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Macular Degeneration

The light-receiving surface called the retina lies at the back of each eye. At its center is the macula, which takes full advantage of having center stage: Only 5 millimeters wide, the macula accounts for only 2% of the retina’s area, but is the spot most concentrated with the visual nerve cells called cones. Hence the macula is responsible for much of our detailed visual ability. This is also reflected in the brain: Almost half of the brain’s vision areas are devoted to only the sensory input from the macula. The other 98% of the retina gets the attention of just a little over half of the brain’s visual areas! So the macula is small but enormously important for vision.

Macular degeneration occurs in people fifty years of age and older and is properly called age-related macular degeneration (AMD). This is distinct from rarer conditions affecting the macula of younger people, referred to as macular dystrophies. Dystrophies result from a deficiency in growth, while degeneration is the breaking down of what had been once fully formed.

AMD comes in two varieties, and there is some good news in that the more severe form, called ‘wet’ AMD, is less common, seen in only about 10% of AMD cases. On the other hand, the less severe ‘dry’ form has no good treatments, although taking strong dietary antioxidants may slow the deterioration. In this more common form of AMD, cellular debris called drusen begin to accumulate between the retina and the cell layer beneath it, which is full of blood capillaries. The particles of drusen, whose origin is unknown, apparently interfere with oxygen and nutrients getting from the capillaries to the retina. The retina may detach, which is a painless yet serious condition possibly leading to blindness. A doctor should be seen as soon as possible.

In the less common, wet form of AMD, capillaries in the layer below the retina grow through a membrane normally keeping them out of direct contact with the retina. This leads to bleeding at the retina, within the eye, harming the cells of the retina, the rods and cones, and leading to vision loss if untreated. Although serious, wet AMD can be treated with lasers that cause blood within the protruding capillaries to coagulate, bringing bleeding under control. Medications that slow the growth of new blood capillaries, called angiogenesis inhibitors, can also be given.

AMD is more common in Caucasians than other racial groups, for reasons unknown. It can also run in families. Those having a relative with the condition have a 50% chance of developing it themselves, compared to a 12% chance for the overall population. The most general and unavoidable risk factor is age. About ten percent of people ages 65-75 have AMD, while almost 30% of those 76 to 85 suffer from it. The most preventable risk factor is smoking, which raises the risk of AMD, along with the other conditions and diseases this expensive habit contributes to.

High levels of cholesterol or high blood pressure can each raise the risk of developing AMD, and a diet low in saturated fats (meat, dairy products) is recommended to reduce risk of AMD. Another possible risk factor is lifelong exposure to bright sunlight without adequate use of sunglasses, however the study results on this have given conflicting results. The ultimate cause of AMD may be genetic, with environmental factors being important for further development of the disease. Doctors are studying a number of different genes that may be linked to AMD, and these may shed light on the exact processes causing AMD to develop. 

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