Causes and Symptoms (Magill’s Medical Guide, Sixth Edition)
Glaucoma is an eye disease caused by higher-than-normal pressure inside the eye. The intraocular pressure can increase slowly or suddenly for various reasons but always with detrimental results. Of all the causes of blindness, glaucoma is among the most common, but it is also the most preventable. If diagnosed early, it can be controlled and the loss of sight avoided. What complicates the problem is that the most common form of glaucoma shows no symptoms until extensive, irreversible damage has occurred. There is no pain, and the first sign that something is amiss may be that peripheral vision and seeing out of the corner of the eye is diminished, while frontal vision remains clear.
To understand this disease, it is necessary to know what occurs within the eye when the intraocular pressure increases. The inner surface of the cornea is nourished by the aqueous humor, which is also called the aqueous fluid. This secretion from the ciliary body flows into the space behind the iris and then through the pupil into the space in front of the iris. Where the front of the iris joins the back of the cornea is a point called the venous sinus, at the anterior drainage angle. Here the aqueous humor is reabsorbed and transported to the bloodstream. In a normal eye, this drainage process works correctly and the balance between the amount secreted and the amount reabsorbed maintains a constant intraocular pressure. In glaucoma, the...
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Treatment and Therapy (Magill’s Medical Guide, Sixth Edition)
The treatments available for glaucoma include eyedrops, ointments, pills, and surgery, using both scalpels and lasers. In both acute and congenital glaucoma, there is no time for the use of medications. Patients need to be admitted to the hospital and operated on immediately if their eyesight is to be saved. For open-angle glaucoma, medications may be topical—eye drops or ointments, or inserts, thin medicated strips put in to the corner of the eye—or oral (pills and tablets). Some of the more recent medications are unoprostone isopropyl/ophthalmic solution, brinzolamide ophthalmic suspension, dorzdamide hydrochloride-timolo meleate ophthalmic solution, and brimonidine tartrate ophthalmic solution. Studies in the 1970’s which suggested that marijuana might be an effective treatment agent have since shown it to be no more effective than are a number of drugs already on the market.
If diagnosed early, cases of both chronic simple and chronic secondary glaucoma can often be effectively treated by medications. The first drug given in the form of eyedrops was discovered in the nineteenth century. Called pilocarpine, it is obtained from the leaves or roots of a South American bush. The drug is classified as a miotic because it constricts the pupil of the eye. Constriction of the pupil draws it away from the drainage angle, automatically increasing the drainage of aqueous fluid and therefore decreasing the pressure. To be...
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Perspective and Prospects (Magill’s Medical Guide, Sixth Edition)
The development of ways to diagnose glaucoma has paralleled the general development of the ophthalmologist’s tools. These devices in turn reflect the links between the science of those branches of physics that study pressure, lenses, mirrors, and light and the science that studies the normal and abnormal functioning of the eye.
In 1851, the German doctor Hermann von Helmholtz invented the ophthalmoscope, which enables one to study the interior of the eye. His instrument focuses a beam of light into the patient’s eye and then magnifies its reflection. If this test reveals early signs of cupping of the optic disc, glaucoma can be diagnosed long before other symptoms have appeared.
Intraocular pressure can be measured with an instrument called a tonometer. The two basic varieties are called Schiötz tonometry and applanation tonometry. Both became possible only after biochemists developed anesthetic drops to put in the eye so that the patient would not feel the device touching the very sensitive cornea. The earlier of the two devices, developed in 1905 by the Norwegian physician Hjalmar Schiötz, is a very simple device that is still the most widely used tonometer in the world. With the patient lying down and looking upward, the physician places the hand-sized instrument directly on the cornea. A simple lever is moved by the pressure within the eye to indicate whether that pressure is within the normal range...
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For Further Information: (Magill’s Medical Guide, Sixth Edition)
Buettner, Helmut, ed. Mayo Clinic on Vision and Eye Health: Practical Answers on Glaucoma, Cataracts, Macular Degeneration, and Other Conditions. Rochester, Minn.: Mayo Foundation for Medical Education and Research, 2002. A helpful handbook on all the medical, social, and emotional facets of vision impairment.
Eden, John. The Physician’s Guide to Cataracts, Glaucoma, and Other Eye Problems. Yonkers, N.Y.: Consumer Reports Books, 1992. This excellent book provides the reader with nontechnical yet truly accurate explanations of the functioning of the normal eye and of the disease conditions glaucoma and cataracts.
Epstein, David L., et al., eds. Chandler and Grant’s Glaucoma. 4th ed. Baltimore: Williams & Wilkins, 1997. A standard text on glaucoma. Includes bibliographic references and an index.
Galloway, N. R., et al. Common Eye Diseases and Their Management. 3d ed. London: Springer, 2006. While this text may be difficult for the general reader, it is useful for obtaining more precise medical information. Intended for medical students but accessible to nonscientists because of the author’s writing style.
