The Global Target
WHO’s Universal Eye Health: Global Action Plan 2014 – 2019 (GAP) set a global target of a 25% reduction in the prevalence of avoidable visual impairment by 2019, compared with the base line prevalence for the year 2010.
In setting the target, WHO includes only Uncorrected Refractive Error and Cataract as avoidable causes and references the crude prevalence. WHO established the 2010 baseline using the global prevalence estimates published by Pascolini and Mariotti , giving rise to a baseline prevalence of avoidable visual impairment of 3.18% and a target prevalence of 2.37% by 2019.
The August and October 2017 publications of the Vision Loss Expert Group (VLEG) are now the most recent source of global estimates and are the only sources currently available which enable progress since 2010 to be monitored. It should be noted that the VLEG estimates employ different methodologies and additional data sources than those used by Pascolini and Marriotti and thus one must exercise caution when making comparisons.
Using the VLEG estimates then, the 2010 baseline crude prevalence of avoidable visual impairment (Cataract and Uncorrected Refractive Error only) was 2.5% and the corresponding target for 2019, to achieve a reduction of 25%, would be 1.9%.
Changing prevalence estimates compared with the GAP target
The VLEG estimates for 2015 and 2020 suggest that the crude prevalence of avoidable visual impairment is in fact increasing and by 2020 is expected to be in the order of 2.7% (see Figure 1).
Rather than achieving the target of a 25% reduction, the VLEG estimates predict an increase of 5.6% in the prevalence of avoidable visual impairment by 2020 compared with the 2010 baseline. The VLEG estimates for the longer term predict a further deterioration of the situation. Clearly this is not the result desired within the Global Action Plan.
The recent resurgence in the prevalence of avoidable visual impairment is mainly driven by population ageing, increased prevalence of Uncorrected Refractive Error, and, to a lesser extent, Cataract, as shown in Figure 2.
Changing Prevalence across all 21 GBD Regions
The change in the prevalence of avoidable blindness in the 21 GBD regions is shown in Figure 3. As can be seen, the declining prevalence trends observed in most of the regions between 1990 and 2005-10 has slowed and in some regions gone into reverse in more recent years.
The upturn is particularly marked in South Asia and East Asia and, given the high populations of these two regions, this is driving the global prevalence upwards too. In East Asia, both an increase in the Uncorrected Refractive Error prevalence and the Cataract prevalence is observed, whilst in South Asia the upturn is mainly attributable to Uncorrected Refractive Error (Figure 4).
These changes are probably due to the combination of fast and significant ageing in these two regions, combined with the impact of the steep increase in Myopia. Scaling up of provision of services is urgently warranted everywhere and especially in East and South Asia where the situation is deteriorating.