Citation: Atowa UC, Hansraj R, Wajuihian SO. Visual problems: a
review of prevalence studies on visual impairment in school-age children. Int
J Ophthalmol 2019;12(6):1037-1043
DOI:10.18240/ijo.2019.06.25
·Review Article·
Visual
problems: a review of prevalence studies on visual impairment in school-age
children
Uchenna C. Atowa, Rekha Hansraj, Samuel O. Wajuihian
Discipline
of Optometry, University of KwaZulu-Natal, Durban 4000, South Africa
Correspondence
to: Uchenna C.
Atowa. Discipline of Optometry, University of KwaZulu-Natal, Durban 4000, South
Africa. atowauc@gmail.com
Received:
Abstract
Childhood visual impairment
(VI) have a significant impact on the educational achievement, career choices
and social life of affected individual, and in children, is mainly due to
either preventable or treatable causes. Reliable data on the prevalence and
causes of VI in children will guide the development of a systematic vision
screening program for its early detection and successful treatment of possible
causes. The purpose of this literature review is to summarize the available
data on prevalence and causes of VI in school-age children from various regions
globally. A discussion on the major findings highlighting the definition
criteria, classifications and limitations for further studies is also
presented.
KEYWORDS: visual impairment; school-age
children; vision screening; school performance
DOI:10.18240/ijo.2019.06.25
Citation: Atowa UC, Hansraj R, Wajuihian
SO. Visual problems: a review of prevalence studies on visual impairment in
school-age children. Int J Ophthalmol 2019;12(6):1037-1043
INTRODUCTION
Visual impairment (VI) has a considerable impact on the
lives of the affected individuals as well as their families and society. Its
effect on development and learning is more significant when it is present at
birth or shortly afterwards compared to when it is acquired later in life. Loss of vision in children influences
their academic opportunities, career choices, and social life, with defective
near vision influencing their ability to perform a variety of tasks that
involve reading[1-2]. As more
than 85% of what a child learns in school is through visual presentation, their
ability to perform optimally will be affected[3-4]. Visual
field deficits also affect the child’s ability to accomplish tasks that require
ambulation in challenging environments or the application of peripheral vision[1]. In addition, approximately 90% of visually impaired
children are not receiving adequate education due to factors that include
discrimination, stigmatisation and lack of access to appropriate schools[5-6].
Reports suggests that in both developed and developing
countries, the majority of VI is either preventable or treatable[7-8]. Early
detection and effective treatment of underlying causes at the ‘sensitive’
period of visual development therefore remains an important approach for
preventing VI[9-11]. Reliable data on the prevalence and
causes of VI in children are necessary for developing a systematic vision
screening program with valid and reliable test protocols. Such data will help
to direct the application of available resources and efforts for early
detection to people who are at risk, thereby reducing the high short- and
long-term costs to the health system and society. The purpose of this
literature review is to document the prevalence and causes of VI in school-age
children from various regions globally. A discussion on the major findings
highlighting the definition criteria, classifications and limitations for
further studies is also presented.
METHODS
The online databases of PubMed, Medline, OVID, Google
Scholar, Science Direct and Embase were explored for the keywords, and VI
(prevalence and causes) in school children. The search was restricted to
primary research published in the English language and in peer-reviewed
journals. Only epidemiological studies with stated the measures of prevalence
and causes of VI among school-age children between 5-18y of age were included.
However, two studies on VI among Nigerian children with participants in the age
groups 4-24y[12] and 9-21y[13]
were included due to insufficient data on visual anomalies in these age groups
in Nigeria.
In this narrative review, a summary of each study that
met the outlined criteria is presented first and then evaluated in relation to
other studies. Parameters of interests for review included: sample size and
sampling method; participant characteristics, including gender and age;
prevalence rates and causes of VI; information on diagnostic criteria and
measurement techniques. The studies were compared according to geographic
regions or ethnicity.
Studies on School-Age Children
African region
Table 1 shows the various studies that have reported on
prevalence and causes of VI in paediatric populations in Africa and elsewhere,
while Table 2 presents the major causes of VI for these studies, where
available. The exact
prevalence and causes of childhood VI and blindness are difficult to establish
due to the infrequent occurrence of relevant pediatric eye conditions and the lack of
well-designed epidemiological studies, particularly in developing countries.
