What is Glaucoma?

Glaucoma is a group of diseases that result in degeneration of the optic nerve and many are caused by increased pressure inside the eye. Glaucoma can lead to vision loss and even blindness. In most patients, glaucoma occurs when pressure inside the eye is at a level sufficient to damage to the optic nerve. The optic nerve is a bundle of more than 1 million nerve fibers. It connects the retina to the brain. (See diagram below.) The retina is the light-sensitive tissue at the back of the eye. A healthy optic nerve is necessary for good vision.

Glaucoma is one of the leading causes of blindness. Glaucoma causes blindness in little over 12 percent of people with the condition. However, early treatment can often prevent serious vision loss.

What causes optic nerve damage in glaucoma?

Glaucoma is often associated with increased pressure inside the eye.

In the front of the eye is a space called the anterior chamber. A clear fluid flows continuously in and out of the chamber and nourishes nearby tissues. In normal eyes, fluid leaves the chamber through the open angle, the area where the cornea and iris meet. When the fluid reaches the angle, it flows through a spongy meshwork, like a drain, and leaves the eye.

In eyes with glaucoma, the drainage of fluid is either slowed down or blocked. The pressure inside the eye then rises to a level that can damage the optic nerve. When the optic nerve is damaged from increased pressure, it can cause vision loss. This is why controlling pressure inside the eye is important.

What are the types of glaucoma?

There are three main types of glaucoma:

Open-angle glaucoma– In this type, the angle in the eye is open, but it does not function properly. This prevents the fluid inside the eye from draining and causes the pressure in the eye to rise.

Closed-angle glaucoma – In this type, the angle in the eye is closed, or blocked. This prevents the fluid inside the eye from draining and causes the pressure in the eye to rise. In some people, the blockage happens very suddenly and causes severe pain and vision loss. This is called "acute closed-angle glaucoma." In other people, it happens slowly over time, and might cause periods of headaches. This is called "chronic closed-angle glaucoma." Closed-angle glaucoma is a serious condition and needs to be treated immediately.

Congenital glaucoma – This happens when a child is born with a defect in the angle of the eye that slows the normal drainage of fluid. These children usually have obvious symptoms, such as cloudy eyes, sensitivity to light, and excessive tearing.

Other types of glaucoma include:

  • Low-tension or normal-tension glaucoma – In this type, the optic nerve is damaged without an increase in eye pressure. People with this condition might also have problems with side vision. In some people with this type of glaucoma, medications or surgery can lower the eye pressure and slow the disease. In other people, lowering the eye pressure will not stop the glaucoma from getting worse. If you have low-tension or normal-tension glaucoma, make sure your eye doctor knows your complete medical history. This can help him or her identify other risk factors that might be contributing to your condition, such as low blood pressure. In people with no other risk factors, treatment options for low-tension or normal-tension glaucoma are the same as those for open-angle glaucoma.
  • Secondary glaucoma – These are types of open-angle glaucoma that are caused by medication or other medical conditions. They include:
  • Pseudoexfoliative glaucoma – People with this type have deposits of a protein-like material in their eye.
  • Pigmentary glaucoma – In this type, pigment from the iris flakes off and blocks the meshwork of the angle. This slows fluid drainage.
  • Neovascular glaucoma – This is a severe form of glaucoma that can happen in people with diabetes.
  • Uvetic glaucoma – This type of glaucoma can happen from eye inflammation.

In some people, corticosteroid drugs used to treat eye inflammations and other diseases can also cause secondary glaucoma.