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Primary Open-Angle Glaucoma

What Is Primary Open-Angle Glaucoma?

Primary open-angle glaucoma is one of the leading preventable causes of blindness in the world, and it is the most common cause of blindness in African-Americans. Glaucoma is a condition that leads to optic nerve damage and possible irreversible visual loss. Progression of this optic nerve damage can usually be halted with treatment but cannot be reversed once the damage is done.

There are several types of glaucoma, and primary open-angle glaucoma (POAG) is the most common.

In POAG, there are characteristic optic nerve changes (damage) associated with open angles (the area between the iris and cornea) and elevated eye pressure. This is in contrast to other types of glaucoma, which are associated with abnormal angles (for example, narrow-angle glaucoma, closed-angle glaucoma, primary congenital glaucoma, and other secondary glaucomas) or low eye pressures (normal tension glaucoma).

What all types of glaucoma have in common is a pattern of progressive optic nerve damage that eventually may lead to irreversible vision loss if not found and treated in time. In many forms, there are no symptoms at all during the initial stages. For this reason, screening for glaucoma is very important.

What Causes Primary Open-Angle Glaucoma?

The exact cause of primary open-angle glaucoma is unknown. Certain genes have been identified that are associated with glaucoma, and more research is under way to study these genetic factors. Identification of any family history of glaucoma is therefore helpful.

What Are Risk Factors for Primary Open-Angle Glaucoma?

There are several risk factors for open-angle glaucoma:

  • Elevated intraocular pressure (high IOP): Average eye pressures range from 10-21 mm Hg. The higher the pressure, the higher the risk of developing glaucoma. However, not all people with a pressure in the 20s will go on to develop glaucoma, and conversely, there are people with pressures at the low end of the range who can have rapidly progressive glaucoma.
  • Age: Glaucoma becomes more common as we age.
  • Race: People of African descent get glaucoma more frequently and at a younger age than Caucasians.
  • Family history is important as some cases of glaucoma are hereditary.
  • Corneal thickness: Thin corneas are associated with a higher risk for glaucoma. Corneal thickness is measured by the eye doctor using specialized instruments. Possibly more important than the thickness of the cornea is the stiffness of the cornea, with less stiff (more pliable) corneas being associated with higher glaucoma risk. Instruments to measure the corneal stiffness are being developed and may in the future be used for routine screening.
  • Myopia (nearsightedness), diabetes mellitus, and hypertension are also often associated with glaucoma.
Medically Reviewed by a Doctor on 9/28/2016
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Types of Glaucoma

The two main types of glaucoma are open-angle glaucoma and angle-closure glaucoma. In angle-closure glaucoma, the normal drainage canals within the eye are physically blocked. Angle-closure glaucoma can be acute (sudden in onset) or chronic (lasting a long time), while open-angle glaucoma is usually chronic. In open-angle glaucoma, the drainage system itself is open but microscopic abnormalities within it prevent normal outflow of fluid. Both angle-closure glaucoma and open-angle glaucoma may cause optic nerve damage and vision loss with or without symptoms. Glaucoma is either primary (occurring without an underlying other cause or other eye disease) or secondary (related to other reasons, such as trauma, inflammation or medication).

Read What Your Physician is Reading on Medscape

Glaucoma, Primary Open Angle »

The definition of glaucoma has changed drastically since its introduction around the time of Hippocrates (approximately 400 BC).

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