Glaucoma, a leading cause of irreversible blindness worldwide, is often associated with elevated intraocular pressure (IOP). The trabecular meshwork (TM), Schlemm’s canal (SC), and collector channels play crucial roles in regulating IOP by facilitating aqueous humor outflow. Minimally invasive glaucoma surgery (MIGS) has revolutionized glaucoma treatment by targeting these structures to enhance outflow and reduce IOP.1 Embryology and Anatomy of Aqueous Drainage Structures The development of SC and post-trabecular structures is a complex process that begins early in foetal life. By 24 weeks of gestation, SC is present throughout its circumference, and the anlage of an outer collector canal (OCC) is visible. The OCC develops in parallel with SC, becoming more defined by 33–36 weeks, and connects to SC via intercanal links. The intra-scleral plexus grows and matures postnatally, with adult-like structures evident by 8 years of age. Abnormalities in SC and OCC development may contribute to increased outflow resistance, elevating IOP and glaucoma risk.2 In adults, the anterior chamber angle is a well-defined, circular structure with fully developed TM, SC, and collector channels. The juxta-canalicular connective tissue (JCT) is mature, with an established extracellular matrix and myofibroblast regulation. In glaucoma, JCT changes, including increased stiffness and myofibroblast activation, contribute to elevated IOP.1,2 Collector channels serve as the distal conduit for aqueous humor drainage from SC to the episcleral veins. Their patency is essential for maintaining normal IOP. Recent advances in SC-based surgeries, such as trabecular bypass and canaloplasty, underscore the importance of collector channel patency in determining surgical success. Assessing collector channel function and morphology is vital for selecting optimal glaucoma management strategies as it influences aqueous humor drainage and IOP regulation.3 Investigations for Collector Channels and Glaucoma Investigations aid in diagnosing glaucoma subtypes, assessing collector channel function, guiding MIGS procedures, and monitoring treatment outcomes. The following investigations could be done: Intraoperative indirect channelography is a diagnostic technique used to assess the patency of SC and collector channels during glaucoma surgery. By inducing mild hypotony via paracentesis, retrograde blood filling of SC is observed on gonioscopy. This helps identify patients with intact drainage systems, making them suitable candidates for trabecular bypass stent implantation. Patients with absent or insufficient blood filling may require alternative drainage procedures, such as supraciliary or subconjunctival stents. This simple technique aids in individualized selection of glaucoma stent implantation, optimizing surgical outcomes.4 Advanced anatomic imaging modalities have revolutionized the visualization of collector channels and SC, enabling precise assessment of their morphology. Swept-source optical coherence tomography (SS-OCT) and spectral domain OCT (SD-OCT) provide high-resolution images of these structures, while micro-computed tomography (Micro-CT) offers detailed 3D reconstructions. Immunohistochemistry allows for the study of collector channel morphology and protein expression. Scanning electron microscopy provides ultra-structural details. Functional assessment of collector channels is crucial for understanding aqueous humor dynamics in glaucoma. Techniques such as episcleral venous outflow evaluation and observation of the episcleral venous fluid wave enable clinicians to assess outflow patterns and the patency of the collector channel. Additionally, tracer studies using fluorescein, indocyanine green, or trypan blue provide valuable insights into collector channel function, aqueous humor outflow pathways, and vascular structures, thereby guiding therapeutic interventions and improving patient outcomes.3–5 Ultrasound biomicroscopy (UBM) provides detailed imaging of anterior segment structures, enabling assessment of the collector channel and SC morphology. Gonioscopy provides direct visualization of the angle and trabecular meshwork and can identify anatomical abnormalities, neovascularization, or synechiae. Histological analysis of tissue samples further elucidates collector channel morphology and pathological changes in glaucoma, informing diagnosis and management.3,4 Management The advent of MIGS has revolutionized the management of glaucoma, shifting the paradigm toward preserving the structural and functional integrity of the aqueous outflow facility. MIGS procedure includes: Trabecular Meshwork Bypass: iStent inject is a trabecular micro-bypass implant with two small stents, offering proven efficacy and quick recovery, but may have complications like rebound iritis. Hydrus Microstent: A scaffold that dilates SC, providing broad area coverage and effective IOP reduction, but with risks of hyphema and steroid response. Suprachoroidal Outflow Augmentation: CyPass Micro stent and iStent Supra target suprachoroidal outflow. Goniotomy: Kahook Dual Blade excisional goniotomy removes a strip of trabecular meshwork, providing a foreign-body-free approach with significant IOP reduction (28.0% at 6 years), medication reduction (30.8%), and surgical success (46.2% at 6 years). Schlemm’s Canal Expansion: Canaloplasty dilates SC, enhancing collector channel function and outflow. Conjunctival Bleb-Forming Procedures: EX-PRESS, Xen Gel Stent, and PreserFlo MicroShunt create a controlled filtration pathway. By leveraging these microanatomical approaches, MIGS offers a safer and more effective alternative to traditional glaucoma surgeries.6–11 Emerging Technologies Ongoing innovations in MIGS are expected to further optimize outcomes, with emerging technologies focusing on: Trabecular Stem Cell Therapy: Regenerating damaged trabecular meshwork to restore physiological outflow. Gene Therapy: Modulating gene expression to enhance aqueous outflow or to reduce inflammation. Advanced Surgical Devices: Next-generation stents and implants designed for improved efficacy and safety. Personalized Medicine: Tailoring treatment strategies based on individual anatomical and physiological characteristics. These advancements are poised to redefine glaucoma management, emphasizing earlier intervention, improved patient outcomes, and potentially disease-modifying therapies.6–9 Conclusion MIGS has emerged as a highly effective approach to managing glaucoma, offering sustained reductions in IOP and medication dependence. By targeting the trabecular meshwork and SC, MIGS procedures restore physiological aqueous outflow, and clinical evidence supports their efficacy over 3–6 years. Ongoing advancements in imaging and technology are expected to further optimize patient selection, procedural techniques, and treatment outcomes, solidifying MIGS as a cornerstone in glaucoma management.9
Parihar et al. (Wed,) studied this question.