Advanced Search

Preplanned Studies: Combined Effect of Outdoor Time and Other Modifiable Factors on Myopia Incidence Among Children and Adolescents — 9 PLADs, China, 2020

View author affiliations
  • Summary

    What is already known about this topic?

    Myopia has been identified as a significant emerging challenge and policy priority among children and adolescents in China by the Ministry of Education and seven other departments. Limited research has been conducted to investigate the collective impact of outdoor time and other modifiable factors on the incidence of myopia.

    What is added by this report?

    This study provides support for the protective effect of combining increased outdoor time with other prevention strategies in reducing the incidence of myopia. The results indicate the presence of a dose-response relationship.

    What are the implications for public health practice?

    To effectively prevent myopia, it is important to implement comprehensive interventions that encompass various aspects such as outdoor time, eye-use habits, eye-use environments, and lifestyle modifications.

  • loading...
  • Funding: Supported by the China Medical Board (Grant #21-434 to YS) and Capital’s Funds for Health Improvement and Research (2022-1G-4251 to YS)
  • [1] Holden BA, Fricke TR, Wilson DA, Jong M, Naidoo KS, Sankaridurg P, et al. Global prevalence of myopia and high myopia and temporal trends from 2000 through 2050. Ophthalmology 2016;123(5):1036 − 42. https://doi.org/10.1016/j.ophtha.2016.01.006CrossRef
    [2] Qiao J, Wang YY, Li XH, Jiang F, Zhang YT, Ma J, et al. A Lancet Commission on 70 years of women’s reproductive, maternal, newborn, child, and adolescent health in China. Lancet 2021;397(10293):2497 − 536. https://doi.org/10.1016/s0140-6736(20)32708-2CrossRef
    [3] Ministry of Education and other seven departments. the Comprehensive National Children’s Myopia Management Plan. 2018. http://www.moe.gov.cn/srcsite/A17/moe_943/s3285/201808/t20180830_346672.html. [2023-09-05]. (In Chinese). 
    [4] Jan C, Li L, Keay L, Stafford RS, Congdon N, Morgan I. Prevention of myopia, China. Bull World Health Organ 2020;98(6):435 − 7. https://doi.org/10.2471/blt.19.240903CrossRef
    [5] Morgan IG, Wu PC, Ostrin LA, Tideman JWL, Yam JC, Lan WZ, et al. IMI Risk Factors for Myopia. Invest Ophthalmol Vis Sci 2021;62(5):3. https://doi.org/10.1167/iovs.62.5.3CrossRef
    [6] Dong YH, Jan C, Chen L, Ma T, Liu JY, Zhang Y, et al. The cumulative effect of multilevel factors on myopia prevalence, incidence, and progression among children and adolescents in China during the COVID-19 pandemic. Transl Vis Sci Technol 2022;11(12):9. https://doi.org/10.1167/tvst.11.12.9CrossRef
    [7] GBD 2019 Risk Factors Collaborators. Global burden of 87 risk factors in 204 countries and territories, 1990-2019: a systematic analysis for the Global Burden of Disease Study 2019. Lancet 2020;396(10258):1223 − 49. https://doi.org/10.1016/s0140-6736(20)30752-2CrossRef
    [8] Morgan IG, French AN, Ashby RS, Guo XX, Ding XH, He MG, et al. The epidemics of myopia: Aetiology and prevention. Prog Retin Eye Res 2018;62:134 − 49. https://doi.org/10.1016/j.preteyeres.2017.09.004CrossRef
    [9] Rose KA, French AN, Morgan IG. Environmental factors and myopia: paradoxes and prospects for prevention. Asia Pac J Ophthalmol (Phila) 2016;5(6):403 − 10. https://doi.org/10.1097/apo.0000000000000233CrossRef
    [10] National Health Commission of the People’s Republic of China. the appropriate technical guidelines for prevention and control of myopia in children and adolescents (update version). 2021. http://www.nhc.gov.cn/jkj/s5899tg/202110/65a3a99c42a84e3f8a11f392d9fea91e.shtml. [2023-09-05]. (In Chinese). 
  • FIGURE 1.  The combined effect of outdoor time and other modifiable factors on myopia incidence. (A) The combined effect of outdoor time and ten modifiable factors on myopia incidence; (B) the combined effect of outdoor time and five modifiable factors of eye-use habits on myopia incidence; (C) the combined effect of outdoor time and three modifiable factors of eye-use environment on myopia incidence; (D) the combined effect of outdoor time and two modifiable factors of lifestyle on myopia incidence.

