Terapias visuales para todas las edades

1. ORIGINAL ARTICLE
Refractive Errors and Amblyopia in Children
Entering School: Shahrood, Iran
Payman Jamali*, Akbar Fotouhi†
, Hassan Hashemi*, Masud Younesian†
, and Alireza Jafari‡
ABSTRACT
Purpose. To determine the prevalence of amblyopia, strabismus, and refractive errors in children entering school.
Methods. In this cross-sectional population-based study, 6-year-old children enrolling in Shahrood schools were
randomly sampled. Those with organic blindness or mental retardation were excluded. Ocular alignment, visual acuity,
stereopsis, cover testing, and cycloplegic refraction were recorded for all children by an optometrist. A diagnosis of
amblyopia was based on a best-corrected visual acuity of 6/12 or less in one or both eyes, or a bilateral difference of at
least two best-corrected visual acuity lines.
Results. A total of 902 children were invited for optometry examinations, among which 827 (91.7%) responded and 815
children (98.5%) were included in the study. The prevalence of significantly reduced visual acuity (uncorrected VA Յ6/12
in either eye) and amblyopia was 3.6 and 1.7%, respectively. The prevalence of hyperopia (ϩ2.00 D or worse), myopia
(Ϫ0.50 D or worse), astigmatism (0.75 D or worse), and anisometropia (1.00 D or more) were 20.5, 1.7, 19.6, and 2.2%,
respectively. Significant refractive error, defined as hyperopia Ͼϩ3.50 D, myopia ϾϪ3.00 D, astigmatism Ͼ1.50 D in
the orthogonal meridian or Ͼ1.00 D in the oblique meridian, or anisometropia (hyperopic Ͼ1.00 D, myopic Ͼ3.00 D)
was detected in 2.1, 0.1, 5.0, and 0.9% of the sample, respectively. Strabismus was diagnosed in 1.2% of children.
Overall, 52 children (6.4%; 95% confidence interval [CI], 4.7–8.1%) were at risk of amblyopia; of these, 81% had
significant refractive errors, 11% had strabismus, and 8% had both.
Conclusion. A considerable proportion of 6-year-old children have strabismus and/or significant, potentially amblyogenic
refractive errors. The relatively high rate of hyperopia and astigmatism in the studied population needs more attention.
The results of the study emphasize the need for adequate diagnostic and therapeutic eye care services for preschool
children.
(Optom Vis Sci 2009;86:364–369)
Key Words: amblyopia, amblyogenic refractive errors, strabismus
V
isual acuity and stereopsis develop during the first years of
life. Distorted visual acuity, as a result of refractive errors or
strabismus, can place a substantial burden on the affected
child. If not corrected, such disorders may impair learning capa-
bility and educational potential in children entering school, and
could interfere with the development of the visual pathways in the
brain if left untreated before the age of 8 years. In other words,
children affected by significant refractive error and strabismus, if
not treated, are vulnerable to functional reduction in the visual
acuity, namely amblyopia.1–3
Unlike adults, who have different visual needs, young children
can function normally with uncorrected mild to moderate myopia
or astigmatism, and they can overcome a fairly large amount of
hyperopia through accommodation.4
Children with strabismus
strongly favor one eye for fixation, so most of them report no
complaint.5
To detect these types of visual impairment before
entering school and prevent future complications, adequate eye
care services should be provided to perform proper diagnostic tests
and therapeutic measures.
The prevalence of refractive errors, strabismus, and amblyopia
reported in the literature has been shown to vary dependent on the
study population, the definition of the disease or disorder, and on
the measurement methods.6
In the last decade, several population-
based surveys of visual impairment in school-aged children were
*MD
†
MD, PhD
‡
MSc
Shahrood Welfare Organization, Shahrood, Iran (PJ), Epidemiology and Biostatis-
tics Department, School of Public Health, Tehran University of Medical Sciences,
Tehran, Iran (AF), Farabi Eye Hospital, School of Medicine, Tehran University of
Medical Sciences, Tehran, Iran (HH), Environmental Health Engineering Depart-
ment, School of Public Health, Tehran University of Medical Sciences, Tehran, Iran
(MY), and Shahrood Welfare Organization, Shahrood, Iran (AJ).
