Brown University BI108 Glaucoma Valves

In This Page:
What is Glaucoma?
The Eye and How It Works
Glaucoma Statistics
Risk Factors
Types of Glaucoma
Treatments
Diagnosis


What is Glaucoma?

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Glaucoma is a group of eye diseases that gradually steal sight without warning. In the early stages of the disease, there may be no symptoms. Experts estimate that half of the people affected by glaucoma may not know they have it. Glaucoma is caused by a number of different eye diseases which in most cases produce increased pressure within the eye. This elevated pressure is caused by a backup of fluid in the eye. Over time, it causes damage to the optic nerve. Through early detection, diagnosis and treatment, you and your doctor can help to preserve your vision. Think of your eye as a sink, in which the faucet is always running and the drain is always open. The aqueous humor is constantly circulating through the anterior chamber. It is produced by a tiny gland, called the ciliary body, situated behind the iris. It flows between the iris and the lens and, after nourishing the cornea and lens, flows out through a very tiny spongy tissue, only one-fiftieth of an inch wide, called the trabecular meshwork, which serves as the drain of the eye. The trabecular meshwork is situated in the angle where the iris and cornea meet. When this drain becomes clogged, aqueous can not leave the eye as fast as it is produced, causing the fluid to back up. But since the eye is a closed compartment, your `sink´ doesn´t overflow; instead the backed up fluid causes increased pressure to build up within the eye. We call this open (wide) angle glaucoma. To understand how this increased pressure affects the eye, think of your eye as a balloon. When too much air is blown into the balloon, the pressure builds, causing it to pop. But the eye is too strong to pop. Instead, it gives at the weakest point, which is the site in the sclera at which the optic nerve leaves the eye. As we mentioned earlier, the optic nerve is the part of the eye which carries visual information to the brain. It is made up of over one million nerve cells, and while each cell is several inches long, it is extremely thin -- about one twenty-thousandth of an inch in diameter. When the pressure in the eye builds, the nerve cells become compressed, causing them to become damaged and, eventually, die. The death of these cells results in permanent visual loss. Early diagnosis and treatment of glaucoma can help prevent this from happening. Adult glaucoma falls into two categories— open angle glaucoma and closed angle glaucoma.

For more information about the types of glaucoma, click here.

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The Eye and How It Works

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The outer layer of the eyeball is called the sclera. The sclera is a thin, yet tough, leathery protective shell which is the "white of the eye." The front portion of the shell is called the cornea. The cornea is a clear tissue through which light rays enter the eye. The cornea is much like the lens of a camera, providing the eye with much of its light-focusing power. The colored portion of the eye is called the iris. The iris not only determines whether your eyes appear blue or brown, but functions like the diaphragm of a camera. The iris contains muscles which control the size of the pupil, regulating the amount of light allowed to enter the eye.

The pupil, which is the dark-colored area in the center of the iris, opens and closes depending upon how much light is present. When there is a great deal of light, as outdoors on a bright, sunny day, the iris constricts the pupil, or makes it smaller. This limits the amount of light which passes through the pupil to the retina at the back of the eye. The retina may be thought of as the camera´s film. When there is little or no light, the iris dilates the pupil, widening it so that more light can enter the eye.

The lens, which is behind the iris, adjusts its shape and thickness to focus the image onto the retina. The retina then delivers the image to the brain via nerve signals which are sent through the optic nerve to the brain, which processes these signals into a "picture," or visual image.

The interior of the eye is filled with fluid. A gel-like substance called vitreous fills the center region of the eye. This region is called the vitreous cavity.

The anterior chamber, or front compartment of the eye, is bounded by the cornea, iris, pupil, and lens. It is filled with a watery fluid called the aqueous humor. This fluid nourishes the cornea and the lens, providing them with oxygen and vital nutrients. The aqueous humor also provides the necessary pressure to help maintain the shape of the eye. We call this pressure the intraocular pressure (IOP). Maintaining the right amount of pressure within the eye is very important to protecting your vision. Measuring the IOP is one of the ways in which your eye doctor tests for glaucoma.

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Glaucoma Statistics

Glaucoma is a leading cause of blindness. Glaucoma can cause blindness if it is left untreated. And unfortunately approximately 10% of people with glaucoma who receive proper treatment still experience loss of vision.

There is no cure (yet) for glaucoma. Glaucoma is not curable, and vision lost cannot be regained. With medication and/or surgery, it is possible to halt further loss of vision. Since glaucoma is a chronic condition, it must be monitored for life.

Diagnosis is the first step to preserving your vision.

Everyone is at risk for glaucoma. Everyone is at risk for glaucoma from babies to senior citizens. Yes, older people are at a higher risk for glaucoma but babies can be born with glaucoma (approximately 1 out of every 10,000 babies born in the United States ). Young adults can get glaucoma, too. African-Americans in particular are susceptible at a younger age.

