Content uploaded by Serge Resnikoff
Author content
All content in this area was uploaded by Serge Resnikoff on Mar 13, 2017
Content may be subject to copyright.
Content uploaded by Serge Resnikoff
Author content
All content in this area was uploaded by Serge Resnikoff on Jan 12, 2015
Content may be subject to copyright.
Content uploaded by Serge Resnikoff
Author content
All content in this area was uploaded by Serge Resnikoff on Feb 05, 2014
Content may be subject to copyright.
844 Bulletin of the World Health Organization | November 2004, 82 (11)
Paper from: Programme for the Prevention of Blindness and Deafness, World Health Organization, 20 Avenue Appia, 1211 Geneva 27, Switzerland.
1 Coordinator. Correspondence should be sent to this author (email: resnikoffs@who.int).
2 Technical Officer.
3 Medical Officer.
4 Consultant.
Ref. No. 04-012831
(
Submitted: 2 March 2004 – Final revised version received: 15 June 2004 – Accepted: 25 June 2004
)
Global data on visual impairment in the year 2002
Serge Resnikoff,1 Donatella Pascolini,2 Daniel Etya’ale,3 Ivo Kocur,3 Ramachandra Pararajasegaram,4
Gopal P. Pokharel,3 & Silvio P. Mariotti3
Policy and Practice
Abstract This paper presents estimates of the prevalence of visual impairment and its causes in 2002, based on the best available
evidence derived from recent studies. Estimates were determined from data on low vision and blindness as defined in the
International
statistical classification of diseases, injuries and causes of death
, 10th revision. The number of people with visual impairment worldwide
in 2002 was in excess of 161 million, of whom about 37 million were blind.
The burden of visual impairment is not distributed uniformly throughout the world: the least developed regions carry the
largest share. Visual impairment is also unequally distributed across age groups, being largely confined to adults 50 years of age
and older. A distribution imbalance is also found with regard to gender throughout the world: females have a significantly higher
risk of having visual impairment than males.
Notwithstanding the progress in surgical intervention that has been made in many countries over the last few decades, cataract
remains the leading cause of visual impairment in all regions of the world, except in the most developed countries. Other major causes
of visual impairment are, in order of importance, glaucoma, age-related macular degeneration, diabetic retinopathy and trachoma.
Keywords Vision, Low/epidemiology; Blindness/epidemiology; Vision, Low/etiology; Blindness/etiology; Cataract/complications;
Glaucoma/complications; Macular degeneration/complications; Refractive errors/complications; Cost of illness; Age factors; Sex factors
(
source: MeSH, NLM
).
Mots clés Baisse vision/épidémiologie; Cécité/épidémiologie; Baisse vision/étiologie; Cécité/étiologie; Cataracte/complication;
Glaucome/complication; Dégénérescence maculaire/complication; Troubles réfraction oculaire/complication; Coût maladie; Facteur
âge; Facteur sexuel (
source: MeSH, INSERM
).
Palabras clave Visión subnormal/epidemiología; Ceguera/epidemiología; Visión subnormal/etiología; Ceguera/etiología; Catarata/
complicaciones; Glaucoma/complicaciones; Degeneración macular/complicaciones; Errores de refracción/complicaciones; Costo de la
enfermedad; Factores de edad; Factores sexuales (
fuente: DeCS, BIREME
).
Bulletin of the World Health Organization 2004;82:844-851.
Voir page 850 le résumé en français. En la página 850 figura un resumen en español.
Introduction
The first estimate of the global data on blindness was published
in 1995 (1), based on the world population data for 1990. This
estimate was extrapolated to the 1996 world population, and
to the world population and demographic shifts projected for
2020. These data provided the basis for the 1999 launch of the
Global Initiative for the Elimination of Avoidable Blindness,
which is known as “VISION 2020: the Right to Sight” (2).
Since the publication of the Global Data on Blindness
in 1995, population-based studies on the prevalence of blind-
ness and visual impairment have been carried out in nearly all
WHO regions. Most of these surveys have used the WHO
simplified population-based assessment methodology for
visual impairment and causes (3), with some adaptation in a
few instances.
In several countries rapid assessment of cataract surgical
services (RACSS) (4) has been conducted (see for example 5–8).
The results of these studies also provide general information on
the status of visual impairment in adults 50 years of age and
older. In addition to the RACSS surveys, many recent studies
have specifically targeted older adults.
The availability of new data has allowed the update of
the global and regional estimates of visual impairment and its
causes.
