Glaucoma is a disease of the eye in which damage is caused by elevated pressure within the eye.  This elevated pressure is caused by a backup of fluid (aqueous humour) in the eye. Over time, it causes damage to the optic nerve. Normal pressure in the eye varies between 10–20 mmHg.

There are several different types of glaucoma which are generally grouped in to two large categories: open-angle glaucoma and closed angle glaucoma. 

Open-angle glaucoma: Glaucoma in which the aqueous (fluid) that flows through the pupil into the anterior (front) chamber of the eye cannot get through a filtration system called the trabecular meshwork into the drainage canals, causing pressure to build up within the eye which can damage the optic nerve and impair vision. Open-angle glaucoma is the most common form of glaucoma.

Closed angle glaucoma, (also called acute glaucoma or angle closure glaucoma), accounts for about 9 percent of all glaucoma cases and occurs when the opening between the cornea and iris narrows, such that the fluid cannot get to the trabecular meshwork and normal drainage channels. This narrowing results in fluid build-up and intraocular pressure. The fluid build-up happens very quickly.

Increased risk factors for developing glaucoma include:

• Age (People over the age of 45 - it occurs more frequently as we get older)
• Genetics (People who have a family history of glaucoma)
• High intraocular pressure (IOP).
• Race (People of African descent have a greater tendency for developing primary open –angle glaucoma than do people of other races)
• Other risk factors: diabetes, myopia (nearsightedness), regular, long-term steroid/cortisone use, a previous eye injury