Possible Effects of Topical Rho-Kinase Inhibitor on Schlemm's Canal Morphology Parameters

Background: To evaluate the effects of preoperative topical ripasudil, a Rho-associated protein kinase (ROCK) inhibitor, on Schlemm's canal (SC) morphology in patients with primary open-angle glaucoma (POAG). Methods: This study included 95 SC specimens obtained during trabeculectomy from 95 patients with POAG. Based on preoperative treatment, patients were divided into two groups: ripasudil (-) group (n = 68) receiving four topical medications [FP receptor agonist, β-blocker, carbonic anhydrase inhibitor (CAI), and α₂ agonist], and ripasudil (+) group (n = 27) receiving the same four medications plus ripasudil. SC morphology parameters were assessed in thrombomodulin (TBM)-stained sections, including length parameters [TBM-positive/negative and opened/closed SC lengths] and area parameters [TBM-positive/negative and opened SC areas]. Between-group comparisons were performed using unpaired t-tests, and multiple regression analysis was conducted to adjust for age, gender, preoperative intraocular pressure (IOP), and oral CAI use. Results: The ripasudil (+) group had significantly longer total SC length (TSC: 302.5 µm) than the ripasudil (-) group (273.0 µm, p = 0.023). Among area parameters, the ripasudil (+) group showed significantly larger opened SC area (OSC-A: 2689 µm² vs. 1881 µm², p = 0.008) and TBM-negative opened SC area (NOSC-A: 716 µm² vs. 305 µm², p = 0.001), whereas TBM-positive opened SC area (POSC-A) was not significantly different between groups (2001 µm² vs. 1575 µm², p = 0.096). After multivariate adjustment, ripasudil use remained significantly associated with longer TSC (p = 0.011) and larger OSC-A (p = 0.014) and NOSC-A (p = 0.001). Conclusions: Preoperative use of topical ripasudil was associated with preservation of SC lumen morphology, particularly in regions lacking SC endothelium. These findings provide a theoretical basis for therapeutic strategies employing ROCK inhibitors to maintain SC morphology and function.