845
Bulletin of the World Health Organization | November 2004, 82 (11)
Policy and Practice
Serge Resnikoff et al. Visual impairment in 2002
Methods
Definitions
The definitions for visual impairment, low vision and blindness
used in the present study follow those given in the International
statistical classification of diseases, injuries and causes of death, 10th
revision (ICD-10): H54 (9) where:
• visual impairment includes low vision as well as blindness;
• low vision is defined as visual acuity of less than 6/18, but
equal to or better than 3/60, or a corresponding visual field
loss to less than 20 degrees in the better eye with best possible
correction (ICD-10 visual impairment categories 1 and 2);
• blindness is defined as visual acuity of less than 3/60, or
a corresponding visual field loss to less than 10 degrees in
the better eye with best possible correction (ICD-10 visual
impairment categories 3, 4 and 5).
Regions, subregions and population estimates
The classification of WHO Member States into 17 subregions
was carried out according to the Global Burden of Disease 2000
Project (10); for details see Murray et al. 2001 (11).
Estimates of population size and structure were based
on the 2002 demographic assessment of the United Nations
Population Division (12), as used by theWorld health report
2003 (13).
Sources of epidemiological data
Recent survey results from 55 countries were selected (Table 1);
in some countries there had been several surveys. The selection
criteria were as follows: studies were population-based and rep-
resentative of the area sampled. They provided:
• clear, unequivocal definitions of visual impairment; both
WHO and non-WHO definitions of visual impairment
were acceptable if classifiable within the ICD-10 ranges of
visual loss;
• cross-sectional design with a description of sample design
and sampling plan; sample size; response rate; assessment of
non-sampling errors; and
• a description of ophthalmic examinations and visual acuity
testing.
The 2002 Global update of available data on visual impair-
ment (14) was an important source of data. Results from as yet
unpublished surveys that met the relevant criteria were also
selected. In the case of countries for which data were scarce,
national sources were investigated. These included: ministries of
health, national prevention of blindness programmes, academic
institutions, regional WHO offices and consultants. The data
on childhood blindness were obtained from the report of a 1999
WHO scientific meeting (15), as well as from a comprehensive
review of available data (16).
Estimates of prevalence
Prevalence of blindness (ICD-10 visual impairment
categories 3, 4 and 5)
Prevalences for blindness (Table 2) were obtained for the 17
WHO epidemiological subregions using a model based on the
data from the 55 countries listed in Table 1 and from other sourc-
es, as described below. The model estimated the prevalence of
blindness for three age groups: children less than 15 years; adults
from 15 to 49 years; and adults aged 50 years and older.
The prevalences of blindness in children were estimated
for the 17 WHO subregions. This was done using the data from
Table 1. Studies used for the global estimate of visual
impairment
Subregion Studies
Afr-D Surveys from 13 countries (Benin, Cameroon,
Cape Verde, Equatorial Guinea, Gambia, Ghana,
Mali, Mauritania, Niger, Nigeria, Sierra Leone,
Sudan, Togo)
Afr-E Surveys from 6 countries (Central African
Republic, Congo, Ethiopia, Kenya, South Africa,
United Republic of Tanzania)
Amr-A Surveys from 1 country (United States of America)
Amr-B Surveys from 3 countries (Barbados, Brazil,
Paraguay)
Amr-D Survey from 1 country (Peru)
Emr-B Surveys from 4 countries (Lebanon, Oman,
Saudi Arabia, Tunisia)
Emr-D Survey from 1 country (Morocco)
Eur-A Surveys from 7 countries (Denmark, Finland,
Iceland, Ireland, Italy, Netherlands, United
Kingdom)
Eur-B1 Surveys from 2 countries (Bulgaria, Turkey)
Eur-B2 Survey from 1 country (Turkmenistan)
Eur-C No population-based surveys were identified
Sear-B Surveys from 4 countries (Indonesia, Malaysia,
Philippines, Thailand)
Sear-D Surveys from 4 countries (Bangladesh, India,
Nepal, Pakistan)
Wpr-A Surveys from 1 country (Australia)
Wpr-B1 Surveys from 2 countries (China and Mongolia)
Wpr-B2 Surveys from 3 countries (Cambodia, Myanmar,
Viet Nam)
Wpr-B3 Surveys from 2 countries (Tonga and Vanuatu)
Afr, WHO African Region; Amr, WHO Region of the Americas;
Emr, WHO Eastern Mediterranean Region; Eur, WHO European Region;
Sear, WHO South-East Asia Region; Wpr, WHO Western Pacific Region.
the two reports that had used criteria for grouping of countries
similar to those used in the WHO classification of subregions.
In adults aged from 15 to 49 years the prevalences of
blindness were estimated for each subregion according to the
mortality stratum:
• for subregions with mortality stratum A — 0.1%;
• for subregions with mortality stratum B or C — 0.15%; and
• for subregions with mortality stratum D or E — 0.2%.
