Content uploaded by Kathryn J Saunders
Author content
All content in this area was uploaded by Kathryn J Saunders on Jan 22, 2016
Content may be subject to copyright.
Available via license: CC BY 4.0
Content may be subject to copyright.
RESEARCH ARTICLE
Six Year Refractive Change among White
Children and Young Adults: Evidence for
Significant Increase in Myopia among White
UK Children
Sara J. McCullough*
☯
, Lisa O’Donoghue
☯
, Kathryn J. Saunders
☯
Biomedical Sciences Research Institute, School of Biomedical Sciences, University of Ulster, Cromore Road,
Coleraine, N. Ireland, United Kingdom
☯These authors contributed equally to this work.
*sj.mccullough@ulster.ac.uk
Abstract
Objective
To determine six-year spherical refractive error change among white children and young
adults in the UK and evaluate differences in refractive profiles between contemporary Aus-
tralian children and historical UK data.
Design
Population-based prospective study.
Participants
The Northern Ireland Childhood Errors of Refraction (NICER) study Phase 1 examined
1068 children in two cohorts aged 6–7 years and 12–13 years. Prospective data for six-year
follow-up (Phase 3) are available for 212 12–13 year olds and 226 18–20 year olds in each
cohort respectively.
Methods
Cycloplegic refractive error was determined using binocular open-field autorefraction (Shin-
Nippon NVision-K 5001, cyclopentolate 1%). Participants were defined by spherical equiva-
lent refraction (SER) as myopic SER -0.50D, emmetropic -0.50D<SER<+2.00 or hyper-
opic SER+2.00D.
Main Outcome Measures
Proportion and incidence of myopia.
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 1/19
OPEN ACCESS
Citation: McCullough SJ, O’Donoghue L, Saunders
KJ (2016) Six Year Refractive Change among White
Children and Young Adults: Evidence for Significant
Increase in Myopia among White UK Children. PLoS
ONE 11(1): e0146332. doi:10.1371/journal.
pone.0146332
Editor: Haotian Lin, Sun Yat-sen University, CHINA
Received: August 21, 2015
Accepted: December 14, 2015
Published: January 19, 2016
Copyright: © 2016 McCullough et al. This is an open
access article distributed under the terms of the
Creative Commons Attribution License, which permits
unrestricted use, distribution, and reproduction in any
medium, provided the original author and source are
credited.
Data Availability Statement: All relevant data are
within the paper and its Supporting Information files.
Funding: This work was supported by The College of
Optometrists, London, UK Grant name: The Northern
Ireland Childhood Errors of Refraction Study –Phase
3 Refractive development in childhood and early
adulthood. http://www.college-optometrists.org. The
funders had no role in study design, data collection
and analysis, decision to publish, or preparation of
the manuscript.
Competing Interests: The authors have declared
that no competing interests exist.
Results
The proportion of myopes significantly increased between 6–7 years (1.9%) and 12–13
years (14.6%) (p<0.001) but not between 12–13 and 18–20 years (16.4% to 18.6%, p=
0.51). The estimated annual incidence of myopia was 2.2% and 0.7% for the younger and
older cohorts respectively. There were significantly more myopic children in the UK at age
12–13 years in the NICER study (16.4%) than reported in Australia (4.4%) (p<0.001). How-
ever by 17 years the proportion of myopia neared equivalence in the two populations
(NICER 18.6%, Australia 17.7%, p= 0.75). The proportion of myopic children aged 12–13
years in the present study (2006–2008) was 16.4%, significantly greater than that reported
for children aged 10–16 years in the 1960’s (7.2%, p= 0.01). The proportion of hyperopes
in the younger NICER cohort decreased significantly over the six year period (from 21.7%
to 14.2%, p= 0.04). Hyperopes with SER +3.50D in both NICER age cohorts demon-
strated persistent hyperopia.
Conclusions
The incidence and proportion of myopia are relatively low in this contemporary white UK pop-
ulation in comparison to other worldwide studies. The proportion of myopes in the UK has
more than doubled over the last 50 years in children aged between 10–16 years and children
are becoming myopic at a younger age. Differences between the proportion of myopes in the
UK and in Australia apparent at 12–13 years were eliminated by 17 years of age.
Introduction
There is a growing body of evidence suggesting that myopia is becoming more prevalent in
childhood in many areas of the world, such as in Taiwan, [1] Singapore, [2] the United States
[3] and Australia [4] while estimates of hyperopia prevalence remain relatively static.[4,5]
Although myopia prevalence has been much studied, few prospective studies are available
from which to derive estimates of incidence of myopia, the stability of hyperopia or to explore
individual change in refractive error.[4,6–11] The present study reports the six-year change in
refractive error status within a white, UK based population of children and young adults;
exploring both the incidence of myopia and the stability of hyperopia in pre-teenage children,
teenage children and young adults. Robust sampling and methodology similar to that used in
other large-scale studies of refractive error [12,13] have been employed. Comparisons will be
made with the recent report of six-year change in an Australian population of European Cau-
casian children [4] to determine geographical differences in an ethnically similar group and
with historical data [14] to evaluate whether the refractive profile of UK school children and
young adults has changed over the past 50 years.
Materials and Methods
The Northern Ireland Childhood Errors of Refraction (NICER) Study is a longitudinal study of
refractive error. The study methods have previously been described in detail [15] In brief,
Phase 1 of the NICER study was a cross-sectional epidemiological study investigating the prev-
alence of refractive error in 6–7 and 12–13 year old children in Northern Ireland conducted
between 2006 and 2008. Participants were chosen using stratified random sampling of schools
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 2/19
from geographic areas characteristic of Northern Ireland to obtain a representative sample of
schools and children from urban/rural and deprived/non-deprived areas. Data collection
included cycloplegic autorefraction using the binocular open-field autorefractor (SRW-5000,
Shin-Nippon, Tokyo, Japan). Cycloplegia was induced by one drop of 1.0% cyclopentolate
hydrochloride, after corneal anaesthesia with one drop of 0.5% proxymetacaine hydrochloride.
Autorefraction was performed at least 20 minutes after the instillation of drops. No less than
five readings were taken from which the ‘representative value’as determined by the instrument
was used for further analysis. The representative value is widely used as an output value for this
instrument and has recently been shown to be comparable to other methods of averaging
refractive error.[16] Data collection occurred at the child’s school (6–7 year olds: primary
school; 12–13 year olds: post-primary school) during the school day. After examination of the
child, parents/guardians were asked to complete a questionnaire to determine the child’s birth
history, family history and lifestyle. The study was approved by the University of Ulster’s
Research Ethics committee and adhered to the tenets of the Declaration of Helsinki. Written
informed consent was obtained from parents or guardians and verbal or written assent was
obtained from participants on the day of the examination.
Within Phase 1 of the study, baseline data were collected from 399 6 to 7 year old children
(younger cohort) and 669 12 to 13 year old children (older cohort). Phase 2 of the NICER
study, collected follow-up data on the participants three years later, these data are presented
elsewhere.[11] Phase 3 of the NICER study collected follow-up data on the same participants
six years after their initial participation, 2012–2014. For the younger cohort, the majority of
data collection at Phase 3 occurred at the child’s post-primary school (n = 200, 93%) and for
some children where it was not possible to carry out testing at their post-primary school, data
collection occurred at a University of Ulster campus (n = 15, 7%). For participants within the
older cohort, data collection took place at one of the University of Ulster campuses or at a data
collection site close to the participant’s home address (e.g. local church hall).
