Little evidence for an epidemic of myopia in Australian primary school children over the last 30 years
© Junghans and Crewther; licensee BioMed Central Ltd. 2005
Received: 04 June 2004
Accepted: 11 February 2005
Published: 11 February 2005
Recently reported prevalences of myopia in primary school children vary greatly in different regions of the world. This study aimed to estimate the prevalence of refractive errors in an unselected urban population of young primary school children in eastern Sydney, Australia, between 1998 and 2004, for comparison with our previously published data gathered using the same protocols and other Australian studies over the last 30 years.
Right eye refractive data from non-cycloplegic retinoscopy was analysed for 1,936 children aged 4 to 12 years who underwent a full eye examination whilst on a vision science excursion to the Vision Education Centre Clinic at the University of New South Wales. Myopia was defined as spherical equivalents equal to or less than -0.50 D, and hyperopia as spherical equivalents greater than +0.50 D.
The mean spherical equivalent decreased significantly (p < 0.0001) with age from +0.73 ± 0.1D (SE) at age 4 to +0.21 ± 0.11D at age 12 years. The proportion of children across all ages with myopia of -0.50D or more was 8.4%, ranging from 2.3% of 4 year olds to 14.7% of 12 year olds. Hyperopia greater than +0.50D was present in 38.4%. A 3-way ANOVA for cohort, age and gender of both the current and our previous data showed a significant main effect for age (p < 0.0001) but not for cohort (p = 0.134) or gender (p = 0.61).
Comparison of our new data with our early 1990s data and that from studies of over 8,000 Australian non-clinical rural and urban children in the 1970's and 1980's provided no evidence for the rapidly increasing prevalence of myopia described elsewhere in the world. In fact, the prevalence of myopia in Australian children continues to be significantly lower than that reported in Asia and North America despite changing demographics. This raises the issue of whether these results are a reflection of Australia's stable educational system and lifestyle over the last 30 years.
The prevalence of myopia is currently receiving worldwide attention as many recent studies report dramatic increases over the last 20 years [1, 2]. Myopia and its aetiology is an interesting example of the intertwining of 'nature and nurture' with both genetics and life-style environment as important issues . There is strong evidence indicating that genetic inheritance is a major contributor, both from the examination of prevalences across different racial backgrounds , from family pedigrees  and from twin studies . However, there is increasing evidence suggesting that high heritability does not preclude rapid environmentally-induced increases in prevalence , rather, inherited factors are likely to both drive the susceptibility and resistance to environmentally-induced myopia [6, 8].
Despite much research interest over the last half century, there have been surprisingly few well-designed epidemiological studies of refractive error with large numbers of randomly selected younger school children to form the basis of valid world wide comparisons of the earliest stages of development of myopia [3, 9, 10]. However, a group sponsored by the World Health Organisation in 2001 has devised a protocol to be used during studies of refractive error across different cultural and ethnic settings: the 'Refractive Error Study in Children' (RESC) .
In general, estimates of the prevalence of myopia have shown less increase in the Western world than in Asia, and less increase in rural than in urban populations [1, 10, 12–16]. Five very large studies across two decades and involving over 10,000 children in Taiwan are very important for understanding the changing prevalence of myopia in young Asian children (1.8% in 1986 rising to 12% in 1995 for 6 year olds, 40% rising to 56% for 12 year olds) . A similar change is also reflected in Singaporean studies of myopia in military conscripts aged 17 years (26% to 83% from the late 1970s to the late 1990s as reviewed by ), of whom notably 82% were Chinese .
It has often been suggested that myopia is more prevalent in ethnic Chinese (reviewed ), but only relatively recent studies compare the prevalence of myopia in young ethnic Chinese children living either in China and in other countries [1, 12, 15, 18–22]. For younger Chinese children aged around 5–7 years, the prevalence of myopia was found to range from under 5% in rural China [14, 23] to 24% in Chinese Malays  and 30% in urban Hong Kong [19, 22]. For older Chinese children aged 11–12 years, the prevalence ranged from 23% of rural Chinese[14, 23] to 40% in urban China, 47% of Chinese Malays  and 57% in urban Hong Kong . Japan has a similarly high prevalence of myopia in young school children estimated in recent times to be 43.5% of 12 year olds .