1040-5488/09/8604-0364/0 VOL. 86, NO. 4, PP. 364–369
OPTOMETRY AND VISION SCIENCE
Copyright © 2009 American Academy of Optometry
Optometry and Vision Science, Vol. 86, No. 4, April 2009

2. conducted, using similar definitions and measurement meth-
ods.7–11
None of the studied populations have the same racial or
socioeconomic composition as that in Iran. Nationwide preschool
vision screening has been implemented in Iran since 1998. Accord-
ing to one of the most recent published reports,12
42% of the target
population had not attended screening, and 75% of the children
suspected of being visually impaired had not attended optometric
examinations. These low uptake rates have resulted in limited gen-
eralizability of the findings.
The present survey was conducted in light of the paucity of the
necessary data concerning refractive errors and strabismus to im-
prove the setting of eye care services in Iran. Regardless of their
visual acuity and treatment history, refraction and stereopsis tests
were performed for all participants, giving a potentially more ac-
curate account of the prevalence of significant, potentially amblyo-
genic refractive errors and strabismus.
METHODS
The prevalence of amblyopia and risk factors for amblyopia
in 6-year-old children was determined through a cross-sectional
population-based study.
Study Population
The study targeted children residing in Shahrood who were
born between September 1998 and August 1999 and were brought
to school-entry health checkup centers during summer 2005. Chil-
dren with mental retardation were excluded. Considering previous
estimates of the frequency of visual acuity Ͻ6/9 at this age (about
5%),12
811 children had to be examined to determine the 95% CI
of the prevalence with an accuracy of 1.5%. Assuming an overall
response rate of 90%, it was estimated that a sample size of 902
children needed to be recruited in Shahrood, which is a city located
400 km from Tehran and had an estimated population of 235,000
in 2005.
Every summer, 6-year-old children all over the county undergo
school-entry health checkups at selected schools and health care
centers of urban and rural areas. Standard assessment includes
visual acuity measurement along with mental, motor, and hearing
evaluation. During July to September 2005, a total of 2882 chil-
dren referred to these centers in Shahrood, 902 of which were
enrolled in this study on a random basis.
Field Operations
Although few families seemed to keep their children out of
school, we collected the population data from all rural and urban
public health centers to identify eligible children who might have
been missed. To ensure uniformity, names were recorded from
newborn vaccination charts registered during September 1998 to
August 1999. Those who had not referred to school entry health
checkup centers were followed up to check whether they still re-
sided in Shahrood and were eligible for study.
Examinations
All children participating in this study were initially checked by
an experienced nurse for ptosis, corneal opacities, and cataract and
were excluded if any of these conditions were present.13,14
The
eligible children underwent optometry examinations including
observation and measurement of alignment, visual acuity measure-
ment, the cover test, stereopsis, and cycloplegic refraction.
Visual acuity was measured with retro-illuminated Snellen E-
charts placed at a distance of 6 m; the right eye was tested first, then
the left eye, each time occluding the fellow eye. Cover test was
performed while the child was asked to look at a 6/9 visual acuity
symbol, once 40 cm and then 6 m away, occluding one eye at a
time, observing the uncovered eye to detect any correcting move-
ment. The degree of tropia was measured using corneal light reflex
and neutralizing prisms. TNO test (Lameris Ootech, Groenekan,
Netherlands) was performed with the subject at 40 cm distance,
wearing red-green goggles, and with the test book properly ad-
justed and the visual axis of the subject vertical. Both subjective and
cycloplegic refractions were performed in a dim-lit room using
streak retinoscope (Heine, Germany, ␤ 200) with the examiner at
a distance of 66 cm. Cases with an uncorrected visual acuity
(UCVA) Ͻ6/6 were tested for their best-corrected visual acuity
(BCVA) after subjective refraction. Cycloplegia was induced with
two drops of cyclopentolate 1% instilled 5 min apart. After 20 min,
if a pupillary light reflex was still present, a third drop was admin-
istered. Refractive status was assessed 40 to 60 min after the first
drop. Parents were asked whether their children had been exam-
ined by the annual national preschool (4–6 years) amblyopia
screening program and whether they wore spectacles or had patch-
ing or ophthalmic surgery.
Ethical Issues
The Ethics Committee of Tehran University of Medical Sci-
ences approved the study. The purpose and methods of the study,
including rare but reversible complications of cyclopentolate eye
drops, were explained to the parents before examinations and in-
formed consents were signed.
Data Management and Analysis
Three optometrists with more than 5-year experience in testing
preschool children were selected to do the examinations. They had
a training course to familiarize themselves with the study protocol
and measurement methods. One experienced ophthalmologist ob-
served them throughout the course. The clinical examination data
forms were reviewed for completeness and accuracy before being
entered.
