What Is Glaucoma?

Glaucoma is a group of related diseases in which the optic nerve becomes damaged by excessive fluid pressure within the eyeball.

The human eye houses a self-contained production system to churn out the jelly-like fluid known as aqueous humor. This fluid nourishes the tissues of the eye and keeps the eyeball from collapsing like a deflated beach ball (How the Eye Works).

Simulation of Glaucoma.  A street scene with an approximation of what somebody with Glaucoma sees compared to normal vision

The eye also conceals an ingenious maze of drainage channels known collectively as the trabecula. Normally, pressure inside the eye stays constant because fluid production and outflow maintain a balance.

Types of Glaucoma

The eye’s drainage system is clustered around the edge of the iris, the colored part of the eye. Fluid travels through a mesh of tiny channels (the trabecula) and exits through the angle where the iris and the cornea come together.

Open-angle glaucoma
In open-angle glaucoma, drainage fails to keep pace with the output of new aqueous humor. Pressure on the optic nerve builds as the level of fluid rises. Damaged optic nerve fibers die off one by one, and the nerve bundle begins to resemble a frayed extension cord, no longer able to transmit complete signals from the eye to the brain. This process takes place so gradually that vision loss may be imperceptible until irreversible vision loss has occurred. This is the most common type of glaucoma, representing about 95 percent of all cases. It is referred to as "primary" (first) if it is not the result of some other disease.

Angle-closure (closed angle) glaucoma
In angle-closure glaucoma, fluid pressure mounts rapidly when a sudden protrusion of the iris blocks all drainage channels. Such an attack is a medical emergency because complete vision loss in the affected eye or eyes will occur in 24 to 48 hours if left untreated. Do not hesitate to dial 911 for yourself or anyone else who has symptoms of angle-closure glaucoma (see the list below). Anyone exhibiting such symptoms should be transported to the nearest hospital or trauma center for immediate treatment.

Other types of glaucoma.

  • Low-tension glaucoma. Low-tension glaucoma, sometimes called normal-tension glaucoma, is a type of open-angle glaucoma in which the optic nerve is damaged despite low-to-normal eye pressure (tension). Lowering eye pressure by at least 30 percent can keep the condition from progressing in some patients.
  • Congenital glaucoma. About 1 in 10,000 babies in the United States is born with a narrow drainage angle (see above, under Angle-closure glaucoma), a condition called congenital glaucoma. Such infants have cloudy or teary eyes and may be sensitive to light or glare. Surgical treatment of this congenital glaucoma is generally successful.
  • Secondary glaucoma. Glaucoma is said to be secondary if it is caused by another disease. For instance, glaucoma might be associated with (secondary to) diabetes, which would then be considered the primary disease.


  • Open-angle glaucoma
  • A lack of symptoms in the early stages
  • No pain at any stage
  • Blank spots that enlarge so gradually they are difficult to notice
  • Loss of peripheral (side) vision leading to tunnel vision in one or both eyes

Angle-closure (closed angle) glaucoma

  • Sudden onset of severe eye pain
  • Nausea and vomiting
  • Blurry vision
  • Rainbow halos around lights
  • Eye redness


The air-puff test is more properly called a non-contact tonometer screening. The non-contact tonometer gauges the resistance of your cornea - the eye’s surface - to a quick blast of air. When pressure is too high inside the eye, the cornea becomes more rigid, just as a water balloon has greater surface tension when completely distended than when half filled.

This test is not particularly accurate, however, and is used only to screen patients - that is, to identify those who require further testing. For more reliable results, vision care providers will conduct the following tests:

  • Contact tonometry. Contact tonometry is so called because the pressure gauge makes contact with your eye after anesthetic (numbing) drops are instilled. It is more accurate than non-contact tonometry.
  • Dilated eye examination. Your vision care provider will need to dilate your pupils in order to view the interior structures of the eye, including the optic nerve. Your provide may refer to this test as ophthalmoscopy (pronounced off-thal-MOSS-kuh-pee) because it’s performed with the aid of an ophthalmoscope.
  • Visual field test (perimetry). Your visual field is the radius of your vision when your eyes are fixed on a central point. In other words, it’s the area you can see - in front of you, above, below, and on either side - while looking straight ahead. Testing one eye at a time, a visual field test maps your response to a series of lights flashed in your central and peripheral vision (your perimeter, or side vision). The map indicates which areas you can and can’t see, based on which lights you responded to.
  • Pachymetry. Knowing how thick or thin your corneas are helps your vision care provider interpret your eye pressure reading. A thick cornea, for example, might indicate a falsely high pressure. Your provider will use a pachymeter (pronounced pa-KIM-uh-ter) to scan and measure your corneas.
  • Gonioscopy. Gonioscopy (pronounced gohn-ee-OS-co-pee) is a painless test that measures the angle at which fluid drains from the eye.


Treatment of glaucoma hinges on impeding progression of the disease, since glaucoma-related vision loss irreversible.

Oral medications
Medications taken by mouth move through your bloodstream and have systemic (system-wide) effects. Some oral meds discourage production of aqueous humor, others promote fluid drainage from the eye.


  • Trabeculoplasty. An ophthalmologist can perform laser surgery to improve passage of fluid out of the eye.
  • Conventional surgery. Conventional surgery may be necessary to carve out a tiny new channel by which fluid can exit the eye. Trabeculoplasty is usually attempted first. Each eye will be operated on separately, and you’ll be given several weeks to recover in between.

Topical eye drops
Topical drops lower your eye pressure either by improving flow through the drainage channels or by slowing fluid production.

Your vision depends on using these drops as instructed. Learn more about using your glaucoma drops.

Living with Glaucoma-Related Vision Loss

If you have diminished sight or low vision due to glaucoma, there are services and programs available to help you continue to lead a normal, independent life. Check out the Related Reading below to learn more.

Related Reading



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