For instance, in Nigeria, a national survey[14]
on blindness and VI conducted between 2005 and 2007 reported only on the causes
of VI in an adult population. In addition, the study was constrained by the
sampling method used to identify the paediatric population, which limits the
generalization of findings, as the school-age children were invited to participate
only if they were living in a family of at least one eligible adult[14-16]. In the
study, blindness was defined as presenting visual acuity (VA) of 6/120 or worse
in the better eye, while VI was defined as presenting VA of less than 6/
Table 1
Prevalence of childhood visual impairment across various countries
|
Study |
Country |
Age (y) |
Sample size (n) |
VA threshold |
Prevalence (%) |
||
|
Uncorrected VA |
Presenting VA |
Best corrected VA |
|||||
|
Abdull et al[14] |
Nigeria |
10-15 |
5371 |
<6/12 |
Not reported |
Not reported |
1.2 |
|
Ajaiyeoba et al[12] |
Osun, Nigeria |
4-24 |
1144 |
Not reported |
Not reported |
1.5 |
Not reported |
|
Megbelayin and Asana[13] |
Calabar, Nigeria |
9-21 |
1175 |
≤6/9 |
Not reported |
6.9 |
Not reported |
|
Kumah et al[18] |
Ghana |
12-15 |
2435 |
≤6/12 |
3.7 |
3.5 |
0.4 |
|
Naidoo et al[17] |
South Africa |
5-15 |
4238 |
≤6/12 |
1.4 |
1.4 |
0.32 |
|
Taylor et al[26] |
Australia |
5-15 |
1694 |
<6/12 |
Not reported |
Not reported |
1.7 |
|
Robaei et al[27] |
Sydney, Australia |
6 |
1740 |
<6/12 |
4.1 |
Not reported |
Not reported |
|
Murthy et al[21] |
India (urban) |
5-15 |
6447 |
≤6/12 |
6.4 |
4.9 |
0.81 |
|
Dandona et al[22] |
India (rural) |
7-15 |
4074 |
≤6/12 |
2.7 |
2.6 |
0.78 |
|
Paudel et al[19] |
Vietnam |
12-15 |
2238 |
≤6/12 |
19.4 |
12.2 |
Not reported |
|
Goh et al[20] |
Malaysia |
7-15 |
4634 |
≤6/12 |
17.1 |
10.1 |
1.4 |
|
Salomao et al[23] |
Brazil |
11-14 |
2441 |
≤6/12 |
4.8 |
2.7 |
0.41 |
|
O’Donoghue et al[24] |
United Kingdom |
6-7 |
392 |
<6/12 |
Not reported |
1.5 |
Not reported |
|
12-13 |
661 |
3.6 |
|||||
|
Sauer et al[25] |
Peru |
5-18 |
380 |
≤6/9 |
Not reported |
8.9 |
Not reported |
VA: Visual acuity.
Table 2 Causes of childhood visual impairment across various countries
|
Study |
Percentage of participants (%) |
||||||
|
Refractive error |
Amblyopia |
Corneal opacity |
Retinal disorder |
Cataract |
Other causes |
Unexplained causes |
|
|
Ajaiyeoba et al[12] |
58.8 |
5.9 |
11.8 |
0 |
11.8 |
11.8 |
- |
|
Megbelayin and Asana[13] |
61.1 |
0.3 |
0.2 |
0.7 |
0 |
0.6 |
- |
|
Kumah et al[18] |
71.7 |
9.9 |
4.6 |
5.9 |
0 |
1.88 |
- |
|
Naidoo et al[17] |
63.6 |
7.3 |
3.7 |
9.9 |
0 |
3.1 |
12.0 |
|
Murthy et al[21] |
81.7 |
4.4 |
- |
4.7 |
- |
3.3 |
5.9 |
|
Dandona et al[22] |
61.0 |
12.0 |
- |
- |
- |
15.0 |
13.0 |
|
Paudel et al[19] |
92.7 |
2.2 |
0 |
0.4 |
0.7 |
1.5 |
2.6 |
|
Goh et al[20] |
87.0 |
2.0 |
0 |
0 |
0 |
0.6 |
10.4 |
|
Salomao et al[23] |
76.8 |
11.4 |
0 |
5.9 |
0 |
2.7 |
7.7 |
|
Taylor et al[26] |
47.0 |
19.0 |
0 |
0 |
0 |
0 |
34.0 |
|
Robaei et al[27] |
69.0 |
- |
- |
- |
- |
- |
- |
Two cross-sectional studies[15-16] were reported in some Nigerian cities, although with
an older population than the studies included in this review. The studies were
limited by poor diagnostic criteria, with that by Megbelayin and Asana[13] defining VI as presenting VA of 6/9 or less in one
or both eyes and reported a prevalence of VI of 6.9%. The definition criteria
they adopted has the potential of overestimating the prevalence of VI in the
study sample. In the earlier study by Ajaiyeoba et al[12],
the prevalence of VI was estimated to be 1.5%, but it provided no clearly
defined criteria. However, in both studies[12-13], refractive error (RE) was the major cause of VI.
