Skip to main content
Select Source:

Glaucoma

Glaucoma

Definition

Glaucoma is a group of eye diseases characterized by damage to the optic nerve usually due to excessively high intraocular pressure (IOP).This increased pressure within the eye, if untreated can lead to optic nerve damage resulting in progressive, permanent vision loss, starting with unnoticeable blind spots at the edges of the field of vision, progressing to tunnel vision, and then to blindness.

Description

Between two to three million people in the United States have glaucoma, and 120,000 of those are legally blind as a result. It is the leading cause of preventable blindness in the United States and the most frequent cause of blindness in African-Americans, who are at about a three-fold higher risk of glaucoma than the rest of the population. The risk of glaucoma increases dramatically with age, but it can strike any age group, even newborn infants and fetuses.

Glaucoma can be classified into two categories: open-angle glaucoma and narrow-angle glaucoma. To understand what glaucoma is and what these terms mean, it is useful to understand eye structure.

Eyes are sphere-shaped. A tough, non-leaky protective sheath (the sclera) covers the entire eye, except for the clear cornea at the front and the optic nerve at the back. Light comes into the eye through the cornea, then passes through the lens, which focuses it onto the retina (the innermost surface at the back of the eye). The rods and cones of the retina transform the light energy into electrical messages, which are transmitted to the brain by the bundle of nerves known as the optic nerve.

The iris, the colored part of the eye shaped like a round picture frame, is between the dome-shaped cornea and the lens. It controls the amount of light that enters the eye by opening and closing its central hole (pupil) like the diaphragm in a camera. The iris, cornea, and lens are bathed in a liquid called the aqueous humor, which is somewhat similar to plasma. This liquid is continually produced by nearby ciliary tissues and moved out of the eye into the bloodstream by a system of drainage canals (called the trabecular meshwork). The drainage area is located in front of the iris, in the angle formed between the iris and the point at which the iris appears to meet the inside of the cornea.

Glaucoma occurs if the aqueous humor is not removed rapidly enough or if it is made too rapidly, causing pressure to build-up. The high pressure distorts the shape of the optic nerve and destroys the nerve. Destroyed nerve cells result in blind spots in places where the image from the retina is not being transmitted to the brain.

Open-angle glaucoma accounts for over 90% of all cases. It is called "open-angle" because the angle between the iris and the cornea is open, allowing drainage of the aqueous humor. It is usually chronic and progresses slowly. In narrow-angle glaucoma, the angle where aqueous fluid drainage occurs is narrow, and therefore may drain slowly or may be at risk of becoming closed. A closed-angle glaucoma attack is usually acute, occurring when the drainage area is blocked. This can occur, for example, if the iris and lens suddenly adhere to each other and the iris is pushed forward. In patients with very narrow angles, this can occur when the eyes dilate (e.g., when entering a dark room, or if taking certain medications).

Congenital glaucoma occurs in babies and is the result of incomplete development of the eye's drainage canals during embryonic development. Microsurgery can often correct the defects or they can be treated with a combination of medicine and surgery.

One rare form of open-angle glaucoma, normal tension glaucoma, is different. People with normal-tension glaucoma have optic nerve damage in the presence of normal IOP. As of 1998, the mechanism of this disease is a mystery but is generally detected after an examination of the optic nerve. Those at higher risk for this form of glaucoma are people with a familial history of normal tension glaucoma, people of Japanese ancestory, and people with a history of systemic heart disease such as irregular heart rhythm.

Glaucoma is also a secondary condition of over 60 widely diverse diseases and can also result from injury, inflammation, tumor, or in advanced cases of cataract or diabetes.

Causes and symptoms

Causes

The cause of vision loss in all forms of glaucoma is optic nerve damage. There are many underlying causes and forms of glaucoma. Most causes of glaucoma are not known, but it is clear that a number of different processes are involved, and a malfunction in any one of them could cause glaucoma. For example, trauma to the eye could result in the angle becoming blocked, or, as a person ages, the lens becomes larger and may push the iris forward. The cause of optic nerve damage in normal-tension glaucoma is also unknown, but there is speculation that the optic nerves of these patients are susceptible to damage at lower pressures than what is usually considered to be abnormally high.

It is probable that most glaucoma is inherited. At least ten defective genes that cause glaucoma have been identified.

Symptoms

At first, chronic open-angle glaucoma is without noticeable symptoms. The pressure build-up is gradual and there is no discomfort. Moreover, the vision loss is too gradual to be noticed and each eye fills-in the image where its partner has a blind spot. However, if it is not treated, vision loss becomes evident, and the condition can be very painful.

On the other hand, acute closed-angle glaucoma is obvious from the beginning of an attack. The symptoms are, blurred vision, severe pain, sensitivity to light, nausea, and halos around lights. The normally clear corneas may be hazy. This is an ocular emergency and needs to be treated immediately.

Similarly, congenital glaucoma is evident at birth. Symptoms are bulging eyes, cloudy corneas, excessive tearing, and sensitivity to light.

Diagnosis

Intraocular pressure, visual field defects, the angle in the eye where the iris meets the cornea, and the appearance of the optic nerve are all considered in the diagnosis of glaucoma. IOP is measured with an instrument known as a tonometer. One type of tonometer involves numbing the eye with an eyedrop that has a yellow coloring in it and touching the cornea with a small probe. This quick test is a routine part of an eye examination and is usually included without extra charge in the cost of a visit to an ophthalmologist or optometrist.

Ophthalmoscopes, hand-held instruments with a light source, are used to detect optic nerve damage by looking through the pupil. The optic nerve is examined for changes; the remainder of the back of the eye can be examined as well. Other types of lenses that can be used to examine the back of the eye may also be used. A slit lamp will allow the doctor to examine the front of the eye (i.e., cornea, iris, and lens).

Visual field tests (perimetry) can detect blind spots in a patient's field of vision before the patient is aware of them. Certain defects may indicate glaucoma.

Another test, gonioscopy, can distinguish between narrow-angle and open-angle glaucoma. A gonioscope, which is a hand-held contact lens with a mirror, allows visualization of the angle between the iris and the cornea.

Intraocular pressure can vary throughout the day. For that reason, the doctor may have a patient return for several visits to measure the IOP at different times of the day.

Treatment

Medications

When glaucoma is diagnosed, drugs, typically given as eye drops, are usually tried before surgery. Several classes of medications are effective at lowering IOP and thus preventing optic nerve damage in chronic and neonatal glaucoma. Beta blockers, like Timoptic; carbonic anhydrase inhibitors, like acetazolamide; and alpha-2 agonists, such as Alphagan, inhibit the production of aqueous humor. Miotics, like pilocarpine, and prostaglandin analogues, like Xalatan, increase the outflow of aqueous humor. Cosopt is the first eyedrop that is a combined beta blocker (Timoptic) and carbonic anhydrase inhibitor and may be helpful for patients required to take more than one glaucoma medication each day. The Food and drug administration recently approved two new prostaglandin-related drugs, Travatan and Lumigan on March 16, 2001. These drugs work by decreasing intraocular pressure and may be considered for people with glaucoma that are unable to tolerate other IOP lowering drugs. Additionally, Travatan may work best for African-Americans with glaucoma (a population at high risk for glaucoma).

It is important for patients to tell their doctors about any conditions they have or medications they are taking. Certain drugs used to treat glaucoma should not be prescribed for patients with pre-existing conditions. Some of these drugs mentioned have side effects, so patients taking them should be monitored closely, especially for cardiovascular, pulmonary, and behavioral symptoms. Different medications lower IOP by different amounts, and a combination of medications may be necessary. It is important that patients take their medications and that their regimens are monitored regularly, to be sure that the IOP is lowered sufficiently. IOP should be measured three to four times per year.

Normal-tension glaucoma is treated in the same way as chronic high-intraocular-pressure glaucoma. This reduces IOP to less-than-normal levels, on the theory that overly susceptible optic nerves are less likely to be damaged at lower pressures. Research underway may point to better treatments for this form of glaucoma.

Attacks of acute closed-angle glaucoma are medical emergencies. IOP is rapidly lowered by successive deployment of acetazolamide, hyperosmotic agents, a topical beta-blocker, and pilocarpine. Epinephrine should not be used because it exacerbates angle closure.

Surgery

There are several types of laser surgery used to treat glaucoma. Laser peripheral iridotomy makes an opening in the iris allowing the fluid to drain, argon laser trabeculoplasty is aimed at the fluid channel opening to help the drainage system function and laser cyclophotocoagulation is used to decrease the amount of fluid made. Microsurgery, also called "filtering surgery" has been used in many different types of glaucoma. A new opening is created in the sclera allowing the intraocular fluid to bypass the blocked drainage canals. The tissue over this opening forms a little blister or bleb on the clear conjuctiva that Doctors monitor ensuring that fluid is draining. These surgeries are usually successful, but the effects often last less than a year. Nevertheless, they are an effective treatment for patients whose IOP is not sufficiently lowered by drugs and for those who can't tolerate the drugs. Because all surgeries have risks, patients should speak to their doctors about the procedure being performed.

Alternative treatment

Vitamin C, vitamin B1 (thiamine), chromium, zinc, bilberry and rutin may reduce IOP.

There is evidence that medicinal marijuana lowers IOP, too. However, marijuana has serious side effects and contains carcinogens, and any IOP-lowering medication must be taken continually to avoid optic nerve damage. Although the Food and Drug Administration (FDA) and National Institutes of Health (NIH) currently recommend against treating glaucoma with marijuana, they are supporting research to learn more about it and to determine the feasibility of separating the components that lower IOP from components that produce side effects and carcinogens.

Any glaucoma patient using alternative methods to attempt to prevent optic nerve damage should also be under the care of a traditionally trained ophthalmologist or optometrist who is licensed to treat glaucoma, so that IOP and optic nerve damage can be monitored.

Prognosis

About half of the people stricken by glaucoma are not aware of it. For them, the prognosis is not good, and many of them will become blind. Sight lost due to glaucoma cannot be restored. On the other hand, the prognosis for treated glaucoma is excellent.

Prevention

Because glaucoma may not initially result in symptoms, the best form of prevention is to have regular eye exams.

Patients with narrow angles should avoid certain medications (even over-the-counter medications, such as some cold or allergy medications). Any person who is glaucoma-susceptible (i.e. narrow angles and borderline IOPs) should read the warning labels on over-the-counter medicines and inform their physicians of products they are considering taking. Steroids may also raise IOP, so patients may need to be monitored more frequently if it is necessary to use steroids for another medical condition.

Not enough is known about the underlying mechanisms of glaucoma to prevent the disease itself. However, prevention of optic nerve damage from glaucoma is essential and can be effectively accomplished when the condition is diagnosed and treated. As more is learned about the genes that cause glaucoma, it will become possible to test DNA and identify potential glaucoma victims, so they can be treated even before their IOP becomes elevated.

KEY TERMS

Agonist A drug that mimics one of the body's own molecules.

Alpha-2 agonist (alpha-2 adrenergic receptor agonist) A class of drugs that bind to and stimulate alpha-2 adrenergic receptors, causing responses similar to those of adrenaline and noradrenaline. They inhibit aqueous humor production and a have a wide variety of effects, including dry mouth, fatigue, and drowsiness.

Aqueous humor A transparent liquid, contained within the eye, that is composed of water, sugars, vitamins, proteins, and other nutrients.

Betablocker (beta-adrenergic blocker) A class of drugs that bind beta-adrenergic receptors and thereby decrease the ability of the body's own natural epinephrine to bind to those receptors, leading to inhibition of various processes in the body's sympathetic system. Betablockers can slow the heart rate, constrict airways in the lungs, lower blood pressure, and reduce aqueous secretion by ciliary tissues in the eye.

Carbonic anhydrase inhibitor A class of diuretic drugs that inhibit the enzyme carbonic anhydrase, an enzyme involved in producing bicarbonate, which is required for aqueous humor production by the ciliary tissues in the eye. Thus, inhibitors of this enzyme inhibit aqueous humor production. Some side effects are urinary frequency, kidney stones, loss of the sense of taste, depression, and anemia.

Cornea Clear, bowl-shaped structure at the front of the eye. It is located in front of the colored part of the eye (iris). The cornea lets light into the eye and partially focuses it.

Gonioscope An instrument used to examine the trabecular meshwork; consists of a magnifier and a lens equipped with mirrors, which sits on the patient's cornea.

Hyperosmotic drugs Refers to a class of drugs for glaucoma that increase the osmotic pressure in the blood, which then pulls water from the eye into the blood.

