Schlemm drain aqueous humor

After the transport of aqueous humor into the posterior chamber, it flows through the pupil into the anterior chamber where it provides oxygen and nutrition to the avascular lens and cornea. Aqueous humor then exits the anterior chamber through the trabecular meshwork and drains into Schlemm s canal which drains aqueous humor into the episcleral venous system. 

Muscarinic agonists instilled into the conjunctival sac cause contraction of the smooth muscle of the iris sphincter (resulting in miosis) and of the ciliary muscle (resulting in accommodation). As a result, the iris is pulled away from the angle of the anterior chamber, and the trabecular meshwork at the base of the ciliary muscle is opened. Both effects facilitate aqueous humor outflow into the canal of Schlemm, which drains the anterior chamber. 

The cornea serves as the front part of the AC of the eye. Its exterior is covered by the precorneal tear film, which lubricates, nourishes and protects the corneal surface. The iris and the pupil represent the posterior border of the AC. The AC angle is an important structure which is comprised of Schwalbe s line, Schlemm s canal and trabecular mesh-work, scleral spur, anterior border of the ciliary body and the iris (Figure 5.2). Aqueous humor that fills the AC is produced by the ciliary epithelium located in the posterior chamber. The fluid flows through the pupil and is drained by the trabecular meshwork into Schlemm s canal and subsequently into the episcleral vessels. This passage is named the conventional pathway. Aqueous humor is also drained by a uveoscleral pathway across the ciliary body into the supraciliary space. 

The aqueous humor flows out the eye mainly via the conventional route of the trabecular meshwork and Schlemm s canal. However, about 10-20% of outflow is via the uveoscleral (nonconventional) route whereby the aqueous humor passes between the ciliary muscle bundles and into the episcleral tissues, where it is reabsorbed into orbital blood vessels and drained via the conjunctival vessels. The IOP-lowering effect of these prostanoid drugs occurs predominantly through enhancement of uveoscleral outflow [26], although unoprostone and bimatoprost also increase flow via the trabecular meshwork to a lesser extent. 

Pilocarpine is a commonly used direet-acting cholinergic that is used to treat glaucoma. Pilocarpine reduces intraocular pressure by constricting pupils and opening the Canal of Schlemm enabling aqueous humor (fluid) to drain. 

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