In a large-scale Refractive Error Study in Children
(RESC) study in a South African population, Naidoo et al[17] reported on the prevalence of uncorrected (1.4%),
presenting (1.2%) and best corrected VA of ≤6/12 (0.32%) in children 5-15y of
age in the Durban area. A geographically defined cluster sampling design and a
door-to-door enumeration survey was applied to recruit the participants. RE
(63.6%) was the major cause of VI, with only 12 (19.0%) of those affected
wearing spectacles during examination. A more recent school-based RESC study
was conducted in the Ashanti Region of Ghana[18]
on children whose ages ranged from 12-15y. Reliable VA testing was possible in
all but one of the 2454 children examined for VI and RE, with 119 children
having VI in one or both eyes. Approximately, 3.7%, 3.5%, and 0.4% had
uncorrected, presenting and best VA of 6/12 or worse in the better eye
respectively, with RE being the major cause of reduced vision.
Asian region The
prevalence of VI and RE in school children 12-15y of age was studied in Ba Ria,
Vung Tau Province, Vietnam[19]. The authors
examined each subject with a standardized test protocol and found that 87.8% of
2258 children had normal or near normal vision (≥6/9.5) in the better eye. A
total of 434 (19.4%) children had uncorrected VA of ≤6/
In India, a population-based study involving a random
selection and door-to-door enumeration of children aged 5-15y from 22
geographically defined clusters found that RE (81.7%) was a major contributor
to the cause of VI in children in New Delhi. The prevalence of uncorrected,
presenting, and best corrected VA of 6/12 or worse in the better eye was 6.4%,
4.9%, and 0.81%, respectively[21]. A similar
study with children aged 7-15y from rural India found a lower prevalence of
uncorrected, presenting and best corrected VA of 6/12 or worse in the better
eye, with corresponding values of 2.7%, 2.6%, and 0.78%. RE (61%) was also the
major causes of reduced vision in eyes with VI[22].
The difference between these two studies, despite the age ranges differing by
only two years, may be related to a higher prevalence of RE, especially myopia,
in urban compared to rural areas, due possibly to differing education systems
and the children’s exposure to near-work activities.
Americas and European region Salomao
et al[23] examined 2825 school children aged
11-14y sampled by cluster random technique from 374 schools in three districts
of Sao Paulo, Brazil. VA was measured at
A cross-sectional survey of children aged 5-18y living in
a resource-poor community in Peru reported a high prevalence of VI, which may
be attributed to its definition criteria.
Participants completed a socio-demographic and health risk factor
questionnaire and were screened for reduced distance VA, stereopsis, external
eye examination and colour vision deficiency, with VI being defined as VA less
than 0.2 logMAR (≤6/9). Of the 380 children who were examined, the mean
uncorrected VA was found to be 0.07±0.13 logMAR, the findings indicating that
8.9% of the children were visually impaired in both eyes and 26.3% in one eye.
Severe VI (<6/60) in both eyes was 0.3% and 0.7% in one eye, with the study
recommending the performance of regular vision screening of children in Peru[25].
