There are several different forms of glaucoma, each with different causes and severities. Read on to learn about these different types and how they differ from one another.

Open-angle glaucoma

The most common form of glaucoma is open-angle glaucoma. Open-angle glaucoma accounts for the vast majority of all glaucoma cases. Typically, it is a chronic (long-term) condition with no noticeable symptoms. Elevated IOP is the main risk factor and usually goes unnoticed.

Elevated IOP is caused by a buildup of fluid in the eyes. Eyes naturally produce a clear fluid that keeps them nourished and healthy. This clear fluid drains through the eyes' "drainage pipes." In some individuals, this fluid does not drain properly. The eyes' usual drainage area (at the "open angle" where the cornea and iris meet) becomes backed up like a clogged pipe. The buildup of fluid behind the drainage area causes increased eye pressure.

If IOP remains elevated, this can cause damage to the optic nerve and may result in progressive visual field loss (ie, gradual loss over an extended period of time). Although glaucoma cannot be cured, it may be managed through early detection and by lowering IOP. Clinical studies funded by the National Eye Institute have proven that lowering IOP reduces the risk for visual field loss in patients with glaucoma.

A less common type of open-angle glaucoma is normal-pressure glaucoma, also known as low-tension glaucoma. It is a type of glaucoma in which a patient's IOP is considered "normal," but there is noticeable damage to the optic nerve and visual field loss may have occurred.

To see how open-angle glaucoma can affect sight, visit the interactive ANIMATED TUTORIAL.

Angle-closure glaucoma is a rare type of glaucoma and can be acute, subacute, or chronic:

• Acute angle-closure glaucoma is rare and considered a medical emergency. Acute angle-closure glaucoma happens when IOP rapidly increases to an excessively high level. This type of glaucoma has severe symptoms such as severe eye pain, and patients may experience nausea, vomiting, sweating, severe headaches, slow heart rate, and blurred or "halo" vision. Patients may also have moderate symptoms such as dilated pupils, cloudy corneas, and very red eyes.
  
  
• Subacute angle-closure glaucoma Subacute angle-closure glaucoma is similar to acute angle-closure glaucoma but is considered to be less severe. Patients with subacute angle-closure glaucoma may have a series of minor attacks characterized by blurry or "halo" vision, but without the severe eye pain or redness associated with acute angle-closure glaucoma.
  
  
• Chronic angle-closure glaucoma is a long-term disease. Patients may have some symptoms ranging from mild to severe. Some patients may have no symptoms at all.
  
  
• Secondary glaucoma can occur in both open angle and closed angle forms. Secondary glaucoma may be caused by steroid (topical or systemic), inflammation, prior ocular injury, or as a complication of an underlying disease such as diabetes or cataracts.