There may be no symptoms to warn you. With open angle glaucoma, the most common form, there are virtually no symptoms. Usually, no pain is associated with increased eye pressure. Vision loss begins with peripheral or side vision. You may compensate for this unconsciously by turning your head to the side, and may not notice anything until significant vision is lost. The best way to protect your sight from glaucoma is to get tested. If you have glaucoma, treatment can begin immediately.

Other Statistics About Glaucoma

It is estimated that over 3 million Americans have glaucoma but only half of those know they have it.

Approximately 120,000 are blind from glaucoma, accounting for 9% to 12% of all cases of blindness in the U.S.

About 2% of the population ages 40-50 and 8% over 70 have elevated IOP.

Glaucoma is the second leading cause of blindness in the world, according to the World Health Organization.

Glaucoma is the leading cause of blindness among African-Americans.

Glaucoma is 6 to 8 times more common in African-Americans than Caucasians.

African-Americans ages 45-65 are 14 to 17 times more likely to go blind from glaucoma than Caucasians with glaucoma in the same age group.

The most common form, Open Angle Glaucoma, accounts for 19% of all blindness among African-Americans compared to 6% in Caucasians.

Other high-risk groups include: people over 60, family members of those already diagnosed, diabetics, and people who are severely nearsighted.

Estimates put the total number of suspected cases of glaucoma at around 65 million worldwide.

Glaucoma accounts for over 7 million visits to physicians each year.

In terms of Social Security benefits, lost income tax revenues, and health care expenditures, the cost to the U.S. government is estimated to be over $1.5 billion annually.

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Risk Factors

If your intraocular pressure is higher than what's considered normal, you're at increased risk of developing glaucoma. Intraocular Pressure (IOP ) is the level of fluid pressure inside your eye. Normal intraocular pressure usually ranges from 12-21 mm Hg, although people with relatively low pressure can still have glaucoma and people with high pressure can still have healthy eyes. Yet most people with slightly elevated intraocular pressure don't develop the disease. This makes it difficult to predict who will get glaucoma.

Certain other factors increase your risk. Because chronic forms of glaucoma can destroy vision before any symptoms are apparent, be aware of these factors:

Age. Age is a large risk factor in the development of glaucoma. Everyone older than 60 is at increased risk of the disorder. You are six times more likely to get glaucoma if you are over 60 years old.   For blacks however, the increase in risk becomes apparent earlier, after age 40.

Race. Blacks are significantly more likely to get glaucoma than are whites, and they are much more likely to suffer permanent blindness as a result. Hispanics also face an increased risk. The reasons for these differences aren't clear. Asian-Americans are at higher risk of angle-closure glaucoma, and Japanese-Americans are more prone to low-tension glaucoma.

Family history of glaucoma. If you have a family history of glaucoma, you have a much greater risk of developing glaucoma.   Family history increases risk of glaucoma four to nine times.

Medical conditions. Diabetes increases your risk of developing glaucoma. A history of high blood pressure or heart disease also can increase your risk. Other risk factors include retinal detachment, eye tumors and eye inflammations such as chronic uveitis and iritis. Certain types of eye surgery may trigger secondary glaucoma.

Physical injuries. Severe trauma, such as being hit in the eye, can result in increased eye pressure. Injury can also dislocate the lens, closing the drainage angle.   Injury to the eye may cause secondary open angle glaucoma. This type of glaucoma can occur immediately after the injury or years later.   Blunt injuries that “bruise” the eye (called blunt trauma) or injuries that penetrate the eye can damage the eye's drainage system, leading to traumatic glaucoma.   The most common cause is sports-related injuries such as baseball or boxing.

Nearsightedness. Being nearsighted, which generally means that objects in the distance look fuzzy without glasses or contacts, increases the risk of developing glaucoma.

Prolonged corticosteroid use. Using corticosteroids for prolonged periods of time appears to put you at risk of getting secondary glaucoma.   Some evidence links corticosteroid use to glaucoma. A study reported in the Journal of American Medical Association, March 5, 1997 , demonstrated a 40% increase in the incidence of ocular hypertension and open angle glaucoma in adults who require approximately 14 to 35 puffs of corticosteroid inhaler to control asthma. This is a very high dose, only required in cases of severe asthma.

Eye abnormalities. Structural abnormalities of the eye can lead to secondary glaucoma. For example, pigmentary glaucoma is a form of secondary glaucoma caused by pigment granules being released from the back of the iris. These granules can block the trabecular meshwork.

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Types of Glaucoma

The two main types of glaucoma are primary open angle glaucoma (POAG), and angle closure glaucoma. These are marked by an increase of intraocular pressure (IOP), or pressure inside the eye. When optic nerve damage has occurred despite a normal IOP, this is called normal tension glaucoma. Secondary glaucoma refers to any case in which another disease causes or contributes to increased eye pressure, resulting in optic nerve damage and vision loss.

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Primary Open Angle Glaucoma

Approximately one percent of all Americans have this form of glaucoma, making it the most common form of glaucoma in our country. It occurs mainly in the over 50 age group.