Oceania region
Taylor et al[26] assessed
low vision and blindness in 1694 Australian indigenous school-age children aged
5-15y, with a VA measurement of scholars randomly selected from 30 geographic
areas. The rate of low vision, defined as best VA of less than 6/12 and equal
to 6/60 was 1.5%, and the rate of blindness of best VA of less than 6/60 was
0.2%, with RE accounting for the most of their low vision. Relative risk of
vision loss and blindness in the indigenous compared with the wider population
children in Australia were found to be 0.2 and 0.6, respectively. In another
school-based survey in Sydney, Australia, the prevalence of non-correctable VI
(VA<6/12) was only between 0.03% and 0.08%, which was 45 times lower than
that reported in adults[27]. RE was responsible
for 69.0% of the VI in the children.
Limitations of Previous Studies While all
studies (Table 1), except for Sauer et al[25],
included large sample sizes and traditional VA chart measuring technique, some
flaws inherent in the study designs may have affected the generalizability of
their findings. Some of the studies failed to state the eligibility criteria
for participant recruitment[12]. In others,
amblyopia was identified as a major cause of VI with no stated definition
criterion[13,17,19-20], while others[14,25,27] failed to provide detailed
information on the causes of VI in their study samples. In addition, the study
by Ajaiyeoba et al[12] did not indicate the definition criteria used to
identifying participants with VI. In relation to RE, the emphasis
in some studies was on VI with RE[14,18,26], thereby undermining the quantification of children
at risk of developing VI due to RE and preventing the development of screening
and intervention strategies to prevent VI in this cohort.
DISCUSSION
Definition of Visual Impairment The
definition criterion for identifying children with VI is very important. Until
recently, the definition of VI was predicated on the second revision of the
10th ICD edition[28], which followed from a 1972
World Health Organization (WHO) study of blindness and demonstrated that the
best corrected VA should be used as the basis for estimating VI[29]. At that stage, RE was not considered a priority and
a major cause of VI, and was excluded from reports of the total number of
persons with VI. However, data from recent population-based studies indicates
that uncorrected RE contributes significantly to the total number of persons
with VI[30]. Accordingly, the WHO adopted a new
definition of VI in the revised ICD-10 version: 2016, and uses presenting VA
and visual loss from uncorrected RE[31]. Under
this classification, low vision (moderate and severe impairment) is defined as
a presenting VA of less than 6/18, but equal to or better than 6/120, or a
visual field loss to less than 20 degrees diameter in the better eye with best
possible refractive correction.
In the reviewed studies (Table 1), although VI was mostly
defined as a VA of less than or equal to 6/12, a broad range of definition
criteria was applied in its diagnosis: from a VA of 6/9 or less to less than 6/12,
including Ajaiyeoba et al[12], who
did not indicate the definition criterion for VI. The use of a VA of 6/9 by some studies
will overestimate the prevalence of VI and weigh heavily on the cost of
intervention services for affected individuals, and cause considerable
psychological effect on the affected children and their families. When compared
to other studies on African children, Megbelayin and Asana[13], who defined VI as a VA of 6/9 or
less, reported a higher prevalence of VI than other studies[14,17-18] that utilized a VA of 6/12 or
worse.
The trend
was also observed in the studies conducted in the Americas, where the study in
Peru[25] that applied a VA threshold of 6/9
or less reported a higher prevalence of VI than another study in Brazil[23]. Studies have reported that the mean VA in young
children was 6/7.5[32], and that an acuity of
6/12 or less would have a harmful effect on their vision[33]
and potentially reduce their functional performance. When compared with the WHO
definition of VI, the VA of 6/12 or less used by the RESC studies provides a better indicator to
accurately estimate the magnitude of VI due to RE and a proper assessment of
the demand for eye care services[34], including
those with mild VI. Its use will also ensure timely detection and treatment of
the underlying factors of mild VI before they progress to permanent.
Classification of Visual Impairment The
categories of VI adopted by the majority of the studies reviewed suggest that a
person with a presenting VA of worse than 6/60 should be regarded as blind.
However, a substantial number of children who are classified as blind still
have usable vision and can sustain activities of daily living independently[35]. Reports indicate that in developing countries, such
as in Africa, approximately 20% of children categorized as blind were found to
have significant residual vision[36-37].
