ABSTRACT
Intraocular pressure (IOP) is controlled by the turnover of aqueous humor, a clear fluid that fills the anterior segment of the eye and serves to nourish the avascular tissues of the cornea, lens, and trabecular meshwork (Figure 21.1). Aqueous humor is secreted into the posterior chamber by the ciliary processes, enters the anterior chamber through the pupil, and drains through one of two outflow pathways. The conventional or trabecular outflow pathway carries the majority of outflow and includes the trabecular meshwork, Schlemm's canal, and downstream collecting vessels that lead to the episcleral veins. The secondary uveoscleral outflow pathway appears to account for only 3%–35% of total outflow in the human eye (as surveyed by Nilsson [1]) and likely contributes little toward IOP regulation, although uveoscleral outflow does become important for glaucoma therapies involving prostaglandins and its analogues.
