Home > Encyclopedia of Nursing & Allied Health > Macular Degeneration

Definition

Macular degeneration is the progressive deterioration of a critical region of the retina called the macula. The macula is 3–5 mm and 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 ten million Americans have some vision loss 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.

With wet 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.

Less common forms of macular degeneration include:

• Cystoid macular degeneration: Vision loss 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 (Kuhnt-Junius macular degeneration): A severe type of wet ARMD that involves hemorrhaging in the macular region. It usually occurs in people over 40 years old.

Causes and symptoms

Age-related macular degeneration is intrinsic to aging for some individuals, but not all. People with an ARMD-affected family member have an increased the risk for its development. A slightly higher incidence occurs in females, although males and females are considered to be equally at risk. Whites and Asians are more susceptible to developing ARMD than blacks, in whom the disorder is rare.

The cause of ARMD is thought to be arteriosclerosis in the blood vessels supplying the retina. Certain risks for the heart are considered similar risks to those that contribute to the development of macular degeneration. Smoking increases the risk of developing wet-type ARMD, and may increase the risk of developing dry-type as well. Dietary fat also increases 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. It is generally believed that exposure to ultraviolet (UV) light may contribute to disease development, but this has not been proven conclusively.

A study reported in Ophthalmology in 2000 concluded that hypertension, thyroid hormones, and antacids are associated with certain types of ARMD. The issue of antacids is not widely recognized since no determination has yet been made regarding whether the antacids themselves lead to the disease, or whether it is the stomach problems that are a contributing factor. Obesity was also found to be a factor in this study.

The main symptom of macular degeneration is a central vision change. The patient may experience blurred central vision or a blank spot on the page when reading, visual distortion such as bending of straight lines, and images might appear smaller than is the actual object. Some patients notice a change in color perception, or abnormal light sensations. These symptoms can emerge suddenly and become progressively worse. Patients should be advised that a sudden onset of symptoms, particularly vision distortion, is an indication for immediate evaluation.

Diagnosis

Optometrists and ophthalmologists, with assistance from ophthalmic assistants, technicians and nurses, should carefully screen patients who are at risk for macular degeneration. These include patients older than 60; patients with hypertension or cardiovascular disease; cigarette smokers; patients with a first-degree family (sibling or maternal) history of vision loss from ARMD regardless of age; patients with aphakia or pseudophakia; or someone with a cataract, and patients with a history that indicates significant cumulative light exposure.

The ophthalmic assistant will take a careful history and log these risk factors. The patient then should have a complete ocular examination. Vision tests, performed by the physician or a skilled ophthalmic assistant, examine best corrected visual acuity, as well as near monocular visual acuity; refraction; biomicroscopy; tonometry; and stereoscopic fundus examination with pupillary dilation. Though rarely used even if ARMD is suspected, a central 10-degree computerized automated perimetry might be utilized along with fundus photography and laser ophthalmoscope scanning.

After preliminary testing, specific tests are performed to determine macular degeneration. To make the diagnosis, the doctor dilates the pupil with eye drops and examines the interior of the eye, examining the retina for the presence of drusen, small white-yellow spots in the macular area, and for gross changes in the macula such as thinning. The doctor also administers a visual field test to search for blank spots in the central vision. The doctor might order 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. Retinal pigmented epithelium (RPE) mottling that occurs, like the drusen, due to ateriorsclerotic changes of the macula decreasing the blood supply, can also be indicated through a thorough examination.

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 (also presented for home use every week). When viewing a central dot on the page, the patient should note if any of the lines appear to be wavy or missing. This could be an indication of fluid and the onset of wet ARMD. High-risk patients particularly will be urged to schedule more frequent checkups.

Although ophthalmologists and optometrists can accurately diagnose macular degeneration, attending physicians may want to consult with a retinal specialist for the best treatment protocols.

Treatment

While vision loss cannot be reversed, early detection is important because treatments are available that may halt or slow the progression of the wet form of ARMD. Some treatments for the dry form were still in early clinical trials in 2001.

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 exists that laser therapy causes the laser to destroy 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 be impossible. Because capillaries can grow quickly, this form of macular degeneration should be handled as an emergency and treated immediately.

