Glaucoma - Introduction

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Highlights	Risk Factors	Lifestyle Changes
Introduction	Diagnosis	Resources
Causes	Treatment	References
Symptoms	Medications
Outlook	Surgery

Primary open-angle glaucoma tends to start in one eye but eventually involves both. In about half of patients the damage in the eye is diffuse, that is the nerve damage is generalized. In the other half the disease is localized, causing wedge-shaped abnormalities in the nerve fiber layers of the retina.

Normal Tension Glaucoma

Intraocular eye pressure is normal (between 12 - 22 mmHg) in about 25 - 30% of U.S. glaucoma cases, a condition known as normal-tension glaucoma. (In Japan, the rates may be as high as 70%.) Other factors are present that cause optic nerve damage but do not affect IOP.

Closed-Angle Glaucoma

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Closed-angle glaucoma (also called angle-closure glaucoma) is responsible for 15% of all cases. It is less common than open-angle glaucoma in the U.S., but it constitutes about half of the world's glaucoma cases because of its higher prevalence among Asians. The iris is pushed against the lens, sometimes sticking to it, closing off the drainage angle. This can occur very suddenly, resulting in an immediate rise in pressure. It often occurs in genetically susceptible people when the pupil shrinks suddenly. Closed-angle glaucoma can also be chronic and gradual, a less common condition.

Congenital Glaucoma

Congenital glaucoma, in which the eye's drainage canals fail to develop correctly, is present from birth. It is very rare, occurring in about 1 in 10,000 newborns. This may be an inherited condition and often can be corrected with microsurgery.

The Eye

The Light-Processing Parts. To understand sight, one begins with light and its passage through the eye's sensitive camera-like structures:

Light first passes through the cornea, a clear tissue at the front of the eye.
Behind the cornea, the iris (the colored tissues of the eye) opens and closes like a camera shutter to regulate the passage of light.
The lens, located behind the iris, focuses the light, which then hits the retina.
The retina is an electric fragile membrane of nerve cells called photoreceptors that receive light and translate it into signals.
A layer of cells, called the retinal ganglia, receive signals from the retina. These nerve cells are the front ends of the optic nerve cable, which, in turn, receive the signals.
The optic nerve is actually a cable of about 1.2 million nerve fibers called axons. It carries the signals to the brain, which interprets them as images.
They exit the eye through the optic disc, located in the back of the eye.

The Supportive Chambers. To help support and protect these sensitive structures, the eye contains two fluid-filled chambers:

The posterior (rear) chamber is the large area behind the iris.
Fluid passes from the posterior into the anterior (forward) chamber located in the bulging area between the iris and the front of the eye.

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Review Date: 03/03/2007
Reviewed By: Harvey Simon, MD, Editor-in-Chief, Associate Professor of Medicine, Harvard Medical School; Physician, Massachusetts General Hospital.

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