Glaucoma

Glaucoma is a group of eye disorders in which damage to the optic nerve results in visual loss and blindness. Glaucoma usually occurs when the normal fluid pressure inside the eyes gradually increases, although some people with statistically normal eye pressures may also get glaucoma.

The optic nerve is a bundle of nerve fibers that connects the retina to the brain, The retina is the light-sensitive tissue at the back of the eye. The eye is constantly producing fluid that drains out little by little through a part of the eye called the trabecular meshwork. Anything that blocks the meshwork prevents drainage; the rise in pressure inside the eye can then cause glaucoma.

Glaucoma is the most common form of irreversible blindness, and the second-most common cause of blindness worldwide.

Types

Primary open-angle glaucoma

Primary open-angle glaucoma is the most common type. It happens when the eye’s drainage canals become clogged over time. The pressure inside the eye (intraocular pressure [IOP]) rises because the appropriate amount of fluid is not able to drain from the eye. With open-angle glaucoma, the openings to the drainage canals are clear with no blockages. The clogging occurs further down the drainage canals, similar to a clogged pipe below the drain in a sink.

Most people have no symptoms and no early warning signs. If open-angle glaucoma is not diagnosed and treated, it can cause a gradual loss of vision. This type of glaucoma develops slowly and sometimes without noticeable vision loss for many years. It usually responds well to medication, especially if caught early and treated.

Closed-angle glaucoma

This type of glaucoma is also known as acute narrow-angle glaucoma. It occurs less commonly than open-angle glaucoma. The mechanism of this disorder is also different because the eye pressure usually rises very quickly.

Closed-angle glaucoma happens when the drainage canals get blocked or covered by part of the iris (the colored part of the eye), and the fluid at the front of the eye cannot reach the angle to exit the eye at the drainage duct. The result is a sudden increase in eye pressure. This is a medical emergency and should be treated immediately. Without treatment to improve the flow of fluid, visual loss can occur in just one or two days. Usually, prompt laser surgery and medications can clear the blockage to restore eyesight.

Symptoms of closed-angle glaucoma often include headaches, severe eye pain, blurred vision, nausea, and seeing rainbows around lights. The condition isn't always easy to diagnose, particularly in people who are sedated, handicapped, or who have trouble communicating.^[

Low-tension or normal-tension glaucoma

Optic nerve damage and decreased side vision occur in some people with normal eye pressure. This is called low-tension or normal-tension glaucoma. Lowering eye pressure at least 30% through medicines slows the disease in some people. In others, though, glaucoma may worsen, despite low pressures.

A comprehensive medical history is important in identifying the potential risk factors, such as low blood pressure, that contribute to low-tension glaucoma. If no risk factors are identified, the treatment options for low-tension glaucoma are the same as for open-angle glaucoma.

Congenital glaucoma

Children born with a defect in the angle of the eye that slows the normal drainage of fluid have congenital glaucoma (present at birth). These children usually have symptoms, such as cloudy eyes, sensitivity to light, and excessive tearing. Conventional surgery typically is the suggested treatment, because medications may have unknown effects in infants and be difficult to administer. Surgery is safe and effective. If surgery is done promptly, these children usually have an excellent chance of having good vision.

Secondary glaucoma

Secondary glaucoma is any glaucoma that develops as a complication of other medical conditions. These types of glaucomas are sometimes associated with eye surgery or advanced cataracts, eye injuries, certain eye tumors, or uveitis (eye inflammation). Pigmentary glaucoma occurs when pigment from the iris (the colored part of the eye) is sloughed off and blocks the trabecular meshwork (drainage area). A severe form, called neovascular glaucoma, is linked to diabetes. Corticosteroid drugs used to treat other eye disorders and other diseases can trigger glaucoma in some people. Treatment includes medications, laser surgery, or conventional surgery.

Signs and Symptoms

Open-angle

Most people with open-angle glaucoma have no symptoms until they lose vision. They may notice:

• Gradual loss of peripheral (side) vision
• A feeling of looking through a tunnel
• Straight-ahead vision decreasing over time until no vision remains

Closed-angle

Because closed-angle glaucoma happens suddenly, patients usually have symptoms. These include:

• Decreased or cloudy vision
• Nausea and vomiting
• Pupil does not react to light
• Red eye
• Severe eye pain, facial pain
• Swelling of the eye

Congenital

Congenital glaucoma can present as:

• Cloudiness of the front of the eye
• Enlargement of one eye or both eyes
• Red eye
• Sensitivity to light
• Tearing

Causes

The underlying causes of glaucoma are not completely understood. Although glaucoma is normally associated with increased eye pressure, people with normal or low eye pressure can experience vision loss. Those with higher-than-normal eye pressure may never experience optic nerve damage.

