macular degeneration


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Related to macular degeneration: glaucoma, Cataracts

Macular Degeneration

 

Definition

Macular degeneration is the progressive deterioration of a critical region of the retina called the macula. The macula is a 3-5 mm area in the retina that is responsible for central vision. This disorder leads to irreversible loss of central vision, although peripheral vision is retained. In the early stages, vision may be gray, hazy, or distorted.

Description

Macular degeneration is the most common cause of legal blindness in people over 60, and accounts for approximately 11.7% of blindness in the United States. About 28% of the population over age 74 is affected by this disease.
Age-related macular degeneration (ARMD) is the most common form of macular degeneration. It is also known as age-related maculopathy (ARM), aged macular degeneration, and senile macular degeneration. Approximately 10 million Americans have some vision loss that is due to ARMD.
ARMD is subdivided into a dry (atrophic) and a wet (exudative) form. The dry form is more common and accounts for 70-90% of cases of ARMD. It progresses more slowly than the wet form and vision loss is less severe. In the dry form, the macula thins over time as part of the aging process and the pigmented retinal epithelium (a dark-colored cell layer at the back of the eye) is gradually lost. Words may appear blurred or hazy and colors may appear dim or gray.
In the wet form of ARMD, new blood vessels grow underneath the retina and distort the retina. These blood vessels can leak, causing scar tissue to form on the retina. The wet form may cause visual distortion and make straight lines appear wavy. A central blind spot develops. The wet type progresses more rapidly and vision loss is more pronounced. Treatments are available for some, but not most, cases of the wet form.
Other less common forms of macular degeneration include:
  • Cystoid macular degeneration. Loss of vision in the macula due to fluid-filled areas (cysts) in the macular region. This may be a result of other disorders, such as aging, inflammation, or high myopia.
  • Diabetic macular degeneration. Deterioration of the macula due to diabetes.
  • Senile disciform degeneration (also known as Kuhnt-Junius macular degeneration). A specific and severe type of the wet form of ARMD that involves leaking blood vessels (hemorrhaging) in the macular region. It usually occurs in people over 40 years old.

Causes and symptoms

Age-related macular degeneration is part of the aging process. There may be a hereditary component. Having a family member with ARMD increases a person's risk for developing it. There is a slightly higher incidence in females. Whites and Asians are more susceptible to developing ARMD than blacks, in whom the disorder is rare.
ARMD is thought to be caused by hardening and blocking of the arteries (arteriosclerosis) in the blood vessels supplying the retina. Some of the same things that are bad for the heart are thought to contribute to the development of macular degeneration. These risk factors include smoking and a diet that is rich in saturated fat. Smokers have a risk of developing ARMD that is approximately 2.4-3 times that of non-smokers. Smoking increases the risk of developing wet-type ARMD, and may increase the risk of developing dry-type as well. Dietary fat also increase the risk. In one study of older (age 45-84) Americans, signs of early ARMD were 80% more common in the group who ate the most saturated fat compared to those who ate the least. Low consumption of antioxidants, such as foods rich in vitamin A, is associated with a higher risk for developing ARMD. Consumption of moderate amounts of red wine and foods rich in vitamin A is associated with a lower risk. It is generally believed that exposure to ultraviolet (UV) light may contribute to disease development, but this has not been proven.
The main symptom of macular degeneration is a change in central vision. The patient may notice blurred central vision or a blank spot on the page when reading. The patient may notice visual distortion such as bending of straight lines. Images may appear smaller. Some patients notice a change in color perception and some experience abnormal light sensations. These symptoms may come on suddenly and become progressively more troublesome. Sudden onset of symptoms, particularly vision distortion, is an indication for immediate evaluation by an ophthalmologist.

Diagnosis

To make the diagnosis of macular degeneration, the doctor dilates the pupil with eye drops and examines the interior of the eye, looking at the retina for the presence of yellow bumps called drusen and for gross changes in the macula such as thinning. The doctor also administers a visual field test, looking for blank spots in the central vision. The doctor may call for fluorescein angiography (intravenous injection of fluorescent dye followed by visual examination and photography of the back of the eye) to determine if blood vessels in the retina are leaking.
A central visual field test called an Amsler grid is usually given to patients who are suspected of having ARMD. It is a grid printed on a sheet of paper (so it is easy to take home). When looking at a central dot on the page, the patient should call the doctor right away if any of the lines appear to be wavy or missing. This may be an indication of fluid and the onset of wet ARMD. Patients may also be asked to come in for more frequent checkups.