There are no symptoms associated with POAG. The pressure in the eye slowly rises and the cornea adapts without swelling. Therefore, the disease often goes undetected. It is painless, and the patient often does not realize that he or she is slowly losing vision until the later stages of the disease. However, by the time the vision is impaired, the damage is irreversible.

In POAG, there is no visible abnormality of the trabecular meshwork. It is believed that something is wrong with the ability of the cells in the trabecular meshwork to carry out their normal function, or there may be fewer cells present, as a natural result of getting older. Some believe it is due to a structural defect of the eye´s drainage system. Others believe it is caused by an enzymatic problem.

Glaucoma is really about the problems which occur as a result of increased IOP. The average IOP in a normal population is 14-16 millimeters of mercury (mmHg). In a normal population pressures up to 20 mmHg may be within normal range. A pressure of 22 is considered to be suspicious and possibly abnormal. However, not all patients with elevated IOP develop glaucoma-related eye damage.

This increased pressure can ultimately destroy the optic nerve cells. Once a sufficient number of nerve cells are destroyed, `blind spots´ begin to form in the field of vision. These blind spots usually develop first in the peripheral field of vision, the outer sides of the field of vision. In the later stages, the central vision, which we experience as `seeing,´ is affected. Once visual loss occurs, it is irreversible because once the nerve cells are dead, nothing can restore them at the present time. Later on, we will talk about the many ways your eye doctor can detect glaucoma in its earliest stages -- before any visual damage occurs.

POAG is a chronic disease. It may be hereditary. There is no cure for it at present, but the disease can be slowed or arrested by treatment. Since there are no symptoms, many patients find it difficult to understand why lifelong treatment with expensive drugs is necessary, especially when these drugs are often bothersome to take and have a variety of side effects.

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Angle Closure Glaucoma

Angle-closure glaucoma affects nearly half a million people in the United States. There is a tendency for this disease to be inherited, and often several members of a family will be afflicted. It is most common in people of Asian descent and people who are far-sighted.

In people with a tendency to angle-closure glaucoma, the anterior chamber is smaller than average. As mentioned earlier, the trabecular meshwork is situated in the angle formed where the cornea and the iris meet. In most people, this angle is about 45 degrees. The narrower the angle, the closer the iris is to the trabecular meshwork. With angle closure glaucoma, the iris is not as wide and open as it should be. The outer edge of the iris bunches up over the drainage canals, when the pupil enlarges too much or too quickly. This can happen when entering a dark room. In addition, as we age, the lens routinely grows larger. The ability of aqueous humor to pass between the iris and lens on its way to the anterior chamber becomes decreased, causing fluid pressure to build up behind the iris, further narrowing the angle.

If the pressure becomes sufficiently high, the iris is forced against the trabecular meshwork, blocking drainage, similar to putting a stopper over the drain of a sink. When this space becomes completely blocked, an angle-closure glaucoma attack (acute glaucoma) results.

A simple test can be used to see if your angle is normal and wide or abnormal and narrow. Treatment of angle closure glaucoma usually involves surgery to remove a small portion of the outer edge of the iris. This helps unblock the drainage canals so that the extra fluid can drain. Usually surgery is successful and long lasting. However, you should still receive regular check-ups.

Symptoms of angle closure glaucoma may include headaches, eye pain, nausea, rainbows around lights at night, and very blurred vision.

Acute Glaucoma

Unlike POAG (Primary Open-Angle Glaucoma), where the IOP increases slowly, in acute angle-closure, it increases suddenly. This sudden rise in pressure can occur within a matter of hours and become very painful. If the pressure rises high enough, the pain may become so intense that it can cause nausea and vomiting.

The eye becomes red, the cornea swells and clouds, and the patient may see haloes around lights and experience blurred vision.

An acute attack is an emergency condition. If treatment is delayed, eyesight can be permanently destroyed. Scarring of the trabecular meshwork may occur and result in chronic glaucoma, which is much more difficult to control. Cataracts may also develop. Damage to the optic nerve may occur quickly and cause permanently impaired vision.

Many of these sudden `attacks´ occur in darkened rooms, such as movie theaters. If you recall, darkened environments cause the pupil to dilate, or increase in size. When this happens, there is maximum contact between the eye´s lens and the iris. This further narrows the angle and may trigger an attack. But the pupil also dilates when one is excited or anxious. Consequently, many acute glaucoma attacks occur during periods of stress. A variety of drugs can also cause dilation of the pupil and lead to an attack of glaucoma. These include anti-depressants, cold medications, antihistamines, and some medications to treat nausea.

Acute glaucoma attacks are not always full blown. Sometimes a patient may have a series of minor attacks. A slight blurring of vision and haloes (rainbow-colored rings around lights) may be experienced, but without pain or redness. These attacks may end when the patient enters a well lit room or goes to sleep -- two situations which naturally cause the pupil to constrict, thereby allowing the iris to pull away from the drain.