Iris The colored part of the eye just behind the cornea and in front of the lens that controls the amount of light sent to the retina.

Lens (the crystalline lens) A transparent structure in the eye that focuses light onto the retina.

Laser cyclophotocoagulation A procedure used for severe glaucoma in patients who have not responded well to previous treatments. The laser partially destroys the tissues that make the fluid of the eye.

Laser peripheral iridotomy This procedure makes a drainage hole in the iris allowing the fluid to drain from the eye

Laser Trabeculoplasty In this procedure the laser attempts to open the normal drainage channels of the eye so fluid can drain more effectively.

Miotic A drug that causes pupils to contract.

Ophthalmoscope An instrument, with special lighting, designed to view structures in the back of the eye.

Optic nerve The nerve that carries visual messages from the retina to the brain.

Prostaglandin A group of molecules that exert local effects on a variety of processes including fluid balance, blood flow, and gastrointestinal function.

Prostaglandin analogue A class of drugs that are similar in structure and function to prostaglandin.

Retina The inner, light-sensitive layer of the eye containing rods and cones.

Sclera The tough, fibrous, white outer protective covering that surrounds the eye.

Tonometry The measurement of pressure.

Trabecular meshwork A sponge-like tissue located near the cornea and iris that functions to drain the aqueous humor from the eye into the blood.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Glaucoma." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"Glaucoma." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma

"Glaucoma." Gale Encyclopedia of Medicine, 3rd ed.. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Glaucoma

Glaucoma

Definition

Glaucoma is a slowly progressive eye condition that causes damage to the optic nerve. It is the leading cause of blindness among African-Americans and older adults in the United States. Because there are usually no symptoms early on in the disease, about half of the people with glaucoma do not even know they have it.

Description

Over two million people in the United States have glaucoma, and 80,000 of those are legally blind as a result of the disease. Glaucoma can strike any age group, even newborn infants. Susceptibility to the disease increases with age. African-Americans are at a three times higher risk of glaucoma than the rest of the population.

There are at least 20 different types of glaucoma. These can be divided into four main types:

  • Open-angle glaucoma. Accounts for over 6070% of all cases. It is usually chronic and often bilateral.
  • Closed-angle glaucoma. Usually an acute condition, as opposed to open-angle glaucoma that is chronic.
  • Congenital glaucoma occurs in infants, usually under the age of one.
  • Secondary glaucoma may be associated with eye diseases, other diseases, and certain types of medications.

Causes & symptoms

Glaucoma is the result of disruptions of normal processes to maintain pressure within the eye tissue. The iris, cornea, and lens of the eye are bathed in a nutritive liquid called the aqueous humor, which is made by cells within the eye. Excess fluid is continually removed by a spongy meshwork of drainage canals. Glaucoma occurs if there is a build up of the aqueous humor due to poor drainage or overproduction. As the fluid builds up there is increased pressure on the retina at the back of the eye. This increases the pressure, reducing the blood supply to the nerves of the retina, causing the nerves to die. This may distort and destroy the optic nerve. As nerve cells are destroyed, blind spots develop, and there is a progressive loss of vision. A change in the production and strength of collagen may also contribute to the onset of the disease. Collagen is a protein that helps maintain the structure and function of eye tissue. Stress and allergies may aggravate glaucoma symptoms.

It is probable that most cases of glaucoma are partially due to a genetic predisposition. At least 10 defective genes have been identified that may cause glaucoma. Although there are still many unknown factors that trigger the disease, a number of processes have been implicated. They include age-related changes, congenital abnormalities, injuries to the eye tissue, and problems related to other eye diseases. Vision loss in all forms of glaucoma is caused by damage to the optic nerve, the retina, and the collagen protein that makes up eye tissue. Use of certain medications, including antihypertensives, antihistamines, anticholinergics, and antidepressants may also contribute to the development of glaucoma. Corticosteroid eye drops, which are often used for other eye disorders, may destroy the integrity of eye tissue. Other types of eye drops may cause the pupils to dilate, increasing intraocular eye pressure (IOP), which may also lead to glaucoma in those who have a tendency to the disease.

Chronic open-angle glaucoma at first develops without noticeable symptoms. The pressure buildup is gradual and it does not bring on discomfort. Moreover, the vision loss is too gradual to be noticed at first, and the brain will compensate for blind spots. Over an extended period of time, the elevated pressure pushes against and damages the optic nerve and the retina. If glaucoma is left untreated, vision loss becomes evident and the condition becomes painful.

Acute closed-angle glaucoma is obvious from the beginning. The symptoms are blurred vision, severe eye pain , sensitivity to light, nausea and vomiting , dilated pupils, reddened eyes, and halos visualized around lights. The corneas may become hazy-looking. Acute closed-angle glaucoma is an emergency situation. It needs to be treated immediately. Congenital glaucoma is evident at birth. Symptoms are bulging eyes, cloudy corneas, enlarged corneas, excessive teariness, and sensitivity to light.

Risk factors that increase the probability of developing glaucoma include:

  • ocular hypertension , a slightly increased IOP
  • age over 40
  • diabetic
  • high blood pressure
  • migraine headaches
  • nearsightedness, farsightedness, and other visual disturbances
  • a family history of glaucoma
  • being of African-American ethnicity

Diagnosis

Sometimes glaucoma can be diagnosed with a routine eye exam by an opthamologist, who can make a definitive diagnosis of glaucoma. IOP, defects in the field of vision, and the appearance of the optic nerve, are all considered in the diagnosis of glaucoma. Visual field tests can detect blind spots in a patient's field of vision before the patient is aware of them. An instrument, known as a tonometer, is used to measure eye pressure. Since IOP can vary throughout the day, a person may have to return for several visits to measure eye pressure at different times of the day. An ophthalmoscope is used to examine the inner aspects and the back of the eyes, including the optic nerve, for changes and damage. A slit lamp may be used to allow the doctor further examination of the eye. Another test, gonioscopy, can distinguish between narrow-angle and open-angle glaucoma. A gonioscope allows visualization of the angle between the iris and the cornea.

Treatment

Vitamin C , taken in dosages up to bowel tolerance, is reported to reduce pressure within the eye and restore collagen balance. A vitamin C supplement with bioflavonoids , especially rutin and lutein , are particularly recommended. There is evidence that marijuana (Cannabis sativa ) lowers IOP, as well. Although it is a controlled substance, marijuana can often be prescribed by a professional licensed to treat glaucoma. Bilberry (Vaccinium sp.) helps maintain collagen balance and prevents the breakdown of vitamin C. Many people with glaucoma have been shown to have deficiencies of chromium and zinc . Supplementation with these two minerals may, therefore, deter the onset or progression of the disease. Alpha lipoic acid and other antioxidants may improve visual functioning.

A naturopathic approach called contrast hydrotherapy can be used to stimulate circulation in the eyes.

Compresses can be applied over the eyes, alternating three minutes with hot water and one minute with cold water, always ending with the cold. Biofeedback can be used to reduce the pressure in the eyes by increasing relaxation . Meditation , stress reduction, t'ai chi, yoga, exercise , and acupuncture also may lower IOP. Remedies used to lower IOP must be taken continually to avoid optic nerve damage. In addition to other treatments, a glaucoma patient should always remain under the care of an ophthalmologist or optometrist who is licensed to treat glaucoma, so that IOP and optic nerve damage can be monitored.

Allopathic treatment

The objective of glaucoma treatment is usually to decrease IOP. When glaucoma is diagnosed, drugs, typically given as eye drops, are usually tried before surgery. Several classes of medications are effective at lowering IOP and thus, at preventing optic nerve damage in chronic and neonatal glaucoma. These inlcude beta-blockers, such as Timoptic, and carbonic anhydrase inhibitors, such as acetazolamide. Alpha-2 agonists, such as Alphagan, inhibit the production of aqueous humor. Miotics, such as pilocarpine, and prostaglandin analogues, like Xalatan, increase the drainage of aqueous humor. Different medications lower IOP different amounts, and a combination of medications may be necessary. Attacks of acute closed-angle glaucoma are medical emergencies. In such cases, IOP is rapidly lowered by use of acetazolamide, hyperosmotic agents, a topical beta-blocker, and pilocarpine. All of these drugs have side effects, some of which are rare, but serious and potentially life threatening. Patients taking them should be monitored closely, especially for cardiovascular, pulmonary, and behavioral symptoms. IOP should also be monitored and measured three to four times per year.

Laser peripheral iridiotomy or other microsurgery is used to open the drainage canals or to make an opening in the iris to increase the outflow of aqueous humor. These surgeries are usually successful, but effects often last less than a year. Nevertheless, they are an effective treatment for patients whose IOP is not sufficiently lowered by drugs or for those who cannot tolerate the drugs. Surgery is usually used in cases of congenital glaucoma, since the medications are often too harsh for children. Youngsters often respond to surgery better than adults, and have an excellent chance for preserving lifelong good vision.

Expected results

If glaucoma is left untreated, optic nerve damage will result in a progressive loss of vision. Once blindness develops due to glaucoma, it cannot be reversed. With early treatment and monitoring, however, serious vision loss can usually be prevented.

Prevention

While glaucoma is not preventable, early detection and treatment can help to prevent serious damage to vision. Those with risk factors should have regular eye exams and avoid medicines that tend to be implicated in the development of glaucoma, including some over-thecounter cold and allergy medications. All medications should be checked for their ingredients. Alternatives for drugs that aggravate glaucoma should be discussed with a healthcare provider.

Resources

BOOKS

The Editors of Time-Life Books. The Medical Advisor: The Complete Guide to Alternative and Conventional Treatments. Alexandria, VA: Time-Life, Inc., 1996.

Epstein, David L., R. Rand Allingham, and Joel S. Schuman. Chandler and Grant's Glaucoma. 4th ed. Baltimore: Williams & Wilkins, 1997.

Marks, Edith and Rita Montauredes. Coping with Glaucoma. New York: Avery, 1997.

ORGANIZATIONS

American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. <http://www.eyenet.org/aao_index.html>.

OTHER

drkoop.com. http://www.drkoop.com/conditions/ency/article/001620.htm.

Patience Paradox

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Glaucoma." Gale Encyclopedia of Alternative Medicine. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"Glaucoma." Gale Encyclopedia of Alternative Medicine. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-1

"Glaucoma." Gale Encyclopedia of Alternative Medicine. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-1

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

glaucoma

glaucoma (glôkō´mə), ocular disorder characterized by pressure within the eyeball caused by an excessive amount of aqueous humor (the fluid substance filling the eyeball). This causes pressure against the optic nerve and compression of the blood vessels of the eye—the resulting impairment of vision ranges from slight abnormalities to total blindness. Chronic open-angle glaucoma is the result of impeded drainage of aqueous humor. In acute angle-closure glaucoma, the anterior chamber of the eye is shallower and the iris may obstruct the meshwork at the entrance of the canal of Schlemm. Although glaucoma is a leading cause of blindness in the United States, with timely treatment blindness is almost always avoided.

Chronic glaucoma begins gradually over a period of months or years, usually in patients over the age of 40. There are no symptoms in the early stages, and the condition can be detected only by measurement of the intraocular pressure. Such an examination is recommended every three years for all persons over the age of 20. As the disease progresses, often the only symptom is a gradual loss of peripheral vision. Chronic glaucoma can usually be controlled with eye drops or pills that increase the outflow or decrease the production of aqueous humor; laser treatment is also effective in the early stages. If treatment is continued throughout life, useful vision will be preserved in most cases; untreated individuals will gradually become blind.

Acute closed-angle glaucoma, which accounts for only 10% of the incidence of the disease, begins abruptly with severe pain and blurred vision. It is a medical emergency that causes permanent blindness in two to five days if left untreated. Surgery is usually necessary.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"glaucoma." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"glaucoma." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/glaucoma

"glaucoma." The Columbia Encyclopedia, 6th ed.. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/glaucoma

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

glaucoma

glaucoma (glaw-koh-mă) n. a condition in which loss of vision occurs because of an abnormally high pressure in the eye. angle-closure (or acute) g. primary glaucoma in which there is a sudden rise in pressure due to blockage of the angle between the junction of the cornea and sclera and the margin of the iris, where aqueous humour usually drains from the eye. It is accompanied by pain and marked blurring of vision. open-angle (or chronic simple) g. a more common form of primary glaucoma in which the pressure increases gradually, usually without producing pain, and the visual loss is insidious. primary g. glaucoma that occurs without any other ocular disease. It is an important cause of blindness. secondary g. glaucoma that may occur when other ocular disease impairs the normal circulation of the aqueous humour and causes the intraocular pressure to rise.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"glaucoma." A Dictionary of Nursing. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"glaucoma." A Dictionary of Nursing. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/glaucoma

"glaucoma." A Dictionary of Nursing. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/glaucoma

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Glaucoma

GLAUCOMA

DEFINITION


Glaucoma is a disorder of the eye in which the optic nerve is damaged. The optic nerve carries light messages from the eye to the brain. Left untreated, glaucoma can result in loss of vision.

