Article Text

Download PDFPDF

Risk factors for myopia progression in second-grade primary school children in Taipei: a population-based cohort study
  1. Chih-Chien Hsu1,2,
  2. Nicole Huang3,
  3. Pei-Yu Lin2,4,
  4. Shao-You Fang5,
  5. Der-Chong Tsai4,6,
  6. Shing-Yi Chen7,
  7. Ching-Yao Tsai4,8,
  8. Lin-Chung Woung4,8,
  9. Shih-Hwa Chiou1,2,4,9,10,
  10. Catherine Jui-ling Liu2,4
  1. 1 Institute of Clinical Medicine, National Yang-Ming University, Taipei, Taiwan
  2. 2 Department of Ophthalmology, Taipei Veterans General Hospital, Taipei, Taiwan
  3. 3 Institute of Hospital and Health Care Administration, National Yang-Ming University, Taipei, Taiwan
  4. 4 Faculty of Medicine, National Yang-Ming University School of Medicine, Taipei, Taiwan
  5. 5 Institution of Public Health, National Yang-Ming University, Taipei, Taiwan
  6. 6 Department of Ophthalmology, National Yang-Ming University Hospital, I-Lan, Taiwan
  7. 7 Department of Health, Taipei City Government, Taipei, Taiwan
  8. 8 Department of Ophthalmology, Taipei City Hospital, Taipei, Taiwan
  9. 9 Department of Medical Research and Education, Taipei Veterans General Hospital, Taipei, Taiwan
  10. 10 Institute of Pharmacology, National Yang-Ming University, Taipei, Taiwan
  1. Correspondence to Dr Catherine Jui-ling Liu, Department of Ophthalmology, Taipei Veterans General Hospital, No.201, Shih-Pai Road, Section 2, Taipei 112, Taiwan; jlliu{at}vghtpe.gov.tw

Abstract

Purpose To evaluate the 1-year progression of myopia and associated risk factors in second-grade primary school children.

Methods The myopia investigation study in Taipei provided semiannual visual acuity testing and cycloplegic refraction for all second-grade primary school children (mean age: 7.49 years) in Taipei who provided parental consent. A questionnaire was distributed to the participants’ parents before the first and third examinations. We evaluated 1-year follow-up data for children noted to have myopia on the first examination. Multinomial logistic regression models were applied to assess risk factors associated with myopia progression. Myopia progression was categorised, based on the change in spherical equivalent (ΔSE) over 1 year, as slow (ΔSE>−0.5 dioptres (D)), moderate (−1.0 D<ΔSE≤−0.5 D) or fast (ΔSE≤−1.0 D). Of the 4214 myopic children, data were analysed for 3256 (77.3%) who completed the 1-year follow-up evaluation.

Results The baseline SE was −1.43±1.1 D. The average ΔSE was −0.42±0.85 D, with 46.96%, 28.50% and 24.54% of the study subjects showing slow, moderate and fast myopia progression, respectively. When compared with slow myopia progression, fast myopia progression was associated with a greater myopic SE at baseline (OR: 0.67, 95% CI: 0.61 to 0.72) and a shorter eye–object distance when doing near work (OR: 1.45, 95% CI: 1.18 to 1.78). More outdoor activity time and self-reported cycloplegic treatment were not associated with slow myopia progression.

Conclusions Children with fast annual myopia progression were more myopic at baseline and had a shorter reading distance. Our study results highlight the importance of having children keep a proper reading distance.

  • cycloplegic
  • myopia progression
  • population-based study

Statistics from Altmetric.com

Introduction

Patients with high myopia are more susceptible to ocular morbidities that can lead to irreversible blindness, severely handicap the individual and further burden the social economy.1–3 In Taiwan, the prevalence of high myopia (≤−6.0 dioptres (D)) in 18-year-old students increased from 10.9% in 1983 to 21% in 2000.4 Wang et al reported that 23.5% of freshmen at National Taiwan University had high myopia in 1988, and this prevalence increased to 38.4% in 2005.5 A recent review of myopia progression studies supported the finding of Pärssinen et al that myopia progresses significantly faster in children with a myopia onset at a younger age.6 7 This indicates that the most effective strategies to prevent low vision/blindness, resulting from ocular morbidities associated with high myopia, should target young children.

