Histopathology of the aqueous outflow pathways in primary open-angle glaucoma (clinical case)

Abstract

Purpose: To evaluate trabecular meshwork (TM) structure changes using standard transmission electron microscopy (TEM). Methods: 69 years old female with 20 glaucoma treatment years (multiple hypotension medications) without good clinical effect. At the time of admission to University Eye Clinic optic disc cupping were 0.8, IOP – 29-32 mmHg, severe visual field defects. Trabeculectomy (TLE) was performed, trabecular block was obtained. Tissues were immersed in 2.5% glutaraldehyde and 2% paraformaldehyde in 0.1 M cacodylate buffer, pH 7.4, for fixation at 4°C. Following overnight fixation, tissues were rinsed in 0.1 M cacodylate buffer (15 min.), postfixed in 1% osmium tetroxide for 1 hour, dehydrated in a graded ethanol and acetone series, and embedded in a mixture of Epon 812 and Araldite. Semithin sections (1 mm) were stained with methylene blue according to Ridgway (1986). Ultrathin sections stained with uranyl acetate and lead citrate, and examined with Tecnai Spirit BioTWIN TEM (FEI, Eindhoven, The Netherlands) at 80-120 kV equipped with MegaView III digital camera (Olympus Soft Imaging Solutions GmbH, Munster, Germany). Histologic changes of outflow routes were analyzed by comparing to normative data base. Results: Evaluating ultrathin sections of trabecular block, changes in TM and Schlemm’s canal endothelium cells were detected. Comparing normative data to our patients TM, we found TM stiffness, rigidness and high pigmentation. Spaces between trabecules were filled with fibers of connective tissue (collagenic, elastic), which were not covered with endothelium. Potentially changes in TM and Schlemm’s canal are caused by actomyosin system, which could change cells shape, volume, contractility and affect neighbouring cells. All of this influences outflow resistance and might block drainage process. Conclucion: These alterations of TM provide evidence supporting the essential role of the actomyosin system in TM cells and endothelium of Schlemm’s canal in regulating trabecular aqueous outflow.