A risk factor is a characteristic that increases a person’s chance of having a disease. A risk factor for a disease is not necessarily a cause of the disease, although at times it is. A disease is significantly more likely to occur in a person with the risk factor than those without the risk factor. However, just because a person has a risk factor, this does not mean that they will get the disease. It just means that they are more likely to get the disease than someone who does not have the risk factor.

Risk factors can be divided into two types. Non-modifiable risk factors are those that cannot be changed by any kind of medical treatment, intervention, or lifestyle change. Age is a good example. Modifiable risk factors can be changed by treatment, intervention, or changes in behavior and lifestyle.

Non-Modifiable Risk Factors

Age
Large studies of populations in the US, Europe, and Australia have shown that the strongest risk factor for AMD is advanced age. Very few persons younger than age 50 years have AMD, and the number of affected persons rises dramatically after age 60. Depending on the study, 15-30% of persons older than 75 years have dry AMD, and about 5% have advanced AMD (either dry or wet). People aged 90 years or over have an 8-10 times greater chance of developing AMD, compared to people aged 50 years.

Race
Large population studies have revealed that in the US, African-Americans and Causasians have similar prevalence rates of the early signs of dry AMD (i.e., drusen and changes in the retinal pigment epithelium). However, wet AMD is found less frequently among African-Americans than among Caucasians. Studies from around the world suggest that the type of AMD varies between countries. It is not yet known if these differences reflect genetic differences between populations, lifestyle differences between cultures, or both.

Gender
Women tend to live longer than men, and people who live longer are at greater risk of AMD. It is not yet clear if women are at greater risk for AMD for any reason besides their longevity.

Family history and genetic susceptibility
Individuals with AMD are more likely to have siblings or other close relatives that also have the disease. Both members of identical twins tend to develop disease that looks similar in the fundus. Brothers and sisters of AMD patients have nearly 20 times greater risk of developing AMD, compared to the general population. Recent research has identified several genes that appear to increase a person’s susceptibility to developing AMD. These genes include complement factor H, factor B, LOC387715, LRP, VEGF, and VLDLR. It is becoming increasingly clear through research that AMD emerges from a complex interplay of genetic susceptibility factors and environmental exposures (e.g, smoking, diet, body weight). In other words both a person’s genetic make-up as well as agents one is exposed during a lifetime or characteristics of one’s lifestyle contribute to the development of AMD.

Characteristics of the eye
Hyperopia (far-sightedness) and having a light-colored iris have been investigated as possible risk factors for ARM. There is more evidence supporting increased risk due to hyperopia, but the effect is very small.

Modifiable Risk Factors

Smoking
Tobacco smoke has long been implicated in the development of cancers and heart disease. Tobacco smoke contains compounds that promote oxidative damage to tissues and cells, compounds that constrict blood vessels, and compounds that reduce helpful anti-oxidant substances in the blood stream. Most major studies have found a link between smoking and AMD. Further, some studies found that the risk increases with the number of cigarettes smoked. Finding that smoking is a major risk factor is important, because it suggests that a lifestyle change may be helpful in preventing AMD.

Cardiovascular disease and its risk factors:
Elevated plasma cholesterol
Elevated levels of cholesterol in the blood increase risk for heart disease. One study has shown a strong association between elevated plasma cholesterol and neovascular AMD, and other smaller studies have not. There is no evidence that high plasma cholesterol is a risk factor for dry ARM at this time.

Hypertension
Hypertension, or high blood pressure, is another aspect of personal health that increases one’s risk for cardiovascular disease. The data on hypertension and AMD are mixed, in that some studies have shown increased risk and others have not. The differences in the results may be due to how AMD was defined in each of these studies. However, the recently completed AREDS (Age-related Eye Disease Study), demonstrated the risk conferred by hypertension in a large number of AMD patients.

Light exposure
Light exposure, particularly ultraviolet light, is thought to lead to a lifetime of chronic oxidative damage to the retina. This is an attractive hypothesis which has not yet been convincingly supported by studies of large populations.