What is Glaucoma?
Glaucoma is a disease in which the optic nerve is damaged, leading to progressive, irreversible loss of vision. It is often, but not always, associated with increased pressure of the fluid in the eye. 
It involves loss of retinal ganglion cells in a characteristic pattern. There are many different sub-types of glaucoma but they can all be considered as a type of optic neuropathy. Raised intraocular pressure is a significant risk factor for developing glaucoma (above 22 mmHg or 2.9 kPa). One person may develop nerve damage at a relatively low pressure, while another person may have high eye pressure for years and yet never develop damage. Untreated glaucoma leads to permanent damage of the optic nerve and resultant visual field loss, which can progress to blindness.
Glaucoma can be divided roughly into two main categories, "open angle" and "closed angle" glaucoma. Closed angle glaucoma can appear suddenly and is often painful; visual loss can progress quickly but the discomfort often leads patients to seek medical attention before permanent damage occurs. Open angle, chronic glaucoma tends to progress more slowly and the patient may not notice that they have lost vision until the disease has progressed significantly.
Glaucoma has been nicknamed the "sneak thief of sight" because the loss of vision normally occurs gradually over a long period of time and is often only recognized when the disease is quite advanced. Once lost, this damaged visual field can never be recovered. Worldwide, it is the second leading cause of blindness. It is also the first leading cause of blindness among African Americans.  Glaucoma affects 1 in 200 people aged fifty and younger, and 1 in 10 over the age of eighty. If the condition is detected early enough it is possible to arrest the development or slow the progression with medical and surgical means.
Both laser and conventional surgeries are performed to treat glaucoma. Surgery is the primary therapy for those with congenital glaucoma. Generally, these operations are a temporary solution, as there is not yet a cure for glaucoma.
Signs and Symptoms of Glaucoma
There are rarely any symptoms in the early stages of the disease so regular eye checks by qualified professionals are important. Ophthalmologists and optometrists will diagnose glaucoma on the basis of intraocular pressure, visual field tests and optic nerve head appearance.
Patients will sometimes notice patchy loss of peripheral vision or reduced clarity of colors and these people may benefit from a review by an eye specialist.
Symptoms of angle closure glaucoma can include pain in or around the eyeball, headache, nausea/vomiting and visual disturbances, for example halos around lights. In some cases there are no symptoms.
1. Merck Manual Home Edition, "Glaucoma".
2. "Global data on visual impairment in the year 2002".
3. Online 'Mendelian Inheritance in Man' (OMIM) Glaucoma, Congenital: GLC3 Buphthalmos -231300