Conditions InDepth: Glaucoma
Glaucoma is a group of diseases that can damage the eye’s optic nerve and result in visual loss or blindness. The optic nerve is a bundle of more than 1 million nerve fibers. It connects the retina with the brain. The retina is the light-sensitive layer at the back of the eye; it contains millions of cells called rods and cones. When the rods and cones pick up light, a chemical reaction takes place. This sends an electrical impulse from the retina, through the optic nerve, and to the brain. This is the sensation of sight. A healthy optic nerve is essential for good vision.
Normal Anatomy of the Eye
Glaucoma is usually caused by an increase of pressure inside the eye. At the front of the eye, there is a small space called the anterior chamber, which lies between the iris and the cornea. Clear fluid flows in and out of the chamber to bathe and nourish nearby tissues. In most cases of glaucoma, for unknown reasons, the fluid drains too slowly out of the anterior chamber of the eye. As the fluid builds up, the pressure inside the eye rises. Unless this pressure is controlled, it can damage the optic nerve and other parts of the eye, leading to loss of vision.
It is estimated that 4 million Americans have glaucoma—and half of these people do not know they have it. Glaucoma is the second leading cause of legal blindness in the US, and the first leading cause of blindness in African Americans.
There are several forms of glaucoma. The most common ones include:
Open-angle glaucoma —Fluid can sometimes drain through the drainage angle of the eye too slowly, which leads to a fluid backup and a gradual but persistent elevation in intraocular pressure (IOP). The angle between structures of the eye appears normal or open. This is the most common type of glaucoma.
Angle-closure glaucoma —Drainage from the eye becomes physically blocked when eye structures occlude an already narrowed angle of exit. This traps fluid in the eye and leads to an increase in IOP. Angle-closure glaucoma may be acute, subacute, intermittent, or chronic. Acute angle-closure glaucoma is a medical emergency that must be treated quickly to prevent visual loss or blindness.
Normal or low-tension glaucoma —The optic nerve is damaged even though the IOP is not elevated. This form is poorly understood.
Congenital glaucoma —This type of glaucoma occurs either at birth or within the first few years. It is usually related to defects in the eye that slow the normal drainage of fluid.
Secondary glaucoma —This type of glaucoma can develop as a complication of another medical condition. Examples include tumor, inflammation, diabetes, eye injury, or long-term corticosteroid therapy.
American Academy of Ophthalmology website. Available at: http://www.aao.org/ .
Glaucoma Research Foundation website. Available at: http://www.glaucoma.org/ . Accessed August 18, 2008.
Mayo Clinic website. Available at: http://www.mayoclinic.com/health/glaucoma/DS00283/DSECTION=1 . Accessed Feb 1, 2007.
National Eye Institute website. Available at: http://www.nei.nih.gov/ .
Weinreb RN, Khaw PT. Primary open-angle glaucoma. Lancet. 2004;363:1711.
Last reviewed June 2008 by
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