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Myopia Prevention and Outdoor Light
Intensity in a School-Based Cluster
Randomized Trial
Pei-Chang Wu, MD, PhD,
1
Chueh-Tan Chen, MS,
1
Ken-Kuo Lin, MD,
2
Chi-Chin Sun, MD, PhD,
3
Chien-Neng Kuo, MD,
4
Hsiu-Mei Huang, MD,
1
Yi-Chieh Poon, MD,
1
Meng-Ling Yang, MD,
2
Chau-Yin Chen, MD,
4
Jou-Chen Huang, MD,
4
Pei-Chen Wu, MD,
4
I-Hui Yang, MD,
1
Hun-Ju Yu, MD,
1
Po-Chiung Fang, MD,
1
Chia-Ling Tsai, DDS,
5
Shu-Ti Chiou, PhD,
6,7,8,
*Yi-Hsin Yang, PhD
9,
*
Purpose: To investigate the effectiveness of a school-based program promoting outdoor activities in Taiwan
for myopia prevention and to identify protective light intensities.
Design: Multi-area, cluster-randomized intervention controlled trial.
Participants: A total 693 grade 1 schoolchildren in 16 schools participated. Two hundred sixty-seven
schoolchildren were in the intervention group and 426 were in the control group.
Methods: Initially, 24 schools were randomized into the intervention and control groups, but 5 and 3 schools
in the intervention and control groups, respectively, withdrew before enrollment. A school-based Recess Outside
Classroom Trial was implemented in the intervention group, in which schoolchildren were encouraged to go
outdoors for up to 11 hours weekly. Data collection included eye examinations, cycloplegic refraction, noncontact
axial length measurements, light meter recorders, diary logs, and questionnaires.
Main Outcome Measures: Change in spherical equivalent and axial length after 1 year and the intensity and
duration of outdoor light exposures.
Results: The intervention group showed significantly less myopic shift and axial elongation compared with
the control group (0.35 diopter [D] vs. 0.47 D; 0.28 vs. 0.33 mm; P¼0.002 and P¼0.003) and a 54% lower risk of
rapid myopia progression (odds ratio, 0.46; 95% confidence interval [CI], 0.28e0.77; P¼0.003). The myopic
protective effects were significant in both nonmyopic and myopic children compared with controls. Regarding
spending outdoor time of at least 11 hours weekly with exposure to 1000 lux or more of light, the intervention
group had significantly more participants compared with the control group (49.79% vs. 22.73%; P<0.001).
Schoolchildren with longer outdoor time in school (200 minutes) showed significantly less myopic shift
(measured by light meters; 1000 lux: 0.14 D; 95% CI, 0.02e0.27; P¼0.02; 3000 lux: 0.16 D; 95%
CI, 0.002e0.32; P¼0.048).
Conclusions: The school-based outdoor promotion program effectively reduced the myopia change in both
nonmyopic and myopic children. Outdoor activities with strong sunlight exposure may not be necessary for
myopia prevention. Relatively lower outdoor light intensity activity with longer time outdoors, such as in hallways
or under trees, also can be considered. Ophthalmology 2018;125:1239-1250 ª2018 by the American Academy of
Ophthalmology
Supplemental material available at www.aaojournal.org.
The increasing prevalence of myopia has become an
important public health issue in recent decades.
1
In East
Asia, myopia is found to progress rapidly, by
approximately 1 diopter (D) per year in schoolchildren;
up to 24% of young adults are highly myopic.
2
The
prevalence of myopia is 20% to 30% for 6- to 7-year-old
children and is as high as 84% for high school students in
Taiwan.
2
In contrast, a much lower prevalence of 1.6% to
1.9% for myopia was reported in cities of mainland China
for children of this age.
3,4
One of the reasons that a lower
prevalence was reported in China may be associated with
more rigorous cycloplegia and exclusion of children with
incomplete cycloplegia.
3
However, future studies are
required to determine the optimal regimen to use for
cycloplegia in East Asian children of this age. In general,
as soon as myopia sets in for young children, it will
progress until the end of adolescence.
5e7
Early myopia
onset generally results in fast and longer duration for
myopia progression and, consequently, a higher risk of
becoming highly myopic later in life. High myopia (more
than 5D)
8
can result in cataracts, glaucoma, retinal
detachments, choroid neovascularization, macular
degeneration, and blindness.
9e11
Currently, myopia macul-
opathy is the leading cause of blindness in Taiwan, Japan,
1239ª2018 by the American Academy of Ophthalmology
Published by Elsevier Inc.
https://doi.org/10.1016/j.ophtha.2017.12.011
ISSN 0161-6420/17
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and China.
12e14
Therefore, a strategy to postpone the age of
myopia onset is important and necessary for decreasing the
high myopia prevalence in future generations.
Recently, evidence has shown that children who spend
more time outdoors have a lower incidence of
myopia.
4,15e17
From the self-report questionnaires, it seems
that approximately 10 to 14 hours weekly could abolish the
additional myopia associated with higher amount of near
work or parental myopia.
15,18
However, although encour-
aging children to participate in outdoor activities during
recess is important, exposure to direct sunlight also can
result in the development of other health concerns, such as
skin cancer. There is a need both for an objective assessment
of time spent outdoors and for determining the amount of
sunlight necessary for reducing the incidence of myopia.
Our previous study indicated that the 1-year intervention of
the Recess Outside Classroom program, which recommends
that children should go outdoors during recess (approxi-
mately 80 minutes daily) could reduce myopia incidence by
half after 1 year (8.4% vs. 17.7%).
17
Recently, a cluster
randomized trial with the addition of 40 minutes of
outdoor activity per day at school resulted in a reduced
incidence rate of myopia after 3 years (30.4% vs. 39.5%).
4
However, no randomized study yet has used objective and
quantitative measures to record participants’outdoor time
and sunlight intensity and the association with myopia.