Glaucoma Research Foundation. http://www.glaucoma .org. A group that strives to maintain the sight and independence of individuals with glaucoma through research and education with the ultimate goal of finding a cure.
Marks, Edith. Coping...
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Risk Factors (Genetics & Inherited Conditions)
The likelihood of glaucoma increases when the IOP climbs above the mid-twenties (mmHG). However, glaucomatous damage may occur in the absence of high IOP (low tension or normal tension glaucoma) or above-normal IOP may not result in glaucoma. Loss of neurons or abnormalities in the optic nerve is a better predictor of glaucoma than is IOP.
The prevalence of glaucoma is positively associated with ethnicity and family history. People of African descent are more likely to develop POAG than are those of Caucasian origin; those of Asian origin have the highest risk of developing PCAG. Other risk factors include increasing age, abnormal blood pressure, heavy alcohol use, myopia, diabetes, corticosteroid use, and eye trauma or malformations.
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Etiology and Genetics (Genetics & Inherited Conditions)
Glaucoma is genetically heterogeneous, with late-onset forms having a more complex, multifactorial basis. Numerous genetic locations have been linked with diverse types of glaucoma.
Open angle glaucoma is the most prevalent form of the disease, typically beginning in adulthood but sometimes present at birth (primary congenital glaucoma, or PCG) or developing in childhood (juvenile open angle glaucoma, or JOAG). PCG inheritance is primarily autosomal recessive and has been linked to four chromosomal locations (1p36/GLC3B, 2p21/GLC3A, 6p25/IRID1, 14q24.3/GLC3C) and one gene at the GLC3C location, CYP1B1. Primarily autosomal dominance characterizes JOAG and POAG inheritance. Two loci have been linked with JOAG (9q22/GLC1J, 20p12/GLC1K); one with JOAG and POAG (1q23-24/GLC1A); and several with POAG (2cen-q13/GLC1B, 2p16.3-p15/GLC1H, 3q21-24/GLC1C, 5q22.1/GLC1G, 7q35-36/GLC1F, 8p23/GLC1D, 10p14-15/GLC1E, 15q11-q13/GLC1I). Defects in the myocilin gene (MYOC/GLC1A) appear to be a significant factor in causing increased IOP in JOAG and POAG. Optineurin (OPTN/GLC1E) variations have been linked with POAG and the rarer low tension forms of the disease. The WDR36 (GLC1G) gene is thought to be a modifier gene that influences the severity of glaucoma.
Among the secondary glaucomas, the most common form is pseudoexfoliation syndrome, in which cells of the lens are deposited in the...
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Symptoms (Genetics & Inherited Conditions)
The early stages of POAG typically have no noticeable symptoms. As POAG progresses, small spots of diminished vision appear, followed by loss of peripheral vision that advances to tunnel vision in later stages of the disease. In contrast, the symptoms of PCAG may appear suddenly with blurred vision, seeing halos around lights, eye pain, nausea, headaches, and/or reddening of the eyes.
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Screening and Diagnosis (Genetics & Inherited Conditions)
Initial glaucoma screening typically includes tonometry to measure IOP, pachymetry to measure corneal thickness (thicker corneas may inflate IOP readings, while thinner corneas may deflate IOP readings), visual field testing to evaluate peripheral vision, and assessment of risk factors. More detailed diagnostic methods used include gonioscopy to determine drainage angle and imaging techniques to inspect the optic nerve for damage or abnormalities.
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Treatment and Therapy (Genetics & Inherited Conditions)
Glaucoma treatment usually begins with eyedrops. Prostaglandin-like compounds (such as Lumigan), cholinergic agents (such as Pilopine), and epinephrine compounds (such as Propine) increase aqueous humor outflow; beta blockers (such as Betagan), carbonic anhydrase inhibitors (such as Trusopt) decrease aqueous humor production; alpha-a agonists (such as Lopidine) do both. Orally, carbonic anhydrase inhibitors, cannabinoids, and serotonin agonists are efficacious.
Laser surgery is usually the second line of treatment. Common procedures include trabeculoplasty, which opens the trabecular network; iridotomy, in which a hole is made in the iris; and cycloablation, in which ciliary body oblation decreases fluid production. If laser surgery fails, then conventional surgical procedures such as trabeculectomy, in which a portion of the trabecular network is removed, or the insertion of drainage implants may be used.
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Prevention and Outcomes (Genetics & Inherited Conditions)
People with a family history of glaucoma and who are over the age of forty-five should be tested for glaucoma at least once a year. Although glaucoma has no cure, keeping IOP down can prevent visual loss and blindness. Vigorous exercise, chronic head-down postures, drinking large amounts of fluid in a short time, and tight clothing around the neck can elevate IOP.
