MONDAY, May 9 (HealthDay News) -- Researchers say they've pinpointed a number of factors that may be key to the progression of the eye disease glaucoma.

Glaucoma is most often caused by an increase in the normal fluid pressure inside the eye, according to the U.S. National Eye Institute. The added pressure damages the optic nerve, the bundle of more than a million nerve fibers that send signals from the eye to the brain. In most cases, people first notice that they have glaucoma when they begin to lose their peripheral vision. By then, it's too late to save much of their eyesight.

In the new study, researchers analyzed data from 587 patients enrolled in the New York Glaucoma Progression Study. The information they used came from photographs, analysis of patients' visual field, and measurement of their peak intraocular pressure (IOP) -- the highest level of pressure in the fluid within the eye.

The researchers concluded that key risk factors for glaucoma progression included a thinning of the cornea, loss of the visual field and an IOP of 18 mmHg (millimeters of mercury) or higher.

The effect of intraocular pressure may be the most significant finding, the study authors said.

"We demonstrated that for each increase in millimeters of mercury in IOP, there is a significant increase in the risk of progression for treated glaucoma patients," Dr. Carlos Gustavo V. De Moraes, from the New York Eye and Ear Infirmary, and colleagues wrote.

The study authors noted that IOP measurement is easy to do and "may help clinicians decide how aggressively to treat specific patients to slow the rate of glaucoma progression."

The study is published in the May issue of the journal Archives of Ophthalmology.

More information

The U.S. National Eye Institute has more about glaucoma.