Aqueous outflow system (AOS)

The aqueous outflow system is the primary physiological mechanism responsible for the drainage of aqueous humor from the anterior chamber of the eye to maintain a stable intraocular pressure (IOP). This system is anatomically divided into the conventional pathway, which includes the trabecular meshwork, Schlemm's canal, and collector channels, and the unconventional (uveoscleral) pathway, where fluid exits through the ciliary muscle and suprachoroidal space (StatPearls, 2023). In many forms of glaucoma, particularly primary open-angle glaucoma, increased resistance within the trabecular meshwork leads to inadequate drainage and subsequent elevation of IOP, which can damage the optic nerve (NIH/NEI, 2023). Pharmacological treatments target this system to lower IOP; for instance, prostaglandin analogs enhance uveoscleral outflow, while newer classes like Rho kinase inhibitors specifically target the trabecular meshwork to decrease resistance (Journal of Ocular Pharmacology and Therapeutics, 2021). Because this is an integrated anatomical system rather than a single molecular target, it is classified as a therapeutic system containing multiple specific molecular targets such as the Prostaglandin F receptor and Rho-associated protein kinases.

Other names

Aqueous humor outflow pathwayConventional outflow pathwayUnconventional outflow pathwayTrabecular outflow pathwayUveoscleral outflow pathway

Drugs targeting the aqueous outflow system act by increasing the drainage of aqueous humor through either the conventional (trabecular) or unconventional (uveoscleral) pathways. Prostaglandin analogs primarily increase uveoscleral outflow by remodeling the extracellular matrix in the ciliary muscle. Rho kinase inhibitors reduce resistance in the trabecular meshwork by inducing cellular relaxation and increasing the permeability of the Schlemm's canal inner wall. Cholinergic agonists contract the ciliary muscle, which physically pulls on the trabecular meshwork to open the drainage pores.