What is pressure behind the eye mean?

Eye pressure (intraocular pressure) is controlled by a watery fluid called aqueous humour, which fills the front part of the eye. This fluid is made in the ciliary body (a ring of tissue behind the coloured part of the eye, which is called the iris). It flows through the pupil and drains away through tiny drainage channels called the trabecular meshwork. This is situated in the drainage angle between the cornea (the clear window at the front of the eye) and the iris. In a normal eye there is a balance between the production and drainage of this fluid, but in some eyes there is an imbalance. Most cases of glaucoma occur because the flow of fluid out of the eye becomes restricted and the pressure in the eye rises.