    Note: We conducted a binomial generalized linear mixed model with the log link function in every cutoff point of CES, respectively, and every model had a PR of the combined effect of outdoor time and modifiable factors on myopia incidence. The model adjusted sex, residence (urban or rural), grade, parents’ myopia status (0 or 1 or 2 parents with myopia), and the cluster effect of the PLAD.

    Abbreviation: CES=cumulative effect score; PR=prevalence ratio; CI=confidence interval; PLAD=provincial-level administrative division.

    TABLE 1.  Assignment of modifiable factors.

    VariablesQuestionAssignment
    01
    Outdoor timeWhat was your daily exposure to sunlight? (Time spent in direct sunlight)<2 h≥2 h
    Eye-use habits
    Eye exercisesOn average, how many times a day do you do eye exercises during school days this semester?<2 times/day≥2 times/day
    Screen timeIn the past 7 days, how much time did you spend watching TV, using computer, mobile phone and tablet every day (including surfing the Internet, watching movies, browsing the web, and playing games)?≥2 h<2 h
    Lying down while watching/readingIn the past 7 days, have you read a book or watched a video (tablet or phone) lying down?OftenOccasionally/never
    Watching a screen in darknessIn the past 7 days, have you continued to look at your phone or tablet after turning off the lights?OftenOccasionally/never
    Posture remindingIn the past 7 days, have your parents or teachers reminded of your reading and writing posture?Occasionally/neverOften
    Eye-use environment
    Desktop brightness on sunny daysIs your desktop bright enough on a sunny day?Not very brightVery bright
    Light brightness in the eveningDo you think the lights are bright enough when you study at night?Not bright enoughBright enough
    Seat/desk fitted for heightDo you think your desk and seat are fitted for your height?NoYes
    Lifestyle
    Sleeping durationIn the past 7 days, how long did you sleep on average per day?< 9 h or >11 h for the grade 1–6 children
    <8 h or >10 h for the grade 7–11 children
    ≥9 h and ≤11 h for the grade 1–6 children
    ≥8 h and ≤10 h for the grade 7–11 children
    Sedentary timeIn the past 7 days, how long have you been sitting on average per school day?≥5 h<5 h
    Download: CSV

    TABLE 2.  Effect of single modifiable factors on myopia incidence.

    Variables Total 1–6 grades 7–11 grades
    PR (95% CI) P PR (95% CI) P PR (95% CI) P
    Outdoor time
    0 Ref Ref Ref
    1 0.92 (0.78, 1.08) 0.315 0.93 (0.77, 1.12) 0.434 0.90 (0.64, 1.26) 0.530
    Eye exercises
    0 Ref Ref Ref
    1 0.96 (0.80, 1.14) 0.611 1.00 (0.81, 1.22) 0.974 0.82 (0.57, 1.17) 0.272
    Screen time
    0 Ref Ref Ref
    1 1.04 (0.84, 1.30) 0.697 0.92 (0.69, 1.23) 0.586 1.19 (0.86, 1.66) 0.297
    Lying down watching/reading
    0 Ref Ref Ref
    1 0.96 (0.71, 1.30) 0.785 0.76 (0.50, 1.16) 0.205 1.17 (0.76, 1.80) 0.474
    Watching screen in darkness
    0 Ref Ref Ref
    1 0.98 (0.66, 1.45) 0.911 0.69 (0.37, 1.29) 0.244 1.14 (0.69, 1.87) 0.607
    Posture reminding
    0 Ref Ref Ref
    1 0.98 (0.83, 1.16) 0.845 0.95 (0.79, 1.14) 0.578 1.11 (0.78, 1.59) 0.558
    Desktop brightness in sunny day
    0 Ref Ref Ref
    1 0.86 (0.73, 1.01) 0.070 0.91 (0.75, 1.11) 0.359 0.74 (0.55, 1.00) 0.050
    Light brightness in the evening
    0 Ref Ref Ref
    1 1.15 (0.78, 1.70) 0.484 1.49 (0.85, 2.63) 0.164 0.79 (0.46, 1.34) 0.380
    Seat/desk fitted for height
    0 Ref Ref Ref
    1 0.82 (0.65, 1.03) 0.092 0.89 (0.65, 1.22) 0.477 0.70 (0.49, 0.99) 0.044
    Sleeping duration
    0 Ref Ref Ref
    1 0.90 (0.76, 1.07) 0.229 0.89 (0.74, 1.08) 0.227 0.94 (0.64, 1.38) 0.475
    Sedentary time
    0 Ref Ref Ref
    1 0.93 (0.79, 1.10) 0.403 0.95 (0.79, 1.14) 0.579 0.87 (0.60, 1.26) 0.748
    Note: The model adjusted sex, residence (urban or rural), grade, parents’ myopia status (0 or 1 or 2 parents with myopia), and the cluster effect of the PLAD.
    Abbreviation: PR=prevalence ratio; CI=confidence interval; PLAD=provincial-level administrative division.
    Download: CSV

