In this episode of Interventional Mindset, Nicole Bajic, MD, an anterior segment surgeon and assistant professor of ophthalmology at the Cleveland Clinic’s Cole Eye Institute, reviews a clinical framework for steps to take after a microinvasive glaucoma surgery (MIGS) procedure fails to achieve the target intraocular pressure (IOP).
Failed MIGS fast facts
- When a MIGS procedure fails to achieve target IOP, gonioscopy is a critical first step to identify stent position, peripheral anterior synechiae (PAS), and untreated trabecular meshwork segments.
- Younger patients and those with mild to moderate open-angle glaucoma are ideal candidates for repeat MIGS.
- Trabecular MIGS procedures carry a physiologic IOP floor of ~15 to 16mmHg; targets in the low teens require a different approach.1,2
- After failed iStent implantation or goniotomies, GATT targeting untreated Schlemm's canal segments has demonstrated an 82% qualified success rate at 1 year.3
- In pseudoexfoliation glaucoma, resistance is concentrated in the trabecular meshwork—angle procedures, including repeat interventions on previously untreated trabecular meshwork, remain effective.4
- PAS in the angle limits the utility of additional angle procedures; advanced or rapidly progressing glaucoma requiring very low target IOP warrants referral to a glaucoma specialist.
How MIGS are changing modern glaucoma management
Dr. Bajic explained that over her career she has witnessed how MIGS procedures have profoundly changed glaucoma management, with the number of trabeculectomies decreasing to such a degree that some surgeons are now concerned that trainees will lose the art and technique of performing a trabeculectomy.
This is in part because combined 360° canaloplasty (particularly those that can deliver 100mL of viscoelastic) with GATT enables surgeons to reach a target IOP lower than the physiologic floor of traditional trabecular MIGS.
As such, she has colleagues who no longer need to perform trabeculectomies because they can reach low target IOPs with combined MIGS procedures, highlighting how versatile these techniques are in managing glaucoma.
Performing the initial assessment post-MIGS failure
Dr. Bajic underscored the necessity of a comprehensive reassessment of all clinical variables prior to selecting a subsequent intervention, ensuring that treatment decisions are grounded in a holistic evaluation of the patient's clinical picture.
For example, if the patient underwent a stent-based procedure, performing gonioscopy is a critical next step to confirm the stent position and patency and evaluate for signs of complications, such as PAS.
Optimal patient selection for repeat MIGS procedures
In Dr. Bajic’s experience, the patients who benefit most from repeat MIGS are those with mild to moderate open-angle glaucoma and younger patients. She added that younger patients tend to respond better to repeat MIGS compared to older patients due to their preserved collector channel function and the subsequent reduction in trabecular and distal outflow degeneration.
Setting an achievable IOP target is equally important, she emphasized; the classic teaching is that trabecular MIGS procedures have a physiologic IOP floor in the mid-teens (15 to 16mmHg) due to downstream resistance in the distal outflow pathways and the episcleral venous pressure.1,2 Consequently, a second trabecular MIGS procedure is unlikely to reach a target IOP in the low teens (or lower).
Deeper dive into 360° canaloplasty and GATT
When performed via an ab interno surgical technique, canaloplasty is a tissue-sparing, stent-free procedure that targets the three main sites of outflow resistance, including the trabecular meshwork, Schlemm’s canal, and the collector channels.5 Conversely, GATT addresses resistance at the trabecular meshwork by unroofing it to enhance aqueous outflow into Schlemm’s canal.
Dr. Bajic highlighted two devices that can perform 360° canaloplasties and deliver 100mL of viscoelastic:
- iTrack microcatheter (Nova Eye Medical Limited)6
- Shear Clear Technology transforms cohesive viscoelastic into a low-viscosity fluid during canaloplasty, enabling it to circulate more freely and penetrate deeper into the trabecular outflow pathway, achieving a 190-fold reduction in viscosity as demonstrated via optical rheology testing7
- Pressurized titratable viscoelastic delivery via ViscoInjector
- Illuminated distal tip with real-time transluminal visualization
- VIA360 Surgical System (New World Medical)8
- ActiveInject Technology allows for viscoelastic delivery on-demand, when and where needed
- Catheter can extend up to 40mm or 360° and allows for multi-axial delivery of viscoelastic, both forward and tangential to target areas
- The handpiece has a rotatable cannula, which allows users to move clockwise or counterclockwise without the need for device rotation
Recent research on the efficacy of GATT after failed MIGS
A retrospective study of GATT outcomes in 30 eyes with prior failed glaucoma surgery found that the probability of complete and qualified success for target IOP of < 21mmHg at the end of 1 year was 20% and 82%, respectively.3
The study authors noted that the probability of complete success was lower because the majority of patients were initiated on glaucoma medications due to their advanced glaucoma, which necessitated maintaining IOP in the lower teens.
Note: The iTrack Advance received FDA clearance in 2023 and features updates to the device, such as an all-in-one ergonomic handheld injector handpiece with an integrated actuator and single-hand use and a rotating cannula.9
Additional considerations for failed MIGS procedures
Following failed MIGS, Dr. Bajic underscored the importance of assessing for multimechanistic outflow resistance prior to selecting a subsequent intervention, as residual IOP elevation may reflect obstruction at a location not addressed by the initial procedure. Additionally, Dr. Bajic recommended referring patients who require a low target pressure but have advanced or progressing glaucoma to a specialist for more intensive treatment.
Conclusion
As the MIGS landscape continues to evolve, the ability to tailor interventions to each patient's unique anatomy, glaucoma severity, and IOP target remains the cornerstone of effective surgical decision-making.
With a growing range of tools available, such as standalone or combined MIGS procedures, surgeons are well-positioned to preserve vision and optimize outcomes following an initial MIGS failure.
This article was written by Mariel Mohns, MS and edited by Sanjana Bhattacharya based on the recorded video from Dr. Bajic.
