Glaucoma is an eye disease that is typically caused by increased pressure in the eyes due to fluid not draining properly. Doctors say if the pressure is not treated, it can lead to damage in the optic nerve, vision loss and even blindness.

They add that while close to 3 million people in the U.S. have glaucoma, only half of them is aware.

"Glaucoma in its early phases is really asymptomatic. People have no idea that they have it," says Dr. David Friedman, director of the glaucoma service at Massachusetts Eye and Ear.

People who are at high risk include anyone over 60, African Americans older than 40, people with a family history of glaucoma and people with diabetes.

Treatment involves reducing pressure with eye drops, medication or surgery.

"The eye, just like a balloon has a pressure…it's water that makes the pressure. We can do things to either allow more of that water to leave the eye or to reduce the amount of water made in the eye," says Friedman.

Friedman recommends people routinely have their eyes looked at.

A person's overall health can also impact their eye health. Doctors say ways to prevent glaucoma include not smoking and making sure your blood pressure is under control.