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.

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.

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

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

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.)
  40–49	290,000	0.7%
  50–59	318,000	1.0%
  60–69	369,000	1.8%
  70–79	530,000	3.9%
  ≥80	711,000	7.7%
  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.

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

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