Global magnitude of visual impairment caused by uncorrected refractive errors in 2004

Global magnitude of visual impairment caused by uncorrected refractive errors in 2004

The global magnitude of visual impairment due to uncorrected refractive errors in 2004 is estimated at 153 million individuals, with 8 million classified as blind. This comprehensive analysis highlights the significant public health issue posed by uncorrected refractive errors, which can severely impact educational and employment opportunities. The findings underscore the need for effective interventions, such as accessible refractive services, to improve quality of life. The report also emphasizes the importance of awareness and policy development to address this hidden problem. It serves as a crucial resource for health professionals and policymakers aiming to reduce visual impairment worldwide.

Key Points

  • Estimates 153 million people globally are visually impaired from uncorrected refractive errors.
  • Highlights that uncorrected refractive errors are the main cause of low vision and the second leading cause of blindness.
  • Discusses the impact of visual impairment on education, employment, and quality of life.
  • Calls for improved access to refractive services as a cost-effective intervention in eye care.
  • newtopiccyclegrowin
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Bulletin of the World Health Organization | January 2008, 86 (1)
Abstract Estimates of the prevalence of visual impairment caused by uncorrected refractive errors in 2004 have been determined at
regional and global levels for people aged 5 years and over from recent published and unpublished surveys. The estimates were based
on the prevalence of visual acuity of less than 6/18 in the better eye with the currently available refractive correction that could be
improved to equal to or better than 6/18 by refraction or pinhole.
A total of 153 million people (range of uncertainty: 123 million to 184 million) are estimated to be visually impaired from
uncorrected refractive errors, of whom eight million are blind. This cause of visual impairment has been overlooked in previous
estimates that were based on best-corrected vision. Combined with the 161 million people visually impaired estimated in 2002
according to best-corrected vision, 314 million people are visually impaired from all causes: uncorrected refractive errors become the
main cause of low vision and the second cause of blindness.
Uncorrected refractive errors can hamper performance at school, reduce employability and productivity, and generally impair quality
of life. Yet the correction of refractive errors with appropriate spectacles is among the most cost-effective interventions in eye health care.
The results presented in this paper help to unearth a formerly hidden problem of public health dimensions and promote policy
development and implementation, programmatic decision-making and corrective interventions, as well as stimulate research.
Bulletin of the World Health Organization 2008;86:63–70.
Une traduction en français de ce résumé figure à la fin de l’article. Al final del artículo se facilita una traducción al español.
Global magnitude of visual impairment caused by uncorrected
refractive errors in 2004
Serge Resnikoff,
a
Donatella Pascolini,
a
Silvio P Mariotti
a
& Gopal P Pokharel
a
لم     في لا   تر
a
Chronic Disease Prevention and Management, WHO, 20 avenue Appia, 1211 Geneva 27, Switzerland.
Correspondence to Serge Resnikoff (e-mail: resnikoffs@who.int).
doi:10.2471/BLT.07.041210
(Submitted: 11 February 2007 – Revised version received: 28 May 2007 – Accepted: 11 June 2007 – Published online: 16 November 2007 )
Introduction
Refractive errors (myopia, hyperopia
and astigmatism; presbyopia is not in-
cluded in this study given the present
paucity of data, but it is recognized that
uncorrected, it could lead to an impaired
quality of life) affect a large proportion
of the population worldwide, irrespec-
tive of age, sex and ethnic group. Such
refractive errors can be easily diagnosed,
measured and corrected with spectacles
or other refractive corrections to attain
normal vision. If, however, they are
not corrected or the correction is inad-
equate, refractive errors become a major
cause of low vision and even blindness
(for a selection of studies, see http://ftp.
who.int/nmh/references/RE-estimates-
references.pdf).
Visual impairment from uncor-
rected refractive errors can have imme-
diate and long-term consequences in
children and adults, such as lost educa-
tional and employment opportunities,
lost economic gain for individuals, fami-
lies and societies, and impaired quality
of life. Various factors are responsible for
refractive errors remaining uncorrected:
lack of awareness and recognition of the
problem at personal and family level, as
well as at community and public health
level; non-availability of and/or inability
to afford refractive services for testing;
insufficient provision of affordable cor-
rective lenses; and cultural disincentives
to compliance.
The definition of visual impairment
in the International statistical classifica-
tion of diseases, injuries and causes of
death, 10th revision (ICD-10), H54,
is based on “best-corrected” vision, i.e.
visual acuity obtained with the best pos-
sible refractive correction.