DESCRIPTION


Over two million people in the United States have glaucoma. About eighty thousand of these individuals are legally blind because of the disorder. Glaucoma is the leading cause of preventable blindness in the United States. The condition is about three times as common among African Americans as among whites. The risk for glaucoma increases rapidly with age, but the condition can affect any age group, including newborn infants and fetuses.

Glaucoma is actually a class of disorders. More than twenty different forms of the condition have been identified. They all develop in a similar way, however. The amount of aqueous (pronounced a-kwee-us) humor, a watery fluid that fills the inside of the eyeball, begins to build up. As more of this fluid collects, it places greater pressure on all parts of the eye, including the optic nerve. Eventually the excess pressure destroys the nerve.

The many forms of glaucoma are grouped into two large categories: open-angle glaucoma and closed-angle glaucoma. Open-angle glaucoma is a progressive disease. That is, it gets worse over time if not treated. At first, only a few nerve cells in the optic nerve are destroyed. Blind spots develop in areas where those nerve cells are located. Over time, more and more nerve cells are destroyed. A larger and larger area of vision is lost. Eventually, a person may lose his or her sight completely.

Closed-angle glaucoma happens very quickly. Some type of accident or change in the eye causes aqueous humor to build up very suddenly. The effects of glaucoma appear in a very short time.

CAUSES


Aqueous humor is produced by tissues in the front of the eyeball. Aqueous humor brings nourishment to the cornea and lens. It also maintains the proper pressure inside the eyeball. Proper pressure is necessary for the eyeball to maintain the correct shape. The amount of pressure produced by aqueous humor is called the intraocular ("inside the eye") pressure (IOP).

Aqueous humor drains out of the eyeball through a network of tiny tubes also located in the front of the eyeball. Glaucoma develops when the flow of aqueous humor is altered. In some cases, the fluid is produced too rapidly. In other cases, it is not removed from the eyeball fast enough. In either case, too much aqueous humor collects in the eyeball. The fluid causes pressure that pushes on blood vessels in the retina of the eye. The retina is a thin membrane at the back of the eyeball. It receives light rays that pass through the eyeball and transmits them to the optic nerve. Over time, excess pressure in the eye can damage cells in the retina and optic nerve. The cells die and the optic nerve is no longer able to carry messages to the brain. A person's vision is reduced.

SYMPTOMS


There are usually no noticeable symptoms of open-angle glaucoma. The loss of vision occurs very slowly, often over a period of years. If only one eye is affected, the other eye takes over the task of seeing for both eyes. The person with glaucoma does not realize that vision is being affected. Eventually, however, loss of vision becomes severe. The patient becomes aware that a problem exists. By this time, the glaucoma is more difficult to treat.

Glaucoma: Words to Know

Aqueous humor:
A watery fluid that fills the inside of the eyeball, providing nourishment to the eye and maintaining internal pressure in the eyeball.
Blind spot:
An area on the retina that is unable to respond to light rays.
Cornea:
The tough, transparent tissue that covers the front of the eyeball.
Intraocular pressure (IOP):
The amount of pressure caused by aqueous humor inside the eyeball.
Laser:
A device for producing very intense beams of light of a single color.
Optic nerve:
A nerve at the back of the eyeball that carries messages from the retina to the brain.
Retina:
A thin membrane at the back of the eyeball that receives light rays that pass through the eyeball and transmits them to the optic nerve.
Tonometer:
A device used to measure intraocular pressure in the eyeball.

The symptoms of closed-angle glaucoma are more obvious. A person may experience blurred vision, severe pain, sensitivity to light, and nausea. The cornea, the transparent tissue at the front of the eye, becomes cloudy. Closed-angle glaucoma is a medical emergency and requires immediate treatment.

DIAGNOSIS


Glaucoma is usually diagnosed during a routine visit to an eye specialist. Because of its mild symptoms, patients are less likely to visit a doctor about the condition.

The fastest test for glaucoma is a measurement of the IOP. The eye specialist first numbs the patient's eye with eye drops that have a yellow coloring. The pressure inside the eyeball is then measured with an instrument called a tonometer (pronounced toe-NAHM-etter). The test takes only a few seconds and provides a fast diagnosis of glaucoma.

If glaucoma is suspected, the eye specialist can then examine the back of the patient's eye for possible damage or changes. The specialist uses an ophthalmoscope (pronounced ahf-THAL-muh-skope) for this purpose. An ophthalmoscope is a device that shines light on the retina. The eye specialist is able to see if the retina and optic nerve are damaged in any way.

TREATING GLAUCOMA

An interesting footnote in the history of medicine is the role played by the study of the eye, ear, nose, and throat. These parts of the body are now regarded as important special fields of medicine. However, until the nineteenth century, they were not regarded as legitimate topics of medical study. They were left to "quacks." A quack is someone who treats human disease without having adequate medical preparation.

Thus, the first scientific discussion of glaucoma appeared around 1850. At that time, the German physician Albrecht von Graefe (17871840) described a surgical method for treating glaucoma.

He tells of operating on patient's whose vision was "perfectly restored in all cases."

At about the same time, drugs were being developed for treatment of the disorder. The first such drugs were actually discovered by Christian missionaries. The missionaries were introduced by native people to plants that had the effect of reducing the worst symptoms of glaucoma. Those plants were later found to contain a chemical known as physostigmine. Nearly a century later, the great black American chemist Percy Julian (18991975) discovered a way to make physostigmine synthetically in the laboratory. Physostigmine has now largely been replaced by other drugs for the treatment of glaucoma.

Visual tests can also be used to find blind spots in the patient's field of vision. The patient is asked to look at cards with various geometric patterns on them. Difficulty in seeing any one part of a pattern tells the eye specialist where a blind spot may be.

TREATMENT


Glaucoma may be treated with either medication or surgery. Medication is usually tried first. The drugs used are substances that reduce intraocular pressure. In general, they either decrease the rate at which aqueous humor is produced in the eye, or they increase the rate at which it is drained off. All of the medications used for glaucoma have side effects. Various individual drugs and combinations of drugs may have to be tried to see which works best for any one patient.

Some patients do not respond well to medication. In such cases, surgery may be necessary. The purpose of surgery is to open up the canals through which aqueous humor drains out of the eye. The surgery is often done with lasers.

Surgery is usually quite effective in solving glaucoma problems. However, its effects may not last very long. In many cases, surgery is required again in a year or less.

Alternative Treatment

Some vitamins and minerals are thought to reduce intraocular pressure. These include vitamins C and B1 (thiamine) and chromium and zinc.

Research suggests that marijuana reduces IOP. However, there is some dispute as to whether the drug should be used for this purpose. Researchers are currently weighing the advantages of using marijuana to relieve the symptoms of glaucoma against public concerns about the drug.

PROGNOSIS


About half of the people who develop glaucoma are not aware of their condition until fairly late in the course of the disorder. Many of these individuals will lose part or all of their vision. Vision loss caused by glaucoma cannot be repaired. Patients who are diagnosed with glaucoma usually respond to treatment. The prognosis for those individuals is very good.

PREVENTION


Researchers currently do not know the factors that cause glaucoma. As a result, there is no way to prevent the disorder. However, it is relatively easy to diagnose glaucoma in its early stages. The best preventive step is to have regular eye checkups. A normal part of those checkups is a tonometer test for glaucoma. Early detection of glaucoma can prevent the most serious consequences of the condition.

FOR MORE INFORMATION


Books

Marks, Edith, and Rita Montauredes. Coping with Glaucoma. Garden City Park, NY: Avery, 1997.

Trope, Graham E. A Patient's Guide to the Disease. Toronto: University of Toronto Press, 1997.

Organizations

American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 941207424. (415) 5618500. http://www.eyenet.org/aao_index.html.

Glaucoma Research Foundation. 490 Post Street, Suite 830, San Francisco, CA 94102. (415) 9863162; (800) 8266693. http://www.glaucoma.org.

Prevent Blindness America. 500 East Remington Rd., Schaumburg, IL 60173. (800) 3312020. http://www.prevent-blindness.org.

Web sites

"Ask NOAH About: The Eye." NOAH: New York Online Access to Health. [Online] http://www.noah.cuny.edu/eye/eye.html#G (accessed on October 20, 1999).

Titcomb, Lucy. "Treatment of Glaucoma." http://www.pharmacymag.co.uk/glau.htm (accessed on April 29, 1998).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Glaucoma." UXL Complete Health Resource. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"Glaucoma." UXL Complete Health Resource. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/medicine/news-wires-white-papers-and-books/glaucoma

"Glaucoma." UXL Complete Health Resource. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/medicine/news-wires-white-papers-and-books/glaucoma

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Glaucoma

Glaucoma

How Does Glaucoma Affect the Eye?

How Is Glaucoma Diagnosed?

Why Are Early Diagnosis and Treatment Important?

Resources

Glaucoma (glaw-KO-ma) is a group of disorders that cause fluid pressure to rise inside the eye, which may result in vision loss.

KEYWORDS

for searching the Internet and other reference sources

Ophthalmology

Vision

If a balloon is slowly filled with water, eventually it will burst. But if the same balloon has several pin-sized holes at one end, then it becomes possible to continue adding water to the balloon to maintain its round shape, without breaking the balloon, as long as the amount of water being added is equal to the amount escaping through the pinholes.

The eye has a similar system of liquid that continuously flows in and out of a small chamber at the front of the eyeball. The problem for people with glaucoma is that the drainage out of the eye is blocked or not working properly. It is similar to the balloon that is filling with water. Without a way to make room for more liquid, pressure builds up. Although a pressure buildup will not cause the eye to burst, it may damage nerves at the rear of the eyeball that carry images to the brain.

Glaucoma is one of the leading causes of blindness in the United States. It affects more than 3 million people, especially the elderly and people of African ancestry. The disease also is one of the sneakiest eye disorders. Pressure can grow in the eye for years before the effects on vision are noticed. By then, often the damage has been done.

How Does Glaucoma Affect the Eye?

The eye is about the same size as a ping-pong ball and is divided into two compartments. The larger compartment at the rear of the eye contains a gel-like substance called vitreous (VIT-re-us) humor, which helps to maintain the eyeballs shape and to transmit light. The front compartment, or anterior chamber, is smaller and is filled with a watery liquid called aqueous (AY-kwee-us) humor. This clear liquid brings in nutrients vital to the eyes health and carries out waste that can damage it.

The aqueous humor flows from behind the front colored portion of the eye, which is called the iris. It moves through the pupil, the opening in the center of the iris, into the front chamber of the eye. The liquid flows through the chamber and out a tiny drainage canal that has a fine, mesh-like covering. The small hole on the canal rests at an angle where the colored iris meets the cornea, the clear cup-shaped disc at the front of the eyeball.

About 90 to 95 percent of people with glaucoma have a problem with this drainage system. The cause is unknown, as there is no visible blockage. It appears that the cells in the mesh covering the drainage canal do not do their job properly, or lose their ability to allow proper drainage over time. Glaucoma develops gradually, but there is a rarer acute* form of glaucoma that develops suddenly when the iris closes off the drainage canal. This causes a painful medical emergency that requires immediate treatment.

* acute
means sudden, short, and severe.

The cause of most cases of glaucoma is not understood, although people of African ancestry, people who have diabetes or other family members with glaucoma, or those who have suffered eye injuries are at greater risk. Aging is another risk factor for glaucoma.

How Is Glaucoma Diagnosed?

Except for the rare cases of acute glaucoma that develop suddenly, most people do not realize they have glaucoma. As pressure is building in the eye, many of the millions of nerve cells at the rear of the eye are destroyed. The nerves that die first affect peripheral (pe-RIF-er-al) vision, or how well people see out of the sides of the eyes. When the loss of vision becomes severe enough for a person to notice, the damage is so great that little can be done.