Data collection protocols were the same at all phases of the study. Cycloplegic autorefraction
was measured using the latest version of the binocular open-field autorefractor at Phase 3
(NVision-K 5001, Shin-Nippon, Tokyo, Japan). This instrument has been shown to be accurate
and repeatable over a wide range of refractive errors.[17,18]
Refractive Classifications
The representative value was used to calculate spherical equivalent refraction (SER) using sphere
+ cylinder/2. There was a strong correlation between SER data from right and left eyes (Spear-
man’srho,allp<0.001) therefore only data from right eyes are presented. SER was used to
group participants into the following refractive classifications: a participant was classified as a
myope if SER was -0.50 dioptre (D) or less; an emmetrope if SER was greater than -0.50D but
less than +2.00D; and a hyperope if SER was +2.00D or greater. These classifications are similar
to those used previously to define refractive error by the NICER study, [11,19] by the Refractive
Error in School Children Study (RESC), [12,20] the Sydney Myopia Study (SMS)[13] and the
Sydney Adolescent and Vascular Eye Study (SAVES).[4] Raw data from Sorsby et al.[14] were
obtained and analysed using the same refractive criteria as the current study to aid comparison.
Statistical Analysis
Data were analysed using Intercooled Stata 10.1 software (StataCorp LP, Texas, USA). Non-
participants are defined as individuals who participated in Phase 1 of the study but did not par-
ticipate in Phase 3. Differences between participants and non-participants for both cohorts
were investigated using Mann-Whitney analysis (SER & socioeconomic rank), student t-tests
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 3/19
(age) and chi-squared analysis (gender, refraction classification, spectacle wear at Phase 1,
parental education & parental myopia). Socio-economic rank was determined using a Geo-
graphical Information Systems (GIS) approach. Unit postcode address information and the
Northern Ireland multiple deprivation measure were applied to assign an area-based rank mea-
sure of economic deprivation to each child. The measure, calculated at the small scale census
Output Area (OA) level, is based on three weighted domains of deprivation: income (41.7%),
employment (41.7%) and proximity to services (16.6%). Level of parental education and paren-
tal myopia were established through parent/guardian questionnaire based survey at Phase 1.
For parental education, participants were dichotomised as having at least one parent with third
level education (college or university degree) or neither parent had third level education and
for parental myopia, participants were dichotomised as having at least one myopic parent or
having no myopic parents.
Cross-sectional distribution of refractive errors are presented for Phase 1 and Phase 3.
Cumulative incidence of myopia was calculated as the number of individuals who were classi-
fied as myopic at Phase 3 but were not classified as myopic at Phase 1. Cumulative reduction in
hyperopia (+2.00DS) was also assessed and is reported as the number of individuals classified
as hyperopic at Phase 1 but not classified as hyperopic by Phase 3. Annual incidence of myopia
(or reduction of hyperopia) were calculated by dividing the cumulative incidence (or reduc-
tion) by the mean follow-up interval (years) for each cohort as a whole. Six-year cumulative
change in SER was calculated as “measurement at Phase 3”–“measurement at Phase 1”. Esti-
mated annual change in SER was calculated by dividing the change from Phase 1 to Phase 3 by
the time interval between examinations for each individual. The Shapiro-Wilk test was used to
determine normality of the data. Mann-Whitney and Kruskal-Wallis tests or their parametric
equivalents (Student t-test or analysis of variance) where appropriate, were used to analyse dif-
ferences between cohorts and refractive error groups. Mixed effect logistic regression analyses
and two sample tests of proportion were used to compare distribution differences within the
NICER study and between the NICER study data and that of Sorsby et al.[14] and French et al.
[4]. Chi-squared analyses were used for categorical and percentage comparisons. A pvalue of
less than 0.05 was considered statistically significant.
Results
Participants
All participants who took part in Phase 1 were eligible to participate in Phase 3 irrespective of
their participation in Phase 2. We were unable to contact a number of participants at Phase 3
in both the younger (n = 25, 6.0%) and older cohorts (n = 8, 1.2%). From Phase 1, overall par-
ticipation in Phase 3 was 54% and 34% for the younger and older cohorts respectively. The
majority of participants at Phase 3 were white (99%), reflective of the Northern Irish popula-
tion, [21] therefore data are reported for white participants only. One participant in the older
cohort was also excluded from data analysis due to emergent ocular pathology (keratoconus).
Data are presented for 212 participants within the younger cohort (50% male) and for 226 par-
ticipants within the older cohort (43% male). Fig 1 describes the number of participants con-
tacted, recruited and examined at Phase 3.
Younger Cohort. The mean age of the younger cohort at Phase 3 was 13.1±0.4 years
(range 12.4 to 13.9 years). There was no statistically significant difference between participants
and non-participants at Phase 3 in terms of age (t = 1.39, p= 0.17), gender (Χ
2
= 0.0014,
p= 0.97), refractive error (SER [z = -0.18, p= 0.86] or refractive classification [Χ
2
= 0.95,
p= 0.81]), spectacle wearers vs non-spectacle wearers (Χ
2
= 0.41, p= 0.52) and socio-economic
indicators (socio-economic rank [z = -1.46, p= 0.14], and parental education [Χ
2
= 0.05,
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 4/19
p= 0.83]). Those who had at least one myopic parent were more likely to participate at Phase 3
compared to those with no myopic parents (Χ
2
= 10.51, p= 0.001).
Older Cohort. The mean age of the older cohort at Phase 3 was 19.2±0.5 years (range 18.0
to 20.2 years). Females within the older cohort were statistically more likely to participate than
males (Χ
2
= 7.82, p= 0.005). There was no statistically significant difference in age (t = -1.90,
Fig 1. Flow diagram describing participant contactability, recruitment and exclusion from Phase 1 to
Phase 3.
doi:10.1371/journal.pone.0146332.g001
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 5/19
p= 0.06), refractive error (SER [z = -0.40, p= 0.69] or refractive classification [Χ
2
= 5.60,
p= 0.13]), socio-economic indicators (socio-economic rank [z = -1.72, p= 0.09], parental edu-
cation [Χ
2
= 0.12, p= 0.73]) or parental myopia (Χ
2
= 1.02, p= 0.31) between participants and
non-participants at Phase 3. Spectacle wearers in the older cohort were statistically significantly
more likely to participate at Phase 3 compared to non-spectacle wearers (Χ
2
= 5.45, p= 0.02)
however the range of spherical error of those who were spectacle wearers was wide (-7.00D to
+9.00D).
Follow-up Interval
The majority of follow-up examinations at Phase 3 occurred within 72 ±3 months of the initial
participation in Phase 1 (younger 92.5%; older 73.9%). There was no statistically significant dif-
ference between cohorts with regard to the time interval between Phase 1 and 3 examinations
(Mann-Whitney z = 0.71, p= 0.48) (younger median 73.2 months, IQR 70.3 to 73.9 months,
range 68.8 to 76.7 months; older median 72.5 months, IQR 69.7 to 74.1 months, range 67.7 to
81.8 months).