1
However, to
assess the extent of visual impairment
caused by uncorrected refractive errors,
estimates need to be based on “present-
ing” vision, i.e. visual acuity obtained
with currently available refractive cor-
rection, if any. Thus, presenting vision,
as opposed to best-corrected vision,
provides the prevalence of visual impair-
ment that could be improved simply by
appropriate corrective refraction. Basing
the definition of visual impairment on
presenting vision extends the current
definition to one that characterizes visual
impairment faced by people in day-to-
day activities.
Using best-corrected vision, visual
impairment was estimated to affect 161
million people globally in 2002, of
whom 37 million were blind.
2
The main
cause of blindness and low vision was
cataract; however, it was recognized
that unless uncorrected refractive errors
were included among the causes, visual
impairment at global level was signifi-
cantly underestimated.
This paper presents the estimate
of the prevalence of visual impairment
from uncorrected refractive errors for all
ages over 5 years at regional and global
levels, based on recent published and
unpublished surveys. Some results from
this paper were reported in a WHO
press release on 11 October 2006 to
mark World Sight Day.
3
Methods
Definitions
Presenting vision is defined by the visual
acuity in the better eye using currently
available refractive correction, if any.
Policy and practice
Global visual impairment caused by uncorrected refractive errors
64
Serge Resnikoff et al.
Bulletin of the World Health Organization | January 2008, 86 (1)
Best-corrected vision is the visual acuity
in the better eye achieved by subjects
tested with pinhole or refraction.
Visual impairment caused by un-
corrected or inadequately corrected re-
fractive errors is defined as visual acuity
of less than 6/18 in the better eye that
could be improved to equal to or better
than 6/18 by refraction or pinhole, thus
spanning the low vision and blindness
categories as currently defined in the
ICD-10.
It should be noted that in the
revision of the ICD-10 categories of
visual impairment proposed in 2003 by
a WHO consultation on the develop-
ment of standards for characterization
of vision loss, low vision is replaced by
two categories: moderate visual impair-
ment (presenting visual acuity less than
6/18 but equal to or better than 6/60)
and severe visual impairment (presenting
visual acuity less than 6/60 but equal to
or better than 3/60).
4
Population estimates and WHO
subregions
Estimates of population size and struc-
ture were based on the latest estimates
of world population (for 2004) in the
World population prospects: the 2004
revision; estimates of demographics were
based on the World urbanization pros-
pects 2003 – both sources from the
United Nations Population Division.
5,6
For the classification of WHO
Member States into 17 epidemiological
subregions, see Murray & Lopez, 1996.
7
General inclusion criteria
The following criteria were used to select
studies.
The prevalence of best-corrected and •
presenting visual acuity of less than
6/18 had to be reported or, alterna-
tively, the distribution of causes of
presenting visual impairment.
In children, refractive diagnostics •
had to be determined by objective
refraction under cycloplegia plus sub-
jective refraction.
8
The studies had to be population-•
based, representative of the area
sampled, with definitions of visual
impairment clearly stated. Studies
with inadequate sample sizes and re-
sponse rate were not included.
Data reported only for eyes or for •
the worse eye could not be included
in the estimates calculated for people
and the better eye.
For further discussion of selection cri-
teria, see Resnikoff et al.,
2
and Pascolini
et al., 2004.
9
Sources of epidemiological data
Literature sources were searched sys-
tematically in Medline up to April
2006. Most surveys meeting the selec-
tion criteria were conducted within the
past five years; the earliest surveys date
from 1995. Unpublished data were
provided by academic institutions and
national programmes for the prevention
of blindness.
Table 1 shows the 31 countries for
which surveys that met the selection
criteria were available, the bibliography
can be found at http://ftp.who.int/nmh/
references/RE-estimates-references.pdf
and in the WHO Prevention of Blind-
ness and Deafness Programme’s global
data on visual impairment.
10
For the age group 5–15 years, 16
surveys were found to fit the selection
criteria. Of these, 10 were conducted
in different countries using a specially
designed protocol to estimate the preva-
lence of visual impairment from uncor-
rected refractive errors (the refractive
error study in children (RESC; see
Négrel et al., 2000, for the details of the
protocol).
11
The RESC studies provided
extensive information on visual acuity,
refractive errors and use of spectacles.
