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. 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.
How common is glaucoma?
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 3 million people have glaucoma. As many as half of the individuals with glaucoma, however, may not know that they have the disease. The reason they are unaware is that glaucoma initially causes no symptoms, and the loss of vision on the side (periphery) is hardly noticeable.
What causes glaucoma?
Elevated pressure in the eye is the main factor leading to glaucomatous damage to the eye (optic) nerve. Glaucoma with normal intraocular pressure is discussed below in the section on the different types of glaucoma. The optic nerve, which is located in back of the eye, is the main seeing nerve for the eye. This nerve transmits the images we see back to the brain for interpretation. The eye is firm and round, like a basketball. Its tone and shape are maintained by a pressure within the eye (the intraocular pressure), which normally ranges between 8 and 22 mm (millimeters) of mercury. When the pressure is too low, the eye becomes softer, while a too high pressure causes the eye to become harder. It turns out that the optic nerve is the most susceptible part of the eye to high pressure because the delicate fibers in this nerve are easily damaged.
The front of the eye is filled with a clear fluid called the aqueous humor, which provides nourishment to the structures in the front of the eye. This fluid is produced constantly by the ciliary body, which surrounds the lens of the eye. The aqueous humor then flows through the pupil and leaves the eye through tiny channels called the trabecular meshwork. These channels are located at what is called the filtering, or drainage angle of the eye. This angle is where the clear cornea, which covers the front of the eye, attaches to the base (root or periphery) of the iris, which is the colored part of the eye. The cornea covers the iris and the pupil, which are in front of the lens. The pupil is the small, round, black-appearing opening in the center of the iris. Light passes through the pupil, on through the lens, and to the retina at the back of the eye. Please see the figure, which is a diagram that shows the filtering angle of the eye.
Legend for figure: This diagram of the front part of the eye is in cross section to show the filtering, or drainage angle. This angle is between the cornea and the iris, which join each other right where the drainage channels (trabecular meshwork) are located. The arrow shows the flow of the aqueous fluid from the ciliary body, through the pupil, and into the drainage channels.
What are the risk factors for glaucoma?
Glaucoma is often called "the sneak thief of sight." This is because, as already mentioned, in most cases, the intraocular pressure can build up and destroy sight without causing obvious symptoms. Thus, awareness and early detection of glaucoma are extremely important because this disease can be successfully treated when diagnosed early. 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. The major risk factors include:
- Age over 45 years
- Family history of glaucoma
- Black racial ancestry
- Diabetes
- History of elevated intraocular pressure
- Nearsightedness (high degree of myopia), which is the inability to see distant objects clearly
- History of injury to the eye
- Use of cortisone (steroids), either in the eye or systemically (orally or injected)
- 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.)
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). 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.
Open-angle glaucoma
Chronic open-angle glaucoma (COAG) is by far the most common type of glaucoma. Moreover, 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.
Chronic open-angle glaucoma (COAG) is by far the most common type of glaucoma. Moreover, 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. It is thought to be due to decreased blood flow to the optic nerve. This condition 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. This type of glaucoma can be diagnosed by repeated examinations by the eye doctor to detect the nerve damage or the visual field loss. Currently, normal pressure glaucoma is receiving a lot of research attention because its cause and treatment are uncertain.
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.
Secondary glaucoma is another type of open-angle glaucoma. It can result from an eye (ocular) injury, even one that occurred many years ago. Other causes of secondary glaucoma are inflammation in the iris of the eye (iritis), diabetes, cataracts, or in steroid-susceptible individuals, the use of topical (drops) or systemic (oral or injected) steroids (cortisone). It can also be associated with a retinal detachment or retinal vein occlusion or blockage. (The retina is the layer that lines the inside of the back of the eye.) The treatments for the secondary glaucomas vary, depending on the cause.
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 another 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
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.
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.
How is glaucoma treated?
General approach
Although nerve damage and visual loss from glaucoma cannot usually be reversed, glaucoma is a disease that can generally be controlled. That is, treatment can make the intraocular pressure normal and, therefore, prevent or retard further nerve damage and visual loss. Treatment may involve the use of eye drops, pills (rarely), laser, or surgery.
In the United States, eye drops are usually used first in treating most types of open-angle glaucoma. In contrast, in Europe, laser or surgery is sometimes the first choice, at least more often than it is in the United States. One or more types of eye drops may have to be taken up to several times a day to lower intraocular pressure. These drops work either by reducing the production of the aqueous fluid (shutting the faucet) or by increasing the drainage of the fluid out of the eye. Each type of therapy has its benefits and potential complications.
Glaucoma At A Glance
- Glaucoma is a disease that is often associated with elevated intraocular pressure, in which damage to the eye (optic) nerve can lead to loss of vision and even blindness.
- Glaucoma is the leading cause of blindness in the world.
- Glaucoma usually causes no symptoms early in its course, at which time it can only be diagnosed by regular eye examinations (screenings with the frequency of examination based on age and the presence of other risk factors).
- Intraocular pressure increases when either too much fluid is produced in the eye or the drainage or outflow channels (trabecular meshwork) of the eye become blocked.
- While anyone can get glaucoma, some people are at greater risk.
- The two main types of glaucoma are open-angle glaucoma, which has several variants and is a long duration (chronic) condition, and closed-angle glaucoma, which is a sudden (acute) condition.
- Damage to the optic nerve and impairment of vision from glaucoma are irreversible.
- Several painless tests that determine the intraocular pressure, the status of the optic nerve and drainage angle, and visual fields are used to diagnose glaucoma.
- Glaucoma is usually treated with eye drops, although lasers and surgery can also be used. Most cases can be controlled well with these treatments, thereby preventing further loss of vision.
- Much research into the causes and treatment of glaucoma is being carried out throughout the world.
- Early diagnosis and treatment is the key to preserving sight in people with glaucoma.
NATURAL PREVENTION:
