Hydrus^®: Designed with Purpose

Professor Norbert Pfeiffer explores the features and benefits of the Hydrus^® Microstent

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.

^{Designed with purpose}

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%.”

Hydrus^® Microstent in action

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.”

Truly functional

References

1. Hydrus® Microstent, Instructions for Use (2020).
2. TW Samuelson et al., “US iStent Study Group. randomised evaluation of the trabecular micro-bypass stent with phacoemulsification in patients with glaucoma and cataract,” Ophthalmology, 118, 459 (2011). PMID: 20828829.
3. CB Toris et al., “Outflow Facility Effects of 3 Schlemm's Canal Microinvasive Glaucoma Surgery Devices,” Ophthalmol Glaucoma, 3, 114 (2020). PMID: 32672594.
4. WD Stamer. “The cell and molecular biology of glaucoma: Mechanisms in the conventional outflow pathway. Investigative Opthalmology & Visual Science. 2012;53(5):2470. doi:10.1167/iovs.12-9483f
5. JE Dickerson, RH Brown. Circumferential Canal Surgery: A brief history. Current Opinion in Ophthalmology. 2020;31(2):139-146. doi:10.1097/icu.0000000000000639

Hydrus^®: The Long-Term Evidence

Professor Gus Gazzard* outlines the five-year results of the HORIZON study, evaluating the safety and efficacy of the Hydrus^® Microstent

*Paid Alcon Consultant

Presenting at Alcon’s Hydrus symposium at the European Glaucoma Society Congress in Dublin (June 1-4, 2024), Gus Gazzard – Professor of Ophthalmology at UCL & Director of Glaucoma Service, Moorfields Eye Hospital, London – detailed the results of the 5-year HORIZON study: “the largest prospective pivotal randomised control trial for a MIGS device to date” (1).

Horizon study data

HORIZON – a large, multicentre randomised controlled trial designed to evaluate the safety and efficacy of the Hydrus® Microstent – saw 80% of patients complete a full five-year follow-up. “This wasn’t simply a retrospective check-in years later,” Professor Gazzard explained. “It was a planned prospective follow up; these are patients that continued to be monitored.” As such, Gazzard went on, the study has yielded “reliability and robustness of data, and – for a surgical trial – a staggeringly impressive rate of patient retention.”

Gazzard noted that the Hydrus has been shown to reduce intraocular pressure (IOP) and reduce medication usage when used in combination with cataract surgery at 24 months in patients who have had washed out IOP measurements (1-4). Illustrating the HORIZON finding that 77.2% of Hydrus patients achieved an unmedicated IOP reduction of >/= 20% from baseline at 24 months(4)^a Gazzard explained that there were no concurrent medications confounding the results. He added that the HORIZON trial design, which involved washing out medications before measuring IOP, meant that the results represented a true effect of the surgical intervention rather than an inflated outcome from medication use.

Reducing IOP and medication usage

Why long-term data matters

Turning to the importance of the longer-term follow-up, Gazzard argued, “We should be asking all our device studies, whether of lasers or MIGS, to continue out to at least five or more years.” The five-year data showed that a significant proportion (59%) of Hydrus patients remained entirely medication-free (4).^b This is one of the statistics I reach for when patients are saying, ‘Is it worth me having a Hydrus?’” noted Gazzard.

As expected, more patients who had fewer glaucoma drops at the beginning of the HORIZON trial (66%) remained medication-free at five years.^c "Clearly, if you require three medications to get your pressure under control when you enter a study, you're less likely to be completely free of medication,” Gazzard explained.

Exceptional long-term drop elimination

Immediate postoperative safety

Another advantage Gazzard emphasised was Hydrus’s role in reducing day-one postoperative IOP spikes (1.4% rate of IOP > 40 mmHg on post-op day 1 among Hydrus patients versus 14.4% among CS-only patients)^d – a risk that is often overlooked. In many European countries, he noted, patients are not routinely checked on the first postoperative day, meaning these spikes can go unnoticed.