The best way to diagnose glaucoma is through an eye exam that uses an instrument called a tonometer (to-NOM-e-ter) to measure the pressure in the eye. One type of tonometer registers eye pressure by lightly touching the eyes surface. Eyedrops are used to make this procedure painless. Another tonometer uses a puff of air to measure eye pressure. The doctor or eye specialist (ophthalmologist or optometrist) also may use a scope that shines light in the eye to look for damage to the optic nerve. Peripheral vision can be checked as part of the eye exam.

Why Are Early Diagnosis and Treatment Important?

Diagnosis

Early diagnosis of glaucoma is the key to preventing vision loss. If glaucoma is discovered before the increased eye pressure has destroyed many nerves, vision can be saved in many cases. Routine eye exams, including tests for glaucoma, are important, especially as adults pass age 35. Such eye exams are especially important for people at greatest risk for glaucoma, including people of African ancestry, people with relatives who have glaucoma, people with diabetes, and people with previous eye injuries.

No Mountain Too High

Glaucoma rarely occurs in young people, but Erik Weilenmayer was born with an eye disease that caused glaucoma. By age 13, he was totally blind. Erik did not let glaucoma prevent him from becoming a teacher and a mountain climber. He has scaled some of the toughest peaks, including Alaskas Mt. McKinley, the highest in the United States.

When I first went blind, I wondered what I could do, Weilenmayer said in 1998. Its really a kick to do extreme activities and do them welland no more dangerously than anyone else.

Eriks accomplishments are a reminder that physical challenges and differences do not have to prevent people from participating in lifes most difficult and demanding activities.

Treatment

The most common treatment involves eyedrops that reduce pressure. Sometimes surgery is necessary either to open the drainage canal or to create a new one.

See also

Blindness

Cataracts

Resources

Glaucoma Research Foundation, 200 Pine Street, Suite 200, San Francisco, CA 94104. The Glaucoma Research Foundation offers helpful publications about glaucoma, including Childhood Glaucoma: A Reference Guide for Families. Telephone 800-826-6693 http://www.glaucoma.org

The U.S. National Eye Institute posts a fact sheet about glaucoma at its website.http://www.nei.nih.gov/publications/glaucoma.htm

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Glaucoma." Complete Human Diseases and Conditions. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"Glaucoma." Complete Human Diseases and Conditions. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-0

"Glaucoma." Complete Human Diseases and Conditions. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

glaucoma

glau·co·ma / glôˈkōmə/ • n. Med. a condition of increased pressure within the eyeball, causing gradual loss of sight. DERIVATIVES: glau·co·ma·tous / -mətəs/ adj. ORIGIN: mid 17th cent.: via Latin from Greek glaukōma, based on glaukos ‘bluish-green, bluish-gray’ (because of the gray-green haze in the pupil).

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"glaucoma." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"glaucoma." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma-0

"glaucoma." The Oxford Pocket Dictionary of Current English. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

glaucoma

glaucoma Incurable condition in which pressure within the eye is increased due to an excess of aqueous humour, the fluid within the chamber. It occurs when normal drainage of fluid is interrupted, posing a threat to vision. Most frequently found in the over 40s, glaucoma is managed with drugs and surgery.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"glaucoma." World Encyclopedia. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"glaucoma." World Encyclopedia. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/glaucoma

"glaucoma." World Encyclopedia. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/glaucoma

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

glaucoma

glaucoma XVII. — L. — Gr. glaúkōma, f. glaukós; see next and -OMA.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"glaucoma." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"glaucoma." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma-1

"glaucoma." The Concise Oxford Dictionary of English Etymology. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma-1

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

glaucoma

glaucomadormer, former, korma, Norma, performer, pro-forma, stormer, transformer, trauma, warmer •sixth-former • barnstormer •aroma, carcinoma, chroma, coma, comber, diploma, glaucoma, Homer, lymphoma, melanoma, misnomer, Oklahoma, Omagh, roamer, Roma, romer, sarcoma, soma •beachcomber •bloomer, boomer, consumer, Duma, humour (US humor), Nkrumah, perfumer, puma, roomer, rumour (US rumor), satsuma, stumer, Sumer, tumour (US tumor) •zeugma • fulmar •bummer, comer, drummer, hummer, midsummer, mummer, plumber, rummer, strummer, summa, summer •latecomer • newcomer • agama •welcomer •astronomer, monomer •ashrama • isomer • gossamer •customer •affirmer, Burma, derma, Irma, murmur, squirmer, terra firma, wormer

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"glaucoma." Oxford Dictionary of Rhymes. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"glaucoma." Oxford Dictionary of Rhymes. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma

"glaucoma." Oxford Dictionary of Rhymes. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Glaucoma

Glaucoma

Definition

Glaucoma is a condition where the optic nerve is subject to damage—usually, but not always, because of excessively high intraocular pressure (pressure within the eye, also called IOP). If untreated, the optic nerve damage results in progressive, permanent vision loss, starting with unnoticeable blind spots in the field of vision, progressing to tunnel vision, and then to blindness.

Description

More than 2 million people in the United States have glaucoma, and 80,000 of them are legally blind as a result. It is the leading cause of preventable blindness in the United States and the most frequent cause of blindness in African-Americans, whose glaucoma risk is three times higher than the rest of the population. The risk of glaucoma increases with age, but it can strike any age group, even newborns and fetuses.

Glaucoma is a class of diseases. There are at least 20 different forms that can be divided into two categories: open-angle glaucoma and narrow-angle glaucoma. To understand glaucoma, it is useful to understand eye structure.

The eyes are spherical. A tough, non-leaky protective sheath (the sclera) covers the eye with the exception of the clear cornea at the front and the optic nerve at the back. Light comes into the eye through the cornea, then passes through the lens, which focuses it onto the retina (the innermost surface at the back of the eye). The rods and cones of the retina transform the light energy into electrical messages, which are transmitted to the brain by the optic nerve.

The iris is located between the dome-shaped cornea and the lens. It controls the amount of light that enters the eye by opening and closing the pupil. The iris, cornea, and lens are bathed in a liquid called the aqueous humor, which is similar to plasma. This liquid is continually produced by the nearby ciliary body and moved out of the eye into the bloodstream by a system of drainage canals (the trabecular meshwork). The drainage area is located in front of the iris, in the angle formed between the iris and the cornea.

Glaucoma occurs if the aqueous humor is not removed rapidly enough or if it is made too rapidly, causing pressure to build up. This high pressure distorts the shape of the optic nerve and destroys nerve cells. The destruction of nerve cells results in blind spots—spots where the image from the retina is not transmitted to the brain.

Open-angle glaucoma accounts for over 90% of all cases. It is called "open-angle" because the angle between the iris and the cornea is open, allowing drainage of the aqueous humor. It is usually chronic and progresses slowly. In narrow-angle glaucoma, the angle where aqueous fluid drainage occurs is narrower than normal, thus causing the fluid to drain more slowly and increasing the risk that the flow may be blocked. When the drainage area is blocked, a closed-angle glaucoma attack results. This can occur, for example, if the iris and lens suddenly adhere to each other and the iris is pushed forward. In patients with very narrow angles, this can occur when the eyes dilate (e.g., when entering a dark room or when taking certain medications).

One rare form of open-angle glaucoma is different. People with normal-tension glaucoma have optic nerve damage in the presence of normal IOP. The mechanism of this disease is unknown.

Glaucoma is also a secondary condition of over 60 widely diverse diseases and can result from injury as well.

Causes and symptoms

The cause of vision loss in all forms of glaucoma is optic nerve damage. There are many underlying causes and forms of glaucoma. Most causes are not known, but it is evident that different processes are involved, and a malfunction in any one of them could cause glaucoma. For example, eye trauma may result in the angle becoming blocked, or, as a person ages, the lens may become larger and push the iris forward. The cause of optic nerve damage in normal-tension glaucoma is also unknown, but there is speculation that the optic nerves of these patients are susceptible to damage at lower pressures than what is usually considered to be abnormally high. It is probable that most glaucoma is inherited. At least 10 defective genes that cause glaucoma have been identified.

Initially, chronic open-angle glaucoma has no noticeable symptoms. The pressure build-up is gradual and there is no discomfort. Moreover, the vision loss is gradual and one eye fills-in the image where its partner has a blind spot. However, left untreated, vision loss becomes evident, and the condition can be painful.

Acute closed-angle glaucoma is obvious from the beginning of an attack. The symptoms are blurred vision, severe pain, sensitivity to light, nausea, and halos around lights. The normally clear cornea may be hazy. This is an ocular emergency and needs to be treated immediately. Similarly, congenital glaucoma is evident at birth. Symptoms include bulging eyes, cloudy corneas, excessive tearing, and sensitivity to light.

Diagnosis

The initial glaucoma diagnosis is made through an eye examination by an optometrist (O.D.) or ophthalmologist (M.D.). The examination begins with an ophthalmic assistant, technician, or scribe gathering patient information, including any family history of glaucoma. Then the ophthalmic assistant takes a reading of the patient's intraocular pressure (IOP). IOP is measured with an instrument called a tonometer, using a technique called applanation tonometry. The test is performed after anesthetic drops are administered to the eye. The anesthetic allows the examiner to touch the patient's eyeball without causing discomfort for the patient. Another type of tonometry called noncontact applanation shoots a puff of air into the patient's eye. This is slightly less accurate than applanation tonometry.

Next, an O.D., M.D., or skilled ophthalmic assistant uses an ophthalmoscope (a hand-held instrument with a light source) to examine the optic nerve, retina, and back of the eye. Other types of lenses may also be used to examine the back of the eye. A slit lamp (biomicroscope) allows the physician or assistant examine the cornea, iris, and lens.

Visual field tests (perimetry), performed by an O.D., M.D., or ophthalmic assistant, can detect blind spots in a patient's field of vision before the patient is aware of them. Certain defects may indicate glaucoma.

Another test, gonioscopy, is used to distinguish between narrow-angle and open-angle glaucoma. A gonioscopy lens, which is a hand-held contact lens with a mirror, allows visualization of the angle between the iris and the cornea.

Physicians may also perform a nerve fiber layer assessment which can show early damage to the eye. Fundus photography or stereoscopic photography through a dilated pupil may also be performed by an O.D., M.D., or ophthalmic assistant to document the appearance of the optic nerve so that changes may be detected on subsequent examinations.

Blood pressure also is monitored, as some prescribed treatments may raise pressure and heart rate.

Intraocular pressure can vary throughout the day. For that reason, patients should schedule several return visits to measure the IOP at different times of day. This yields the most accurate diagnosis.

Treatment

The first line of glaucoma treatment is the use of prescription eyedrops. Several classes of medications are effective at lowering IOP and thus preventing optic nerve damage in chronic and neonatal glaucoma. Beta blockers (e.g., timolol), carbonic anhydrase inhibitors (e.g., acetazolamide), and alpha-2 agonists (e.g., brimonidine tartrate) inhibit aqueous humor production. Miotics (e.g., pilocarpine) and prostaglandin analogues (e.g., latanoprost) increase the outflow of aqueous humor.

It is important for patients to inform their doctors of any health conditions they have or any medications they take, including over-the counter drugs. Certain drugs used to treat glaucoma are not prescribed for patients with pre-existing conditions. The drugs prescribed to treat glaucoma all have side effects, so patients taking them should be monitored closely, especially for cardiovascular, pulmonary, and behavioral symptoms. Each medication lowers IOP by a different amount, and a combination of medications may be necessary. To ensure that IOP is lowered sufficiently, it is important that patients take their medications and be monitored regularly. IOP should be measured three to four times per year.

Normal-tension glaucoma is treated by reducing IOP to less-than-normal levels, on the theory that overly susceptible optic nerves are less likely to be damaged at lower pressures. Research underway may point to better treatments for this form of glaucoma.

Attacks of acute closed-angle glaucoma are medical emergencies. IOP is rapidly lowered by successive deployment of acetazolamide, hyperosmotic agents, a topical beta-blocker, and pilocarpine. Epinephrine should not be used because it exacerbates angle closure.

Trabeculectomy, to open the drainage canals or make an opening in the iris, can be effective in increasing the outflow of aqueous humor. This surgery is usually successful, but the effects often last less than one year. Nevertheless, this is an effective treatment for patients whose IOP is not sufficiently lowered by drugs and for those who can't tolerate the drugs.

Laser peripheral iridotomy is a procedure used almost exclusively to treat narrow angle glaucoma. It involves creating a small opening in the peripherial iris that allows aqueous fluid to drain from behind the iris directly to the anterior chamber. This procedure typically result in "opening up" the narrow angle between the iris and the cornea, in essence converting a narrow angle into an open angle.