Prevalence of myopia in Australia school children.
Robbins & Bailey 
4, 8, 12
"suspected of having myopia"
5.6% 4 yrs
6.4% 12 yrs
Amigo, McCarthy & Pye 
7 to 12
"any tendency for myopia"
4 to 14
Representative government schools
6 to 11
Junghans et al 
14 government & church schools
4 to 12
2.0% 4 yrs
10.9% 12 yrs
In 2003 we reported the relative proportions of refractive errors in a large unselected primary school population of 2,535 children drawn from a very broad range of socio-economic backgrounds in Sydney, the largest city in Australia, in the early 1990s . The children attended fourteen primary schools and two preschools. As in the earlier studies, the proportion of children with myopia greater than -0.50 DS spherical equivalence, as determined by non-cycloplegic retinoscopy, was found to be low by world standards (1.0% of 4 year olds rising to 8.3% of 12 year olds). We have now analysed the prevalence of refractive error in a new similar group of 1,936 children unselected primary school children drawn generally from the same area as our first study.
The study design is a retrospective examination of records of the Vision Education Centre (VEC)  school vision screenings (so named because parents were not present to ratify history) conducted in the Clinic of the School of Optometry and Vision Science, UNSW. Approvals for the study and permission to approach schools were obtained from the Committee for Use of Humans in Research at the University of New South Wales (UNSW), Sydney, Australia. The protocols adhered to the tenets of the Declaration of Helsinki. Parents or guardians were provided with an information sheet and requested an outline of known symptoms. Signed consent was required prior to a child's participation.
Sampling and recruitment
Permission was obtained from the NSW Department of Education and the NSW Catholic Education Office to approach all schools in the eastern region of Sydney (some thirty coeducational primary schools) to send entire classes to the VEC. A flyer was sent describing the VEC science excursion and age-appropriate eye examination, inviting Years 1, 3 and 5 particularly to participate.
The group of 1,936 children examined came from the eastern suburbs along the southern beaches of Sydney, and may be thought of as randomly selected with little likelihood of bias to the data as individual classes were free to respond. Children were drawn from twelve government and non-government primary schools and one pre-school and attended the clinic only once. During the 1996 Australian Bureau of Statistics census 14,785 children aged 4 to 12 years were recorded in this region (Randwick and Waverley precincts of Eastern Sydney) who came from a very broad range of ethnic and socio-economic backgrounds present, where 37 different languages might be spoken in the home . This was reflected in the children attending VEC. Census data indicate approximately 9% of the children in the current study were likely to be of Asian origin , a figure supported by our interpretation of family name for each child . Participation in the eye examinations was typically well over 90% for each class, with teachers reporting non-participation to be predominantly due to illness on the day. Less than 3% of parents intentionally prevented participation, even if eye care had previously been sought. This particularly high participation rate was largely due to the attraction of a an age-appropriate student-centred hands-on science lesson about eyes and vision  delivered alongside the eye examination.
The comprehensive optometric examination by experienced paediatric practitioners included all age-appropriate tests meeting Australian Optometric Competency Standards, except that parents/guardians were not present to ratify history. Refractive error was determined by non-cycloplegic retinoscopy with optical fogging while the child maintained fixation on a distant non-accommodative (6 metre) target. In most cases refractive status was confirmed by subjective refraction. Other tests included letter visual acuity at 6 m and 33 cm, cover test for strabismus, motilities, saccades, pupil reactions, near point of convergence, heterophoria, stereopsis, accommodative facility, colour vision and ophthalmoscopy.
Justification of choice of testing procedures
Cycloplegic retinoscopy was not undertaken for many reasons including the fact that VEC studies started prior to the 2000 convention suggesting use of cycloplegic retinoscopy for studies of refractive error prevalence . Secondly, the VEC visit was meant as an excursion and the children had to return to normal classes with near work demands after the morning outing. Thirdly, it was important for comparison purposes to use refractive data procured under the same conditions as that used for the earlier groups of children. Fourthly, an initial evaluation without cycloplegia is necessary in order to understand daily function. Fifthly, non-cycloplegic retinoscopy was only one component of the exam. Outcomes regarding a decision to refer would not alter for most children had a cycloplegic refraction been carried out, as several other near function tests that would also indicate the possible existence of latent hyperopia or pseudo-myopia were included. Lastly, the degree of refractive error may in fact be influenced by cycloplegia (see Discussion for elaboration [33–38]).
