What is Glaucoma?

Glaucoma is the name for a group of eye diseases that cause damage to the optic nerve. If left untreated, glaucoma leads to gradual loss of sight and can eventually lead to complete blindness.

The optic nerve carries information from the light sensitive layer of the eye (the retina) to the brain, where it is interpreted as a visual image. Some people have lost as much as 40% of the optic nerve before noticing any loss of vision.

The eye keeps its shape by maintaining a certain level of pressure (intra-ocular pressure or IOP). The pressure remains stable if the flow of fluid (aqueous humour) into the eye is the same as that leaving the eye. The fluid is produced by a tiny gland called the ciliary body, situated behind the iris (coloured part of the eye). It flows between the iris and the lens and flows out of the eye through a very tiny spongy tissue called the trabecular meshwork, which serves as the drain of the eye (drainage channels). This is situated in the drainage angle between the iris and the cornea.

Most cases of glaucoma occur because the flow of fluid out of the eye becomes restricted and the pressure within the eye rises above the normal range. This increased pressure causes optic nerve damage.

Flow of aqueous humour in the eye

Outflow of aqueous humour through the drainage angle

The diagram above shows a section through the eye, with the front of the eye on the left.

In many people who develop glaucoma, the pressure of fluid within their eye is much higher than usual. By reducing this pressure, any further damage to the optic nerve may be prevented. However, some people develop glaucoma when the pressure inside their eyes is normal.