For the age group 50 years and
older, 38 surveys met the inclusion cri-
teria. Of these, 30 were surveys for the
Table 1. Surveys used to estimate global visual impairment from uncorrected
refractive errors by WHO subregion, 2004
WHO subregion
a,b
Number of
surveys
Countries
Afr-D 2 Mali, Mauritania
Afr-E 1 South Africa
Amr-A 3 United States of America
Amr-B 5 Argentina, Brazil, Chile, Paraguay, Venezuela
(Bolivarian Republic of)
Amr-D 2 Guatemala, Peru
Emr-B 5 Iran (Islamic Republic of), Lebanon, Oman, Qatar
Eur-A 2 Ireland, Italy
Eur-B2 2 Armenia, Turkmenistan
Sear-B 6 Malaysia, Philippines, Singapore
Sear-D 13 Bangladesh, India, Nepal, Pakistan
Wpr-A 4 Australia
Wpr-B1 7 China
Wpr-B2 16 Cambodia, Myanmar, Viet Nam
a
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.
b
In subregions Emr-D, Eur-B1, Eur-C and Wpr-B3, no population-based surveys met the selection criteria.
rapid assessment of cataract surgical
services (RACSS), which also provide
prevalence of presenting and best-
corrected visual acuity.
12
An additional 14 surveys reported
age-specific prevalence of presenting vi-
sual impairment and its causes in other
age groups.
Estimation of prevalence of visual
impairment from uncorrected
refractive errors
For the age group from 5 to 15 years,
the prevalence is estimated by the dif-
ference between the prevalence of pre-
senting and best-corrected visual acuity
of less than 6/18 with refraction under
cycloplegia: this difference corresponds
to the prevalence of presenting visual
acuity that could be improved to equal
to or better than 6/18 by appropriate
correction. In the case of studies report-
ing only the prevalence of presenting
visual acuity, the prevalence of visual
impairment due to refractive error was
determined from the distribution of
causes determined in the surveys.
The prevalence for people aged
16–39 years was estimated to be the
same as that for those aged 5–15 years,
on the assumption that from the ages of
16 years to 39 years, the refractive status
generally does not undergo changes that
require further correction.
13
The prevalence for people aged
40–49 years was either estimated from
Policy and practice
Global visual impairment caused by uncorrected refractive errors
65
Serge Resnikoff et al.
Bulletin of the World Health Organization | January 2008, 86 (1)
the results of surveys that reported
age-specific data for this age group or
calculated by a linear fit between the
prevalence at age 39 and 55 years.
For the population aged 50 years
and older, the prevalence was estimated
from the difference between visual acu-
ity of less than 6/18 with the available
correction and visual acuity of less than
6/18 with best correction determined
using refraction or pinhole, assuming
that pinhole approximates complete
refraction.
Estimation of prevalence of
blindness from uncorrected
refractive errors
Uncorrected refractive errors in adults
aged 50 years and older have been
shown to lead to blindness in some
regions: the corresponding prevalence
of blindness was determined from the
difference between prevalence of pre-
senting and best-corrected visual acuity
of less than 3/60.
Blindness from uncorrected refrac-
tive errors was also reported in some
surveys for the age group 40–49 years.
Since there were insufficient data world-
wide, it was assumed that the global
number of people blind from this cause
in this age group was 5.13 times lower
than the corresponding number in
people aged 50 years and over, based on
the ratio of the total number of people
visually impaired 50 years and over and
those aged 40–49 years.
Estimation of refractive services
coverage
The RESC studies also report the preva-
lence of uncorrected visual acuity in the
age group 5–15 years: the prevalence
of uncorrected, presenting and best-
corrected visual acuity (VA < 6/18)
provides an estimate of the percentage
coverage of refractive services using the
formula:
100 – [ × 100]
(presenting VA –
best corrected VA)
(uncorrected VA –
best corrected VA)
Since percentage coverage is based on
presenting visual acuity, it is an esti-
mate of both the provision of refractive
services and the compliance to prescrip-
tion.
