Glaucoma refers to a group of eye disorders that usually have few or no initial symptoms and eventually cause harm to the optic nerve that carries information from the eye to the brain.

In most cases, glaucoma is associated with higher-than-normal pressure inside the eye (ocular hypertension). If untreated or uncontrolled, glaucoma first causes peripheral vision loss and eventually can lead to blindness.

According to the American Academy of Ophthalmology (AAO), the most common type of glaucoma — called primary open-angle glaucoma — affects an estimated 2.2 million people in the United States, and that number is expected to increase to 3.3 million by 2020 as the U.S. population ages.

Also, open-angle glaucoma is three times more likely to affect African-Americans, compared with non-Hispanic whites in the United States, and blindness from glaucoma is at least six times more prevalent among African-Americans than non-Hispanic whites. Studies also suggest open-angle glaucoma affects Hispanics and Latinos at comparable rates to African-Americans.

Globally, glaucoma is the second leading cause of blindness (behind cataracts), according to the World Health Organization.