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Further Reading (Genetics & Inherited Conditions)
Cioffi, George A., ed. 2009-2010 Basic and Clinical Science Course Section 10: Glaucoma. San Francisco: American Academy of Ophthalmology, 2009. A scholarly text that summarizes the most recent developments in glaucoma research.
Stamper, Robert L., Marc F. Lieberman, and Michael V. Drake. Becker-Shaffer’s Diagnosis and Therapy of the Glaucomas. 8th ed. St. Louis: Mosby, 2009. A comprehensive guide to glaucoma intended for the professional.
Trope, Graham E. Glaucoma: A Patient’s Guide to the Disease. 3d ed. Toronto: University of Toronto Press, 2004. An accessible and concise introduction to glaucoma is presented.
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Glaucoma (Encyclopedia of Genetic Disorders)
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.
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...
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Glaucoma (Encyclopedia of Medicine)
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...
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Glaucoma (Encyclopedia of Alternative Medicine)
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 600% 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...
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Glaucoma (Encyclopedia of Nursing & Allied Health)
Glaucoma is a condition where the optic nerve is subject to damagesually, 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.
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 spotspots 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. As of 2001, 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.
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.
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% of adult glaucoma. As of 2001, 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.
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.
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.
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 patients, so they can be treated before IOPs become elevated.
Agonist drug that mimics one of the body's own molecules.
Alpha-2 agonist (alpha-2 adrenergic receptor agonist) 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 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) 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 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.
Cornealear, 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.
Gonioscopen 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 class of drugs for glaucoma that increases the osmotic pressure in the blood, which then pulls water from the eye into the blood.
Irishe 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) transparent structure in the eye that focuses light onto the retina.
Miotic drug that causes pupils to contract.
Ophthalmoscopen instrument, with special lighting, designed to view structures in the back of the eye.
Optic nervehe nerve that carries visual messages from the retina to the brain.
Prostaglandin group of molecules that exerts local effects on a variety of processes including fluid balance, blood flow, and gastrointestinal function.
Prostaglandin analogue class of drugs that are similar in structure and function to prostaglandin.
Retinahe inner, light-sensitive layer of the eye containing rods and cones.
Sclerahe tough, fibrous, white outer protective covering that surrounds the eye.
Tonometryhe measurement of pressure.
Trabecular meshwork sponge-like tissue located near the cornea and iris that functions to drain the aqueous humor from the eye into the blood.
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.
American Academy of Ophthalmology. P.O. Box 7424, San Francisco, CA 94120-7424. (415) 561-8500. <<a href="http://www.eyenet.org">http://www.eyenet.org>.
American Glaucoma Society. P.O. Box 193940, San Francisco, CA 94119-3940. (415) 561-8587. Fax: (415) 561-8531. <<a href="http://www.glaucomaweb.org">http://www.glaucomaweb.org>.
Glaucoma Research Foundation. 490 Post Street, Suite 830, San Francisco, CA 94102. (415) 986-3162. (800) 826-6693. email@example.com. <<a href="http://www.glaucoma.org/">http://www.glaucoma.org/>.
National Eye Institute. 2020 Vision Place, Bethesda, MD 20892-3655. (301) 496-5248. <<a href="http://www.nei.nih.gov">http://www.nei.nih.gov>.
Prevent Blindness America. 500 East Remington Road, Schaumburg, IL 60173. (800) 331-2020. <<a href="http://www.prevent-blindness.org">http://www.prevent-blindness.org>.
"FDA Approves Two New Intraocular Pressure Lowering Drugs for the Management of Glaucoma." FDA Online. <<a href="http://www.fda.gov/bbs/topics/NEWS/2001/NEW00757.html">http://www.fda.gov/bbs/topics/NEWS/2001/NEW00757.html>.
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Helzner, Jerry. "You Can Provide Cost-Effective Glaucoma Care." Ophthalmology Management Online. <<a href="http://www.ophmanagement.com/archive_results.asp?loc=archive/2001/april/0401067.htm">http://www.ophmanagement.com/archive_results.asp?loc=archiv... >.
"Optometric Clinical Practice Guideline: Care of the Patient with Open Angle Glaucoma." American Optometric Association Online. <<a href="http://www.aoanet.org/cpg-9-cpoag.html">http://www.aoanet.org/cpg-9-cpoag.html>.
Ronge, Laura J. "Glaucoma: What We Know About Glaucoma Genetics." EyeNet Magazine Online. <<a href="http://www.eyenet.org/eyenet_mag/05_00/glaucoma.html">http://www.eyenet.org/eyenet_mag/05_00/glaucoma.html>.
Titcomb, Lucy. "Treatment of Glaucoma." Pharmacy Magazine. <<a href="http://www.pharmacymag.co.uk/glau.htm">http://www.pharmacymag.co.uk/glau.htm> (29 April 1998).