(See 13 for the current assignment of mortality stratum to the
WHO subregions.)
These estimates were based on data from the studies
selected and on interpolations previously derived from the data
on childhood blindness and data for subjects aged 50 years and
older (15).
The prevalences for the age group 50 years and older were
taken from population-based surveys. Prevalences calculated for
the age group as a whole, adjusted for sex and age composition
of the sample and/or of the survey area, were used. For areas for
which no data were available, prevalence was extrapolated from
areas similar in terms of availability of eye and health care and
846 Bulletin of the World Health Organization | November 2004, 82 (11)
Policy and Practice
Visual impairment in 2002 Serge Resnikoff et al.
epidemiology of eye diseases and services for which data were
available. Population size in different areas was estimated from
national census data; population structure was determined from
the United Nations estimate for that country.
In other instances, the data from one area were estimated
to be representative of the country as a whole and applied to
all the population. Finally, some surveys provided nationwide
results.
For countries for which recent epidemiological data were
not available, the prevalence of blindness was extrapolated from
data collected in countries within the same subregion or from
neighbouring subregions that share similar epidemiological,
socioeconomic, ecological and eye care service characteristics.
Age-group-specific prevalence was used to estimate the
total number of blind people in each country of a subregion.
This number was then used to calculate the subregional preva-
lence of blindness. This method could not be applied to the
subregion Eur-C, as no suitable population-based surveys
were available for any of the countries of this subregion: in
this case the prevalences were assumed to be the same as for
the subregion EurB1.
Prevalence of low vision (ICD-10 visual impairment
categories 1 and 2)
The prevalences of low vision for each subregion was estimated
from the same surveys as were used to determine the prevalence
of blindness. Owing to the paucity of data on age-specific preva-
lence of low vision it was not possible to construct a model
similar to that described above for blindness. Specific preva-
lences for both blindness and low vision were reported in 43
studies from 15 subregions; additional studies that reported data
on low vision in children were also taken into account (17–20).
The extrapolations between countries made for blindness were
Table 2. Age-specific prevalence of blindness and number of blind people, by age and WHO subregion, 2002a
Prevalence of blindness (%) No. of blind persons (millions)
<15 years of age 15–49 years 50 years <15 years of age 15–49 years 50 years
Afr-D 0.124 0.2 9 0.191 0.332 3.124
Afr-E 0.124 0.2 9 0.196 0.336 3.110
Amr-A 0.03 0.1 0.4 0.021 0.114 0.560
Amr-B 0.062 0.15 1.3 0.085 0.369 0.937
Amr-D 0.062 0.2 2.6 0.017 0.075 0.241
Emr-B 0.08 0.15 5.6 0.039 0.117 0.920
Emr-D 0.08 0.2 7 0.043 0.146 1.217
Eur-A 0.03 0.1 0.5 0.021 0.204 0.713
Eur-B1 0.051 0.15 1.2 0.020 0.136 0.462
Eur-B2 0.051 0.15 1.3 0.009 0.043 0.090
Eur-C 0.051 0.15 1.2 0.021 0.192 0.822
Sear-B 0.083 0.15 6.3 0.102 0.332 3.779
Sear-D 0.08 0.2 3.4 0.390 1.423 6.530
Wpr-A 0.03 0.1 0.6 0.007 0.070 0.315
Wpr-B1 0.05 0.15 2.3 0.162 1.166 6.404
Wpr-B2 0.083 0.15 5.6 0.041 0.120 1.069
Wpr-B3 0.083 0.15 2.2 0.002 0.006 0.017
World 1.368 5.181 30.308
Afr, WHO African Region; Amr, WHO Region of the Americas; Emr, WHO Eastern Mediterranean Region; Eur, WHO European Region; Sear, WHO South-East Asia
Region; Wpr, WHO Western Pacific Region.
a Blindness defined as in the ICD-10:H54 tables refers to visual acuity in the better eye with best possible correction (see ref.
9
).
WHO
subregion
assumed also to be valid for low vision. All-ages prevalences of
low vision were calculated as described for blindness. The ratio
of low vision to blindness was calculated. The mean value of
the ratios from 15 subregions was applied to the subregions
Eur-C and Wpr-B1 because ratios for these regions could not
be calculated due to lack of data.
Causes of visual impairment
The causes of visual impairment were ascertained from the
cause attributions reported in the surveys listed in Table 1. Data
were available to determine causes of blindness in all subregions
except Eur-C. Due to scarcity of data, the causes of low vision
could not be quantified with confidence either at regional or
global level.