Incidence of Myopia and Reduction in Hyperopia between Phase 1 and
Phase 3
Tables 1and 2describe the changing distribution of myopia and hyperopia for the younger
and older cohorts. SER at Phase 1 and 3 are also plotted (Fig 2A & 2B) to show the number of
new myopes by Phase 3 and the refractive classification in which they were originally grouped
at Phase 1. The number of participants with reducing hyperopia are also highlighted.
For those participants within the younger cohort classified as myopic at Phase 3 the cumula-
tive median change in SER was -1.38D (IQR -0.63 to -2.75D) over the six-year period. Esti-
mated annual median change for this group of participants was -0.23D (IQR -0.11 to -0.45D)
with the largest estimated annual change for one individual of -0.51D. For the older cohort,
those classified as myopic at Phase 3 showed a cumulative median change of -0.63D (IQR -0.13
to -1.00D) over the six-year period. Estimated annual median change for these participants was
-0.10D (IQR -0.02 to -0.17D) with the largest estimated annual change of -0.51D. There was no
statistically significant difference between genders for the annual rate of change in SER for
Table 1. Proportion of myopes and incidence of myopia between Phase 1 and 3.
Cohort Proportion of Myopes
Phase 1 (%)
Proportion of Myopes
Phase 3 (%)
pCumulative
Incidence (%)
pEstimated Annual
Incidence (%)
Younger
All (n = 212) 1.9 (n = 4) 14.6 (n = 31) <0.001 13.0 - 2.2
Males
(n = 105)
1.0 (n = 1) 14.3 (n = 15) 0.006 13.5 Reference 2.3
Females
(n = 107)
2.8 (n = 3) 15.0 (n = 16) 0.005 12.5 0.63 2.1
Older
All (n = 226) 16.4 (n = 37) 18.6 (n = 42) 0.51 4.2 - 0.7
Males (n = 98) 15.5 (n = 16) 16.5 (n = 17) 0.84 2.4 Reference 0.4
Females
(n = 128)
17.1 (n = 21) 20.2 (n = 25) 0.49 5.6 0.38 0.9
Summary of the proportion of myopes at Phase 1 and 3 and the incidence of new myopes between Phase 1 and Phase 3 for the younger and older
cohorts, stratified by gender. n = number of participants
doi:10.1371/journal.pone.0146332.t001
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 6/19
those classified as myopic by Phase 3 for either the younger (Mann-Whitney, z = 0.41,
p= 0.68) or older cohorts (Mann-Whitney, z = -1.26, p= 0.21).
There was no statistically significant difference between the cross-sectional proportion of
participants aged 12–13 years classified as myopic at baseline (2006–2008, 16.4%) and those
classified as myopic at Phase 3 (2012–2014, 14.6%) (Two-sample test of proportion z = -0.51,
p= 0.62). Participants in both cohorts who were classified as myopic at 12–13 years of age had
similar levels of myopia (median = -1.25DS, IQR -0.81 to -1.69DS in 2006–2008; median =
-1.25D, IQR -0.88 to -2.38DS in 2012–2014) (Mann-Whitney, z = -0.85, p= 0.40).
There was a significant decline in the proportion of hyperopes in the younger cohort
between age 6–7 years (21.7%) and 12–13 years (14.2%) (z = -2.05, p= 0.04). Children who
were hyperopic at 6–7 years and remained hyperopic at 12–13 years had a significantly more
positive SER at 6–7 years (median +3.69DS) compared to those who lost their hyperopia
(median +2.19DS at 6–7 years) (Mann-Whitney, z = 4.62, p<0.001). The proportion of hype-
ropes within the older cohort remained relatively stable between 12–13 years (15.0%) and 18–
20 years (17.7%) and there were few participants who lost their hyperopia over the six-year
period (n = 4). Similar to the younger cohort, participants who were classed as hyperopic aged
12–13 years and remained hyperopic at age 18–20 years had a significantly greater SER at 12–
13 years of age (median +4.13DS) compared to those who lost their hyperopia (median
+2.07DS at 12–13 years) (Mann-Whitney, z = 2.84, p= 0.005). Hyperopic participants showed
on average an annual change in SER of -0.09DS (IQR -0.17 to -0.02DS) and +0.02DS (IQR
-0.04 to 0.11DS) for the younger and older cohorts respectively.
Proportion, Incidence and Progression of Myopia among the NICER
Study participants compared with a contemporary Sydney population
and a historical UK based population
Proportion of Myopia. Data from the current study are compared with data from the
recent report from French et al.[4] (Sydney Myopia Study [SMS] and Sydney Adolescent Vas-
cular and Eye Study [SAVES]) who present the prevalence, incidence and progression of myo-
pia in two similar age cohorts of Australian European Caucasian children (aged 6 years and 12
years at baseline) and longitudinal follow-up after 5–6 years during a similar time period as the
present study (2004 to 2011). These data are presented in Fig 3.
Table 2. Proportion of hyperopes and decline of hyperopia between Phase 1 and 3.
Cohort Proportion of Hyperopes
Phase 1 (%)
Proportion of Hyperopes
Phase 3 (%)
pCumulative
Reduction (%)
pEstimated Annual
Reduction(%)
Younger
All (n = 212) 21.7 (n = 46) 14.2 (n = 30) 0.04 43.5 - 7.3
Males
(n = 105)
21.0 (n = 22) 13.3 (n = 14) 0.14 50.0 Reference 8.3
Females
(n = 107)
22.4 (n = 24) 15.0 (n = 16) 0.15 37.5 0.97 6.3
Older
All (n = 226) 15.0 (n = 34) 17.7 (n = 40) 0.44 11.8 - 2.0
Males (n = 98) 17.4 (n = 17) 19.4 (n = 19) 0.71 5.9 Reference 1.0
Females
(n = 128)
13.3 (n = 17) 16.4 (n = 21) 0.48 17.6 0.39 2.9
Summary of the proportion of hyperopes at Phase 1 and 3 and the decline of hyperopia between Phase 1 and Phase 3 for the younger and older cohorts,
stratified by gender. n = number of participants.
doi:10.1371/journal.pone.0146332.t002
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 7/19
Fig 2. Scatterplots of SER at Phase 1 versus SER at Phase 3 for the younger and older cohorts
respectively. Data are grouped into refractive classifications as illustrated in the key. The gray boxes
indicate participants who became myopic (younger cohort n = 27; older cohort n = 8) or lost their hyperopia
(younger cohort n = 20; older cohort n = 4) between Phase 1 and 3. The dashed lines represent the myopia
cut-off point of -0.50D or less and the dotted line represents the hyperopia cut-off of +2.00D or greater. The
solid black line represents unity- those falling below the line are showing a myopic change in SER.
doi:10.1371/journal.pone.0146332.g002
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 8/19
Data from the current study are also compared with historical UK data from Sorsby et al.
[14](Fig 4). Sorsby et al. present data for two age groups; children who were between three and
ten years of age at baseline (younger cohort) and children who were ten to 15 years of age at
baseline (older cohort). Longitudinal data are also presented with a mean follow-up examina-
tion occurring at 3.1±0.9 years (range 2.2 to 5.3 years) and 3.7±0.9 years (range 2.0 to 5.3
years) for their younger and older cohorts respectively.
