Wednesday March 16 2011
AMD is the leading cause of visual impairment in the UK
“UK experts are predicting a steep rise in the rate of an eye condition that is already a leading cause of blindness,” BBC News reported. It said that the number of people with age-related macular degeneration (AMD) could rise by a quarter by 2020.
The news report is based on computer predictions of the numbers of people with AMD, and associated sight loss, over the coming decade. The predictions used current AMD prevalence, the ageing population, mortality rates, and the effects of a drug treatment for wet AMD.
With an ageing population, an increase in the prevalence of age-related conditions such as AMD is to be expected, and these predictions are feasible. However, the accuracy of these predictions are subject to several caveats. All modelling studies rely on assumptions and the input of data from various sources, which can introduce inaccuracies. Also, the impact of only one drug treatment was considered; but there are other drug treatments in development (including the commonly used laser), and their use may affect these predictions.
The researchers call for “more effective and broadly applicable therapies for AMD” seems appropriate.
Where did the story come from?
The study was carried out by researchers from the Institute of Opthalmology, London Metropolitan University, the Royal National Institute of Blind People, and Moorfields Eye Hospital, all in London. Funding was provided by the Royal National Institute of Blind People. The study was published in the peer-reviewed British Journal of Ophthalmology.
BBC News reported the findings of this study accurately.
What kind of research was this?
The aim of this study was to predict how the number of people in the UK with age-related macular degeneration (AMD) will change between 2010 and 2020, and the number of people with sight loss due to the condition. AMD is the leading cause of sight loss in the UK, caused by degeneration of the light-sensitive cells in the retina that occurs with age. The macula is the area of the retina responsible for central vision.
There are two types of macular degeneration:
- Dry AMD - the retinal pigment epithelium gradually deteriorates, causing sight loss.
- Wet AMD - this is the next stage in some people, where new and abnormal blood vessels start to grow to supply the damaged retina. Wet AMD usually causes quite severe visual loss over a short period, compared to the more gradual progression of dry AMD.
There is no specific treatment for dry AMD, but wet AMD can be treated by laser, photodynamic therapy, or a group of anti-VEGF drugs (anti-vascular endothelial growth factor – a protein involved in the growth of the new blood vessels). The researchers were particularly interested in how the use of anti-VEGF drugs would affect AMD numbers. They said, ‘anti-VEGF treatment is already expected to make a substantial contribution to the reduction of blindness from AMD, with an accompanying impact on the structure of service delivery’.
To predict how AMD will change over this decade, the researchers constructed a computer model based on:
- current estimates of the prevalence and incidence of AMD and sight loss due to AMD
- expected changes in population demographics
- predicted mortality
- the expected effects of the anti-VEGF drug ranibizumab for wet AMD. Ranibizumab is licensed and recommended by the National Institute for Health and Clinical Excellence (NICE) for the treatment of wet AMD
- how many people could be expected to be eligible for treatment with ranibizumab
- the proportion of those who would actually receive ranibizumab.
What did the research involve?
This computer model required data from various sources.
Data on the projected population change per age group between the years 2010 and 2011, and age- and sex-specific mortality rates per calendar year, were obtained from the Government Actuary’s Department (GAD).
Information on AMD prevalence was obtained from several previous studies: the European Eye Study (a multicentre study in seven countries), the Eye Disease Prevalence Research Group 2004 (a review and meta-analysis of large population-based studies), a 2003 meta-analysis, a 2004 cross-sectional prevalence study, and a study from 1995. All studies were of predominantly white populations.
Two of these studies also provided data on the proportions of people with sight loss due to AMD.
Estimates of age-specific incidence (new cases during the period being studied) were made from calculations that took account of prevalence figures (obtained from the gathered studies), mortality rates and population projections.
Two clinical trials of the anti-VEGF drug ranibizumab were used to gain estimates of the relative risk figures for progression to blindness and the proportion of people who had significant improvement in visual acuity with the drug. Information on patient eligibility and indications for ranibizumab treatment were based on NICE guidance and clinician’s guidance from the Royal College of Opthalmologists. The researchers assumed that 75% of those eligible would receive treatment.
What were the basic results?
Briefly, the model estimates that 608,213 people had AMD in the UK in 2010. By 2020, this figure is predicted to rise to 755,867. For wet AMD, these figures are 414,561 in 2010 projected to rise to 515,509 in 2020. The overall numbers with sight loss due to AMD were estimated to be 223,224 in 2010, rising to 291,982 by 2020. The number of people with sight loss due to wet AMD is expected to rise from 145,697 cases in 2010 to 189,890 by 2020.
How did the researchers interpret the results?
The researchers conclude that their model predicts that any benefits of the new treatments for AMD will be overshadowed by a rise in the condition’s prevalence due to the increasingly ageing population. They say that this highlights the need for the development of more effective therapies for AMD that can be used for a wider range of people with the condition.
This modelling study predicts that the numbers of people with AMD will increase over this decade. This is because AMD is a condition of ageing, and the predicted rise in the ageing population over the coming years will also increase the prevalence of age-related conditions such as AMD. The study authors found that numbers can be expected to rise, despite the use of the drug ranibizumab, which can be used to treat the ‘wet’ form of the condition.
It must be remembered that all modelling studies rely on assumptions, and the input of data from studies and numerous sources. This may result in some inaccuracies. Also, with this modelling study, the researchers only considered the use of one drug treatment - ranibizumab - for wet AMD. Although this drug is licensed and widely used for the condition, other drug treatments are in development. In the future, they may be considered to be more clinically and cost effective. The effects of other treatments already in use for AMD, such as laser and photodymanic therapy, were not accounted for in the model.
The model’s prediction that the numbers of people with AMD will increase because of the ageing population is logical and feasible. The researchers call for “more effective and more broadly applicable therapies for AMD” seems appropriate.