Precision Glaucoma Surgery: A Mechanism-Based Review of MIGS and Contemporary Surgical Pathways

Glaucoma surgery is entering a precision-based era in which surgical success is determined not only by intraocular pressure reduction, but also by the anatomical mechanism targeted, the expected durability of effect, safety profile, medication burden, quality of life, and preservation of future therapeutic options. Microinvasive glaucoma surgery (MIGS) has become an important component of this paradigm by expanding the surgical continuum toward earlier, anatomically targeted, and tissue-sparing intervention. However, MIGS does not represent a homogeneous procedural category; rather, it encompasses distinct approaches that modulate different components of aqueous humor dynamics, including the trabecular meshwork, Schlemm's canal, distal collector channels, the subconjunctival space, the suprachoroidal pathway, and aqueous production. This narrative review synthesizes contemporary evidence and proposes a mechanism-based framework for glaucoma surgery, with particular emphasis on trabecular and Schlemm's canal-based procedures as representative examples of physiologically oriented conventional outflow enhancement. Canal-based interventions, trabecular bypass, goniotomy, trabeculotomy, and canaloplasty are most appropriate when enhancement of conventional outflow can achieve clinically meaningful pressure and medication reduction, particularly in mild-to-moderate open-angle glaucoma. By contrast, subconjunctival filtration, trabeculectomy, and aqueous shunt surgery remain indispensable when lower target pressures are required, especially in advanced or rapidly progressive disease. Lens extraction and ciliary body-directed procedures further illustrate the importance of aligning surgical strategy with disease phenotype and anatomical mechanism. The future of glaucoma surgery will therefore depend on individualized procedure selection guided by glaucoma stage, target pressure, angle and lens anatomy, outflow pathway integrity, safety considerations, and long-term surgical sequencing.