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In open-angle glaucoma, the intraocular pressure is consistently elevated. Over a period of months or years, this results in optic atrophy with loss of vision varying from slight constriction of the upper nasal peripheral fields to complete blindness.

The cause of the decreased rate of aqueous outflow in open-angle glaucoma has not been clearly established. The disease is bilateral. Glaucoma occurs at an earlier age and more frequently in blacks and may result in more severe optic nerve damage. There is increasing evidence that factors other than the level of intraocular pressure--particularly vascular abnormalities--may play a role in certain individuals in the pathogenesis of glaucomatous optic nerve damage.

In a normal eye, aqueous humor--a clear, nutrient-rich fluid--passes continuously through the pupil and into a small space at the front of the eye, called the anterior chamber. As it leaves this area, the aqueous humor flows to the periphery of the chamber, or angle, where it exits through a complex channel system and drains into blood vessels in and near the sclera, the white outer coat of the eye. In an eye with open-angle glaucoma, the aqueous humor drains too slowly through the channel system, creating a chronic rise in fluid pressure inside the eye. This elevated pressure may gradually interrupt the metabolic processes of cells in the optic nerve, leading to a progressive destruction of nerve fibers that are essential for vision.

The name open-angle glaucoma comes from the angle of the anterior chamber open to aqueous humor outflow. It is the slow drainage of aqueous humor through the drainage system that increases fluid pressure. Conversely, in angle-closure glaucoma, part of the iris suddenly obstructs the angle and blocks the aqueous humor from reaching the drainage system. This causes a very painful rise in intraocular pressure, and requires emergency medical attention.

Although open-angle glaucoma can affect anyone, it is most prevalent in blacks over age 40 and anyone over age 60. As people grow older, age-related changes in the eyes make them more susceptible to open-angle glaucoma.

At its onset, open-angle glaucoma usually has no symptoms. There is no pain, no blurring of vision, and no ocular inflammation to alert someone that he/she has the disease. But, as open-angle glaucoma progresses, it will slowly and insidiously begin to destroy peripheral vision. It is at this point that most people seek treatment, but tragically, vision that has already been lost from glaucoma cannot be restored.

The most reliable way to detect open-angle glaucoma is through a comprehensive eye examination with dilated pupils--which, when indicated, includes a visual field test. To dilate, or enlarge, the pupils, the eye care professional places medicated drops into the eye. By so doing, the practitioner can better examine the back of the eye for early signs of disease, such as optic nerve damage, before noticeable vision loss occurs.

Tonometry is a common and painless test to measure intraocular pressure. In this test, an eye care professional uses an instrument called a tonometer to measure the fluid pressure in the anterior chamber. However, because elevated fluid pressure is only one characteristic of open-angle glaucoma, tonometry does not always indicate whether or not a person has the disease. In fact, many people with elevated fluid pressure never develop any form of glaucoma, while people with seemingly "normal pressure" during an examination will develop the disease.

For this reason, tonometry should be viewed as one important component of the overall examination for glaucoma, but should not be the only test used for glaucoma detection. Open-angle glaucoma treatments include medications, laser surgery, and other surgical procedures.