The exact cause of primary open-angle glaucoma is unknown. A number of conditions, alone or in combination, are needed to trigger the processes leading to increased pressure and then to the nerve damage that destroys sight. The damage done to the optic nerve in glaucoma is triggered in most cases by the excessive pressure on the optic nerve that, over time, causes damage. Because optic nerve damage occurs in patients with normal as well as high intraocular pressure, however, there are other factors that occur and can damage the optic nerve.
People with acute closed-angle glaucoma often have a structural defect that causes a narrow angle between the iris and cornea where the aqueous humor circulates. Conditions that suddenly dilate the pupils may cause this shallow angle to close and precipitate attacks of acute glaucoma in susceptible people. Such conditions may include:
When glaucoma is caused by other diseases or conditions, it is known as secondary glaucoma. Both open-angle glaucoma and closed-angle glaucoma can be a secondary condition.
Medical Conditions. A number of diseases can contribute to the development of glaucoma:
Corticosteroids. Corticosteroids, commonly called steroids, have multiple effects on the trabecular meshwork. Steroids pose a higher or lower risk depending on the form:
Specific syndromes have been identified with glaucoma. Many have an inherited component, although in most cases other factors must be present to activate the disease process.
Pseudoexfoliation Syndrome. Pseudoexfoliation (PEX) syndrome (also known as exfoliation syndrome) is the most common identifiable condition associated with glaucoma. The substance is composed of proteins produced by the lens, iris, and other parts of the eye. People can have this condition and not develop glaucoma, but they are at high risk. PEX has a strong genetic component but other factors (possibly sunlight, an autoimmune response, or slow virus) may be needed to trigger the disease.
Pigment Glaucoma. Pigment glaucoma starts with a condition called pigment dispersion syndrome, an inherited condition in which granules of pigment (the substance that colors the iris) flakes off into the intraocular fluid. These fragments clog the trabecular meshwork and pressure builds up, causing glaucoma.
Irido Corneal Endothelia Syndrome. In irido corneal endothelial syndrome (ICE), cells on the back surface of the cornea spread to the drainage angle, sometimes forming scars that connect the iris to the cornea.
Neovascular Glaucoma. Neovascular glaucoma is always associated with other disorders, usually diabetes, that result in abnormal formation of new blood vessels on the iris and in the drainage system.
Aniridia. Aniridia is a rare inherited disorder in which the iris is abnormal and increases the risk for glaucoma.
Congenital Glaucoma. When an infant is born with glaucoma (congenital glaucoma), it is usually caused by an inherited genetic abnormality that affects the drainage canal.
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