Histologic Findings of Trabecular Meshwork and Schlemm's Canal After Microhook Ab Interno Trabeculotomy

Introduction: Trabeculotomy (LOT) and related goniotomy surgeries are classified based on excision or incision of the trabecular meshwork (TM); however, histologic evidence of the incision/excision pattern is insufficient. Case Presentations: Two cases of glaucomatous eyes in which trabeculectomy specimens previously "incised" during LOT were assessed histologically. A 39-year-old man with juvenile open-angle glaucoma (case 1) and a 70-year-old man with exfoliation glaucoma (case 2) underwent trabeculectomy for insufficient intraocular pressure reduction or visual field progression after initial microhook ab interno trabeculotomy (mu LOT). In case 1, Schlemm's canal (SC) opened into the anterior chamber due to extensive absence of the inner wall of SC and TM. In case 2, SC endothelium (SCE)-marker CD34 staining showed the slit-like entry site of a previous LOT, the SC lumen was sealed partially by scleral tissue, and CD34-positive and CD34-negative areas in the SC wall suggested SCE dropout and partial conversion of SC into ghost vessels. Active aqueous outflow-marker podoplanin (D2-40) staining showed intense immunolabeling in the sclera between the entry site and collector channels, indicating aqueous outflow. Discussion: The mu LOT cleft can appear as both incisional and excisional patterns. In addition to incremental conventional outflow with reduced TM resistance, another unconventional outflow may be a mechanism of IOP reduction after LOT procedures.