An acute attack may be stopped with a combination of drops which constrict the pupil, and drugs that help reduce the eye´s fluid production. As soon as the IOP has dropped to a safe level, your ophthalmologist will perform a laser iridotomy. A laser iridotomy is an outpatient procedure in which a laser beam is used to make a small opening in the iris. This allows the fluid to flow more freely. Drops will be used to anesthetize your eye and there is no pain involved. The entire procedure should take less than thirty minutes. Laser surgery may be performed prophylactically on the other eye, as well. Since it is common for both eyes to suffer from narrowed angles, operating on the unaffected eye is done as a preventive measure.

Routine examinations using a technique called gonioscopy can predict one´s chances of having an acute attack. A special lens which contains a mirror is placed lightly on the front of the eye and the width of the angle examined visually. Patients with narrow angles can be warned of early symptoms, so that they can seek immediate treatment. In some cases, laser treatment is recommended as a preventive measure.

Not all angle-closure glaucoma sufferers will experience an acute attack. Instead, some may develop what is called chronic angle-closure glaucoma. In this case, the iris gradually closes over the drain, causing no overt symptoms. When this occurs, scars slowly form between the iris and the drain and the IOP will not rise until there is a significant amount of scar tissue formed -- enough to cover the drainage area. If the patient is treated with medication, such as pilocarpine, an acute attack may be prevented, but the chronic form of the disease may still develop.

Normal Tension Glaucoma (NTG)

Normal-tension glaucoma, also known as low-tension glaucoma, is characterized by progressive optic nerve damage and visual field loss with a statistically normal intraocular pressure (12—21mmHg). This form of glaucoma may account for as many as one-third of the cases of open-angle glaucoma in the United States. Normal-tension glaucoma is thought to be related, at least in part, to poor blood flow to the optic nerve, which leads to death of the cells which carry impulses from the retina to the brain. In addition, these eyes appear to be susceptible to pressure-related damage even in the high normal range, and therefore a pressure lower than normal is often necessary to prevent further visual loss.

Since so little is known about why normal eye pressure damages some eyes, most doctors treat normal tension glaucoma by reducing the eye pressure as low as possible using medications, laser treatments and filtering surgery.

Pediatric Glaucoma

The pediatric glaucomas consist of congenital glaucoma (present at birth), infantile glaucoma (appears during the first three years), juvenile glaucoma (age three through the teenage or young adult years), and all the secondary glaucomas occurring in the pediatric age group.

Congenital glaucoma is present at birth and most cases are diagnosed during the first year of life. Sometimes symptoms are not recognized until later in infancy or early childhood.

The range of treatment is very different from that for adult glaucoma. It is very important to catch pediatric glaucoma early in order to prevent blindness.

In an uncomplicated case, surgery can often correct such structural defects. Both medication and surgery are required in some cases.

Medical treatments may involve the use of topical eye drops and oral medications. These treatments help to either increase the exit of fluid from the eye or decrease the production of fluid inside the eye. Each results in lower eye pressure.

There are two main types of surgical treatments: filtering surgery and laser surgery. Filtering surgery (also known as micro surgery) involves the use of small surgical tools to create a drainage canal in the eye. In contrast, laser surgery uses a small but powerful beam of light to make a small opening in the eye tissue.

Secondary Glaucoma

Glaucoma can occur as the result of an eye injury, inflammation, tumor or in advanced cases of cataract or diabetes. It can also be caused by certain drugs such as steroids. This form of glaucoma may be mild or severe. The type of treatment will depend on whether it is open angle or angle closure glaucoma.

Pseudoexfoliative Glaucoma

This common cause of glaucoma is found everywhere in the world, but is most common among people of European descent. In about 10% of the population over age 50, a whitish material, which looks on slit-lamp examination somewhat like tiny flakes of dandruff, builds up on the lens of the eye. This exfoliation material is rubbed off the lens by movement of the iris and at the same time, pigment is rubbed off the iris. Both pigment and exfoliation material clog the trabecular meshwork, leading to IOP elevation, sometimes to very high levels. Exfoliation syndrome can lead to both open-angle glaucoma and angle-closure glaucoma, often producing both kinds of glaucoma in the same individual. Not all persons with exfoliation syndrome develop glaucoma. However, if you have exfoliation syndrome, your chances of developing glaucoma are about six times as high as if you don´t. It often appears in one eye long before the other, for unknown reasons. If you have glaucoma in one eye only, this is the most likely cause. It can be detected before the glaucoma develops, so that you can be more carefully observed and minimize your chances of vision loss.   Treatment usually includes medications or surgery.

Pigmentary Glaucoma

Pigmentary glaucoma is a type of inherited open-angle glaucoma which develops more frequently in men than in women. It most often begins in the twenties and thirties, which makes it particularly dangerous to a lifetime of normal vision. Nearsighted patients are more typically afflicted. The anatomy of the eyes of these patients appears to play a key role in the development of this type of glaucoma. Let us examine why. Myopic (nearsighted) eyes have a concave-shaped iris which creates an unusually wide angle. This causes the pigment layer on the back of the iris to rub on the lens. This rubbing action causes the iris pigment to shed into the aqueous humor and onto neighboring structures, such as the trabecular meshwork. Small pigment granules may plug the pores of the trabecular meshwork, causing it to clog, and thereby increasing the IOP.