Photodynamic therapy (PDT) is a promising new treatment approved by the Food and Drug Administration in 2000. With PDT, the patient is given a light-activated drug intravenously with no damage to the retina. The drug, Visudyne, is absorbed by the damaged blood vessels. The affected area on the retina is exposed to a nonthermal laser light that activates the drug exactly 15 minutes after the infusion begins. It must be exactly 15 minutes for the treatment to be successful. The light chemically alters the drug, and any leakage from choroidal neovascularization (CNV) ceases. Patients require treatment every three months during the first year of therapy, and should be advised to avoid bright light or sun exposure for several days after therapy.

Another form of treatment for the wet form of ARMD is radiation therapy with either x rays, or a proton beam. Growing blood vessels are sensitive to treatment with low doses of ionizing radiation. The growth of nerve cells in the retina is stunted. They are insensitive and thus are not harmed by this treatment. External beam radiation treatment has shown promising results at slowing progression in limited, early trials.

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. A controversial treatment called rheotherapy involves pumping the patient's blood through a device that removes some proteins and fats. As of 2001, 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 antioxidant nutritional supplements, may help prevent macular degeneration, particularly if started early in life. Research has shown that nutritional therapy can prevent ARMD or slow its progression once established.

Researchers also are working on therapies to treat the dry form of macular degeneration. Low-energy laser treatment for drusen is currently in clinical trials as of 2001. In this treatment the ophthalmologist uses a diode laser to reduce the drusen level. Some ophthalmologists were already performing this procedure "off-label," without FDA approval.

Another treatment, approved overseas but not in the United States, treats dry ARMD by implanting a miniaturized telescope to magnify objects in the central field of vision. This does not treat the disease, but aids the patient's vision in only the very severe cases of ARMD.

Prognosis

The dry form of ARMD is self-limiting and eventually stabilizes, with permanent vision loss. 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 this type are usually left without acute central vision.

Many macular degeneration patients lose their central vision permanently and may become legally blind. However, macular degeneration rarely causes total vision loss. Peripheral vision is retained. Patients can compensate for central vision loss, even when macular degeneration renders them legally blind. Improved lighting and low-vision aids can help even if visual acuity is poor. Vision aids include special magnifiersallowing patients to read, and provide telescopic aids for long-distance vision. The use of these visual aids plus the retained peripheral vision assist in maintaining patient independence.

Health care team roles

Ophthalmic assistants, technicians, and nurses assist optometrists and ophthalmologists in testing for macular degeneration. Skilled ophthalmic staff take patient history and perform refraction; biomicroscopy; tonometry; stereoscopic fundus examination with pupillary dilation, only rarely; computerized automated perimetry; and fundus photography.

Registered ophthalmic nurses also play an important role in preparing patients for PDT. Only registered nurses and physicians are allowed to mix the drug used for PDT. RNs familiar with infusion are best-suited for this task. Nurses and ophthalmic staff also play an important role in PDT follow-up care. They are critical in issuing patient instructions to stay out of bright light and sunlight after treatment, and to wear sun-protective clothing for each treatment.

Patient education

Ophthalmic staff should reinforce the physician's instructions when assessing macular degeneration. They

should emphasize the importance of the Amsler grid and regular check-ups to monitor the progression of the disease.

Staff should also reaffirm doctor's orders with patients being treated with PDT. They should review that PDT is not a cure, but a slowing of the disease, and that retreatment is necessary for its success. Staff should also reinforce restrictions on patients' activities, such as staying out of direct sunlight or bright light for several days after PDT. They should also make follow-up calls to patients to ensure they are returning for PDT on time and to see if they have any questions about retreatment. Ophthalmic personnel should also be considerate of the age of most macular degeneration patients and provide large, easy-to-read instructions, and not rush them through the therapy or aftercare.

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 and rich in antioxidants. Some doctors suggest that wearing UV-blocking sunglasses reduces risk. Use of estrogen in post-menopausal women is associated with a lower risk of developing ARMD.

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KEY TERMS

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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.

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Mary Bekker