Histopathology of the Trabecular Meshwork and Schlemm's Canal in Primary Angle-Closure Glaucoma

Purpose.: To investigate the detailed histopathology of trabecular meshwork changes associated with primary angle closure glaucoma (PACG). Methods.: Thirty trabecular blocks obtained from trabeculectomy (TLE) of 25 PACG patients were embedded in paraffin for immunohistochemical staining of thrombomodulin, CD68, D2-40, and epon for transmission electron microscopy. Eleven TLE blocks obtained from normal-tension glaucoma patients were used as a control. Histologic changes of outflow routes were analyzed by comparing the existence of iridotomy, gonioscopy-evaluated angle closure, intraocular pressure (IOP), episodes of acute attack, visual field defect classified by Aulhorn-Greve, anterior chamber depth, lens thickness, and axial length. Results.: Occlusion of the Schlemm's canal (SC) of <150 μm was observed in 11 eyes, which significantly correlated with gonioscopy-evaluated angle closure (T = 19.33 > χ2 (f,α) = 9.488). Moderate correlation between SC occlusion and IOP before TLE was also observed (correlation coefficient: −0.540). Slightly negative or no correlations were found between SC occlusion and the other parameters. Thinned SC endothelium at the junction or degenerated SC endothelium and various degrees of SC occlusion and fusion of the trabecular beams where trabecular cells degenerated with damaged mitochondria were the general findings in the PACG eyes involved in this study. Conclusions.: Persistent trabecular-iris contact or peripheral anterior synechia may block aqueous outflow resulting in a progressive process of SC endothelial damage and subsequent SC occlusion, as well as trabecular cell damage possibly due to impairment of mitochondrial function and subsequent fusion of the trabecular beams. These changes may be the reason for residual glaucoma after laser iridotomy or cataract surgery.