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Treatment options expand for patients along continuum of mild-to-severe disease
MIGS continues to be a surgery option for glaucoma and is a key technology disrupter in ophthalmology.
Reviewed by Michele C. Lim, MD
Minimally invasive glaucoma surgery (MIGs) represents one of the most exciting innovations in ophthalmology, according to Michele C. Lim, MD. Dr. Lim is professor of ophthalmology and vice chair and medical director of the University of California Davis Eye Center, Sacramento, CA. With MIGS becoming more commonplace among glaucoma surgeons, Dr. Lim reviewed the literature to provide a summary of safety and efficacy findings.
MIGS study guidelines
FDA guidelines for study design of MIGS devices recommend that the primary endpoint be the percentage of subjects with at least 20% reduction in mean diurnal IOP from baseline and that the secondary endpoint should be the mean diurnal IOP change from baseline. These guidelines were followed in some of the studies Dr. Lim discussed during the American Glaucoma Society annual meeting earlier this year. MIGS procedures in which an implant is placed in Schlemm’s canal include the iStent Trabecular Micro-Bypass Stent, the newer iStent inject (both from Glaukos), and the Hydrus microstent (Ivantis). The MIGS literature is “robust” regarding both the iStent and iStent inject, a dual-stent system approved by the FDA in 2018, Dr. Lim said.
Focusing on the iStent inject, she discussed two prospective studies in which the system was combined with cataract surgery. In a study by Arriola-Villalobos et al. (n = 20), 86% of patients reached the primary effectiveness endpoint, as did 78% in a study by Hengerer et al. (n = 81).
However, in both studies the mean IOP remained in the mid-teens at follow-up visits 3 to 4 years postoperatively. Dr. Lim also described two studies of the iStent inject implanted as a standalone procedure. Fea et al. reported that 95% of patients (using no medications) reached the primary endpoint versus 92% of patients taking two medications.
In a noncomparative study, Voskanyan et al. found that 72% of patients (using no medications) achieved the primary endpoint. The mean IOP reduction at 12 months was –13 mm Hg for patients in the iStent cohort and –13.2 mm Hg for those using medication in the Fea et al. study and –14.7 mm Hg in the Voskanyan study. The most common adverse events reported in these studies were that the iStent was not visible (1% to 13%), the iStent was obstructed (1% to 3%), or that the IOP was elevated (10%).
The Hydrus microstent, which sits in and dilates Schlemm’s canal, received FDA approval in August 2018 and has been the subject of two prospective studies when combined with cataract surgery. Pfeiffer et al. showed that at 24 months, 80% of the patients in the Hydrus and cataract surgery cohort (n = 50) had a 20% reduction in IOP compared with 46% in the cataract surgery alone group (n = 50).
At 24 months, the washed out mean diurnal IOP was 17 mm Hg for the combined procedure patients and 19 mm Hg for those undergoing cataract surgery alone; Dr. Lim noted a medication advantage favoring the Hydrus patients; at 24 months, 73% of this group was not using any hypotensive medications compared with 58% of the cataract surgery group.
Peripheral anterior synechiae was a notable adverse event in the Samuelson et al. study and occurred at a rate of 18% (14.9% nonobstructive, 3.8% obstructive). However, a post-hoc analysis suggested that it was not related to IOP outcomes. Dr. Lim also discussed bleb-forming MIGS, which require the use of mitomycin-C to suppress fibrosis. The XEN gel stent (Allergan) received FDA approval in 2016, whereas the InnFocus subconjunctival microshunt (Santen Pharmaceutical) is still under FDA review. Grover et al. conducted a prospective study of the XEN gel stent as a stand-alone procedure in patients with refractory glaucoma. At 12 months, IOP lowering ≥20% from baseline with medication was reported in 75% of the patients. The change in IOP from baseline was –9.1 mm HG, and the mean diurnal IOP was 16 mm Hg.
These results were relatively good, especially given the patient population. “When you compare the outcomes to trabeculectomy, we’re still not quite there,” Dr. Lim said. In the Tube versus Trabeculectomy Study, the mean IOP at 5 years was 12.7 mm Hg in the trabeculectomy group.
Dr. Lim also added that the study’s safety profile seemed reasonable but there is a significant needling rate (32%). Early published data on the InnFocus subconjunctival microshunt are promising, according to Dr. Lim. Batlle et al. conducted a retrospective study in which 9 of the 14 patients received the microshunt as well as cataract surgery.
Three-year follow-up data indicated that treatment resulted in profound pressure lowering, almost on the level of trabeculectomy. The mean medicated IOP was 10.7 mm Hg, a 55% drop from the preoperative level. A caveat to these results is that the study was retrospective, it had a small sample size, and the patient population was a mix of those receiving the shunt alone as well as in combination with cataract surgery.
The blebs in the Batlle et al study were low profile, small in area, and minimally vascular and were positioned slightly posterior to the limbus. Further investigation may determine whether this confers an advantage over the blebs seen in trabeculectomy, Dr. Lim said. An ongoing clinical trial for FDA approval is being conducted comparing the InnFocus microshunt with trabeculectomy.
Despite bumps in the road, such as the voluntary recall of the CyPass suprachoroidal stent by Alcon Laboratories last summer, MIGS likely has secured a place in glaucoma surgery, said Dr. Lim. “The more tools we have to be able to lower IOP, the more treatment options we have to offer our patients who exist along the continuum of mild to severe glaucoma,” she concluded.
Michele C. Lim, MD
This article was adapted from Dr. Lim’s presentation at the 2019 meeting of the American Glaucoma Society. Dr. Lim is a speaker for Alcon Laboratories and an investigator for Santen.