Extrapolations
Since data were not available for every
country, extrapolations were made to
estimate the global prevalence of visual
Table 2. Number of people visually impaired from uncorrected refractive errors and corresponding prevalence, by age group and
WHO subregion or country, 2004
WHO subregion
a
or country
Age 5–15 years Age 16–39 years Age 40–49 years
Age >50 years Total (5 to >50 years)
No. in millions
(prevalence %)
No. in millions
(prevalence %)
No. in millions
(prevalence %)
No. in millions
(prevalence %)
Population
in millions
No. in millions
(prevalence %)
Afr-D, Afr-E 0.534 (0.24) 0.683 (0.24) 0.647 (1.13) 4.529 (5.94) 640.4 6.393 (1.00)
Amr-A 0.501 (1.00) 1.098 (1.00) 0.810 (1.60) 3.417 (3.60) 305.4 5.826 (1.91)
Amr-B 0.709 (0.70) 1.331 (0.70) 0.998 (1.81) 3.204 (4.07) 432.4 6.242 (1.44)
Amr-D 0.137 (0.70) 0.209 (0.70) 0.127 (1.81) 0.486 (4.86) 66.4 0.959 (1.44)
Emr-B, Emr-D 0.405 (0.55) 0.688 (0.55) 0.356 (1.20) 1.708 (4.76) 264.3 3.157 (1.19)
Eur-A 0.516 (1.00) 1.379 (1.00) 0.991 (1.60) 5.289 (3.60) 398.3 8.175 (2.05)
Eur-B1, Eur-B2, Eur-C 0.721 (1.00) 1.740 (1.00) 1.065 (1.60) 3.335 (2.80) 431.7 6.861 (1.59)
Sear-B, Wpr-B1,
Wpr-B2, Wpr-B3
(China excluded)
1.098 (0.79) 1.806 (0.74) 1.244 (1.70) 4.511 (4.67) 554.0 8.659 (1.56)
Sear-D
(India excluded)
0.606 (0.63) 0.986 (0.73) 0.909 (2.39) 9.295 (19.45) 317.5 11.796 (3.71)
Wpr-A 0.034 (0.20) 0.097 (0.20) 0.039 (0.20) 1.177 (1.99) 144.4 1.347 (0.93)
China 5.940 (2.66) 14.414 (2.66) 7.209 (3.95) 26.903 (9.61) 1229.0 54.466 (4.43)
India 1.610 (0.63) 2.695 (0.63) 4.042 (3.39) 30.970 (18.70) 966.9 39.317 (4.07)
World 12.811 (0.97) 27.126 (1.11) 18.437 (2.43) 94.824 (7.83) 5750.7 153.198 (2.67)
a
See Table 1, footnote a.
impairment from uncorrected refractive
errors. The rationale for the extrapola-
tions was the similarity of the epidemi-
ology of refractive errors, the availability
and/or affordability of refractive services
and compliance. Various kinds of ex-
trapolations were made, based on the
data selected:
the prevalence in urban and rural •
areas within a country was extrapo-
lated to all urban and rural areas, re-
spectively, of the country; the coun-
try prevalence was determined by
weighting the prevalence by the ru-
ral–urban distribution of the popu-
lation;
in subregions with data from several •
countries, an average prevalence was
determined and applied to all other
countries in the subregion. The av-
erage was calculated by weighting
the prevalence from the countries by
their share of the population in the
subregion and taking into account
the urban and rural distribution of
the population;
in the case of whole subregions lack-•
ing data, the prevalence was extrapo-
lated from other subregions with
similar epidemiology of refractive
errors and with similar WHO epide-
miological classification.
6
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FAQs of Global magnitude of visual impairment caused by uncorrected refractive errors in 2004

What is the main finding regarding visual impairment in 2004?
In 2004, it was estimated that 153 million people suffered from visual impairment due to uncorrected refractive errors, with 8 million classified as blind. This significant number highlights the urgent need for public health interventions to address refractive errors, which are often easily correctable with spectacles. The report indicates that uncorrected refractive errors are the leading cause of low vision and the second leading cause of blindness globally. These findings emphasize the importance of awareness and accessibility in refractive services to improve overall eye health.
How do uncorrected refractive errors affect quality of life?
Uncorrected refractive errors can severely hinder educational performance, reduce employability, and diminish overall productivity. Individuals with visual impairment often face challenges in daily activities, which can lead to a lower quality of life. The report stresses that addressing these refractive errors through proper correction can significantly enhance individuals' ability to participate fully in society. By improving access to eye care services, communities can foster better educational and economic outcomes.
What recommendations does the report make for addressing visual impairment?
The report recommends implementing community-level screening for refractive errors, integrating these efforts into school health programs. It emphasizes the need for awareness campaigns to ensure that individuals utilize available corrections and overcome cultural barriers to compliance. Additionally, it calls for training eye-care personnel in refraction techniques and developing reliable, affordable equipment for assessments. Monitoring the provision of refractive services is also crucial to identify communities in need and evaluate effective interventions.
What is the significance of the findings in this report?
The findings in this report are significant as they reveal the extensive public health issue posed by uncorrected refractive errors, which have often been overlooked in previous estimates. By highlighting the scale of visual impairment, the report aims to stimulate policy development and programmatic decision-making to address this issue. It serves as a vital resource for health professionals and policymakers, providing a framework for interventions that can lead to improved eye health and quality of life for millions.

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