UCVA of 6/12 or less in either eye was considered as significant
reduced visual acuity. Amblyopia was defined as a BCVA equal or
Ͻ6/12 in either eye, or a difference of two or more lines of BCVA
between the two eyes without an organic cause.15
Children were
considered to have refractive error if hyperopia Նϩ2.00 D, myo-
pia ՅϪ0.50 D, astigmatism Ն0.75 D, or anisometropia Ͼ1.00 D
were reported in one or both eyes.7
Young children with mild to
moderate refractive errors can function normally and do not need
to wear glasses. Higher degrees of refractive errors are more likely to
be associated with amblyopia but the definitive degree to consider
them amblyogenic is not clear cut.4,16–18
Hyperopia more than
ϩ3.50 D, myopia more than Ϫ3.00 D, hyperopic anisometropia
Ͼ1.00 D, myopic anisometropia Ͼ3.00 D, orthogonal astigma
Refractive Errors and Amblyopia in Iranian Children Entering School 365
Optometry and Vision Science, Vol. 86, No. 4, April 2009

3. tism over 1.50 D, and oblique astigmatism over 1.00 D may lead to
amblyopia if not corrected.18
These degrees of refractive errors
were considered as significant or potentially amblyogenic in our
study.
Asymmetric alignment or abnormal cover test results, in addi-
tion to stereopsis Ͻ120 arc sec, were used as the definition for
strabismus (tropia).6
The 95% CI for prevalence estimates are
reported with an assumption of normal distribution.
RESULTS
During July to September 2005, a total of 2882 6-year-old
children (50.8% boys, 49.2% girls) referred to school entry health
checkup centers; 902 of them (476 boys, 426 girls) were invited to
have eye examinations. Eight hundred twenty-seven children (445
boys, 382 girls) responded, 12 of which (9 boys, 3 girls) were
excluded. The final study sample consisted of 436 boys (53.5%)
and 379 girls (46.5%); 524 children (64.7%) from urban and 291
(35.7%) from rural areas.
When matched against the name list from public health centers,
there were 45 children who did not show up for school entry health
checkups. Further enquiry from these centers revealed that 25
children had immigrated and another seven were not identified,
probably for the same reason. The remaining 13 were mentally
disabled children.
Response Rate
Eight hundred twenty-seven (91.7%) of the invited children
responded, 815 (98.5%) of which met the inclusion criteria. Table
1 shows reasons why children did not enter or were excluded from
the study.
Prevalence of Significant Reduced Visual Acuity
and Amblyopia
The UCVA was 6/12 or worse in one or both eyes of 29 children
(3.6%; 95% CI 2.3–4.9%). The BCVA was 6/12 or worse in one
or both eyes of six children (0.7%). Considering a difference of two
or more lines of BCVA between the two eyes as an additional
criterion, eight other cases were categorized as amblyopic, bringing
the total to 14 children (1.7%; 95% CI 0.7–2.6%). Unilateral
amblyopia was detected in 10 children (71.4%) with equal fre-
quency in both eyes. Four children (28.6%) had bilateral amblyo-
pia. Results of visual acuity tests are summarized in Table 2.
Prevalence of Refractive Errors
One third of the studied children had some type and level of
refractive error (Table 3). Of the 815 examined children, 46
TABLE 1.
Frequency of different reasons children did not participate
or were excluded from the study
Cause N (%) of total invited
Guardian’s unwillingness 75 (8.3)
Child’s uncooperativeness 2 (0.2)
Mental retardation 6 (0.7)
Organic blindnessa
4 (0.4)
Total 87 (9.6)
a
Two cases of traumatic blindness, one case of congenital
cataract, and one case of systemic disease.
TABLE 2.
Distribution of corrected and uncorrected visual acuity
categories in the examined sample in terms of number,
percentage, and 95% CI
Visual acuity
n (%) ͓95% CI͔
Uncorrected Corrected
Both eyes
Ͼ6/12
786 (96.4) ͓95.1–97.7͔ 809 (99.3) ͓98.7–99.9͔
Only one eye
Ͼ6/12
9 (1.1) ͓0.4–1.8͔ 2 (0.2) ͓0.0–0.5͔
Both eyes
Յ6/12
20 (2.5) ͓1.4–3.6͔ 4 (0.5) ͓0.0–1.0͔
Total 815 (100) 815 (100)
TABLE 3.
