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ORLANDO, FL — Findings from population-based eye disease studies conducted on three continents provide strong evidence that smoking is the principal known risk factor associated with age-related macular degeneration (AMD), according to an Australian ophthalmologist. Speaking at the annual meeting of the American Academy of Ophthalmology, Paul Mitchell MD, PhD said AMD is the leading cause of new blindness in older, developed communities and as current treatment options are limited, identifying modifiable risk factors could substantially stem the development of the disease. “The findings from this pooled analysis provide support for health advocacy approaches to reducing smoking rates, even in the older elderly, and point to the important role ophthalmic clinicians can play in encouraging smoking cessation,” Dr Mitchell said, The pooled study was undertaken to gain statistical power in identifying significant risk factors of AMD. The ability of previous studies to find statistical significance of true risk factors may have been hindered by the relative infrequency of AMD in the population. That problem would be further aggravated when attempting to assess risk factors for each of the two subtypes of AMD — geographic atrophy and neovascular disease, Dr Mitchell explained. The pooled analysis incorporated data from the Beaver Dam Eye Study in the US, the Rotterdam Eye Study in Europe and the Blue Mountains Eye Study in Australia. Those investigations were chosen because they used similar methods, including masked grading of stereo macular photographs. The studies also measured similar risk factors and had racially similar northern European-derived populations. Age, gender, smoking, body mass index, iris colour, hormonal factors and cardiovascular among other diseases, were assessed as potential risk factors using logistic regression analysis techniques. The results showed a strong increase in AMD prevalence with increasing age, but smoking was the only other significant risk factor clearly associated with both types of AMD. The data included approximately 12,500 people aged 55 to 86 years. AMD prevalence rates were less than 0.5% for persons under 65 years, 1% for those aged 65 to 74 and 5% for those aged between 75 and 84. The rate rose sharply to almost 15% for those aged 85 years and older. Compared with a reference group of people under age 70, those in their 70s had a six-fold increased risk of AMD, while those in their 80s were 25 times more likely to have AMD. The association between smoking and AMD was found in each study. It was maintained in the pooled data analysis and was very strong for current smokers while decreasing appreciably after subjects stopped smoking. Compared with lifelong non-smokers, past smokers had a 30% increased risk of AMD while the risk was increased 300-fold among current smokers. Dr Mitchell added that more recently published five-year incidence data from the Blue Mountains Eye Study [Mitchell, P, et al. Archives of Ophthalmology 2002;120:1357-63] is also consistent with the pooled prevalence data in linking smoking with AMD. In the incidence analysis, the age-adjusted relative risk of AMD was also 300-fold higher for current smokers compared with those who never smoked, and current smokers developed AMD 10 years earlier than non-smokers. Additional analyses point to the potential value of anti-smoking public health messages for reducing AMD development. Dr Mitchell reported that in the Blue Mountains population, only about 5% of persons in their 80s were still smoking. However, smokers were disproportionately represented among those presenting with AMD. “Using population attributable risk estimates, we determined that smoking may now cause or contribute to up to 20% of new blindness in Australians over 50 years old. That is a very high proportion due to an avoidable risk factor. “Older smokers and their physicians often struggle to find a compelling reason for giving up smoking. Perhaps the risk of blindness may be more persuasive than concern about sudden death from myocardial infarction or stroke,” Dr Mitchell said. A recent Australian national campaign to encourage smokers to quite focused on the habit as a risk factor for blindness. In addition, Dr Mitchell has called for a new cigarette pack warning: Smoking causes blindness. “But there are many other avenues to explore to reinforce this message. Ophthalmologists have an important role in this,” Dr Mitchell said. |
