Harrisburg — Glaucoma sneaks up on people, coming on so gradually that many don’t notice that they’re developing blind spots or losing peripheral vision.

Glaucoma affects more than 2.3 million Americans aged 40 and older, while another two million don’t know they have it. If untreated, glaucoma causes blindness.

This January, during Glaucoma Awareness Month, the Pennsylvania Academy of Ophthalmology and the American Academy of Ophthalmology’s EyeSmart campaign remind you that knowing your risk for glaucoma can save your sight.

“We need to catch and treat glaucoma as early as possible, because there’s no way to restore vision once this disease steals it,” said Dr. Roger Zelt, academy president, in a news release.

In the United States, higher-risk groups include people with African or Latino heritage and others with a family history of the illness. Older African Americans are five times more likely to develop glaucoma and 14 to 17 times more likely to become blind from the disease than those with European ancestry. The risk for Latino Americans rises sharply after age 60.

People of any ethnicity who have a family history of glaucoma are four to nine times more susceptible.