Prevalence of refractive errors in the studied population
Refractive
error
Right eye,
n (%)
Left eye,
n (%)
Children, n (%)
͓95% CI͔
Hyperopia
Նϩ2.0 D
114 (14.0) 158 (19.4) 169 (20.7) ͓17.9–23.5͔
Myopia
ՅϪ0.5 D
13 (1.6) 9 (1.1) 14 (1.7) ͓0.8–2.6͔
Anisometropia
Ͼ1.0 D
18a
(2.2) ͓1.2–3.2͔
Astigmatism
Ն0.75 D
110 (13.5) 136 (16.7) 160 (19.6) ͓16.9–22.3͔
Any typeb
192 (23.6) 243 (29.8) 271 (33.3) ͓30.1–36.5͔
a
Fifteen cases with hyperopia Նϩ2.0 D in one or both eyes, 3
cases with myopia ՅϪ0.5 D in one or both eyes.
b
Includes those with one or more type of refractive error.
TABLE 4.
Prevalence of significant (potentially amblyogenic) refractive
errors in the studied population
Refractive
error
Right eye,
n (%)
Left eye,
n (%)
Children, n (%)
͓95% CI͔
Hyperopia Նϩ3.5 D 11 (1.3) 14 (1.7) 17 (2.1) ͓1.1–3.1͔
Myopia ՅϪ3.0 D 1 (0.1) 1 (0.1) 1 (0.1) ͓0.1–0.3͔
Hyperopic anisometropia
Ͼ1.0 D
— — 7a
(0.9) ͓3.5–6.5͔
Myopic anisometropia
Ͼ3.0 D
— — 0 (0)
Astigmatism (orthogonal
Ն1.5 D, oblique
Ն1.0 D)
33 (4.0) 34 (4.2) 41 (5.0) ͓3.5–6.5͔
Any typeb
36 (4.4) 37 (4.5) 46 (5.6) ͓4.1–7.1͔
a
Four cases with hyperopia Նϩ3.5 D in one or both eyes.
b
Includes those with one or more type of refractive error.
366 Refractive Errors and Amblyopia in Iranian Children Entering School
Optometry and Vision Science, Vol. 86, No. 4, April 2009

4. (5.6%) had significant refractive errors and were at risk of devel-
oping amblyopia (Table 4).
Prevalence of Strabismus
Manifest strabismus was observed in 10 children (1.2%; 95%
CI 0.5–1.9%). Using the abnormal cover test result, plus a TNO
Ͻ120 arc sec as another criterion, did not add any cases of tropia to
those of manifest strabismus. Of 10 children with manifest strabis-
mus, 5 (50%) had esotropia, 4 (40%) had alternate exotropia, and
1 (10%) had hypertropia. As there were four children who had
strabismus and potentially amblyogenic refractive errors, a total of
52 children (6.4%; 95% CI 4.7–8.1%) were at risk of amblyopia
related to these two causes.
Causes of Visual Impairment
The causes of decreased UCVA found in the studied population
are listed in Table 5. The cause of amblyopia was anisometropia in
4 children (28.6%), strabismus in 3 (21.4%), mixed in 2 (14.3%),
isoametropia in 4 (28.6%), and undetermined in 1 (7.1%).
Screening and Treatment History
Of all the participants, 695 (85.3%) had completed a preschool
amblyopia screening. Only 4 (15.2%) of the 32 subjects who had
been wearing a refractive correction had developed amblyopia,
compared with 4 (40.0%) of 10 cases who had not worn an appro-
priate refractive correction. Eight of the 10 children who had stra-
bismus with or without significant refractive error reported current
or previous occlusion therapy and/or glass wearing; 4 (50.0%) of
them had amblyopia. The other four subjects were affected by
alternate exotropia and did not develop amblyopia. These findings
are summarized in Table 6.
DISCUSSION
In the present study, the prevalence rates of common visual
problems of childhood (including amblyopia, refractive errors, and
strabismus) were assessed among a population of 6-year-old chil-
dren. A UCVA of 6/12 or worse was detected in one or both eyes
of 3.6%. Compared with the 9.0 and 31.3% reported in 5 to
15-year-old children in India10
and China,9
respectively, vision
impairment is relatively uncommon in our population. Our find-
ings are close to the 2.7% reported in South Africa8
(5–15-year-old
children) and 4.1% found in 6-year-old children in Australia.11
Amblyopia and refractive errors are common causes of vision
impairment. In the present study, significant reduced visual acuity
was due to refractive errors and amblyopia in 62.1 and 37.9% of
cases, respectively.
