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Glaucoma: What it Is, How it Occurs, Who is at Risk, and How It Can Be Treated E-mail
Written by Jeff Behar, MS, MBA   
What is glaucoma?

Glaucoma is a disease of the major nerve of vision, called the optic nerve. The optic nerve receives light from the retina and transmits impulses to the brain that we perceive as vision.

The glaucomas usually affect both eyes, but the disease can progress more rapidly in one eye than in the other. Involvement of just one eye occurs only when the glaucoma is brought on by factors such as a prior injury, inflammation, or the use of steroids in that eye.

What are the different types of glaucoma?

There are many different types of glaucoma. Most, however, can be classified as either open-angle glaucomas, which are conditions of long duration (chronic), or closed-angle (angle closure) glaucomas, which include conditions occurring suddenly (acute).

Chronic open-angle glaucoma (COAG) is by far the most common type of glaucoma and its frequency increases greatly with age. This increase occurs because the drainage mechanism gradually may become clogged with aging. As a consequence, the aqueous fluid does not drain from the eye properly. The pressure within the eye, therefore, builds up painlessly and without symptoms. Furthermore, as mentioned previously, since the resulting loss of vision starts on the side (peripherally), people are usually not aware of the problem until the loss encroaches on their central visual area.

Normal tension (pressure) glaucoma is a variant of open-angle glaucoma that is being recognized more frequently than in the past. Currently, normal pressure glaucoma is receiving a lot of research attention because its cause and treatment are uncertain. Normal tension (pressure) glaucoma is thought to be due to decreased blood flow to the optic nerve and is characterized by progressive optic nerve damage and loss of peripheral vision (visual field) despite intraocular pressures in the normal range or even below normal.

Secondary glaucoma is another type of open-angle glaucoma. It can result from:

  • cataracts
  • diabetes
  • eye (ocular) injury (even one that occurred years prior)
  • inflammation in the iris of the eye (iritis)
  • steroid-susceptible individuals
  • retinal detachment
  • retinal vein occlusion or
  • retinal blockage (The retina is the layer that lines the inside of the back of the eye.)

Pigmentary glaucoma is a type of secondary glaucoma that is more common in younger men. In this condition, for reasons not yet understood, granules of pigment detach from the iris, which is the colored part of the eye. These granules then may block the trabecular meshwork, which, as noted above, is the drainage system of the eye. Finally, the blocked drainage system leads to elevated intraocular pressure, which results in damage to the optic nerve.

Exfoliative glaucoma (pseudoexfoliation) is a  type of glaucoma that can occur with either open or closed angles. This type of glaucoma is characterized by deposits of flaky material on the front surface of the lens (anterior capsule) and in the angle of the eye. The accumulation of this material in the angle is believed to block the drainage system of the eye and raise the eye pressure. While this type of glaucoma can occur in any population, it is most prevalent in older people and people of Scandinavian descent.

Closed-angle glaucoma is a relatively rare type of glaucoma. In this condition, the patient's intraocular pressure, which ordinarily is normal, can go up very suddenly (acutely). This sudden pressure increase occurs because the filtering angle becomes closed and blocks off the drainage channels. This type of glaucoma can occur when the pupil dilates (widens or enlarges). As a result, the peripheral edge of the iris can become bunched up against its corneal attachment, thereby causing the filtering angle to close. Thus, the problem in closed-angle glaucoma is the difficulty with access of the eye fluid to the drainage system (trabecular meshwork). In contrast, remember that the problem in open-angle glaucoma is clogging within the drainage system itself. People with small eyes are predisposed to developing closed-angle glaucoma because they tend to have narrow filtering angles. Individuals who are farsighted or of Asian descent may have small eyes, narrow filtering angles, and an increased risk of developing closed-angle glaucoma. Furthermore, this condition may be triggered by medications that can dilate the pupils. These agents can be found in certain eye drops, cold remedies, or patches used to prevent seasickness. This condition can also occur spontaneously in a darkened room or a movie theater, wherein the pupil automatically dilates to let in more light. Sometimes, therefore, people with narrow angles are given eye drops to keep their pupils small. (See the section below on parasympathomimetic agents.)

Congenital (infantile) glaucoma is a relatively rare, inherited type of open-angle glaucoma. In this condition, the drainage area is not properly developed. This results in increased pressure in the eye that can lead to the loss of vision from optic nerve damage and to an enlarged eye. The eye of a young child enlarges in response to increased intraocular pressure because it is more pliable than the eye of an adult. Early diagnosis and treatment with medicine and/or surgery are critical in these infants and children to preserve their sight.

Symptoms

 

Glaucoma is often called "silent thief of sigh."because intraocular pressure can build up and destroy sight without causing obvious symptoms. 

Glaucoma is characterized by a particular pattern of progressive damage to the optic nerve that generally begins with a subtle loss of side vision (peripheral vision). If glaucoma is not diagnosed and treated, it can progress to loss of central vision and blindness.

Glaucoma is usually, but not always, associated with elevated pressure in the eye (intraocular pressure). Generally, it is this elevated eye pressure that leads to damage of the eye (optic) nerve. In some cases, glaucoma may occur in the presence of normal eye pressure. This form of glaucoma is believed to be caused by poor regulation of blood flow to the optic nerve.

A sudden glaucoma attack may be associated with severe eye pain and headache, a red (inflamed) eye, nausea, vomiting, and blurry vision. In addition, the high intraocular pressure leads to corneal swelling (edema), which causes the patient to see haloes around lights.

Statistics

Worldwide, glaucoma is the leading cause of irreversible blindness. In fact, as many as 6 million individuals are blind in both eyes from this disease. 

