What causes glaucoma?
The cause of glaucoma is generally a failure of the eye to maintain an appropriate balance between the amount of fluid produced inside the eye and the amount that drains away. Underlying reasons for this imbalance usually relate to the type of glaucoma you have.
Just as a basketball or football requires air pressure to maintain its shape, the eyeball needs internal fluid pressure to retain its globe-like shape and ability to see. But when glaucoma damages the ability of internal eye structures to regulate intraocular pressure (IOP), eye pressure can rise to dangerously high levels and vision is lost.
Types of glaucoma
The two major types of glaucoma are chronic or primary open-angle glaucoma (POAG) and acute angle-closure glaucoma. The “angle” refers to the structure inside the eye that is responsible for fluid drainage from the eye, located near the junction between the iris and the front surface of the eye near the periphery of the cornea. Some of the more common types of glaucoma include:
Primary open-angle glaucoma (POAG): About half of Americans with this form of chronic glaucoma don't know they have it. POAG gradually and painlessly reduces your peripheral vision. But by the time you notice it, permanent damage has already occurred. If your IOP remains high, the destruction can progress until tunnel vision develops, and you will be able to see only objects that are straight ahead.
Acute angle-closure glaucoma: Angle-closure or narrow angle glaucoma produces sudden symptoms such as eye pain, headaches, halos around lights, dilated pupils, vision loss, red eyes, nausea and vomiting. These signs may last for a few hours, and then return again for another round. Each attack takes with it part of your field of vision.
Normal-tension glaucoma: Like POAG, normal-tension glaucoma (also termed normal-pressure glaucoma, low-tension glaucoma, or low-pressure glaucoma) is an open-angle type of glaucoma that can cause visual field loss due to optic nerve damage. But in normal-tension glaucoma, the eye's IOP remains in the normal range. Also, pain is unlikely and permanent damage to the eye's optic nerve may not be noticed until symptoms such as tunnel vision occur.
The cause of normal-tension glaucoma is not known. But many doctors believe it is related to poor blood flow to the optic nerve. Normal-tension glaucoma is more common in those who are Japanese, are female and/or have a history of vascular disease.
Congenital glaucoma: This inherited form of glaucoma is present at birth, with 80% of cases diagnosed by age one. These children are born with narrow angles or some other defect in the drainage system of the eye. It's difficult to spot signs of congenital glaucoma, because children are too young to understand what is happening to them. If you notice a cloudy, white, hazy, enlarged or protruding eye in your child, consult your eye doctor. Congenital glaucoma typically occurs more in boys than in girls.
Pigmentary glaucoma: This rare form of glaucoma is caused by pigment deposited from the iris that clogs the draining angles, preventing aqueous humor from leaving the eye. Over time, the inflammatory response to the blocked angle damages the drainage system. You are unlikely to notice any symptoms with pigmentary glaucoma, though some pain and blurry vision may occur after exercise. Pigmentary glaucoma affects mostly white males in their mid-30s to mid-40s.
Secondary glaucoma: Symptoms of chronic glaucoma following an eye injury could indicate secondary glaucoma, which also may develop with presence of infection, inflammation, a tumor or an enlarged cataract.