In this episode of Interventional Mindset, Nathan Radcliffe, MD, and Manjool Shah, MD, discuss surgical pearls for implanting the Hydrus Microstent during a microinvasive glaucoma surgery (MIGS) procedure.
Dr. Shah’s first experience using a Hydrus Microstent was in training during a standalone clinical trial, and shortly after approval from the Food and Drug Administration (FDA), he introduced it to the Kellogg Eye Center at the University of Michigan, Ann Arbor.
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Surgical pearls for ophthalmologists new to the Hydrus Microstent
Early on, Dr. Shah used the Hydrus Microstent in a similar fashion to how he would use any other Schlemm’s canal-based procedure for milder glaucoma patients at the time of cataract surgery. However, over time, he was struck by the reproducible efficacy and ease of administration, which eventually made the Hydrus Microstent his go-to MIGS approach for a variety of glaucoma patients.
Dr. Shah highlighted that one key aspect to remember while operating with Hydrus is that a separate incision (i.e., the Hydrus wound) is necessary to implant the device. This incision is a 1 to 1.5mm paracentesis, angled at the nasal angle about 4 clock hours away from the area of intended implantation. Not only does this make it easier to access the necessary area for implantation, but it also allows the surgeon to work through a small incision, creating a stable inner chamber, he explained.
He has found that this is particularly helpful for patients who are unable to cooperate with specific directions regarding eye movement during surgery to participate in Schlemm’s canal surgery/gonioscopy, which is one of the most difficult elements of this type of procedure.
Similarly, Dr. Radcliffe noted how he realized after a few years of performing angle surgeries that floppy iris syndrome is a problem not only for cataract surgeons but MIGS procedures as well. Luckily, implanting the Hydrus Microstent in the chamber prevents this issue because the Hydrus incision is only 1mm large, and the chamber tends to be tighter.
Additionally, because the microstent is 8mm large, it can be beneficial to surgeons, as it is more likely to slide into the right position due to its physical size. If it lands in the wrong place, this will be quickly apparent to the surgeon, and the injector is designed to be easy to retract the Hydrus to reposition and deploy it yet again.
Combining Hydrus with canaloplasty
Dr. Shah explained that he tends to reserve canaloplasty in combination with Hydrus for more advanced glaucoma patients with high intraocular pressure (IOP) and on multiple medications along with those who he believes have more global trabecular meshwork (TM) disease such as pigmentary and uveitic glaucoma.
As he observed, the nice thing about doing an ab interno canaloplasty is that it requires a very small incision into Schlemm’s canal, which can be used as a focal entry point to perform the viscodilation and then place the stent in the same space. Once that is completed, the Hydrus is incredibly easy to implant because the dilated canal lends itself to taking the stent in.
The HORIZON flagship study on the Hydrus device
The HORIZON trial is one of the largest microstent trials and has been ongoing for multiple years. It compares the pressure reduction observed in two cohorts: phacoemulsification (phaco) versus phacoemulsification plus Hydrus. The washed-out 2-year data showed that 77% of patients implanted with a Hydrus plus phaco experienced a >20% IOP reduction, compared to only 57% of those in the phaco alone group.1
Additionally, significant changes were observed in terms of washed-out diurnal IOP; at 2 years, patients implanted with Hydrus had, on average, a 7.6mmHg IOP reduction, compared to 5.3mmHg with phaco alone.1 At this point, the HORIZON trial has demonstrated that compared to other Schlemm’s canal interventions, Hydrus has a significant impact on IOP, as well as durability of effect, which hasn’t been observed in previous clinical trials of other microstents.