In contrast to contemporary literature, and to the data presented in Fig 4, Sorsby et al.[14]
applied an SER of less than zero dioptres to define myopia in his published report. Using this
criterion and applying it to the NICER study data, 23% of children aged 12–13 years in the
NICER study were classified as myopic at Phase1 (2006–2008) compared to 10% reported by
Sorsby et al. in the 1960’s for their older cohort of children aged between 10–16 years. These
data and those in Fig 5 indicate a two-fold increase in the proportion of myopia in the UK over
the last five decades in children aged between 10 and 16 years (Two sample test of proportion
z = 3.12, p= 0.002).
Fig 5 presents the distribution of SER for 6–7 year old children within Phase 1 of the NICER
study (2006–2008) and from Sorsby’s report.[14] The median SER for Sorsby’s6–7 year olds in
the 1950’s-1960’s was +1.80DS (IQR +1.30 to +2.70DS) which is significantly more hyperopic
than the median SER (+1.13DS, IQR +0.63 to +1.75DS) for the 6–7 year olds in the NICER
study in 2006–2008 (Mann-Whitney z = 7.15, p<0.001).
Fig 3. Comparison of refractive error prevalence in the UK (NICER Study) to Australia (SMS/SAVES) at baseline and 5–6 year follow-up. The
brackets show the statistical comparisons of the proportions of myopes between the two studies; black indicates statistically significant difference, gray
indicates no statistically significant difference (Two sample test of proportion).
doi:10.1371/journal.pone.0146332.g003
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 9/19
Table 3 describes the mean annual change in SER for those classified as myopic at baseline
and the estimated annual incidence of myopia for the NICER and Sydney data. The Sydney
study [4] reported no statistically significant difference in the annual progression rate between
children of European Caucasian or East Asian ethnicity when myopia was present at baseline,
therefore change in SER data for all ethnicities in the Sydney study are used for comparison.
Isolated European Caucasian data are not available for the Sydney data for this metric.
Discussion
The present study reports the six-year change in refractive error status including the incidence
of myopia and reduction of hyperopia, within a white, UK based population of children and
young adults. In the present study, the proportion of participants defined as myopic is similar
to previous reports of European Caucasian children of similar age.[4,10,22,23] However it is
relatively low in comparison to reports among children of Asian background whether living in
Asia or elsewhere.[1,4,6,8,20,23] French et al.[4] report a significant increase in the prevalence
of myopia in Australian Caucasian children between 2004 and 2011 and infer that the preva-
lence of myopia is increasing in Australia, similar to reports in many other parts of the world.
[1–3] The results from the present study demonstrate a two-fold increase over 50 years in the
proportion of teenagers who are myopic in the UK, but no significant short-term increases in
myopia prevalence during the past decade in our population.
Fig 4. Comparison of UK refractive error distribution between 1950’s-1960’s (Sorsby study) and 2006–2014 (NICER study) at baseline and follow-
up. The brackets indicate the statistical comparisons of the proportions of myopes between the two studies; black indicates statistically significant difference,
gray indicates no statistically significant difference (Two sample test of proportion).
doi:10.1371/journal.pone.0146332.g004
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 10 / 19
Fig 5. Distribution of spherical equivalent refractive errors in 6–7 year old children within the NICER study Phase 1 (2006–2008) and 6–7 year old
children from Sorsby et al.[14]. Data points represent a one dioptre interval (for example, the % of participants represented at point 0 on the x-axis have an
SER of less than or equal to 0DS but greater than -1 DS. Data points at the extremes of the x-axis represent participants with SER of greater than or equal to
+5DS or less than or equal to -5DS.
doi:10.1371/journal.pone.0146332.g005
Table 3. Comparison of the incidence and progression of myopia between the NICER and Sydney studies for the younger and older cohorts.
YOUNGER COHORT OLDER COHORT
Current Study NICER Age range 6–7to12–13 years 12–13 to 18–20 years
Estimated Annual Incidence of myopia 2.2%*0.7%*
Mean Annual Change in SER for participants classed as
myopic at Phase 1 (D) (Range)
n = 4; -0.18; (-0.47 to
-0.02)
n = 37; -0.09; (-0.51 to
+0.19)
Sydney, Australia
French et al.[4]
Age Range 6–7to12–13 years 12–13 to 17 years
Estimated Annual Incidence of myopia 1.3%*2.9%*†
Mean Annual Change in SER for participants classed as
myopic at Phase 1 (D)
n = 11; -0.41; (range not
available)
n = 128; -0.31; (range not
available)
n = number of participants.
*= statistically significant difference in annual incidence between younger and older cohorts within the same study (Χ
2
,p<0.05).
†
= statistically significant difference in annual incidence between the NICER study and the Sydney data (within the same age cohort) (Χ
2
,p<0.05).
doi:10.1371/journal.pone.0146332.t003
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 11 / 19
Proportion and Onset of Myopia
There was a statistically significant increase in the number of myopes between 6–7 and 12–13
years. The estimated annual incidence in myopia within this younger cohort (2.2%) did not dif-
fer significantly from that found in European Caucasian children in Sydney (1.3%) and is com-
parable with annual incidences reported in the ethnically diverse populations described in the
full Sydney data set (2.2%) (French et al.[4]-including all ethnicities) and in the Collaborative
Longitudinal Evaluation of Ethnicity in Refractive Error (CLEERE) study. The latter reports an
annual incidence of myopia of 2.8% for children in the United States aged six years at baseline
who were reviewed annually for seven years.[24] In general, children living within the UK, US
and Australia appear to have similar low annual incidences of myopia, regardless of ethnicity,
compared to the high annual incidences reported for children living in East Asia. Saw et al.[8]
report an annual incidence of myopia of 15.9% among Singaporean children aged seven years
at baseline (reviewed after three years) and Fan et al.[6] report on average a 14.4% annual inci-
dence of myopia among children from Hong Kong (aged between 7–11 years at baseline,
reviewed after one year). Prospective data from ethnically diverse groups living in the UK
would be beneficial to identify how ethnicity and environment interact in the UK.
Gender did not significantly impact on myopia incidence in the NICER study in either age
cohort. Although the proportion of myopes who were females was higher than males in both
cohorts, this did not reach statistical significance. Zhao et al.[20] in the Refractive Error of
School-Children (RESC) study in the Shunyi District, China, report an annual incidence of
myopia of 2.2% among children who were five years old at baseline (followed up after 28.5
months), similar to our younger cohort. However among children who were 12 years at baseline
in Zhao et al.’s study, the annual incidence of myopia had risen to 10.7% for males and 16.7%
for females in stark contrast to the present study. French et al.[4] also report significantly greater
myopia incidence in females in their older group of children (aged 12–13 years at baseline) but
no significant difference between genders for their younger cohort (aged 6–7 years at baseline).
Saw et al.[8] also report a higher annual incidence of myopia in female Singaporean children
(15.2%) (aged 7–9 years at initial visit, reviewed after three years) compared to males (13.2%)
however similar to the NICER study, this difference did not reach statistical significance.