One third of the study subjects had some type of refractive error;
hyperopia (Նϩ2.00 D) and astigmatism (Ն0.75 D) were the most
common with a prevalence of 20.7 and 19.6%, respectively. About
1.7% of children were myopic (ՆϪ0.50 D). A bilateral difference
of 1.00 D or more was found in 10% of hyperopic or myopic
children. Hyperopia seems to be more prevalent among 6-year olds
in Iran than reported by other studies, whereas myopia is less
frequent compared with countries experiencing a myopic epidemic
(Table 7). In our study, astigmatism proved to be more common
than that in South Africa,8
India,10
and Australia21
but less com-
TABLE 5.
Causes of decreased uncorrected visual acuity (Յ6/12) in
the studied population
Right eye,
n (%)
Left eye,
n (%)
No. children
(%)
Amblyopia 6 (26.1) 9 (34.6) 11 (37.5)
Refractive errors without
amblyopia
17 (73.9) 17 (65.4) 18 (62.1)
Strabismus without
amblyopia or refractive
errors
0 (0.0) 0 (0.0) 0 (0.0)
Total 23 (100) 26 (100) 29 (100)
TABLE 6.
Frequency of amblyopia in participants with strabismus
and/or significant refractive error by treatment
Type of impairment
Treatment
history
Amblyopia at the
time of study, n (%)
Yes No
Significant refractive error Yes 4 (15.2) 28 (84.8)
No 4 (40.0) 6 (60.0)
Strabismus Ϯ refractive
error
Yes 4 (50.0) 4 (50.0)
No 1 (100) 0 (0)
Total Yes 8 (20.0) 32 (80.0)
No 5 (41.7) 7 (58.3)
TABLE 7.
Prevalence of hyperopia and myopia in school-entry age children with cycloplegic refraction reported from selected
population-based studies
Study Country
Sample
size
Age range
(yr)
Hyperopia
definition
Myopia prevalence
(%) Definition
Prevalence
(%)
Barnes et al.19
Great Britain 7600 7 Ͼ2.00 D 5.9 ՅϪ1.00 D 1.1
Preslan et al.20
United States 680 4–7 Ͼ4.00 D 0.9 ϽϪ0.5 D 3.1
Naidoo et al.8
South Africa 458 6 Ն2.00 D 3.8 ՅϪ0.5 D 1.6
He et al.9
China 295 6 Ն2.00 D 14.6 ՅϪ0.5 D 2.7
Murthy et al.10
India 494 6 Ն2.00 D 13.0 ՅϪ0.5 D 5.9
Present study Iran 815 6 Ն2.00 D 20.7 ՅϪ0.5 D 1.7
Refractive Errors and Amblyopia in Iranian Children Entering School 367
Optometry and Vision Science, Vol. 86, No. 4, April 2009

5. mon than in China9
(Table 8). However, over 70% of cases had
mild forms (0.75 D), and the prevalence of Ն1.00 D astigmatism
was similar to that reported by Huynh et al.21
for 6–7-year-old
children in Australia.
Of the examined children, 1.2% had manifest strabismus. This
is lower than the 2.3% (3.4% if clinically significant latent devia-
tions included) described in a population-based cohort of 7-year-
old children in the United Kingdom.23
The prevalence also differs
from that in China9
and India,10
where tropia with near fixation
was present in 1.9 and 0.53% of school-aged children, respectively,
but is more comparable with the 1.3% found in South Africa.8
Mild forms of childhood visual problems do not lead to ambly-
opia and often need no correction. Using conservative criteria to
define amblyogenic risk factors (see Methods section), 6.4% of our
study subjects were considered to have risk factors for amblyopia
including refractive error (81%), strabismus (11%), or both (8%).
Of those with significant, potentially amblyogenic refractive er-
rors, 89% had significant astigmatism with or without hyperopia.
