The Hydrus Microstent was approved as a treatment option for glaucoma in 2018 by the FDA. The Hydrus Microstent procedure is done in conjunction with cataract surgery to reduce intraocular pressure in adult patients with mild to moderate primary open-angle glaucoma (POAG). Compared with other surgical glaucoma treatments, the Hydrus Microstent gets equal or better results.*

What is the Hydrus Microstent?

The Hydrus Microstent is “an approximately 8 mm long, curved device that comprises alternating spines for structural support and windows for aqueous outflow,” according to the American Academy of Ophthalmology (AAO). The device is made of nitinol, a highly elastic nickel-titanium alloy, and is inserted through a 1.5 millimeter-long incision in the cornea. 

The procedure done to implant the stent is one of several recent minimally-invasive glaucoma surgery (MIGS) innovations. 

When compared to selective laser trabeculoplasty

To date, there is only one study that compares the Hydrus Microstent and selective laser trabeculoplasty (SLT). The study was a 12-month, non-randomized interventional case series that involved 56 patients with uncontrolled mild to moderate POAG. There were no significant baseline demographics between the groups. 

In total, 31 eyes received the Hydrus Microstent, while 25 eyes underwent SLT. Both groups saw significant decreases in intraocular pressure (IOP) compared to baseline. At 12 months, 90% of Hydrus Microstent patients and 88% of SLT patients had more than a 20% reduction in IOP.

Despite practically equivalent outcomes in IOP between the group, there was a significant difference in drug reduction, in that:

• Only Hydrus Microstent patients achieved a significant drug reduction from baseline.
• 47% of Hydrus Microstent patients were medication-free versus only 4% of SLT patients.

When compared to the iStent

These two MIGS treatments were compared in a prospective, multicenter, randomized controlled single-masked clinical trial. In this clinical trial, 152 eyes with OAG received either one Hydrus Microstent or two iStents. At 12 months, Hydrus Microstent outcomes were superior to those of the iStent group.

When compared with the iStent group, the Hydrus group:

• Had a slightly larger reduction in mean IOP (though not statistically significant)
• Achieved a greater decrease in the number of medications taken
• Had a significantly higher proportion of medication-free patients
• Had fewer patients who needed three or more medications (8.2% vs. 29.3%)

When compared to a canaloplasty

Another study explored the efficacy of the Hydrus Microstent versus a canaloplasty (CP), which is a relatively new technique that lowers IOP using a microcatheter to insert a tension suture. Of 45 eyes, 21 underwent Hydrus Microstent implantation, while 24 eyes received CP. 

At 24 months, both groups had experienced significant reduction in IOP and achieved approximately equivalent reductions in medication number, with:

• 33.3% of Hydrus eyes and 50% of CP eyes required no hypotensive meds.
• 57.1% of Hydrus eyes and 41.7% of CP eyes required some hypotensive meds. 

When compared to cataract surgery alone

In several studies, concurrent Hydrus Microstent implantation with cataract surgery (CS) appears to be superior in lowering IOP and reducing the number of glaucoma medications than cataract surgery alone—and equivalently safe. 

In the HYDRUS II study, in which participants underwent either CS and the Hydrus Microstent procedure or CS alone. At 24 months, more patients in the Hydrus Microstent and CS group (73%) versus patients in the CS-only group (38%) were medication-free. 

Moreover, in a two-year retrospective on the Hydrus II study:

• In group 1 (42 eyes with an IOP ≤ 18 mmHg):
  • The mean IOP did not change significantly. 
  • The number of medications was significantly reduced. 
  • 69% of patients were off medication at final follow-up. 
• In group 2 (50 eyes with an IOP ≥ 19 mmHg):
  • Mean IOP decreased significantly from baseline. 
  • The number of medications used significantly decreased.
  • 60% of patients were off medications at final follow-up. 
  • One patient required a trabeculectomy at 18 months.

In the HORIZON study, researchers analyzed 556 eyes, with 369 receiving only the Hydrus Microstent and 187 receiving only cataract surgery. At 24 months, outcomes for the Hydrus Microstent were significantly superior. 

What possible complications are there?

Though rare, reported complications of the Hydrus Microstent procedure include:

• Hyphema (malpositioning of the device), which occurs in 1-2% of cases and usually resolves within a week following surgery. 
• Adhesion of the iris to the front of the trabecular meshwork (the eye’s drainage system), which has been observed in about 10-20% of cases
• Loss of endothelial cells (needed for eye hydration)
• Spikes in IOP, which are frequently reported with MIGS, but less frequently with the Hydrus Microstent specifically

Overall, clinical trials have demonstrated that the Hydrus Microstent can serve as a useful complement to cataract surgery for reducing IOP and the need for eye drops in people with mild to moderate OAG. As a standalone procedure, Hydrus appears to be safe and somewhat effective, though further research is needed to evaluate long-term effects.

Additional information on the Hydrus Microstent can be found on the Ivantis website.

*Michael, R., Chen, J. L., & Aref, A. A. (2020, Apr. 5). Hydrus Microstent. American Academy of Ophthalmology. https://eyewiki.aao.org/Hydrus_Microstent

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