Within the present study there was no statistically significant increase in the proportion of
participants classed as myopic between 12–13 years and 18–20 years of age. The cumulative
incidence of myopia for this cohort was 4.2% with an estimated annual incidence of 0.7%. By
contrast, the younger cohort demonstrated a greater cumulative incidence of myopia in the
six-year sampling period (13% vs 4.2%) revealing that children were three times more likely to
become myopic between 6–7 and 12–13 years than between 12–13 and 18–20 years in our pop-
ulation. Compared to Sorsby et al.[14](Fig 5) our results show that children are becoming
myopic at a younger age in present day UK compared to 50 years ago. Children within the
NICER study also demonstrated a significantly less hyperopic SER at 6–7 years of age com-
pared to those of corresponding age within Sorsby’s study. Williams et al.[25] have recently
reported a similar trend of increasing myopia prevalence in adults in Northern and Western
Europe where the prevalence of myopia was almost twice as high in young adults aged 25–29
years (47.2%) compared to those of middle age (27.5%, aged between 50–59 years). They also
report a significantly higher prevalence of age-standardised myopia among adults born
between 1940–1979 (23.5%) compared to those born between 1910–1939 (17.8%).
Cumulative incidence of myopia decreased with increasing age from the younger to the
older NICER cohort. This contrasts strongly with data in a sample of Chinese children (aged
5–15 years at baseline, reviewed after 28.5 months) for which Zhao et al.[20] report a 27%
increase in cumulative risk of myopia with each additional year of age. French et al.[4] also
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 12 / 19
report that the incidence of myopia increased with increasing age among their Australian chil-
dren, describing the annual incidence of myopia in their older cohort (aged 12 years at base-
line) as 2.9% compared with 1.3% in their younger cohort (aged six years at baseline) with an
annual incidence of 1.3%. Inspection of Fig 3 suggests that although the prevalence of myopia
among younger Australian children is lower than that found in our UK population, by age 17
years the proportion of myopes in the two studies nears equivalence. It is also seen in Fig 3 and
reported by French et al.[4] that cross-sectional data indicate a shift towards earlier onset myo-
pia in Australia in a relatively short space of time; the prevalence of myopia in 12–13 year old
children tested in 2004–2005 is reported as 4.4% compared with 8.6% in 2009–2011. This shift
has been attributed to a change in lifestyle amongst younger Australian children; including
increased use of computers and hand-held technology and less time spent playing outside.
Spending time outdoors has been postulated to protect against the onset and progression of
myopia [26–29] and French et al.[28] suggests that while young children may have tradition-
ally been protected by the sunny climate and outdoor lifestyle prevalent in Australia, modern
lifestyle pressures mean that time outdoors is sacrificed to the growing demands of study and
the attraction of computer games and tablets, and hence susceptibility to myopia is intensified.
The data from the present study do not support a rapid change in the timing of myopia onset
in the UK as reported in Australia, but do reveal that myopia occurs at a younger age in the UK
in the 21
st
century than reported in the 1960’s. This, in addition to the evidence of a twofold
increase in the number of myopes, is likely to reflect the significant changes in lifestyle and
environment that have occurred over the last 50 years in the UK (e.g. time spent indoors, use
of electronic devices, change in diet, obesity, onset of puberty, sedentary lifestyles).
Rate of Change
The annual rate of change of SER for those classified as myopic at Phase 1 was greater at 6–7
years than at 12–13 years similar to trends reported in other white [4,14] and Asian childhood
populations.[8] The annual rate of change for those classified as myopic at baseline is much
greater in the Sydney study (Table 3) across both the younger and older cohorts than for the
NICER study participants. In the younger cohort of the NICER study the annual rate of change
of SER from 6–7to12–13 years for those who were classified as myopic by Phase 3 (n = 31)
also shows myopic progression occurring at a slower rate than their Australian contemporaries.
Pärssinen and Lyyra [30] report an average annual change of -0.55D among myopic Finnish
children who were approximately 10 years old at baseline and were reviewed every year for
three years, and report that females progressed significantly faster than males. This annual rate
of progression is over twice that of the younger cohort of the present study and in contrast to
Pärssinen and Lyyra we found no significant difference in the incidence or progression of myo-
pia between genders. The average annual change in SER for participants who were classified as
myopic at Phase 3 was -0.23D and -0.10D for the younger and older cohorts respectively. Con-
sidering a clinically significant change in SER to be -0.25D or more, our data suggest that to
ensure children have appropriate, up-to-date refractive correction the following guidance
could be applied: those children aged 6–7 years who are myopic or at risk of developing myopia
(e.g. those with a positive family history, those who are emmetropic or have low levels or
hyperopia (<+0.75D) in early childhood, those with sedentary lifestyles, those spending less
than three hours outdoors per day-[31–36]) should be advised to have an annual eye examina-
tion. At 12–13 years, myopic children or for those at risk of developing myopia (as above for
6–7 years and in addition those in academically selected schooling [35]) it may be appropriate
to extend this routine sight test interval to two years unless symptoms indicate a need for more
rapid intervention. This guidance relates only to monocular spherical equivalent refractive
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 13 / 19
error and does not consider the dynamics of other visually important refractive features such
as astigmatism and anisometropia. Clinicians should be aware that these data apply to a UK
based population where myopia progression appears slower than that of other populations.
Change in Hyperopia
The proportion of participants classified as hyperopic within the present study was high for both
cohorts in comparison to the Sydney population [4] but comparable to that recorded under
cycloplegia by Logan et al.[23] for white UK children of the same age. Czepita et al.[22]reporta
higher prevalence of hyperopia (30.8%) in Polish children aged 10–14 years living in rural areas
compared to urban areas (7.1%) in Poland. Northern Ireland has a relatively rural population
(population density of 250–1000 per km
2
)[37] which is similar to that of rural Poland (popula-
tion density of <1000 per km
2
)[38] and in contrast to the urban population of Sydney (7000-
8000/km
2
).[39]However,Loganet al.’s data represent children schooled in a large UK city and
present a relatively similar situation to that found in Northern Ireland. Further work is needed to
fully understand why hyperopia is more common in some populations than in others.
The present study reports a significant annual reduction in hyperopia of 7.3% within the
younger cohort as they progress from 6–7to12–13 years of age. There are few studies which
have prospectively investigated change in hyperopia, however French et al.[4] report a greater
annual rate of reduction in hyperopia over a 5–6 year time period in both their cohorts of Austra-
lian children living in Sydney (aged six and 12 years at baseline) compared to the present study;
with an annual reduction of hyperopia of 12.3% and 10.2% for the younger and older cohorts
respectively. French et al.’s data are from children of mixed ethnicity (22% East Asian) which
may explain the greater myopic shift in refractive error compared to the present study. Zhao
et al.[20] also report a large annual reduction of hyperopia of 17.6% among children within the
Shunyi District of China (aged 5–15 years at baseline). Baseline prevalence of hyperopia within
Zhao’s Chinese population was also much lower (3%) than that found in the NICER study.