Argon laser trabeculoplasty is usually recommended when medications have not been able to sufficiently control IOP, although it is increasingly advocated as primary therapy for patients who are not good candidates for the use of glaucoma medications or who cannot use eyedrops. In this procedure, the beam of an argon laser is directed at the trabecular meshwork. Typically about 180 of the trabecular meshwork is treated with laser spots. As a result of this procedure, the drainage of aqueous fluid out of the eye increases, thus lowering IOP.

Gene therapy may also be part of future treatments. A mutation in the gene myocilin is believed to cause most cases of juvenile glaucoma, and 3-4% of adult glaucoma. Researchers are investigating drugs that inhibit myocilin production. The drug therapy would not just treat IOP, but also could be used before glaucoma's onset.

Vitamin C, vitamin B1 (thiamine ), chromium, zinc, and rutin may reduce IOP.

Patients using alternative methods to attempt to prevent optic nerve damage should be advised they also need the care of a traditionally trained ophthalmologist or optometrist who is licensed to treat glaucoma, so that IOP and optic nerve damage can be monitored.

Prognosis

About half of the people who have glaucoma are not aware of it. For them, the prognosis is not good, and many of them will become blind. On the other hand, the prognosis for treated glaucoma is excellent.

Health care team roles

Nursing and allied health professionals play an important part in the diagnosis and treatment of glaucoma. Skilled ophthalmic technicians and assistants record the patient history and perform many of the preliminary tests. Depending on skill level, these ophthalmic assistants may perform measurement of visual acuity under both low and high illumination, assessment of ocular motility and binocularity, visual fields, measurement of IOPs with tonometers, evaluation of pupillary responses, and refraction.

Before surgical procedures, nurses and assistants also prepare the operating room (OR). Many ophthalmologists now have their own ambulatory surgery centers where skilled technicians and ophthalmic nurses play a critical role in preparing the OR and patients for the surgery. Ophthalmic nurses also assist the ophthalmologists during surgery and discuss outcomes with patients post-operatively.

Nurses and assistants assist patients by explaining the sometimes difficult regimen of glaucoma medication. In some cases, patients require several doses of a combination of medications. Ophthalmic nurses and assistants show patients the correct technique for inserting eyedrops, and reinforce the physician's instructions for medication compliance.

Patient education

Ophthalmic assistants and nurses help to ensure that patients return to the physician's office in a timely manner so that IOPs can be monitored. Nurses and assistants also emphasize the importance of adhering to the eyedrop schedule to keep IOPs at a lower level, and answer any questions concerning proper eyedrop instillation.

Prevention

Because glaucoma may not initially cause symptoms, the best form of prevention is to have regular eye exams.

Patients with narrow angles should avoid certain medications (including some over-the-counter medications, such as some cold or allergy medications). Patients who are glaucoma-susceptible (i.e., have narrow angles and borderline IOPs) should be advised to read the warning labels on over-the-counter medicines and inform physicians of products they are considering taking. Steroids may also raise IOP, so patients may need to be monitored more frequently if it is necessary for them to use steroids.

Not enough is known about the underlying mechanisms of glaucoma to prevent the disease itself. However, prevention of optic nerve damage from glaucoma is essential and can be accomplished when glaucoma is diagnosed and treated. As more is learned about the genes that cause glaucoma, it may become possible to test DNA and identify potential glaucoma victims, so they can be treated before IOPs become elevated.

KEY TERMS

Agonist— A drug that mimics one of the body's own molecules.

Alpha-2 agonist (alpha-2 adrenergic receptor agonist)— A class of drugs that binds to and stimulates alpha-2 adrenergic receptors, causing responses similar to those of adrenaline and noradrenaline. They inhibit aqueous humor production and have a wide variety of side effects, including dry mouth, fatigue, and drowsiness.

Aqueous humor— A transparent liquid, contained in the anterior chamber (between the cornea and lens) of the eye, that is composed of water, sugars, vitamins, proteins, and other nutrients.

Beta blocker (beta-adrenergic blocker)— A class of drugs that binds to beta-adrenergic receptors and thereby decreases the ability of the body's own natural epinephrine to bind to those receptors, leading to inhibition of various processes in the body's sympathetic system. Beta blockers can slow the heart rate, constrict airways in the lungs, lower blood pressure, and reduce aqueous secretion by ciliary tissues in the eye.

Carbonic anhydrase inhibitor— A class of diuretic drugs that inhibits the enzyme carbonic anhydrase, an enzyme involved in producing bicarbonate, which is required for aqueous humor production by the ciliary tissues in the eye. Thus, inhibitors of this enzyme decrease aqueous humor production. Some side effects of these drugs are urinary frequency, kidney stones, loss of the sense of taste, depression, and anemia.

Cornea— Clear, bowl-shaped structure at the front of the eye. It is located in front of the colored part of the eye (iris). The cornea lets light into the eye and partially focuses it.

Gonioscope— An instrument used to examine the trabecular meshwork. It consists of a magnifier and a lens equipped with mirrors, which sits on the patient's cornea.

Hyperosmotic drugs— A class of drugs for glaucoma that increases the osmotic pressure in the blood, which then pulls water from the eye into the blood.

Iris— The colored part of the eye just behind the cornea and in front of the lens that controls the amount of light sent to the retina.

Lens (the crystalline lens)— A transparent structure in the eye that focuses light onto the retina.

Miotic— A drug that causes pupils to contract.

Ophthalmoscope— An instrument, with special lighting, designed to view structures in the back of the eye.

Optic nerve— The nerve that carries visual messages from the retina to the brain.

Prostaglandin— A group of molecules that exerts local effects on a variety of processes including fluid balance, blood flow, and gastrointestinal function.

Prostaglandin analogue— A class of drugs that are similar in structure and function to prostaglandin.

Retina— The inner, light-sensitive layer of the eye containing rods and cones.

Sclera— The tough, fibrous, white outer protective covering that surrounds the eye.

Tonometry— The measurement of pressure.

Trabecular meshwork— A sponge-like tissue located near the cornea and iris that functions to drain the aqueous humor from the eye into the blood.

Resources

BOOKS

Epstein, David L., R. Rand Allingham, and Joel S. Schuman. Chandler and Grant's Glaucoma. 4th ed. Baltimore: Williams & Wilkins, 1997.

Marks, Edith, and Rita Montauredes. Coping with Glaucoma. Garden City Park, NY: Avery, 1997.

ORGANIZATIONS

American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. 〈http://www.eyenet.org〉.

American Glaucoma Society. P.O. Box 193940, San Francisco, CA 94119-3940. (415) 561-8587. Fax: (415) 561-8531. 〈http://www.glaucomaweb.org〉.

Glaucoma Research Foundation. 490 Post Street, Suite 830, San Francisco, CA 94102. (415) 986-3162. (800) 826-6693. [email protected] 〈http://www.glaucoma.org/〉.

National Eye Institute. 2020 Vision Place, Bethesda, MD 20892-3655. (301) 496-5248. 〈http://www.nei.nih.gov〉.

Prevent Blindness America. 500 East Remington Road, Schaumburg, IL 60173. (800) 331-2020. 〈http://www.prevent-blindness.org〉.

OTHER

"FDA Approves Two New Intraocular Pressure Lowering Drugs for the Management of Glaucoma." FDA Online. 〈http://www.fda.gov/bbs/topics/NEWS/2001/NEW00757.html〉.

Helzner, Jerry. "You Can Provide Cost-Effective Glaucoma Care." Ophthalmology Management Online. 〈http://www.ophmanagement.com/archive_results.asp?loc=archive/2001/april/0401067.htm〉.

"Optometric Clinical Practice Guideline: Care of the Patient with Open Angle Glaucoma." American Optometric Association Online. 〈http://www.aoa.org/×815.xml〉 (〈http://www.aou.org/documents/CPG-9.pdf〉).

Titcomb, Lucy C. "Treatment of Glaucoma." 〈http://www.pjonline.com/Editorial/19990828/education/glaucoma.html〉. Also in Pharmaceutical Journal 263, no. 7060 (August 28, 1999): 324-29.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Glaucoma." Gale Encyclopedia of Nursing and Allied Health. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"Glaucoma." Gale Encyclopedia of Nursing and Allied Health. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-2

"Glaucoma." Gale Encyclopedia of Nursing and Allied Health. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-2

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Glaucoma

Glaucoma

Definition

Glaucoma is a group of eye diseases that damage the optic nerve and gradually cause vision loss.

Description

The optic nerve, located at the back of the eye, consists of more than a million of nerve fibers that carry images from the retina to the brain. Glaucoma damages optic nerve fibers, with the result that blind spots develop in the visual field. If the entire nerve is destroyed, blindness results.

There are five types of glaucoma that all share as a common feature the damage that they inflict to the optic nerve:

  • Primary open angle glaucoma (POAG). With POAG, the drainage canals of the eye become clogged over time. The inner eye pressure, also called intraocular pressure (IOP), increases because the correct amount of fluid cannot drain out of the eye. The entrances to the drainage canals are clear and the clogging occurs further inside the drainage canals. This type of glaucoma develops gradually over time and sometimes without apparent sight loss for many years.
  • Closed angle glaucoma (CAG). CAG rarely occurs and is very different from POAG because the eye pressure usually increases very quickly due to clogged drainage canals. With CAG, the iris does not open as wide as it should. The outer edge of the iris bunches up over the drainage canals when the pupil enlarges too much or too quickly.
    Prevalence of open-angle glaucoma among adults 40 years and older in the United States
     Glaucoma
    Years Persons (%)
    source: Adapted from Archives of Ophthalmology, Vol. 122,
    April 2004
    (Illustration by GGS Information Services. Cengage Learning, Gale.)
    40–49290,0000.7%
    50–59318,0001.0%
    60–69369,0001.8%
    70–79530,0003.9%
    ≥80711,0007.7%
    Total 2,218,000 1.9%
  • Normal tension glaucoma (NTG). In NTG, the optic nerve is damaged even though the IOP is often in the normal range.
  • Secondary glaucoma. This type of glaucoma can result from an eye injury, inflammation, tumor, or occur in advanced cases of cataract or diabetes. It can also be caused by drugs such as steroids.
  • Pediatric glaucoma. This type of glaucoma includes glaucoma present at birth (congenital glaucoma), glaucoma that appears during the first three years (infantile glaucoma), or between age three and ten or young adult years (juvenile glaucoma), as well as all the secondary glaucomas occurring in these age groups.

Demographics

It is estimated that there are 60 million people with glaucoma worldwide with six million people becoming blind in both eyes as a result. According to the National Eye Institute (NEI), 50 million Americans are at risk for vision loss from glaucoma, a leading cause of blindness in the United States. People over the age of 60 are at increased risk for glaucoma, particularly Mexican Americans. Other groups at increased risk include African Americans over the age of 40 and people with a family history of glaucoma. In a study sponsored by the National Eye Institute (NEI), researchers at the Johns Hopkins University reported that glaucoma is three to four times more likely to occur in African Americans than in Whites. Glaucoma is also six times more likely to cause blindness in African Americans than in Whites. POAG is the most common form of glaucoma, affecting about three million Americans.

Causes and symptoms

The inner pressure of a healthy eye usually ranges from 12ȓ22 mm Hg. An OIP in this range is important for the eye to hold its shape and function properly. This optimal pressure is maintained by the fluids of the eye, of which there are two types. The first is the vitreous, the colorless gelatinous mass that fills the rear two-thirds of the eyeball between the lens and the retina. The second is the aqueous humor, the clear, watery fluid in the front of the eyeball. Aqueous humor is continuously produced before draining out of the eye. It nourishes the lens and the cornea while removing unwanted matter. In a healthy eye, aqueous humor is generated at the same rate as the eye drains fluid, and a normal OIP is maintained. The eye drains aqueous humor through a meshwork system (trabecular meshwork) located at the angle formed where the iris and the cornea meet, from which it passes into the bloodstream through a channel called “Schlemm's canal.” In people with glaucoma, the eye drainage mechanism becomes clogged, preventing the discharge of aqueous humor which then builds up, thus increasing the OIP.

Although glaucoma tends to run in families, a hereditary basis has not been firmly established. Some people are born with the iris too close to the drainage angle. In such eyes, the iris can be aspired into the drainage angle and block it completely. Since the fluid cannot exit the eye, pressure inside the eye builds up and causes glaucoma.