Thus, a quantitative method to estimate objectively the
required outdoor time and sunlight strength is needed. Based
on the principal protective factor which is outdoor activities,
and principal risk factor, which is prolonged duration of
near work (e.g., reading, painting, writing, screen
time),
19e21
we developed the school-based Recess Outside
Classroom Trial 711 (ROCT711) program to increase out-
door time for schoolchildren, including recess outside the
classroom, incentive-based outdoor homework, and other
assignments. In this study, we performed a multi-area,
cluster-randomized ROCT711 program trial in Taiwan to
investigate its effect on myopia and axial length change in 6-
to 7-year-old schoolchildren. A light meter was used to
measure objectively the outdoor time and light intensity to
validate the relationship between time spent outdoors and
myopia.
Methods
Study Design and Participants
We conducted a multi-area cluster-randomized controlled trial for
myopia prevention from September 2013 through February 2015.
This study adhered to the tenets of the Declaration of Helsinki.
Ethics approval for this study was obtained from the institutional
review board of the Chang Gung Memorial Hospital and the trial is
registered with the Clinical Trials registry (identifier,
NCT02082743). Study participants and parents provided written
informed consent. Schoolchildren in both groups underwent as-
sessments of cycloplegic refraction and noncontact axial length
measurements, wore a light meter recorder for 1 week, and
completed weekly activity diary logs and questionnaires with the
help of their parents at baseline and at the end of the study.
Measurements were performed by ophthalmologists and trained
research assistants who were blinded to intervention conditions.
Four geographical areas (north, central, south, and west) in
Taiwan were identified first. Within each area, 1 or 2 cities or
counties were selected based on local weather and sunshine time so
that the selected schools would cover a variety of weather condi-
tions. For example, Keelung has the most rainy days, and Kaoh-
siung and Taitung have more sunny days. In total, 6 cities or
counties were chosen. Within each city or county, we obtained
their districts’education statistics from the Department of House-
hold Registration, Ministry of the Interior. The proportions of
adults with education of college or more were ranked within each
city or county, and the districts that are the median of these pro-
portions were selected. Finally, 4 schools in each of the 6 districts
were selected randomly as an intervention group or a control
group. The random allocation sequence was generated by a
computer-based random number-producing algorithm and
completed by a researcher not involved in the project to ensure an
equal chance of a school being allocated to each group.
Procedures
The ROCT711 intervention program was devised based on the
Recess Outside Classroom pilot study,
17
which required first-grade
schoolchildren to go outdoors during recess and while out of
school for a minimum amount of time. The ROCT711 program
encourages schoolchildren to participate in outdoor activities dur-
ing recess. During a normal school day in Taiwan, there are 4
classes and 3 recesses (10, 20, and 10 minutes in duration) in the
morning for first-grade schoolchildren. If a child goes outside the
classroom during every recess, then he or she would have 200
minutes of in-school outdoor time during the 5 school days every
week. Teachers were invited to assign homework that included
outdoor activities during weekends, holidays, and summer vaca-
tion. Parents were encouraged to bring children for outdoor ac-
tivities during out-of-school time.
During our study period, there were 2 initiatives for myopia
prevention: Sport & Health 150 promoted an additional 150 mi-
nutes of exercise time per week and Tien-Tien 120 promoted
outdoor activities for 120 minutes every day. Although the latter
initiative was not compulsory, schools were encouraged to promote
these activities. Thus, the control schools were already receiving
some intervention to minimize myopia. Table 1 is a summary of
intervention items in both groups.
In the intervention group, participants were encouraged to have
11 hours or more of outdoor time every 7 days (ROCT711).
Teachers, children, and parents received eye health education from
ophthalmologists regarding a new concept of myopia prevention
using evidence-based medicine as well as possible complications
induced by myopia. Children were encouraged to take specific
breaks from near work that included reading, writing, painting,
screen time, and others (30 minutes of near work followed by a
10-minute break [30/10]). We designed a series of ROCT711 pro-
gram components to enhance the compliance of outdoor activities.
To encourage family weekend outdoor activities, there were routine
learning assignments, honor rewards for students, and local up-
coming outdoor family event information for outdoor activities and
near-work breaks. A detailed outline of the program components is
given in the Appendix (available at www.aaojournal.org). The same
eye health education was provided for teachers, children, and parents
in the control group, but no ROCT711 intervention was performed
during the study period.
To investigate the compliance of students spending recess time
outside of the classroom, we performed 2 school audits during the
study period without prior notice. The classroom clearance rate
during recess in each school was calculated by dividing the number
of children outside the classroom by the total children in the class.
The average classroom clearance rate for the intervention schools
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was 81.29% (standard deviation [SD], 13.88%) and for control
schools was 61.11% (SD, 11.85%; P¼0.007).
Outcomes
Refraction measurements were performed at the beginning of the
study, when the schools initiated participation, and at the end of
the study. Changes in spherical equivalence refraction (SER) and
axial length were computed from values measured at baseline and
at the end of the study. Myopia was defined as at least 0.5 D of
SER on cycloplegic autorefraction performed using an autore-
fractometer (KR-8100; Topcon, Tokyo, Japan). Corneal anes-
thesia was used to minimize the discomfort caused by the
cycloplegic drops. For cycloplegia, 1 drop of 0.5% proparacaine
was followed by 1 drop of 1% tropicamide (Mydriacyl; Alcon,
Puurs, Belgium) and 1% cyclopentolate hydrochloride (Cyclogyl;
Alcon Laboratories, Fort Worth, TX) administered 5 minutes
apart. Measurements were obtained 30 minutes after the initial
drop was administered and the pupil size was more than 6 mm in
diameter. Five to 8 consecutive readings were obtained for each
child. Measurements of ocular biometric parameters (axial length
and keratometry) were performed with a noncontact ocular
biometry system (Lenstar LS 900; Haag-Streit AG, Köniz,
Switzerland). This instrument works on the principle of optical
low-coherence reflectometry. Children with best-corrected visual
acuity not achieving 20/25 or those diagnosed with amblyopia
were excluded from this study. Those undergoing orthokeratology
treatment or atropine eye drop treatment also were excluded from
this study.
Outdoor time was evaluated for schoolchildren. Participants
wore light meters (HOBO, Contoocook, NH) on their collars for 7
consecutive days and completed a 1-week diary in which they
recorded activities every half hour to determine their outdoor ac-
tivity time. The light meter records light intensity (lux) every 5
minutes, which corresponds to a total of 288 readings per day.
