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Friday, April 28, 2017

Age-related Macular Degeneration (AMD)

What is AMD?

Age-related macular degeneration is a common, serious disease of the eye’s retina. This condition is associated with aging and gradually destroys the sharp, central vision that is needed for seeing objects clearly and for common daily tasks such as reading and driving. The disease progresses faster in some people than in others and may lead to a loss of vision in one or both eyes. AMD is the leading cause of legal blindness in the United States.

The retina is the paper-thin tissue that lines the back of the eye and sends visual signals to the brain. In the center of the retina is a small area (about 1 fifth of an inch in diameter) called the macula. It is made up of millions of closely packed, light-sensing cells that produce your central vision. In AMD there is a slow breakdown of the cells in and behind the macula, accompanied by a gradual loss of central vision.

Late-stage AMD occurs in two forms—dry (or atrophic) and wet (or exudative). Ninety percent of all people with late AMD have the dry type; its basic cause is not yet known and online viagra without prescription paypal is a topic of much scientific investigation. The wet form, although only 10% of all people with late AMD have it, accounts for 90% of legal blindness from the disease. As AMD worsens, new blood vessels may begin to grow. Because these new vessels tend to be very fragile, they will often leak blood and fluid under the macula, resulting in wet AMD. This causes rapid damage to the macula that can lead to the loss of central vision in a short period of time.

Who is at risk for AMD?

The greatest risk factor is older age; people over age 60 are at much greater risk than other age groups; although the chance of having AMD is only 1% at age 55-64, this prevalence rises to 4% for those over 65, and 30% of the population over age 75. 

Because women live, on average, several years longer than men, women are twice as likely as men to develop the condition. The lifetime risk for getting AMD is 6% for females and only 3% for males. Therefore, women need to be more aware of AMD, and older women should be sure to visit an eye care professional at least every other year.

After increasing age, smoking is the strongest predictor of who will get AMD; this habit can double the risk of the disease. Family history is also important; people whose immediate family members (including grandparents) had AMD are at higher risk of developing the disease. Scientists are trying to find out which genes are responsible for this hereditary component.

What are the signs and symptoms of AMD?

The early sign of susceptibility to AMD is deposits behind the retina called drusen. These are visible to the ophthalmologist or optometrist examining your eyes. Most older people have some small, “hard” drusen, which are not a cause for concern. However, large, “soft” drusen (sometimes called ARM, or age-related maculopathy) are often a sign that the person will progress to symptomatic AMD. Neither dry nor wet AMD causes any pain.

The most common early symptom of dry AMD is blurred central vision, even when glasses or contact lenses are being worn. When fewer cells in the macula are able to function, patients will see details in front of them, such as faces or words in a book, less clearly. Often this blurry spot will, at first, go away in brighter light. But if the loss of the central, light-sensing cells becomes great, people may see a constant small and growing, dark, or empty area in the middle of their field of vision.

The classic early symptom of wet AMD is that straight lines appear curved or distorted. This results when fluid from the leaking blood vessels gathers and lifts the macula, distorting vision. Eye-care professionals may suspect AMD if a patient is over age 60 and has had recent changes in his or her central vision. To look for signs of the disease, the doctor will use eye drops to dilate, or enlarge, the pupils, allowing a clear view of the back of the eye. The patient may also be asked to view an Amsler grid, a pattern that looks like a checkerboard. Early changes in central vision will cause the grid to appear distorted, a sign of AMD.

As the loss of central vision progresses, the decrease in ability to drive, read, and see faces can result in loss of independence. Because of poor eyesight, there is an increased risk of falling, which can result in hip fracture, especially in women (because osteoporosis is much more common in women than in men).

What can be done to help prevent or limit AMD?

There is no way to prevent getting older or to change your genes. However, you can protect yourself in other ways. Most importantly, this is one more reason to stop smoking.

There is strong evidence that a diet rich in fruits and dark green vegetables lowers the risk of AMD. However, it is not yet clear which of the many compounds in food are important for prevention, so the best advice is to eat healthfully. The carotenoids lutein and zeaxanthin may be two of the protective compounds. One study showed that a diet supplemented with an antioxidant combination (vitamins C and E, beta-carotene, and zinc with copper) may retard the progression in some people who already have moderate AMD; however, these food supplements appeared to have no effect in preventing the disease in otherwise healthy individuals.

Bright light may be involved in the process that starts AMD, so it is prudent for you and your children to wear hats and sunglasses to protect your eyes in bright sunlight.

Because of the genetic component to AMD, if a close relative had the disease there is more reason to monitor your vision closely and to have frequent eye examinations.

It is recommended that everyone over age 60 be examined at least every two years by an eye care professional. One reason is to detect AMD early, as there is no pain or other symptoms in early stages. In this way, the disease can be followed and arrested before a disastrous retinal hemorrhage occurs. 

If you already have wet AMD in one eye, this disease will usually eventually affect the other. You need to see your eye-care professional often and check an Amsler grid at home.

What treatment is available for AMD?

Unfortunately, no effective treatment now exists for the dry form of AMD. However, it is crucial that patients who progress to wet AMD and need treatment have it done before the disease destroys their central vision. For this reason, if you have early AMD you should have your eyes examined through dilated pupils at least once a year.

Laser therapies to seal off leaking blood vessels can help reduce the risk of advancing vision loss in most wet AMD cases. This treatment involves aiming a strong light beam onto the new blood vessels to destroy them. Photodynamic therapy (PDT) is a recent improvement in laser surgery that causes much less damage to the retina; a drug (usually Visudyne) is injected into the patient’s arm and travels through the bloodstream to the abnormal vessels in eye. The laser beam is then aimed at these vessels to activate the drug, which works to stop or slow the blood leakage. Several repeated treatments are usually required, and the disease process is just slowed, not stopped. Any lost vision cannot be restored.

A promising new treatement for wet AMD uses antibodies to inhibit a growth factor (VEGF) that is largely responsible for forming the new blood vessels. This treatment is very successful at slowing the progression of the vessels, and actually improves the vision of the average patient. The drugs (typically Lucentis or Avastin) need to be injected monthly directly into the vitreous jelly of the ailing eye. However, the rate of serious complications is very low.

Research in molecular biology, genetics, and epidemiology has shown that inflammatory processes may trigger AMD; learning more about this aspect of the disease may lead to novel treatments in the future.

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