Most glaucoma cases do not have any symptoms. Half of all people with loss of vision resulting from glaucoma are not aware that they have glaucoma. By the time the condition is diagnosed, the eye damage is often severe. In some rare cases, a person can have an acute attack of glaucoma, where the eye becomes red and very painful. Nausea, vomiting and blurred vision may also occur.

Typically, POAG has no symptoms in its early stages, and vision remains normal. Symptoms of CAG may include headaches , eye pain , nausea, rainbows around lights at night, and very blurred vision.

Diagnosis

Tests commonly used to establish diagnosis may include:

  • Tonometry. A test using an instrument to measure the intraocular pressure. Drops are used to numb the eye and a special device is used to measure the eye's inner pressure.
  • Ophthalmoscopy. Examination of the inside of the eye, especially the optic nerve, using a lighted instrument called an ophthalmoscope.
  • Visual field test (Perimetry). During this test, the patient is asked to look straight ahead and indicate when a moving light passes the peripheral vision. The result is a map of the vision.
  • Dilated eye exam. In this test, drops are placed in the eyes to dilate the pupils. A magnifying lens is then used to examine the retina and optic nerve for signs of damage and other eye problems.
  • Gonioscopy. This test checks if the angle where the iris meets the cornea is open or closed, showing if either open angle or closed angle glaucoma is present.
  • Scanning laser polarimetry (GDx). This test measures the thickness of the nerve fiber layer on the retinal surface just before the fibers pass over the optic nerve margin to form the optic nerve.
  • Confocal laser ophthalmoscopy (Heidelberg Retinal Tomography or HRT II). This test scans the retinal surface and optic nerve with a laser to build a 3D image of the optic nerve including a contour outline of the optic cup. The nerve fiber layer thickness is also measured.
  • Optical coherence tomography (OCT). This technique creates images using special light beams to obtain a contour map of the optic nerve, optic cup, and measure the retinal nerve fiber thickness.

QUESTIONS TO ASK YOUR DOCTOR

  • How is glaucoma treated?
  • How do I know if surgery is right for me?
  • Is glaucoma surgery effective?
  • Are there different types of glaucoma surgery?
  • What are the risks of surgery?
  • Can problems develop after surgery?
  • What can I do to prevent deterioration of my vision?

Increased eye pressure is indicative of increased risk for glaucoma, but does not establish diagnosis, because a person only has glaucoma if the optic nerve is damaged. A measurement of eye pressure by tonometry is therefore not sufficient to detect glaucoma. Glaucoma is detected most often during an eye examination through a dilated eye exam. If tonometry reveals that the pressure in the eye is not in the normal range, and if the dilated eye exam shows that the optic nerve looks unusual, then perimetry, gonioscopy, GDx, HRT II or OCT tests can be performed to confirm diagnosis.

Treatment

There is no cure for glaucoma, but it can usually be controlled by eyedrops or pills, conventional surgery, or laser surgery. Eye care practitioners often recommend a combination of surgery and medication. The appropriate treatment depends upon the type of glaucoma diagnosed.

Nutrition/Dietetic concerns

According to the Glaucoma Research Foundation, the carotenoids lutein and zeaxanthin, the only carotenoids found in the eye and which are also antioxidants , may protect against cataracts and glaucoma. They are found in foods such as spinach, parsley, celery, broccoli, lettuce, green peas, pumpkin, Brussel sprouts, corn, green peppers, cucumbers and green olives.

Therapy

A number of medications can be prescribed to treat glaucoma. Typically, medications are intended to decrease the amount of fluid forming in the eye so as to reduce elevated IOP and prevent damage to the optic nerve.

Surgery is carried out to lower pressure when medications are not effective; however surgical approaches cannot reverse vision loss. Common procedures involve either laser treatment or making a cut in the eye to reduce the IOP. The type of surgery performed depends on the type and severity of the glaucoma and the general health of the eye. One option is laser surgery. In this type of operation, a tiny beam of light is used to make several small scars in the eye's trabecular meshwork. The scars then help increase the flow of fluid out of the eye. Another option is filtering microsurgery, which involves creating a drainage hole. The procedure is usually performed when laser surgery does not successfully lower eye pressure, or if it starts increasing again.

Prognosis

Vision loss from glaucoma is permanent. However, with early detection and treatment, the progression of visual loss can be slowed, or stopped, which lowers the risk of blindness. POAG usually responds well to medication, especially if caught early and treated.

Prevention

Early detection is vital to stopping the progress of glaucoma. Prompt treatment of glaucoma can prevent damage to the eye's nerve cells and prevent vision loss. Regular and comprehensive eye exams are recommended every two to four years after age 40, and every one to two years after age 64.

Caregiver concerns

Glaucoma blindness is expected to increase because of the increasing aging population. However, awareness about glaucoma in this age group is still lacking. Visual impairment by glaucoma amongst the elderly is also underrecognized because the elderly are not part of the active workforce. They also tend to be more reclusive, resigned to their condition, and with a tendency to delay seeking treatment.

KEY TERMS

Antioxidant —Any substance that reduces damage due to reactive oxygen such as that caused by free radicals.

Aqueous humor —The clear, watery fluid in the front of the eyeball.

Carotenoids —Red to yellow pigments responsible for the characteristic colour of many plant organs or fruits, such as tomatoes, carrots, etc.

Cornea —Transparent front part of the eye that covers the iris, pupil, and anterior chamber and provides most of an eye's optical power.

Intraocular pressure (IOP) —The inner pressure of the eye. Normal intraocular pressure usually ranges from 12–22 mm Hg, although people with relatively low pressures can still have glaucoma.

Iris —Pigmented tissue lying behind the cornea that gives color to the eye and controls amount of light entering the eye by varying the size of the pupil.

Lens —Transparent, biconvex crystalline tissue that helps bring rays of light to a focus on the retina.

Peripheral vision —The seeing of objects displaced from the primary line of site and outside of the central visual field.

Pupil —Variable—sized black circular opening in the center of the iris that regulates the amount of light that enters the eye.

Retina —Light—sensitive tissue at the back of the eye.

Trabecular meshwork —The series of canals or tubes behind the iris that filters the aqueous humor and allows it to drain into the bloodstream.

Vitreous —Transparent, colorless gelatinous mass that fills the rear two—thirds of the eyeball, between the lens and the retina.

Resources

BOOKS

Gupta, Deepack. Glaucoma Diagnosis and Management. Philadelphia, PA: Lippincott Williams & Wilkins, 2004.

Galloway, Nicholas R. Common Eye Diseases and their Management. 3rd ed., New York, NY: Springer, 2005.

Harmon, Gregory K., and Nancy Intrator. What Your Doctor May Not Tell You About Glaucoma: The Essential Treatments and Advances That Could Save Your Sight. Lebanon, IN: Grand Central Publishing, 2004.

Mayo Clinic. Mayo Clinic On Vision And Eye Health: Practical Answers on Glaucoma, Cataracts, Macular Degeneration & Other Conditions. Scottsdale, AZ: Mayo Clinic Trade Paper, 2002.

Netland, Peter, editor. Glaucoma Medical Therapy: Principles and Management. Oxford, UK: Oxford University Press, 2007.

Trope, Graham E. Glaucoma: A Patient's Guide to the Disease. Toronto, ON: University of Toronto Press, 2004.

PERIODICALS

de Voogd, S., et al. “Incidence of open-angle glaucoma in a general elderly population: the Rotterdam Study.” Ophthalmology 112, no. 9 (September 2005):1487–1493.

Gupta, N., and Y. H. Yücel. “What changes can we expect in the brain of glaucoma patients?” Survey of Ophthalmology 52, suppl. 2 (November 2007): S122–S126.

Kanner, E., and J. C. Tsai. “Glaucoma medications: use and safety in the elderly population.” Drugs and Aging 23, no. 4 (2006): 321–332.

OTHER

Cyclophotocoagulation. Foundation of the American Academy of Ophthalmology, Information Page. (March 08, 2008) http://www.eyecareamerica.org/eyecare/treatment/cyclophotocoagulation/index.cfm.

Glaucoma. American Academy of Family Physicians, Patient Information Page (March 08, 2008) http://familydoctor.org/online/famdocen/home/seniors/common-older/216.printerview.html.

Glaucoma. Foundation of the American Academy of Ophthalmology, Information Page. (March 08, 2008) http://www.eyecareamerica.org/eyecare/conditions/glaucoma/index.cfm.

Glaucoma. Mayo Foundation for Medical Education and Research, Fact Sheet (March 08, 2008) http://www.mayoclinic.com/print/glaucoma/DS00283/DSECTION=all&METHOD=print.

Glaucoma. National Eye Institute, Information Page (March 08, 2008) http://www.nei.nih.gov/health/glaucoma.

ORGANIZATIONS

American Academy of Ophthalmology (AAO), P.O. Box 7424, San Francisco, CA, 94120-7424, (415) 561-8500, (415) 561-8500, [email protected], http://www.aao.org.

EyeCare America, 655 Beach St., San Francisco, CA, 94109 1336, (877) 887-6327, (800) 222-3937, http://www.eyecareamerica.org/eyecare.

Glaucoma Foundation, 80 Maiden Lane, Suite 700, New York, NY, 10038, (212) 285-0080, [email protected], http://www.glaucomafoundation.org.

National Eye Institute, 2020 Vision Place, Bethesda, MD, 20892-3655, (301) 496-5248, [email protected], http://www.nei.nih.gov.

Monique Laberge Ph.D.

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Glaucoma." The Gale Encyclopedia of Senior Health: A Guide for Seniors and Their Caregivers. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"Glaucoma." The Gale Encyclopedia of Senior Health: A Guide for Seniors and Their Caregivers. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/caregiving/encyclopedias-almanacs-transcripts-and-maps/glaucoma

"Glaucoma." The Gale Encyclopedia of Senior Health: A Guide for Seniors and Their Caregivers. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/caregiving/encyclopedias-almanacs-transcripts-and-maps/glaucoma

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Glaucoma

Glaucoma

Definition

Glaucoma is a group of eye disorders that results in vision loss due to a failure to maintain the normal fluid balance within the eye. If detected in its early stages, vision loss can be prevented through the use of medications or surgical procedures that restore the proper fluid drainage of the eye.

Description

Vision is an important and complex special sense by which the qualities of an object, such as color, shape, and size, are perceived through the detection of light. Light that bounces off an object first passes through the cornea (outer layer) of the eye and then through the pupil and the lens to project onto a layer of cells on the back of the eye called the retina. When the retina is stimulated by light, signals pass through the optic nerve to the brain, resulting in a visual image of an object.

The front chamber of the eye is bathed in a liquid called the aqueous humor. This liquid is produced by a nearby structure called the ciliary body and is moved out of the eye into the bloodstream by a system of drainage canals known as the trabecular meshwork. The proper amount of fluid within the chamber is maintained by a balance between fluid production by the ciliary body and fluid drainage through the trabecular meshwork. When fluid accumulates in the front chamber, either because of an overproduction of fluid or because of a failure of the normal drainage routes, fluid pressure builds up within the eye. Over time, this increased fluid pressure causes damage to the optic nerve, resulting in progressive visual impairment. The condition of increased eye fluid pressure leading to vision loss is known as glaucoma.

Glaucoma is actually a group of many different eye disorders and can manifest alone or as a sign of over 60 different diseases, or even in a healthy person who has experienced an injury to the eye. Physicians classify glaucoma by the type of abnormality in the drainage system. When the drainage passage is narrowed, but still open, it is termed open-angle glaucoma. If the drainage passage is completely blocked, it is termed closed-angle glaucoma. Glaucoma can also be classified by the age of the affected individual: infantile or congenital glaucoma affects infants at birth or children up to three years old, juvenile glaucoma affects individuals from three to 30 years old, and adult glaucoma affects people greater than 30 years old.

Genetic profile

As stated above, there are different forms of glaucoma that either occur alone or as the result of a genetic syndrome. In some cases, specific genetic abnormalities have been identified, while in other forms, the cause is unknown. The known types of glaucoma and the corresponding genetic defect are described in the table below. Many forms of glaucoma are not inherited and thus, are not represented in the table.

As illustrated in the table, glaucoma can be inherited in either an autosomal recessive or an autosomal dominant fashion. In autosomal recessive inheritance , two abnormal genes are needed to display the disease. A person who carries one abnormal gene does not display the disease and is called a carrier. A carrier has a 50% chance of transmitting the gene to a child, who must inherit one abnormal gene from each parent to display the disease. Alternatively, in autosomal dominant inheritance, only one abnormal gene is needed to display the disease, and the chance of passing the gene and the disease to offspring is 50%.

