Factors contributing to estimates of the numbers and prevalence of vision loss
This section presented the VLEG’s estimated change in the numbers and prevalence of distance vision loss between 1990 and 2015. In summary, the absolute numbers increased for both blindness and MSVI over this period, though an encouraging decline in the percentage prevalence was observed.
The influence of three factors that contributed to this change was estimated by the VLEG. Comparing 1990 with 2015 it concluded that for blindness:
- The increase in global population gave rise to an increase in numbers of 38%
- The ageing population gave rise to an increase in numbers of 35%
- A number of factors such as including a decline in poverty levels, a reduction of the incidence of certain conditions or later onset, improved public health measures and eye health service development resulted in a decrease in numbers of -37%.
The VLEG endeavoured to estimate how these three factors might influence the future global estimates of vision loss; and specifically for the period 2020 – 2050.
Changes in the global population to 2050 and the impact of ageing
The VLEG used the estimates within the UN 2015 World Population Prospects to assess the impact of future population growth. This source estimates that in 2015 the global population was 7.3bn. By 2020 it predicts this will rise to 7.8bn and 9.7bn by 2050. These predictions represent a 33% increase in the global population between 2015 and 2050.
The UN estimates include predictions for different age groups. In 2015 there were 901 million people over the age of 60, some 12% of the global population. By 2050 the number of people over the age of 60 is predicted to increase to 2.1 billion – 22% of the population. Even greater relative increases in the numbers of people aged 80 or more is expected – 125 million in 2015 increasing more than threefold by 2050 to 434 million.
As noted here and illustrated in Figures 1 and 2 of that section, the prevalence of visual impairment increases rapidly with age. By age 60 around 1 in 9 people will be either blind or MSVI. By age 80 the ratio increases considerably to around 1 in 3 people.
Estimates for the future
The combination of a growing population and an ageing population threaten a massive increase in the numbers of people who are blind or are MSVI. We can be less certain that the positive impact on the underlying prevalence rate of factors such as continued socio-economic improvement, investment in eye health services etc. will continue to 2050 but the VLEG did factor this into its calculations based on current trends. Table 1 summarises the VLEG estimates across the period 1990 to 2050, and Figure 1 below illustrates all-too-clearly the potential scale of the problem.
Figure 1 – VLEG estimates for the global number of blind and MSVI – 1990 to 2050
Obviously the further out in terms of time the less certainty one can attribute to these estimates; but undoubtedly there is a very significant risk that there will be considerably more persons blind and MSVI by 2050 than there are presently.
A major investment in eye health services, which targets the poorest and ensures universal access to eye health for all, is needed over the next 30 years to avert the very significant risk that there will be considerably more persons blind and MSVI by 2050.
Table 1 – VLEG estimates for the global number of blind and MSVI persons – 1990 to 2050