For both cohorts within the present study, those whose hyperopia was greater than +3.50DS
showed a relatively stable SER over the six-year period, in contrast to less hyperopic peers
whose hyperopia tended to reduce towards emmetropia during the study. Prospective studies
of infants’and young children’s refractive development also demonstrate that hyperopia that
fails to resolve through emmetropisation within the first year or two of life is likely to be persis-
tent.[40–42] Mutti et al.[43] states that infants with hyperopic errors of 4D or more are signifi-
cantly less likely to emmetropise than infants with lower levels of hyperopia and that
hyperopia of this level or greater is persistent. We have demonstrated that this persistent infan-
tile hyperopia endures through later childhood and early adulthood. Several researchers have
identified an association between retention of significant hyperopia in infancy (4D or more)
and poor accommodative function [44–47]. When retained beyond infancy higher levels of
hyperopia signal a resistance of the visual system to modification through visual feedback usu-
ally associated with emmetropisation. Kulp et al.[48] have suggested that the presence of het-
erotropia may reduce the rate of hyperopic decline and within our study, one third of those
with persistent hyperopia demonstrated heterotropia. In contrast to studies exploring hyper-
opic decline in childhood in other geographic and ethnic populations [4,49], the current study
reports a greater proportion of significant hyperopia throughout childhood and early adult-
hood and a much lower annual rate of refractive change in hyperopia. It appears that genetic or
environmental variance influences the persistency of hyperopia. Our data would support
Mezer et al.’s[49] findings that children with mild hyperopia may be able to cease spectacle
wear in later childhood, however those with moderate to high hyperopia will need to retain
their refractive correction.
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 14 / 19
Strengths and Limitations
Study methods and refractive classifications used in the NICER study were similar to other
large studies of refractive error in children for ease of comparison.[4,12,23] The epidemiologi-
cal design of the initial NICER study did not give consideration to sample size for future pro-
spective studies, therefore sample sizes at six year follow-up while favourable in comparison to
the only other published UK based prospective study evaluating cycloplegic refractive data in
childhood, [14] are modest in comparison to other published data.[4,20,31] While most partic-
ipants in the present study were contactable at Phase 3 and participation rates are comparable
to other longitudinal studies over similar time frames, [4,31] a significant number of partici-
pants were not re-examined particularly within the older cohort. Within the younger cohort,
there were no differences between those who participated at Phase 3 and those lost to follow-
up in age, gender, refractive error and socioeconomic factors. Children who had at least one
myopic parent were more likely to participate at Phase 3 than those with no myopic parents
which may have a genetic influence on the incidence of myopia within the younger cohort.
Within the older cohort, females were significantly more likely to participate than males.
We also report a higher percentage of myopic females than males and a greater incidence of
myopia in females to males within this cohort; however the differences were not statistically
significant. These retention issues could potentially bias our data towards more myopia in the
older cohort. Within the older cohort, spectacle wearers were more likely to participate at
Phase 3 than non-spectacle wearers possibly due to a greater interest in their eye care, however
spectacles wearers included both hyperopes and myopes.
The NICER study data have been compared with the data from Sorsby et al.[14] and
although efforts have been made to compare refractive classifications and rate of change of
myopia, there are limitations in these comparisons due to differences in the exact age of the
cohorts compared, the informal sampling methodology, method of refraction and lack of uni-
formity in the follow-up intervals in Sorsby’s study. Data from 6–7 year old children from the
Sorsby study have been directly compared with 6–7 year old children from the NICER study
due to a large number of data points within the Sorsby study at this age; participant numbers in
the Sorsby study were limited in other comparable age groups to the NICER study and have
not been directly compared. Given that Sorsby’s work is widely cited and well known in the
UK and beyond, it is useful to examine it in light of the contemporary findings of the NICER
study in an attempt to explore how refractive error has altered over the 50 year period.
The data presented on change in refractive error within this study are supported by ocular
biometric data that are presented in Supporting Information (S1,S2,S3 and S4 Tables).
Conclusions
In comparison to other worldwide studies the proportion of children and young adults classi-
fied as myopic remains relatively low in this white, UK based population and the proportion of
myopes is similar to other populations of European Caucasians of similar age. Differences
between the proportion of myopes in the NICER study and a comparable study of Australian
children of European Caucasian ethnicity apparent at 12–13 years were eliminated by 17 years
of age. Our data suggest that the proportion of myopes has remained relatively stable in the UK
over the short-term but has doubled in the last 50 years. Our results also suggest white children
in the UK are becoming myopic at a younger age than previously demonstrated; children are
more likely to develop myopia in the UK between 6–7 and 12–13 years than during teenage
years. Hyperopic errors above +3.50D tend to be persistent and stable across the school years,
but lower levels of hyperopia often decrease.
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 15 / 19
Supporting Information
S1 Table. Raw data set for the change in ocular biometrics (AL = axial length, corneal
power & ACD = anterior chamber depth) and SER (spherical equivalent refraction)
between Phase 1 and Phase 3 (6–7 years to 12–13 years) for participants classified as myo-
pic within the younger cohort. Participants shown in bold were classified as myopic at both
Phase 1 and Phase 3. Outlined below are the Spearman correlations between the change in SER
and change in AL, corneal power and ACD. Change in SER vs Change in AL, Spearman’s Cor-
relation, ρ= -0.7510, p<0.001. Change in SER vs Change in Corneal Power, Spearman’s Corre-
lation, ρ= -0.036, p= 0.985. Change SER vs Change in ACD, Spearman’s Correlation, ρ=
-0.347, p= 0.061.
(PDF)
S2 Table. Raw data set for the change in ocular biometrics (AL = axial length, corneal
power & ACD = anterior chamber depth) and SER (spherical equivalent refraction)
between Phase 1 and Phase 3 (12–13 years to 18–20 years) for participants classified as
myopic within the older cohort. Participants shown in bold were classified as myopic at both
Phase 1 and Phase 3 and participants shown in italics were classified as myopic at Phase 1 but
not at Phase 3. Outlined below are the Spearman correlations between the change in SER and
change in AL, corneal power and ACD. Change in SER vs Change in AL, Spearman’s Correla-
tion, ρ= -0.740, p<0.001. Change in SER vs Change in Corneal Power, Spearman’s Correla-
tion, ρ= 0.045, p= 0.768. Change SER vs Change in ACD, Spearman’s Correlation, ρ= -0.302,
p= 0.0047.
(PDF)
S3 Table. Raw data set for the change in ocular biometrics (AL = axial length, corneal
power & ACD = anterior chamber depth) and SER (spherical equivalent refraction)
between Phase 1 and Phase 3 (6–7 years to 12–13 years) for participants classified as hyper-
opic at Phase 1 within the younger cohort. Outlined below are the Spearman correlations
between the change in SER and change in AL, corneal power and ACD. Change in SER vs
Change in AL, Spearman’s Correlation, ρ= -0.707, p<0.001. Change in SER vs Change in Cor-
neal Power, Spearman’s Correlation, ρ= -0.114, p= 0.457. Change SER vs Change in ACD,
Spearman’s Correlation, ρ= -0.520, p<0.001.