Demographics

Glaucoma is the leading cause of preventable blindness in the United States, affecting more than two million Americans, and is the third leading cause of blindness worldwide. The prevalence of glaucoma increases with age, but the eye condition can also be present in infants and young children. The adult types of open-angle glaucoma account for the majority (70%) of glaucoma cases, while the infantile and juvenile types of glaucoma are relatively uncommon.

The types and rates of glaucoma are not distributed equally among different ethnic groups. For example, the prevalence of glaucoma in Caucasians over 70 years old is 3.5%, while the prevalence in African-Americans is 12%. Also, the primary closed-angle type of glaucoma is much more common in people of Asian or Inuit descent. Apart from ethnicity, risk factors for the development of glaucoma include elevated eye pressure, increasing age, diabetes, and presence of glaucoma in a family member.

Signs and symptoms

In the adult and juvenile forms of open-angle glaucoma, vision loss begins at the periphery (outer edges) of the visual field, resulting in tunnel vision. Because the visual loss in not in the individual's central vision, they may not notice this change. However, if the glaucoma is left untreated, loss of vision progresses and the central vision is often affected, sometimes resulting in blindness. The average time from development of high eye fluid pressures to the appearance of visual loss is 18 years in the adult form, but much shorter in the juvenile form.

In contrast to the adult and juvenile forms, congenital or infantile open-angle glaucoma is noted at birth or

Types of glaucoma and related genetic information
Disorder Alternative names Inheritance Abnormal protein Abnormal gene Gene location
Glaucoma 1, open angle, A (GLC1A) Juvenile onset primary open-angle glaucoma; Hereditary juvenile glaucoma Autosomal dominant Trabecular meshwork-induced glucocorticoid response protein (myocilin) MYOC, (also known as TIGR, GLC1A, JOAG, GPOA) 1q24.3–q25.2;
      Unknown Unknown 9q34.1
Glaucoma 1, open angle, B (GLC1B) Adult onset primary open-angle glaucoma; Hereditary adult glaucoma Autosomal dominant Unknown Unknown 2qcen–q13; (additional loci under investigation)
Glaucoma 1, open angle, C (GLC1C) Adult onset primary open-angle glaucoma; Hereditary adult glaucoma Autosomal dominant Unknown Unknown 3q21–q24
Glaucoma 1, open angle, D (GLC1D) Adult onset primary open-angle glaucoma; Hereditary adult glaucoma Autosomal dominant Unknown Unknown 8q23
Glaucoma 1, open angle, E (GLC1E) Adult onset primary open-angle glaucoma; Hereditary adult glaucoma Autosomal dominant Unknown Unknown 10p15–p14
Glaucoma 1, open angle, F (GLC1F) Adult onset primary open-angle glaucoma; Hereditary adult glaucoma Autosomal dominant Unknown Unknown 7q35–36
Glaucoma 3, primary infantile, A (GLC3A) Congenital glaucoma; Buphthalmos Autosomal recessive Cytochrome P4501B1 CYP1B1 2p22–p21
Glaucoma 3, primary infantile, B (GLC3B) Congenital glaucoma Autosomal recessive Unknown Unknown 1p36.2–36.1
Iridogoniodysgenesis, type 1 (IRID1) Iridogoniodysgenesis anomaly; familial glaucomaIridogoniodysplasia Autosomal dominant Forkhead Transcription factor FKHL7 6P25
Iridogoniodysgenesis, type 2 (IRID1) Iridogoniodysgenesis anomaly; Iris hypoplasia with early-onset glaucoma Autosomal dominant Paired-like homeodomain transcription factor-2 PITX2 (also known as; IDG2, RIEG1, RGS, IGDS2) 4q25–q26
Rieger syndrome, type 1 (RIEG1) Iridogoniodysgenesis with Somatic anomalies Autosomal dominant Paired-like homeodomain transcription factor-2 PITX2 (also known as; IDG2, RIEG1, RGS, IGDS2) 4q25–q26
Rieger syndrome, type 2 (RIEG2) Iridogoniodysgenesis with Somatic anomalies Autosomal dominant Unknown Unknown 13q14
Glaucoma-related pigment dispersion syndrome (GPDS1) Pigment dispersion syndrome and pigmentary glaucoma Autosomal dominant Unknown Unknown 7q35–q36

within the first three years of life. Symptoms include cloudy corneas, excessive tearing, and sensitivity to light. Because the eye is very flexible in infants, increased fluid pressure may cause bulging of the eye (buphthalmos, or "ox eye"). Children with glaucoma in only one eye are usually diagnosed earlier because a difference in eye size can be noticed. When the disorder affects both eyes, many parents view the large eyes as attractive and do not seek help until other symptoms develop, delaying the diagnosis.

With closed-angle glaucoma, symptoms come on suddenly. People may experience blurred vision, severe pain, headache, sensitivity to light, and nausea. The development of this type of glaucoma is an emergency and requires immediate treatment.

Diagnosis

The diagnosis of glaucoma may be suggested by certain physical findings, especially in infants, but is confirmed by tests with special instruments. Parents may bring their young infant to a physician if they notice signs of infantile glaucoma, such as changes in the eye shape and size. In adults, who do not show obvious signs of glaucoma, the condition is frequently detected by routine screening eye exams and other tests.

Using an ophthalmoscope (a hand-held or machine mounted instrument using a light source), a physician or optometrist will look through the pupil to the back of the eye. There, they may detect characteristic changes in the region where the optic nerve meets the eye, called the optic disk.

In another portion of a routine eye exam, an ophthalmologist or optometrist will measure the fluid pressure of the eye through the use of a special instrument called a tonometer. The test is painless and involves brief contact of a small probe with the surface of the eye. Presence of elevated pressure (more than 21 mm Hg) means that a person is at risk for glaucoma.

Once high pressures or changes in the optic disk are noted, an ophthalmologist can also use a gonioscope (small lens with a reflecting mirror) to inspect the drainage passageways of the eye and determine if they are blocked. Visual field tests (in which a patient indicates whether they can see small flashing lights that are directed in different spots of the patient's visual field) are used as a final indicator for the presence of glaucoma or a measurement of how far glaucoma-related visual loss has progressed.

Treatment and management

Although there is no treatment for the optic nerve injury and vision loss caused by glaucoma, it is possible to prevent further visual loss by lowering eye fluid pressure. In the adult, this is primarily achieved through medications. Medications can reduce eye fluid pressure by either decreasing fluid production or by increasing fluid drainage from the eye, and can be taken by mouth or applied to the eye through drops. The names of different classes of medications used to treat glaucoma include beta-blockers, alpha agonists, carbonic anhydrase inhibitors, and prostaglandin analogues.

For infantile glaucoma, the treatment is primarily surgical. Laser surgery or microsurgery to open the drainage canals can be effective in increasing drainage of eye fluid. Other types of surgery can be performed to reduce the amount of fluid production. Many children require several operations to lower or maintain their eye fluid pressures adequately, and long-term treatment with medications may still be necessary. For closed-angle glaucoma, immediate hospitalization and treatment with medication is required. Once the person's condition has been stabilized, laser surgery is used to create a passageway for fluid drainage.

All individuals with glaucoma should see an ophthalmologist regularly to evaluate progress of the condition and whether it is being adequately treated. Beginning at the age of 40, all people should receive regular screening exams to detect early signs of glaucoma. People with a family history of glaucoma or with diabetes should receive these screening tests beginning in young adulthood.

Prognosis

Since even small amounts of vision loss due to glaucoma cannot be reversed, early detection of the condition through regular eye examinations is critical. If glaucoma is detected early, lifelong medical treatment can halt the progress of the disease and result in relatively normal vision. If left undiagnosed or untreated, many people with glaucoma will progress to blindness.

Closed-angle glaucoma is an emergency and the prognosis depends on how quickly medical attention is obtained and the severity of the attack. If left untreated, the condition can quickly lead to total vision loss in the affected eye.

Resources

BOOKS

Marks, E., and R. Mountauredes. Coping With Glaucoma. Garden City Park, NY: Avery Publishing Group, 1997.

Trope, G. E. Glaucoma: A Patient's Guide to the Disease. Toronto: University of Toronto Press, 1996.

PERIODICALS

Coleman, A. L. "Glaucoma." Lancet 354 (November 1999): 1803-1810.

Migdal, C. "Glaucoma Medical Treatment: Philosophy, Principles and Management." Eye 14 (June 2000): 515-518.

ORGANIZATIONS

Glaucoma Foundation. 33 Maiden Lane, New York, NY 10038. (800) 452-8266 <http://www.glaucoma-foundation.org>.

Glaucoma Research Foundation. 200 Pine St., Suite 200, San Francisco, CA 94104. (800) 826-6693

WEBSITES

"Glaucoma." Online Mendelian Inheritance in Man. National Center for Biotechnology Information, National Center for Biotechnology Information, National Library of Medicine. Building 38A, Room 8N805, Bethesda, MD 20894. <http://www3.ncbi.nlm.nih.gov/htbin-post/Omim>

Glaucoma Resources on the Internet. <http://www.healthcyclopedia.com/glaucoma.html>.

Oren Traub, MD, PhD

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Glaucoma." Gale Encyclopedia of Genetic Disorders. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"Glaucoma." Gale Encyclopedia of Genetic Disorders. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/glaucoma

"Glaucoma." Gale Encyclopedia of Genetic Disorders. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/glaucoma

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.

Glaucoma

Glaucoma

Definition

Glaucoma is a group of eye disorders that results in vision loss due to a failure to maintain the normal fluid balance within the eye. If fluid pressure builds up, then damage to the optic nerve occurs, leading to vision loss. If detected in its early stages, vision loss can be prevented through the use of medications or surgical procedures that restore the proper fluid drainage of the eye.

Description

Vision is an important and complex special sense by which the qualities of an object, such as color, shape, and size, are perceived through the detection of light. Light that bounces off an object first passes through the cornea (outer layer) of the eye and then through the pupil and the lens to project onto a layer of cells on the back of the eye called the retina. When the retina is stimulated by light, signals pass through the optic nerve to the brain, resulting in a visual image of an object.

The front chamber of the eye is bathed in a liquid called the aqueous humor. This liquid is produced by a nearby structure called the ciliary body and is moved out of the eye into the bloodstream by a system of drainage canals known as the trabecular meshwork. The proper amount of fluid within the chamber is maintained by a balance between fluid production by the ciliary body and fluid drainage through the trabecular meshwork. When fluid accumulates in the front chamber, either because of an overproduction of fluid or because of a failure of the normal drainage routes, fluid pressure builds up within the eye. Over time, this increased fluid pressure causes damage to the optic nerve, resulting in progressive visual impairment. The condition of increased eye fluid pressure leading to vision loss is known as glaucoma.

Glaucoma is actually a group of many different eye disorders and can manifest alone or as a sign of more than 60 different diseases, or even in a healthy person who has experienced an injury to the eye. Physicians classify glaucoma by the type of abnormality in the drainage system. When the drainage passage is narrowed, but still open, it is termed open-angle glaucoma. If the drainage passage is completely blocked, it is termed closed-angle glaucoma. Glaucoma can also be classified by the age of the affected individual: infantile or congenital glaucoma affects infants at birth or children up to three years old, juvenile glaucoma affects individuals from 3–30 years old, and adult glaucoma affects people greater than 30 years old.