Citation:

通讯作者: 陈斌, bchen63@163.com
  • 1. 

    沈阳化工大学材料科学与工程学院 沈阳 110142

  1. 本站搜索
  2. 百度学术搜索
  3. 万方数据库搜索
  4. CNKI搜索
Turn off MathJax
Article Contents

Article Metrics

Article views(1640) PDF downloads(17) Cited by()

Share

Related

Combined Effect of Outdoor Time and Other Modifiable Factors on Myopia Incidence Among Children and Adolescents — 9 PLADs, China, 2020

View author affiliations

Summary

What is already known about this topic?

Myopia has been identified as a significant emerging challenge and policy priority among children and adolescents in China by the Ministry of Education and seven other departments. Limited research has been conducted to investigate the collective impact of outdoor time and other modifiable factors on the incidence of myopia.

What is added by this report?

This study provides support for the protective effect of combining increased outdoor time with other prevention strategies in reducing the incidence of myopia. The results indicate the presence of a dose-response relationship.

What are the implications for public health practice?

To effectively prevent myopia, it is important to implement comprehensive interventions that encompass various aspects such as outdoor time, eye-use habits, eye-use environments, and lifestyle modifications.

  • 1. Institute of Child and Adolescent Health, School of Public Health, Peking University; National Health Commission Key Laboratory of Reproductive Health, Beijing, China
  • 2. Department of Sport, Physical Education & Health, Hong Kong Baptist University, Kowloon Tong, Hong Kong Special Administrative Region, China
  • 3. Department of Medicine, Stanford Prevention Research Center, Stanford University School of Medicine, Stanford, CA, United States
  • Corresponding author:

    Yi Song, songyi@bjmu.edu.cn

  • Funding: Supported by the China Medical Board (Grant #21-434 to YS) and Capital’s Funds for Health Improvement and Research (2022-1G-4251 to YS)
  • Online Date: March 01 2024
    Issue Date: March 01 2024
    doi: 10.46234/ccdcw2024.031
  • Myopia is a global public health concern, affecting approximately 30% of the world’s population and is expected to reach 50% by 2050 (1). In China, myopia was recognized as a significant health issue by the Lancet Commission in 2021 and identified as a major emerging challenge and policy priority for children and adolescents by the Ministry of Education and seven other departments of the People’s Republic of China (23). Increasing outdoor time has been identified as a preventive measure against myopia in children (4). However, other modifiable factors, with equivocal to modest evidence of a relationship with myopia, which have not been studied in depth, are worth investigation, given a looming myopia epidemic (5). In this study, researchers analyzed follow-up data to examine the combined impact of outdoor time and other modifiable factors on myopia incidence. Its findings revealed a dose-response relationship between these factors and myopia risk. To effectively combat myopia, comprehensive interventions addressing multiple factors are necessary.

