Choosing Between Bleb- and Trabecular Meshwork–Based MIGS

The target IOP, disease severity, and risk-benefit ratio all require consideration.

Vishal Shah, MA, FRCOphth, and Keith Barton, MD, FRCP, FRCS

Glaucoma Today

Key Takeaways When a patient's target IOP is not lower than the midteens, a small reduction in the medication burden is desirable, a visually significant cataract is present, and the patient has mild to moderate glaucoma that is not progressing rapidly, trabecular meshwork–based MIGS can provide a well-tolerated solution with an excellent safety profile. When a significant IOP reduction is required, an ab externo bleb-based MIGS procedure is likely the better option, assuming the patient is not at increased risk of failure. MIGS has increased in popularity around the world,1 with demand leading to an ever-increasing number of devices coming to market and procedures in development. The widespread appeal of these solutions can be attributed to the perception that they are low-risk and well-tolerated and that they achieve the benefits of lowering IOP, reducing the drop burden, and even halting the progression of mild to moderate glaucoma. According to the US FDA, MIGS encompasses ab interno, non–bleb-forming procedures and ab externo minimally invasive bleb-forming procedures.2 Trabecular meshwork (TM)–based MIGS represents the most popular therapeutic approach. These procedures circumvent the inherent resistance of the TM to access the conventional outflow pathway. The episcleral venous pressure (typically 8–10 mm Hg) provides a ceiling of potential pressure lowering in this setting. Additionally, less quantifiable resistance is provided by the distal outflow system (ie, collector channels) and the veins themselves from segmental flow limitation, distal collector channel collapse, and pressure-dependent variation. TM-based MIGS typically achieves a modest IOP reduction to the midteens.3,4 The most relevant ab externo minimally invasive bleb-forming procedure is Preserflo MicroShunt (Santen/Glaukos) implantation. These ab externo procedures are typically augmented with the application of an antifibrotic agent such as mitomycin C (MMC), and they facilitate drainage into the sub-Tenon space, akin to flow through the flap of a trabeculectomy.

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