Tuesday February 14 2012
In the UK most blindness and sight loss is linked to ageing
It is feared that the UK could face a “Blindness epidemic”, the Daily Express has claimed today. The newspaper has reported that Britain faces a sight loss epidemic, caused by progressive eye conditions, that is being grossly underestimated by the NHS.
The story is based on research that estimates the number of people affected by advanced age-related macular degeneration (AMD). AMD affects the part of the retina at the back of the eye that is responsible for central vision. It is the most common cause of age-related sight loss in the developed world. AMD is thought to affect half of the 370,000 people registered as blind or partially sighted in the UK.
The study estimates that the current UK prevalence of late stage AMD is actually 2.4% of the adult population (513,000 cases) and that this figure is set to rise by one-third over the next decade, totalling nearly 700,000 cases by 2020.
AMD is a progressive condition that causes loss of vision and leads to loss of independence. Therefore, it is important to have an accurate estimate of projected numbers who have, or will develop, this disorder. While estimates provided by this research are higher than previous ones, they do not represent an ‘epidemic’ or an increase in cases of the disorder per se. Indeed, the risk of AMD increases sharply with age and the principal reason for the projected increase in cases by 2020 is the growing proportion of elderly people in the UK population.
Where did the story come from?
The study was carried out by researchers from the University of London and was funded by the Macular Diseases Society. A spokesperson for the society reportedly called for the government to give AMD a higher priority.
The study was published in the peer-reviewed British Journal of Opthalmology. It was generally covered accurately in the papers, aside from the Daily Express’ alarmist headline predicting a forthcoming ‘blindness epidemic’.
What kind of research was this?
Age-related macular degeneration affects the macula, a highly sensitive part of the retina at the back of the eye that is responsible for central vision. As the name implies, the condition is associated with ageing, and it is a leading cause of visual impairment among the elderly. As AMD progresses a person will gradually lose the ability to see things in their central field of vision, which is needed for important activities, such as reading, writing and driving. There are two different types of the disease: dry AMD and wet AMD (also called neovascular AMD or NVAMD). Wet AMD involves the formation of new blood vessels.
Dry AMD, the most common form, is associated with a gradual breakdown of the cells in the retina. Dry AMD is usually subdivided into early and late stages. In early-stage dry AMD there may be a few characteristic yellow deposits (known as drusen) under the retina, but there is minimal effect on vision. In advanced or later-stage dry AMD, there will be both drusen deposits and breakdown (atrophy) of the retinal cells.
This later-stage dry AMD is sometimes called ‘geographical atrophy’ and is associated with gradual loss of vision.
A small proportion of those with dry AMD will go on to develop wet AMD. This is where new and abnormal blood vessels start to grow in an attempt to re-supply the damaged retina with oxygen and nutrients. These vessels are fragile and can leak blood and fluid, causing more sudden and rapid loss of vision than dry AMD.
While little can be done to prevent the progression of dry AMD, the blood vessel growth of wet AMD is usually treated by laser, photodynamic (light) drugs or injections of drugs that prevent the growth of the abnormal blood vessels (called anti-vascular endothelial growth factors, anti-VEGFs).
The authors point out that AMD is a major cause of eye disease, accounting for more than half of those registered as blind or partially sighted in the UK. However, they add that registered numbers do not reflect the full proportion of people who experience visual loss caused by the condition, and that estimates of incidence vary. They argue that accurate estimates are needed to help provide sufficient healthcare in the future.
This research was an analysis of the data from a recent systematic review and meta-analysis of the prevalence of ‘late’ AMD. This was based on 31 populations of European ancestry, ranging in age from 50 to 97 years. They used these figures to produce models to estimate the prevalence and incidence of late AMD in the UK population, both now and in the future. They then constructed separate models to look at the prevalence of:
- late/advanced dry AMD (or geographical atrophy [GA])
- wet AMD (or neovascular AMD, NVAMD)
- late AMD overall (both GA and NVAMD)
‘Prevalence’ is a specific term referring to the number of cases of a disease within a population at any given time. The related term ‘incidence’ refers to the number or rate of new cases that develop in a specified period.
What did the research involve?
The researchers based their models on a meta-analysis of 31 population studies featuring a combined population of 57,173 participants. They say it is the most complete meta-analysis of late AMD prevalence in white populations. The study populations were from Europe, North America and Australia, which they say are largely similar to the middle-aged and older population of the UK.
They applied these figures to the UK population aged 50 to 97 years old, calculating prevalence using statistics for the years 2007 to 2009 obtained from the Office of National Statistics. They calculated prevalence in the UK by year, by age (from 50 to 97 years), by gender and for both genders combined.
They used projections of numbers within these age groups in the UK population to calculate prevalence figures up to 2020. Their estimates allow for a 95% ‘credible interval’, representing the range within which true prevalence is expected to lie with a 95% probability.
The researchers then used the models of age-specific prevalence to estimate the annual incidence (new cases) of age of late AMD overall, GA and NVAMD in men and women between the ages of 50 and 97 years.
What were the basic results?
Overall prevalence of late AMD in the UK population aged 50 or over was 2.4% (95% credible interval [CrI] 1.7% to 3.3%). This is equivalent to 513,000 cases (95% CrI 363,000 to 699,000) and is estimated to increase to 679,000 cases by 2020.
- In those aged 65 or over, prevalence of late AMD was 4.8% and in those aged 80 or over, 12.2%.
- Prevalence of GA was 1.3% overall (95% CrI 0.9% to 1.9%), 2.6% in those aged 65 and above (95% CrI 1.8% to 3.7%) and 6.7% in those aged 80 and above (95% CrI 4.6% to 9.6%).
- Prevalence of wet AMD (NVAMD) was 1.2% overall (95% CrI 0.9% to 1.7%), 2.5% in those aged 65 and above (95% CrI 1.8% to 3.4%) and 6.3% in those aged 80 and above (95% CrI 4.5% to 8.6%).
- The estimated number of cases of late AMD were 60% higher in women than men (314,000 cases in women, 192,000 in men).
- The authors say that by 2020 there will be 394,000 women and 285,000 men (679,000 in all) with late AMD. This equates to an increase of a third over current rates.
- They calculate that until 2020 there will be 71,000 new cases of late AMD each year, with higher numbers in women.
- Annual incidence (new cases each year) of late AMD overall was estimated at 4.1 per 1,000 women (95% CrI 2.4 to 6.8) and 2.6 per 1,000 men (95% CrI 1.5 to 4.4).
How did the researchers interpret the results?
The researchers say that their review provides the best estimates of the prevalence and incidence of late AMD in the largely white older population in the UK, and suggest that by 2020 cases of AMD will increase steadily by one-third. The authors say these evidence-based estimates are higher than previous estimates, and argue that they can be used to help plan both social and healthcare support, now and in the future.
This study has provided estimates of the current prevalence and incidence of late-stage AMD in the UK (including late-stage dry AMD and wet AMD). It predicts that the prevalence of the condition will rise over the coming decade. These late stages of AMD can lead to loss of vision and of independence, so it is important to have an estimate that is as accurate as possible of projected numbers who have, or will develop, this disorder.
It is important to point out that the projected increase in numbers of those with the disorder is not due to an increase in the condition per se but to the UK’s ageing population. It is also worth noting that these estimates are based on complex statistical models and, as is clear from the results, the probable range within which true prevalence lies is quite wide.
The authors also point out that their figures are based on cases of AMD in ‘either eye’ so may overestimate the potential visual loss associated with the condition, though, as they say, late stage disease in only one eye may still need treatment.