Glaucoma FAQs

Reviewed on 11/8/2021

What Is Glaucoma?

Glaucoma is an eye disease that is often associated with elevated intraocular pressure, in which damage to the eye (optic) nerve can lead to loss of vision and even blindness.

Glaucoma is an eye disease in which the optic nerve is damaged, usually from elevated pressure within the eye. The optic nerve damage may cause peripheral or central visual loss.

  • High pressure within the eye, optic nerve damage, and vision loss are not all required to diagnose glaucoma.
  • However, a diagnosis of glaucoma is almost certain when all three of these criteria are present.
Illustration of the eye.
Illustration of the eye. 
Illustration of the eye.
Illustration of the eye.

What Causes High Pressure Inside the Eye?

High pressure inside of the eye is caused by an imbalance in the production and drainage of the fluid in the front of the eye (aqueous humor). The channels that normally drain the fluid from inside the eye consequently do not function properly or are blocked. There is no change in the internal volume of the eye.  The system operates at a higher internal pressure in order to maintain balance of outflow with input.  An analogy would be the effect of pinching a water hose.  Flow rate remains constant, but the pressure within the hose is increased.

Are There Different 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 diseases) or secondary (related to other reasons, such as trauma, inflammation or medication).
  • Subtypes of glaucoma include, among others,
    • congenital glaucoma,
    • childhood glaucoma, and
    • normal (or low) tension glaucoma.

Who Gets Glaucoma?

Anyone can get glaucoma. This disease affects approximately 3 million people in the United States and more than 60 million people worldwide. Many of these individuals are unaware that they have glaucoma. It is the second leading cause of blindness both in the United States and worldwide.

Glaucoma tends to run in families. If a person has several family members with glaucoma, he or she is at a significantly increased risk of developing glaucoma. Glaucoma is more prevalent as people get older. It is also more common in people with diabetes, uncontrolled hypertension (high blood pressure), or certain other medical conditions. A person's risk also increases if he or she is severely nearsighted or farsighted or if they have a history of certain eye conditions or eye injuries.

No one knows why certain ethnic groups, such as African Americans, have higher rates of glaucoma that lead to blindness.

  • Primary open-angle glaucoma is the leading cause of blindness among African Americans and Alaskan natives, occurring 6 to 8 times more often than in Caucasians, often in the earlier stages of life.
  • People of Asian origin have a much higher incidence of angle-closure glaucoma than Caucasians or African Americans. In the United States, most cases of glaucoma are the open-angle type, while in China and Japan, the two types are approximately equal.

What Causes Glaucoma?

The most common type of glaucoma, primary open-angle glaucoma, has no specific cause.

  • Angle-closure glaucoma is usually a result of an anatomic anomaly where the peripheral anterior chamber of the eye is shallow and the iris comes into contact with the trabecular meshwork of the eye (an area of tissue around the base of the cornea that is responsible for draining the aqueous humor from the eye).
  • Eye injuries/trauma, inflammation of the eye, prior ocular surgery, use of steroid eye drops, eye tumors and certain diseases such as diabetes and uncontrolled hypertension (high blood pressure), or other structural abnormalities of the eye can cause secondary glaucoma.

What Are the Symptoms of Glaucoma?

Although acute angle-closure glaucoma may cause

  • pain,
  • redness,
  • haloes, and
  • blurred vision,
  • most people with glaucoma do not experience any symptoms until they have lost a significant amount of vision.

This loss of vision is a result of optic nerve damage and is permanent; it cannot be reversed. Because of this, regular eye examinations with an ophthalmologist (a medical doctor who specializes in diseases and surgery of the eye) are very important.

How Is Glaucoma Diagnosed?

An ophthalmologist can diagnose glaucoma during an eye examination. Findings consistent with glaucoma are

  • abnormally high pressure inside the eye,
  • optic nerve damage, and/or
  • vision loss.

What Can Someone Expect During an Eye Examination for Glaucoma?

  • An ophthalmologist initially checks the patient's central vision using an eye chart.
  • The fronts of the eyes are examined using a special magnifying device called a slit lamp microscope.
  • The pressure inside the eyes is checked using an instrument called a tonometer.
  • The optic nerves are examined for any damage; this may require dilation of the pupils to ensure an adequate examination of the optic nerves.
  • The peripheral vision may be checked, typically by using an automated visual field machine.
  • The drainage channels in the eyes may be examined using a painless technique called gonioscopy, which involves the use of a special contact lens that is placed onto the surface of the eye that has been numbed with an eye drop.

If Eye Pressure Is High, Does That Mean a Person Has Glaucoma?

