Avoidable visual impairment

GBM roundelBoth VISION 2020 and the current Global Action Plan focus on the elimination of avoidable blindness and visual impairment. The term ‘avoidable’ includes eye conditions that can be treated and conditions that can be prevented.

Defining which eye conditions are avoidable is not straightforward. The WHO, in setting its target on reducing avoidable visual impairment, only included Cataract and Uncorrected Refractive Error in its calculation.

The VLEG in its recent publication includes Cataract, Uncorrected Refractive Error, Trachoma, Glaucoma, Diabetic Retinopathy and Corneal Opacity, and thus estimated that 81% of distance visual impairment was avoidable in 2015.

Some conditions such as Cataract and Uncorrected Refractive Error are certainly treatable and Trachoma is undoubtedly preventable. For many non-communicable conditions it is less clear – Diabetic Retinopathy and Glaucoma are certainly partially preventable and treatable, though achieving this requires long-term investment in health systems and, for those affected, adherence to treatment regimes over many years and modification of lifestyles. Even with the best possible treatment and case management, conditions such as AMD, Glaucoma and DR may progress to vision loss. Corneal Opacity includes a range of conditions some of which are avoidable and some which are not.

A further difficulty is the considerable number of eye conditions that are pooled into the ‘Other’ category and the relatively high percentage of blindness and MSVI attributed to ‘Other’ in the causes data. Some conditions within the ‘Other’ category are avoidable and others are not.

A very conservative estimate of the percentage of blindness that is avoidable can be made by summing the data for Cataract, Uncorrected Refractive Error and Trachoma and expressing the number in terms of ‘at least x% of blindness is avoidable’, or alternatively as >x%.

Using this measure we can state that globally at least 75% of distance visual impairment is avoidable (>56% of blindness and >78% of MSVI).

All regions of the world continue to have unacceptably high levels of avoidable distance visual impairment as illustrated in Figure 6 below.

Figure 6 – Percentage of avoidable distance visual impairment in the 21 GBD regions of the world

The highest levels of avoidable distance visual impairment were found in the less developed regions. More than 87% of distance visual impairment was considered avoidable in South Asia, while six other of the lower income regions had levels of between >76% and >79%. Even the High-Income regions had levels of avoidable visual impairment at >60% – a sad indictment of the low priority afforded to eye health all over the world.

Defining which eye conditions are avoidable is not straightforward. The WHO, in setting its target on reducing avoidable visual impairment, only included Cataract and Uncorrected Refractive Error in its calculation.

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