This is the most common form of glaucoma in the United States. It occurs as a result    of aging, The drainage angle of the eye becomes less efficient with time, and    pressure within the eye gradually increases.

If the increases pressure results in optic nerve damage, it is known as chronic open- angel glaucoma. Over 90% of adult glaucoma patients have this type of glaucoma.

Chronic open-angle glaucoma damages vision so gradually and painlessly that you    are not aware of trouble until the optic nerve is already badly damages.