Glaucoma: What Are the Basics?

Glaucoma is a collection of diseases linked by a common outcome: irreversible damage to delicate nerve fibers and the optic nerve that sends information to the brain. It’s often called "the silent thief of sight," because major, irreversible damage can take place before you know you have it.

Glaucoma is often associated with increased eye pressure.  The eye has a normal level of pressure, just like a tire.  But abnormally high levels of pressure can result in glaucoma damage.

It works like this: All day long, your eye makes and drains away a fluid called aqueous humor. As new batches are made, an equal amount of liquid must exit through a passageway called the trabecular meshwork. In certain forms of glaucoma, this internal drainage system is partially blocked which leads to increase in eye pressure and damage to the optic nerve. If the pressure stays high to long (we’re talking years), it can damage your retinal and your optic nerve fibers.

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

What Are the Different Types?

Chronic open-angle glaucoma is the most common type of glaucoma outside of Asia. It accounts for about 75%-90% of cases. This type has multiple causes, but doctors think it may be genetic: One in five people with it has a close relative who also has it. It can affect both eyes at the same time, but one may be worse than the other.

This form generally shows up in middle age. It takes your sight away in stages. Your vision will first begin to fade in the outer edges (your doctor will call this peripheral vision). If you don’t treat it, it’ll narrow down to tunnel vision and then blindness.

Narrow or closed-angle glaucoma is less common and may come on fast. It can start with a glaucoma attack, which ususally affects one eye. You’ll notice blurred vision, pain in your eye and head, and redness. It completely blocks the outflow of liquid. That can cause a sudden and severe rise in pressure inside your eye. When the pressure is high enough, it can add nausea to the head and eye discomfort.  And just like in open-angle glaucoma, the high pressure permanently damages your nerves.


This form is a medical emergency. You need medical care right away to reverse the glaucoma attack, ease eye pressure, and prevent permanent damage or even blindness. It, too, can slowly and silently damage your nerves. This type is more common in Asia. In certain countries, it’s the more common form of glaucoma. Fortunately, when caught early enough, it often can be cured or prevented with a simple laser treatment. Or the doctor might treat it by performing cataract surgery to relieve the crowding of eye structures.

Congenital glaucoma is rare. Some infants have it at birth or get it within the first few years of life. You’ll notice that your child’s corneas (the front of his eye) are cloudy and that his eyes are sensitive to light and tear up all the time. If the problem isn’t diagnosed and treated early, he could lose some or all of his vision. There’s a similar type that shows up between age 3 and adulthood. It’s called juvenile glaucoma.

Secondary glaucoma is a broad category of problems usually linked to another eye disease or disorder, like a very mature cataract, inflammation inside your eye (the doctor will call this uveitis), bleeding, eye tumor, or a previous eye injury. If you have diabetes, extra blood vessels can form inside your eye and block the outflow of fluid. This severe form of the disease is called neovascular glaucoma.

WebMD Medical Reference Reviewed by Alan Kozarsky, MD on October 15, 2017



American Glaucoma Society.

Weinreb, R. Lancet, 2004.

Curcio, C. Journal of Comparative Neurology, Oct. 1, 1990.

American Academy of Ophthalmology.

Glaucoma Research Foundation.

U.S. Preventive Services Task force: "Screening for Primary Open-Angle Glaucoma in the Primary Care Setting."

Mayo Clinic.

Distelhorst, J. American Family Physician, May 1, 2003.

© 2017 WebMD, LLC. All rights reserved.