Ultrastructural Characteristics oyf the Trabecular Meshwork in Primary Open-Angle Glaucoma versus Chronic Angle-Closure Glaucoma: A Comparative Study

Background The trabecular meshwork (TM), the principal site of aqueous humor outflow resistance, plays a pivotal role in the regulation of intraocular pressure (IOP), the key modifiable risk factor for glaucoma. This study aimed to compare the ultrastructural characteristics of the TM in primary open-angle glaucoma (POAG) and chronic angle-closure glaucoma (CACG) using transmission electron microscopy (TEM). Methods TM specimens were obtained via Kahook Dual Blade goniotomy from 11 POAG and 9 CACG patients, immediately fixed, and processed for TEM analysis. The ultrastructural features examined included cellular morphology, extracellular matrix (ECM) organization, and collagen fibril architecture, with fibril diameters quantitatively measured using Feret’s diameter. Results Both POAG and CACG samples exhibited a marked reduction in TM cell numbers accompanied by pronounced ultrastructural abnormalities, including plasma membrane rupture, mitochondrial swelling, chromatin aggregation, and dilated endoplasmic reticulum. ECM alterations in both groups included trabecular beam fusion and narrowed intertrabecular spaces, indicative of compromised tissue architecture and impaired aqueous humor outflow pathways. Quantitative analysis revealed that collagen fibrils were significantly larger in CACG compared to POAG (60.27 ± 12.97 nm vs. 43.61 ± 8.62 nm, p = 0.018), with a larger cross-sectional area (p = 0.027). Conclusion These findings highlight distinct ultrastructural differences in the TM of POAG and CACG, with POAG characterized by thinner and CACG by larger fibrils, suggesting divergent ECM remodeling pathways that may contribute to subtype-specific outflow resistance and disease mechanisms.