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What do the numbers tell us about the iStent?
More studies and longer-term follow-up continue to show good results for glaucoma patients implanted with the MIGS device.
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As a cataract surgeon, my primary concern is managing a patient’s cataract. I want to provide my patient with the best vision and fewest postoperative issues possible. When I finish a case that in my mind went perfect, do I really want to tilt the patient’s head, tilt the microscope and deal with a glaucoma stent?
It is easy to convince ourselves that if a patient with concomitant glaucoma is controlled on drops, we should leave well enough alone. But my feeling is I have a responsibility to help these patients have better IOP control and relieve them of topical drops. Patients from 30 to 80 years old, whether they are truck drivers or physicians, are always going to miss some drops. And experience with the iStent trabecular micro-bypass stent (Glaukos) has shown increasingly that it reduces pressure, gets patients off drops and does not negatively impact cataract surgery outcomes.
Recent and significant improvements in real-world results
The initial U.S. pivotal study for the iStent was submitted to the FDA in 2008. It compared a total of 240 eyes with mild to moderate open-angle glaucoma that underwent either cataract surgery alone or cataract surgery in conjunction with a single iStent. The primary efficacy measure was unmedicated IOP less than 21 mm Hg at 1 year, and 72% of eyes with the iStent met this goal, compared with 50% of eyes that underwent cataract surgery alone. The iStent achieved the necessary endpoints, the FDA approved the device, and a new category for treating glaucoma was launched.
One of the most exciting aspects of the evolution of microincision glaucoma surgery is the continued and significant improvement in clinical results that we have seen since then. Mark Gallardo, MD, presented his clinical results at the 2016 American Society of Cataract and Refractive Surgery meeting. His consecutive case series of 72 eyes of 48 patients were all implanted with a single iStent at the time of cataract surgery. Mean IOP was 15.3 ± 3.2 mm Hg at baseline, and 75% were taking two to four medications. At 6-month follow-up, 86% had met the surgical goal of IOP less than 14 mm Hg, and medication reduction was greater than one.
A paper presented by Michael Stiles, MD, also at ASCRS, described one surgeon’s positive experience with a series of glaucoma patients with prior medical and/or surgical therapy for glaucoma. In this series of 50 eyes of 41 patients with a mean baseline IOP of 18.6 ± 4.6 mm Hg, 48% were taking two or more medications, and 36% had undergone prior glaucoma surgery. At 1 year, mean IOP was 15.4 ± 2.4 mm Hg with 63% on no medications and 26% on a single medication. IOP reduction ranged from a mean of 3.2 mm Hg in eyes with a preoperative IOP between 16 mm Hg and 20 mm Hg, to a mean reduction of 10.7 mm Hg in eyes with a preoperative IOP greater than 25 mm Hg. This shows that in patients farther from the normal episcleral back pressure, the reductions in IOP are greater.
Duration of efficacy
While the initial iStent pivotal trial was only powered for 1 year, more recent studies demonstrate the durability of efficacy of the iStent. A prospective, non-randomized case series was published in 2012 that followed patients for a mean of 53.68 ± 9.26 months. Although there were only 19 patients in this series, they showed a mean decrease in IOP from 19.42 ± 1.89 mm Hg at baseline to 16.26 ± 4.23 mm Hg at follow-up, indicating a 16.33% decrease in IOP in addition to a reduction in hypotensive medications from 1.32 ± 0.48 to 0.84 ± 0.89.
A study published last year by Tobias Neuhann, MD, also showed excellent results and efficacy out to 3 years. iStent implantation in conjunction with cataract surgery was performed in 62 eyes of 43 consecutive patients. From the 41 eyes that have 3 years of follow-up, mean IOP dropped from 24.1 ± 6.9 mm Hg at baseline to 14.9 ± 2.3 mm Hg at 36 months. In addition, 75% of eyes no longer required medication.
Looking to the future
While current FDA labeling only indicates the implantation of a single iStent in conjunction with cataract surgery, clinical studies outside the U.S. have evaluated the placement of multiple iStents and standalone iStent procedures. Buchacra and colleagues published a prospective, non-randomized case series of 10 patients with secondary open-angle glaucoma who underwent ab interno implantation of the iStent. At 12 months, patients saw a mean drop in IOP of 6.6 ± 5.4 mm Hg, as well as a mean drop in medications of 1.1 ± 0.6.
Several studies have also evaluated implantation of multiple iStents. A dose response study by Jay Katz, MD, and colleagues compared one, two and three stents implanted as sole procedures. With a single stent, 65% of patients achieved IOP less than 15 mm Hg without the use of medications through 18 months. Of the 41 subjects who received two stents, 85.4% achieved unmedicated IOP of less than 15 mm Hg, and of the 40 subjects who received three stents, 92.1% achieved the same endpoint. A pilot study evaluated placement of two iStents in 39 eyes and found a mean reduction in IOP from baseline of 44%, with most of those subjects maintaining target IOP through 36 months.
As surgeons become increasingly proficient with the placement of these devices, I expect that we will see continued broad improvements in iStent clinical results in mild to moderate open-angle glaucoma patients. These results are occurring independent of targeted or “intelligent” placement of these devices. Intelligent placement promises even further potential clinical gains in the use of these trabecular bypass stents.
My personal experience
I used to perform trabeculectomy in conjunction with cataract surgery for patients who needed it, and I stopped because of the increased risks involved with performing trabeculectomy. Additionally, we had excellent glaucoma surgeons in our practice who would do the surgery. Now that we have the option to surgically manage glaucoma that does not increase the risk factor beyond typical cataract surgery, I am once again treating my patients’ glaucoma. I have found that approximately 70% of my patients are able to eliminate their glaucoma medications following iStent placement. This represents a significant cost savings for patients and the health care system, along with more consistent pressure control and less treatment burden for patients. I look forward to seeing what the next generations of iStents and other upcoming MIGS procedures will bring.
- References:
- Arriola-Villalobos P, et al. Br J Ophthalmol. 2012;doi:10.1136/bjophthalmol-2011-300218.
- Buchacra O, et al. Clin Ophthalmol. 2011;doi:10.2147/OPTH.S15025.
- Donnenfeld ED, et al. Clin Ophthalmol. 2015;doi:10.2147/OPTH.S91732.
- Gallardo M. Intraocular pressure control with reduced medication burden after cataract surgery and ab interno trabecular stent implantation for OAG and cataract. Presented at ASCRS annual meeting; May 7, 2016; New Orleans.
- Katz LJ, et al. Clin Ophthalmol. 2015;doi:10.2147/OPTH.S96695.
- Neuhann TH. J Cataract Refract Surg. 2015;doi:10.1016/j.jcrs.2015.06.032.
- Samuelson TW, et al. Ophthalmology. 2011;doi:10.1016/j.ophtha.2010.07.007.
- Stiles M. Trabecular bypass stent and cataract surgery in glaucoma patients with previous medical/surgical therapy: 2-year single-site outcomes. Presented at ASCRS annual meeting; May 7, 2016; New Orleans.
- For more information:
- Robert J. Cionni, MD, can be reached at The Eye Institute of Utah, 755 East 3900 South, Salt Lake City, UT 84107; email: rcionni@theeyeinstitute.com.
Disclosure: Cionni reports no relevant financial disclosures.