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Vision Atlas and VLEG data - FAQ

How are the estimates for vision loss generated?

Data for vision loss on the IAPB Vision Atlas comes from the modelled estimates by the Vision Loss Expert Group (VLEG) in 2020. The VLEG data incorporates data from 512 studies in 112 countries to estimate distance vision impairment in each country and region based on certain characteristics and demographics.

How does the 2020 version of the Vision Atlas compare to the previous version (2017)?

There are several key differences:

  • The new VLEG data features a dramatically enhanced data set to improve the accuracy of the estimates. This update incorporates data from 512 studies in 112 countries to estimate distance vision impairment, an addition of 224 studies (including data from a further 14 countries).
  • Previously, mild vision impairment was modelled by extrapolating from moderate or worse distance vision estimates due to lack of data. However, in this update, data from 59 studies were available to separately estimate mild vision impairment.
  • Finally, 25 studies were used to estimate for vision loss from uncorrected presbyopia, compared to 18 last time.
  • The maps have a new design and the data can be accessed via several filters. We feature a new narrative, telling the key stories behind the Vision Atlas, providing a rich mix of information and new evidence.

Can we compare VLEG data from 2020 with the VLEG data published in 2017?

The new VLEG estimates for 2020 includes revised estimates for the 1990-2010 period from a new model based on an expanded data set. This mean that the 2020 estimates supersede the 2017 estimates. We strongly recommend everyone to use the new data which gives a consistent estimate of the past, present and future numbers.

How does the new data compare with the data in the World Report on Vision?

The estimated number of people with vision impairment in the World Report on Vision was based on data from various sources, including:

  • Distance: VLEG estimates from 2017 on global magnitude and causes of bilateral distance vision impairment and blindness
  • Near: Global Prevalence of Presbyopia and Vision Impairment from Uncorrected Presbyopia (Fricke et al., 2018)

Estimates of distance and near vision loss in the 2020 Vision Atlas are both based on the 2020 VLEG estimates.

What is the difference between crude and age-standardised prevalence?

Please see more information about using data to make comparisons at this page.

How much vision loss is treatable or preventable?

Historically, it was widely reported that >75% of visual impairment was avoidable. This definition was based on cataract, uncorrected refractive errors and trachoma, for distance vision loss only.

The IAPB Vision Atlas and the Lancet Global Health Commission on Global Eye Health now report that 90% of vision loss can be prevented or treated, as near vision impairment is now considered in the calculation. At this page, we explain how this number was calculated, and the relationship to previous estimates.

Where can I access the source data?

The VLEG data is published in The Lancet. Please find the full text at the following links:

The IAPB Vision Atlas also hosts detailed current prevalence data from VLEG, from 2020 to 1990.

The Lancet Global Health Commission on Global Eye Health: vision beyond 2020 is also published in The Lancet. Access the full text at this link.

Can I reuse the charts from the Vision Atlas?

You are free to reuse the charts from the Vision Atlas as long as you reference the source (IAPB Vision Atlas and VLEG, for example). You can find more information on how to reference the VLEG studies here.