Increased intraocular pressure

 

In the front of the eye is a space called the anterior chamber. A clear fluid flows continuously in and out of the chamber and nourishes the tissues. The fluid leaves the chamber at the open angle where the cornea and iris meet. When the fluid reaches the angle, it flows through the spongy trabecular meshwork, like a drain, and leaves the eye.

Sometimes, when the fluid reaches the angle, it passes too slowly through the meshwork drain. As the fluid builds up, the pressure inside the eye rises to a level that may damage the optic nerve. When the optic nerve is damaged from increased pressure, open-angle glaucoma and vision loss may result. That's why controlling pressure inside the eye is important.

Increased eye pressure increases the risk for glaucoma, but it is not a guarantee of getting the disease, because some people can tolerate higher eye pressure better than others. Glaucoma is diagnosed only if the optic nerve is damaged. If a person has increased eye pressure but no damage to the optic nerve, a diagnosis of glaucoma cannot be made.

Whether a person develops glaucoma depends on the level of pressure the optic nerve can tolerate without being damaged. This level is different for each person. An eye exam helps the eye care professional determine what level of eye pressure is normal for each person.

Low-tension or normal-tension causes

Glaucoma can develop without increased eye pressure. This form of glaucoma is called low-tension or normal-tension glaucoma.^[1] It is not as common as open-angle glaucoma. Although its cause is not completely understood, normal-tension glaucoma is generally believed to occur either because of an unusually fragile optic nerve that can be damaged despite a normal pressure inside the eye or because of reduced blood flow to the optic nerve.

• Unusually fragile optic nerves may be inherited.
• Reduced blood flow to the optic nerve can be due to disorders of the blood vessels (called vascular diseases), including vasospasm and ischemia.
  • Vasospasm is spasm or constriction of the blood vessels.
  • Ischemia is reduced oxygen delivered to the tissue, in this case the optic nerve, because the blood vessels are either narrowed or obstructed.

Diagnosis

Exams and tests

Glaucoma is detected through a comprehensive eye exam that includes:

1. Visual acuity test. This eye chart test measures vision at various distances. A tonometer measures pressure inside the eye to detect glaucoma.
2. Visual field test. This test measures peripheral vision, the loss of which is a sign of glaucoma.
3. Dilated eye exam. Drops are placed in the eyes to widen, or dilate, the pupils. The eye care professional uses a special magnifying lens to examine the retina and optic nerve for signs of damage and other eye problems. After the exam, close-up vision may remain blurred for several hours.
4. Tonometry. An instrument measures the pressure inside the eye. Numbing drops may be applied to the eye for this test.
5. Pachymetry. A numbing drop is applied to the eye. The eye care professional uses an ultrasonic wave instrument to measure the thickness of the cornea.

Treatment

Immediate treatment for early stage, open-angle glaucoma can delay progression of the disease, which is why early diagnosis is important.

Glaucoma treatments include medications, laser trabeculoplasty, conventional surgery, or a combination of any of these. While these treatments may prevent further vision loss, they do not improve vision loss that occurred before the treatment was started.

Holistic and alternative treatments

Treatment for impaired vision

An eye care professional can recommend services and devices for people who have lost some sight from glaucoma in order to make the most of the remaining vision. He or she can also give a referral for a specialist in low vision.

Many community organizations and agencies offer information about low-vision counseling, training, and other special services for people with visual impairments. A nearby school of medicine or optometry may also provide low-vision services.

Medications

Medications in the form of eyedrops or pills are the most common early treatment for glaucoma. Some medicines cause the eye to make less fluid. Others lower pressure by helping fluid drain from the eye. Before glaucoma treatment is started, the eye care professional should be informed of other medicines being taken. Sometimes the drops can interfere with the way other medicines work. Glaucoma medicines may be taken several times a day. Most people have no problems, but some medicines can cause headaches or other side effects. For example, drops may cause stinging, burning, and redness in the eyes.

Many drugs are available to treat glaucoma. Treatment with a different dose or a new drug may be possible if problems are experienced with what is initially prescribed.

Eyedrops

For proper application of eyedrops, these steps should be followed:

• Hands should be washed.
• Bottle should be held upside down.
• Head should be tilted back.
• Bottle should be held in one hand and placed as close as possible to the eye.
• The other hand should be used to pull down the lower eyelid to form a pocket.
• The prescribed number of drops should be placed into the lower eyelid pocket. Be sure to wait at least five minutes before applying a second eyedrop if required.
• Eye should be closed OR the lower lid should be pressed lightly with the finger for at least one minute. Either of these steps keeps the drops in the eye and helps prevent the drops from draining into the tear duct, which can increase the risk of side effects.