This rise in eye pressure can damage the optic nerve, the nerve in the back of the eye that carries visual images to the brain. If this happens, pigment dispersion syndrome becomes pigmentary glaucoma.

Doctors usually treat pigmentary glaucoma with eyedrops such as Betagan, Timoptic, Optipranlol and Xalatan. These eyedrops have a relatively low incidence of side effects and are generally well-tolerated in younger patients. Doctors may also use medications such as Pilocar, and Ocusert, which are from a class of drugs called miotics. These medications cause the pupil to constrict (become smaller) and inhibit the iris from rubbing against the supporting fibers of the eye's lens, helping to prevent further release of pigment. However, miotics have side effects such as blurred vision which can limit their use.

In some patients, a laser treatment called argon laser trabeculoplasty works well. This procedure helps open up the drainage system in the eye to increase fluid flow, which lowers eye pressure and protects the optic nerve.

Another treatment for pigmentary glaucoma is a procedure called a laser iridotomy. A laser is used to make a small hole in the iris, causing the iris to move away from the lens of the eye. This prevents the lens fibers from scraping the pigment from the iris and clogging the eye's fluid flow. However, it has limitations and does not always achieve its desired effect.

Traumatic Glaucoma

Traumatic glaucoma is any glaucoma caused by an injury to the eye. This type of glaucoma can occur both immediately after an injury to the eye or years later. It can be caused by injuries that “bruise” the eye (called blunt trauma) and injuries that penetrate the eye. Conditions such as severe nearsightedness, previous injury, infection or prior surgery may also make the eye more vulnerable to a serious eye injury.

Blunt Trauma

As a result of an immediate injury, traumatic glaucoma is most commonly caused by blunt trauma, which is an injury that doesn't penetrate the eye, such as a blow to the head or an injury directly on the eye. The most common cause is from sports-related injuries, such as baseball or boxing. Normally, the eye fluid flows out of the front part of the eye through the pupil and then is absorbed into the bloodstream through a meshwork of drainage canals around the outer edge of the iris. When a blunt trauma occurs, damage to this system can occur. The most common cause is the ciliary body, the part of the eye that produces eye fluid, inside the eye tearing. This can cause bleeding inside the eye. The excess amount of blood, plasma and debris can accumulate and clog the drainage system. This can lead to an increase in eye pressure, which can damage the optic nerve.

Elevated eye pressure due to blunt trauma is treated by keeping the eye pressure at safe levels while the eye drains the excess blood out. Glaucoma medications to control the eye pressure are usually tried first. If this is not sufficient to control the eye pressure, surgery may be necessary.

The elevated eye pressure following blunt trauma is temporary in most cases. It is important, however, to make sure to get regular follow-up eye exams. In some cases, the damaged drainage canals in the eye can build up excess scarring. This scarring blocks fluid flow and can lead to glaucoma. This type of glaucoma, called angle recession glaucoma, can occur many years after the initial injury. The angle recession is seen on an exam as a tear at the base of the iris where the drainage canals are. Angle recession glaucoma can be difficult to treat. Treatments can include medications that reduce fluid production in the eye, laser surgery or filtering surgery.

Penetrating Eye Injury

Traumatic glaucoma can also be caused by penetrating injuries to the eye, such as those caused by a sharp instrument or flying debris. The eye pressure is usually lower right after the injury occurs. Once the wound is closed, tissue inside the eye can become swollen and irritated, and bleeding can occur, causing the eye pressure to rise.

Short term rises in eye pressure are controlled in ways similar to cases of blunt trauma. However, damaged tissue and scarring from a penetrating eye injury can lead to blocked drainage canals. Glaucoma due to a penetrating eye injury is best treated by preventive measures when the initial wound occurs. Corticosteroid therapy to help prevent tissue damage and scarring and antibiotics are an important component of initial treatment. Initial treatment can also include surgery to remove excess eye fluid or reduce swollen tissue.

If glaucoma does develop over the long term, medications that reduce the production of eye fluid are usually the first method of treatment, followed by filtering surgery.

Neovascular Glaucoma

The abnormal formation of new blood vessels on the iris and over the eye's drainage channels can cause a form of secondary open angle glaucoma.

Neovascular glaucoma is always associated with other abnormalities, most often diabetes. It never occurs on its own. The new blood vessels block the eye's fluid from exiting through the trabecular meshwork (the eye's drainage canals), causing an increase in eye pressure. This type of glaucoma is very difficult to treat.

Irido Corneal Endothelial Syndrome (ICE)

This rare form of glaucoma usually appears in only one eye, rather than both. Cells on the back surface of the cornea spread over the eye's drainage tissue and across the surface of the iris, increasing eye pressure and damaging the optic nerve. These corneal cells also form adhesions that bind the iris to the cornea, further blocking the drainage channels.

