Macular degeneration

Our eyes, like the rest of our bodies, change with age. Most of these changes are subtle and gradual. We may find that our eyes are drier than they once were, that it is more difficult to read fine print, or that it isn't as easy to distinguish objects in the dark. These conditions --dry eye, presbyopia, and diminished night vision -- usually affect most of us to some degree and are more annoying than serious. However, some vision changes, in which central objects become blurred, are symptomatic of a sight-threatening condition: age-related macular degeneration (AMD).

What it is
AMD is the degradation of the cells at the center of the retina -- the layer of tissue at the back of the eye that registers light. The macula is responsible for central vision, which enables us to read, drive, play golf and tennis, and do anything else that requires focusing directly ahead. Macular degeneration distorts the heart of the visual field.

AMD is the most common cause of legal blindness in people over 60. It affects about 8.5 million Americans and is more common in women than in men. It has two forms: dry, which accounts for 90% of cases, and wet.

Dry AMD (also called nonexudative, atrophic, or nonneovascular AMD) is identified by the presence of drusen -- small, white lesions against the yellowish macula. Both the pigmented epithelial cells of the retina and the photoreceptors that overlie them become atrophied.

Wet AMD (also called neovascular AMD) is characterized by an overgrowth of blood vessels to the retina. Although the cause hasn't been identified, some scientists theorize that the development of drusen triggers the release of compounds that promote blood-vessel growth. The fragile new vessels often bleed and scar. Because scarred cells no longer register light, vision loss is irreversible.

Who gets AMD?
A number of observational studies have pointed to factors that increase the risk of AMD. People whose parents have wet macular degeneration, particularly those who have inherited a gene called ABCR, have two to three times the risk of developing it as well. Early menopause or surgical menopause also appears to raise the risk. Risk also increases with the number of children borne.

Smoking is associated with AMD in all major studies, as are low levels of antioxidant vitamins, particularly vitamins A, C, and E, as well as the lutein and zeaxanthin. Conversely, reduced risk was often associated with a high consumption of spinach, collards, and other yellow or leafy green vegetables -- a fact that is thought to contribute to maintaining the yellow-pigmented macula. Atherosclerosis repeatedly emerged as a risk factor for AMD, though not in people aged 85 and older.

Symptoms
Although neither form of AMD brings any pain, the signs are readily recognizable. The center of the visual field becomes distorted -- an effect akin to having a smear of vaseline on the center of one's eyeglass lens. Clinicians often use the Amsler grid, illustrated at right, as a test of AMD. The patient is asked to look at the dark square in the center of the grid (top). Those who have AMD see an image similar to the bottom diagram. The greater the severity of the condition, the more distorted the lines are.

Patients with the visual symptoms of AMD are examined with an ophthalmoscope -- an instrument that affords a view of the retina. The presence and numbers of drusen are another indication of the severity of the disease. Although there is no treatment for dry AMD, it is monitored carefully once it is diagnosed. Certain types of drusen indicate an increased risk of developing wet AMD.

Wet AMD is diagnosed through fluorescein angiography -- a procedure that entails injecting a phosphorescent dye into the blood vessels and taking an x-ray of the eye. The resulting image can indicate whether the new vessels are distributed throughout the macula or occur in discrete "knots" called foci.

Treatment
While watchful waiting is the only approach to dry AMD, some types of wet AMD are amenable to laser coagulation, a process in which laser energy is employed to eliminate the vessels before they can bleed and scar. Unfortunately, some surrounding cells are damaged during laser treatment, and preserving vision in the long term usually means losing some vision immediately after surgery. For example, in the Macular Photocoagulation Study -- a multicenter randomized study -- 24% of patients who underwent laser surgery for wet AMD had severe vision loss, characterized as being able to read six fewer lines on the eye chart. During the same period, 41% of those who remained untreated had similar losses. Because vessels tend to continue to proliferate in laser-treated eyes, most improvements are temporary. Thus, laser treatment is recommended only for those with vision worse than 20/160.

Researchers are investigating other approaches. Some are testing microsurgery to remove the new vessels. Others are employing photodynamic therapy, which uses a light-sensitive dye that, when activated by bright light, produces blood clots that strangle the new vessels. Other techniques under study include irradiation and retinal-cell transplantation, neither of which appears promising.

Thus, most researchers are pinning their hopes on drug treatments, principally with agents that inhibit the growth of new blood vessels. These include thalidomide and antibodies to blood-vessel growth factors.

Prevention
The only way to reduce AMD risk is to avoid the practices that increase it, particularly for those whose parents developed the condition.

The prospect of losing one's vision should be sufficient reason for smokers to enter cessation programs. Although no authorities are willing to recommend antioxidant supplements to reduce AMD risk, most health and nutrition experts already advocate a diet rich in antioxidants, which would include copious amounts of green and yellow vegetables. Emerging evidence that estrogen therapy reduces AMD risk should be taken into consideration for perimenopausal and postmenopausal women pondering hormone replacement therapy.

Living with AMD
Since no clear means of prevention and no effective treatments have yet emerged, AMD can be disheartening. Vision loss can complicate daily life and lead to isolation. Yet, although it may take a little more doing, it is possible to compensate for diminished sight, stay socially connected, and preserve one's independence.

Simply equipping the home with bright lamps placed where they are convenient and reachable can help enormously. So can contrast. Light walls make dark objects easier to locate.

There are a host of aids to facilitate reading, from large-type editions of publications, to hand-held and stand-mounted magnifying lenses. Computers and "reading machines," which employ closed-circuit television to amplify type, can make it possible to read just about anything.

There are other aids that avoid relying on vision altogether. Many of these are based on using the senses other than sight -- for example, listening to books on tape and taking advantage of television programs for the visually impaired.

It may be necessary to employ new techniques for executing daily chores -- for instance, learning to make better use of peripheral vision, identifying frequently used objects by their shape, or folding each denomination of currency a different way. An occupational therapist can be an excellent ally in setting up systems that are suitable to your lifestyle.

For further information
American Foundation for the Blind -- Directory of Services for Blind and Visually Impaired Persons in the United States and Canada, 25th Edition (1998), 11 Penn Plaza, Suite 300, New York, NY 10001, 1-800-232-3044, http://www.afb.org

Council of Citizens with Low Vision International, 5707 Brockton Drive, Suite 302, Indianapolis, IN 46220-5481, 1-800-733-2258

Lighthouse International, Aging and Vision -- Director of Programs and Services for Older Adults with Impaired Vision (1996), 111 E. 59th Street, New York, NY 10022, 1-800-334-5497, 1-800-829-0500, http://www.lighthouse.org

National Association for the Visually Handicapped, 22 W. 21st Street, 6th Floor, New York, NY 10010, 212-889-3141, http://www.navh.org

National Federation for the Blind, 1800 Johnson Street, Baltimore, MD 21230, 410-659-9314, http://www.nfb.org

Resources for Rehabilitation, Living with Low Vision: A Resource Guide for People with Sight Loss, 5th Edition (1998), 33 Bedford Street, Suite 19A, Lexington, MA 02173, http://www.rfr.org

Visions, 500 Greenwich Street, 3rd Floor, New York, NY 10013, 212-625-1616

PHOTO (BLACK & WHITE): Macula

Share this with your friends