The implications for rehabilitation and education is that children with low
vision may be educated using techniques that are appropriate for those who are
totally blind, despite their having some useful vision that can support other activities
of daily living if they can be taught how to use it appropriately[38-39]. For instance, approximately
66% and 1.45% of children who were initially classified as blind but reading
with the aid of Braille were found to have low and normal vison, respectively,
after best refraction[40]. In view of the
importance of functional vision, the WHO in 1992 added another perspective to
the definition of VI that covers both distance and near vision[35]. The definition states that: a person with low vision
is one who has impairment of visual functioning even after treatment and/or
refractive correction, and has a vision in the better eye of less than 10 degrees
from the point of fixation (or 20 degrees across), but who uses or is
potentially able to use vision for planning or execution of a task. This
functional definition ensures that people who have low vision, but with a VA of
less than 6/120, are included in low vision programs and are eligible for
appropriate services.
Regional Variations in the Prevalence and Causes of
Visual Impairment The
prevalence and causes of VI varied across the different regions[1] (Table 2). A lower prevalence of VI was reported for African
children compared to other regions, especially Southeast Asian countries. This
may be explained by the lack of robust epidemiological studies in developing
countries such as Africa. The higher prevalence of VI in Southeast Asian
countries compared to other regions may be related to the reported high
prevalence and severity of myopia in these populations. Myopigenic factors
including: 1) genetic predisposition, such as ethnicity and a family history of
high myopia; 2) intensive near work activities due to competitive education and
schooling systems are common among Southeast Asian children[41],
with myopic eyes being at risk of developing functional VI at a relatively
young age[42]. In addition, the causes of VI
varied widely among studies, which may be attributed to differences in
socio-economic developments as well as the availability of efficient and broad
screening strategies. These factors can all influence the prevalence and causes
of VI in different regions.
Causes of Visual Impairment in School-Age Children Uncorrected
RE is a leading cause of VI and the second leading cause of treatable blindness
among people of all age groups[43]. This is
evident in the reviewed studies (Table 2), where 47%-92.7% of the reduced
vision in school-age children was caused by uncorrected RE, and 0.3%-19.0% were
caused by amblyopia. The risk factors for amblyopia include strabismus,
anisometropia and congenital cataract or the less prevalent media
opacification. Unlike VI associated with amblyopia, simple RE (RE not
associated with amblyopia) is correctable with the use of appropriate
spectacles and is thought to not affect normal visual development. According to
the WHO, there would be over 19 million children less than 15y of age with VI
worldwide, with 12.8 million being due to uncorrected RE. Consequently, Vision
2020 initiative: The Right to Sight, identified the correction of RE as one of
its major objectives. The initiative advocates vision screening in schools with
the provision of affordable spectacles[44].
Similarly, amblyopia can also be effectively treated with early detection and
correction of the underlying amblyogenic risk factor[45].
However, the available evidence indicates that amblyopia
is treatable, even in the teenage years[45-46]. Other studies show that
improvements in binocularity and VA in the amblyopic eye can also be realized
in adulthood[47-48]. Available
treatments for amblyopia include patching or atropine therapy of the affected
eye; surgery for strabismus and cataracts; and RE correction with spectacles or
contact lenses. Overall, treatable causes were responsible for majority of the
VI in the study populations (Table 2).
CONCLUSION
The present review has highlighted the prevalence and
causes of VI in various countries as well as some methodological concerns
regarding the reported studies. Diagnostic criteria for VI varied across the
studies, and in some cases, the adopted definition criteria can overestimate
the prevalence of VI. As the variation in diagnostic criteria can make
comparing the results very difficult, it is important to develop a standard and
uniform diagnostic criterion that is appropriate for detecting children at risk
of developing a VI. Nonetheless, regional variations in the prevalence of VI
were significant, and may be attributed to differences in socio-economic development, race,
cultural factors, as well as, the availability of interventions, and implies
that the prevalence data in one population cannot necessarily be extrapolated
to another. The review also demonstrated that treatable
causes were responsible for the most of the VI in the study populations, and
highlights the need for adequate strategies that will promote vision screening
in school children and the wider community, with the goal of timely detection
and treatment of common visual problems.
ACKNOWLEDGEMENTS
Authors’ contributions: The
manuscript was written by Atowa UC with Hansraj R and Wajuihian SO providing feedback on the structure and content of the
manuscript.
Conflicts of
Interest: Atowa
UC, None; Hansraj R, None; Wajuihian SO, None.
REFERENCES