Types of glaucoma and related genetic information

Disorder Alternative names Inheritance Abnormal protein Abnormal gene Gene location
Glaucoma 1, open angle, A (GLC1A)Juvenile onset primary open-angle glaucoma; Hereditary juvenile glaucomaAutosomal dominantTrabecular meshwork-induced glucocorti-coid response protein (myocilin)MYOC, (also known as TIGR, GLC1A, JOAG, GPOA)1q24.3–q25.2;
UnknownUnknown9q34.1
Glaucoma 1, open angle, B (GLC1B)Adult onset primary open-angle glaucoma; Hereditary adult glaucomaAutosomal dominantUnknownUnknown2qcen-q13; (additional loci under investigation)
Glaucoma 1, open angle, C (GLC1C)Adult onset primary open-angle glaucoma; Hereditary adult glaucomaAutosomal dominantUnknownUnknown3q21–q24
Glaucoma 1, open angle, D (GLC1D)Adult onset primary open-angle glaucoma; Hereditary adult glaucomaAutosomal dominantUnknownUnknown8q23
Glaucoma 1, open angle, E (GLC1E)Adult onset primary open-angle glaucoma; Hereditary adult glaucomaAutosomal dominantUnknownUnknown10p15–p14
Glaucoma 1, open angle, F (GLC1F)Adult onset primary open-angle glaucoma; Hereditary adult glaucomaAutosomal dominantUnknownUnknown7q35–36
Glaucoma 3, primary infantile, A (GLC3A)Congenital glaucoma; BuphthalmosAutosomal recessiveCytochrome P4501B1CYP1B12p22–p21
Glaucoma 3, primary infantile, B (GLC3B)Congenital glaucomaAutosomal recessiveUnknownUnknown1p36.2–36.1
Iridogoniodysgenesis, type 1 (IRID1)Iridogoniodysgenesis anomaly; familial glaucomaIridogonio-dysplasiaAutosomal dominantForkhead Transcription factorFKHL76P25
Iridogoniodysgenesis, type 2 (IRID1)Iridogoniodysgenesis anomaly; Iris hypoplasia with early-onset glaucomaAutosomal dominantPaired-like homeodomain transcription factor-2PITX2 (also known as; IDG2, RIEG1, RGS, IGDS2)4q25–q26
Rieger syndrome, type 1 (RIEG1)Iridogoniodysgenesis with Somatic anomaliesAutosomal dominantPaired-like homeodomain transcription factor-2PITX2 (also known as; IDG2, RIEG1, RGS, IGDS2)4q25–q26
Rieger syndrome, type 2 (RIEG2)Iridogoniodysgenesis with Somatic anomaliesAutosomal dominantUnknownUnknown13q14
Glaucoma-related pigment dispersion syndrome (GPDS1)Pigment dispersion syndrome and pigmentary glaucomaAutosomal dominantUnknownUnknown7q35–q36

Genetic profile

There are different forms of glaucoma that either occur alone or as the result of a genetic abnormality. In some cases, specific genetic abnormalities have been identified, while in other forms, the cause is unknown. The known types of glaucoma and the corresponding

genetic defect include forms of glaucoma are not inherited and thus are not represented in the table.

Glaucoma can be inherited in either an autosomal recessive or an autosomal dominant fashion. In autosomal recessive inheritance, two abnormal genes are needed to display the disease. A person who carries one abnormal gene does not display the disease, and is called a carrier. A carrier has a 50% chance of transmitting the gene to a child, who must inherit one abnormal gene from each parent to display the disease. Alternatively, in autosomal dominant inheritance, only one abnormal gene is needed to display the disease, and the chance of passing the gene and the disease to offspring is 50%.

Research is ongoing concerning the heritability of genetic risk factors for primary open-angle glaucoma. This type of glaucoma is particularly troublesome since it is common, progressive, and one of the leading causes of blindness around the world. A major study done in Wisconsin, the Beaver Dam Eye Study investigated the family aggregation and heritability of risk factors of primary open-angle glaucoma among 5,924 participants. The researchers found that there are strong genetic familial effects on risk factors for open-angle glaucoma. The researchers noted that there was a strong and consistent relationship between intraocular pressure and optic cup measurements in siblings, parents, and children, with a lack of correlation of those measurements in spouses.

The genetics of juvenile open-angle glaucoma have been widely studied. Research done in the late 1990s identified a trabecular meshwork-induced glucocorticoid TIGR gene strongly associated with juvenile open-angle glaucoma. Further research identified a protein associated with the cytoskeleton of the retina that was coded for by the myocilin gene. While the exact function of the protein coded for the myocilin gene is unknown, studies have shown a high rate of mutations in this gene in patients with juvenile open-angle glaucoma.

Demographics

Glaucoma is the leading cause of preventable blindness in the United States, affecting more than two million Americans, and is the third leading cause of blindness worldwide. The prevalence of glaucoma increases with age, but the eye condition can also be present in infants and young children. The adult types of open-angle glaucoma account for the majority (70%) of glaucoma cases, while the infantile and juvenile types of glaucoma are relatively uncommon.

The types and rates of glaucoma are not distributed equally among different ethnic groups. For example, the prevalence of glaucoma in Caucasians over 70 years old is 3.5%, while the prevalence in African Americans is 12%. Also, the primary closed-angle type of glaucoma is much more common in people of Asian or Inuit descent. Apart from ethnicity, risk factors for the development of glaucoma include elevated eye pressure, increasing age, diabetes , and presence of glaucoma in a family member.

Signs and symptoms

In the adult and juvenile forms of open-angle glaucoma, vision loss begins at the periphery (outer edges) of the visual field, resulting in tunnel vision. Because the visual loss in not in the individual's central vision, they may not notice this change. However, if the glaucoma is left untreated, loss of vision progresses and the central vision is often affected, sometimes resulting in blindness. The average time from development of high eye fluid pressures to the appearance of visual loss is 18 years in the adult form, but much shorter in the juvenile form.

In contrast to the adult and juvenile forms, congenital or infantile open-angle glaucoma is noted at birth or within the first three years of life. Symptoms include cloudy corneas, excessive tearing, and sensitivity to light. Because the eye is very flexible in infants, increased fluid pressure may cause bulging of the eye (buphthalmos, or ox eye). Children with glaucoma in only one eye are usually diagnosed earlier because a difference in eye size can be noticed. When the disorder affects both eyes, many parents view the large eyes as attractive and do not seek help until other symptoms develop, delaying the diagnosis.

With closed-angle glaucoma, symptoms come on suddenly. People may experience blurred vision, severe pain, headache, sensitivity to light, and nausea. The development of this type of glaucoma is an emergency and requires immediate treatment.

Diagnosis

The diagnosis of glaucoma may be suggested by certain physical findings, especially in infants, but is confirmed by tests with special instruments. Parents may bring their young infant to a physician if they notice changes in the eye shape and size, signs of infantile glaucoma. In adults, who do not show obvious signs of glaucoma, the condition is frequently detected by routine screening eye exams and other tests.

Using an ophthalmoscope (a hand-held or machine-mounted instrument with a light source), a physician or optometrist will look through the pupil to the back of the eye. There, they may detect characteristic changes in the region where the optic nerve meets the eye, called the optic disk.

In another portion of a routine eye exam, an ophthalmologist or optometrist will measure the fluid pressure of the eye through the use of a special instrument called a tonometer. The test is painless and involves brief contact of a small probe with the surface of the eye. Presence of elevated pressure (more than 21 mm Hg) means that a person is at risk for glaucoma.

Once high pressures or changes in the optic disk are noted, an ophthalmologist can also use a gonioscope (small lens with a reflecting mirror) to inspect the drainage passageways of the eye and determine if they are blocked. Visual field tests (in which individuals indicate whether they can see small flashing lights that are directed in different spots of their visual field) are used as a final indicator for the presence of glaucoma or a measurement of how far glaucoma-related visual loss has progressed.

Treatment and management

Although there is no treatment for the optic nerve injury and vision loss caused by glaucoma, it is possible to prevent further visual loss by lowering eye fluid pressure. In the adult, this is primarily achieved through medications. Medications can reduce eye fluid pressure by either decreasing fluid production or by increasing fluid drainage from the eye, and can be taken orally (by mouth) or applied to the eye through drops. The names of different classes of medications used to treat glaucoma include beta-blockers, alpha agonists, carbonic anhydrase inhibitors, and prostaglandin analogues.

For infantile glaucoma, the treatment is primarily surgical. Laser surgery or microsurgery to open the drainage canals can be effective in increasing drainage of eye fluid. Other types of surgery can be performed to reduce the amount of fluid production. Many children require several operations to lower or maintain their eye fluid pressures adequately, and long-term treatment with medications may be necessary. For closed-angle glaucoma, immediate hospitalization and treatment with medication is required. Once the person's condition has been stabilized, laser surgery is used to create a passageway for fluid drainage.

All individuals with glaucoma should see an ophthalmologist regularly to evaluate progress of the condition and whether it is being adequately treated. Beginning at the age of 40, all people should receive regular screening exams to detect early signs of glaucoma. People with a family history of glaucoma or with diabetes should receive these screening tests beginning in young adulthood.

Prognosis

Since even small amounts of vision loss due to glaucoma cannot be reversed, early detection of the condition through regular eye examinations is critical. If glaucoma is detected early, lifelong medical treatment can halt the progress of the disease and result in relatively normal vision. If left undiagnosed or untreated, many people with glaucoma will progress to blindness.

Closed-angle glaucoma is an emergency and the prognosis depends on how quickly medical attention is obtained and the severity of the attack. If left untreated, the condition can quickly lead to total vision loss in the affected eye.

Resources

BOOKS

Marks, E., and R. Mountauredes. Coping With Glaucoma. Garden City Park, NY: Avery Publishing Group, 1997.

Trope, G. E. Glaucoma: A Patient's Guide to the Disease. Toronto: University of Toronto Press, 1996.

PERIODICALS

Coleman, A. L. "Glaucoma." Lancet 354 (November 1999): 1803–1810.

Klein, B. E. K., R. Klein, and K. E. Lee. "Heritability of Risk Factors for Primary Open-angle Glaucoma: The Beaver Eye Dam Study." Investigative Ophthalmology and Visual Science 45 (January 2004): 59–62.

Migdal, C. "Glaucoma Medical Treatment: Philosophy, Principles and Management." Eye 14 (June 2000): 515–518.

Satoko, S., P. R. Lichiter, A. T. Johnson, et al. "Age-dependent Prevalence of Mutations at the GLCIA Locus in Primary Open-angle Glaucoma." American Journal of Opthalmology 130 (2000): 165–177.

ORGANIZATIONS

Glaucoma Foundation. 33 Maiden Lane, New York, NY 10038. (800) 452-8266. (April 19, 2005.) <http://www.glaucoma-foundation.org>.

Glaucoma Research Foundation. 200 Pine St., Suite 200, San Francisco, CA 94104. (800) 826-6693.

WEBSITES

"Glaucoma." Online Mendelian Inheritance in Man. National Center for Biotechnology Information, National Library of Medicine. Building 38A, Room 8N805, Bethesda, MD 20894. (April 19, 2005.) <http://www.ncbi.nlm.nih.gov/entrez/query.fcgi?db=OMIM&cmd=search&term=glaucoma>.

Glaucoma Resources on the Internet. (April 19, 2005.) <http://www.healthcyclopedia.com/glaucoma.html>.

Oren Traub, MD, PhD

Edward R. Rosick, DO, MPH, MS

Cite this article
Pick a style below, and copy the text for your bibliography.

  • MLA
  • Chicago
  • APA

"Glaucoma." Gale Encyclopedia of Genetic Disorders. . Encyclopedia.com. 21 Sep. 2018 <http://www.encyclopedia.com>.

"Glaucoma." Gale Encyclopedia of Genetic Disorders. . Encyclopedia.com. (September 21, 2018). http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/glaucoma-0

"Glaucoma." Gale Encyclopedia of Genetic Disorders. . Retrieved September 21, 2018 from Encyclopedia.com: http://www.encyclopedia.com/science/encyclopedias-almanacs-transcripts-and-maps/glaucoma-0

Learn more about citation styles

Citation styles

Encyclopedia.com gives you the ability to cite reference entries and articles according to common styles from the Modern Language Association (MLA), The Chicago Manual of Style, and the American Psychological Association (APA).

Within the “Cite this article” tool, pick a style to see how all available information looks when formatted according to that style. Then, copy and paste the text into your bibliography or works cited list.

Because each style has its own formatting nuances that evolve over time and not all information is available for every reference entry or article, Encyclopedia.com cannot guarantee each citation it generates. Therefore, it’s best to use Encyclopedia.com citations as a starting point before checking the style against your school or publication’s requirements and the most-recent information available at these sites:

Modern Language Association

http://www.mla.org/style

The Chicago Manual of Style

http://www.chicagomanualofstyle.org/tools_citationguide.html

American Psychological Association

http://apastyle.apa.org/

Notes:
  • Most online reference entries and articles do not have page numbers. Therefore, that information is unavailable for most Encyclopedia.com content. However, the date of retrieval is often important. Refer to each style’s convention regarding the best way to format page numbers and retrieval dates.
  • In addition to the MLA, Chicago, and APA styles, your school, university, publication, or institution may have its own requirements for citations. Therefore, be sure to refer to those guidelines when editing your bibliography or works cited list.