Results
Prevalence and causes of visual impairment by
subregion
According to the model presented, based on the most recent
available data, and using the ICD-10 definition of best-cor-
rected visual acuity and the 2002 world population, the
estimated number of people with visual impairment was in
excess of 161 million: 37 million were blind and 124 million
had low vision (Table 3). The ratios of people with low vision
to those with blindness, by subregion, ranged from 2.4 to 5.8
with a median value of 3.7. The leading cause of blindness
was cataract, followed by glaucoma and age-related macular
degeneration (Table 4).
Distribution of visual impairment by age and gender
Although childhood blindness remains a significant problem
(there are an estimated 1.4 million blind children below the age
847
Bulletin of the World Health Organization | November 2004, 82 (11)
Policy and Practice
Serge Resnikoff et al. Visual impairment in 2002
Table 3. Global estimate of visual impairment by WHO subregion, 2002a
WHO Total No. of Prevalence No. of people Prevalence No. of persons
subregion population blind people of blindness with low vision of low vision visually impaired
(millions) (millions) (%) (millions) (%) (millions)
Afr-D 354.324 3.646 1.0 10.715 3.0 14.361
Afr-E 360.965 3.642 1.0 10.573 3.0 14.215
Amr-A 322.309 0.694 0.2 4.029 1.2 4.723
Amr-B 456.432 1.392 0.3 7.600 1.7 8.992
Amr-D 73.810 0.332 0.5 1.488 2.0 1.820
Emr-B 142.528 1.076 0.8 3.580 2.5 4.656
Emr-D 144.405 1.406 0.97 4.116 2.9 5.522
Eur-A 415.323 0.937 0.2 5.435 1.3 6.372
Eur-B1 169.716 0.618 0.4 2.546 1.5 3.164
Eur-B2 53.130 0.142 0.3 0.590 1.1 0.731
Eur-C 239.717 1.035 0.4 4.219 1.8 5.254
Sear-B 405.313 4.214 1.0 9.669 2.4 13.883
Sear-D 1394.045 8.344 0.6 28.439 2.0 36.782
Wpr-A 150.867 0.393 0.3 1.883 1.2 2.276
Wpr-B1 1374.838 7.731 0.6 26.397 1.9 34.128
Wpr-B2 148.469 1.229 0.8 2.898 1.9 4.127
Wpr-B3 7.677 0.025 0.3 0.090 1.2 0.115
World 6213.869 36.857 0.57 124.264 2 161.121
Afr, WHO African Region; Amr, WHO Region of the Americas; Emr, WHO Eastern Mediterranean Region; Eur, WHO European Region; Sear, WHO South-East Asia
Region; Wpr, WHO Western Pacific Region.
a Visual impairment defined as in the ICD-10:H54 tables refers to visual acuity in the better eye with best possible correction (see ref.
9
).
of 15 years), its magnitude is relatively small when compared
to the extent of blindness in older adults: more than 82% of
all blind people are 50 years and older (Table 2).
The number of women with visual impairment, as esti-
mated from the available studies, is higher than that in men even
after adjustment for age. Female/male prevalence ratios indicate
that women are more likely to have a visual impairment than
men in every region of the world: the ratios range from 1.5 to
2.2 (data not shown).
Discussion
Limitations
The model of visual impairment presented is based partly on
population-based surveys and partly on assumptions: both
sources place limitations on the accuracy of the estimates. Poten-
tial sources of error arise due to one or more of the following:
• heterogeneity of the survey methods with regard to data
collection and ophthalmic examinations, despite the use of
the standardized WHO protocol (3);
• extrapolations of data from different areas of a country to
provide national estimates;
• different estimates of population structure used in the sur-
veys;
• correction factors used to determine the prevalences of
best-corrected visual acuity in studies that used non-WHO
definitions;
• extrapolation to present populations of prevalences deter-
mined in studies conducted over the last 5–10 years;
• assumptions made in obtaining estimates of blindness for
the age group 15–49 years;
• extrapolation of data for countries and regions for which no
data are available;
• extrapolations of survey results from a specific area of a highly
populated and diverse country to the country as a whole;
• reporting bias in the determination of causes of visual im-
pairment in surveys designed for specific pathologies; and
• possibly non-standardized definitions of eye diseases, criteria
for diagnosis, examination methods and comorbidity.
To minimize the bias introduced by the limitations listed above,
the studies were selected according to the criteria described in
Methods. The extrapolations between countries were made
according to information gathered internally by prevention
of blindness programmes in the course of their activities
throughout the world. Country estimates were compared with
the information from national sources to check for significant
inconsistencies.
For the age group 15–49 years it was assumed that preva-
lences were similar in subregions with the same mortality stra-
tum. These prevalences were consistent with data from surveys.
