Aqueous Humor Determines Intraocular Pressure

Aqueous humor is a clear liquid found in the anterior and posterior chambers of the eye. Its rate of production and absorption is sufficiently high to replace the entire chamber's volume several times a day.

Aqueous humor is secreted by the ciliary process, a system of fingerlike projections on the ciliary body of the posterior chamber. Aqueous humor is thought to be formed by the active transport of sodium, chloride, and possibly bicarbonate ions into the posterior chamber. This establishes an osmotic gradient, causing water to flow passively into the posterior chamber. Aqueous humor flows from the posterior to the anterior chamber through the pupil. Flow is caused by a pressure gradient established by the active process of formation in the posterior chamber.

Aqueous humor is then absorbed into the venous system at the angle between the cornea and the iris. This absorption is driven by a pressure gradient and is assisted, in many species, by a system of trabeculae and canals. If this absorption into the venous system is obstructed, intraocular pressure increases because the production of aqueous humor continues. This pathologic increase in intraocular pressure is called glaucoma.

As intraocular pressure exceeds intravascular pressure in the blood supply to the retina, blindness results.