Dr. Radcliffe also noted that 65% of patients implanted with the Hydrus reported not needing additional medications, even at 48 months, compared to 41% of patients who underwent phaco alone.2 Interestingly, at 4 years, 6% of patients who underwent phaco alone required additional incisional glaucoma surgery, compared to only 2% of those who had the Hydrus implanted.2
Dr. Shah mentioned having a “use the best bullet in your gun today” mentality is helpful to get ahead of progression when surgeons have that opportunity during cataract surgery. Additionally, the lower percentage of patients implanted with Hydrus needing incisional glaucoma surgery indicates that this microstent possibly modifies the physiological outflow pathway to improve the overall quality of pressure management over time, which could have a profound effect on optic nerve tissue and visual preservation.
Comparing the results of the HORIZON and LiGHT trials
Similar deviations in IOP and secondary surgical interventions were noted in the LiGHT trial, where even though the pressure was relatively similar between the groups, there was a very clear distinction between the cohorts in surgical interventions required.
The LiGHT trial compared the efficacy of selective laser trabeculoplasty (SLT) versus IOP-lowering eye drops for patients with early glaucoma or ocular hypertension (OHT). It was observed that 2.4% of patients treated with SLT needed a trabeculectomy after 3 years, and the results were similar for the Hydrus cohort in the HORIZON trial.2,3
This shows that Hydrus is a compelling offer for cataract surgeons who want to help patients potentially avoid future glaucoma surgeries by implanting the microstent during cataract extraction, remarked Dr. Radcliffe.
Lastly, the Hydrus Microstent provides strong data to support the safety profile. In terms of endothelial cell density, there is 4-year data for both cataract surgery and cataract surgery with Hydrus groups. In both cohorts, a 12 to 13% endothelial cell density reduction was noted following cataract surgery.2 From 3 months on, both groups maintained similar and stable levels of endothelial cells.2
Dr. Shah added that, based on the profile of the stent and how it is implanted, this is not surprising, as the Hydrus Microstent should be parallel to the trabecular meshwork, so when implanted correctly, it does not engage the peripheral corneal tissue.
A brief overview of the COMPARE study
The COMPARE study was an off-label investigation that evaluated IOP reduction associated with patients implanted with two iStent G1s versus one Hydrus without phacoemulsification.4 This trial analyzed a different patient population in contrast to the LIGHT and HORIZON trials as it evaluated patients who had IOP levels between 23mmHg and 39mmHg. The patients were randomized at the time of surgery for either of the microstents.4
Dr. Shah expressed that he appreciated that this study attempted to target the ideal stent placement to focal areas of collector channels, pigment in the trabecular meshwork, and focal heme reflux. This was done to “elevate the game” in terms of iStent insertion beyond what was seen in the initial investigational device exemption (IDE) trials that were published almost 10 years ago.
In terms of IOP reduction, the end result was relatively similar between both groups; however, significant differences were noted in the number of medications needed to achieve the target pressure for patients implanted with the iStents.4
For patients implanted with Hydrus, 38% of patients were off medications, compared to 18.7% of patients with the two iStent G1s.4 A similar number of patients were on one to two medications between the groups, but for patients on three medications or more, there were fewer Hydrus patients (18%) compared to the patients with iStents (33%).4
Closing thoughts on the Hydrus Microstent and MIGS procedures
To conclude, Dr. Shah expressed that surgeons who have performed one type of MIGS have already unlocked one of the hardest parts of the experience, which is understanding the mindset for integrating new devices and techniques into their toolkit. Each of the MIGS devices offers unique value to patients, and it is the responsibility of surgeons to evaluate the different devices and decide which is best for the patient based on their individual needs.
Dr. Radcliffe added that to test out new MIGS devices, the best approach is to contact a representative, and if it is unclear who that would be, the next step is to reach out to a surgeon who performs the procedure and ask them for their representative.
Oftentimes, there is an online course or even wet lab training available to ophthalmologists that can help with integrating the procedure or device into surgical practice. There can be a lot of variability in how involved the surgical device company might be in training based on the preferences of the surgeon.
Take home
Hydrus is a compelling addition to the armamentarium for ophthalmologists due to its safety profile and efficacy in not only reducing IOP but also reducing the medication burden on patients.
