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.
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.
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.