In the present study, the prevalence of amblyopia was 1.7%
using the BCVA Յ6/12 or a difference of two or more lines of
BCVA between the two eyes as the definition. Therefore, ambly-
opia seems to be more prevalent in our population than that in the
United Kingdom24
(0.7% of children who had preschool screen-
ing) and Australia (0.7%).25
However, the definition criteria were
more limited in these two studies; BCVA Ͻ6/12 in the first and
BCVA Ͻ6/12 plus two lines difference between two eyes in the
latter. Using the sole criterion of BCVA Յ 6/12, only 0.7% of our
study subjects would be amblyopic. The finding that the rate of
children considered to be potentially at risk for developing ambly-
opia (6.4%) was higher than those with a diagnosis of amblyopia
(1.7%) is not unexpected: (1) individuals seem to vary in their
susceptibility to developing amblyopia. About 58.3% of untreated
children with significant visual impairments had not developed
amblyopia. (2) The commencement and effect of treatment on
children at risk of amblyopia might have precluded its develop-
ment. Eight percent of treated children with significant visual con-
ditions were not amblyopic.
Health checkups are obligatory for all Iranian children before
enrolling in school. So, it would be expected that nearly all 6-year-
old children refer to school entry health checkup centers. Collect-
ing data from all urban and rural public health centers implied
that few children had not referred to school entry health
checkup centers, mainly because they had mental handicap.
These facts indicate that the studied sample was selected from
the general population.
The random selection of samples guaranteed the generalizability
of results. Although examinations were done at easily accessible
centers, and health center nurses and technicians were employed to
encourage family cooperation, 75 families did not want their chil-
dren to participate in the study. Potential reasons of their refusal
were that they believed the examinations were redundant, they
were informed of their children’s visual status – whether normal or
with refractive errors – and they had concerns regarding cyclople-
gic eye drops. The apparent difference of participation in the study
between boys and girls was not statistically significant (p Ͻ0.05).
As the rate of absentees was not outstanding (8.3%), a significant
effect on the accuracy of results is not assumed.
CONCLUSIONS
A considerable proportion of the studied 6-year-old children
had some degree of refractive error and strabismus, which if un-
treated, may impair their future learning capability and educa-
tional potential. Even 1.7% of the examined children had been
affected with amblyopia. Assuming a similar situation for the
whole population would be acceptable. The high rate of hyperopia
and astigmatism in the studied population needs special attention.
Adequate eye care services should be provided for Iranian school-
entry age children.
ACKNOWLEDGMENTS
This study was supported by Tehran University of Medical Sciences and
Shahrood Welfare Office.
Received November 22, 2007; accepted October 14, 2008.
REFERENCES
1. Webber AL, Wood J. Amblyopia: prevalence, natural history, func-
tional effects and treatment. Clin Exp Optom 2005;88:365–75.
2. Simons K, Preslan M. Natural history of amblyopia untreated owing
to lack of compliance. Br J Ophthalmol 1999;83:582–7.
3. Woodruff G, Hiscox F, Thompson JR, Smith LK. The presentation
of children with amblyopia. Eye 1994;8(Pt 6):623–6.
4. Tongue AC, Grin TR. Refractive errors and glasses for children. In:
TABLE 8.
Prevalence of astigmatism in school age children from selected population-based studies
Study Country
Sample
size
Age range
(Y) Refraction method
Prevalence (%)
(definition: Ն0.75 D)
Prevalence (%)
(definition: Ն1.00 D)
Huynh et al.22
Australia 1765 6–7 Autorefraction 10.3 4.8
Kleinstein et al.22
United States 680 5–17 Autorefraction NA 28.4
Naidoo et al.8
South Africa 4890 5–15 Autorefraction 14.6 NA
Retinoscopy 9.2 NA
He et al.9
China 4364 5–15 Autorefraction 42.7 NA
Retinoscopy 33.6 NA
Murthy et al.10
India 6447 5–15 Autorefraction 14.6 NA
Retinoscopy 7.0 NA
Present study Iran 815 6 Retinoscopy 19.6 5.0
NA, not available.
368 Refractive Errors and Amblyopia in Iranian Children Entering School
Optometry and Vision Science, Vol. 86, No. 4, April 2009

6. Tongue AC, Grin TR, eds. Decision Making in Pediatric Ophthal-
mology. St. Louis: B. C. Decker; 1993:186–7.
5. Von Noorden GK. Examination of the patient—IV In: Burian and
Von Noorden’s Binocular Vision and Ocular Motility: Theory and
Management of Strabismus, 4th ed. St Lovis: Mosby; 1990:249–51.
6. Logan NS, Gilmartin B. School vision screening, ages 5–16 years: the
evidence-base for content, provision and efficacy. Ophthal Physiol
Opt 2004;24:481–92.
