The study was the work of lead author Dr Anne Coleman, professor of ophthalmology at the Jules Stein Eye Institute at University of California, Los Angeles (UCLA), and colleagues, and is published in the January issue of the American Journal of Ophthalmology.
AMD causes a darkening and/or blurring of central vision, and prevents you from being able to read, drive and recognize people you know. It is a progressive degeneration of the macula, the centre of the retina, the part of the membrane inside the back of the eye that allows us to see fine details.
Advanced AMD with loss of vision affects about 1.75 million Americans: this figure is expected to rise to just under 3 million by 2020.
Smoking is the second most common risk factor for AMD: age is the first. Coleman and colleagues wanted to find out whether age was linked to the effect of smoking on AMD risk.
Coleman told the press that age was the strongest predictor for AMD, yet most of the research done on the disease only looked at people aged 75 and under.
"Our population was considerably older than those previously studied," said Coleman.
"This research provides the first accurate snapshot of how smoking affects AMD risk later in life," she added.
For the study, Coleman and her team compared the retinal photographs of nearly 2,000 women taken at age 78 and 83, looked for signs of AMD and then did logistical regression statistical tests to find out whether smoking affected the women's risk of developing the disease.
The women were already taking part in a study called the Study of Osteoporotic Fractures, where 45 degree stereoscopic fundus retinal photographs were part of the observations taken at clinic follow ups in year 10 and 15 of the study.
They found that:
- Overall, the smokers had 11 per cent higher rates of AMD than the non-smokers of the same age.
- But among the over 80s, the smokers were 5.5 times more likely to develop AMD than the non-smokers.
"The magnitude of the greater-than-additive effect of smoking on the age-adjusted risk of AMD reinforces recommendations to quit smoking even for older individuals."
"The take-home message is that it's never too late to quit smoking," said Coleman.
"We found that even older people's eyes will benefit from kicking the habit," she added.
Speculating on the underlying biological reasons for this link, the authors said there is a theory that smoking increases AMD risk by reducing levels of antioxidants in the blood, changing the blood flow to the eyes and reducing the amount of pigmentation in the retina.
Dr Paul Sieving, director of the National Eye Institute, which funded the research with the National Institute on Aging, said this study gives:
"Yet another compelling reason to stop smoking and suggests that it is never too late to quit."
"The Association of Smoking and Alcohol Use With Age-related Macular Degeneration in the Oldest Old: The Study of Osteoporotic Fractures."
Anne L. Coleman, Robin L. Seitzman, Steven R. Cummings, Fei Yu, Jane A. Cauley, Kristine E. Ensrud, Katie L. Stone, Marc C. Hochberg, Kathryn L. Pedula, Edgar L. Thomas, Carol M. Mangione, The Study Of Osteoporotic Fractures Research Group.
American Journal of Ophthalmology, January 2010: Vol. 149, Issue 1, Pages 160-169.