Glaucoma

Summary

Glaucoma is a group of diseases that affect the optic nerve, which connects the eye to the brain. It is a leading cause of vision loss and blindness in the United States and worldwide. It is the leading cause of blindness in working–age African–Americans.

Glaucoma can affect one or both eyes. It typically involves gradually increased pressure inside the eye.  It usually is painless and has no other signs or symptoms. Any damage caused by glaucoma is irreversible, but diagnosis and treatment can avert further loss of vision. There is also an acute form of glaucoma that is sudden, painful and a medical emergency.

There is an increased risk of glaucoma in people over age 60, diabetes patients, people with a family history of glaucoma and certain racial groups. Other risk factors include eye injury and use of corticosteroid drugs.

Early detection and treatment can minimize or prevent eye damage. Tests to detect glaucoma include the dilated pupil examination and tonometry (a measure of pressure inside the eye). Prescription eye drops can reduce the risk of developing glaucoma by about half. Other medications, laser therapy and open surgery may also be options for treatment.

About glaucoma

Glaucoma is a group of diseases affecting the optic nerve in one or both eyes. It usually, but not always, involves increased pressure inside the eye. Glaucoma can impair vision or lead to blindness, but early detection and treatment can prevent serious damage.

Each optic nerve contains about 1.2 million nerve fibers in a cable–like structure that connects the retina to the brain. When the nerve fibers are damaged, the nerve impulses to the brain are thwarted and blind spots develop. Peripheral (side) vision can be reduced so that a person experiences tunnel vision. If untreated, the disease destroys the optic nerve and blindness results.

There is a space in the front of the eye called the anterior (front) chamber. It is filled with aqueous humor, a clear liquid containing nutrients. This fluid needs to flow freely in and out of the chamber to nourish the surrounding tissues. There is an angle where the cornea (clear tissue over the front of the eye) and iris (colored part of the eye around the pupil) meet. Here the fluid drains through the trabecular meshwork (a spongy drain) and leaves the eye. If the fluid passes through too slowly, pressure builds. This pressure against the blood flow to optic nerve is believed to damage the nerve and destroy vision.

Having increased eye pressure does not mean someone has glaucoma but does increase the risk of developing the disease. Some individuals tolerate above–normal eye pressure. Conversely, some people with relatively low eye pressure develop glaucoma. This is called low–tension or normal–tension glaucoma.

A recent study, known as the OHTS (Ocular Hypertension Treatment Study), showed that early treatment of patients who have high eye pressure reduces the risk of vision loss. The study also showed that patients with thinner corneas have higher pressures than those measured in the ophthalmologist's office, and may constitute a large portion of the patients with normal–tension glaucoma. These findings have made corneal pachymetry (measurement of the thickness of the cornea) a routine part of a glaucoma examination.

The most common type of glaucoma, open–angle glaucoma, develops gradually and is largely symptomless. The patient will not notice any change in vision until the end stage of the disease when most vision is gone. Early detection of glaucoma is therefore crucial to preventing optic nerve damage and resulting vision loss. Regular eye examinations are necessary, especially for those with risk factors, including people over age 60, people with diabetes, people with a family history of glaucoma, blacks and Hispanics.

If detected and treated early, vision can often be saved.  But lifetime monitoring and treatments are required.

Types and differences of glaucoma

Many types of glaucoma exist. Some have stronger hereditary links than others, meaning blood relatives of glaucoma patients should pay special attention to their family history and their own eye health. The types of glaucoma include:

Open–angle glaucoma. Damage to the optic nerve (which connects the retina to the brain) caused by increased eye pressure due to poor drainage of aqueous humor (fluid inside the eye). The process is gradual and painless. Vision loss may be significant and irreversible by the time a problem is detected. This is the most common form of glaucoma. The risk of open–angle glaucoma increases with age, and heredity may be a factor. Varieties of open–angle glaucoma include:

Normal–tension glaucoma (also called low–tension glaucoma). Optic nerve damage accompanied by normal or low eye pressure and eventual loss of vision. Often seen in patients with thin corneas. This form of glaucoma accounts for one–third of glaucoma cases in the United States, according to the Glaucoma Research Foundation. This condition is not fully understood.  Experts believe that hypersensitivity in the optic nerve fibers or reduced blood flow to the optic nerve due to a variety of diseases leads to death of optic nerve cells. Below–normal pressure is required in such cases to prevent further nerve damage and loss of vision.