Autorefractors were not employed as hand-held versions were unavailable when the first cohort was seen. Equally as important, there is no convincing evidence that the proportion of myopes identified in the sample would have changed .
Comparison with earlier data
To compare the estimated prevalence of myopia in this urban population of 'Australian children' over the last decade, this more recent 2000s data set was analysed against data from an earlier cohort of 2,322 children with similar demographics seen in the early 1990's, using the same testing protocols and seen at the same venue . The optometric results of that earlier cohort have previously been reported , and it was noted that 7.1% of those children were already wearing spectacles , indicating that our recruitment procedure did not preclude children already under the care elsewhere. The data for any child examined in both cohorts was deleted from the earlier data set to avoid bias in the analysis. The mean date of assessment for this last 2000s cohort was September 2000, and for the early 1990s cohort was June 1992. Thus, the average gap between assessments of children from the two cohorts was 8 years and 3 months.
Data was analysed by Analysis of Variance ANOVA (StatView software). Only refractive data from right eyes was used for the current refractive class analysis, as the correlation between right and left eye refractions was extremely high (p < 0.0005). The preferred criterion to define myopia in this study is that used clinically in Australia: a spherical equivalent equal to or more minus than -0.50 D. However, as myopia more minus than -0.50 D has occasionally been used to define myopia in epidemiological studies [13, 19, 41], analyses using the criterion 'myopia more minus than -0.50 D' were also performed for comparison. Hyperopia was defined as spherical equivalents greater than +0.50 D. Thus, emmetropia for this study was defined as refractions in the range -0.25 to +0.50 dioptres spherical equivalence inclusive. Means are quoted with the associated standard error.
Estimated prevalence of refractive error (%) by age in children aged 4 to 12 years.
More than -3.75
-0.50 to -3.75
-0.25 to +0.50
+0.75 to +1.25
More than +1.25
Mean estimated prevalence of myopia and hyperopia in children aged 4 to 12 years.
Myopia of -0.50
Comparison with previous data
A three-way analysis of variance was carried out for cohort, age and gender. There was a main effect for age (p < 0.0001), but no main effect for either cohort (p = 0.134) or gender (p = 0.61). However, there were age/gender/cohort interactions that indicate a trend towards an increasing shift away from the hyperopic refraction in the later cohort.
An analysis of the prevalence of refractive errors in young school children in eastern Sydney during the last thirteen years has been presented. The latest data gathered from 1,936 unselected primary school-aged children in the last 6 years, indicates that the prevalence of myopia remains quite low compared to that reported for the western world and Asia, especially as refractive error was established by non-cycloplegic retinoscopy (as will be discussed later). These findings are not significantly different (p = 0.13) to our previous report  indicating that 6.5% of 2,535 unselected children aged 4 to 12 years seen in the early 1990s were myopic by at least 0.50 D. Notably, those children were of similar socio-economic and ethnic status drawn from the same region of Sydney and seen at the same Centre using the same testing protocol.
Therefore, if we take the total 4,258 children seen since 1990, the relative frequency of refractive error across all is: 54.2% emmetropic by our criteria, 32.3% low to moderate hyperopes, 5.3% myopic greater than -0.50D spherical equivalence and 7.4% myopic by at least -0.50 DS. The number with myopia of at least -4.00 DS was an extremely small 0.6%.
The prevalence of myopia in Sydney primary school children compared to the rest of the world
As alluded to in the introduction, the proportion of Sydney children with myopia is dramatically less than in Asia. Indeed, the proportion appears significantly lower than in the USA  and Canada  (4% and 6% of 6 year olds respectively, or 20% of 12 year olds in USA), but higher than urban India with only 4.4% of all school children under 16 years myopic  and higher particularly than in other less developed countries .
In the past, a lack of internationally accepted definitions for 'myopia' has hampered valid comparisons across the various studies . Commonly the criteria 'greater than -0.50 DS' or 'at least -0.50 DS' are employed. However, our separate analyses using both of these criteria only resulted in a difference of 1.5% of all children included as myopic, in keeping with other dual analyses [13, 41], and is low either way when compared with Asia or North America.