    Data were collected from a follow-up investigation conducted in China across nine provincial-level administrative divisions (PLADs): namely Guangxi, Chongqing, Gansu, Hunan, Henan, Shanxi, Fujian, Shanghai, and Jiangsu. The investigation took place between September and November of 2020, with baseline information gathered in June of the same year. Supplementary Figure S1 provides an overview of the sampling and investigation procedures, which have been previously published (6). A total of 3,993 children and adolescents in grades 1–6, 7–8, and 10–11 who did not have myopia at baseline were included in the analysis. Students with missing information regarding their parents’ myopia status, outdoor time, and more than three other modifiable factors were excluded (Supplementary Figure S2). In this population-based study, myopia was defined as low unaided distance visual acuity (<5.0) and non-cycloplegic spherical equivalent refractive error (spherical equivalent <−0.50 Diopter). Questionnaires were used to measure outdoor time and ten other modifiable factors, including eye-use habits (eye exercises, screen time, lying down while watching/reading, watching a screen in darkness, posture reminding), eye-use environment (desktop brightness on sunny days, light brightness in the evening, seat/desk fitted for height), and lifestyle (sleep duration, sedentary time). Outdoor time and the other modifiable factors were categorized as binary variables (assigned 0 or 1 point according to Table 1). The ten other modifiable factors were then summed up to create a cumulative effect score (CES) ranging from 0 to 10, using multiple imputations to account for missing information. We performed several regressions according to different cutoff points of CES, assigning the combined effect of outdoor time and modifiable factors based on cutoff points of CES and outdoor time. For example, if the cutoff point was defined as 4, the CES was transformed into a binary variable called “binary cumulative effect score (BCES),” with 1 point for CES≥4 and 0 points for CES<4. Regression analysis was performed six times with cutoff points from 3 to 8. A cutoff point of 3 tested those with CES<3 to those with CES≥3. The more extreme cutoff points (1, 2, 9, and 10) did not provide meaningful information due to the creation of very small comparison groups. A binomial generalized linear mixed model with a log link function was employed to explore the combined effect of outdoor time and modifiable factors on the incidence of myopia. The combined effect was defined as a binary variable, that was “positive” when outdoor time was ≥2 hours daily and BCES was 1 point, and was “negative” when outdoor time was <2 hours daily or BCES was 0 points (Supplementary Figure S3). The regression model adjusted for sex, residence (urban or rural), grade, parents’ myopia status (0 or 1 or 2 parents with myopia), and the cluster effect of the PLAD. The same analyses were conducted for the three categories of modifiable factors. All statistical analyses were performed using R (version 4.2.2; R Core Team, 2022, R Foundation for Statistical Computing, Vienna, Austria), with the mice package (version 3.16.0) used for multiple imputation and the lme4 package (version 1.1.34) used for the regression analyses.

    VariablesQuestionAssignment
    01
    Outdoor timeWhat was your daily exposure to sunlight? (Time spent in direct sunlight)<2 h≥2 h
    Eye-use habits
    Eye exercisesOn average, how many times a day do you do eye exercises during school days this semester?<2 times/day≥2 times/day
    Screen timeIn the past 7 days, how much time did you spend watching TV, using computer, mobile phone and tablet every day (including surfing the Internet, watching movies, browsing the web, and playing games)?≥2 h<2 h
    Lying down while watching/readingIn the past 7 days, have you read a book or watched a video (tablet or phone) lying down?OftenOccasionally/never
    Watching a screen in darknessIn the past 7 days, have you continued to look at your phone or tablet after turning off the lights?OftenOccasionally/never
    Posture remindingIn the past 7 days, have your parents or teachers reminded of your reading and writing posture?Occasionally/neverOften
    Eye-use environment
    Desktop brightness on sunny daysIs your desktop bright enough on a sunny day?Not very brightVery bright
    Light brightness in the eveningDo you think the lights are bright enough when you study at night?Not bright enoughBright enough
    Seat/desk fitted for heightDo you think your desk and seat are fitted for your height?NoYes
    Lifestyle
    Sleeping durationIn the past 7 days, how long did you sleep on average per day?< 9 h or >11 h for the grade 1–6 children
    <8 h or >10 h for the grade 7–11 children
    ≥9 h and ≤11 h for the grade 1–6 children
    ≥8 h and ≤10 h for the grade 7–11 children
    Sedentary timeIn the past 7 days, how long have you been sitting on average per school day?≥5 h<5 h

    Table 1.  Assignment of modifiable factors.