Pigmentary glaucoma, in which shedding of pigment from the iris (colored part of the eye) clogs drainage of the aqueous humor. This hereditary condition is found more often in myopic (nearsighted) people and men, according to the Glaucoma Foundation. The condition begins in the 20s and 30s, threatening eyesight at an early age.

Angle–closure glaucoma (also called closed–angle or narrow–angle glaucoma). The aqueous humor is partially or totally blocked from draining by the iris. This uncommon condition involves less commonly an acute, painful attack that is a medical emergency requiring immediate treatment. If untreated, blindness can result within a day or two. Whereas most cases of glaucoma are painless and gradual, acute angle closure is typically excruciating and sudden. Often inherited, it is found more often among Asians and farsighted people, according to the Glaucoma Foundation. More common than acute angle–closure glaucoma is the chronic variation, in which the iris intermittently blocks the drainage, with less apparent symptoms. Both forms are treated surgically with a peripheral iridotomy treatment using a laser in the ophthalmologist's office, or if necessary, surgically in an operating room.

Congenital glaucoma. An inherited birth defect where the drainage angle of the eye is blocked by a membrane and slows the normal fluid drainage and increases eye pressure. Children with this birth defect will have cloudy eyes, large eyes (buphthalmos) or one eye bigger than the other. They may also have a lot of tearing and turn away from bright lights. In children under age 3, the eye pressure increases the size of the eyes. Surgery (goniotomy) done promptly can sometimes spare vision.

Secondary glaucoma. Acute or chronic glaucoma caused by trauma or related to another condition, such as diabetes or cataracts. In one kind of secondary glaucoma, neovascular glaucoma, new blood vesselsproliferate from the iris and block the flow of water from the eyes. Neovascular glaucoma  is often associated with a type of diabetic retinopathy known as proliferative retinopathy (involving new blood vessels growing in and scarring the retina) and is strongly linked to diabetes. Neovascular glaucoma is painful, progresses rapidly and damages vision.

Risk factors and potential causes of glaucoma

The underlying causes of glaucoma are unknown. There are genetic links to several types of glaucoma.  Contributing and risk factors include:

Increased eye pressure. People with elevated pressure inside the eye are more prone to, but do not always develop, glaucoma. In addition, some people with normal or low eye pressure develop the disease.

Age and race. High–risk groups are blacks over age 40 and anyone over age 60, especially Mexican–Americans, according to the U.S. government’s National Eye Institute. Asians are susceptible to angle–closure glaucoma. Japanese people are susceptible to normal–tension glaucoma.

Family medical history. A family history of glaucoma indicates likelihood of developing the disease.

High blood pressure (hypertension). Glaucomatous damage is exacerbated by above–normal blood pressure.

Diabetes. Elevated glucose (blood sugar), high blood pressure and heart disease related to diabetes all raise the odds of developing glaucoma. People with type 2 diabetes have higher rates of cataracts (clouding of the lens) and glaucoma leading to vision loss compared to the general population, in addition to their risk of diabetic retinopathy.

Eye injuries. Severe physical trauma to the eye, burns from chemicals or penetrations can all lead to increased eye pressure, lens dislocations or blockage of drainage.

Nearsightedness or farsightedness. Inability to see objects at far or close distances without glasses or contact lenses increases the likelihood of developing this disease.

Prolonged use of corticosteroids.  Anti–inflammatory medication commonly used to prevent asthma, arthritis and allergy attacks. Secondary glaucoma is more likely in prolonged users of corticosteroids, including cortisone.

Eye abnormalities. Structural eye abnormalities increase susceptibility to certain kinds of glaucoma, such as reduced thickness of the central cornea.

Exfoliation syndrome. A condition involving exfoliation (shedding) of cells due to friction between the lens and the iris. Pigment and exfoliation material clogs the trabecular meshwork, elevating intraocular pressure. A whitish material builds up on the lens and can be seen by slit–lamp examination. This syndrome increases the risk of glaucoma (open–angle, closed–angle or both) by six times, according to the Glaucoma Foundation. Ten percent of people over age 50 have this syndrome, the organization reports.

Other medical conditions. Migraines, poor circulation, retinal detachment, eye tumors and eye inflammations increase the risk of developing glaucoma. Some types of eye surgery may lead to secondary glaucoma.

Signs and symptoms of glaucoma

There are several types of glaucoma.  Signs and symptoms vary depending on which type the patient is experiencing.

