Vision 2020 - World Health Organization

1. AVOIDABLE VISUAL
IMPAIRMENT –
A HUMAN, SOCIAL AND
DEVELOPMENTAL ISSUE
In the 10th revision of the WHO International Statistical Classifi cation of Diseases, Injuries and Causes
of Death, ‘low vision’ is defi ned as visual acuity of less than 6/18 but equal to or better than 3/60, or
a corresponding visual fi eld loss to less than 20°, in the better eye with the best possible correction.
‘Blindness’ is defi ned as visual acuity of less than 3/60, or a corresponding visual fi eld loss to less
than 10°, in the better eye with the best possible correction. ‘Visual impairment’ includes both low
vision and blindness (4).
1.1 CHANGING PATTERNS
Levels and causes of visual impairment at the time of the launch of VISION 2020
The fi rst global estimate of the extent of visual impairment, in 1975, indicated that there were 28 million
blind people. In the 1990s, it was estimated that the global population was likely to increase from 5.8
billion in 1996 to 7.9 billion by 2020, and most of the increase was expected to occur in the developing
world. These population growth projections were used in turn to estimate the expected increase in the
number of blind people. Estimates based on the 1990 world population indicated that there were 38
million blind people and almost 110 million with low vision (5). This estimate was later extrapolated,
fi rst to the 1996 world population (45 million blind and 135 million people with low vision) and then to
the projected 2020 population (76 million blind). These estimates indicated that the global extent of
visual impairment would double in the period 1990–2020, and this realization provided the impetus
for the launch of VISION 2020 in 1999.
The estimated prevalence of blindness in 1990 ranged from 0.08% of children to 4.4% of persons
aged over 60 years, with an overall global prevalence of 0.7%. It was also estimated that at least 7
million people become blind each year and that the number of blind people worldwide was increasing
by 1–2 million per year.
Of the estimated 45 million cases of blindness by 1996, approximately 60% were due to either cataract
(16 million people) or refractive errors. A further 15% were due to trachoma, vitamin A defi ciency or
onchocerciasis, with another 15% due to diabetic retinopathy or glaucoma. The remaining 10% of cases
were attributable to age-related macular degeneration and other diseases. In view of the proportion of
treatable eye diseases or treatable causes of blindness, such as cataract, trachoma, onchocerciasis
and some eye conditions in children, it was estimated that 75% of all blindness in the world could
have been avoided.
1