The Role of the Ciliary Body in Aqueous Humor Dynamics Structural Aspects

Abstract

The main structural elements of the ciliary body are the ciliary processes and the ciliary muscle, which both play key roles for aqueous humor dynamics in the anterior eye. The ciliary processes are the site of aqueous secretion into the posterior chamber. This process involves ultrafiltration of water and ions from the ciliary process capillaries into the stroma followed by an active ion transport across the ciliary epithelium. The ciliary epithelium is two-layered and consists of an inner nonpigmented epithelium (NPE) and an outer pigmented epithelium. Structural requirements for ultrafiltration are diaphragmed fenestrae in the endothelium of ciliary body capillaries. For active secretion of aqueous humor, tight junctions need to be present between cells of the NPE to form the blood–aqueous barrier. In addition, the cells of the ciliary epithelium need to be electrically coupled through numerous gap junctions to form a functional syncytium. The ciliary muscle facilitates trabecular aqueous humor outflow upon contraction as its anterior insertion connects with scleral spur and trabecular meshwork. Moreover, the ciliary muscle provides the pathways for uveoscleral or alternative aqueous humor outflow.