Refractive errors and_amblyopia_in_children.12

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ORIGINAL ARTICLE

Refractive Errors and Amblyopia in ChildrenEntering School: Shahrood, Iran

Payman Jamali*, Akbar Fotouhi†, Hassan Hashemi*, Masud Younesian†, and Alireza Jafari‡

ABSTRACTPurpose. 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 wererandomly 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 ofamblyopia was based on a best-corrected visual acuity of 6/12 or less in one or both eyes, or a bilateral difference of atleast two best-corrected visual acuity lines.Results. A total of 902 children were invited for optometry examinations, among which 827 (91.7%) responded and 815children (98.5%) were included in the study. The prevalence of significantly reduced visual acuity (uncorrected VA �6/12in either eye) and amblyopia was 3.6 and 1.7%, respectively. The prevalence of hyperopia (�2.00 D or worse), myopia(�0.50 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 ��3.50 D, myopia ��3.00 D, astigmatism �1.50 D inthe orthogonal meridian or �1.00 D in the oblique meridian, or anisometropia (hyperopic �1.00 D, myopic �3.00 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% hadsignificant refractive errors, 11% had strabismus, and 8% had both.Conclusion. A considerable proportion of 6-year-old children have strabismus and/or significant, potentially amblyogenicrefractive 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 preschoolchildren.(Optom Vis Sci 2009;86:364–369)

Key Words: amblyopia, amblyogenic refractive errors, strabismus

Visual acuity and stereopsis develop during the first years oflife. Distorted visual acuity, as a result of refractive errors orstrabismus, 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, andcould interfere with the development of the visual pathways in thebrain 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 visualacuity, namely amblyopia.1–3

Unlike adults, who have different visual needs, young childrencan function normally with uncorrected mild to moderate myopiaor astigmatism, and they can overcome a fairly large amount ofhyperopia through accommodation.4 Children with strabismusstrongly favor one eye for fixation, so most of them report nocomplaint.5 To detect these types of visual impairment beforeentering school and prevent future complications, adequate eyecare services should be provided to perform proper diagnostic testsand therapeutic measures.

The prevalence of refractive errors, strabismus, and amblyopiareported in the literature has been shown to vary dependent on thestudy population, the definition of the disease or disorder, and onthe measurement methods.6 In the last decade, several population-based surveys of visual impairment in school-aged children were

*MD†MD, PhD‡MScShahrood 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 ofMedical 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. 364–369OPTOMETRY AND VISION SCIENCECopyright © 2009 American Academy of Optometry

Optometry and Vision Science, Vol. 86, No. 4, April 2009

conducted, using similar definitions and measurement meth-ods.7–11 None of the studied populations have the same racial orsocioeconomic composition as that in Iran. Nationwide preschoolvision screening has been implemented in Iran since 1998. Accord-ing to one of the most recent published reports,12 42% of the targetpopulation had not attended screening, and 75% of the childrensuspected of being visually impaired had not attended optometricexaminations. These low uptake rates have resulted in limited gen-eralizability of the findings.

The present survey was conducted in light of the paucity of thenecessary data concerning refractive errors and strabismus to im-prove the setting of eye care services in Iran. Regardless of theirvisual acuity and treatment history, refraction and stereopsis testswere 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 amblyopiain 6-year-old children was determined through a cross-sectionalpopulation-based study.

Study Population

The study targeted children residing in Shahrood who wereborn between September 1998 and August 1999 and were broughtto school-entry health checkup centers during summer 2005. Chil-dren with mental retardation were excluded. Considering previousestimates of the frequency of visual acuity �6/9 at this age (about5%),12 811 children had to be examined to determine the 95% CIof the prevalence with an accuracy of 1.5%. Assuming an overallresponse rate of 90%, it was estimated that a sample size of 902children needed to be recruited in Shahrood, which is a city located400 km from Tehran and had an estimated population of 235,000in 2005.

