Glaucoma refers to a group of eye conditions that lead to damage to the optic nerve, the nerve that carries visual information from the eye to the brain.

In many cases, damage to the optic nerve is due to increased pressure in the eye, also known as intraocular pressure (IOP).

Glaucoma is the second most common cause of blindness in the United States. There are four major types of glaucoma:

• Open-angle (chronic) glaucoma
• Angle-closure (acute) glaucoma
• Congenital glaucoma
• Secondary glaucoma

The front part of the eye is filled with a clear fluid called aqueous humor. This fluid is always being made in the back of the eye. It leaves the eye through channels in the front of the eye in an area called the anterior chamber angle, or simply the angle.

Anything that slows or blocks the flow of this fluid out of the eye will cause pressure to build up in the eye. This pressure is called intraocular pressure (IOP). In most cases of glaucoma, this pressure is high and causes damage to the major nerve in the eye, called the optic nerve.

Open-angle (chronic) glaucoma is the most common type of glaucoma.

• The cause is unknown. An increase in eye pressure occurs slowly over time. The pressure pushes on the optic nerve and the retina at the back of the eye
• Open-angle glaucoma tends to run in families. Your risk is higher if you have a parent or grandparent with open-angle glaucoma. People of African descent are at particularly high risk for this disease

Angle-closure (acute) glaucoma occurs when the exit of the aqueous humor fluid is suddenly blocked. This causes a quick, severe, and painful rise in the pressure within the eye (intraocular pressure).

• Angle-closure glaucoma is an emergency. This is very different from open-angle glaucoma, which painlessly and slowly damages vision
• If you have had acute glaucoma in one eye, you are at risk for an attack in the second eye, and your doctor is likely to recommend preventive treatment
• Dilating eye drops and certain medications may trigger an acute glaucoma attack

Congenital glaucoma often runs in families (is hereditary).

• It is present at birth
• It results from the abnormal development of the fluid outflow channels in the eye

Secondary glaucoma is caused by:

• Drugs such as corticosteroids
• Eye diseases such as uveitis
• Systemic diseases