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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

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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.


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It is estimated over 3 million Americans have glaucoma, a leading cause of legal blindness in the US.

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.

What are the risk factors for glaucoma?
What are the symptoms of glaucoma?
How is glaucoma diagnosed?
What are the treatments for glaucoma?
Are there screening tests for glaucoma?
How can I reduce my risk of glaucoma?
What questions should I ask my healthcare provider?
What is it like to live with glaucoma?
Where can I get more information about glaucoma?


Facts about glaucoma. National Eye Institute website. Available at: Accessed July 16, 2013.

Open-angle glaucoma. EBSCO DynaMed website. Available at: Updated June 6, 2013. Accessed July 16, 2013.

Weinreb RN, Khaw PT. Primary open-angle glaucoma. Lancet. 2004;363:1711.

What is glaucoma? American Academy of Ophthalmology website. Available at: Accessed July 16, 2013.

What is glaucoma? Glaucoma Research Foundation website. Available at: Accessed July 16, 2013.

Last reviewed March 2015 by Michael Woods, MD

Please be aware that this information is provided to supplement the care provided by your physician. It is neither intended nor implied to be a substitute for professional medical advice. CALL YOUR HEALTHCARE PROVIDER IMMEDIATELY IF YOU THINK YOU MAY HAVE A MEDICAL EMERGENCY. Always seek the advice of your physician or other qualified health provider prior to starting any new treatment or with any questions you may have regarding a medical condition.

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