Every summer, 6-year-old children all over the county undergoschool-entry health checkups at selected schools and health carecenters of urban and rural areas. Standard assessment includesvisual acuity measurement along with mental, motor, and hearingevaluation. During July to September 2005, a total of 2882 chil-dren referred to these centers in Shahrood, 902 of which wereenrolled in this study on a random basis.

Field Operations

Although few families seemed to keep their children out ofschool, we collected the population data from all rural and urbanpublic health centers to identify eligible children who might havebeen missed. To ensure uniformity, names were recorded fromnewborn vaccination charts registered during September 1998 toAugust 1999. Those who had not referred to school entry healthcheckup 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 byan experienced nurse for ptosis, corneal opacities, and cataract and

were excluded if any of these conditions were present.13,14 Theeligible children underwent optometry examinations includingobservation 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, thenthe left eye, each time occluding the fellow eye. Cover test wasperformed while the child was asked to look at a 6/9 visual acuitysymbol, once 40 cm and then 6 m away, occluding one eye at atime, observing the uncovered eye to detect any correcting move-ment. The degree of tropia was measured using corneal light reflexand 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 andcycloplegic refractions were performed in a dim-lit room usingstreak retinoscope (Heine, Germany, � 200) with the examiner ata distance of 66 cm. Cases with an uncorrected visual acuity(UCVA) �6/6 were tested for their best-corrected visual acuity(BCVA) after subjective refraction. Cycloplegia was induced withtwo 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 firstdrop. Parents were asked whether their children had been exam-ined by the annual national preschool (4–6 years) amblyopiascreening 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 eyedrops, 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 testingpreschool children were selected to do the examinations. They hada training course to familiarize themselves with the study protocoland measurement methods. One experienced ophthalmologist ob-served them throughout the course. The clinical examination dataforms were reviewed for completeness and accuracy before beingentered.

UCVA of 6/12 or less in either eye was considered as significantreduced visual acuity. Amblyopia was defined as a BCVA equal or�6/12 in either eye, or a difference of two or more lines of BCVAbetween the two eyes without an organic cause.15 Children wereconsidered to have refractive error if hyperopia ��2.00 D, myo-pia ��0.50 D, astigmatism �0.75 D, or anisometropia �1.00 Dwere reported in one or both eyes.7 Young children with mild tomoderate refractive errors can function normally and do not needto wear glasses. Higher degrees of refractive errors are more likely tobe associated with amblyopia but the definitive degree to considerthem amblyogenic is not clear cut.4,16–18 Hyperopia more than�3.50 D, myopia more than �3.00 D, hyperopic anisometropia�1.00 D, myopic anisometropia �3.00 D, orthogonal astigma

Refractive Errors and Amblyopia in Iranian Children Entering School 365


tism over 1.50 D, and oblique astigmatism over 1.00 D may lead toamblyopia if not corrected.18 These degrees of refractive errorswere considered as significant or potentially amblyogenic in ourstudy.

Asymmetric alignment or abnormal cover test results, in addi-tion to stereopsis �120 arc sec, were used as the definition forstrabismus (tropia).6 The 95% CI for prevalence estimates arereported with an assumption of normal distribution.

RESULTS

During July to September 2005, a total of 2882 6-year-oldchildren (50.8% boys, 49.2% girls) referred to school entry healthcheckup centers; 902 of them (476 boys, 426 girls) were invited tohave eye examinations. Eight hundred twenty-seven children (445boys, 382 girls) responded, 12 of which (9 boys, 3 girls) wereexcluded. 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 healthcheckups. Further enquiry from these centers revealed that 25children had immigrated and another seven were not identified,probably for the same reason. The remaining 13 were mentallydisabled children.

Response Rate

Eight hundred twenty-seven (91.7%) of the invited childrenresponded, 815 (98.5%) of which met the inclusion criteria. Table

1 shows reasons why children did not enter or were excluded fromthe study.