Treatment

While loss of vision cannot be reversed, early detection is important because treatments are available that may halt or slow the progression of the wet form of ARMD. Treatment for the dry form is not available as of 1998, but cell transplantation studies are under study.
In wet-type ARMD and in senile disciform macular degeneration, new capillaries grow in the macular region and leak. This leaking of blood and fluid causes a portion of the retina to detach. Blood vessel growth, called neovascularization, can be treated with laser photocoagulation in some cases, depending upon the location and extent of the growth. Argon or krypton lasers can destroy the new tissue and flatten the retina. This treatment is effective in about half the cases but results may be temporary. A concern with laser therapy is that the laser also destroys the photoreceptors in the treated area. If the blood vessels have grown into the fovea (a region of the macula responsible for fine vision), treatment may not be possible. Because capillaries can grow very quickly, this form of macular degeneration should be handled as an emergency and treated quickly. Patients who are experiencing visual distortion should seek help immediately.
Another form of treatment for the wet form of ARMD is radiation therapy with either x rays or a proton beam. Blood vessels that are proliferating (growing) are sensitive to treatment with low doses of ionizing radiation. Nerve cells in the retina are not growing and are insensitive, so they are not harmed by this treatment. External beam radiation treatment has shown promising results at slowing progression in limited, early trials. An alternative treatment is internal beam radiation therapy. For this treatment, the patient is given a local anesthetic and an applicator containing strontium 90 is inserted into the affected eye. This brief and localized radiation therapy prevents the growth of blood vessels.
Other therapies that are under study include treatment with alpha-interferon, thalidomide, and other drugs that slow the growth of blood vessels. Subretinal surgery also has shown promise in rapid-onset cases of wet ARMD. This surgery carries the risk of retinal detachment, hemorrhage, and acceleration of cataract formation. Other experimental treatments include photodynamic therapy (PDT). For this treatment, a photosensitizing dye is injected, followed by irradiation of the area of new blood vessel growth with a special, low-intensity diode laser. This treatment damages the cells in the blood vessel walls and causes them to stop growing.
A controversial treatment called rheotherapy involves pumping the patient's blood through a device that removes some proteins and fats. As of 1998, this had not been proven to be safe or effective.

Alternative treatment

Consumption of a diet rich in antioxidants (beta carotene and the mixed carotenoids that are precursors of vitamin A, vitamins C and E, selenium, and zinc), or taking antioxidant nutritional supplements, may help prevent macular degeneration, particularly if started early in life. Good dietary sources of antioxidants include citrus fruits, cauliflower, broccoli, nuts, seeds, orange and yellow vegetables, cherries, blackberries, and blueberries. Research has shown that nutritional therapy can prevent ARMD or slow its progression once established. Some doctors recommend taking beta carotene and zinc as a precautionary measure. Some vitamins are marketed specifically for the eyes.

Prognosis

The dry form of ARMD is self-limiting and eventually stabilizes. The loss of vision is permanent. The vision of patients with the wet form of ARMD often stabilizes or improves even without treatment, at least temporarily. However, after a few years, patients with the wet form of ARMD are usually left with only coarse peripheral vision remaining.
Many patients with macular degeneration lose their central vision permanently and may become legally blind. However, macular degeneration rarely causes total loss of vision. Peripheral vision is retained. The patient can compensate, to some extent, for the loss of central vision, even though macular degeneration may render them legally blind. Improved lighting and special low-vision aids may help even if sharpness of vision (visual acuity) is poor. Vision aids include special magnifiers that allow the patient to read and telescopic aids for long-distance vision. The use of these visual aids plus the retained peripheral vision usually allow the patient to remain independent. Registration as a legally blind person will enable a patient to obtain special services and considerations.

