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.
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
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.
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.
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.
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.
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.
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.
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.
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.
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.
"Glaucoma." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma
"Glaucoma." Gale Encyclopedia of Medicine, 3rd ed.. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma
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.
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 60–70% 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
- high blood pressure
- migraine headaches
- nearsightedness, farsightedness, and other visual disturbances
- a family history of glaucoma
- being of African-American ethnicity
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.
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.
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.
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.
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.
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.
"Glaucoma." Gale Encyclopedia of Alternative Medicine. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-1
"Glaucoma." Gale Encyclopedia of Alternative Medicine. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-1
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.
"glaucoma." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/glaucoma
"glaucoma." The Columbia Encyclopedia, 6th ed.. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/glaucoma
"glaucoma." A Dictionary of Nursing. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/glaucoma
"glaucoma." A Dictionary of Nursing. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/glaucoma
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.
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.
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.
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.
- 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.
- 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.
- 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.
- 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.
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.
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 (1787–1840) 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 (1899–1975) 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.
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.
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.
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.
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
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.
Glaucoma Research Foundation. 490 Post Street, Suite 830, San Francisco, CA 94102. (415) 986–3162; (800) 826–6693. http://www.glaucoma.org.
Prevent Blindness America. 500 East Remington Rd., Schaumburg, IL 60173. (800) 331–2020. http://www.prevent-blindness.org.
"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).
"Glaucoma." UXL Complete Health Resource. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/medicine/news-wires-white-papers-and-books/glaucoma
"Glaucoma." UXL Complete Health Resource. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/news-wires-white-papers-and-books/glaucoma
Glaucoma (glaw-KO-ma) is a group of disorders that cause fluid pressure to rise inside the eye, which may result in vision loss.
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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.
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 eyeball’s 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 eye’s 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.
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 eye’s 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.
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 Alaska’s Mt. McKinley, the highest in the United States.
“When I first went blind, I wondered what I could do,” Weilenmayer said in 1998. “It’s really a kick to do extreme activities and do them well—and no more dangerously than anyone else.”
Erik’s accomplishments are a reminder that physical challenges and differences do not have to prevent people from participating in life’s most difficult and demanding activities.
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.
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
"Glaucoma." Complete Human Diseases and Conditions. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-0
"Glaucoma." Complete Human Diseases and Conditions. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/glaucoma-0
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).
"glaucoma." The Oxford Pocket Dictionary of Current English. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma-0
"glaucoma." The Oxford Pocket Dictionary of Current English. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma-0
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"glaucoma." World Encyclopedia. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/environment/encyclopedias-almanacs-transcripts-and-maps/glaucoma
"glaucoma." The Concise Oxford Dictionary of English Etymology. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma-1
"glaucoma." The Concise Oxford Dictionary of English Etymology. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma-1
"glaucoma." Oxford Dictionary of Rhymes. . Encyclopedia.com. (February 23, 2017). http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma
"glaucoma." Oxford Dictionary of Rhymes. . Retrieved February 23, 2017 from Encyclopedia.com: http://www.encyclopedia.com/humanities/dictionaries-thesauruses-pictures-and-press-releases/glaucoma