The Hydrus Microstent, now owned by Alcon, has helped change the game when it comes to surgical options in glaucoma. Associate Professor ASHISH AGAR reflects on the MIGS device’s past, present and future in Australia.
It was important for the national health system, and indeed global ophthalmology, when Australia became the first global market to access the Hydrus Microstent. That was officially in 2018, but the minimally invasive glaucoma surgery (MIGS) device had been in use in Australia since 2013/14 when the manufacturer tested its real-world performance with a select group of local surgeons.
NSW glaucoma specialist Associate Professor Ashish Agar was part of that first wave of surgeons to implant the canal-based device for adult patients with primary open-angle glaucoma (POAG) almost 10 years ago.
“At the time it was the only device available to us as part of the new MIGS category, and I was lucky enough to be trained in-person by the bioengineer who designed the Hydrus Microstent,” Agar explains. “He travelled from the US to take me through my first list at Marsden Eye Specialists in western Sydney, which was in the very first week that the device was used in Australia. It was the most amazing introduction.”
“In the outback, it’s been a game changer to provide an option that you can safely do in a remote area, with very little follow up care required.”
Since then, the Hydrus Microstent (acquired by Alcon in 2022) has cemented its place as one of the most commonly used MIGS devices in Australia, in addition to the iStent system (Glaukos, first approved in 2015), and iTrack (Nova Eye Medical). Xen (Allergan, approved 2017) and Preserflo Microshunt (Glaukos, approved 2021) are part of another category Agar describes as MIBS or ‘minimally invasive bleb-forming surgery’ for later stage glaucoma.
Since their arrival, MIGS devices have come to occupy the middle ground of glaucoma treatment in Australia, addressing the gulf between first line therapies such as eye drops and selective laser trabeculoplasty (SLT) and more invasive interventions such as trabeculectomy and tube shunt surgery. Being a new type of medical technology, MIGS have navigated uncharted waters with the TGA, before eventually securing Medicare reimbursement as a standalone or combined treatment with cataract surgery.
In the case of the Hydrus Microstent, it is 8 mm in length, contoured to match the curvature of Schlemm’s canal, and made of nitinol – considered a highly biocompatible material. Using a gonioprism, the device is inserted through a clear corneal incision and guided through the trabecular meshwork into the canal. Once in position, it is advanced until the device has scaffolded approximately 90° of Schlemm’s canal, ensuring access to collector channels. Ultimately, the stent provides outflow pathways for aqueous, helping lower intraocular pressure (IOP) and reduce medication burden.
The device was developed by Californian firm Ivantis, which was acquired by Alcon in 2022 in a deal worth well over AU$600 million.
What the studies say
Agar points to several reasons for the Hydrus Microstent’s success. The most notable is the robust data showing, among other findings, that it:
• Is consistent over time – critical when considering glaucoma is a long-term disease.
• Significantly lowers IOP with or without cataract surgery.
• Real-world data matches that published in a randomised trial.
The HORIZON and SPECTRUM studies have been the most notable studies for Hydrus.
HORIZON is described as the largest prospective, randomised, controlled MIGS pivotal trial to date, while SPECTRUM is a global registry initiated in Australia to understand how it worked in the real world.
In HORIZON, Alcon says the device is the first and only MIGS implant to report clinical results from a pivotal trial at five years.1,2 The study included 556 patients at 38 centre from nine countries.
Importantly, it showed 66% of Hydrus Microstent patients remained medication-free at five years. The study has also demonstrated a relative reduction in incisional secondary surgical interventions (SSI) such as trabeculectomy, tube shunt and gel stent, for Hydrus Microstent patients compared to cataract surgery alone (2.4% in Hydrus+CS vs. 5.3% in CS only).3 And the Hydrus group included a higher proportion of eyes with IOP of 18 mmHg or less without medications than the cataract surgery group.
More recently, the HORIZON results have shown the device lowers the rate of visual field loss by 47% versus cataract surgery alone. This finding was delivered in November 2021 by world renowned glaucoma specialist Dr Iqbal “Ike” Ahmed who said since the inception of MIGS, the narrative has been largely restricted to IOP lowering, medication reduction and invasive secondary surgery rates. However, the visual fields finding was important because there was now data indicating Hydrus is affecting the underlying disease itself.4*
In terms of safety, the device has shown this over the long-term with comparable serious adverse rates reported vs cataract surgery alone. The five-year HORIZON data also showed “no clinical or statistically significant differences” in the key measure of endothelial cell loss from three to 60 months between the Hydrus and cataract surgery alone groups.1
For Agar, when he started using the Hydrus Microstent, safety was the most important consideration, given this was an entirely new field for glaucoma specialists.
“In the early days, we were very much still learning about it. Even though MIGS is considered an intermediate step that can be used frequently today, early on we didn’t want to take any risks, so at that stage, we were trialling it in patients who were running out of options,” he says.
