Registry data finds microstent lowers pressure in patients with primary-open angle glaucoma
This article was reviewed by Prof. Gus Gazzard, FRCOpthMA, MBBCHIR, MD
The International Spectrum Registry recently completed enrollment of patients for the Hydrus Microstent (Ivantis Inc.), a microinvasive glaucoma surgery device used to treat patients with mild to moderate primary open-angle glaucoma. In the United States, the device is indicated for placement in combination with cataract surgery or as a stand-alone procedure.
The Spectrum Registry currently includes almost 3,000 eyes enrolled; of these, 700 surgeries in which the Hydrus Microstent was implanted were stand-alone glaucoma procedures. Seventy percent of the patients have completed the three-year follow-up examination.
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At the three-year time point, probably the most important findings are not only the marked stability of the intraocular pressure (IOP) over the long-term following placement in the eye but also the improvement following the wearing off of the effect of phacoemulsification in the patients who underwent the combination procedure, said Prof. Gus Gazzard, FRCOphth MA, MBBChir, MD.
Prof. Gazzard, professor of ophthalmology University College and consultant ophthalmic surgeon, Moorfields Eye Hospital, London, said patients seem to have stable pressures out that far and beyond that point.
“I have been implanting the microstent for several years and, thus far, have implanted between 250 and 300 of the devices,” he said. “The device provides great pressure control and it may even be greater than we are seeing with alternative devices.”
He emphasized that the microinvasive glaucoma surgery (MIGS) effect in patients implanted with the microstent in combination with cataract surgery seems to be increasing with time as the phaco effect wears off.
“The data are both reassuring and powerful because they show that the Hydrus effects are increasing, which is both surprising and gratifying,” he explained.
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The key to this control may be the manner in which the implantation process modifies Schlemm’s canal. This microstent, which lives up to its name in that it is the size of an eyelash, focusses on the natural outflow system of the eye with a trimodal mechanism of action. A large opening is created in the trabecular meshwork, the canal is dilated and scaffolded, which increases the cross-sectional area of the outflow system, and about 90 degrees of the outflow system is covered.
“What is exciting for me is that the microstent keeps the canal open, it does not simply obtain access to the physiologic Schlemm’s canal,” Prof. Gazzard said. “The fact that there is scaffolding dilatation of the drainage duct provides more robust long-term pressure lowering.”
Practically speaking, he continued, surgeons can be absolutely certain that they have achieved access to the canal and that there is viable communication between the anterior chamber and the natural outflow channels. Other mechanisms and devices may not access the natural drainage channels and there is no real certainty of the correct placement of the devices.
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Recent reported results
Results achieved with the microstent were presented at the 2019 meeting of the American Academy of Ophthalmology.
In the Horizon Trial, which compared pure phacoemulsification with phacoemulsification and Hydrus Microstent placement and cataract extraction, found that at three years, which is the longest outcome reported with a MIGS device, the microstent enhanced the IOP lowering achieved by cataract surgery alone.
“There was persistent, maintained, greater pressure lowering with the Hydrus device compared with only cataract extraction,” Prof. Gazzard said. “Fewer drops were used and the procedure was seen to be very safe.”
Another noteworthy finding was that the rate of trabeculectomy decreased with the use of the microstent. In the control arm of the trial, 3.9% of patients went on to trabeculectomy because of glaucoma progression compared with 0.6% in the treatment arm, which Prof. Gazzard described as a robust clinical outcome. The endothelial cell count showed a positive result in patients who had completed four years of follow-up.
The full results of the Horizon Trial will be released in the spring of 2020 with more to follow in 2021.
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Placing the Hydrus is a safe procedure with low risk of adverse events. Prof. Gazzard reported no problems with chronic inflammation, allergy, obstruction, and uveitis in his patients.
Outside of the U.S., the microstent can be placed in patients with angle closure glaucoma, uveitis, trauma, congenital anomalies, and neovascular glaucoma. In the U.S,. the stent is limited to patients with mild to moderate primary open-angle glaucoma in conjunction with cataract surgery.
“The results provide a glimpse into what the future of MIGS in the US might look like once the indications are expanded. It also speaks to how important following patients is over the long term,” said Dave Van Meter, president and chief executive officer of Ivantis.
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Spectrum Registry results
The three-year results reflect the findings of the microstent in more than 900 eyes, in more than 200 of which the microstent was implanted during a stand-alone procedure. These results are likely indicative of what to expect in 2020 from the U.S. results.
The patients in the Australia registry had the full spectrum of glaucoma, ranging from very mild disease that was addressed with the microstent in conjunction with cataract surgery to patients with moderate disease that was refractory to medical therapy who received the microstent as a stand-alone procedure and finally to severe cases for which conventional surgery was unsuccessful and required placement of the microstent during a stand-alone procedure. More than 70% of the eyes completed the three-year follow-up evaluation.
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When placed in the eye in conjunction with cataract surgery, the microstent achieved an IOP decrease in excess of 20% with discontinuation of all anti-glaucoma medications.
When positioned during a stand-alone procedure, the microstent achieved in a mean IOP decrease of approximately 30% and all anti-glaucoma medications were discontinued.
The average IOP achieved in all patients was 15 mm Hg or less in both the combination cataract surgery and standalone treatment groups.
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Gus Gazzard, FRCOpthMA, MBBCHIR, MD
Prof. Gazzard is supported by a grant from the National Institute for Health Research-Health Technology Assessment. He reports that he has no financial interest in any ophthalmic products, company, or related stocks.