Glaucoma remains a leading cause of irreversible blindness worldwide, with elevated intraocular pressure (IOP) as its most important modifiable risk factor. While medications and laser therapy are often the first-line approaches, patients with progressive disease have traditionally been managed with trabeculectomy or tube shunt surgery.1
Although these procedures can provide substantial IOP reduction, they are associated with notable risks, including hypotony, infection, and long-term complications, which often make them less appealing until advanced disease necessitates intervention.1,2
The emergence of minimally invasive glaucoma surgery (MIGS) has transformed this paradigm, providing a safer surgical alternative for patients earlier in their disease course.
MIGS: A brief overview
First coined by Iqbal Ike K. Ahmed, MD, FRCSC, in 2009, MIGS encompasses a range of ab interno procedures designed to achieve effective IOP reduction while minimizing disruption to ocular anatomy.1 The hallmarks of MIGS include a high safety profile, quicker post-operative recovery, and the potential to reduce dependence on topical medications.
Unlike traditional filtering surgeries, MIGS procedures prioritize preserving future surgical options, improving patient quality of life, and broadening treatment opportunities for those with mild-to-moderate glaucoma or patients intolerant to drops.1,3
Though efficacy in terms of absolute IOP lowering may be more modest, the balance between safety and effectiveness positions MIGS as a cornerstone in the evolving concept of “interventional glaucoma.”4
To review a new consensus-based treatment protocol for glaucoma, check out Demystifying Interventional Glaucoma: A New Protocol!
How does MIGS reduce IOP?
MIGS achieves IOP reduction through several distinct mechanisms:1
- Enhancing trabecular outflow by bypassing or excising the trabecular meshwork
- Directing aqueous humor into the subconjunctival space with microshunts
- Augmenting uveoscleral outflow by accessing the suprachoroidal space
- Reducing aqueous production via ciliary body ablation with endocyclophotocoagulation
These mechanisms translate into different categories of procedures, including trabecular bypass stents such as iStent and Hydrus, subconjunctival devices like the XEN gel stent, suprachoroidal implants, and energy-based techniques like endoscopic cyclophotocoagulation.1,4
Each category carries its own balance of efficacy, safety, and indications, allowing ophthalmologists to tailor interventions to individual patient needs and disease severity.
In this article Alexis Pascoe, MD, shares her expertise on the insertion of the Hydrus Microstent, an FDA-approved MIGS device designed to reduce IOP in patients with primary open-angle glaucoma (POAG).
Made of a biocompatible nickel-titanium alloy, the device is an 8mm intracanalicular scaffold that transects the trabecular meshwork and opens approximately 90° of Schlemm’s canal for better drainage.
Patient selection is key for success with MIGS procedures, including the Hydrus Microstent.
Indications and exclusions for use include:
- Mild to moderate POAG, the Hydrus Microstent is not approved for severe POAG
- Eyes with visually significant cataract; the Hydus Microstent cannot be done as a standalone procedure
- Patients adequately controlled on medical therapy can be candidates with the goal of decreasing drop burden, which alleviates ocular surface disease considerations for glaucoma patients in the long term
- Patients inadequately controlled on medical therapy with mild to moderate disease, but not to the degree of needing a more traditional glaucoma filtering surgery (trabeculectomy or anterior chamber tube shunt)
Contraindications include angle closure, neovascular or uveitic glaucoma, and eyes with significant angle pathology or scarring. Gonioscopy should be a mainstay in your evaluation for this patient population.
Surgical pearls for Hydrus Microstent insertion
1. Properly place the entry wound
For the Hydrus Microstent, a separate wound needs to be made prior to insertion. As demonstrated in the video, the insertion device is aligned with the limbus and used as a guide to determine the location of the entry wound.
2. Optimize visualization.
Proper gonioscopic view is critical. Tilting the microscope towards the surgeon and the patient’s head away enhances angle exposure; 30° to 45° is typically adequate. Cohesive viscoelastic insertion maintains anterior chamber stability to allow for a clear view of the angle. Holding the gonioprism and tilting it slightly toward the patient pushes the viscoelastic into the angle and opens the view more.
3. Control entry.
Abut the injector against the trabecular meshwork with gentle, deliberate pressure. Avoid pushing too deep into Schlemm’s canal to prevent creating false passages. Pointing the tip of the insertion device upward helps ensure the proper position, as demonstrated in the video.
The procedure should be painless. If the patient is feeling discomfort, this is a sign that the device is not in the proper location.
4. Be patient. Reload the microstent and try again.
The inserter can be realigned with the notch at the outlet of the microstent and then reloaded if repositioning is necessary. As previously mentioned, if the patient is in discomfort, the microstent is likely in need of repositioning.
Final thoughts
Hydrus implantation offers a safe, effective, and minimally invasive approach to IOP reduction in well-selected patients. Mastery lies in case selection, meticulous angle visualization, and gentle, precise delivery of the stent.
For cataract surgeons interested in MIGS, the Hydrus is a valuable tool in the ever-expanding toolbox for glaucoma care.
