To understand the basic mechanism let me give you an analogy. Imagine a sink with a water tap. The tap is on and water flows at a constant rate into the sink ; while the drainage hole of the sink is unblocked the sink will not overflow. Consider the eye: fluid (aqueous) is produced at a constant rate by the ciliary processes (see figure 1) which flows around the lens into the anterior chamber and drains into the angle between the cornea (window of the eye) and the iris (colored part of the eye) . This drainage angle is like the drainage hole of the sink; if it becomes blocked then fluid builds up and because the eye is a closed chamber, instead of overflowing the pressure rises within the eye. There are three main consequences of raised intraocular pressure:-
In congenital glaucoma there is abnormal development of the drainage angle such that it is blocked by abnormal tissue referred to as Barkans membrane after the man who first suggested its presence in such eyes. In our analogy imagine that someone has placed a film of cellophane over the drainage hole of the sink; now the sink will overflow. Similarly the pressure in the eye will go up.