There are many types of glaucoma but this discussion concentrates on the most common type, Primary Open Angle Glaucoma.

The eyeball is a bit like a small ball full of liquid. This liquid is continuously being produced inside the eye and at the same time the fluid drains away, while maintaining a certain amount of pressure to keep the eyeball "inflated" with fluid.  
The optic nerve damage that occurs in glaucoma is related to the fluid pressure inside the eye (which has nothing to do with blood pressure). In most cases the eye pressure is higher than the upper limit of normal (20mmHg) but in some cases optic nerve damage occurs  even if the pressure inside the eye is within normal levels.

Treatment for glaucoma involves lowering the pressure inside the eye. The aim of lowering the eye pressure is to stop, or at least slow down the damage of the optic nerve and maintain vision. In some cases, apparent cessation of optic nerve damage occurs while in others even with the most aggressive treatment, the worsening is only slowed down. Eye pressure control can often be achieved with a single type of eye drop or a combination of eye drops. When the pressure control using eye drops is not enough to control the eye pressure, an operation may be considered, which creates a new pathway for the fluid inside the eye to drain. A special medication called Mitomycin, also used in treating some forms of cancer, is used at the time of the operation to slow down the scarring process of the eye and reduce the risk of allowing the body to "repair" the new drainage pathway and cause the operation to fail.

Note: Dr Aristodemou has the clinical experience and equipment to assess, monitor and treat glaucoma. Before his subspeciality training in retinal disease, he has had considerable experience in managing glaucoma. Nevertheless, Dr Aristodemou is not a glaucoma expert.