Irido Corneal Endothelial Syndrome occurs more frequently in light-skinned females. Symptoms can include hazy vision upon awakening and the appearance of halos around lights. Treatment can include medications and filtering surgery. Laser therapy is not effective in these cases.

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Treatments

Medication

Eyedrops. Glaucoma treatment often starts with medicated eyedrops. Doctors prescribe several types of drops. The types of eyedrops that doctors most commonly prescribe include:

Beta blockers. These reduce the production of aqueous humor. Side effects can include low blood pressure, reduced pulse rate, and fatigue. Beta blockers can also cause a shortness of breath in people who have a history of asthma or other respiratory disorders. Additionally, beta blockers can change cardiac activity by decreasing the amount of blood the heart pumps out, which may reduce the pulse rate and/or slow down the heart's response rate during exercise. Rare side effects include reduced libido and depression. They are not suitable for patients who have asthma, bronchitis or emphysema, or patients who have diabetes and use insulin.

Alpha-adrenergic agents. These reduce the production of aqueous humor. Examples include apraclonidine (Iopidine) and brimonidine (Alphagan). Possible side effects include increased blood pressure; dizziness; red, itchy or swollen eyes; dry mouth; and allergic reactions.   Allergic reactions to these drops are frequent. Blurred vision can also occur. Vision can also be decreased in people who have had cataracts removed. Headaches and burning of the eyes are also common. Cardiac side effects may include rapid heart rate or fluctuations in heart rhythm.

Carbonic anhydrase inhibitors. These medications, which include dorzolamide (Trusopt), reduce the amount of aqueous humor. Possible side effects include frequent urination and a tingling sensation in the fingers and the toes, but these occur more frequently when a carbonic anhydrase inhibitor is taken orally. If you're allergic to sulfa drugs, this type of medication shouldn't be used unless no alternative is possible, and then only with great care.

Prostaglandin analogues. These eyedrops increase the outflow of aqueous humor. These hormone-like substances, which include latanoprost (Xalatan), may be used in conjunction with a drug that reduces production of aqueous humor. Possible side effects include mild reddening and stinging of the eyes and darkening of the iris, changes in the pigment of the eyelid skin, and mild swelling of the central retina (a condition known as cystoid macular edema).

Prostamides. These include bimatoprost (Lumigan). They increase the outflow of aqueous humor. Possible side effects include mild to moderate reddening of the eyes and itchy eyes.

Miotics. Miotics, such as pilocarpine (Isopto Carpine, Pilocar) increase the outflow of aqueous humor. Possible side effects include pain around or inside the eyes, brow ache, blurred or dim vision, nearsightedness, allergic reactions, a stuffy nose, sweating, increased salivation and occasional digestive problems.

Epinephrine compounds. These also increase the outflow of aqueous humor. Possible side effects include red eyes, allergic reactions, palpitations, an increase in blood pressure, headache and anxiety.

Alpha Agonist.   These compounds work to both decrease production of fluid and increase drainage.   Side effects can include burning or stinging upon instillation of the eye drop, fatigue, headache, drowsiness, dry mouth and dry nose.

Oral medications If eyedrops alone don't bring eye pressure down to the desired level, the doctor may also prescribe an oral medication. Carbonic anhydrase inhibitors, such as acetazolamide and methazolamide, are commonly prescribed oral medications for glaucoma. They are taken with meals to reduce side effects. Possible side effects of carbonic anhydrase inhibitors include rashes, depression, fatigue, kidney stones, lethargy, stomach upset, a metallic taste in carbonated beverages, impotence and weight loss.

 

Glaucoma Surgery

Surgery involves either laser treatment or making a cut in the eye to reduce the intraocular pressure (IOP). The type of surgery your doctor recommends will depend on the type and severity of your glaucoma and the general health of your eye. Surgery can help lower pressure when medication is not sufficient, however it cannot reverse vision loss.

Doctors often recommend laser surgery before filtering microsurgery, unless the eye pressure is very high or the optic nerve is badly damaged. During laser surgery, a tiny but powerful beam of light is used to make several small scars in the eye's trabecular meshwork (the eye's drainage system). The scars help increase the flow of fluid out of the eye.

In contrast, filtering microsurgery involves creating a drainage hole with the use of a small surgical tool. When laser surgery does not successfully lower eye pressure, or the pressure begins to rise again, the doctor may recommend filtering microsurgery.

Filtering Microsurgery

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When medicines and laser surgeries do not lower eye pressure adequately, doctors may recommend a procedure called filtering microsurgery (sometimes called conventional or cutting surgery).

In filtering microsurgery, a tiny drainage hole is made in the sclera (the white part of the eye) in a procedure called a trabeculectomy or a sclerostomy. The new drainage hole allows fluid to flow out of the eye and helps lower eye pressure. This prevents or reduces damage to the optic nerve.

In most cases, there is no pain involved. The surgery is usually done with a local anesthetic and relaxing medications. Often a limited type of anesthesia, called intravenous (I.V.) sedation, is used.

