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Age-related macular degeneration (AMD) is a degenerative eye disease caused by the breakdown
of the macula, the small part of the eye’s retina that is responsible for central vision. This condition affects both distance and close vision and can make some activities, such as driving or reading, very difficult or impossible. Macular degeneration is the leading cause of severe vision loss in people over the age of 65.

The incidence of the disease has been shown to be low in people under 55, but it increases with advancing age. It’s estimated that 30 percent of individuals over 75 have early macular degeneration. A family history of AMD, high blood pressure and smoking also have been identified as risk factors, and although it has not been proven with certainty, it appears females, those with light-colored irises and cardiovascular disease, and people who have been continually exposed to intense sunlight are among those who are most susceptible.

There are two types of AMD—dry and wet. Ninety percent of the people who have AMD have the dry type, which is characterized by a build-up of material under the macula. This condition often takes many years to develop, and vision loss tends to occur gradually. People with dry-type AMD typically have difficulty reading small print, and often need magnification aids and bright lights to read.

The wet type of AMD is more serious and occurs in 10 percent of those diagnosed with the disease. Abnormal blood vessels grow in a layer beneath the macula, leaking fluid and blood that damage the retina. Side vision is not affected; the most obvious symptom involves distortion or a large blind spot in the center of one’s vision—the sharp, straight-ahead vision necessary for driving, reading, recognizing faces and looking at details. Straight lines may appear crooked. Vision loss for those with wet-type AMD may be slow or sudden; for example, their vision may decline from normal to seeing just motion or worse in a few weeks.

A dye test is performed to help diagnose which form of AMD is present. In both cases, the eyes can be affected at different rates; that is, vision in one eye may get worse before the other eye. Once people have been diagnosed with AMD, an Amsler grid is used to monitor changes in their vision. If they start to notice breaks or waves in horizontal or vertical lines on the grid, this might indicate that the disease is progressing. When this happens, more vision loss and distortion will be evident.

Although there is no treatment for dry-type AMD, it is important to be examined regularly because wet-type AMD also may develop. Treatment for the latter is focused on preserving what central vision remains. Laser treatment has been used for years in an attempt to seal leaking vessels. It has been found, however, that this causes some loss of central vision and retreatment often is necessary.

A procedure known as photodynamic therapy (PDT) was developed in the past decade to target abnormal blood vessels and to help prevent further loss of vision. The benefit of PDT is that it may inhibit the abnormal blood vessel leakage associated with wet-type AMD while limiting further damage to the overlying retina. Its potential advantage over laser treatment is that it focuses on abnormal vessels so the rest of the macula is not damaged. Unfortunately, abnormal blood vessels may regrow or begin to leak again, requiring a repeat examination, including a dye test, every three months. Like laser treatment, multiple procedures may be necessary.

The newest treatment for wet-type AMD is the use of medications specifically aimed at the chemical messenger called vascular endothelial growth factor (VEGF), which is responsible for spurring the growth of new blood vessels. Simply put, anti-VEGF drugs prevent the transmittal of the brain’s instructions to grow new blood vessels.

Studies have shown these medications, including Macugen and Lucentis, stabilize the disease, and, in many cases, improve vision that has been lost due to the disease. In clinical trials, patients on Lucentis, in particular, have noted stable or improved vision during the first year of taking it. The drawback is that a patient needs to return for treatment every few weeks.

Surgical options, including repositioning the macula, are currently being investigated. A recent study shows that antioxidant vitamins and zinc may reduce the impact of AMD, but they don’t provide a cure for the disease nor will they restore lost vision.

Since AMD has no cure, annual exams are essential to monitor the course of the disease. Still, many people who have AMD are able to live independently and pursue the activities they enjoy.

February is National Age-Related Macular Degeneration and Low Vision Awareness Month; check newspaper listings for special AMD events. More information on macular degeneration and other vision disorders can be found on the Internet. Two good resources are the Research to Prevent Blindness at www.rpbusa.org/index.htm and the National Eye Institute at www.nei.nih.gov/health/.

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Taking a Look at
Age-Related
Macular Degeneration