The causes of distance vision loss

GBM roundelThe VLEG was able to make reliable estimates on the proportion of blindness and distance Moderate and Severe Visual Impairment (MSVI), attributable to seven eye conditions for the year 2015. The term ‘distance visual impairment’ is used to mean blindness and MSVI combined.

Global cause estimates

Figures 1, 2 and 3 show the contribution made by these eye conditions to the global burden of distance visual impairment, blindness and MSVI respectively.

As in earlier estimates, Cataract continues to be the leading cause of blindness, and Uncorrected Refractive Error the leading cause of MSVI.

These two conditions account for almost three quarters (74.4%) of all cases of distance visual impairment.

A limitation of the cause estimates is the relatively high percentage of ’other‘ causes (25.5% for blindness; and 13.2% for MSVI with an overall figure of 14.9% for visual impairment). This is because a substantial number of the population studies only report on the more prevalent causes and do not identify or disaggregate the less-common causes such as macular degenerative conditions, retinopathies, optic neuropathies, and amblyopia, which become subsumed within an ‘other/non-specific’ category in the study’s report or publication.

Protocols often dictate that population-based studies report one cause as the principal cause for an individual examined in that particular study, in order to arrive at the causal prevalence. When there are co-existing disorders contributing equally to blindness or visual impairment, only the ‘most readily curable’ or the ‘most easily preventable’ is recorded. This approach has the potential to underestimate the impact of Diabetic Retinopathy, Glaucoma, or other diseases when the survey participant presented with Cataract, while underestimating the burden of Cataract when participants also have an Uncorrected Refractive Error.

The global number of blind, MSVI and visually impaired persons attributable to each cause is shown in Table 1.

Table 1 – Number of people globally with distance visual impairment by cause
 Number in Millions
All Causes36217253
CauseBlindMSVIVisual Impairment (Blind + MSVI)
Age-Related Macular Degeneration (AMD)1.968.4110.37
Cataract12.6052.6065.20
Corneal Opacity1.282.894.17
Diabetic Retinopathy (DR)0.362.572.93
Glaucoma2.964.057.01
Uncorrected Refractive Error (URE)7.42116.34123.76
Trachoma0.401.602.00
Other9.0428.1337.17

Cataract continues to be the leading cause of blindness, and Uncorrected Refractive Error the leading cause of MSVI. These two conditions account for almost three quarters (74.4%) of all cases of distance visual impairment.

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Figure 1 – Causes of global visual impairment (all ages – blindness & MSVI)

  • AMD 4.23%

  • Cataract 25.54%

  • Corneal Opacity 1.6%

  • Diabetic Retinopathy 1.22%

  • Glaucoma 2.82%

  • URE 49.00%

  • Trachoma 0.68%

  • Other 14.91%


Figure 2 – Causes of global blindness (all ages)

  • AMD 5.64%

  • Cataract 34.47%

  • Corneal Opacity 3.46%

  • Diabetic Retinopathy 1.07%

  • Glaucoma 8.30%

  • URE 20.62%

  • Trachoma 0.98%

  • Other 25.46%


Figure 3 – Causes of global MSVI (all ages)

  • AMD 4.00%

  • Cataract 24.04%

  • Corneal Opacity 1.29%

  • Diabetic Retinopathy 1.25%

  • Glaucoma 1.91%

  • URE 53.72%

  • Trachoma 0.63%

  • Other 13.16%

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