Wednesday December 2 2009
In AMD damage to the central retina gradually destroys vision
Aspirin “could stop you going blind”, according to the Daily Express, which reports that taking aspirin daily can cut the risk of developing age-related macular degeneration by almost a fifth.
Age-related macular degeneration is a common cause of visual loss in the elderly. It occurs when the cells in the centre of the retina become progressively damaged. This damage eventually causes the loss of central vision, making reading and writing impossible for some people.
The research behind this study was robust and well-conducted, but the results have been incorrectly reported in the Daily Express. The large study, which lasted several years, found that aspirin had no significant effect on the risk of developing age-related macular generation, a point the researchers clearly highlight in their written results.
Where did the story come from?
This research was conducted by William Christen and colleagues from a number of institutions in the US, including the Harvard Schools of Medicine and Public Health, and the National Eye Institute. The study was funded by the US National Institutes of Health, and it was published in the peer-reviewed medical journal, Opthalmology.
The findings of this research have been completely misinterpreted by the Daily Express, which has claimed that aspirin could prevent blindness, and that risk of developing age-related macular degeneration was significantly reduced when using aspirin. In contrast, the study found non-significant results, a point made clear by the researchers themselves.
What kind of research was this?
This was a large, double-blind, randomised controlled trial, which was designed to investigate whether taking low-dose aspirin on alternate days affects the development of age-related macular degeneration (AMD). The condition is a major source of sight loss in the elderly, and it causes the gradual deterioration of the central field of vision.
This was a well-designed piece of research, which has used the best study model to investigate this question. However, this study drew its data from a larger study on aspirin that was not looking specifically at outcomes of AMD. This may be a potential limitation of the study.
What did the research involve?
This piece of research used data on the population of another study, the Women’s Health Study. This study enrolled 39,876 healthy, female health professionals aged 45 years or older, and followed them for an average of 10 years. The trial was investigating how a low-dose of aspirin (100mg) taken every other day might lower the risk of cardiovascular disease and cancer. At the start of the study, women were given assessments of their medical history, family medical history and lifestyle. This included assessing the presence of AMD. Women were randomly entered into groups taking either aspirin or placebo pills.
In this subsequent study, the researchers included all participants of the Women’s Health Study who had not been diagnosed with AMD at the study’s start (39,421; 99% of the total sample). Compliance in aspirin use and medical conditions, including AMD, were assessed by questionnaire at various times during follow-up.
Those who responded “yes” to the development of AMD had this confirmed by checking medical and ophthalmology records. Risk of AMD was compared in those who received aspirin compared to placebo. Overall, across the 10-year study period, 73% of participants were followed-up.
This is a good study design, and it has assessed a large number of women over 10 years. It has some drawbacks in that investigating AMD was not likely to have been a primary goal of the Women’s Health Study. Also, the earlier stages of AMD can be symptomless, but the condition was initially identified by self-report. Numbers may have been underestimated due to some women not knowing that they had AMD.
What were the basic results?
The researchers found that after 10 years of treatment and follow-up, there were more cases of AMD in the placebo group than the aspirin group (134 and 111 respectively). However, this difference was not statistically significant (hazard ratio 0.82, 95% confidence interval 0.64 to 1.06).
How did the researchers interpret the results?
The researchers concluded that their large, randomised trial of female health professionals with 10 years of treatment and follow-up has found no large beneficial or harmful effect of low-dose aspirin on the risk of AMD.
This is a well-designed and well-conducted study, the results of which have been incorrectly reported in the press. This study found that low-dose aspirin had no effect in preventing age-related macular degeneration, a common cause of sight loss in the elderly.
There are a few points to note when interpreting this study:
- While the trial itself was well-conducted and followed a large number of women over a long-period of time, the research it was based on did not appear to be directly assessing AMD risk. It is likely that the study’s design may have had limitations in its ability to assess AMD. For example, AMD was initially identified by self-report. This may mean that it could have underestimated numbers of AMD cases because some women may not have been aware that they had the condition.
- The study findings are only applicable to women (although AMD is more common in women than men).
- When calculating risk, the researchers only adjusted for the influence of age and vitamin E and beta carotene use (which were given as part of the trial in addition to aspirin). Besides age and nutrition, other possible risk factors are family history, smoking and the eye’s exposure to sunlight. However, randomisation should have balanced these confounders, and other unidentified ones, between the groups.
- There are risks associated with taking daily or alternate-day aspirin, which should be weighed against the benefits. Elderly people, to whom this research will be most relevant, are most at risk of gastric irritation if they regularly use aspirin.
Despite the news headlines, this research has found no evidence of that alternate-day aspirin affects the chances of developing age-related macular degeneration.