“It’s very reassuring to know that the Hydrus reduces these day-one postoperative IOP spikes in a very large proportion of patients,” he continued. For some patients with brittle, advanced disease, the margin of safety could be crucial.

Reducing future surgery

The HORIZON study also demonstrated a significant reduction in the proportion of patients needing later incisional glaucoma surgery,^e Gazzard explained. While he said this doesn’t amount to a “get out of jail free card,” he noted that the difference between the control and treatment groups was meaningful, with fewer patients in the cataract surgery with Hydrus® Microstent (CS-HMS) group requiring further surgery over five years. These surgical decisions were reviewed by a masked panel of glaucoma specialists, including Gazzard himself, ensuring that judgments were unbiased.

In translating these findings to daily practice, Gazzard said he tells Hydrus implant patients: “While this doesn’t guarantee that you won’t need surgery, there’s a chance that you might not if we do this.” Additionally, he explained that combining Hydrus implantation with cataract extraction means that if a patient later needs trabeculectomy, they would be pseudophakic.

_{[a] n=369 eyes receiving Hydrus Microstent + cataract surgery
[b] vs. 35.8% of eyes in the control group of a 5-year pivotal trial follow-up: Hydrus Microstent + cataract surgery (n=308 eyes) vs. cataract surgery alone (n=134 eyes); p<0.001.
[c] Patients previously on 1 medication: Hydrus Microstent + cataract surgery (n=308 patients) vs. cataract surgery alone (n=134 patients); 41.1% of the cataract surgery-alone patients remained drop-free.
[d] 2-year pivotal trial: Hydrus Microstent + cataract surgery (n=369 eyes) vs. cataract surgery alone (n=187 eyes). IOP > 40 mmHg was 14.4% in cataract surgery alone group .
[e] Secondary Surgical Interventions (SSI) include trabeculectomy, tube shunt, gel stent, ECP/TSCP, non-penetrating; (9/369 Hydrus Microstent +cataract surgery and 10/187 cataract surgery); vs. cataract surgery alone: 2.4% in Hydrus + cataract surgery vs. 5.3% in cataract surgery only}

© 2026 Alcon Inc. GLB/IMG-HDM-2500026

References

1. IIK Ahmed et al. (HORIZON Investigators), “Long-term Outcomes from the HORIZON Randomised Trial for a Schlemm's Canal Microstent in Combination Cataract and Glaucoma Surgery,” Ophthalmology, 129, 742 (2022). Erratum in: Ophthalmology, 131, 1471-1472 (2024). PMID: 35218867.
2. TW Samuelson et al, “iStent inject Study Group. Prospective, Randomised, Controlled Pivotal Trial of an Ab Interno Implanted Trabecular Micro-Bypass in Primary Open-Angle Glaucoma and Cataract: Two-Year Results,” Ophthalmology, 126, 811 (2019). PMID: 30880108.
3. Hydrus Microstent Instructions for Use (2020).
4. Alcon Data on File (2024). REF-24145.

Surgical Confidence with Hydrus^®

Nishani Amerasinghe shares surgical tips and pearls for the Hydrus^® Microstent

Nishani Amerasinghe, Ophthalmic Surgeon at University Hospital Southampton NHS Foundation Trust, has been performing Hydrus® Microstent procedures for over a year and says she is “really impressed at how well my patients are doing.”

Speaking at Alcon’s Hydrus symposium during the European Glaucoma Society Congress in Dublin (June 1–4, 2024), she shared her surgical pearls, ergonomic tips, and step-by-step approach to ensure safe, effective implantation, as well as practical ways to identify and resolve intra-operative problems in real time.

Achieving optimal visualisation

“The key to perfect implantation with any MIGS, of course, is good visualisation,” Amerasinghe began. She went on to summarise her gonio “ergonomic pearls” for optimising the surgical view:

• Adopt a temporal approach.
• Tilt the microscope and the patient’s head to achieve a 35–45° angle.
• Set the microscope rotation to around 30–40°.
• Lightly balance the gonio lens on the eye using an OVD coupling agent, ensuring it does not press on the cannula.
• Increase magnification for the clearest possible image.

