Glaucoma is a group of eye diseases characterized by progressive optic neuropathy and visual field loss related to elevated intraocular pressure (IOP). Severity is commonly categorized as mild, moderate, severe, or indeterminate based on optic nerve/RNFL findings and visual field testing.
Procedures differ by mechanism and expected IOP reduction: traditional filtering surgeries (e.g., trabeculectomy) and many glaucoma drainage devices (GDDs) create external filtration and generally achieve the largest IOP reductions, appropriate for more advanced or refractory disease; minimally invasive glaucoma surgeries (MIGS) are typically ab interno, cause less tissue disruption, and are usually pursued in patients with mild-to-moderate glaucoma where a more modest IOP lowering (often ≥ 20% or reduction of at least one medication) is acceptable.
Canaloplasty (ab externo or ab interno) and ab interno canal viscodilation aim to restore physiologic outflow by viscodilating Schlemm's canal and collector channels; ab externo canaloplasty historically uses a microcatheter and tensioning suture, while ab interno approaches use micro-incisions and viscodilation.
Trabeculectomy removes part of the trabecular meshwork and creates a subconjunctival filtering bleb to lower IOP, and remains the standard filtration surgery for substantial IOP lowering. Trabeculotomy and goniotomy incise or excise trabecular meshwork to improve outflow and are established procedures in pediatric glaucoma.
Gonioscopy-assisted transluminal trabeculotomy (GATT) is a circumferential ab interno trabeculotomy using an illuminated microcatheter or suture to achieve 360° trabeculotomy. Canaloplasty combined with trabeculotomy (ab interno) uses sequential viscodilation then trabeculotomy to address multiple outflow resistance points.
Glaucoma drainage devices (GDDs) such as Ex-PRESS, Molteno, Baerveldt, Ahmed, and Krupin-Denver divert aqueous to an external plate/bleb and are commonly used for refractory glaucoma. Other implants (e.g., iStent, Hydrus, XEN) provide stenting/shunting into Schlemm's canal or subconjunctival/suprachoroidal spaces.