These values of light intensity then were transformed into an Excel
(Microsoft, Redmond, WA) file for each individual student. As
shown in Figure 1, the lower left column indicates the date, time (AM
or PM, hour, minute, second), and the values of light intensity. The
individual data files were imported into Statistical Analysis
Software version 9.3 (SAS Institute, Cary, NC). The actual light
intensities at different areas of schools are shown in Figure 2,
which shows that in any areas outside of the classroom, the light
intensities were measured to be at least 1000 lux. Therefore, we
defined the child as being outdoors when a value of light intensity
of more than 1000 lux was measured from the light meter (Fig
1C). Because the light meter records the light intensity every 5
minutes, we calculated the time spent outdoors as the number of
light intensity readings of 1000 lux or more times 5 minutes. The
total minutes of exposure to 3000 lux or more, 5000 lux or more,
or 10 000 lux or more light intensities also were calculated in a
similar manner. The first-grade schoolchildren in Taiwan attend
half-day morning courses during all weekdays except Tuesday,
which includes a full-day course. The weekly outdoor time was
calculated by the light meters, which recorded outdoor time during
weekday mornings and Tuesday afternoons (in-school outdoor
time); outdoor time during the afternoon (afternoon out-of-school
outdoor time) and outdoor time during the weekend (weekend out-
door time) were obtained from the diary log.
The weather conditions also may affect the time spent outdoors.
Therefore, to obtain the total hours of sunshine corresponding to
the week that each schoolchild wore the light meter, daily hours of
sunshine for the study period of the 6 cities or counties were ob-
tained from the Taiwan Central Weather Bureau. We then matched
the same dates that the light meter was worn and summed the total
hours of sunshine during the week. To minimize missing data,
teachers were responsible for reminding participants to wear the
light meters during school time and parents were educated about
the importance of using the light meter and diary log that were sent
home during off-school time on weekdays and weekends. Activ-
ities that were performed outside a building during the day, such as
riding bicycles, park visits, walking around the neighborhood, and
outdoor sports, were all classified as outdoor activities. Indoor
activities were defined as inside a building or an enclosed space or
travelling in a car or train.
Dharani et al
22
recommended using a diary and light meter in
randomized control trials of outdoor intervention. The light meter
has the advantage of objectively and precisely recording the
duration and intensity of light exposure. In this study, the
compliance of wearing light meters was monitored by teachers
during school time. However, during the time out of school,
wearing light meters was not monitored closely and the
compliance decreased. Therefore, we used the diary log to
calculate outdoor time during the period out of school. In
addition, because of the changing climate in different regions of
Taiwan, our analysis also adjusted for the daily regional sunlight
hours when calculating outdoor times for all schools.
The habit of near-work breaks (30/10) was evaluated by
questionnaires filled out at baseline and at the end of the study.
Parents accompanied by their children answered the question “Do
you use the 30/10 rule: 30 minutes followed by a 10-minute break
during near-work activities, such as reading, writing, painting,
computer or smartphone, and so on?”Weekly diopter-hours of near
work were computed by summing up 3 number of hours of
reading, 2 number of hours of other mid-distance near work, 2
number of hours of using computer, and 1 number of hours of
watching television.
Statistical Analysis
A power calculation was conducted to determine the sample size
necessary to detect changes in the primary outcome of SER
Table 1. Summary of Intervention Items between Recess Outside
Classroom Trial 711 Program and Control Groups
Intervention items
Recess Outside
Classroom
Trial 711 Control
Recess outside classroom program Yes No
Outdoor-oriented school activities Yes No
Weekend sun-time passport assignment Yes No
Booklet for teachereparent communication Yes No
Outdoor learning assignments in summer
vacation
Yes No
Eye health education for teachers and students,
promote outdoor activity and 30/10 rule for
myopia prevention.
Yes Yes
Sport & Health 150: an initiative to promote
an additional 150 minutes of exercise per
week. This initiative was started during the
late period of this study.
Yes Yes
Tien-Tien 120: an initiative that promotes
outdoor activities for 120 minutes daily.
Although this initiative was not compulsory,
5% of the elementary schools in Taiwan
were selected by the Bureau of Education for
monitoring compliance with time outdoors.
None of the schools in this study were
among the selected schools.
Yes Yes
30/10 ¼30 minutes of near work followed by a 10-minute break.
Wu et al Myopia Prevention and Outdoor Light Intensity
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changes. According to our previous result of a difference in myopia
shift of 0.13 D/year between intervention and control groups
(0.25 D/year vs.0.38 D/year; P¼0.029),
17
a myopia shift of
0.13 D/year was regarded as clinically important and achievable
in children. Using an
a
of 0.05 and power of 80%, a sample size
of 443 students per group was needed to detect a 0.13-D/year
difference (SD, 0.69 D/year) between groups. Therefore, the
ROCT711 study consisted of a cluster-randomized controlled trial
Figure 1. Images showing light meter wearing and recording. A, Setting light meter. B, Wearing meter during school time. C, Examples of intensity readings
from recorders. The light meter records light intensity (lux) every 5 minutes, which corresponds a total of 288 readings per day. These values of light
intensity then were transformed into an Excel (Microsoft, Redmond, WA) data sheet for each individual student. D, Line plots from readings on weekdays.
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with first-grade students from 24 primary schools. Of these 24
schools, 16 were followed up for 1 year and 8 schools were fol-
lowed up for half of a year because of a delayed administration
process.
Descriptive statistics, 2-sample ttests, and chi-square tests
were used to compare baseline characteristics between the
intervention and control groups. Analyses of primary and sec-
ondary outcomes were conducted using the generalized esti-
mating equation to account for possible deviations from the
normal distribution and cluster effects. The covariates in the
analysis models included the corresponding baseline measures,
age, gender, area, parental myopia, and the total sun hours during
light meter wearing week. SAS software version 9.3 (SAS
Institute, Inc., Cary, NC) was adapted for the analysis. All P
values were considered statistically significant when they were
less than 0.05.
