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.
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.
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.
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.
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.
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.
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.
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.
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." Gale Encyclopedia of Medicine, 3rd ed.. . Encyclopedia.com. (September 25, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/macular-degeneration-0
"Macular Degeneration." Gale Encyclopedia of Medicine, 3rd ed.. . Retrieved September 25, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/macular-degeneration-0
Macular degeneration (MD) is the progressive deterioration of the macula, the light-sensitive cells of the central retina, at the back of the eye. The retina is the sensitive membrane (soft layer) of the eye that receives the image formed by the lens and is connected with the brain by the optic nerve. As these macular cells malfunction and die, central vision becomes gray, hazy, or distorted, and eventually is lost. Peripheral (away from the center) vision is unaffected.
Millions of people suffer from MD and it accounts for about 12% of all blindness in the United States. The macula contains the highest concentration of photosensitive cells in the retina. These cells transform light into electrical signals that are sent to the brain for processing into vision. Fine detail vision and critical color vision are located in the macula. The macula depend on nutrient diffusion from the choroid layer, a region of several delicate vascular (pertaining to blood vessels) membranes or structures behind the retina and under the macula. Anything that interferes with this nutrient supply can lead to MD.
Age-related macular degeneration (AMD or ARMD) is by far the most common type of MD. One in six Americans develops AMD between the ages of 55 and 64 and one in three Americans over 75 has AMD. About 10% of those with AMD eventually suffer severe vision loss. The incidence of AMD is expected to triple by 2025, as the population ages. Whites and Asians are more susceptible than blacks. Women and those with lighter-colored eyes are somewhat more susceptible. AMD may occur in only one eye. However there is a very high likelihood that the other eye will be affected eventually.
About 90% of AMD is the dry form. Over time, the macula thins and the pigmented retinal epithelium, a dark-colored cell layer that supports the retina, is gradually lost. About 10% of dry AMD cases progress to the wet form. In a process called choroidal neovascularization (CNV), new blood vessels proliferate in the choroid and may invade the retina. These fragile vessels can leak blood and fluid into the retina, damaging or killing macular cells and resulting in scar tissue that interferes with vision. If untreated, the macula may be destroyed. Wet AMD progresses more rapidly than dry AMD and severe vision loss typically occurs within two years.
Less common forms of MD include:
- juvenile macular degeneration (JMD), a group of inherited disorders affecting children and younger adults
- cystoid macular degeneration, the development of fluid-filled cysts (sacs) in the macular region, associated with aging , inflammation, or severe myopia (nearsightedness)
- diabetic macular degeneration
- retinal pigment epithelial detachment, a rare form of wet MD in which fluid leakage from the choroid causes the detachment or disappearance of the pigmented retinal epithelium
Causes & symptoms
Age-related macular degeneration (AMD) appears to result from a combination of hereditary, environmental, and metabolic factors. Over time, highly reactive free-oxygen radicals damage and destroy macular cells. Free radicals are produced by:
- bombardment of light on the macula, particularly long-term exposure to ultraviolet and blue light, including sunlight and sunlamps
- smoking , which increases the risk of AMD two- to four-fold
- a high-fat diet
The body's antioxidant systems that destroy free radicals become less effective with aging.
Factors that contribute to the hardening and blocking of the capillaries supplying the retina and lead to AMD include:
- diets high in saturated fat and cholesterol
- low dietary consumption of antioxidants
The cause of choroidal neovascularization (CNV) in wet AMD is unknown. However many people with AMD also have cataracts and cataract surgery increases the risk of dry AMD progressing to wet AMD.
AMD is painless, and in the early stages, the brain easily compensates for vision loss, particularly if AMD is restricted to one eye. Symptoms of AMD include:
- requiring more light for reading
- reduction, blurring, a blank spot, or loss of central vision while peripheral vision is unaffected
- difficulty recognizing faces
- visual distortions such as the bending of straight lines
- images appearing smaller
- changes in color perception or abnormal light sensations
- a decline of at least two lines in visual acuity as measured on a standard eye chart. For example, 20/20 vision declining to 20/80
- phantom visions, called "Charles Bonnet syndrome"
Although vision loss is irreversible, early detection may halt or slow the progression of dry to wet AMD. However AMD is often fairly advanced by the time an ophthalmologist (a physician specializing in eye defects and diseases) is consulted. Tests for MD include:
- An Amsler grid, a checkerboard pattern with a black dot at the center. While staring at the dot with one eye, MD causes the straight lines to appear wavy or disappear or some areas to appear blank.
- A dilated eye exam whereby drops are used to dilate the pupils and a special magnifier called an ophthalmoscope shines a very bright light on the back of the lens to examine the retina. Gross macular changes, including scarring, thinning, or atrophy, may indicate MD. Numerous mid-sized yellow bumps called drusen, or one or more large drusen, can indicate intermediate-stage AMD. However, most people over age 42 have drusen in one or both eyes.
