Age-related macular degeneration (AMD) occurs when the macula, the area at the back of the retina that produces the sharpest vision, begins to deteriorate and is the leading cause of blindness after age 60.

The condition affects approximately 30 percent of Americans age 75 years and older, and is the most common cause of blindness among the elderly; all three studies involved senior citizens.

Researchers also suspect that many of the risk factors for cardiovascular disease, including atherosclerosis or blocked arteries, may also contribute to the development of AMD, possibly by affecting blood flow to the eye.

One study from found that those who smoked had nearly a twofold increased risk of age-related macular degeneration compared to those who had never smoked and there was also a higher risk for those who had smoked in the past but quit.

The first study, by Johanna M. Seddon, M.D., Sc.M., of the Massachusetts Eye and Ear Infirmary, Boston, and colleagues examined genetic and environmental risk factors for AMD in 681 elderly male twins.

Other risk factors included smoking, alcohol consumption and physical activity habits and AMD was diagnosed using photographs of the inner eye.

The researchers found that those who smoked had an increased risk of AMD while those who ate more fish and more omega-3 fatty acids as is found in salmon and other fish, were less likely to have AMD.

The researchers say that a third of the risk of AMD in the study was down to cigarette smoking, and visual impairment and blindness due to AMD could be prevented with attention to healthy lifestyles.

In the second study, Brian Chua, B.Sc., M.B.B.S., M.P.H., Westmead Millennium Institute and Vision Co-operative Research Centre, Sydney, Australia, and colleagues looked at the link between dietary fat intake and AMD risk in 2,895 Australians age 49 years or older, over a 5 year period.

Participants had a comprehensive eye examinations at the outset and then 5 years later and completed a questionnaire on diet which included specific information about margarines, butters, oils and supplements.

The researchers found that of the 2,335 participants who participated in the five-year follow-up, 158 had developed early AMD and 26 late-stage AMD.

After other risk factors were considered including smoking, age, sex and vitamin C intake, those in the group with the highest intake of polyunsaturated fat had a 50 percent reduced chance of developing early AMD compared with those who ate the least.

No link was found between AMD and consumption of butter, margarine or nuts, which all contain high levels of unsaturated fats but those ate fish at at least once a week reduced their risk of early AMD by as much as 40 percent.

The third study by Mary N. Haan, M.P.H., Dr.P.H., University of Michigan, Ann Arbor, and colleagues studied 4,262 women age 65 years and older who were part of the Women's Health Initiative clinical trial of hormone therapy.

They found that hormone therapy does not appear to increase or decrease the overall risk of AMD among postmenopausal women, although combination hormones may slightly reduce the chances of developing certain risk factors or types of the condition.

The team reached the conclusion that treatment with hormones does not influence the occurrence of early AMD.