Macular degeneration is a disorder that affects the macula (the central part of the retina of the eye) causing decreased vision and possible loss of central vision.

The macula is the part of the retina that allows the eye to see fine details at the center of the field of vision. Degeneration results from a partial breakdown of the retinal pigment epithelium (RPE).

The RPE is the insulating layer between the retina and the choroid (the layer of blood vessels behind the retina). The RPE acts as a filter to determine what nutrients reach the retina from the choroid. Many components of blood are harmful to the retina and are kept away from the retina by normal RPE.

Breakdown of the RPE interferes with the metabolism of the retina, causing thinning of the retina (the "dry" phase of macular degeneration). These harmful elements may also cause new blood vessel to form and fluid to leak (the "wet" phase of macular degeneration).

This disorder results in the loss of central vision only -- peripheral fields usually stay normal. Although loss of ability to read and drive may be caused by macular degeneration, the disease does not lead to complete blindness.

The disease becomes increasingly common as people age over 50. By age 75, almost 15% of people have this condition. Other risk factors are family history, cigarette smoking, and being Caucasian.

• Blurred, distorted, dim, or absent central vision

Tests to evaluate the retina may include:

• Visual acuity
• Refraction test
• Pupillary reflex response
• Slit lamp examination
• Retinal examination by various techniques
• Fluorescein angiography, and sometimes indocyanine green angiography
• Amsler grid
• Optical coherence tomography (OCT), a test that creates a color picture of the macula or retina

There is no specific treatment for dry macular degeneration, although zinc supplements may slow the progression of the disease (see zinc in diet).

Laser photocoagulation (laser surgery to stop the leaking in choroidal blood vessels) may be useful in the early stages of the wet form of the disease. It involves the use of a thermal laser, which burns the abnormal, leaky blood vessels and stops them from spreading.

A newer treatment option for patients with wet macular degeneration is photodynamic therapy, which can be performed in a doctor's office. In this procedure, a light-sensitive medication called Visudyne (verteporfin) is injected into a vein in the patient's arm. The drug circulates through the body to the eyes. When a non-thermal laser is shone into the eyes, Visudyne produces a chemical reaction that destroys abnormal blood vessels. If the vessels grow back, the procedure can be repeated.

Photodynamic therapy is expensive and is not a cure, but it can be successful in managing a particular area of leakage from the choroid through the RPE.

Your physician may recommend that you use an Amsler grid to discover possible new leaks before scarring occurs.

Macugen, Avastin, Lucentis, and Kenalog are all medications that may also be used to treat the wet form of AMD. Each of these medications is injected directly into the eye at various intervals.

Low-vision aids and therapy can be vital to improvement of vision and quality of life.

AMD Alliance International is a nonprofit organization committed to raising the awareness level of Age-related Macular Degeneration (AMD). Their website, www.amdalliance.org, contains additional information and resources, including an Amsler grid. AMD Alliance International maintains a toll-free international hotline at 1 (877) AMD-7171.

Most people with mild dry macular degeneration will never have disabling central vision loss. However, there is no way to predict who will progress to a more severe form of the disease. This disorder results in the loss of central vision only -- macular degeneration cannot cause peripheral vision loss.

The wet form of macular degeneration often leads to significant vision loss.

Loss of central vision may interfere with many activities of daily living. Reading may require magnification or may become impossible. The ability to drive may be lost.

Call your health care provider if you notice any dim or distorted areas in your vision. Routine dilated eye exams can monitor for the condition.

There is no known effective prevention. If you have a family history of macular degeneration, avoid all use of tobacco. Studies have shown that good nutrition and use of AREDS formula vitamins, as recommended by the Age-Related Eye Disease Study (AREDS), may reduce the risk of developing macular degeneration.