More than 2 million Americans age 40 and older suffer from glaucoma and nearly half do not know they have the disease since it causes no early symptoms. If untreated, glaucoma can cause blindness. And unfortunately approximately 10% of people with glaucoma who receive proper treatment still experience loss of vision. To learn more about this sight-robbing disease, the Prevent Blindness America website has a wealth of information. Since there may be no symptoms and glaucoma is painless, frequent testing by your eye doctor is essential.