These adjustments, she explained, allow the surgeon to achieve and maintain the best possible view of the trabecular meshwork – the starting point for any successful Hydrus procedure.

Good visualisation

Four surgical steps

Amerasinghe outlined the four principal stages of Hydrus implantation:

1. Incision – Create the incision three to four clock hours away from the intended implantation site.
2. Engagement – Incise the trabecular meshwork with the cannula, then tilt the cannula 15–20° anteriorly to engage the tissue correctly.
3. Implantation – With the cannula tip up and engaged, advance the first scaffold window, align the cannula, and then guide the rest of the Hydrus through the canal. “You know exactly when you’re in the right plane,” she explained.
4. Confirmation – Verify that 50–75% of the transition zone is covered by trabecular meshwork, with the inlet visible in the anterior chamber.

“When you follow these four main surgical steps meticulously, it’s very easy to insert the Hydrus,” she said, noting that these fundamentals form the basis of consistent success.

Four surgical steps

Refined incision technique

Drawing on her faculty experience, Amerasinghe described a preferred nonradial corneal incision technique designed to optimise entry and streamline stent delivery. The incision is made three to four clock hours from the trabecular meshwork entry point, in clear cornea, approximately 1.5 mm in length, and directed toward the trabecular meshwork target.

This approach allows the surgeon to rest the cannula over the cornea before entry to determine the optimal incision site. If desired, the site can be marked with ink for accuracy. The goal, she stressed, is to enter efficiently while maintaining a trajectory that facilitates smooth Hydrus delivery.

Placement verification

Placement confirmation, Amerasinghe emphasised, is a visual process supported by key anatomical cues. Proper positioning is achieved when:

• 50–75% of the transition zone is covered by trabecular meshwork.
• The inlet is visible in the anterior chamber and parallel to the trabecular meshwork.
• The distal tip is observed in the canal.

Additional signs include the appearance of three scaffold windows in the canal and the characteristic “dull” look of the stent when correctly embedded in the trabecular meshwork. Once placement is verified, the viscoelastic is evacuated, the anterior chamber reformed, and the corneal incision hydrated.

Non-radial corneal incision

Recognising and resolving problems

Amerasinghe devoted part of her talk to intraoperative problem-solving, noting that the Hydrus offers the advantage of immediate visual feedback, enabling swift correction.

One potential issue is superficial delivery, visible when the stent appears shiny rather than dull. In such cases, the surgeon should recapture the device by reversing the delivery wheel, withdraw it, and reimplant in the correct plane.

Another complication is posterior delivery, often the result of an overly steep or acute cannula approach. This can make advancement difficult, cause excess pressure on the eye, and result in the stent diving too far posteriorly. If identified early, the solution is to retract the device and re position it further downstream from the original incision.

These scenarios, she stressed, illustrate the value of the Hydrus system: “Straight away you can retract and reposition the stent… the confirmation of placement you get is immediate.”

Identifying and avoiding posterior delivery

While there is a learning curve with Hydrus implantation, Amerasinghe reassured the audience that precision and consistency come quickly. “If you’re meticulous with each of the steps, you’ll find actually that the placement is easy… It’s very easy to recite it straight away.”

Amerasinghe also shared her positive experience using the Hydrus with the Ingenuity 3D Visualisation System. This, she said, offers exceptional clarity of the surgical field, aiding both the procedure itself and teaching opportunities.

In closing, Amerasinghe underscored the straightforward nature of Hydrus implantation when performed with good visualisation and adherence to her stepwise technique. “I wouldn’t say it’s a difficult operation at all,” she told delegates. “You know you’re exactly in the right place straight away while you’re operating. And if you’re not… you can deal with that on the table. The confirmation and feedback you get gives you the confidence to do it well.”

With disciplined technique, ergonomic efficiency, and an eye for intraoperative cues, she added, surgeons can approach the Hydrus® Microstent safe in the knowledge that any deviations can be spotted and corrected in real time.

© 2025 Alcon Inc. GLB/IMG-HDM-2500027