Surgery

Laser trabeculoplasty

Laser trabeculoplasty helps fluid drain out of the eye. The doctor may suggest this step at any time. In many cases, glaucoma drugs should be continued after this procedure. Laser trabeculoplasty is performed in the doctor's office or eye clinic. Before the surgery, numbing drops are put in the eye. The patient sits facing the laser machine, and the doctor holds a special lens to the eye. A high-intensity beam of light is aimed at the lens and reflected onto the meshwork inside the eye. The patient may see flashes of bright green or red light. The laser makes several evenly spaced burns that stretch the drainage holes in the meshwork. This allows the fluid to drain better. Like any surgery, laser surgery can cause side effects, such as inflammation. The doctor may give the patient eyedrops to take home for any soreness or inflammation inside the eye. Several follow-up visits may be required to monitor eye pressure. If glaucoma is present in both eyes, only one eye will be treated at a time. Laser treatments for each eye will be scheduled several days to several weeks apart. Studies show that laser surgery is very good at reducing the pressure in some patients. However, its effects can wear off over time. The doctor may suggest further treatment.

Conventional surgery

Conventional surgery makes a new opening for the fluid to leave the eye. The doctor may suggest this treatment at any time. Conventional surgery often is done after medications and laser surgery have not been able to control intraocular pressure.

Conventional surgery is performed in an eye clinic or hospital. Before the surgery, the patient is given medicine for relaxation. The doctor makes small injections around the eye to numb it. A small piece of tissue is removed to create a new channel for the fluid to drain from the eye.

For several weeks after the surgery, drops must be put in the eye to prevent infection and inflammation. These drops will be different from those used before surgery.

As with laser surgery, conventional surgery is performed on one eye at a time. Usually the operations are four to six weeks apart. Conventional surgery is about 60%-80% effective at lowering eye pressure. If the new drainage opening narrows, a second operation may be needed. Conventional surgery works best if the patient has not had previous eye surgery, such as a cataract operation.

In some instances, vision may not be as good as it was before conventional surgery. Conventional surgery can cause side effects, including cataracts, problems with the cornea, and inflammation or infection inside the eye. The buildup of fluid in the back of the eye may cause some patients to see shadows in their vision.

Other types of surgery involve the implantation of drainage devices, called glaucoma drainage implants.

Prevention

Glaucoma cannot be prevented, but vision can be protected, so that vision loss is less likely if glaucoma develops.

Studies have shown that the early detection and treatment of glaucoma, before it causes major vision loss, is the best way to control the disease. It is recommended that those in high-risk groups for the disease have their eyes examined every two years by an eye care professional.

Lowering eye pressure in primary open-angle glaucoma's early stages (ocular hypertension) slows progression of the disease and helps save vision. However, there isn't enough evidence to support this statement for normal-tension glaucoma.

Chances of Developing Glaucoma

About one in 10 people will eventually develop glaucoma.

Risk factors

Anyone can develop glaucoma. Some people are at higher risk than others. They include:

• African Americans over age 40.
• Everyone over age 60, especially Mexican Americans.
• People with a family history of glaucoma.

Among African Americans, studies show that glaucoma is:

• Five times more likely to occur in African Americans than in Caucasians.
• About four times more likely to cause blindness in African Americans than in Caucasians.
• Fifteen times more likely to cause blindness in African Americans between the ages of 45 and 64 than in Caucasians of the same age group.

A comprehensive dilated eye exam can reveal more risk factors, such as:

• high eye pressure
• thinness of the cornea
• abnormal optic nerve anatomy

In some people with certain combinations of these high-risk factors, medicines in the form of eyedrops reduce the risk of developing glaucoma by about half.

Medicare pays for an annual comprehensive dilated eye exam for some people at high risk for glaucoma.

Research

A large amount of research is being done in Canada to learn what causes glaucoma and to improve its diagnosis and treatment.By learning more about this process, doctors may be able to find the exact cause of the disease and learn better how to prevent and treat it. The NEI also supports clinical trials of new drugs and surgical techniques that show promise against glaucoma.

Expected Outcome

Open-angle glaucoma: Open-angle glaucoma can be managed and vision may be maintained, but the condition cannot be cured. Following up with the doctor is important. With good care, most patients with open angle glaucoma will not lose vision.

Angle-closure glaucoma: Rapid diagnosis and treatment of an attack is the key element to saving vision. If sudden eye pain or headache occurs, or any other symptoms of angle-closure attack, the person should get immediate emergency attention.

Congenital glaucoma: Early diagnosis and treatment is important. If surgery is done early enough, many children will have no future problems.

History

The term glaucoma was used in Hippocratic times, but it is likely that it was actually referring to cataracts. The knowledge that hypertension was related to glaucoma was obtained in the 1800s.

Statistics

In 1994, glaucoma was estimated to account for 5.2 million cases of blindness around the world. Millions more people who are not yet blind are affected by some form of vision loss from the disease.

Glaucoma affects about 2.5 million Americans, about 120,000 of whom are blind as a result of glaucoma. Many patients do not realize they have the disease.