    No individual modifiable factor, including outdoor time, showed a significant association with incident myopia (Table 2, all P>0.05). However, there was a dose-response relationship between the combined effect and outdoor time with respect to myopia risk. As the number of modifiable factors increased, the prevalence ratio (PR) decreased. Furthermore, in the total sample, a statistically significant association between the combined effect and myopia was observed when the combined effect score (CES) reached 7 [PR=0.81, 95% confidence interval (CI), 0.67, 0.98]. Similar results were found in children in grades 1–6; the statistically significant association appeared when the CES reached 8 (PR=0.76, 95% CI: 0.60, 0.97), and a dose-response relationship existed. However, no statistically significant associations or dose-response relationships were observed in children in grades 7–11 (Figure 1A).

    Variables Total 1–6 grades 7–11 grades
    PR (95% CI) P PR (95% CI) P PR (95% CI) P
    Outdoor time
    0 Ref Ref Ref
    1 0.92 (0.78, 1.08) 0.315 0.93 (0.77, 1.12) 0.434 0.90 (0.64, 1.26) 0.530
    Eye exercises
    0 Ref Ref Ref
    1 0.96 (0.80, 1.14) 0.611 1.00 (0.81, 1.22) 0.974 0.82 (0.57, 1.17) 0.272
    Screen time
    0 Ref Ref Ref
    1 1.04 (0.84, 1.30) 0.697 0.92 (0.69, 1.23) 0.586 1.19 (0.86, 1.66) 0.297
    Lying down watching/reading
    0 Ref Ref Ref
    1 0.96 (0.71, 1.30) 0.785 0.76 (0.50, 1.16) 0.205 1.17 (0.76, 1.80) 0.474
    Watching screen in darkness
    0 Ref Ref Ref
    1 0.98 (0.66, 1.45) 0.911 0.69 (0.37, 1.29) 0.244 1.14 (0.69, 1.87) 0.607
    Posture reminding
    0 Ref Ref Ref
    1 0.98 (0.83, 1.16) 0.845 0.95 (0.79, 1.14) 0.578 1.11 (0.78, 1.59) 0.558
    Desktop brightness in sunny day
    0 Ref Ref Ref
    1 0.86 (0.73, 1.01) 0.070 0.91 (0.75, 1.11) 0.359 0.74 (0.55, 1.00) 0.050
    Light brightness in the evening
    0 Ref Ref Ref
    1 1.15 (0.78, 1.70) 0.484 1.49 (0.85, 2.63) 0.164 0.79 (0.46, 1.34) 0.380
    Seat/desk fitted for height
    0 Ref Ref Ref
    1 0.82 (0.65, 1.03) 0.092 0.89 (0.65, 1.22) 0.477 0.70 (0.49, 0.99) 0.044
    Sleeping duration
    0 Ref Ref Ref
    1 0.90 (0.76, 1.07) 0.229 0.89 (0.74, 1.08) 0.227 0.94 (0.64, 1.38) 0.475
    Sedentary time
    0 Ref Ref Ref
    1 0.93 (0.79, 1.10) 0.403 0.95 (0.79, 1.14) 0.579 0.87 (0.60, 1.26) 0.748
    Note: The model adjusted sex, residence (urban or rural), grade, parents’ myopia status (0 or 1 or 2 parents with myopia), and the cluster effect of the PLAD.
    Abbreviation: PR=prevalence ratio; CI=confidence interval; PLAD=provincial-level administrative division.

    Table 2.  Effect of single modifiable factors on myopia incidence.

    Figure 1. 

    The combined effect of outdoor time and other modifiable factors on myopia incidence. (A) The combined effect of outdoor time and ten modifiable factors on myopia incidence; (B) the combined effect of outdoor time and five modifiable factors of eye-use habits on myopia incidence; (C) the combined effect of outdoor time and three modifiable factors of eye-use environment on myopia incidence; (D) the combined effect of outdoor time and two modifiable factors of lifestyle on myopia incidence.

    Note: We conducted a binomial generalized linear mixed model with the log link function in every cutoff point of CES, respectively, and every model had a PR of the combined effect of outdoor time and modifiable factors on myopia incidence. The model adjusted sex, residence (urban or rural), grade, parents’ myopia status (0 or 1 or 2 parents with myopia), and the cluster effect of the PLAD.

    Abbreviation: CES=cumulative effect score; PR=prevalence ratio; CI=confidence interval; PLAD=provincial-level administrative division.