(PDF)
S4 Table. Raw data set for the change in ocular biometrics (AL = axial length, corneal
power & ACD = anterior chamber depth) and SER (spherical equivalent refraction)
between Phase 1 and Phase 3 (12–13 years to 18–20 years) for participants classified as
hyperopic at Phase 1 within the older cohort. Outlined below are the Spearman correlations
between the change in SER and change in AL, corneal power and ACD. Change in SER vs
Change in AL, Spearman’s Correlation, ρ= -0.594, p<0.001. Change in SER vs Change in Cor-
neal Power, Spearman’s Correlation, ρ= 0.008, p= 0.964. Change SER vs Change in ACD,
Spearman’s Correlation, ρ= -0.322, p= 0.063.
(PDF)
Acknowledgments
The authors thank the College of Optometrists (London, UK) for their ongoing support for the
NICER study, and the participants in the NICER study for their ongoing commitment to this
research and to the schools where the research is conducted.
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 16 / 19
Author Contributions
Conceived and designed the experiments: KJS LOD. Performed the experiments: SJM KJS
LOD. Analyzed the data: SJM KJS LOD. Contributed reagents/materials/analysis tools: SJM
KJS LOD. Wrote the paper: SJM KJS LOD.
References
1. Lin LL, Shih YF, Hsiao CK, Chen CJ. Prevalence of myopia in Taiwanese schoolchildren:1983 to 2000.
Ann Acad Med Singapore. 2004; 33(1):27–33. PMID: 15008558
2. Seet B, Wong TY, Tan DT, Saw SM, Balakrishnan V, Lee LK, et al. Myopia in Singapore: taking a public
health approach. Br J Ophthalmol. 2001; 85(5):521–6. PMID: 11316705
3. Vitale S, Sperduto RD, Ferris FL III. Increased prevalence of myopia in the United States between
1971–1972 and 1999–2004. Arch Ophthalmol. 2001; 127(12):1632–9.
4. French AN, Morgan IG, Burlutsky G, Mitchell P, Rose KA. Prevalence and 5- to 6- Year Incidence and
Progression of Myopia and Hyperopia in Australian Schoolchildren. Ophthalmology. 2013; 120
(7):1482–91. doi: 10.1016/j.ophtha.2012.12.018 PMID: 23522969
5. Castagno VD, Fassa AG, Carrett ML, Vilela MA, Meucci RD. Hyperopia: a meta-analysis of prevalence
and review of associated factors among school-aged children. BMC Ophthalmol. 2014; 14:163. doi:
10.1186/1471-2415-14-163 PMID: 25539893
6. Fan DS, Lam DS, Lam RF, Lau JT, Chong KS, Lai RY et al. Prevalence, incidence, and progression of
myopia of school children in Hong Kong. Invest Ophthalmol Vis Sci. 2004; 45(4):1071–5. PMID:
15037570
7. Jones LA, Mitchell GL, Mutti DO, Hayes JR, Moeschberger ML, Zadnik K. Comparison of ocular com-
ponent growth curves among refractive error groups in children. Invest Ophthalmol Vis Sci. 2005; 46
(7):2317–27. PMID: 15980217
8. Saw SM, Tong L, Chua WH, Chia KS, Koh D, Tan DT et al. Incidence and progression of myopia in Sin-
gaporean school children. Invest Ophthalmol Vis Sci. 2005; 46(1): 51–7. PMID: 15623754
9. Williams C, Northstone K, Howard M, Harvey I, Harrad RA, Sparrow JM. Prevalence and risk factors for
common visual problems in children: data from the ALSPAC study. Br J Ophthalmol. 2008; 92(7):959–
64. doi: 10.1136/bjo.2007.134700 PMID: 18480306
10. Guggenheim JA, Northstone K, McMahon G, Ness AR, Deere K, Mattocks C et al. Time Outdoors and
Physical Activity as Predictors of Incident Myopia in Childhood: A Prospective Cohort Study. Invest
Ophthalmol Vis Sci. 2012; 53(6):2856–65. doi: 10.1167/iovs.11-9091 PMID: 22491403
11. Breslin KMM, O'Donoghue L, Saunders K. A Prospective Study of Spherical Refractive Error and Ocu-
lar Components Among Northern Irish Schoolchildren (The NICER Study). Invest Ophthalmol Vis Sci.
2013; 54(7):4843–50. doi: 10.1167/iovs.13-11813 PMID: 23745004
12. 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(4):421–426. PMID:
10764848
13. Ojaimi E, Rose KA, Smith W, Morgan IG, Martin FJ, Mitchell P. Methods for a population-based study
of myopia and other eye conditions in school children: the Sydney Myopia Study. Ophthalmic Epide-
miol. 2005; 12(1):59–69. PMID: 15848921
14. Sorsby A, Benjamin B, Sheridan M, Stone J, Leary GA. Refraction and its components during the
growth of the eye from age of three. Memo Med Res Counc. 1961, 301(special):1–67. PMID:
13915328
15. O'Donoghue L, Saunders KJ, McClelland JF, Logan NS, Rudnicka AR, Owen CG. Sampling and mea-
surement methods for a study of childhood refractive error in a UK population. Br J Ophthalmol. 2010;
94(9):1150–54. doi: 10.1136/bjo.2009.167965 PMID: 20558427
16. Tang WC, Tang YY, Lam CS. How representative is the ‘Representative Value’of refraction provided
by the Shin-Nippon NVision-K 5001 autorefractor? Ophthalmic Physiol Opt. 2014; 34(1):89–93. doi:
10.1111/opo.12098 PMID: 24325438
17. Davies LN, Mallen EA, Wolffsohn JS, Gilmartin B. Clinical evaluation of the Shin-Nippon NVision-K
5001/Grand Seiko WR-5100K autorefractor. Optometry & Vision Science. 2003; 80(4):320–4.
18. Mallen EA, Gilmartin B, Wolffsohn JS, Tsujimura S. Clinical evaluation of the Shin-Nippon SRW-5000
autorefractor in adults: an update. Ophthalmic Physiol Opt. 2015; 35(6):622–7. doi: 10.1111/opo.
12254 PMID: 26497294
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 17 / 19
19. O’Donoghue L, McClelland JF, Logan NS, Rudnicka AR, Owen CG, Saunders KJ. Refractive error and
visual impairment in school children in Northern Ireland. Br J Ophthalmol. 2010; 94(9):1155–9. doi: 10.
1136/bjo.2009.176040 PMID: 20494909
20. Zhao J, Pan X, Sui R, Munoz SR, Sperduto RD, Ellwein LB. Refractive error study in children: results
from Shunyi District, China. Am J Ophthalmol. 2000; 129(4):427–35. PMID: 10764849
21. Northern Ireland Statistics and Research Agency [Internet], Census 2011, Key Statistics for Northern
Ireland [cited 20
th
August 15] Available from http://www.nisra.gov.uk/Census/key_stats_bulletin_2011.
pdf
22. Czepita D, Mojsa A, Zejimo M. Prevalence of myopia and hyperopia among urban and rural schoolchil-
dren in Poland. Ann Acad Med Stetin. 2008; 54(1):17–21. PMID: 19127805
23. Logan NS, Shah P, Rudnicka AR. Childhood ethnic differences in ametropia and ocular biometry: the
Aston Eye Study. Ophthalmic Physiol. Opt. 2011; 31(5):550–8. doi: 10.1111/j.1475-1313.2011.00862.
xPMID: 21762431
24. Jones LA, Sinnott LT, Mutti DO, Mitchell GL, Moeschberger ML, Zadnik K. Parental history of myopia,
sports and outdoor activities and future myopia. Invest Ophthalmol Vis Sci. 2007; 48(8):3524–32.