- Fluorescein or eye angiography, or retinal photography. An indicator dye is injected and photographs are taken to detect dye leakage from retinal blood vessels.
- Indocyanine green angiography examines choroid blood vessels that cannot be seen with fluorescein.
- Optical coherence tomography. Light waves are used to obtain cross-sectional views of eye tissue. This is easier and quicker than fluorescein angiography.
- An electroretinogram, whereby a weak or missing electrical signal from an illuminated point in the macula indicates MD.
- In a family history of MD suggesting hereditary juvenile macular degeneration (JMD), molecular genetic screening can reveal the presence of JMD-causing genes, facilitating early detection.
Those with dry AMD should have a complete dilated eye examination at least once a year and use an Amsler grid daily to check for signs of wet AMD.
Dietary factors that can speed the progression from early-stage to advanced MD include:
- high fat consumption (70 gm versus 24 gm daily) triples the risk of advancement
- trans-fats consumption (4 gm versus 0.5 gm daily) doubles the risk
- consumption of commercial baked goods (two or more servings weekly) doubles the risk
- obesity doubles the risk of advancement
Foods containing omega-3 fats, such as nuts and fish, lower the risk of progression to advanced MD.
One study found that those with the highest dietary intake of lutein had a 57% lower risk for AMD. Foods high in lutein and zeaxanthin include:
- mustard greens
- collard greens
- romaine lettuce
- broccoli (cooked)
- yellow squash
- orange bell peppers
- red grapes
Many multi-vitamins also contain lutein.
Other factors for preventing AMD include:
- the use of sunglasses with UV protection
- maintaining normal blood pressure
- avoiding the risk factors, including smoking and secondhand smoke
- the use of supplemental estrogen by postmenopausal women is associated with a lower risk for AMD
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American Macular Degeneration Foundation. P.O. Box 515, Northampton, MA 01061-0515. 888-MACULAR. 413-268-7660. email@example.com. <http://www.macular.org>.
American Optometric Association. 243 North Lindbergh Blvd., St. Louis, MO 63141-7851. 314-991-4100. <http://www.aoanet>.
Macular Degeneration Foundation. P.O. Box 531313, Henderson, NV 89053. 888-633-3937. <http://www.eyesight.org>.
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Margaret Alic, Ph.D.
"Macular Degeneration." Gale Encyclopedia of Alternative Medicine. . Encyclopedia.com. (September 25, 2017). http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/macular-degeneration
"Macular Degeneration." Gale Encyclopedia of Alternative Medicine. . Retrieved September 25, 2017 from Encyclopedia.com: http://www.encyclopedia.com/medicine/encyclopedias-almanacs-transcripts-and-maps/macular-degeneration
macular degeneration, eye disorder causing loss of central vision. The affected area, the macula, lies at the back of the retina and is the part that produces the sharpest vision. The most serious visual impairment occurs when abnormal blood vessels form and leak serous fluid or bleed into the tissue of the macula, ultimately producing scar tissue. Peripheral (side) vision is unaffected. Onset may be acute with hemorrhage but usually is gradually progressive. Although some vision is retained, the ability to read, recognize faces, and drive a motor vehicle is greatly reduced. The condition is painless.
Macular degeneration is a major cause of vision impairment among elderly people. Although its underlying cause is unknown, it sometimes appears to run in families. Serious macular degeneraton, if diagnosed early, may have its progress stemmed by laser or photodynamic (cold laser and drug) treatment that closes leaking vessels. Antiangiogenic drugs, which inhibit the formation of new blood vessels, can be injected into the eye to stop degeneration and in some cases even improve vision. Sudden change in vision in someone over age 50 thus requires immediate medical attention.
See H. Grunwald, Twilight: Losing Sight, Gaining Insight (1999).
"macular degeneration." The Columbia Encyclopedia, 6th ed.. . Encyclopedia.com. (September 25, 2017). http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/macular-degeneration
"macular degeneration." The Columbia Encyclopedia, 6th ed.. . Retrieved September 25, 2017 from Encyclopedia.com: http://www.encyclopedia.com/reference/encyclopedias-almanacs-transcripts-and-maps/macular-degeneration
www.rnib.org.uk/xpedio/groups/public/documents/publicwebsite/public_rnib003635.hcsp Information about macular degeneration from the Royal National Institute of the Blind
"macular degeneration." A Dictionary of Nursing. . Encyclopedia.com. (September 25, 2017). http://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/macular-degeneration
"macular degeneration." A Dictionary of Nursing. . Retrieved September 25, 2017 from Encyclopedia.com: http://www.encyclopedia.com/caregiving/dictionaries-thesauruses-pictures-and-press-releases/macular-degeneration