Results
A total of 930 students in 16 schools (365 in the intervention group
and 565 in the control group) consented and attended baseline
assessments. Overall, the average age was 6.34 years (SD, 0.48
years) and 47.85% were girls. At baseline, 10.53% of participants
were myopic after excluding myopic children with current treat-
ment. Table 2 displays the baseline demographic information of
both groups. The intervention and control groups were fairly
comparable, and there was no statistically significant difference
between the 2 groups when considering various baseline factors
(all P0.05; Table 2). After excluding 120 students with
ongoing myopia treatments, a total of 693 students in 16 schools
completed the full 1-year program (267 in the intervention group
and 426 in the control group; Appendix, available at
www.aaojournal.org). Figure 3 illustrates the flowchart of
participant recruitment.
Primary Outcome: Myopia Change
After the students completed the 1-year trial, the myopic shift was
significantly less for the intervention group than for the control
group (0.35 D vs. 0.47 D; difference, 0.12 D; 95% confidence
interval [CI], 0.05e0.19; P¼0.002; Table 3). There was
significantly less axial length elongation in the intervention
group than in the control group (0.28 mm vs. 0.33 mm;
difference, 0.05 mm; 95% CI, 0.02e0.08; P¼0.003). The
incidence of new myopia onset in the intervention group was
Figure 2. Photographs showing light intensity in different areas of the school. Light intensities were measured using the Digital Lux Tester (YF-1065; Tecpel,
Taipei, Taiwan) at Kaohsiung Niaosong Elementary School. CM ¼centimeter.
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less than that in the control group (14.47% vs. 17.40%), and there
was 35% less risk of myopia (odds ratio, 0.65; 95% CI, 0.42e1.01;
P¼0.054). The fast myopia shift rate (more than 0.5 D/year) for
the intervention group was significantly less than that for the
control group (21.7% vs. 31.0%), and there was a 54% lower
risk of fast myopia progression (odds ratio, 0.46; 95% CI,
0.28e0.77; P¼0.003). We also computed the event rates based
on the intention-to-treat approach with the last observation car-
ried forward strategy. Based on the intention-to-treat approach, the
event rates for new incidences of myopia were 10.86% (34/313)
and 14.14% (67/474) for the intervention and control groups,
respectively, and the percentages of myopia shift of 0.5 D or
more were 15.89% (58/365) and 23.36% (132/565), respectively
(data not shown in Tables). The statistical significance remained
the same for the intention-to-treat approach.
The changes from baseline for nonmyopic and myopic children
were analyzed further separately. For the nonmyopic children at
baseline, the myopic shift was significantly less in the intervention
group than in the control group (0.32 D vs. 0.43 D; difference, 0.11 D;
95% CI, 0.02e0.20; P¼0.02). There was significantly less axial
length elongation in the intervention group than in the control group
(0.26 mm vs. 0.30 mm; difference, 0.03 mm; 95% CI, 0.01e0.06;
P¼0.02). For the myopic children at baseline, the myopic pro-
gression was significantly less in the interventional group than the
control group (0.57 D vs. 0.79 D; difference, 0.23 D; 95% CI,
0.06e0.39; P¼0.007). There was significantly less axial length
elongation in the intervention group than in the control group (0.45
mm vs. 0.60 mm; difference, 0.15 mm; 95% CI, 0.02e0.28;
P¼0.02).
Secondary Outcome: Outdoor Time
Table 4 shows the weekly outdoor time spent by both groups at
different light intensities (1000, 3000, 5000, and 10 000 lux).
The intervention and control groups were not significantly
different at baseline. At the end of the study, the intervention
group had spent more time outdoors than the control group
during weekdays in school, out of school during weekdays, and
weekends, although these were not statistically different.
However, when analyzing the time spent outdoors per week,
which combines the amount of time with exposure to 1000 lux
or more during school and the amount of time recorded on self-
reported diaries outside of school, schoolchildren in the interven-
tion group spent significantly more time outdoors (mean, 669.36
minutes; SD, 22.98 minutes) than the control group (598.8116.20
minutes), with a difference of 70.55 minutes (95% CI,
16.51e124.59 minutes; P¼0.01). Similarly, when evaluating the
time spent outdoors per week, combining the amount of time
recorded on self-reported diaries and the time during school with
exposures of 3000 lux or more, 5000 lux or more, or 10 000 lux or
more, significant differences between the 2 groups also were found
(P¼0.04, P¼0.047, and P¼0.04, respectively). When assessing
whether a goal of ROCT711 of spending at least 11 hours of
outdoor time weekly had been reached, we found that a signifi-
cantly higher percentage of participants in the intervention group
(119/239 participants [49.79%]) had spent more than 11 hours of
outdoor time per week compared with the control group (85/374
participants [22.73%]; P<0.001).
Noncompliance occurred in the intervention group, and the
control group also may have included schoolchildren who spent
time outdoors. We further pooled all participants (including inter-
vention and control groups) and conducted a post hoc analysis for
the different durations of weekly outdoor time during school.
Table 5 shows the relationship between time spent outdoors (at
different levels of light intensity) during school and SER
changes. We separated the participants into 3 groups according
to their weekly in-school outdoor time (<125 minutes, 125199
minutes, and 200 minutes). The group with the least time out-
doors in school was the reference group. When assessing SER
changes compared with the reference group, participants who had
200 minutes or more of weekly outdoor time during school hours
in the 1000 lux or more, or 3000 lux or more environment had
significantly less myopic shift (1000 lux: 0.14 D [95% CI,
0.02e0.27; P¼0.02]; 3000 lux: 0.16 D [95% CI, 0.002e0.32;
P¼0.048]).
