The front of your eye is filled with a watery fluid called aqueous humour whose function is to provide your eye with all the oxygen and nutrients it requires.
The amount of fluid in the eye also helps create pressure in your eye so that it keeps to its correct shape. In a healthy eye, the fluid is kept at a constant level, so the pressure in your eye remains stable. A part of your eye called the Ciliary body constantly produces aqueous (fluid) bringing in a fresh supply of oxygen and nutrients. At the same time, the old aqueous flows out of the eye through drainage channels in your eye called the Trabecular Meshwork, taking out the waste products. It is this constant production and drainage of the aqueous that helps keep your Intra-ocular pressure (IOP) at a healthy and constant level.
If anything interrupts the drainage (Trabecular meshwork) and the eye keeps producing a constant level of aqueous, then there will be a net gain in aqueous and the pressure inside the eye will start to rise. Imagine you are filling a sink with water and then the drainage pipe starts to narrow. If the amount of water being added stays the same, then before long the water will start flowing over the sides. The eye, however, is a closed system so the fluid will just ‘back up’ and so the pressure will consequently start to rise.
It is this rise in pressure that can cause slow damage to the optic nerve which affects your peripheral vision. Acute closed-angle Glaucoma is another type of Glaucoma that causes the pressure to increase much quicker as there is normally a much bigger blockage.
This information is provided purely as a guide and in no way constitutes medical advice. If you are in doubt about the health of your eyes you should consult your doctor or optometrist.