Hydrus Stent versus iStent in Glaucoma Management: A Comparative Overview of Research Outcomes
Glaucoma is a leading cause of irreversible blindness worldwide, characterized by the progressive loss of retinal ganglion cells and optic nerve damage. Elevated intraocular pressure (IOP) is a major risk factor for glaucoma, particularly in open-angle glaucoma (OAG), which is the most common form of the disease. While medical management (such as eye drops) and traditional surgical approaches like trabeculectomy have long been the mainstays of glaucoma treatment, newer minimally invasive glaucoma surgeries (MIGS) have emerged to offer safer, less invasive options. Two such devices—the Hydrus Microstent and the iStent—have become popular in the treatment of mild to moderate glaucoma, often performed in combination with cataract surgery. This essay will explore and compare the outcomes of research studies focusing on the Hydrus stent and the iStent, examining their efficacy, safety, and overall impact on glaucoma management.
Overview of the Hydrus Microstent and iStent
Before diving into the comparative research outcomes, it’s important to understand the basic differences between the two devices.
• Hydrus Microstent: The Hydrus Microstent, developed by Ivantis, is a crescent-shaped device approximately 8 mm in length. It is inserted into Schlemm’s canal to create a larger opening for aqueous humor to flow through, which in turn reduces intraocular pressure (IOP). The device is designed to scaffold the canal and expand a significant portion of its circumference (approximately 90 degrees), enhancing aqueous outflow through multiple collector channels.
• iStent: The iStent, developed by Glaukos, is a tiny titanium device that is inserted into Schlemm’s canal to enhance aqueous humor outflow. It is often described as the smallest medical device implanted in humans, measuring only 1 mm in length. The iStent bypasses the trabecular meshwork, allowing fluid to flow more easily into Schlemm’s canal, which lowers IOP. The iStent inject (second-generation iStent) has two stents implanted to further improve the outflow.
Both devices are typically implanted during cataract surgery and are aimed at reducing IOP in patients with mild-to-moderate open-angle glaucoma. They offer a less invasive alternative to traditional glaucoma surgeries and are suitable for patients who may not yet need or qualify for more aggressive surgical intervention.
Research Outcomes: Hydrus Stent vs. iStent
Numerous studies have evaluated the efficacy, safety, and long-term outcomes of the Hydrus and iStent devices in lowering IOP and reducing the need for glaucoma medications. The following sections provide a comparative analysis of the key research findings.
1. Efficacy in Reducing Intraocular Pressure (IOP)
A key measure of success for any glaucoma intervention is its ability to lower IOP effectively. Several randomized controlled trials and observational studies have investigated the IOP-lowering effects of both the Hydrus stent and iStent, often comparing their outcomes in patients undergoing cataract surgery.
• Hydrus Stent: In a pivotal study known as the HORIZON trial, the Hydrus stent demonstrated significant IOP reductions in patients with mild to moderate open-angle glaucoma. The trial, which followed patients for two years, found that those implanted with the Hydrus stent had an average IOP reduction of 7.6 mmHg from baseline. Importantly, 77.2% of patients in the Hydrus group achieved an unmedicated IOP reduction of 20% or more at 24 months, compared to 57.8% in the cataract surgery-only control group. This suggests that the Hydrus stent can provide sustained IOP reduction over time.
• iStent: The iStent has also been shown to reduce IOP in glaucoma patients, with multiple studies demonstrating its efficacy. A randomized clinical trial comparing the iStent with cataract surgery alone found that patients receiving the iStent had a greater reduction in IOP (a decrease of 8.4 mmHg) compared to cataract surgery alone. However, the iStent generally shows smaller IOP reductions compared to the Hydrus in similar patient populations. For example, in a study comparing the two devices head-to-head, the Hydrus group had a greater mean IOP reduction than the iStent group at 12 months.
Overall, both devices effectively lower IOP, but evidence suggests that the Hydrus stent may achieve more significant IOP reductions, especially in long-term follow-up.
2. Medication Reduction
Another key goal of MIGS devices is to reduce or eliminate the need for glaucoma medications, which are often burdensome for patients due to side effects, costs, and adherence issues.
• Hydrus Stent: In the HORIZON trial, 78% of patients in the Hydrus group were medication-free at 24 months, compared to only 48% in the cataract surgery-only group. Additionally, the number of medications used by Hydrus patients decreased significantly over the study period, highlighting the potential for the Hydrus stent to reduce dependence on medications.
• iStent: Similar results have been observed with the iStent. In a study with a 12-month follow-up, 72% of iStent-treated eyes were medication-free compared to 50% in the control group. However, comparative studies between the Hydrus and iStent have shown that the Hydrus stent tends to achieve a greater reduction in medication use.
While both devices can reduce the need for glaucoma medications, the Hydrus appears to provide a more significant reduction in medication burden, according to current research.
3. Safety and Complications
Safety is a major concern when it comes to glaucoma surgery, especially since MIGS devices are designed to offer lower complication rates than traditional surgeries like trabeculectomy or tube shunts.
• Hydrus Stent: In the HORIZON trial, the safety profile of the Hydrus stent was comparable to that of cataract surgery alone. The most common adverse events were mild, transient complications such as hyphema (blood in the anterior chamber), which resolved without intervention. There were no significant differences in endothelial cell loss between the Hydrus and control groups at 24 months, which is important since endothelial cell damage can lead to corneal decompensation.
• iStent: The iStent also has a strong safety profile, with a low incidence of serious complications. Like the Hydrus, the iStent is associated with transient complications like hyphema, but these are typically self-limiting. Endothelial cell loss has not been a major concern in most iStent studies.
Comparative studies show that both devices have similar safety profiles, with no significant differences in the rates of adverse events. Both Hydrus and iStent offer a safer alternative to more invasive glaucoma surgeries, with a low risk of serious complications.
4. Surgical Complexity and Learning Curve
• Hydrus Stent: The Hydrus Microstent is relatively easy to implant, but its larger size and the need to scaffold 90 degrees of Schlemm’s canal may make it slightly more complex to position compared to the iStent. Surgeons must be familiar with the anatomy of Schlemm’s canal and ensure that the stent is correctly positioned to avoid complications such as malposition or occlusion.
• iStent: The iStent is known for its ease of implantation, given its small size and straightforward insertion process. However, because it is smaller, ensuring precise placement is critical for optimal outflow, and improper positioning can reduce the device’s effectiveness.
Both devices require surgeon experience and familiarity with MIGS techniques, but the learning curve is considered manageable for both.
Conclusion
The Hydrus Microstent and iStent have both proven to be effective tools in the management of mild to moderate open-angle glaucoma. Research outcomes show that while both devices can significantly reduce intraocular pressure and decrease the need for glaucoma medications, the Hydrus stent generally offers slightly superior IOP reductions and medication-free outcomes over time. In terms of safety, both devices have similar profiles, with low rates of serious complications and transient adverse events. Surgical complexity is modest for both devices, though the Hydrus may require slightly more attention to positioning given its larger size.
Ultimately, the choice between the Hydrus stent and iStent depends on individual patient factors, surgeon experience, and specific clinical goals. As research on these devices continues to evolve, both the Hydrus and iStent are likely to remain vital components of the minimally invasive glaucoma surgery landscape, offering patients effective alternatives to more invasive procedures.