FRIDAY, April 27 (HealthDay News) -- Two genetic variations are linked to a common form of glaucoma, known as primary open-angle glaucoma, according to new research.

Glaucoma affects about 2.2 million people in the United States, the U.S. National Eye Institute said in a news release.

"Loss of vision from glaucoma, a common cause of blindness worldwide, is due to irreversible damage to the optic nerve," noted one expert, Dr. Mark Fromer, an ophthalmologist at Lenox Hill Hospital in New York City. "Glaucoma is usually associated with high eye pressure leading to optic nerve damage. There is also a form of glaucoma with normal pressure."

In the new study, Janey Wiggs, of Harvard Medical School and Massachusetts Eye and Ear Infirmary in Boston, and colleagues analyzed the DNA sequences of more than 6,000 people. Half of them had primary open-angle glaucoma. This form of the disease is typically associated with increased eye pressure, but one-third of these patients had normal-pressure glaucoma.

The study, published online April 26 in PLoS Genetics, found that two genetic variations were linked with primary open-angle glaucoma, including those who have normal-pressure glaucoma.

One variant is in a gene located on chromosome 9. The second variant is in a region of chromosome 8, where it may affect the expression of one or two other genes. These genes may interact with a molecule that regulates cell growth and survival throughout the body, the researchers explained in the news release.

The investigators believe future studies could focus on this molecule as a treatment for various forms of glaucoma.

Fromer concurred. "These results reveal new insights into the genetic pathways of optic nerve disease in glaucoma for the first time and are an important step toward the development of preventative and protective therapies," he said.

More information

The U.S. National Library of Medicine has more about glaucoma.