Key terms

Drusen — Tiny yellow dots on the retina that can be soft or hard and that usually do not interfere with vision.
Fovea — A tiny pit in the macula that is responsible for sharp vision.
Neovascularization — Growth of new capillaries.
Photoreceptors — Specialized nerve cells (rods and cones) in the retina that are responsible for vision.
Retina — The light-sensitive membrane at the back of the eye that images are focused on. The retina sends the images to the brain via the optic nerve.

Prevention

Avoiding the risk factors for macular degeneration may help prevent it. This includes avoiding tobacco smoke and eating a diet low in saturated fat. Some other behaviors that may help reduce the risk of wet-type ARMD are eating a diet rich in green, leafy vegetables and yellow vegetables such as carrots, sweet potatoes, and winter squash; drinking moderate amounts of alcohol, such as one or two glasses of red wine a day; and taking an antioxidant vitamin supplement, especially vitamin A. Some vitamins may be toxic in large doses, so patients should speak with their doctors. Vitamins C and E have not been shown to reduce risk, nor did selenium in one large study. The use of zinc is controversial: some studies showed a benefit, others showed no benefit, and one actually showed an increased risk of ARMD with increased levels of zinc in the blood. Some doctors suggest that wearing UV-blocking sunglasses reduces risk. Use of estrogen in postmenopausal women is associated with a lower risk of developing ARMD.

Resources

Organizations

American Academy of Ophthalmology. 655 Beach Street, P.O. Box 7424, San Francisco, CA 94120-7424. http://www.eyenet.org.
American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141. (314) 991-4100. http://www.aoanet.org.
Prevent Blindness America. 500 East Remington Road, Schaumburg, IL 60173. (800) 331-2020. http://www.preventblindness.org.

macular degeneration

 
breakdown of cells in the macula lutea, resulting in a loss of central vision in the affected eye; peripheral vision is not affected. There are several varieties; most appear in persons 50 to 60 years of age (age-related macular degeneration), but one variety is congenital and is seen in younger people (stargardt's disease or Stargardt's macular degeneration). In about 75 per cent of cases the cause is not known, and nothing can be done to prevent, arrest, or reverse the process.
Patient Care. Since a large majority of cases of macular degeneration cannot be arrested or treated, care is aimed at making the most of the vision that the patient has. The condition does not progress to total blindness and usually is self-limiting. The inability to perceive detail can be compensated for in part by using large-type books and magazines and a magnifying lens for reading, and having adequate lighting whenever detail work is necessary.

Patients with macular degeneration are given a sheet of paper on which is printed a grid of horizontal and vertical lines. They are instructed to look at this grid daily and note whether there is any change in distortion of lines in the center of vision. This same technique can be used as a screening test to evaluate central vision. However, seeing distorted lines in the grid is not necessarily symptomatic of macular degeneration. Further examination by an ophthalmologist is necessary for a definitive diagnosis.
Grid for evaluating macular degeneration.
age-related macular degeneration (ARMD) a type having its onset between the ages of 50 and 60, the leading cause of blindness in persons over the age of 65. There are two main types, involutional and exudative age-related macular degeneration.

The involutional (dry or non-exudative) type accounts for 90 per cent of cases and is characterized by the gradual wearing out of the cells in the retinal pigment epithelium, resulting in a slow, progressive loss of central vision. Although visual acuity loss usually does not progress beyond the 20/200 level, this is a significant disability. Treatment is not generally available.

The exudative (neovascular or wet) type is characterized by the growth of a neovascular membrane within or very close to the macula, resulting in distorted and blurred vision. The vision loss from this type of macular degeneration may be only of hand movements. Laser photocoagulation of this form of macular degeneration is aimed at destroying the neovascular membrane; if diagnosed and treated very early when the membrane is small, significant loss of central vision may be avoided.
Patient Care. Health care providers can be of great help for early diagnosis of this devastating disease through ongoing patient education programs. After laser treatment, which is performed under a retrobulbar anesthetic, the patient should be instructed to leave the patch in place for at least six hours. Any increase in distortion or blurred vision should be immediately reported and followed up by an urgent outpatient exam. Low vision aids and services can improve quality of life for persons with this disorder.
Stargardt's macular degeneration Stargardt's disease.

