Thursday, March 09, 2006

AMD Risks 28

Chapter Three
Important Risk Factors in AMD


Epidemiological Studies

Two main types of studies have been used to try to determine which factors increase or decrease the risk of AMD. One type is the population-based study, in which the scientist questions and examines everyone in a given population; such a study was performed, for example, in the town of Beaver Dam, Wisconsin. The other type of study is called a case-control study, in which a group of patients with AMD is compared to a closely matched group of people who do not have AMD.

In each type of study, researchers ask each patient a number of questions about their health and habits. They then examine the patient to see if they have the disease in question – in this case AMD – or any other diseases associated with it. The researchers compare those who have AMD to those who do not. They search for differences between the two groups. For instance, if most of the patients with AMD smoke whereas most of the patients without AMD don’t smoke, this is a difference or imbalance that suggests that smoking may be related to AMD. The researchers may then say that there is an association between smoking and AMD.

Even if an association is found, it does not mean this is a cause of the AMD. For instance, those who have atherosclerotic plaques on their carotid arteries seem to have an increased risk of AMD, but this does not necessarily mean that the plaques are causing the eye disease. There is more evidence that high cholesterol or systemic inflammation may be the cause of both the plaques and the AMD. Therefore, the plaques on the arteries and the eye disease are associated, but one isn’t causing the other.
The study of which factors affect the presence or absence of a disease is called epidemiology. Epidemiologic studies have found that the two main risk factors for AMD are age and family history.

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