Prevalence of Significant Reduced Visual Acuityand 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 oneor both eyes of six children (0.7%). Considering a difference of twoor more lines of BCVA between the two eyes as an additionalcriterion, eight other cases were categorized as amblyopic, bringingthe total to 14 children (1.7%; 95% CI 0.7–2.6%). Unilateralamblyopia 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 ofrefractive error (Table 3). Of the 815 examined children, 46

TABLE 1.Frequency of different reasons children did not participateor 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)

aTwo cases of traumatic blindness, one case of congenitalcataract, and one case of systemic disease.

TABLE 2.Distribution of corrected and uncorrected visual acuitycategories in the examined sample in terms of number,percentage, and 95% CI

Visual acuity

n (%) �95% CI�

Uncorrected Corrected

Both eyes�6/12

786 (96.4) �95.1–97.7� 809 (99.3) �98.7–99.9�

Only one eye�6/12

9 (1.1) �0.4–1.8� 2 (0.2) �0.0–0.5�

Both eyes�6/12

20 (2.5) �1.4–3.6� 4 (0.5) �0.0–1.0�

Total 815 (100) 815 (100)

TABLE 3.Prevalence of refractive errors in the studied population

Refractiveerror

Right eye,n (%)

Left eye,n (%)

Children, n (%)�95% CI�

Hyperopia��2.0 D

114 (14.0) 158 (19.4) 169 (20.7) �17.9–23.5�

Myopia��0.5 D

13 (1.6) 9 (1.1) 14 (1.7) �0.8–2.6�

Anisometropia�1.0 D

18a (2.2) �1.2–3.2�

Astigmatism�0.75 D

110 (13.5) 136 (16.7) 160 (19.6) �16.9–22.3�

Any typeb 192 (23.6) 243 (29.8) 271 (33.3) �30.1–36.5�

aFifteen cases with hyperopia ��2.0 D in one or both eyes, 3cases with myopia ��0.5 D in one or both eyes.

bIncludes those with one or more type of refractive error.

TABLE 4.Prevalence of significant (potentially amblyogenic) refractiveerrors in the studied population

Refractiveerror

Right eye,n (%)

Left eye,n (%)

Children, n (%)�95% CI�

Hyperopia ��3.5 D 11 (1.3) 14 (1.7) 17 (2.1) �1.1–3.1�Myopia ��3.0 D 1 (0.1) 1 (0.1) 1 (0.1) �0.1–0.3�Hyperopic anisometropia

�1.0 D— — 7a (0.9) �3.5–6.5�

Myopic anisometropia�3.0 D

— — 0 (0)

Astigmatism (orthogonal�1.5 D, oblique�1.0 D)

33 (4.0) 34 (4.2) 41 (5.0) �3.5–6.5�

Any typeb 36 (4.4) 37 (4.5) 46 (5.6) �4.1–7.1�

aFour cases with hyperopia ��3.5 D in one or both eyes.bIncludes those with one or more type of refractive error.

366 Refractive Errors and Amblyopia in Iranian Children Entering School


(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�120 arc sec as another criterion, did not add any cases of tropia tothose of manifest strabismus. Of 10 children with manifest strabis-mus, 5 (50%) had esotropia, 4 (40%) had alternate exotropia, and1 (10%) had hypertropia. As there were four children who hadstrabismus and potentially amblyogenic refractive errors, a total of52 children (6.4%; 95% CI 4.7–8.1%) were at risk of amblyopiarelated to these two causes.

Causes of Visual Impairment

The causes of decreased UCVA found in the studied populationare listed in Table 5. The cause of amblyopia was anisometropia in4 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 preschoolamblyopia screening. Only 4 (15.2%) of the 32 subjects who hadbeen 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 currentor previous occlusion therapy and/or glass wearing; 4 (50.0%) ofthem had amblyopia. The other four subjects were affected byalternate exotropia and did not develop amblyopia. These findingsare summarized in Table 6.

