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Douglas J. Rhee

, MD, University Hospitals/Case Western Reserve University

Last full review/revision Mar 2021| Content last modified Mar 2021

Glaucomas are a group of eye disorders characterized by progressive optic nerve damage (often, but not always, associated with increased eye pressure) that can lead to irreversible loss of vision.

  • Damage to the optic nerve can occur when pressure within the eye increases.
  • Usually, the vision loss occurs so slowly that it may not be noticed for a long time.
  • People at risk should have a complete eye examination, including measurement of eye pressures and testing of side (peripheral) vision.
  • Eye pressure needs to be controlled throughout life, usually with eye drops but sometimes with eye surgery.

Almost 3 million people in the United States and 64 million people worldwide have glaucoma. Glaucoma is the second most common cause of blindness worldwide and the second most common cause of blindness in the United States, where it is the leading cause of blindness among people of African ethnicity and Hispanics. Only half of the people who have glaucoma know they do. Glaucoma can occur at any age but is 6 times more common among people over age 60.

People at highest risk are those with any of the following:

  • Age older than 40
  • African ethnicity
  • Family members who have (or had) the disease
  • Nearsightedness (in open-angle glaucoma) or farsightedness (in closed-angle glaucoma)
  • Diabetes
  • High blood pressure
  • Long-term use of corticosteroids
  • Previous eye injury or surgery

Glaucoma occurs when an imbalance in production and drainage of fluid in the eye (aqueous humor) increases eye pressure to unhealthy levels. Normally the aqueous fluid, which nourishes the eye, is produced by the ciliary body behind the iris (in the posterior chamber) and flows through the pupil to the front of the eye (anterior chamber), where it exits into drainage canals between the iris and cornea (the “angle”). When functioning properly, the system works like a faucet (ciliary body) and a drain in a sink (drainage canals). Balance between fluid production and drainage—between an open faucet and a properly draining sink—keeps the fluid flowing freely and prevents pressure in the eye from building up.

Normal Fluid Drainage

Fluid is produced in the ciliary body behind the iris (in the posterior chamber), passes into the front of the eye (anterior chamber), and then exits through the drainage canals or the uveoscleral pathway (black arrows).

Normal Fluid Drainage

In glaucoma, the drainage canals become clogged, blocked, or covered. Fluid cannot leave the eye even though new fluid is being produced in the posterior chamber. In other words, the sink “backs up” while the faucet is still running. Because there is nowhere in the eye for the fluid to go, pressure in the eye increases. When the pressure becomes higher than the optic nerve can tolerate, damage to the optic nerve occurs. This damage is called glaucoma.

Sometimes eye pressure increases within the range of normal but is nonetheless too high for the optic nerve to tolerate (called low-tension glaucoma or normal-tension glaucoma). In the United States, about one third of people who have glaucoma have low-tension glaucoma. Low-tension glaucoma is more common among Asians.

In most people, the cause of glaucoma is not known. When the cause of glaucoma is not known, it is called primary glaucoma. When the cause of glaucoma is known, it is called secondary glaucoma. Causes of secondary glaucoma include infection, inflammation, tumors, large cataracts, surgery for cataracts, drugs, or other conditions. These causes keep the fluid from draining freely, which leads to increased eye pressure and optic nerve damage.

Types of glaucoma

There are many forms of adult and childhood glaucomas. Most glaucomas fall into two categories:

  • Open-angle glaucoma
  • Closed-angle glaucoma (angle-closure glaucoma)

Open-angle glaucoma is more common than closed-angle glaucoma. In open-angle glaucoma, the drainage canals in the eyes gradually become clogged with tiny, microscopic deposits over months or years. This type of glaucoma is "open" because the canals are not visibly blocked (when examined under magnification, as with a slit lamp), but drainage through them is still inadequate. Pressure in the eye rises slowly because fluid is produced at a normal rate but drains sluggishly.

Closed-angle glaucoma is less common than open-angle glaucoma. In closed-angle glaucoma, the drainage canals in the eyes become blocked or covered because the angle between the iris and cornea is too narrow. This type of glaucoma is "closed" because the canals are visibly blocked. The blockage can occur suddenly (called acute closed-angle glaucoma) or slowly (called chronic closed-angle glaucoma). If the blockage occurs suddenly, pressure in the eye rises rapidly. If the blockage occurs slowly, the pressure in the eye rises slowly as in open-angle glaucoma.

