The aqueous humour is the clear, watery fluid that fills the complex space in the front of the eye which is bounded at the front by the cornea and at the rear by the front surface or face of the vitreous humour. In health the aqueous humour does not mix with the firm, gel-like vitreous humour. The face of the vitreous humour spans the eye transversely behind the lens, and the aqueous-filled space in front of this is divided by the iris plane into the anterior chamber and the posterior chamber (which, despite its name, is still an anterior structure). The aqueous humour allows nutrients to circulate to the corneal endothelium and its pressure maintains the convex shape of the cornea.

The aqueous humour is secreted into the posterior chamber by the ciliary body and flows through the narrow cleft between the front of the lens and the back of the iris, to escape through the pupil into the anterior chamber , and then to drain out of the eye via the trabecular meshwork into the aqueous veins and eventually into the veins of the orbit.

Glaucoma is a condition characterised by increased intraocular pressure (pressure within the eye), usually caused by increased resistance to outflow of aqueous humour through an abnormal trabecular meshwork, or to obliteration of the meshwork caused by injury or disease of the iris. Uncontrolled glaucoma will lead to visual field loss and ultimately blindness.