“And when we had success in those patients, it gave us confidence to say ‘this is something that could make a difference – now, I’m going to start to use it more regularly’.”
Agar says he was also reassured when Hydrus’ manufacturer established the SPECTRUM registry, which was mandatory for all devices implanted early on.
“Every single Hydrus implanted in those early years was tracked in the SPECTRUM Global Registry, which was also granted ethics approval by RANZCO in 2014 and now involves almost 3,000 eyes from around 18 countries. That way we knew there was no way of hiding or trying to message the results, it was there for everyone to see. For me, that meant the highest possible level of monitoring, audit, and evidence collection. I thought that was a brave call from Ivantis at the time,” Agar says.
There’s also a third and important study involving the device. The COMPARE study was the first prospective, randomised, multicentre trial comparing Hydrus Microstent to two iStents Trabecular Micro Bypass implants without the confounding effect of cataract surgery (standalone). The study included 152 patients at 12 centers across nine countries.
According to Alcon, key findings included: ~2x more Hydrus Microstent patients were medication free compared to patients with two iStents at 12 months; mean medication reduction of 1.3 (52%) vs. 0.8 (30%) in the 2 iStents patients at 24 months; and at 24 months, Hydrus Microstent demonstrated a low incidence of secondary glaucoma surgery – none vs 9.1% in the two iStents group.5
The surgical experience
Agar is “device-agnostic” when it comes to glaucoma surgical options. It ultimately comes down to the data and what’s best suited to the patient.
While noting the effectiveness and safety of all MIGS devices are comparable, he says there are differences in the surgical experience for the ophthalmologist.
“When it comes to MIGS, I seem to have greater confidence in terms of effectiveness and reliability with the Hydrus stent. It differs from other techniques allowing me to titrate and adjust my technique until it’s just right. If it’s in a good position, you can easily tell, and if it’s not, you can dial it out and do it again. This can be done as many times as you need until you’re happy,” he explains.
“For me, that ability to adjust it on the operating table until you get it right is key.”
Alcon describes Hydrus as an “intuitive delivery system” that allows for a straightforward procedure with no need to target collector channels or implant multiple devices.3
As such, Agar says the Hydrus Microstent has also benefitted patients as part of his outreach work in Broken Hill, a frontier mining town in the far west of New South Wales, more than 1,100km from Sydney. The first of these was in March 2018 when he performed the first Hydrus procedures outside a major metropolitan city, with four patients receiving the Hydrus Microstent at Broken Hill Base Hospital. At the time, he described it as “a boon for equity of access to specialist medical services for people living in the bush”.
Today, Agar still agrees with that assessment.
“These are places where patients can’t visit your rooms each week for follow up after trabeculectomy to have their sutures done etc. So in the outback, it’s been a game changer to provide an option that you can safely do in a remote area, with very little follow up care required.”
With the introduction of MIGS, Agar says glaucoma specialists can now offer surgical options at a much earlier stage in a patient’s journey, potentially avoiding a trabeculectomy or delaying it until absolutely necessary.
“It’s about getting better control over disease at an earlier point. What’s really changed is that it’s opened up so many more choices to consider for our patients, options we didn’t have before,” he says.
“Now, our ability to control IOP is much better and it means we’re moving to a different paradigm that Dr Ike Ahmed describes as: ‘surgical glaucoma, not as your last resort, but as an anytime resort’. You do it when the patient needs it, not when you’re too worried that nothing else is left.”
NOTE: *Indications for Use: The Hydrus Microstent is intended for the reduction of intraocular pressure (IOP) in patients with primary open angle glaucoma (POAG) as a standalone treatment or in conjunction with cataract surgery.
References
1. Ahmed I, et al; HORIZON Investigators. Long-term Outcomes from the HORIZON Randomized Trial for a Schlemm’s Canal Microstent in Combination Cataract and Glaucoma Surgery. https://www.aaojournal.org/article/S0161- 6420(22)00160-9/fulltext
2. Safety & Effectiveness Study of the Hydrus Microstent for Lowering IOP in Glaucoma Patients. ClinTrials.gov (NCT01539239)
3. Samuelson TW et al, A Schlemmm Canal Micorstent for Intraocular Pressure Reduction in Primary Open-Angle Glaucoma and Cataract: The HORIZON Study. Ophthalmol 2019;126: 29-37.
4. Dr Ike Ahmed, November 2021, “New findings ‘alter forever how we think of MIGS’”. Accessed March 2023. www.insightnews.com.au/new-findings-alter-forever-how-we-think-of-migsdr- ike-ahmed/
5. Ahmed et al.: A prospective randomized trial comparing Hydrus and iStent micro-invasive glaucoma surgery implants for standalone treatment of open-angle glaucoma: The COMPARE Study (Ophthalmology. 2020;127:52-61)
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