[Functional morphology of the outflow pathways of aqueous humor and their changes in open angle glaucoma].

Aqueous humor exits the eye through the trabecular and uveoscleral outflow pathways. Under normal conditions intraocular pressure is maintained in the trabecular outflow pathways in which aqueous humor passes through the trabecular meshwork into Schlemm's canal. Intraocular pressure is generated through an outflow resistance in the juxtacanalicular region which consists of juxtacanalicular tissue and the inner wall endothelium of Schlemm's canal. The resistance of this region is under the influence of two contractile systems, the anterior longitudinal portion of the ciliary muscle and the contractile myofibroblast-like cells in the trabecular outflow pathways. Resistance is lowered through contraction of the ciliary muscle or relaxation of the contractile cells in the trabecular outflow pathways. In primary open angle glaucoma, resistance in the juxtacanalicular region is abnormally high. The cause of the increase is related to an increased activity in transforming growth factor beta and connective tissue growth factor signaling. The cells of the trabecular meshwork outflow pathways are stimulated to form a stronger contractile phenotype involving both an increase in the actin cytoskeleton and the surrounding fibrillar extracellular matrix. As a result there is an increase in cellular tone in the trabecular outflow pathways leading to an increase in rigidity and outflow resistance.