Hydrus®: Designed with Purpose

The Hydrus® Microstent is a canal-based minimally invasive glaucoma surgery (MIGS) device for adult patients with mild to moderate primary open-angle glaucoma. Made of flexible and biocompatible nitinol (1), the Hydrus® – roughly the size of an eyelash – bypasses the trabecular meshwork to restore flow of aqueous from the anterior chamber through the inlet of the microstent into Schlemm’s canal.

During the Alcon Hydrus® symposium at the European Glaucoma Society Congress in Dublin (June 1-4, 2024), Professor Norbert Pfeiffer – Chief Executive Officer and Head of the Department of Ophthalmology at Mainz University Medical Centre, Germany – explored both the features and benefits of what he called this “purposefully crafted” device.

Designing for Better Flow

Professor Pfeiffer reflected on how the eye’s trabecular meshwork is a “wonderful thing, it keeps the intraocular pressure (IOP) at almost always the right level.” Unfortunately, he added, it is a system that fails in glaucoma cases – with clogged pores and increased resistance leading to elevated pressure.

“Wouldn’t it be marvellous,” he went on, “to restore that meshwork to its original shape and function?” This was the goal of the first stenting procedures, noted Pfeiffer. “Schlemm’s canal isn’t like a garden hose you can just hook up to the anterior chamber. It has outflow pathways in some areas, but not in others; the canal is wide in some places and small in others. You may insert the stent in an area with no outflow channels, or where the canal is very narrow.”

To address this problem, Pfeiffer explained, Alcon developed the flexible, 8-mm Hydrus® Microstent. Unlike stents that merely puncture the canal, the Hydrus® creates an inlet for aqueous humour, bypasses the trabecular meshwork, and scaffolds Schlemm’s canal to prevent collapse.

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Hydrus^® in action

Presenting an image of an implanted Hydrus® Microstent, Pfeiffer highlighted the inlet (on the picture’s right-hand side) where the aqueous humour enters the stent. It then bypasses the trabecular meshwork via the Schlemm’s canal and then drains out of the eye. When the stent is removed, he continued, the outer wall of Schlemm’s canal is not destroyed. Similarly, the inner wall and the trabecular meshwork are also not destroyed. (3-5)

As noted, the Hydrus® opens up Schlemm’s canal; pointing to a study from 2020 (3), Pfeiffer added that with the Hydrus®, “the outflow was increased quite remarkably – to about 80%.”

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Truly functional

In summary, Pfeiffer explained that the Hydrus® Microstent spans more than 90 degrees of Schlemm’s canal, eliminating the need to specifically target collector channels; acts as a scaffold to prevent Schlemm’s canal from collapsing; and bypasses the trabecular meshwork, which is often clogged up in glaucoma cases.

Compared with other stenting procedures, the Hydrus® covers “a fairly large area of Schlemm’s canal and the trabecular meshwork,” he said, noting that this coverage is sufficient to lower IOP “to an important extent.” Borrowing a term from cardiology, he explained that the Hydrus® performs “truly functional stenting” meaning the stent both bypasses and maintains the patency of a narrow lumen. “For such a process, you need a certain length, and that is provided with the Hydrus®.”

“In its way, the Hydrus® does restore the natural outflow of fluid from the eye,” Pfeiffer concluded. “And if we liken the trabecular meshwork to artwork, I’d also say its effect is a bit like restoring a piece of art.”

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