Glaucoma results from raised intraocular pressure. The pressure usually builds up due to blockage in the drainage of the aqueous humor from the anterior chamber of the eyes.
Raised intraocular pressure
The anterior chamber of the eyeball is filled with aqueous humor that provides nutrients to the structures of the eye including the lens and the cornea. It also creates a pressure to give the eye its shape. In healthy eyes, this fluid constantly flows in and out of the eye. It drains back into the bloodstream at the same rate that it is produced to maintain the correct pressure.
In glaucoma, the drainage tubes (trabecular meshwork) within the eye become slightly blocked, preventing the aqueous humour from draining properly. Obstruction may also occur if the angle of drainage is narrowed. When the fluid cannot drain properly, the pressure in the eye builds up and can damage the optic nerve.
Risk of glaucoma
Several factors can raise the risk of getting glaucoma. These include:-
With age the risk of glaucoma rises. In the UK, for example, chronic open-angle glaucoma affects one to two people in every 100 who are over 40 years old, and four to five people in every 100 who are over 80 years old. With age the trabecular meshwork cells work less efficiently and this results in build up of aqueous humor within the anterior chamber of the eye. In addition with age, the lens also hardens and increases in size. This further narrows the anterior chamber of the eye and physically narrows the anterior chamber angle.
Ethnicity and origin
People of African or Afro-Caribbean origin are at increased risk of developing chronic open-angle glaucoma. People of Asian origin are at increased risk of developing acute angle-closure glaucoma due to their shallower anterior chamber depth. Inuit also have a twenty to forty times higher risk than Caucasians of developing primary angle closure glaucoma.
Women are three times more likely than men to develop acute angle-closure glaucoma due to their shallower anterior chambers.
Those with glaucoma in their family are at a greater risk of the condition
Myopia or short sightedness
These individuals are more likely to develop chronic open-angle glaucoma
Some individuals naturally have a raised intraocular pressure of greater than 21mm of Hg. These individuals may not develop glaucoma immediately but are at a greater risk of the disease. Ocular hypertension is the largest risk factor in most glaucomas, but in some populations only 50% of patients with primary open angle glaucoma actually have elevated ocular pressure
Diabetic individuals are at a greater risk of glaucoma.
Previous eye injury
Those who have had a previous eye injury are at a risk of secondary glaucomas
Individuals who have been taking corticosteroids for a long duration for another medical condition may develop glaucoma as a side effect.
Reviewed by April Cashin-Garbutt, BA Hons (Cantab)