7. Negrel AD, Maul E, Pokharel GP, Zhao J, Ellwein LB. Refractive
error study in children: sampling and measurement methods for a
multi-country survey. Am J Ophthalmol 2000;129:421–6.
8. Naidoo KS, Raghunandan A, Mashige KP, Govender P, Holden BA,
Pokharel GP, Ellwein LB. Refractive error and visual impairment in
African children in South Africa. Invest Ophthalmol Vis Sci 2003;
44:3764–70.
9. He M, Zeng J, Liu Y, Xu J, Pokharel GP, Ellwein LB. Refractive error
and visual impairment in urban children in southern China. Invest
Ophthalmol Vis Sci 2004;45:793–9.
10. Murthy GV, Gupta SK, Ellwein LB, Munoz SR, Pokharel GP, Sanga
L, Bachani D. Refractive error in children in an urban population in
New Delhi. Invest Ophthalmol Vis Sci 2002;43:623–31.
11. Robaei D, Rose K, Ojaimi E, Kifley A, Huynh S, Mitchell P. Visual
acuity and the causes of visual loss in a population-based sample of
6-year-old Australian children. Ophthalmology 2005;112:1275–82.
12. Hatamizadeh N. National program on amblyopia prevention in Is-
lamic Republic of Iran. Iranian Rehab J 2004;1:16–9.
13. Rosenfield R. Accommodation. In: Zadnik K, ed. The Ocular
Examination: Measurements and Findings. Philadelphia: W. B.
Saunders; 1997:87–121.
14. Kemper AR, Margolis PA, Downs SM, Bordley WC. A systematic
review of vision screening tests for the detection of amblyopia. Pedi-
atrics 1999;104:1220–2.
15. Griffin JR. Binocular Anomalies: Diagnosis and Vision Therapy, 4th
ed. Boston: Butterworth-Heinemann; 2002.
16. Moore BD. Eye Care for Infants and Young Children. Boston:
Butterworth-Heinemann; 1997.
17. Day S. Normal and abnormal visual development. In: Taylor D, ed.
Pediatric Ophthalmology. London: Blackwell Scientific Publications;
1990:7–20.
18. Donahue SP, Arnold RW, Ruben JB. Preschool vision screening:
what should we be detecting and how should we report it? Uniform
guidelines for reporting results of preschool vision screening studies.
J AAPOS 2003;7:314–6.
19. Barnes M, Williams C, Lumb R, Harrad RA, Sparrow JM, Harvey I,
and the ALSPAC study team. The prevalence of refractive errors in a
UK birth cohort of children aged 7 years. Invest Ophthalmol Vis Sci
2001;42:S389.
20. Preslan MW, Novak A. Baltimore Vision Screening Project. Oph-
thalmology 1996;103:105–9.
21. Huynh SC, Kifley A, Rose KA, Morgan I, Heller GZ, Mitchell P.
Astigmatism and its components in 6-year-old children. Invest Oph-
thalmol Vis Sci 2006;47:55–64.
22. Kleinstein RN, Jones LA, Hullett S, Kwon S, Lee RJ, Friedman NE,
Manny RE, Mutti DO, Yu JA, Zadnik K. Refractive error and eth-
nicity in children. Arch Ophthalmol 2003;121:1141–7.
23. Williams C, Northstone K, Howard M, Harvey I, Harrad RA, Spar-
row JM. Prevalence and risk factors for common vision problems in
children: data from the ALSPAC study. Br J Ophthalmol 2008;92:
959–64.
24. Williams C, Northstone K, Harrad RA, Sparrow JM, Harvey I. Am-
blyopia treatment outcomes after preschool screening v school entry
screening: observational data from a prospective cohort study. Br J
Ophthalmol 2003;87:988–93.
25. Robaei D, Rose KA, Ojaimi E, Kifley A, Martin FJ, Mitchell P.
Causes and associations of amblyopia in a population-based sample of
6-year-old Australian children. Arch Ophthalmol 2006;124:878–84.
Akbar Fotouhi
Epidemiology and Biostatistics Department
School of Public Health
Tehran University of Medical Sciences
Postal Box: 14155-6446
Tehran, Iran
e-mail: afotouhi@tums.ac.ir
Refractive Errors and Amblyopia in Iranian Children Entering School 369
Optometry and Vision Science, Vol. 86, No. 4, April 2009