Symptoms of Glaucoma

Open-angle glaucoma

Open-angle glaucoma is painless and causes no early symptoms. Both eyes usually are affected but typically not equally. The main symptom of open-angle glaucoma is the development of blind spots, or patches of vision loss, over months to years. The blind spots slowly grow larger and merge together. Peripheral vision is usually lost first. People may miss stairs, notice portions of words missing when reading, or have difficulty with driving. Vision loss occurs so gradually that it is often not noticed until much of it is lost. Because central vision is generally lost last, many people develop tunnel vision: they see straight ahead perfectly but become blind in all other directions. If glaucoma is left untreated, eventually even tunnel vision is lost, and a person becomes totally blind.

Closed-angle glaucoma

In acute closed-angle glaucoma, eye pressure rises rapidly, and people typically notice severe eye pain and headache, redness, blurred vision, rainbow-colored halos around lights, and sudden loss of vision. They may also have nausea and vomiting as a response to the increase in eye pressure. Acute closed-angle glaucoma is considered a medical emergency because people can lose their vision as quickly as 2 to 3 hours after the appearance of symptoms if the condition is not treated.

In chronic closed-angle glaucoma, eye pressure rises slowly, and symptoms usually begin as in open-angle glaucoma. Some people may have eye redness, discomfort, blurred vision, or a headache that lessens with sleep. The eye pressure may be normal but usually is higher in the affected eye.

People who have had open-angle glaucoma or closed-angle glaucoma in one eye are likely to develop it in the other.

Diagnosis of Glaucoma

  • A doctor's examination of the eyes

If doctors suspect glaucoma (for example, based on what they find during a routine eye examination), they do a comprehensive eye examination for glaucoma. There are five parts to a comprehensive eye examination for glaucoma:

  • Measurement of eye pressure
  • Evaluation of the optic nerve
  • Visual field testing
  • Gonioscopy
  • Measurement of the corneas

Doctors measure pressure in the eye. This measurement is taken painlessly with an instrument called a tonometer. Normal eye pressure readings are in the range of 11 to 21 millimeters of mercury (mm Hg). In general, eye pressure readings greater than 21 mm Hg are considered higher than normal.

But measuring eye pressure is not enough because a third or more of people with glaucoma have eye pressure in the average range, and some people have a high eye pressure reading that is not caused by glaucoma. So doctors also use an ophthalmoscope and sometimes other instruments (such as optical coherence tomography) to look for changes in the optic nerve that indicate damage caused by glaucoma.

In addition, visual field testing (peripheral vision testing) allows a doctor to detect blind spots. Most often, visual field testing is done with a machine that determines the person’s ability to see small dots of light in all areas of the visual field.

Doctors may also use a special lens to examine the drainage channels in the eye, a procedure known as gonioscopy. The gonioscope allows the doctor to determine whether the glaucoma is of the open-angle or closed-angle type.

Doctors also measure the thickness of the corneas. If the corneas are thin, glaucoma is more likely to develop. However, a thin cornea does not mean that glaucoma is present.

Did You Know...

  • Drugs that cause anticholinergic effects (for example allergy, cold, or sleep drugs that contain an antihistamine) can widen the pupils, so before older people take these drugs, their eyes should be checked to see whether development of closed-angle glaucoma is likely.


Because the most common types of glaucoma can cause slow and silent loss of vision over years, early detection of the disease is extremely important. All people at high risk of glaucoma (see the list of risk factors) should have a routine comprehensive eye examination every 1 to 2 years.

Treatment of Glaucoma

  • Drugs
  • Sometimes surgery

Once a person loses vision because of glaucoma, the loss is permanent. But if glaucoma is detected, proper treatment can prevent further vision loss. So the goal of glaucoma treatment is to prevent further optic nerve damage and vision loss by lowering the pressure in the eye.