PMID: 17652719
25. Williams KM, Bertelsen G, Cumberland P, Wolfram C, Verhoeven VJ, Anastasopoulos E, et al. Increas-
ing prevalence of myopia in Europe and the impact of education. Ophthalmology. 2015; 122(7):1489–
97. doi: 10.1016/j.ophtha.2015.03.018 PMID: 25983215
26. Sherwin JC, Reacher MH, Keogh RH, Khawaja AP, Mackey DA, Foster PJ. The association between
time spent outdoors and myopia in children and adolescents: a systemic review and meta-analysis.
Ophthalmology. 2012; 119(10):2141–51. doi: 10.1016/j.ophtha.2012.04.020 PMID: 22809757
27. McKnight CM, Sherwin JC, Yazar S, Forward H, Tan AX, Hewitt AW, et al. Myopia in young adults is
inversely related to an objective marker of ocular sun exposure: the Western Australian Raine cohort
study. Am J Ophthalmol. 2014; 158(5):1079–85. doi: 10.1016/j.ajo.2014.07.033 PMID: 25072831
28. French AN, O’Donoghue L, Morgan IG, Saunders KJ, Mitchell P, Rose KA. Comparison of refraction
and ocular biometry in European Caucasian children living in Northern Ireland and Sydney, Australia.
Invest Ophthalmol Vis Sci. 2012; 53(7):4021–31. doi: 10.1167/iovs.12-9556 PMID: 22562516
29. French AN, Morgan IG, Mitchell P, Rose KA. Patterns of myopigenic activities with age, gender and eth-
nicity in Sydney schoolchildren. Ophthalmic Physiol Opt. 2013; 33(3):318–28. doi: 10.1111/opo.12045
PMID: 23452023
30. Pärssinen O, Lyyra AL. Myopia and myopic progression among schoolchildren: a three year follow-up
study. Invest Ophthalmol Vis Sci. 1993; 34(9):2794–2802. PMID: 8344801
31. Jones-Jordan LA, Sinnott LT, Manny RE, Cotter SA, Kleinstein RN, Mutti DO et al. The Collaborative
Longitudinal Evaluation of Ethnicity and Refractive Error (CLEERE) Study Group. Early childhood
refractive error and parental history of myopia as predictors of myopia. Invest Ophthalmol Vis Sci 2010;
51(1):115–21. doi: 10.1167/iovs.08-3210 PMID: 19737876
32. Zadnik K, Mutti DO, Friedman NE, Qualley PA, Jones LA, Qui P et al. Ocular predictors of the onset of
juvenile myopia. Invest Ophthalmol Vis Sci. 1999; 40(9):1936–43. PMID: 10440246
33. Ip JM, Saw SM, Rose KA, Morgan IG, Kifley A, Wang JJ, et al. Role of near work in myopia: findings in
a sample of Australian school children. Invest Ophthalmol Vis Sci. 2008; 49(7):2903–10. doi: 10.1167/
iovs.07-0804 PMID: 18579757
34. Rose KA, Morgan IG, Ip J, Kifley A, Huynh S, Smith W et al. Outdoor activity reduces the prevalence of
myopia in children. Invest Ophthalmol Vis Sci. 2008, 115(8):1279–85.
35. O’Donoghue L, Kapetanankis VV, McClelland JF, Logan NS, Owen CG, Saunders KJ et al. Risk Fac-
tors for Childhood Myopia: Findings from the NICER Study. Invest Ophthalmol Vis Sci. 2015; 56
(3):1524–30. doi: 10.1167/iovs.14-15549 PMID: 25655799
36. McCullough SJ, Breslin KMM, O’Donoghue L, Saunders KJ. A six year prospective profile of refractive
error status adults in Northern Ireland-The NICER Study. Ophthalmic Physiol Opt 2014; 34(6):685–6.
37. Northern Ireland Statistics and Research Agency. Population and Migration Estimates Northern-Statis-
tical Report 2013 [Internet]. [cited 11th May 2015] Available from: http://www.nisra.gov.uk/archive/
demography/population/midyear/MYE13_Report.pdf
38. Śleszyński P. Distribution of population density in Polish towns and cities. Geographia Polonica. 2014;
87(1):61–75.
39. Australian Bureau of Statistics. Geographic Distribution of the Population, 2010 [Internet].[cited 21st
May 2015] Available from: http://www.abs.gov.au/
40. Ingram RM, Barr A. Changes in refraction between the ages of 1 and 3 ½years. Br J Opthalmol. 1979,
63(5):339–42.
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 18 / 19
41. Dobson V, Sebris SL. Longitudinal study of acuity and stereopsis in infants with or at-risk for esotropia.
Invest Ophthalmol Vis Sci. 1989; 30(6):1146–58. PMID: 2732029
42. Pennie FC, Wood IC, Olsen C, White S, Charman WN. A longitudinal study of the biometric and refrac-
tive changes in full-term infants during the first year of life. Vision Res. 2001; 41(21):2799–2810. PMID:
11587728
43. Mutti DO, Mitchell GL, Jones LA, Friedman NE, Frane SL, Lin Wk et al. Axial growth andchanges in len-
ticular and corneal power during emmetropisation in infants. Invest Ophthlamol Vis Sci. 2005; 46
(9):324–6.
44. Mutti DO, Mitchell GL, Jones LA, Friedman NE, Frane SL, Lin WK, et al. Accommodation, acuity, and
their relationship to emmetropisation in infants. Optom Vis Sci. 2009; 86(6):666–76. PMID: 19417711
45. Candy TR, Gray KH, Hohenbary CC, Lyon DW. The accommodative lag of the young hyperopic patient.
Invest Ophthalmol Vis Sci. 2012; 53(1):143–9. doi: 10.1167/iovs.11-8174 PMID: 22125280
46. Horwood AM, Riddell PM. Hypo-accommodation responses in hypermetropic infants and children. Br J
Ophthalmol. 2012; 95(2):231–7.
47. Tarczy-Hornoch K. Accommodative lag and refractive error in infants and toddlers. J AAPOS. 2012; 16
(2):112–7. doi: 10.1016/j.jaapos.2011.10.015 PMID: 22424817
48. Kulp MT, Foster NC, Holmes JM, Kraker RT, Melia BM, Repka MX, et al. Effect of ocular alignment on
emmetropization in children <10 years with amblyopia. Am J Ophthalmol. 2012; 154(2):297–302. doi:
10.1016/j.ajo.2012.02.035 PMID: 22633344
49. Mezer E, Meyer E, Wygnansi-Jaffe T, Haase W, Shauly Y, Biglan AW. The long-term outcome of the
refractive error in children with hypermetropia. Graefes Arch Clin Exp Ophthalmol. 2015; 253:1013–
1019. doi: 10.1007/s00417-015-3033-z PMID: 25952040
Six Year Refractive Change in the UK - The NICER Study
PLOS ONE | DOI:10.1371/journal.pone.0146332 January 19, 2016 19 / 19