Macular Degeneration (MD)


Macula Degeneration (MD) is a disease that affects your detailed central vision. MD is the most common cause of vision loss among people over age of 60, signs are present in one in 7 people over 50. MD can make it difficult to read, drive, or perform other daily activities that require fine, central vision.

The macula is in the centre of the retina, the light-sensitive layer of tissue at the back of the eye. As you read, light is focused onto your macula. There, millions of cells change the light into nerve signals that tell the brain what you are seeing. This is called your central vision. With it, you are able to read, drive, and perform other activities that require fine, sharp, straight-ahead vision.

MD occurs in two forms:

Dry MD: Affects about 90 percent of those with the disease. Its cause is not well understood. Slowly, the light sensitive cells in the macula break down. With less of the macula working, you may start to lose central vision in the affected eye as the years go by. Dry MD often occurs in just one eye at first. You may get the disease later in the other eye. Doctors have no way of knowing if or when both eyes may be affected.

Wet MD: Although only 10 percent of all people with MD have this type, it accounts for 90 percent of all severe vision loss from the disease. It occurs when new blood vessels behind the retina start to grow toward the macula. Because these new blood vessels tend to be very fragile, they will often leak blood and fluid under the macula. This causes rapid damage to the macula that can lead to the loss of central vision in a short period of time.

Although MD can occur during middle age, the risk increases as a person gets older. Results of a large study show that people in their 50s have about a two percent chance of getting MD. This risk rises to nearly 30 percent in those over age 75. Besides age, other MD risk factors include:

  • Gender: Women may be at greater risk than men, according to some studies.
    Smoking: Smoking may increase the risk of MD.
  • Family History: People with a family history of MD may be at higher risk of getting the disease.
  • UV Damage: Cumulative UV exposure may increase the risk of retinal degeneration with age.
  • Fair Complexion: Fair skinned people often have less pigment inside their eye and so are not able to cope with the effects of UV and high energy light as well as people with more internal pigmentation.
  • High Cholesterol: People with elevated levels of blood cholesterol may be at higher risk for wet MD.

People with Dry MD in one eye often do not notice any changes in their vision. They are still able to drive, read, and see fine details clearly; However people with bilateral changes may notice differences in their vision.

As Dry MD progresses, a blurred spot in the central vision becomes noticeable. This spot is the result of a group of cells in the macula no longer working properly. Over time, the blurred spot may get bigger and darker, affecting more of your central vision. It is common for people to find that they see much better in good light, and poorly when the light is poor. In advanced cases; people will be unable to see detail in their central vision, including reading and recognizing faces.

 

The same scene as it might be viewed by a person with MD.
An early symptom of Wet MD is that straight lines appear wavy and distorted. Newly formed blood vessels grow under the macula causing distortion and may leak fluid, hence the name “Wet” MD. These changes often cause lifting and wrinkling of the macula causing distortions. A more dramatic sign of Wet MD is that of sudden vision loss. This is different from Dry MD in which loss of central vision occurs slowly.

Visual Acuity Test: This eye chart test measures how well you see at various distances.

  • Retinal Examination: This enables your optometrist to examine the retina in more detail. It may be preferable to do this with you pupil dilated with eye drops. One of the most common early signs of MD is the presence of drusen. Drusen are deposits of normal metabolites that accumulate beneath the retina in characteristic patterns. The presence of drusen alone does not indicate a disease, but it might mean that the eye is at risk for developing more severe MD.
  • High Definition Laser Coherenc Tomography (HD-OCT): This is a relatively new procedure in which a 3D model of your retinal tissues is captured on a computer after being scanned by a laser. It is a quick and painless procedure which allows for a unique view of what changes affect the normal anatomy. This technique is particularly useful in following people who have early signs or a high risk profile of the disease.
  • Amsler Grid: This grid is a pattern that resembles a checkerboard. You will be asked to cover one eye and stare at a black dot in the centre of the grid. While staring at the dot, you may notice that the straight lines in the pattern appear wavy to you. You may notice that some of the lines are missing. These may be signs of wet MD (See Amsler Grid below.)

 

 

On the left is what an Amsler grid normally looks like, and the illustration on the right is how it might look to someone with MD.

The National Eye Institute (NEI) is the Federal government’s lead agency for vision research. The NEI is supporting a number of research studies both in the laboratory and with patients to learn more about the cause of MD. This research should provide better ways to detect, treat, and prevent vision loss in people with the disease.

Findings from the NEI-sponsored Age-Related Eye Disease Study (AREDS) ( www.nei.gov/amd/) showed that high levels of antioxidants and zinc significantly reduces the risk of advanced macular degeneration (MD) by about 25 percent.

Scientists have begun to study the possibility of transplanting healthy cells into a diseased retina. Although this work is at a very early stage and still experimental, someday it may help people keep their vision or restore some lost vision.

For more information visit the Macular Dengernation New Zealand website.

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