In the United States alone, according to one estimate, over 4 million Americans have glaucoma but only half of those know they have it.The reason they are unaware is that glaucoma initially causes no symptoms, and the loss of vision on the side (periphery) is hardly noticeable. Source: Prevent Blindness America;

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

Glaucoma is 6 to 8 times more common in African-Americans than Caucasians. and is the leading cause of blindness among African-Americans. Source: National Eye Health Program/National Institutes of Health

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. Source: Quigley, “Number of people with glaucoma worldwide,” 1996;

What causes glaucoma?

Elevated pressure in the eye is the main factor leading to glaucomatous damage to thelicate de eye (optic) nerve; the main seeing nerve for the eye. The optic nerve transmits the images we see back to the brain for interpretation.  The optic nerve is the most susceptible part of the eye to high pressure because the delicate fibers in this nerve are easily damaged.

What are the risk factors for glaucoma?

While everyone is at risk for glaucoma, certain people are at a much higher risk and need to be checked more frequently by their eye doctor. Major risk factors include:

  • age (over 45 years at greater risk)
  • family history
  • black racial ancestry
  • diabetes
  • history of elevated intraocular pressure
  • history of injury to the eye
  • use of cortisone (steroids), either in the eye or systemically (orally or injected)
  • nearsightedness (high degree of myopia), which is the inability to see distant objects clearly
  • farsightedness (hyperopia), which is seeing distant objects better than close ones (Farsighted people may have narrow filtering angles, which predispose them to acute (sudden) attacks of closed-angle glaucoma.)

Early detection is key

Because symptoms of the disease is not always obvious, awareness of the disease and risk factors are important for early detection. Early detection of glaucoma is etremely important because this disease can be successfully treated when diagnosed early.

An eye doctor (ophthalmologist) can usually detect those individuals who are at risk for glaucoma (because of, for example, a narrow filtering angle or increased intraocular pressure) before nerve damage occurs. The doctor also can diagnose patients who already have glaucoma by observing their nerve damage or visual field loss. The following tests, all of which are painless, may be part of this evaluation.

  • Tonometry. Tonometrydetermines the pressure in the eye by measuring the tone or firmness of its surface. Several types of tonometers are available for this test, the most common being the applanation tonometer. After the eye has been numbed with anesthetic eye drops, the tonometer's sensor is placed against the front surface of the eye. The firmer the tone of the surface of the eye, the higher the pressure reading.
  • Pachymetry. Pachymetry is a relatively new test being used for the management of glaucoma. Pachymetry determines the thickness of the cornea. After the eye has been numbed with anesthetic eye drops, the pachymeter tip is touched lightly to the front surface of the eye (cornea). Recent studies have shown that central corneal thickness can affect the measurement of intraocular pressure. Thicker corneas may give falsely high eye pressure readings and thinner corneas may give falsely low pressure readings. Furthermore, thin corneas may be an additional risk factor for glaucoma.
  • Gonioscopy. Gonioscopy is done by numbing the eye with anesthetic drops and placing a special type of thick contact lens with mirrors inside on the eye. The mirrors enable the doctor to view the interior of the eye from different directions. The purpose of this test is to examine the filtering angle and drainage area of the eye. In this procedure, the doctor can determine whether the angle is open or narrow. As indicated earlier, individuals with narrow angles have an increased risk for a sudden closure of the angle, which can cause an acute glaucomatous attack. Gonioscopy can also determine if anything, such as abnormal blood vessels, might be blocking the drainage of the aqueous fluid out of the eye.
  • Ophthalmoscopy. Ophthalmoscopy is an examination in which the doctor uses a handheld device to look directly through the pupil (the opening in the colored iris) into the eye. This procedure is done to examine the optic nerve (seen as the optic disc) at the back of the eye. Damage to the optic nerve, called cupping of the disc, can be detected in this way. Cupping, which is an indentation of the optic disc, can be caused by increased intraocular pressure. Additionally, a pale color of the nerve can suggest damage to the nerve from poor blood flow or increased intraocular pressure. Special cameras can be used to take photographs of the optic nerve to compare changes over time.
  • Visual Field testing. This type of testing actually maps the visual fields to detect any early (or late) signs of glaucomatous damage to the optic nerve. This test can be done by having the patient look straight ahead and count the fingers shown by the examiner from the side. More typically, however, visual fields are measured by a computerized assessment. For this procedure, one eye is covered and the patient places his or her chin in a type of bowl. Then, when the patient sees lights of various intensities and at different locations, he or she pushes a button. This process produces a computerized map of the visual field.
How often should someone be checked (screened) for glaucoma?

Routine screening eye examinations are very important since glaucoma usually causes no symptoms (asymptomatic) in its early stages and once damage to the optic nerve has occurred, it cannot be reversed.

Patients with glaucoma need to be aware that it is a lifelong disease. Compliance with scheduled visits to the eye doctor and with prescribed medication regimens offers the best chance for maintaining vision.

Screening will be dependent upon the risk factors discussed above. The American Academy of Ophthalmology's recommended intervals for eye exams are:

  • Age 20-29: Individuals of African descent or with a family history of glaucoma should have an eye examination every three to five years. Others should have an eye exam at least once during this period.
  • Age 30-39: Individuals of African descent or with a family history of glaucoma should have an eye examination every two to four years. Others should have an eye exam at least twice during this period.
  • Age 40-64: Individuals should have an eye examination every two to four years.
  • Age 65 or older: Individuals should have an eye examination every one to two years.
How is glaucoma treated?

Although nerve damage and visual loss from glaucoma cannot usually be reversed, gthere are treatment methods that can control the progression of the disease. Treatment may involve the use of eye drops, pills (rarely), laser, or surgery.

 
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