Eye pressure is measured in millimeters of mercury (mm Hg). Normal eye pressure ranges from 10 to 21 mm Hg. When a person's pressure is higher than 21 mm Hg, they are at an increased risk for developing glaucoma.

  • Some people can tolerate pressures slightly higher than normal without developing glaucoma. This is called ocular hypertension. If an ophthalmologist diagnoses ocular hypertension, it does not mean that a person has glaucoma, but it does mean that they are at a higher risk for developing the condition and they should be examined routinely to ensure no permanent optic nerve damage and vision loss occur.
  • On the other hand, some people with normal pressures can still go on to develop optic nerve damage and to lose vision. This is called normal (or low) tension glaucoma.

If an Ophthalmologist Says That a Person Is a Glaucoma Suspect, What Does That Mean?

A glaucoma suspect is a person who might have or may develop glaucoma.

  • The ophthalmologist may be concerned about the elevated pressure inside the eyes or the appearance of the optic nerves.
  • Some people may have pressures that are higher than normal, but they do not develop glaucoma.
  • Other people have optic nerves that might appear to be damaged but, in fact, are actually normal for them, just as people can be taller or shorter than average.

How Is Glaucoma Treated?

The treatment of angle-closure glaucoma is primarily surgical while the treatment of open-angle glaucoma is usually medical, through the use of eye drops. To treat glaucoma, an ophthalmologist must first decide whether the glaucoma is of the open-angle or angle-closure variety.

  • In open-angle glaucoma, which is far more common in the United States, the ophthalmologist prescribes eye drops that contain medicine that helps to lower the pressure inside the eye, thereby reducing the risk for future optic nerve damage and preventing further vision loss (see How to Instill Your Eyedrops).
  • Sometimes, if eye drops alone do not lower the pressure enough, laser procedures or surgery performed by an ophthalmologist are necessary to lower the pressure inside the eye.

If a Person Has Glaucoma, How Often Do They Need to Be Checked?

The frequency of checkups depends on the severity of one's glaucoma.

  • If the person is a low-risk glaucoma suspect, they may only need to be examined on an annual basis.
  • For more severe glaucoma, examinations may need to be done monthly, or possibly even more frequently, until the glaucoma stabilizes.
  • Once the glaucoma is stable, examinations every 3 to 4 months are usually appropriate.

Can Glaucoma Be Prevented?

Most types of glaucoma cannot be prevented.

  • Vitamins and other nutritional supplements do not play a role in the prevention of glaucoma.
  • While vision loss due to glaucomatous optic nerve damage cannot be recovered, with appropriate treatment, further vision loss can usually be prevented.

Those types of secondary glaucoma resulting from eye injuries or certain diseases, such as diabetes and uncontrolled hypertension (high blood pressure), may be preventable or even avoidable with certain measures, such as

  • protective eyewear to avoid eye injuries and
  • proper management of diabetes and uncontrolled hypertension.

One type of glaucoma, acute angle-closure glaucoma, can sometimes be prevented if a laser procedure is performed prior to its onset. To determine if a person is at risk for acute angle-closure glaucoma, that person should see an ophthalmologist for an eye examination.

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Reviewed on 11/8/2021
Medically reviewed by William Baer, MD; Board Certified Ophthalmology


"Primary Angle Closure (Preferred Practice Pattern)." American Academy of Ophthalmology. 2005.

"Primary Open-Angle Glaucoma, Limited Revision (Preferred Practice Pattern)." American Academy of Ophthalmology. 2005.

"Primary Open-Angle Glaucoma Suspect (Preferred Practice Pattern)." American Academy of Ophthalmology. Oct. 2010.

Gordon, M. O., et al. "The Ocular Hypertension Treatment Study: baseline factors that predict the onset of primary open-angle glaucoma." Archives of Ophthalmology 120.6 (2002): 714-720.

Lichter, P. R., et al. "Interim clinical outcomes in the Collaborative Initial Glaucoma Treatment Study comparing initial treatment randomized to medications or surgery." Ophthalmology 108.11 (2001): 1943-1953.

Previous contributing editors: Richard W Allinson, MD, Associate Professor, Division of Ophthalmology, Texas A&M University Health Science Center, Associate Professor, Department of Surgery, Scott and White Clinic; Francisco Talavera, PharmD, PhD, Senior Pharmacy Editor, eMedicine; Robert H Graham, MD, Ophthalmologist, Robert H Graham, MD, PC; Affiliated With Department of Ophthalmology, Mayo Clinic, Scottsdale, Arizona and Carl T Hayden VA Medical Center, Phoenix, Arizona.