Participants who had 200 minutes or more of weekly outdoor
time during school and were not myopic at baseline had signifi-
cantly less myopic shift when exposed to moderate light intensity
in the 1000 lux or more, 3000 lux or more, or 5000 lux or more
environments (0.18 D [95% CI, 0.04e0.32; P¼0.01], 0.22 D
[95% CI, 0.06e0.37; P¼0.006], and 0.24 D [95% CI, 0.14e0.33;
P<0.001], respectively). However, when assessing participants
who had 125 to 199 minutes of outdoor time during school, only
those without myopia at baseline who were exposed to a 10 000 lux
or more environment had significantly less myopic shift (0.16 D
[95% CI, 0.08e0.24; P<0.001]). This suggests that school-
children who have less outdoor time may need exposure to high
bright light intensity (10 000 lux) to achieve protective effects
against myopia, whereas in those who have longer durations of
Table 2. Baseline Characteristics of Recess Outside Classroom
Trial 711 and Control Groups
Characteristic
Recess Outside
Classroom
Trial 711 Group Control Group
Total (n ¼930) 365 565
Gender
Male 201 (55.07) 284 (50.27)
Female 164 (44.93) 281 (49.73)
Age (yrs)
6 237 (64.93) 373 (66.02)
7 128 (35.07) 192 (33.98)
Myopia (n ¼927)
Yes 51 (14.01) 89 (15.81)
No 313 (85.99) 474 (84.19)
No. of myopic parents (n ¼796)
0 56 (17.89) 102 (21.12)
1 126 (40.26) 200 (41.41)
2 131 (41.85) 181 (37.47)
Near work breaks 30/10 (n ¼813)*
Yes 95 (29.78) 120 (24.29)
No 224 (70.22) 374 (75.71)
Diopter hours per week (n ¼681;
288 vs. 393), mean SD
y
46.7525.82 46.4723.25
Primary end point baseline
SER (D; n ¼927; 364 vs. 563),
mean SD
0.361.14 0.300.99
AXL (mm; n ¼922; 361 vs. 561),
mean SD
22.780.77 22.810.76
AXL ¼axial length; SD ¼standard deviation; SER ¼spherical equiva-
lence refraction.
Data are no. (%) unless otherwise indicated. Chi-square tests and 2-sample
ttests were used for comparing differences between groups, and none of
these comparisons reached statistical significance.
*Children are encouraged to take breaks from near work (30 minutes of
near work followed by a 10-minute break).
y
Weekly diopter hours are computed by summing up 3 number of hours of
reading, 2 number of hours of other mid-distance near work, 2 number
of hours of using a computer, and 1 number of hours of watching TV.
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outdoor time, moderate levels of light intensity (1000 lux or
3000 lux) may be sufficient to protect against myopia.
Changes in Near Work
After the intervention, there were no significant differences in near-
work breaks and diopter-hours between the intervention and
control groups (33.85% vs. 24.57% and 46.36 vs. 45.85; P¼0.08
and P¼0.80, respectively; data not shown). We further evaluated
improvement in the near-work breaks and found that 18.14% of
children in the intervention group had changed to follow the 30/10
rule from baseline to the end of the study (P¼0.046, McNemar’s
test), whereas only 12.73% in the control group did so (P¼0.37,
McNemar’s test). When assessing the changes of near-work
Table 3. Comparing Primary End Points of Recess Outside Classroom Trial 711 and Control Groups
End Points Total
Recess Outside Classroom
Trial 711 Group Control Group
Estimated
Difference*
95% Confidence
Interval PValueNo.
Adjusted Mean
(Standard Deviation)*No.
Adjusted Mean
(Standard Deviation)*
Total
Changes from baseline SER (D) 693 267 0.35 (0.58) 426 0.47 (0.74) 0.12 0.05e0.19 0.002
Changes from baseline AXL (mm) 688 265 0.28 (0.22) 423 0.33 (0.35) 0.05 0.08 to 0.02 0.003
Nonmyopic children at baseline
Changes from baseline SER (D) 620 235 0.32 (0.58) 385 0.43 (0.75) 0.11 0.02e0.20 0.02
Changes from baseline AXL (mm) 615 233 0.26 (0.18) 382 0.30 (0.32) 0.03 0.06 to 0.01 0.02
Myopic children at baseline
Changes from baseline SER (D) 73 32 0.57 (0.40) 41 0.79 (0.38) 0.23 0.06e0.39 0.007
Changes from baseline AXL (mm) 73 32 0.45 (0.28) 41 0.60 (0.19) 0.15 0.28 to 0.02 0.02
Event/No. (%) Event/No. (%) Odds Ratio
New incidences of myopia 620 34/235 (14.47) 67/385 (17.40) 0.65 0.42e1.01 0.05
Percent of myopia shift of 0.5 D or more 693 58/267 (21.72) 132/426 (30.99) 0.46 0.28e0.77 0.003
AXL ¼axial length; D ¼diopter; SER ¼spherical equivalence refraction.
*Estimates were computed by the generalized estimating equation to account for possible deviations from the normal distribution and cluster effects. The
covariates in the analysis models included the corresponding baseline measures, age, gender, area, parental myopia, and the total sun hours during light meter
wearing week.
Figure 3. Flowchart showing process of recruiting participants. ROCT711 ¼Recess Outside Classroom Trial 711.
Wu et al Myopia Prevention and Outdoor Light Intensity
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Table 4. Comparison of Outdoor Time between Recess Outside Classroom Trial 711 and Control Groups
Measurement Method
Recess Outside Classroom
Trial 711 Group (n [267) Control Group (n [426)
Estimated
Difference*
95% Confidence
Interval PValueNo.
Adjusted Mean
(Minutes)*Standard Error No.
Adjusted Mean
(Minutes)*
Standard
Error
Baseline
Weekdays during school Light meter 1000 lux 252 171.33 22.76 413 162.09 18.86 9.24 34.74 to 53.21 0.68
3000 lux 83.17 9.01 86.31 11.28 3.14 29.77 to 23.49 0.82
5000 lux 62.47 7.36 65.56 8.90 3.09 24.44 to 18.26 0.78
10 000 lux 35.91 6.50 36.29 7.06 0.37 17.55 to 16.80 0.97
Weekdays out of school Self-report diary 223 143.08 7.48 376 146.34 4.56 3.26 12.27 to 5.74 0.48
Weekends Self-report diary 223 271.22 5.38 376 268.47 5.82 2.76 1.41 to 6.92 0.20
End of study
Weekdays during school Light meter 1000 lux 256 216.51 14.44 409 202.35 8.34 14.16 16.79 to 45.11 0.37
3000 lux 118.59 8.18 113.27 6.92 5.32 18.76 to 29.40 0.67
5000 lux 88.09 7.33 85.79 6.98 2.30 20.80 to 25.40 0.85
10 000 lux 51.62 5.59 49.76 5.40 1.86 15.81 to 19.54 0.84
Weekdays out of school Self-report diary 239 156.76 6.94 374 148.28 11.85 8.49 14.50 to 31.47 0.47
Weekends Self-report diary 239 291.33 16.55 374 250.60 10.57 40.74 9.00 to 90.47 0.11
1 week total Light meter 1000 lux & self-report diary 239 669.36 22.98 374 598.81 16.20 70.55 16.51e124.59 0.01
3000 lux & self-report diary 575.23 25.52 503.70 14.13 71.53 3.54e139.52 0.04
5000 lux & self-report diary 543.56 24.94 475.47 13.92 68.09 0.99e135.20 0.047
10 000 lux & self-report diary 505.17 23.16 439.91 12.98 65.26 3.07e127.44 0.04
%of11þhrs by light meter 1000
lux & self-report diary, no. (%)
239 119 49.79% 374 85 22.73% <0.001
*Estimates were computed by the generalized estimating equation to account for possible deviations from the normal distribution and cluster effects. The covariates in the analysis models included the
corresponding baseline measures, age, gender, area, parental myopia, and the total sun hours during light meter wearing week.