In addition, an injection is given around or behind the eye to prevent eye movement. This injection is not painful when I.V. sedation is used first. The patient will be relaxed and drowsy and will not experience any pain during surgery.

Most of the related studies document follow-up for a one year period. In those reports, it shows that in older patients, glaucoma filtering surgery is successful in about 70-90% of cases, for at least one year.

Occasionally, the surgically-created drainage hole begins to close and the pressure rises again. This happens because the body tries to heal the new opening in the eye, as if the opening were an injury. This rapid healing occurs most often in younger people, because they have a stronger healing system. Anti-wound healing drugs, such as mitomycin-C and 5-FU, help slow down the healing of the opening. If needed, glaucoma filtering surgery can be done a number of times in the same eye.

Usually, filtering surgery is an outpatient procedure, requiring no overnight hospital stay. Within a few days after surgery, the eye doctor will need to check on the eye pressure. The doctor will also look for any signs of infection or increase in inflammation.

For at least one week after surgery, patients are advised to keep water out of the eye. Most daily activities can be done, however, it is important to avoid driving, reading, bending, and doing any heavy lifting.

Each case is different, so check with your doctor for specific advice.

The eye will be red and irritated shortly after surgery, and there may be increased eye tearing or watering. The inner eye fluid flows through the surgically-created hole and forms a small blister-like bump called a bleb. The bleb, usually located on the upper surface of the eye, is covered by the eyelid, and is usually not visible.

There may be some vision changes, such as blurred vision, for about six weeks after the surgery. After that time, vision will usually return to the same level it was before surgery.

Vision can sometimes improve after surgery in patients who had been using pilocarpine. After stopping pilocarpine drops, the pupil returns to normal size, allowing more light to enter the eye.

In a few cases, the vision may be worse due to very low pressure. Cataracts or wrinkle in the macula area of the eye may develop.

After surgery, you may need to change your contact lenses or glasses. Gas permeable or soft contact lenses may be worn. However, the bleb may cause fitting problems, and special care will be needed to avoid infection of the bleb. Contact lens users should discuss these problems with their eye doctor following surgery.

Laser Surgery

Laser surgeries have become important in the treatment of different eye problems and diseases.

Laser surgery can carry some risks. Some people experience a short-term increase in their intraocular pressure (IOP) soon after surgery. In others who require YAG CP (Cyclophoto-Coagulation) surgery, there is a risk of the IOP dropping too low to maintain the eye's normal metabolism and shape. The use of anti-glaucoma medication before and after surgery can help to reduce this risk.

There is a slight stinging sensation associated with LPI and ALT. In YAG CP laser surgery, a local anesthetic is used to numb the eye. Once the eye has been numbed, there should be little or no pain and discomfort.

In most cases, medications are still necessary to control and maintain eye pressure. However, surgery may lessen the amount of medication needed.

In general, patients can resume normal daily activities the next day after laser surgery.

The procedure is usually performed in an eye doctor's office or eye clinic. There is a small risk of developing cataracts after some types of laser surgery for glaucoma. However, the potential benefits of the surgery usually outweigh any risks.

The following are the most common laser surgeries to treat glaucoma.

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Laser Peripheral Iridotomy (LPI)

Laser Peripheral Iridotomy (LPI) is used for the treatment of narrow-angle glaucoma.   Narrow-angle glaucoma occurs when the angle between the iris and the cornea in the eye is too small. This causes the iris to block fluid drainage, increasing inner eye pressure. LPI makes a small hole in the iris, allowing it to fall back from the fluid channel and helping the fluid drain.

 

 

 

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Argon Laser Trabeculoplasty (ALT)

Argon Laser Trabeculoplasty (ALT) is used for the treatment of primary open angle glaucoma (POAG). The laser beam opens the fluid channels of the eye, helping the drainage system work better. In many cases, medication will still be needed. Usually, half the fluid channels are treated first. If necessary, the other fluid channels can be treated in a separate session another time. This method prevents over-correction and lowers the risk of increased pressure following surgery. Argon laser trabeculoplasty has successfully lowered eye pressure in up to 75% of patients treated.

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Selective Laser Trabeculoplasty (SLT)

Selective Laser Trabeculoplasty is used for the treatment of primary open angle glaucoma (POAG). SLT uses a combination of frequencies that allow the laser to work at very low levels. It treats specific cells “selectively,” leaving untreated portions of the trabecular meshwork intact. For this reason, it is believed that SLT, unlike other types of laser surgery, may be safely repeated many times.

 

 

 

 

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Neodymium: YAG laser cyclophotocoagulation (YAG CP)

This is a “last-ditch” procedure to save an eye from severe glaucoma damage not being managed by standard glaucoma surgery. This surgery destroys part of the ciliary body, the part of the eye that produces intraocular fluid. The procedure may need to be repeated in order to permanently control glaucoma.