Initially, no symptoms may be present with open–angle glaucoma (e.g., no pain or vision loss). As the disease progresses, peripheral (side) vision is affected, narrowing the field of vision like a tunnel until blindness occurs. Glaucoma can develop in one or both eyes. Usually, both eyes are affected.

An acute attack of angle–closure glaucoma can lead to permanent loss of vision within hours. It involves a rapid rise in eye pressure. These attacks often occur at dusk or dawn or in dark areas such as theaters. The following symptoms indicate a medical emergency requiring immediate treatment:

  • Severe eye and head pain
  • Blurred vision
  • Perception of halos around lights
  • Nausea and vomiting accompanied by eye pain
  • Reddening of the eye

Diagnosis methods for glaucoma

Regular eye examinations by an ophthalmologist are important in detecting glaucoma in time, before damage to the optic nerve takes place. The National Eye Institute advises a comprehensive eye examination every two years for high–risk individuals (black people older than 40, anyone over 60). Earlier or more frequent examinations may be recommended for people with additional risk factors, such as other eye conditions or diabetes.

Screening and tests to detect glaucoma may include:

Tonometry. This painless test measures pressure inside the eye (intraocular pressure [IOP]). Two variations exist. During air puff tonometry, the eye is numbed with drops and a puff of air is blown at it to measure the amount of air deflected by the eye. During applanation tonometry, the eye is numbed and a slit lamp (device emitting powerful light) illuminates the eye so the physician can examine it.  A small pressure–sensitive tip measures IOP by touching the surface of the eye. Eye pressure that exceeds 21 millimeters of mercury (mmHg) indicates a risk for glaucoma.

• Visual field test (perimetry). Various tests, some using computer screens, assess any loss of peripheral (side) vision, a sign of glaucoma.

• Visual acuity test. An eye chart test. This test is used to measure vision.

• Dilated pupil examination. Drops are put into the eyes to enlarge the pupils. The inside of the eye is then examined for damage to the retina or to the optic nerve, a sign of glaucoma. After the exam, vision remains blurred for a short time.

Gonioscopy. A special lens with an angled mirror is placed on the eye to inspect the drainage angle. This procedure can predict the likelihood of a patient having an acute angle–closure attack.

• Funduscopy (ophthalmoscopy). Examination of the back of the eye (fundus) for damage. A funduscope, ophthalmoscope or biomicroscope is used to look through the pupil to the back of the inner eye. Any abnormal &cupping& or depression in the optic nerve can be seen along the back wall of the eye. A laser light and computer tomograph can re–create a three–dimensional image of the optic nerve, revealing changes that may indicate glaucoma.

Pachymetry. Test to measure the thickness of the cornea (the clear covering over the front of the eye). The eyes are numbed and tested with an ultrasonic wave instrument to gauge the thickness of the cornea. People with thin corneas can have glaucoma even if the pressure in the eye is low.

• Other tests. These may include computerized imaging and photographing the optic nerve while the eyes are dilated. The images are then studied and compared over time for changes in the eye.

Treatment options for glaucoma

Damage from glaucoma is irreversible. Treatments focus on preventing further damage to the eyes. Patients should ask their ophthalmologist about the advantages, risks and side effects of treatment options.

Periodic (in some cases every three or four months) and thorough examination is crucial to the prevention of further eye damage and loss of vision. For patients who have already lost some of their vision, low–vision services may be an option to help them compensate and to help maintain remaining sight.

Medications used to treat glaucoma include:

• Eye drops. Prescription eye drops reduce the eye pressure by decreasing the production of aqueous fluid or improving the flow of fluid through the drainage angle. Eye drops, typically applied daily or several times a day, are a common and usually effective treatment for glaucoma and have been found to delay and even prevent the onset of glaucoma. The patient should follow instructions and not skip drops because damage to the optic nerves can occur if eye drops are not applied properly. A physician can advise about possible side effects of the many types of eye drops. Physicians may avoid prescribing certain types of medicated drops, such as drops containing beta blockers, to people with diabetes.

• Oral medications. Carbonic anhydrase inhibitors may be prescribed as supplements to eye drops.

Surgery is recommended if it is needed to prevent further optic nerve damage or if medication is ineffective or not tolerated by the patient. Possible complications of surgical procedures are: infection, loss of vision, scarring, development of cataracts, swelling (edema), bleeding or undesired changes in eye pressure.