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diopter-hours, the control group increased 6.04 hours per week
(SD, 27.42 hours), which was significantly higher than the 0.59
hours (SD, 28.60 hours) of the intervention group (P¼0.02).
Above all, the ROCT711 intervention group had statistically
significant differences in having higher classroom clearance rate,
less myopic shift and axial elongation, less incident myopia, and
less children with rapid myopic shift. Children in the intervention
group spent more time outdoors and a higher percentage of chil-
dren achieved the ROCT711 goal of spending at least 11 hours per
week outdoors. They were also more compliant with the
30/10 rule.
Discussion
This study was a multi-area cluster-randomized intervention
trial of the ROCT711 program, which promotes more out-
door time for schoolchildren to prevent myopic changes. It
used objective measurements to assist in the validation of
the relationship of time spent outdoors and myopia. The
results show that completing the 1-year ROCT711 program
effectively can inhibit a myopic shift and axial elongation
and can decrease the risks of myopia onset and fast myopia
shift. It was effective in retarding both myopia shift in
nonmyopic children and myopia progression in myopic
children. Spending enough time outdoors during school
hours in moderate to high sunlight intensity can slow the
myopic shift. Myopia protection can be achieved by briefer
periods of higher light intensity or longer periods of more
moderate light intensity.
The prevalence of myopia is approximately 20% to 30% in
6- to 7-year-old children in Taiwan,
2
whereas the prevalence
of myopia in our study population was approximately 10%
(Table 1). This discrepancy was the result of the exclusion
of children receiving myopia control treatment, representing
13% (48/365) of the intervention arm and 13% (72/565) of
the control arm. If we include these initially enrolled
children without applying exclusion criteria, then the
myopia prevalence rises to 22% ((32 þ48)/365) in the
intervention arm and 20% ((72 þ41)/565) in the control
arm. Therefore, the prevalence of myopia was similar to
that of previous reports of approximately 20% to 30% in 6-
to 7-year-old children.
In contrast to the usual expectation of a 1-mm increase in
axial length corresponding to the 2.564-D change in
adults,
23
we found that the corresponding change in SER
and axial length was much lower in the children in this
study, which was approximately 1 D of change for
every 1-mm increase in axial length. Because the partici-
pants in this study were approximately 6 to 7 years of age
and most were hyperopic at baseline, this can be explained
readily by the parallel loss of lens power and axial elonga-
tion during the process of emmetropization as part of normal
ocular development in children. It has been reported that
lens thickness, and hence lens power, continues to decrease
from 6 to 10 years of age and then shows little change af-
terward.
24,25
Lens thickness and lens power do not always
run in parallel. After 11 to 13 years of age, the lens starts to
thicken, but it continues to lose power.
Previous studies suggested that the effects of time out-
doors are seen primarily in nonmyopic children, but not in
myopic children.
17,26,27
Our results show that the myopic
progression of myopic children was significantly less in the
interventional group as compared with the control group
(0.57 D vs. 0.79 D; difference, 0.23 D), which is the first
report to reveal that outdoor activities could inhibit
progression in myopic children significantly, with approxi-
mately a 30% (0.23 D/0.79 D) reduction in 1 year. Although
the effectiveness did not reach the clinical significance
(approximately 50% or more reduction of myopia progres-
sion) that usually can be accomplished by atropine or
orthokeratology,
28,29
outdoor activities may be an adjuvant
treatment to control myopia progression. The sample size of
myopic children was relatively small, and therefore a further
large-scale study is warranted.
From our previous outdoor intervention studies, we
defined the myopia incidence reduction rate by calculating
Table 5. Analysis of Myopia Shift with Outdoor Times Measured by Different Cutoff Points of Light Intensity in All Participants
Measured by
Time Outdoors during School (Minutes)
<125
125e199 200þ
Estimate*95% Confidence Interval PValue Estimate*95% Confidence Interval PValue
Students with 1-year of follow-up
1000 lux Ref. 0.10 0.14 to 0.34 0.41 0.14 0.02e0.27 0.02
3000 lux Ref. 0.07 0.05 to 0.20 0.26 0.16 0.002e0.32 0.04
5000 lux Ref. 0.09 0.05 to 0.23 0.19 0.07 0.23 to 0.37 0.65
10 000 lux Ref. 0.07 0.12 to 0.26 0.47 ddd
Students with 1-year of follow-up and no myopia at baseline
1000 lux Ref. 0.12 0.12 to 0.36 0.32 0.18 0.04e0.32 0.01
3000 lux Ref. 0.10 0.04 to 0.23 0.15 0.22 0.06e0.37 0.006
5000 lux Ref. 0.12 0.03 to 0.26 0.13 0.24 0.14e0.33 <0.001
10 000 lux Ref. 0.16 0.08e0.24 <0.001 ddd
Ref. ¼reference group; SER ¼spherical equivalence refraction; d¼not enough observations.
*Estimates are spherical equivalence refraction (in diopters), estimated differences from the reference, and were computed by the generalized linear model
with a generalized estimating equation to account for possible deviations from the normal distribution and cluster effects. The covariates in the analysis
models included the corresponding baseline measures, age, gender, area, parental myopia, and the total sun hours during light meter wearing week.
