Skip to content

Eye Health Center

Font Size

Understanding Glaucoma -- the Basics

What Is Glaucoma?

More than 3 million adult Americans have glaucoma, making it one of the leading causes of blindness in the U.S. 

The most common form, chronic open-angle glaucoma, generally appears in middle age and seems to have a genetic component: One in five people with glaucoma has a close relative with the condition. In chronic, open-angle glaucoma, sight begins to fade in the outer areas (peripheral) of the visual field; if untreated, tunnel vision and then blindness follow.

Understanding Glaucoma

Find out more about glaucoma:





The inside of the eye continuously produces and drains away a fluid called aqueous humor. As fresh aqueous is produced by cells inside the eye, an equal amount must exit through a drainage passageway (trabecular meshwork). If not enough drains away, pressure will increase inside the eye. The effects of intermittent or persistent high pressure on delicate retinal nerve fibers and the optic nerve results in permanent vision loss.

Glaucoma has long been called "the silent thief of sight," because there can be significant damage to the eye before the problem is discovered. Glaucoma damage is irreversible.

Types of Glaucoma

Glaucoma is a collection of diseases, all of which share a common outcome: irreversible damage to delicate nerve fibers and the optic nerve that sends information to the brain. The most common type of glaucoma is called chronic open-angle glaucoma, accounting for about 75%-90% of cases. There are multiple causes of this type of glaucoma. In chronic open-angle glaucoma, both eyes may be affected at the same time, but one eye is often worse than the other.

Narrow or closed-angle glaucoma is less common and occurs suddenly with blurred vision, a great deal of pain in the eye and head, and redness, usually in one eye first. In closed-angle glaucoma, the flow of aqueous is blocked from entering the drainage system, causing a sudden and severe rise in pressure inside the eye. Just like in open-angle glaucoma, the high pressure permanently damages the retinal and optic nerve fibers. Acute closed-angle glaucoma is a medical emergency and needs immediate medical care to restore normal aqueous outflow, reduce pressure, and prevent permanent damage to the eye and blindness.

Today on WebMD

Woman holding tissue to reddened eye
Learn about causes, symptoms, and treatments.
Simple annoyance or the sign of a problem?
red eyes
Symptoms, triggers, and treatments.
blue eye with contact lens
Tips for wearing and caring.
Understanding Stye
human eye
eye exam timing
vision test
is vision correction surgery for you
high tech contacts
eye drop