Surgery can be either laser (photocoagulation) or conventional:

Argon laser trabeculoplasty. An outpatient laser procedure used to modify the trabecular meshwork (drain) to help control eye pressure by allowing fluid to drain from the eye. This procedure is used for open–angle glaucoma. First, numbing drops are applied to the eye.  Then several burns are made in the trabecular meshwork using a high–intensity beam of light aimed at the lens and reflected onto the meshwork. In this way the drainage space is enlarged and the eye pressure is reduced.

This laser treatment is applied to one eye at a time and may take several weeks to treat the other eye. Also, it may be performed in two sessions per eye. According to the Glaucoma Research Foundation, it is 75 percent effective. The benefits of the procedure may be temporary and in some cases last only two years. Repeat procedures are usually ineffective. Glaucoma medication should still be taken after this procedure.

There is a new form of this procedure (SLT), which uses a different laser and may cause less scarring and have better results.

Cyclophotocoagulation. A laser procedure used to destroy parts of the ciliary body to reduce its production of aqueous humor (fluid in the eye). This procedure is used in advanced or severe cases of glaucoma, in eyes with minimal or no vision, to reduce the eye pressure.

• Drainage devices. A special plastic or collagen tube can be surgically implanted into the eye to absorb excess aqueous fluid and lower eye pressure. Such devices may be considered when other treatments have failed.

Filtering microsurgery. An outpatient surgical procedure used to create a new drainage channel in the eye for the aqueous fluid to leave the eye. After the eye area is numbed, a small piece of tissue is removed to create a new area for the fluid to drain from. The patient applies eye drops after surgery to prevent infection.

This procedure is performed on one eye at a time and is scheduled four to six weeks apart for each eye. The success rate is 60 to 80 percent in lowering eye pressure, according to the National Eye Institute. A second operation may be required if the opening narrows from scarring. Possible side effects include infection, cataracts, bleeding or decreased visual acuity.

Iridotomy. An outpatient procedure performed to stop a chronic or acute closed–angle attack of glaucoma. This is an emergency procedure performed by an ophthalmologist, who uses a combination of eye drops to constrict the pupil and provides the patient with medication to reduce the eye's fluid production. Under anesthesia, a laser beam is used to create a small opening in the iris (colored part of the eye) to allow drainage of fluid through the trabecular meshwork. This may be done as a preventative measure for the unaffected eye as well.

Prevention methods for glaucoma

Early detection and treatment of glaucoma can significantly lower the chances of developing glaucoma and its resulting loss of vision. Physicians of high–risk patients, such as patients over 60, people with diabetes, people with a family history of glaucoma, blacks and Hispanics, may recommend comprehensive eye examinations every year. Patients diagnosed with glaucoma should take their medication as prescribed and continue to see their eye care specialist regularly.

Scientists at the U.S. government's National Eye Institute found that eye drops used daily for lowering eye pressure delayed and reduced the development of primary open–angle glaucoma in black Americans as much as 50 percent. This is a significant finding because primary open–angle glaucoma is the nation's most common form of glaucoma and a leading cause of blindness.

According to the American Academy of Ophthalmology, the recommended schedule for comprehensive eye exams in patients without any eye disease is as follows:

Age 20–29. Individuals of African descent and those with a family history of glaucoma should have an eye exam every three to five years. Others should have an eye exam at least once during this period.

Age 30–39. Individuals of African descent and those with a family history of glaucoma should have an eye exam at least every two to four years. Others should have an eye exam at least twice during this period.

Age 40–64. Every two to four years.

Age 65 and older. Every one to two years.

Patients who are diagnosed with glaucoma should inform blood relatives of their condition to alert them to their own potential for developing the disease. Blood relatives should be encouraged to get a comprehensive eye examination at least once every two years. Some insurance plans, including Medicare, cover high–risk individuals for comprehensive eye exams to screen for glaucoma.

Research has shown that exercise may reduce the risk of glaucoma. It also helps control diabetes and high blood pressure, two of the risk factors for glaucoma.

Questions for your doctor regarding glaucoma

Preparing questions in advance can help patients have more meaningful discussions with their physicians regarding their conditions. Patients may wish to ask their doctor the following questions about glaucoma:

  1. How much does having diabetes increase my risk of glaucoma?
  2. If a relative has glaucoma, am I at higher risk?
  3. How often should I have an eye exam? What should it include?
  4. How can I reduce my chances of getting glaucoma?
  5. What are the best treatments for glaucoma?
  6. Do any recommended glaucoma treatments alter blood sugar or otherwise affect my diabetes?
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