy Craven
Two-year results of the iStent clinical trial were published in Journal of Cataract & Refractive Surgery.
Reduced need for drugs
The study found that reliance on ocular hypotensive medication was statistically lower in the stent group at 12 months. It remained lower at 24 months but the difference was no longer statistically significant.
“Without question, there is a reduction in the burden of or the need for medications among patients who received the iStent at the same time as cataract surgery,” Craven said.
At 24 months, 61% of stent patients achieved IOP of 21 mm Hg or lower without medication, compared to 50% in the control group; 53% of the stent group achieved an IOP reduction of at least 20% without medication vs. 44% in the control group.
Visual fields and pachymetry on average were comparable for the two groups.
Safety
In June, the U.S. Food and Drug Administration approved the iStent for management of IOP in patients with mild to moderate open-angle glaucoma. The iStent is the smallest medical device implanted in humans, measures 1 mm × 0.3 mm, and weighs 60 µg, according to Glaukos.
The FDA safety requirements mandated that the iStent be evaluated in combination with cataract surgery.
“By already having the lens removed, the FDA knew the stent would not cause a cataract,” Craven said.
Regarding safety, Craven said he has not encountered any unanticipated or serious problems, but three patients in the stent group required stent repositioning, one of whom also had trabeculoplasty.
Craven was the first U.S. investigator to implant the iStent in a clinical trial and has implanted more than 50 stents over the past 7 years.
It takes about five to 10 cases for surgeons to become confident implanting the iStent, according to Craven, namely positioning the patient in the right angle and titling a gonioscope for the proper view.
“You need to be able to see the trabecular meshwork in the opposite angle,” he said.
“[Safety of the iStent] is high enough that it becomes a very attractive consideration for the cataract surgeon in a patient who is on one or two glaucoma medications and heading into cataract surgery,” Craven said. “The iStent offers many patients added benefits beyond phaco in dropping the pressure.”
It may be beneficial to employ more than one stent so that the aqueous humor can better access Schlemm’s canal to reduce pressure.
“Our study tells us that one stent alone sometimes works very well for most patients, but in some patients it does not,” Craven said.
A permanently implanted iStent could evolve into first-line therapy for mild-to-moderate glaucoma, he said. – by Bob Kronemyer