The following (see below) is a brand new study just published
in Australia which I'm sure Otis will use his "Otis-speak"
(garbage in, garbage out)to hem and haw this very valid study.

frank

Little evidence for an epidemic of myopia in Australian primary school
children over the last 30 years

Barbara M Junghans1  and Sheila G Crewther2
1School of Optometry and Vision Science, University of New South Wales,
Sydney, UNSW Sydney 2052. Australia
2School of Psychological Science, La Trobe University, Bundoora 3083,
Australia

BMC Ophthalmology 2005, 5:1     doi:10.1186/1471-2415-5-1

This is an Open Access article distributed under the terms of the
Creative Commons Attribution License
(http://creativecommons.org/licenses/by/2.0), which permits
unrestricted use, distribution, and reproduction in any medium,
provided the original work is properly cited.

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.

Methods

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.

Results

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).

Conclusions

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 [3]. There is strong evidence
indicating that genetic inheritance is a major contributor, both from
the examination of prevalences across different racial backgrounds [4],
from family pedigrees [5] and from twin studies [6]. However, there is
increasing evidence suggesting that high heritability does not preclude
rapid environmentally-induced increases in prevalence [7], 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) [11].

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) [2]. 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 [1]),
of whom notably 82% were Chinese [17].

It has often been suggested that myopia is more prevalent in ethnic
Chinese (reviewed [18]), 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
[20] 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[12], 47% of Chinese Malays [20]
and 57% in urban Hong Kong [22]. Japan has a similarly high prevalence
of myopia in young school children estimated in recent times to be
43.5% of 12 year olds [24].

By comparison, the epidemiology of refractive error for young
Australian school children is relatively well documented and presents a
very different profile. A number of studies were carried out in the
early 1970s and the 1980s on relatively large groups of unselected
primary school children from the socio-economic extremes (generally
aged 5 to 12 years), and indicated a prevalence of myopia ranging from
approximately 3% to 13% (see Table 1) [25-29]. Two of those early
studies investigated children largely from underprivileged, rural,
families [26,27], and the other was of children from several, middle to
upper socio-economic class private schools [25]. One smaller study was
carried out in the mid 1980s on children from a representative
selection of government schools in Brisbane [29], and would therefore
have investigated children from a broader range of backgrounds.
Interestingly, this latter study was the only Australian study to have
determined refractive error under cycloplegia, yet yielded the highest
prevalence of myopia. Thus, it has been difficult to determine whether
the prevalence of myopia has increased in young school children in
Australia as reported elsewhere. The majority of Australian residents
are of Caucasian extraction living a very western lifestyle, leading
one to expect the prevalence of myopia to be similar to that found in
US or Europe. Yet, studies suggest that the prevalence of myopia in
Australian primary school children is low by world standards [10].

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 [30]. 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) [31] 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 [32].
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 [32], a figure supported by our interpretation of
family name for each child [30]. 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 [31]
delivered alongside the eye examination.

Clinical 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 [11]. 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 [39].

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 [30]. The optometric
results of that earlier cohort have previously been reported [40], and
it was noted that 7.1% of those children were already wearing
spectacles [30], 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.

Statistical analyses

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.

Outline   Results
The records of 1,936 children aged 4 to 12 years from a non-clinical
unselected population examined during the six years from March 1998 to
May 2004 were analysed retrospectively to estimate the prevalence of
different types of refractive error. Primary schools of their own
choice sent more children from years 1, 3, and 5, which resulted in
unequal numbers of children in each of the age groups. There were 925
boys and 951 girls, and the relative numbers for both males and females
in each age group are shown in Table 2. For 59 children, the gender was
not indicated on the record card and could not be inferred with
certainty from the given name. The data not associated with gender has
only been included in analyses entitled 'All' as shown in Tables 2 and
3. Mean age was 8.36 years. The relative proportions of the different
classifications of refractive error for all children combined
(including those of unknown gender) for each age group are shown in
Table 2.

The mean spherical equivalent refraction of all 1,936 children was
+0.45 ± 0.02 DS, however it should be noted that there is a
preponderance of children aged 5-6, 9 and 11 years old corresponding
with Years 1, 3, and 5 of primary school. Overall, there was no
significant difference in spherical equivalent refractive error between
girls and boys (p = 0.697). In general, mean refraction demonstrates a
highly significant shift towards less hyperopia with increasing age (p
< 0.0001) from 0.73 ± 0.1DS for 4 year olds to 0.21 ± 0.11 for 12
year olds, however this is more noticeable after the age of 9 years as
seen in Fig. 1. With increasing age, more children are found in the
emmetropic category and fewer in the low hypermetropic category.

A summary of the relative proportions of myopia and hyperopia for this
cohort of children of all ages seen during the six years ('2000s' data)
is given in Table 3. The majority of children screened are emmetropic
by our criteria: 53.0% averaged across all ages. The proportion of
children manifesting moderate to high degrees of hypermetropia
(=+1.50 DS) is 6.2% across all ages. Only 6.9% of children of all
ages had refractive errors more minus than -0.50 DS, ranging from 2.3%
of 4 year olds to 13.3% of 12 year olds (Fig. 2). If the more liberal
definition of myopia is applied (myopia equal to or more minus than
-0.50), then 8.4% of all children were myopic (ranging from 2.3% of 2
year olds to 14.7% of 12 year olds). Only 0.8% of the 1,936 children
were more than -4.00 DS myopic.

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 [30] 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 [41] and Canada [42] (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 [13] and higher particularly than in other less developed
countries [10].

In the past, a lack of internationally accepted definitions for
'myopia' has hampered valid comparisons across the various studies
[10]. 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 [38] 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 [47], and then the value of 1.5% for myopia of
'approximately 0.50D' [48] 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 [41] 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 [17] 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].
Conclusions
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.

Oits - this was a great post.  Well done!  It sure raises some
interesting and very important questions.  Maybe children
are not meant to do a lot of close work so early in life.  At
least not for extended periods.  The parents were lamenting
the lack of learning in the children if they weren't reading.
Maybe the parents are the ones that should be teaching them.
Then that wouldn't entail extended close work.

Just a thought.

Subject:  A High Percentage Myopia in School and College