DISCUSSION

In the present study, the prevalence rates of common visualproblems of childhood (including amblyopia, refractive errors, andstrabismus) were assessed among a population of 6-year-old chil-dren. A UCVA of 6/12 or worse was detected in one or both eyesof 3.6%. Compared with the 9.0 and 31.3% reported in 5 to15-year-old children in India10 and China,9 respectively, visionimpairment is relatively uncommon in our population. Our find-ings are close to the 2.7% reported in South Africa8 (5–15-year-oldchildren) and 4.1% found in 6-year-old children in Australia.11

Amblyopia and refractive errors are common causes of visionimpairment. In the present study, significant reduced visual acuitywas due to refractive errors and amblyopia in 62.1 and 37.9% ofcases, respectively.

One third of the study subjects had some type of refractive error;hyperopia (��2.00 D) and astigmatism (�0.75 D) were the mostcommon with a prevalence of 20.7 and 19.6%, respectively. About1.7% of children were myopic (��0.50 D). A bilateral differenceof 1.00 D or more was found in 10% of hyperopic or myopicchildren. Hyperopia seems to be more prevalent among 6-year oldsin Iran than reported by other studies, whereas myopia is lessfrequent compared with countries experiencing a myopic epidemic(Table 7). In our study, astigmatism proved to be more commonthan that in South Africa,8 India,10 and Australia21 but less com-

TABLE 5.Causes of decreased uncorrected visual acuity (�6/12) inthe studied population

Right eye,n (%)

Left eye,n (%)

No. children(%)

Amblyopia 6 (26.1) 9 (34.6) 11 (37.5)Refractive errors without

amblyopia17 (73.9) 17 (65.4) 18 (62.1)

Strabismus withoutamblyopia or refractiveerrors

0 (0.0) 0 (0.0) 0 (0.0)

Total 23 (100) 26 (100) 29 (100)

TABLE 6.Frequency of amblyopia in participants with strabismusand/or significant refractive error by treatment

Type of impairmentTreatment

history

Amblyopia at thetime of study, n (%)

Yes No

Significant refractive error Yes 4 (15.2) 28 (84.8)No 4 (40.0) 6 (60.0)

Strabismus � refractiveerror

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 selectedpopulation-based studies

Study CountrySample

sizeAge range

(yr)Hyperopiadefinition

Myopia prevalence(%) Definition

Prevalence(%)

Barnes et al.19 Great Britain 7600 7 �2.00 D 5.9 ��1.00 D 1.1Preslan et al.20 United States 680 4–7 �4.00 D 0.9 ��0.5 D 3.1Naidoo et al.8 South Africa 458 6 �2.00 D 3.8 ��0.5 D 1.6He et al.9 China 295 6 �2.00 D 14.6 ��0.5 D 2.7Murthy et al.10 India 494 6 �2.00 D 13.0 ��0.5 D 5.9Present study Iran 815 6 �2.00 D 20.7 ��0.5 D 1.7



mon than in China9 (Table 8). However, over 70% of cases hadmild forms (0.75 D), and the prevalence of �1.00 D astigmatismwas similar to that reported by Huynh et al.21 for 6–7-year-oldchildren in Australia.

Of the examined children, 1.2% had manifest strabismus. Thisis 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 differsfrom that in China9 and India,10 where tropia with near fixationwas 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 todefine amblyogenic risk factors (see Methods section), 6.4% of ourstudy subjects were considered to have risk factors for amblyopiaincluding 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 �6/12 or a difference of two or more lines ofBCVA between the two eyes as the definition. Therefore, ambly-opia seems to be more prevalent in our population than that in theUnited Kingdom24 (0.7% of children who had preschool screen-ing) and Australia (0.7%).25 However, the definition criteria weremore limited in these two studies; BCVA �6/12 in the first andBCVA �6/12 plus two lines difference between two eyes in thelatter. Using the sole criterion of BCVA � 6/12, only 0.7% of ourstudy subjects would be amblyopic. The finding that the rate ofchildren 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 theirsusceptibility to developing amblyopia. About 58.3% of untreatedchildren with significant visual impairments had not developedamblyopia. (2) The commencement and effect of treatment onchildren 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 beforeenrolling 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 impliedthat 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 fromthe general population.