 

 

 

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Drainage implants

Another type of operation, called drainage implant surgery, may be an option for people with secondary glaucoma or for children with glaucoma. Like the trabeculectomy, drainage implant surgery is performed at a hospital or an outpatient clinic. The patient will be given medication to help the patient relax and eyedrops and an anesthetic to numb the eye. Then the doctor inserts a small silicone tube in the eye to help drain aqueous humor. After the surgery the patient will wear an eye patch for 24 hours and use eyedrops for several weeks to fight infection and scarring. The doctor will check the eyes several times in the weeks that follow.

 

 

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Diagnosis

Regular glaucoma check-ups include two routine eye tests: tonometry and ophthalmoscopy. Others include perimetry, gonioscopy, optic nerve computer imaging, and pachymetry.

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Tonometry. Tonometry is a simple, painless procedure that measures your intraocular pressure. It is usually the initial screening test for glaucoma. Two common techniques are air-puff and applanation. Air-puff tonometry uses a puff of air to measure the amount of force needed to indent your cornea. An applanation tonometer is a sophisticated device that's usually fitted to a slit lamp. Slit lamps use an intense line of light — a slit — providing illumination of the cornea, iris, lens and anterior chamber, and allowing your doctor a good view of these structures. With tonometry, your doctor numbs your eyes with drops and has you sit at the slit lamp, where a small flat-tipped cone pushes lightly against your eyeball. The force required to flatten (applanate) a small area of your cornea translates into a measure of your intraocular pressure. Average normal eye pressures range from 10 to 21 or 22 millimeters of mercury (mm Hg), though most pressures are within 14 to 16 mm Hg. Doctors consider anyone with eye pressure greater than 23 mm Hg to be at risk of developing glaucoma and in need of careful monitoring for early signs of glaucoma.

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Opthalmoscopy. Ophthalmoscopy is used to examine the inside of the eye, especially the optic nerve. In a darkened room, the doctor will magnify your eye by using an ophthalmoscope (an instrument with a small light on the end).   To check the fibers in your optic nerve, your eye doctor uses an instrument called an ophthalmoscope or biomicroscope, which enables him or her to look directly through the pupil to the back of your eye. Your doctor may also use laser light and computers to create a three-dimensional image of your optic nerve. This can reveal slight changes that may indicate the beginnings of glaucoma.   This helps the doctor look at the shape and color of the optic nerve.   If the pressure in the eye is not in the normal range, or if the optic nerve looks unusual, then one or two special glaucoma tests will be done. These two tests are called perimetry and gonioscopy.

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Perimetry. The Goldman perimetry test is also called a visual field test. No computers are used in this test. During this test, you will be asked to look straight ahead and then indicate when a moving light passes your peripheral (or side) vision. This helps draw a “map” of your vision. One method, known as tangent screen perimetry, requires you to look at a screen with a target in the center. Your eye doctor or a technician manipulates a small object on a wand at different locations in your visual field. You indicate whenever you see the object come into view. By repeating this process over and over again, your entire visual field can be mapped. In computerized visual field testing you will be asked to place your chin on a stand which appears before a computerized screen. Whenever you see a flash of light appear, you will be asked to press a button. At the end of this test, your doctor will receive a printout of your field of vision.

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Gonioscopy. Gonioscopy is a painless eye test that 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. In this test a special lens with an angled mirror is placed on the eye to inspect the drainage angle.

 

Optic Nerve Computer Imaging. In recent years three new techniques of optic nerve imaging have become widely available. These are scanning laser polarimetry (GDx), confocal laser ophthalmoscopy (Heidelberg Retinal Tomography or HRT II), and optical coherence tomography (OCT).

The GDx machine does not actually image the optic nerve but rather it 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. The HRT II scans the retinal surface and optic nerve with a laser. It then constructs a topographic (3-D) image of the optic nerve including a contour outline of the optic cup. The nerve fiber layer thickness is also measured. The OCT instrument utilizes a technique called optical coherence tomography which creates images by use of special beams of light. The OCT machine can create a contour map of the optic nerve, optic cup and measure the retinal nerve fiber thickness. Over time all three of these machines can detect loss of optic nerve fibers.

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Pachymetry. A pachymetry test is a simple, quick, painless test to measure the thickness of your cornea. The procedure takes only about a minute to measure both eyes.   The thickness of your corneas is an important factor for accurately diagnosing glaucoma. If you have thick corneas, your eye pressure reading may seem high even though you don't have glaucoma. Conversely, people with thin corneas can have low pressure readings, but have glaucoma.

Many times, patients with thin corneas (less than 555 µm) show artificially low IOP readings. This is dangerous because if your actual IOP is higher than your reading shows, you may be at risk for developing glaucoma and your doctor may not know it. Left untreated, high IOP can lead to glaucoma and vision loss. It is important that your doctor have an accurate IOP reading to diagnose your risk and decide upon a treatment plan.

Those patients with thicker CCT may show a higher reading of IOP than actually exists. This means their eye pressure is lower than thought, a lower IOP means that risk for developing glaucoma is lowered. However, it is still important to have regular eye exams to monitor eye pressure and stay aware of changes.

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BI0108 Organ Replacement Spring 2006 | Brown University Biomedical Engineering| All Rights Reserved

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