Though small variations might exist between subregions they
would not significantly affect the determination of the global
extent of blindness, because the contribution from this age
group to the total is less than 15%.
With regard to correction factors to determine preva-
lences according to ICD-10 from different definitions of visual
impairment, there were a sufficient number of studies reporting
data with both definitions to enable a table of conversion to
be calculated.
Most of the available data on low vision were for the age
group 50 years and older. If the ratio of low vision to blindness
for this age group were applied to the population aged between
15 and 49 years, this would greatly underestimate the magni-
tude of the problem of low vision, because the ratio is higher in
age groups with a low prevalence of blindness. The data on low
848 Bulletin of the World Health Organization | November 2004, 82 (11)
Policy and Practice
Visual impairment in 2002 Serge Resnikoff et al.
Table 4. Causes of blindness as a percentage of total blindness – by WHO subregion, 2002
Region Cataract Glaucoma AMDa Corneal Diabetic Childhood Trachoma Oncho- Others
opacities retinopathy blindness cerciasis
Afr-D 50 15 8 5.2 6.2 6 9.6
Afr-E 55 15 12 5.5 7.4 2 3.2
Amr-A 5 18 50 3 17 3.1 3.9
Amr-B 40 15 5 5 7 6.4 0.8 20.8
Amr-D 58.5 8 4 3 7 5.3 0.5 13.7
Emr-B 49 10 3 5.5 3 4.1 3.2 22.2
Emr-D 49 11 2 5 3 3.2 5.5 21.3
Eur-A 5 18 50 3 17 2.4 4.6
Eur-B1 28.5 15 15 8 15 3.5 15.0
Eur-B2 35.5 16 15 5 15 6.9 6.6
Eur-C 24 20 15 5 15 2.4 18.6
Sear-B 58 14 3 5 3 2.6 14.4
Sear-D 51 9 5 3 3 4.8 1.7 22.5
Wpr-A 5 18 50 3 17 1.9 0.025 5.0
Wpr-B1 48.5 11 15 3 7 2.3 6.4 6.8
Wpr-B2 65 6 5 7 3 3.6 3.5 6.9
Wpr-B3 65 6 3 3 5 9.5 4.3 4.2
World 47.8 12.3 8.7 5.1 4.8 3.9 3.6 0.8 13.0
Afr, WHO African Region; Amr, WHO Region of the Americas; Emr, WHO Eastern Mediterranean Region; Eur, WHO European Region; Sear, WHO South-East Asia
Region; Wpr, WHO Western Pacific Region.
a AMD, age-related macular degeneration.
vision in children have been used when available. The extent
of low vision worldwide is probably underestimated.
No attempt was made in this study to perform uncer-
tainty analysis.
Estimate of the global burden of visual impairment
The model presenting data by WHO region and mortality
stratum, based mostly on recent surveys, is the best available
estimate of visual impairment in 2002 (Table 5 (web version
only, available at http://www.who.int/bulletin) and Table 6).
The estimates had the added strength of being based on recent
data available from countries with large populations.
Because of the structure of the model, the percentage of
the population in each of the three age groups weighs strongly on
the prevalence calculated for all ages. In 2002, the population 50
years and older, with the highest prevalence of visual impairment,
represented more than 30% of the population in developed
countries and 15% of that in developing countries (12).
If the prevalence of blindness is taken as an indicator, all
subregions with prevalences above 0.5% for all ages should be
considered for priority action according to WHO objectives
(21). The eight subregions concerned (Afr-D, Afr-E, Emr-B,
Emr-D, Sear-B, Sear-D, Wpr-B1 and Wpr-B2) are home to
70% of the world’s population and contribute 85% of the total
number of blind people.
The extent of visual impairment in 2002 is not strictly
comparable with the estimates from 1994 or with subsequent
extrapolations, as the models were derived using different meth-
odologies (1). While in 1990 there were an estimated 148 mil-
lion people who were visually impaired, of whom 38 million
were blind, in 2002 the estimated number of visually impaired
people was 161 million, of whom 37 million were blind.
In the developed countries the number of blind people
was estimated to be 3.5 million in 1990 and 3.8 million in
2002, an increase of 8.5 %. During the same period the size
of the population aged 50 years and older in these countries
had increased by 16%. The change in the number of people
with low vision is more significant: there were an estimated
18 million people with low vision in 2002, compared to 10
million in 1990. This figure represents an increase in unavoid-
able causes of visual impairment linked to an increase in the
size of the population over 60 years of age. One report has
also suggested that older members of the population do not
seek eye care (22).