Treatment of glaucoma is lifelong. It involves decreasing eye pressure by increasing fluid drainage out of the eyeball or by reducing the amount of fluid produced inside the eyeball. Some people with high eye pressure who do not have signs of optic nerve damage (known as glaucoma “suspects”) can be monitored closely without treatment.

Drugs, usually in the form of eye drops, and surgery are the main treatments for glaucoma. The type and severity of glaucoma determine the appropriate treatment:

  • Most people with open-angle glaucoma respond well to the drugs used for treatment.
  • These drugs are also used for people with closed-angle glaucoma, but surgery, not eye drops, is the main treatment.


Eye drops containing beta-blockers (such as timolol), prostaglandin-like compounds, alpha-adrenergic agonists, or carbonic anhydrase inhibitors are commonly used to treat glaucoma. Cholinergic drugs (such as pilocarpine) have been used in the past but are no longer very commonly used.

Glaucoma eye drops are typically safe but they may cause a variety of side effects. People need to use them for the rest of their lives, and regular check-ups are necessary to monitor eye pressure, optic nerves, and visual fields. Typically, the drugs are used in only one eye (called a one-eye trial) at first or both eyes. If there is improvement in the treated eye after 1 to 4 weeks, both eyes are treated.

Acute closed-angle glaucoma is a medical emergency, so doctors may use a combination of very strong and fast-acting drugs that rapidly lower the eye pressure. People receive several drugs at once, beginning with eye drops (such as timolol, brimonidine, and pilocarpine). Doctors then give acetazolamide pills and diuretic drugs such as glycerin or isosorbide (by mouth) or mannitol (by vein) if they think the eye is vulnerable to high pressure. Emergency laser surgery is done to both eyes as soon as possible. Both eyes are treated because the unaffected eye is likely to become affected if it is not also treated.

Drugs Used to Treat Glaucoma


Some Side Effects


Prostaglandin-like compounds





Increased eye and skin pigmentation

Elongated and thickened eyelashes

Muscle, joint, and back pain


Possible worsening of inflammation within the front part of the eye (uveitis)

How they work: Increase aqueous humor outflow

Given as: Eye drops

Other comments: These drops have few serious bodywide side effects.








Shortness of breath in people with asthma or other lung disorders that cause wheezing

Slow heart beat





Sexual dysfunction

See table Antihypertensive Drugs

How they work: Decrease aqueous humor production

Given as: Eye drops

Other comments: These drops do not affect pupil size.

Some side effects are worse in people with heart or blood vessel disease.

Some side effects may develop slowly and may be mistakenly attributed to aging or other bodily processes.

Cholinergic drugs*





Involuntary, shaking movement


Excess saliva production

Diarrhea, abdominal cramps, nausea

How they work: Constrict the pupil (miosis) and increase aqueous humor outflow

Given as: Eye drops

Other comments: These drops are not as effective as beta-blockers.

People who have darker pupils may need high-strength drops.

These drugs make it harder for the eyes to adapt to darkness.

Cholinesterase inhibitors*


Same as for cholinergic agonists but more likely to occur

How they work: Constrict the pupil (miosis) and increase aqueous humor outflow

Given as: Eye drops

Other comments: These drops are very long acting.

They can cause cataracts and retinal detachment and should not be taken by people who have closed-angle glaucoma.

These drugs make it harder for the eyes to adapt to darkness.

Rho kinase inhibitor


Eye redness

Broken blood vessels in the eye

Corneal deposits

How they work: Increase aqueous humor outflow

Given as: Eye drops

Alpha-adrenergic agonists



Increase in blood pressure or heart rate

Abnormal heart rhythm

May excessively dilate the pupil

Apraclonidine: High rate of allergic reactions and decreased response if given over a period of time so that larger doses are required to have the same effect (tachyphylaxis)

Brimonidine: May cause dry mouth, has a lower rate of allergic reactions than the other drugs, and can be fatal in children less than 2 years of age

How they work: Decrease aqueous humor production and increase aqueous humor outflow

Given as: Eye drops

Carbonic anhydrase inhibitors





Acetazolamide and methazolamide:


Altered taste

Loss of appetite


Kidney stones

Body salt (electrolyte) abnormalities

Numbness or tingling

Low or high blood cell counts (blood dyscrasias)