Comparison across studies is also difficult when only an 'overall' mean refraction is presented covering all children in a study, due to the well known increasing prevalence of myopia with age. Indeed, the comparison of data from our own two data sets is confounded to some extent by the slightly different age profiles for each cohort. However, in neither cohort was the age range nor mean significantly different, so the similar proportion of myopes is not unexpected.
Comparison of refractive error with and without a cycloplegic agent
The question of optimal ocular conditions for comparison of the prevalence of refractive errors remains controversial. A cycloplegic agent is typically proposed as the gold standard [3, 43, 44] in the belief that it will eliminate ciliary muscle action or spasm, and thus unmask latent hyperopia or pseudomyopia. Thus, the use of a cycloplegic would be firstly predicted to lead to a decrease in the prevalence of myopia, and an increase in the prevalence of hyperopia. However, as a cycloplegic also leads to associated mydriasis and the introduction of unpredictable spherical aberrations, it is arguable that cycloplegia will induce unpredictable errors. In fact, Gao et al  in 2002 reported significant changes in the refractive components of children's eyes under conditions of deep cycloplegia and mydriasis that were greatest in hyperopic eyes and smallest in myopic eyes, adding no definitive evidence as to the relative efficacy of cycloplegia.
Thus there appears to be no scientific concurrence regarding the efficacy of cycloplegia for studies on the prevalence of myopia [35–37], with several major studies electing to use cycloplegia (see review in [10, 9, 11]) and others not [18–21, 23, 42, 45]. Presumably this design variability exists because there is no decisive evidence indicating a difference between refractions determined with and without a cycloplegic agent in eyes that have a myopic refraction. In general, a more positive retinoscopic finding is reported under cycloplegia, though considerable individual variation is seen including a myopic shift in some [33, 35–37, 46]. Not surprisingly, the differences noted decreased both with age and with less positive refraction.
As our refractive data was derived from non-cycloplegic retinoscopy we readily concede that mean refractive error may be less hyperopic than if a cycloplegic had been used. However, we suggest that as the influence of a cycloplegic is uncertain and is of least concern for myopes, the estimated prevalence of myopia will not be significantly altered by our decision to not use a cycloplegic. In support of this notion are new conference data from Rose et al [47, 48] reporting refractive status ascertained by cycloplegic autorefraction in over 1,000 children aged 6–7 years from across the same city of Sydney. They reported values of 'around 3%' for the prevalence of myopia of at least 0.50D , and then the value of 1.5% for myopia of 'approximately 0.50D'  with a participation rate between 73 and 80%. From Table 2 it can be seen that 2.4% of our 6 year olds in the current study were at least 0.50D myopic – a value that is strikingly similar.
Demographics versus lifestyle
Worldwide patterns of the prevalence of myopia suggest significant differences are likely to be due to the different demographics and lifestyles [1, 10, 49]. Zadnik  concedes that the increase in numbers of myopic children in the US Orinda study may be due to changing ethnic demographics. The apparent slight increase in myopia in Australia reported in the current study may also be in part accounted for by our changing ethnic demographics in urban areas. However demographics and ethnic compositions are unlikely to be responsible for the large changes reported in Asian and some other western countries [1, 50].
Whatever way it is argued, our results indicate little evidence for an epidemic of myopia although there is a developmental trend towards an earlier decrease in hyperopia to the point of myopia. Thus, the question of whether it is a matter of lifestyle, or perhaps familial environmental stress, or more, remains. Certainly, the education system and housing has changed little in Australia the last 30 years. By comparison, most Asian children participating in myopia epidemiological studies reportedly are more likely to live in high-rise residential blocks  and have strong demands at school to memorize along with parental and peer pressure to do well, and for some, a competitive entrance examination to enter school [19, 51].
It is concluded that despite some differences in methodology across earlier studies, the prevalence of myopia in young Australian school children does not appear to have increased significantly over the last 30 years if one allows for the change in ethnic demographics. It is also proposed that an explanation for the large increase in prevalence of myopia reported in other countries must include questions relating to lifestyle in addition to genetic propensity.
Supported by a University of New South Wales GoldStar Grant to BM Junghans.
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