mac·u·lar de·gen·er·a·tion

any ocular degeneration affecting predominately the posterior fundus, but most commonly age-related macular degeneration.

macular degeneration

n.
A condition in which the cells of the macula lutea degenerate, causing blurred vision and ultimately blindness.

macular degeneration (MD)

[mak′yələr]
Etymology: L, macula, spot, degenerare, to deviate
a progressive deterioration of the maculae of the retina associated with abnormal retinal pigment epithelium, new vessel formation that can progress to blindness. Treatment includes intraocular injection of antiangiogenic factors, laser, and vitamins.

macular degeneration

Deterioration of the retinal macula, resulting in decreased central vision and destruction of the retinal nerve as fluid leaks into the choroid, forming scar tissue.

Clinical findings
Drusen, pigmentary changes, hard exudates, haemorrhages, subretinal/sub-RPE/intraretinal fluid, atrophy, decreased visual acuity; it is painless.
 
Risk factors
Macular degeneration increases after age 50—affects 35% of general population by age 75; family history; cigarette smoking; Caucasian.

Diagnosis
Fundoscopy.

macular degeneration

Senile macular degeneration Ophthalmology Deterioration of the retinal macula, resulting in ↓ central vision and destruction of the retinal nerve, as fluid leaks into the choroid and forms scar tissue Risk factors ↑ after age 50; affects 35% of general population
by age 75, family Hx, cigarette smoking, White Diagnosis Funduscopy. Cf Retinopathy.

mac·u·lar de·gen·er·a·tion

(mak'yū-lahr dě-jen'ĕr-ā'shŭn)
A progressive deterioration of the macula lutea resulting in the loss of central vision.
Synonym(s): age-related macular degeneration.

macular degeneration

See AGE-RELATED MACULAR DEGENERATION.

macular degeneration (maˑ·ky·ler d·jeˈ·n·rāˑ·shn),

n an eye condition characterized by deterioration of the macula (the central por-tion of the retina) and concomitant decrease of vision. This deterioration may be classified as either “dry” or “wet.” See also macula.
Enlarge picture
Macular degeneration.

degeneration

deterioration; change from a higher to a lower form, especially change of tissue to a lower or less functionally active form. When there is chemical change of the tissue itself it is true degeneration; when the change consists in the deposit of abnormal matter in the tissues, it is infiltration. See also wallerian degeneration, Zenker's necrosis.

albuminoid degeneration
cloudy swelling, an early stage of degenerative change characterized by swollen, parboiled-appearing tissues which revert to normal when the cause is removed.
ballooning degeneration
swelling of the cytoplasm in epidermal cells without vacuolization, enlarged or condensed nuclei and acantholysis. A characteristic of viral infections of the skin. Called also koilocytosis.
caseous degeneration
colloid degeneration
degeneration with conversion of the tissues into a gelatinous or gumlike material.
cystic degeneration
degeneration with formation of cysts.
fatty degeneration
deposit of fat globules in a tissue.
feathery degeneration
said of hepatocytes; a hydropic change in hepatocytes which have suffered long-term exposure to cholestasis.
fibrinoid degeneration
deposition or replacement with eosinophilic fibrillar or granular substance resembling fibrin.
fibroid degeneration
degeneration into fibrous tissue.
hyaline degeneration
a regressive change in cells in which the cytoplasm takes on a homogeneous, glassy appearance; also used loosely to describe the histological appearance of tissues. Called also hyalinosis.
hydropic degeneration
see hydropic degeneration.
macular degeneration
degenerative changes in the macula retinae.
mucoid degeneration
degeneration with increased mucin which can be epithelial or mesenchymal in origin.
mucous degeneration
degeneration with accumulation of mucus in epithelial tissues. Called also myxomatous degeneration.
myxomatous degeneration
see mucous degeneration (above).
reticular degeneration
extreme intracellular edema of epidermal cells, resulting in rupture and multilocular intraepidermal vesicles with septae formed by the remaining cell walls. Seen in acute inflammatory dermatoses.
spongy degeneration
on microscopic examination has the physical appearance of a sponge. Usually applied to tissue of the central nervous system, caused by the loss of myelin.
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