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the difference in the incidence rates between the intervention
and control group (17.65% e8.41% ¼9.24%) and dividing
by the incidence rate of the control group (17.65%). The
myopia incidence reduction rate is approximately 52%
(9.24/17.65).
17
In this ROCT711 study, the myopia
incidence reduction rate was approximately 17% (2.93/
17.40), which was much lower than in our previous ROC
study. One discrepancy is that the participants from our
previous study were 7 to 11 years of age and most
children were required to have 80 minutes of outdoor time
per day, whereas the current participants were 6 to 7 years
of age and were encouraged to spent approximately 40
minutes outdoors per day during school time. In Taiwan,
the first- and second-grade school children attend school
for only a half day in the morning for all weekdays except
Tuesday, which has a full-day course. Usually, the total
recess time is 40 minutes during the morning half-day
course and 80 minutes for a full-day course. We speculate
that noncompulsory with less compliance and spending less
time outdoors may have contributed to the lower myopia
incidence reduction rate.
The children in the current study of ROCT711 are very
similar in age and ethnicity to those who were involved in
the 3-year Guangzhou Outdoor Activity Longitudinal Study,
although the current study covered only 1 year. In the
Guangzhou Outdoor Activity Longitudinal Study, the 3-year
cumulative incidence rate of myopia was 30.4% in the
intervention group and 39.5% in the control. The difference
of 9.1% in the incidence rate of myopia represents a 23%
relative reduction in incident myopia after 3 years. In
ROCT711, there was a 17% relative reduction in incident
myopia after 1 year. It could be anticipated that a longer
intervention period for ROCT711 would result in greater
cumulative reduction.
For the in-school outdoor time, there was no significant
difference between the 2 groups. During our study period, 2
national initiatives were ongoing that promoted greater time
spent outdoors for students, and these programs were
encouraged in response to our published results from the
initial Recess Outside Classroom study.
17
We speculate that
the Sport & Health 150 project and the Tien-Tien 120
program initiated by the Ministry of Education of Taiwan
may have contributed to the nonsignificant difference be-
tween the groups when considering in-school outdoor time.
The time spent outdoors was not significantly different be-
tween the groups when in-school or outside-school time
were analyzed separately. However, for the total 1-week
outdoor time including in school and outside school, the
intervention group had significantly greater time outdoors
than the control group. During our 2 audits of the classroom
evacuation rate during recess, there were significant differ-
ences between the 2 groups. In addition to better adherence
to the 30/10 rule, these results suggest that the ROCT711
policy has been well implemented in the intervention
schools.
One of the special characteristics of the ROCT711 pro-
gram is that it encourages schoolchildren to go outside the
classroom during recess, which increases the intermittent
outdoor time during school. Chicken and primate experi-
ments have shown that high levels of ambient light can
inhibit the developmental form of deprivation myopia.
30,31
The most likely biological explanation for this association
is that the retina responds to high levels of light by releasing
dopamine, which inhibits axial length growth.
32,33
It also
should be noted that the animal studies and the human
studies do not really correspond. In the animal studies, the
increased protection was observed only at much higher light
intensity than the ROC programs. In this study, we found
that the intervention group had less myopic shift and axial
elongation. The ROCT711 program encourages school-
children to participate in outdoor activities during recess.
During a normal school day, there are 4 classes and 3 re-
cesses (10 minutes, 20 minutes, and 10 minutes) during the
morning for first-grade schoolchildren. Recently, an animal
study showed that intermittent episodes of bright light
suppressed myopia in chickens more than continuous bright
light did
34
; the strategy of having recess outside the
classroom provides intermittent episodes of bright light for
the children.
This study also showed that the participants with 200
minutes of outdoor time during school in 1000-lux or more
or 3000-lux or more environments showed significantly less
myopic shift. However, in those who had 125 to 199 mi-
nutes of outdoor time during school, only the participants
without myopia at baseline and those exposed to a 10 000-
lux or more environment showed significantly less myopic
shift. This suggests that in those with shorter outdoor time,
high bright light exposure (10 000 lux) had protective
effects against myopia, but longer durations under moderate
light intensity conditions (1000 lux or >3000 lux) also
may have protective effects against myopia. This is in
contrast to the animal studies
35,36
where high bright light
exposure (10 000 lux) was required for the prevention of
myopia. In relation to the animal studies, it is worth noting
that the myopia-inducing stimulus is constant. In contrast,
although we do not know precisely what it is, in humans it is
likely to be intermittent. This may help to explain the
different response to light intensities. Our findings in this
study are in agreement with a previous study by Read
et al,
37
who found that the duration of light exposure to
1000 lux or more may be the contributing factor that sets
emmetropic and myopic children apart, and therefore
gives support to the concept that exposure to light
intensity of less than 10 000 lux may be sufficient to
protect against myopia. In this study, recess outside the
classroom with light intensities of 1000 or 3000 lux (such
as in the hallway or under the shade of a tree) with
enough time was sufficient for myopia protection. This
finding has an important implication in reducing the
possible side effects of very bright sunlight exposure, such
as cataracts, maculopathy, or skin cancer.
To our knowledge, no previous trials have shown the as-
sociation between light intensity and time outdoors in terms of
myopia prevention. The limitations of this study are the
relatively short intervention period and that some schools
withdrew and did not complete the 1-year program. A longer
interventional trial is warranted. Initially, the school princi-
pals of all 24 schools agreed to participate. However, when the
informed consent forms were presented to principals and
parents, a number of them withdrew from the study. We
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obtained our ethical approval from a medical center, so the
informed consent forms conformed to their requirements and
the seal of the Human Clinical Trial Committee was printed
on the forms. We admit that we did not expect refusals for this
reason. Because classes had already started at that time, we
did not have enough time to recruit other schools for
completing 1-year study. Although this fact may raise con-
cerns about the effectiveness of the randomization, our
comparisons of drop-out rates between intervention and
control groups were not significantly different (5 of 12 schools
vs. 3 of 12 schools; P¼0.3865; 267 of 779 participants vs.
426 of 1247 participants; P¼0.9585). In Taiwan, there is no
academic classification in the primary school system, and
there is practically minimal academic stress on the first-grade
schoolchildren. All of the schools follow the same curriculum
and have the same amount of recess time and physical edu-
cation classes; however, this does not mean that students have
similar times outdoors. Although the drop-out rates of the 2
groups were similar, the effect on randomization should not
be overlooked.