In developing countries, excluding China and India, 18.8
million people were blind in 1990 compared to 19.4 million
in 2002, an increase of 3%. In China and India the estimated
numbers of blind people in 1990 were 6.7 and 8.9 million,
respectively; in 2002 there were an estimated 6.9 million blind
people in China and 6.7 million in India. These figures indicate
an increase of 3% in the number of blind people in China and
a decrease of 25% in India.
The world population in 2002 had increased by 18.5%
compared to that in 1990; the population 50 years of age and
older had increased by 30%. In developed countries the increase
in the population aged 50 years and older was 16%; in devel-
oping countries, excluding China, it was 47%, and in China,
the increase was 27%. Taking into account these changes, the
extent of visual impairment in 2002 appears to be lower than
in past estimates and projected extrapolations. The difference
could be due to either an overestimate in previous projections
or to underestimates in the present model; however, it is likely
that this change reflects the more accurate data now available.
Differences could also be the direct consequence of concerted
national efforts such as that made in India (23) and of the
improvements in factors such as political and professional com-
mitments to the prevention of blindness, the delivery of ser-
vices, patient awareness, and socioeconomic development.
849
Bulletin of the World Health Organization | November 2004, 82 (11)
Policy and Practice
Serge Resnikoff et al. Visual impairment in 2002
Table 6. Global estimate of visual impairment, by WHO region (millions), 2002
Afr Amr Emr Eur Sear Wpr
Population 672.238 852.551 502.823 877.886 1590.832 1717.536
No. of blind People 6.782 2.419 4.026 2.732 11.587 9.312
No. with low vision 19.996 13.116 12.444 12.789 33.496 32.481
No. with visual impairment 26.778 15.535 16.469 15.521 45.083 41.793
Afr, WHO African Region; Amr, WHO Region of the Americas; Emr, WHO Eastern Mediterranean Region; Eur, WHO European Region; Sear, WHO South-East Asia
Region; Wpr, WHO Western Pacific Region.
Because the above estimates exclude refractive error as a
cause of visual impairment, by virtue of the definition used,
they significantly underestimate the actual burden of uncor-
rected disabling refractive error. The prevalence of blindness
when defined as “presenting vision” is higher than when defined
as “best corrected vision” by about 15%, for all ages. However,
for older adults this difference could be as high as 25–30%,
as indicated by the results of many studies (4–8, 24, 25). The
increase in prevalence of low vision in older adults could be up
to 60% (26, 27). Given the significance of the unmet need for
correction of visual impairment due to refractive errors, changes
in the definitions of visual impairment are being proposed for
the next ICD revision.
Causes of visual impairment
The largest proportion of blindness is necessarily related to
ageing. Although cataract is not a major cause of blindness in
developed countries, globally it is still the leading cause, ac-
counting for almost half of all cases, despite improved delivery
of cataract surgical services in many parts of the world (Fig. 1).
Cataract is even more significant as a cause of low vision; it is
the leading cause of low vision in all subregions.
According to the surveys, glaucoma is the second leading
cause of blindness globally as well as in most regions; age-related
macular degeneration is the third leading cause. Trachoma, other
corneal opacities, childhood blindness and diabetic retinopathy
are all of approximately equal magnitude (i.e. all roughly 4–5%).
It is noteworthy that trachoma has decreased in significance as
a cause of blindness as compared to earlier estimates.
As would be expected given the growing number of
people over 70 years of age, age-related macular degeneration
is increasing in significance as a cause of blindness; it is the
primary cause of blindness in the developed countries and the
third leading cause worldwide. Corneal blindness may be pri-
marily attributed to trachoma in areas in which this condition
is known to be endemic. In other areas it is caused primarily
by trauma and vitamin A deficiency (16).
Conclusions
Periodic estimations of the magnitude and causes of all catego-
ries of visual impairment are essential to improve global efforts
aimed at monitoring and eliminating avoidable blindness and
for use in priority-setting and resource allocation. Disaggre-
gated, within-country data are important in ensuring greater
equity in service provision and monitoring.
To this end, countries are encouraged to carry out peri-
odic population-based surveys, particularly densely populated
countries and countries in regions where data are scarce. They
are advised to use the standardized WHO protocol (3) with the
following refinements:
• adding the measure of presenting vision, to include visually
disabling refractive errors;
• in those studies that use definitions other than those given in
the WHO ICD-10, visual acuity consistent with the WHO
definitions should also be recorded; and
• diagnosis and recording of the causes of low vision in ad-
dition to those of blindness. Particular attention should be
paid to glaucoma and macular degeneration. O
Conflicts of interest: none declared.
aAMD = Age-related macular degeneration.
