AQUEOUS HUMOUR

watery, alkaline liquid that occupies the anterior and posterior chambers of the eyethe space in front of the iris and lens and the ringlike space encircling the lens. The aqueous humour resembles blood plasma in composition, but contains much less protein, less glucose, more lactic acid, and much more ascorbic acid. Aqueous humour is formed from the blood by filtration through the surface of the back of the iris and of the ciliary body, the muscular structure that controls the curvature of the lens. It leaves the eye through a porous tissue into Schlemm's canal, a ringlike passageway around the outer angle of the anterior chamber. From the canal the liquid enters the veins. When the aqueous humour does not adequately drain from the eye, pressure builds up and glaucoma can result.