their families and friends. It provides information about open-angle glaucoma,
the most common form of glaucoma. This booklet answers questions about the cause
and symptoms of the disease and discusses diagnosis and types of
The National Eye Institute (NEI) conducts and supports research
that leads to sight-saving treatments and plays a key role in reducing visual
impairment and blindness. The NEI is part of the National Institutes of Health
(NIH), an agency of the U.S. Department of Health and Human Services.
What is glaucoma?
Glaucoma is a group of diseases that can damage the eye’s optic nerve and
result in vision loss and blindness. However, with early treatment, you can
often protect your eyes against serious vision loss.
What is the optic nerve?
The optic nerve is a bundle of more than 1 million nerve fibers. It connects
the retina to the brain. (See diagram below.) The retina is the light-sensitive
tissue at the back of the eye. A healthy optic nerve is necessary for good
In the front of the eye is a space called the anterior chamber. A clear fluid
flows continuously in and out of the chamber and nourishes nearby tissues. The
fluid leaves the chamber at the open angle where the cornea and iris meet. (See
diagram below.) When the fluid reaches the angle, it flows through a spongy
meshwork, like a drain, and leaves the eye.
Sometimes, when the fluid reaches the angle, it passes too slowly through the
meshwork drain. As the fluid builds up, the pressure inside the eye rises to a
level that may damage the optic nerve. When the optic nerve is damaged from
increased pressure, open-angle glaucoma–and vision loss–may result. That’s why
controlling pressure inside the eye is important.
Not necessarily. Increased eye pressure means you are at risk for glaucoma,
but does not mean you have the disease. A person has glaucoma only if the optic
nerve is damaged. If you have increased eye pressure but no damage to the optic
nerve, you do not have glaucoma. However, you are at risk. Follow the advice of
your eye care professional.
Not necessarily. Not every person with increased eye pressure will develop
glaucoma. Some people can tolerate higher eye pressure better than others. Also,
a certain level of eye pressure may be high for one person but normal for
Whether you develop glaucoma depends on the level of pressure your optic
nerve can tolerate without being damaged. This level is different for each
person. That’s why a comprehensive dilated eye exam is very important. It can
help your eye care professional determine what level of eye pressure is normal