Fig. 1. Global causes of blindness as a percentage of total
blindness in 2002
WHO 04.138
13
47.8
12.3
8.7
5.1
4.8
3.9
3.6
0.8
Others
Cataract
Glaucoma
AMDa
Corneal opacities
Diabetic retinopathy
Chilhood blindness
Trachoma
Onchocerciasis
850 Bulletin of the World Health Organization | November 2004, 82 (11)
Policy and Practice
Visual impairment in 2002 Serge Resnikoff et al.
Résumé
Données mondiales sur les déficiences visuelles pour l’année 2002
Le présent article estime la prévalence des déficiences visuelles et
de leurs causes en 2002 à partir des meilleures données disponibles
tirées d’études récentes. Les estimations ont été établies d’après
les données de malvoyance et de cécité, telles que définies dans la
Classification statistique internationale des maladies, traumatismes
et causes de décès de l’OMS
, 10e révision. Le nombre de personnes
dans le monde atteintes d’une déficience visuelle dépassait en
2002 les 161 millions, dont environ 37 millions d’aveugles.
La charge des déficiences visuelles n’est pas répartie
uniformément à travers le monde : ce sont les régions les moins
développées qui en supportent la plus forte part. Les déficiences
visuelles se répartissent aussi inégalement selon les tranches d’âge,
les adultes de 50 ans et plus étant de loin les plus touchés. On
relève également un déséquilibre entre les sexes dans le monde
entier : les femmes présentent un risque significativement plus
important de souffrir de déficience visuelle que les hommes.
Nonobstant les progrès réalisés par la chirurgie dans de
nombreux pays au cours des dernières décennies, la cataracte
demeure la cause principale de déficience visuelle dans toutes
les régions du monde, à l’exception des pays les plus développés.
Les autres causes majeures de déficience visuelle sont, par ordre
d’importance, le glaucome, la dégénérescence maculaire liée à
l’âge, la rétinopathie diabétique et le trachome.
Resumen
Datos mundiales sobre la deficiencia visual en el año 2002
En este artículo se estima la prevalencia de la deficiencia visual
y sus causas en 2002 a partir de la mejor evidencia disponible
aportada por los estudios más recientes. Las estimaciones se han
basado en datos referentes a la disminución de la agudeza visual
y la ceguera, según se definen en la Clasificación Estadística
Internacional de Enfermedades, Traumatismos y Causas de
Defunción, 10ª revisión. En 2002 el número de personas con
deficiencia visual en todo el mundo superó los 161 millones, y de
ellos 37 millones sufrían ceguera.
La carga de deficiencia visual no se distribuye uniformemente
en todo el mundo, pues las regiones menos desarrolladas son las
más afectadas. La deficiencia visual se distribuye también de forma
dispar entre los grupos de edad, pues la padecen sobre todo
adultos de más de 50 años. Se observa también un desequilibrio
en lo tocante al género en todo el mundo: el riesgo de deficiencia
visual es significativamente mayor en las mujeres que en los
hombres. A pesar de los progresos de la cirugía logrados en muchos
países durante los últimos decenios, la catarata sigue siendo la
principal causa de deficiencia visual en todas las regiones del
mundo, exceptuando los países más desarrollados. Otras causas
importantes de deficiencia visual son, en orden de importancia,
el glaucoma, la degeneración macular relacionada con la edad,
la retinopatía diabética y el tracoma.
References
1. Thylefors B, Négrel A-D, Pararajasegaram R, Dadzie KY. Global data on
blindness.
Bulletin of the World Health Organization
. 1995;73(1):115-21.
2. World Health Organization.
Prevention of blindness and deafness. Global
initiative for the elimination of avoidable blindness
. Geneva: WHO; 2000.
WHO document WHO/PBL/97.61 Rev2.
3. World Health Organization.
Coding instructions for the WHO/PBL eye
examination record (version III)
. Geneva: WHO; 1988. WHO document
PBL/88.1.
4. Limburg H, Kumar R, Indrayan A, Sundaram KR. Rapid assessment of
prevalence of cataract blindness at district level.
International Journal of
Epidemiology
1997; 26:1049-54.
5. Limburg H, Kumar R. Follow-up study of blindness attributed to cataract in
Karnataka State, India.
Ophthalmic Epidemiology
1998;5:211-23.
6. Limburg H, Vasavada AR, Muzumdar G, Khan MY, Vaidyanathan K, Trivedi R,
et al. Rapid assessment of cataract blindness in an urban district in Gujarat.
Indian Journal of Ophthalmology
1999;47:135-41.
7. Amansakhatov S, Volokhovskaya ZP, Afanasyeva AN, Limburg H. Cataract
blindness in Turkmenistan: results of a national survey.
British Journal of
Ophthalmology
2002;86:1207-10.
8. Duerksen R, Limburg H, Carron JE, Foster A. Cataract blindness in Paraguay
– results of a national survey.