The study’s enrollment criteria included an informed
consent signature and attending the baseline assessment
including cycloplegia. Before cycloplegic examination, the
parents and children were given an introduction to the pro-
cedure. On the day of cycloplegia assessment, the ophthal-
mologist and nurse stayed in the school and every participant
received a new pair of sunglasses to prevent photophobia.
Therefore, the compliance of the enrolled participants was as
high as 100%. Fifty of 365 participants in the intervention
group and 67 of 565 participants in the control group did not
attend the final assessment, so the compliance was approxi-
mately 86% and 88%, respectively. With regard to wearing
the light meter, compliance was quite high (665/693 [96%]) at
the end of study during weekday in-school time. Because
teachers could not monitor the children’s use, there was
relatively poor compliance during the out-of-school time and
on weekends. Therefore, we used the self-report diary to
represent the children’s outdoor time (Table 4).
In conclusion, the school-based ROCT711 program may
stabilize the myopic shift effectively, may decrease the axial
length elongation, and may decrease the risk of myopia
onset and fast myopia shift. Both nonmyopic and myopic
children benefitted from this outdoor activity program for
myopia control. Although parents may be concerned about
children’s direct exposure to strong light intensities, we
found that longer duration of exposure to moderate light
intensities such as 1000 lux or more or 3000 lux or more
outdoors also may have a myopia prevention effect. A
program involving recess outside the classroom that pro-
vides these light intensity-level environments, such as in
hallways or under a tree, also may reduce the concerns of
possible side effects from exposure to strong sunlight. To
prevent myopia shift and progression, children are encour-
aged to spend enough outdoor time both in school and out of
school every week in the elementary school system.
Acknowledgments
The authors thank Dr. Gabriel Gordon for reading and editing the
manuscript and the elementary schools in Taitung, including
Ren-Al, Sin-Sheng, Ma-Lan, Fong-Rong, Bao-Sung, and Dong-
Hai; in Kaohsiung, including Fu-Shan, Sin-Min, Sin-Shang,
Zhao-Ming, Zhong-Zhuang, and Yong-Fang; in Keelung,
including Chi-Du and Nuan-Shi; in Taipei, including Xin-Yi, Wu-
Xing, Yon-Gji, and Xing-Ya; in Taichung, including Du-Xing and
Jian-Xing; in Chiayi County, including Put-Zu and Da-Tong; and
in Chiayi City, including Min-Tzu and Ta-Tung for assistance and
providing essential equipment for this project.
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Footnotes and Financial Disclosures
Originally received: February 6, 2017.
Final revision: November 13, 2017.
Accepted: December 6, 2017.
Available online: January 19, 2018. Manuscript no. 2017-264.
1
Department of Ophthalmology, Kaohsiung Chang Gung Memorial Hos-
pital and Chang Gung University College of Medicine, Kaohsiung, Taiwan.
2
Department of Ophthalmology, Chang Gung Memorial Hospital, Linkou,
Taiwan, and College of Medicine, Chang Gung University, Taoyuan,
Taiwan.
3
Department of Ophthalmology, Chang Gung Memorial Hospital, Keelung
and Department of Chinese Medicine, College of Medicine, Chang Gung
University, Taoyuan, Taiwan.
4
Department of Ophthalmology, Chang Gung Memorial Hospital Chiayi,
Chiayi, Taiwan, and Chang Gung University College of Medicine, Tao-
Yuan, Taiwan.
5
Department of Dentistry, Kaohsiung Chang Gung Memorial Hospital and
Chang Gung University College of Medicine, Kaohsiung, Taiwan.
6
Health Promotion Administration, Ministry of Health and Welfare, Taipei
City, Taiwan.
7
Institute of Public Health, School of Medicine, National Yang-Ming
University, Taipei, Taiwan.
8
Cheng Hsin General Hospital, Taipei, Taiwan.
9
School of Pharmacy, Kaohsiung Medical University, Kaohsiung, Taiwan.
*Both authors contributed equally as first authors.
Financial Disclosure(s):
The author(s) have no proprietary or commercial interest in any materials
discussed in this article.
Supported by the Bureau of Health Promotion, Department of Health,
Taiwan (grant nos.: C1010603, C1020515, and C1020515-103).
HUMAN SUBJECTS: Human subjects were included in this study. This
study adhered to the tenets of the Declaration of Helsinki. The institutional
review board of the Chang Gung Memorial Hospital approved the study,
and informed consent to participate in the study was obtained from all
patients.
No animal subjects were used in this study.
Author Contributions:
Conception and design: Pei-Chang Wu, S.-T. Chiou, Y.-H. Yang
Analysis and interpretation: Pei-Chang Wu, C.-T. Chen, Y.-H. Yang
Data collection: Pei-Chang Wu, C.-T. Chen, K.-K. Lin, C.-C. Sun, C.-N.
Kuo, H.-M. Huang, Y.-C. Poon, M.-L. Yang, C.-Y. Chen, J.-C. Huang,
Pei-Chen Wu, I.-H. Yang, H.-J. Yu, P.-C. Fang, C.-L. Tsai, S.-T. Chiou,
Y.-H. Yang
Obtained funding: Pei-Chang Wu
Overall responsibility: Pei-Chang Wu, Y.-H. Yang
Abbreviations and Acronyms:
CI ¼confidence interval; D¼diopter; ROCT711 ¼Recess Outside
Classroom Trial 711; SD ¼standard deviation; SER ¼spherical equiva-
lence refraction; 30/10 ¼30 minutes of near work followed by a 10-minute
break.
Correspondence:
Yi-Hsin Yang, PhD, School of Pharmacy, Kaohsiung Medical University,
Division of Medical Statistics and Bioinformatics, Kaohsiung Medical
University Hospital, No. 100 Shih-Chuan 1st Road, Kaohsiung 807,
Taiwan. E-mail: yihsya@kmu.edu.tw; and Shu-Ti Chiou, PhD, Institute of
Public Health, School of Medicine, National Yang-Ming University, Taipei,
Taiwan. E-mail: stchiou@ym.edu.tw.
Ophthalmology Volume 125, Number 8, August 2018
1250
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