    In terms of eye-use habits, a statistically significant association between the combined effect of outdoor time and eye-use habits on myopia was observed when the CES subset (ranging from 0 to 5) reached a score of 5 points. This association was found in both the total sample (PR=0.60, 95% CI: 0.40, 0.89) and grade 1–6 children (PR=0.63, 95% CI: 0.42, 0.94), but not in grades 7–11. Regarding the eye-use environment, a statistically significant association was found when the CES subset (ranging from 0 to 4) reached a score of 3 points. However, this association was only observed in the total sample (PR=0.79, 95% CI: 0.65, 0.96). For lifestyle factors, a statistically significant association was present when the CES subset (ranging from 0 to 2) reached a score of 1 point. This association was found in both the total sample (PR=0.67, 95% CI: 0.49, 0.93) and grade 1–6 children (PR=0.67, 95% CI: 0.48, 0.93) (Figure 1B–D).

    • Although no significant individual modifiable factors were found to be associated with myopia, there was a statistically significant combined effect of outdoor time and modifiable factors on the incidence of myopia when the CES reached seven points. This finding supports conclusions about the protective effects of the combination of outdoor time and modifiable factors in preventing myopia. It also confirms that modifiable factors, which have insufficient evidence of a direct association with myopia, do have a protective effect against myopia. These effects may be obscured by their weak individual influences, but when they are cumulated and combined with outdoor time, their protective effects become apparent and can contribute to reversing the myopia epidemic (6). These findings align with the 2018 national plan launched by the Ministry of Education and seven other departments of the People’s Republic of China, which emphasized the need for comprehensive interventions to protect children from myopia (3). Rather than focusing solely on factors with the highest level of evidence, the government should address modifiable factors that have the potential to harm the public. Ignoring these factors could delay the implementation of beneficial policies and perpetuate preventable burdens (7).

      A similar pattern was observed in children from grades 1–6 but not in children from grades 7–11, potentially due to the weakening effect of educational pressure (89). In China, children from grades 7–9 face the pressure of the national high school entrance exam, while children from grades 10–12 face the pressure of the national college entrance exam. This highlights the need for differentiated recommendations for myopia prevention, taking into account the specific challenges faced by middle school students compared to primary school students.

      In this study, researchers aimed to examine the combined effects of outdoor time and various modifiable factors on myopia. The study’s findings demonstrate that the combination of modifiable factors and outdoor time significantly influences myopia when an adequate CES is achieved. These modifiable factors encompass three categories: eye-use habits, lifestyle, and eye-use environments. Effective interventions for all these categories should be implemented at multiple levels, including individuals, families, and schools. While the proactive engagement of children is crucial in shaping eye-use habits and lifestyles, the support and guidance from families and schools should not be underestimated. Moreover, creating a vision-friendly environment in schools and at home, such as ensuring bright lighting and appropriately fitted seats and desks, is essential. Children themselves should also be aware of these influential factors and express their needs accordingly. In line with “The appropriate technical guidelines for prevention and control of myopia in children and adolescents (update version)”(10), which provides detailed, comprehensive interventions for individuals, families, schools, medical and health institutions, government departments, media, and social groups, this study provides supporting evidence for these guidelines. Furthermore, its findings emphasize the benefits of implementing multiple-level comprehensive interventions, especially among younger children (10).

      This study had several limitations that need to be acknowledged. First, the definition and measurement of myopia used in this study, although acceptable for population assessment, may not be considered the gold standard for clinical diagnosis. Unfortunately, conducting cycloplegic refraction was not feasible due to the large sample size. Second, the measurement of outdoor time and other modifiable factors relied on questionnaires, which may introduce recall bias and self-reporting bias. Third, the relatively short six-month interval between the two waves of follow-up may have limited the ability to demonstrate the significant protective effect of some modifiable factors, such as outdoor time, which has been confirmed in other studies. Fourth, the small sample size of grade 7–11 children might have influenced the statistical power of the analysis. Lastly, this study’s statistical strategy required the dichotomization of each modifiable factor, which reduced the statistical efficiency of the analysis.

      Myopia prevention among children and adolescents is a complex undertaking that necessitates comprehensive interventions and collaborative efforts from schools, families, children themselves, governments, and society as a whole.

    • No conflicts of interest.

Reference (10)

Citation:

Catalog

    /

    DownLoad:  Full-Size Img  PowerPoint
    Return
    Return