Ophthalmic Epidemiology
2003;10:349-57.
851
Bulletin of the World Health Organization | November 2004, 82 (11)
Policy and Practice
Serge Resnikoff et al. Visual impairment in 2002
9. World Health Organization.
International statistical classification of
diseases, injuries and causes of death, tenth revision
. Geneva: WHO; 1993.
10. Murray CJL, Lopez AD, editors.
The global burden of disease: a
comprehensive assessment of mortality and disability from diseases, injuries
and risk factors in 1990 and projected to 2020
. Cambridge, MA: Harvard
School of Public Health on behalf of the World Health Organization and the
World Bank; 1996 (Global Burden of Disease and Injury Series, Vol. 1).
Available from URL: http:/www.who.int/entity/en/
11. Murray CJL, Lopez AD, Mathers CD, Stein C.
The Global Burden of Disease
2000 Project: aims, methods and data sources
. Geneva: World Health
Organization; 2001. Global Programme on Evidence for Health Polic y
Discussion paper N. 36. Available from URL: http:/www.who.int/entity/en/
12. United Nations, Population Division.
World population prospects — the
2002 revision
. New York (NY) : United Nations; 2003.
13. World Health Organization.
The world health report 2003: shaping the
future
. Geneva: WHO; 2003. Available from URL: http:/www.who.int/whr/en/
14. Pascolini D, Mariotti S, Pokharel GP, Pararajasegaram R, Etya’ale D, Négrel
A-D, et al. 2002 Global update of available data on visual impairment: a
compilation of population-based prevalence studies.
Ophthalmic
Epidemiology
, 2004;11:67-115.
15. World Health Organization.
Preventing blindness in children
. Report of a
WHO/IAPB scientific meeting Hyderabad, India 1999. Geneva: WHO; 2000.
WHO document WHO/PBL/00.77.
16. Gilbert CE, Anderton L, Dandona L, Foster A. Prevalence of visual
impairment in children: a review of available data.
Ophthalmic Epidemiology
1999;6:73-82.
17. Zhao J, Pan X, Sui R, Munõz SR, Sperduto RD, Ellwein LB. Refractive error
study in children; results from Shunyi District, China.
American Journal of
Ophthalmology
2000;129:427-35.
18. Pokharel GP, Nègrel AD, Munõz SR, Ellwein LB. Refrac tive error study in
children: results from Mechi Zone, Nepal.
American Journal of
Ophthalmology
, 2000;129:436-44.
19. Dandona R, Dandona L, Srinivas M, Sahare P, Norsaiah S, Munõz SR, et al.
Refractive error in children in a rural population in India.
Investigative
Ophthalmology and Visual Science
2002;43:615-22.
20. Murthy GVS, Gupta SK, Ellwein LB, Munõz SR, Pokharel GP, Sanga L, et al.
Refractive error in children in an urban population in New Delhi.
Investigative Ophthalmology and Visual Science
2002;43:623-31.
21. World Health Organization.
Formulation and management of national
programmes for the prevention of blindness
. Geneva: WHO; 1990. WHO
document PBL/90.18.
22. VanNewkirk MR, Weih LA, McCarty CA, Stanislavsky YL, Keeffee JE,
Taylor HR. Visual impairment and eye diseases in elderly institutionalised
Australians.
Ophthalmology
2000;107:2203-8.
23. National Programme for Control of Blindness and Vision 2020.
The right
to sight initiative. Cataract surgery rate 2002–2003
, Vol. 2. New Delhi
India: National Programme for Control of Blindness-India, Ophthalmology
Section, Directorate General health services, Ministry of Health and
Family Welfare.
24. Michon JJ, Lau J, Chan WS, Ellwein LB. Prevalence of visual impairment,
blindness, and cataract surgery in the Hong Kong elderly.
British Journal
of Ophthalmology
2002;86:133-9.
25. Nrmalan PK, Thulasiraj RD, Maneksha V, Rahmathullah R, Ramakrishnan R,
Padmavathi A, et al. A population based eye survey of older adults in
Tirunelveli district of south India: blindness, cataract surgery, and visual
outcomes.
British Journal of Ophthlamology
2002;86:505-12.
26. National Programme for the Control of Blindness.
National survey on
blindness and visual outcomes after cataract surgery
. 2002. New Delhi,
India: Directorate General of Health Services, Ministry of Health and
Family Welfare; 2002.
27. Dineen BP, Bourne RRA, Ali SM, Noorul Huq DM, Johnson GJ. Prevalence
and causes of blindness and visual impairment in Bangladeshi adults:
results of the national blindness and low vision survey of Bangladesh.
British Journal of Ophthalmology
2003;87:820-8.