Weight loss



Brinzolamide and dorzolamide:

Bad taste in the mouth


How they work: Decrease aqueous humor production

Given as: For acetazolamide: By mouth or by vein

For methazolamide: By mouth

For brinzolamide and dorzolamide: Eye drops

Osmotic diuretics



Increase urine production

Can have serious side effects in some people (for example, worsening of heart failure or brain dysfunction) by changing body salt (electrolyte) levels or may cause dehydration

How they work: Increase concentration of salts in the blood, which draws fluid from the eye by osmosis

Given as: For glycerin: By mouth

For mannitol: By vein

Other comments: These drugs are used most often to treat acute closed-angle glaucoma.

* These drugs are rarely used.


Surgery may be needed for people whose eye pressure is extremely high, whose eye pressure is not effectively controlled by eye drops, who cannot take eye drops, who develop intolerable side effects from the eye drops, or who already have severe visual field damage when they initially see a doctor.

Laser surgery can be used to increase drainage (laser trabeculoplasty) in people with open-angle glaucoma or to make an opening in the iris (laser peripheral iridotomy) in people with acute or chronic closed-angle glaucoma. Laser surgery is done in the doctor’s office or in a hospital or clinic. Anesthetic eye drops are used to prevent pain. People are usually able to go home the day of the procedure. Recent evidence suggests that treatment with laser surgery is at least as effective as drug therapy in open-angle glaucoma.

The most common complication of glaucoma laser surgery is a temporary increase in eye pressure, which is treated with glaucoma eye drops. Rarely, the laser used in laser surgery may burn the cornea, but these burns usually heal quickly.

Glaucoma filtration surgery is the other form of surgery doctors use to treat glaucoma. With traditional glaucoma filtration surgery, doctors manually create a new drainage system (trabeculectomy or tube shunt) to allow fluid to bypass the clogged or blocked canals and filter out of the eye. Traditional glaucoma filtration surgery is typically done in a hospital. People can usually go home the same day.

Partial thickness procedures (viscocanalostomy, deep sclerectomy, and canaloplasty) are newer filtration procedures that are used to remove only part of the drainage system to enhance the outflow of fluid. These procedures may be done in a hospital or in an outpatient surgery center. People can usually go home the same day.

The trabeculectomy filtration procedure can rarely cause severe infection in the eye (endophthalmitis). Glaucoma filtration surgery may cause acceleration of cataract growth, eye pressures that are too low, or swelling in the back of the eye.

Secondary glaucoma

The treatment of glaucoma caused by other disorders depends on the cause.

For infection or inflammation, antibiotic, antiviral, or corticosteroid eye drops may provide a cure.

A tumor that blocks fluid drainage should be treated, as should a cataract that is so large it causes eye pressure to rise. Removing such a cataract can help prevent secondary glaucoma but occasionally increases eye pressure. High eye pressure that results from cataract surgery is treated with glaucoma eye drops that reduce eye pressure. If eye drops do not work, glaucoma filtration surgery can be done.

More Information about Glaucoma

The following are some English-language resources that may be useful. Please note that THE MANUAL is not responsible for the content of these resources.

  • The Glaucoma Research Foundation: Access to information on innovative research to find a cure for glaucoma as well as basic information on care and treatment of people with the condition.
  • American Council of the Blind (ACB): Programs and services to enhance the quality of life for blind and visually impaired people, including Braille forums and publications, ACB Radio programs, and other relevant media.
  • American Foundation for the Blind: Access to research, educational, and employment initiatives to expand opportunities for people with blindness or visual impairment.

Drugs Mentioned In This Article

Generic Name Select Brand Names
Methazolamide No US brand name
Apraclonidine IOPIDINE
acetazolamide DIAMOX
Brinzolamide AZOPT
brimonidine ALPHAGAN P
Levobunolol BETAGAN
Dorzolamide TRUSOPT
Bimatoprost LUMIGAN
Latanoprost XALATAN
Travoprost TRAVATAN Z
Tafluprost ZIOPTAN
Betaxolol BETOPTIC
Carbachol MIOSTAT
Carteolol OCUPRESS
timolol TIMOPTIC

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