Glaucoma is an eye disease in which the optic nerve is damaged in a characteristic pattern.
This can permanently damage vision in the affected eye(s) and lead to blindness if
left untreated. It is normally associated with increased fluid pressure in the eye
(aqueous humour).1 The term "ocular hypertension" is used for people with
consistently raised intraocular pressure (IOP) without any associated optic nerve damage.
However, if the ocular hypertension is associated with optic nerve damage, the condition is
labeled as glaucoma. The nerve damage involves loss of retinal ganglion cells in a
characteristic pattern. Raised intraocular pressure (above 21 mmHg or 2.8 kPa) is the most
important and only modifiable risk factor for glaucoma. However, some people may have
high eye pressure for years and never develop damage, while others can develop
nerve damage at a relatively low eye pressure. Untreated glaucoma can lead to
permanent damage of the optic nerve and resultant visual field loss, which over time
can progress to blindness. Glaucoma can be roughly divided into two main categories,
"open-angle" and "closed-angle"(or "angle closure") glaucoma. The angle refers to
the area between the iris and cornea, through which fluid must flow to escape via
the trabecular meshwork. 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 at a slower rate and patients may not notice they have lost vision until the
disease has progressed significantly. Glaucoma has been called the "silent thief of sight"
because the loss of vision often occurs gradually over a long period of time, and
symptoms only occur when the disease is quite advanced. Once lost, vision cannot
normally be recovered, so treatment is aimed at preventing further loss.