The random selection of samples guaranteed the generalizabilityof results. Although examinations were done at easily accessiblecenters, and health center nurses and technicians were employed toencourage family cooperation, 75 families did not want their chil-dren to participate in the study. Potential reasons of their refusalwere that they believed the examinations were redundant, theywere informed of their children’s visual status – whether normal orwith refractive errors – and they had concerns regarding cyclople-gic eye drops. The apparent difference of participation in the studybetween boys and girls was not statistically significant (p �0.05).As the rate of absentees was not outstanding (8.3%), a significanteffect on the accuracy of results is not assumed.

CONCLUSIONS

A considerable proportion of the studied 6-year-old childrenhad 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 beenaffected with amblyopia. Assuming a similar situation for thewhole population would be acceptable. The high rate of hyperopiaand 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 andShahrood 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 owingto lack of compliance. Br J Ophthalmol 1999;83:582–7.

3. Woodruff G, Hiscox F, Thompson JR, Smith LK. The presentationof 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 CountrySample

sizeAge range

(Y) Refraction methodPrevalence (%)

(definition: �0.75 D)Prevalence (%)

(definition: �1.00 D)

Huynh et al.22 Australia 1765 6–7 Autorefraction 10.3 4.8Kleinstein et al.22 United States 680 5–17 Autorefraction NA 28.4Naidoo et al.8 South Africa 4890 5–15 Autorefraction 14.6 NA

Retinoscopy 9.2 NAHe et al.9 China 4364 5–15 Autorefraction 42.7 NA

Retinoscopy 33.6 NAMurthy et al.10 India 6447 5–15 Autorefraction 14.6 NA

Retinoscopy 7.0 NAPresent study Iran 815 6 Retinoscopy 19.6 5.0

NA, not available.

368 Refractive Errors and Amblyopia in Iranian Children Entering School


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 andVon Noorden’s Binocular Vision and Ocular Motility: Theory andManagement of Strabismus, 4th ed. St Lovis: Mosby; 1990:249–51.

6. Logan NS, Gilmartin B. School vision screening, ages 5–16 years: theevidence-base for content, provision and efficacy. Ophthal PhysiolOpt 2004;24:481–92.

7. Negrel AD, Maul E, Pokharel GP, Zhao J, Ellwein LB. Refractiveerror study in children: sampling and measurement methods for amulti-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 inAfrican 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 errorand visual impairment in urban children in southern China. InvestOphthalmol Vis Sci 2004;45:793–9.

10. Murthy GV, Gupta SK, Ellwein LB, Munoz SR, Pokharel GP, SangaL, Bachani D. Refractive error in children in an urban population inNew Delhi. Invest Ophthalmol Vis Sci 2002;43:623–31.

11. Robaei D, Rose K, Ojaimi E, Kifley A, Huynh S, Mitchell P. Visualacuity and the causes of visual loss in a population-based sample of6-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 OcularExamination: Measurements and Findings. Philadelphia: W. B.Saunders; 1997:87–121.

14. Kemper AR, Margolis PA, Downs SM, Bordley WC. A systematicreview of vision screening tests for the detection of amblyopia. Pedi-atrics 1999;104:1220–2.

15. Griffin JR. Binocular Anomalies: Diagnosis and Vision Therapy, 4thed. 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? Uniformguidelines 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 aUK birth cohort of children aged 7 years. Invest Ophthalmol Vis Sci2001;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 inchildren: 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 entryscreening: observational data from a prospective cohort study. Br JOphthalmol 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 of6-year-old Australian children. Arch Ophthalmol 2006;124:878–84.

Akbar FotouhiEpidemiology and Biostatistics Department

School of Public HealthTehran University of Medical Sciences

Postal Box: 14155-6446Tehran, Iran

e-mail: [email protected]



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