Causes

No single factor has been identified as a cause of primary open-angle glaucoma. A number of conditions, alone or in combination, are needed to trigger the processes leading to pressure in the first place 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, researchers are investigating several other abnormal events that occur and can damage the optic nerve.

Genetic Factors

A number of genes have now been identified as possible factors in many cases of glaucoma. Researchers hope that identification of genes will help improve screening of high-risk patients.

Syndromes Associated with Increased Optic Pressure and Glaucoma

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. In one study, 2% of patients had this form of 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) that is difficult to treat. (A surgical approach called goniosurgery may help prevent glaucoma in young people with aniridia.)

Congenital Glaucoma. When an infant is born with glaucoma (congenital glaucoma), it is usually caused by an inherited abnormality in the drainage canal. Researchers have identified the gene responsible for 85% of these cases.

Causes of Nerve Cell Death (Apoptosis) and Optic Nerve Damage

A natural process called apoptosis (cellular self-destruction) may contribute to damage in the retinal ganglion nerve cells, the nerve cells that are the front line of the optic nerve. Cell death can occur with or without elevated eye pressure. It is not clear what triggers apoptosis and cell death in such cases, but there are a number of suspects.