Classification of glaucoma

Glaucoma is a group of eye disorders in which damage to the optic nerve causes some vision loss. There are three basic types of glaucoma.

Open-angle glaucoma

Open-angle glaucoma (OAG) is the most common type of glaucoma. In open-angle glaucoma, slow damage to the nerve in the back of the eye (optic nerve) causes gradual loss of eyesight. At first, the person loses side or outer (peripheral) vision. If open-angle glaucoma is not treated, vision loss continues until total blindness develops.

This type of glaucoma can occur in both eyes at the same time. However, often one eye is more severely affected than the other. Sometimes much of the person's eyesight is affected before the condition is noticed.

• Open-angle glaucoma has been called simple glaucoma, chronic glaucoma, and wide-angle glaucoma.
• Many people with open-angle glaucoma have higher-than-normal pressure in their eyes. However, some people with open-angle glaucoma have normal pressure in their eyes. This type is called low-tension or normal-tension glaucoma.

Closed-angle glaucoma

Closed-angle glaucoma (CAG) may cause sudden blurred vision with pain and redness, usually in one eye first. In closed-angle glaucoma, the colored part of the eye (iris) and the lens block the movement of fluid between the chambers of the eye. The blockage of fluid causes pressure to build and makes the iris press on the drainage system (trabecular meshwork) of the eye (see an illustration of the iris and lens). The increased pressure can cause damage to the optic nerve, leading to vision loss and possible blindness. It is also sometimes referred to as primary angle-closure glaucoma (PACG).

See an illustration of closed-angle glaucoma.

Closed-angle glaucoma may cause sudden blurred vision with pain and redness, usually in one eye first. See an illustration of possible areas of pain associated with CAG.

• One type of closed-angle glaucoma (acute closed-angle glaucoma) can be an emergency situation and usually needs immediate medical care to prevent permanent damage to the affected eye. The opposite eye is also usually examined and eventually treated because the condition could affect the other eye in the future.
• Some people develop a form of closed-angle glaucoma called subacute angle-closure glaucoma. If you have this form of glaucoma, you have brief episodes of symptoms that develop and then go away on their own without treatment. But, over time, these episodes damage your eyesight and the drainage system in your eyes.
• Closed-angle glaucoma can also become a long-term problem (chronic angle-closure glaucoma). Chronic closed-angle glaucoma develops slowly over time.

Congenital glaucoma

Congenital glaucoma is a rare form of glaucoma that is present in babies at birth. It is often caused by a birth defect that can cause abnormal development of structures in the eye. Some birth defects may develop because of an inherited condition, such as neurofibromatosis or Marfan's syndrome.

• Congenital glaucoma is usually diagnosed by the end of the first year of life. About one-half of these children are diagnosed at birth.
• Congenital glaucoma must be treated as soon as possible to avoid loss of eyesight or blindness.
• Glaucoma that develops between birth and age 3 is called infantile glaucoma.
• People between the ages of 3 and young adulthood can develop another type of developmental glaucoma called juvenile glaucoma.

Glaucoma can also be classified as:

• Primary glaucoma. Primary glaucoma refers to glaucoma that is not caused by another eye or medical condition.
• Secondary glaucoma. Secondary glaucoma refers to glaucoma that develops as a result of another condition.
  • Secondary glaucoma may develop as a result of eye injury or eye tumors or after eye surgery.
  • Secondary glaucoma can develop as a complication of a disease, such as diabetes. Diabetes can cause new blood vessels to grow into the drainage angle of the eye (trabecular meshwork) and create scarring. This scarring can limit drainage of the fluid (aqueous humor) out of the eye. This blood vessel problem is called neovascular glaucoma.
  • Certain medications (corticosteroids) may cause secondary glaucoma when they are used to treat eye inflammation and other diseases. They unintentionally cause a rise in pressure within the eye.
  • Glaucoma may develop as a result of the breakdown and flaking off of the coloring (pigment) found in the iris and the part of the eye that produces fluid (ciliary body). These flakes of pigment block the fluid drainage system of the eye. This type of secondary glaucoma is called pigmentary glaucoma.
  • Another type of common secondary glaucoma can occur when a different type of flaky material is produced in the eye. The origin of this white, flaky material is not clearly known but it can block the fluid drainage system of the eye. This type of secondary glaucoma is called pseudoexfoliation glaucoma or exfoliation syndrome
  • A set of diseases called the ICE syndrome affect the iris and cornea and can cause glaucoma.

Health professionals classify glaucoma according to the severity of the disease.¹

• Ocular hypertension. Consistently elevated pressure inside the eye (greater than 21 millimeters of mercury [mm Hg]) without any evidence of damage to the optic nerve or loss of visual field is called ocular hypertension. Some people with ocular hypertension may still need treatment if the pressure in the eye is high enough to pose a risk of damaging the optic nerve over the long term.
• Mild glaucoma. Mild glaucoma refers to optic nerve damage with a normal visual field or minimal loss of outer (peripheral) vision. If there are signs of optic nerve damage without visual loss, the person may be considered as possibly having glaucoma (a glaucoma suspect).
• Moderate glaucoma. Moderate glaucoma refers to optic nerve damage with moderate loss of vision in at least one eye. However, sight in the center of the eye (central vision) is not affected in moderate glaucoma.
• Severe glaucoma. Severe glaucoma refers to optic nerve damage with loss of vision in both eyes or loss of sight in one eye that includes central vision loss.