In 2013, the Taipei City Government launched the citywide myopic investigation study (MIT) for second-grade primary school children. The prevalence of myopia (spherical equivalent (SE)≤−0.50 D) after cycloplegic refraction was 36.4% in the second-grade primary school children (age: 7.49±0.32 years) in Taipei.8 These subjects are more likely to have high myopia by early adulthood, and some of them may be vision-impaired due to complications of high myopia, causing a heavy socioeconomic burden; therefore, it is critical to adopt measures that help curb myopia progression. Atropine (0.01%–1%),9–11 orthokeratology12 13 and pirenzepine14 effectively slowed the progression of myopia in clinical trials. Pirenzepine is not commercially available in many parts of the world. Treatment with atropine often results in photophobia and blurred near vision, which causes inconvenience and difficulty in daily life activity. In addition, orthokeratology is expensive and there are concerns of infectious keratitis. The abovementioned disadvantages and possible side effects of various myopia treatments may prohibit children and their parents from adopting and adhering to them.

This population-based study, which is part of the MIT, aimed to explore the 1-year progression of myopia and risk factors associated with it in children noted to have myopia when they were second graders in primary school. The effects of ‘cycloplegics’ on myopia control for children at such a young age were also investigated.

Methods

Design and subjects

In the light of the increasingly high prevalence of high myopia among university students and the decreasing age of myopia onset in Taiwan, the Taipei City Government launched the MIT in July 2013. The study design, rationale and methods of the MIT have been published previously.15 In brief, the MIT project provided free vision and refraction evaluation once every semester for children who were older than 7 years but younger than 8 years in September 2013. The first cohort received their first evaluation between July and September 2013, when they were second graders. All eligible children were invited and those who provided parental consent received examinations at an MIT-associated medical facility each semester for three consecutive years (six evaluations in total). Written informed consent was obtained from the parents of the participating children before the study start. Parents answered one questionnaire before their children received the examinations in an MIT-associated eye care medical unit. After the first eye examination period was completed (at the end of September 2013), all primary school children were exposed to a large-scale eye care education programme, which included lecture sessions, an animated cartoon and an educational video, to teach them about the vision-threatening ocular morbidities associated with high myopia, as well as the prevention, progression and treatment of myopia. Moreover, we implemented case manager-led telecoaching for children who were identified to have myopia (SE≤−0.50 D) in at least one eye after cycloplegic refraction. One year later, questionnaires were distributed again to all parents of this cohort before the third eye examination, which was performed from July to September 2014.

In this study, we analysed the 1-year progression of myopia among children who were identified to have myopia on the first eye examination in 2013 and aimed to identify risk factors for myopia progression in children inhabiting a metropolitan city. The Institutional Review Board of Taipei City Hospital approved the protocols of this study (TCHIRB-1020501), and the principles of the Declaration of Helsinki were adhered to throughout.

Refraction assessment

Each eye examination was performed in compliance with the standard operation procedure set by the MIT monitoring committee.15 Briefly, a slit lamp examination was performed to rule out anterior segment conditions that would contraindicate the use of cycloplegic agents in each child. Three kinds of cycloplegic eye drops were approved for use in this study: Cyclogyl (1% cyclopentolate), Mydriacyl (1% tropicamide) and Mydrin-P (0.5% phenylephrine hydrochloride/0.5% tropicamide). Each hospital or clinic could use only one kind of cycloplegic eye drop, from these three drugs, to assess cycloplegic refraction in the MIT participants. Two doses of cycloplegic were given 10 min apart, and the refraction was checked 30 min after the second drop. If the pupil still responded to pen light stimulation, the examiner waited an additional 10 min before performing cycloplegic autorefraction. The SE of the refractive error was calculated as the spherical value of the refractive error plus one half of the cylindrical value. Myopia was defined as an SE≤−0.50 D after cycloplegia. Only the more myopic eye in each child in 2013 was included in the study analysis. The third eye examination was performed 1 year later and myopia progression was evaluated in the same eye in each child. We defined myopia progression as slow (ΔSE>−0.5 D), moderate (−1.0 D<ΔSE≤−0.5 D) and fast (ΔSE≤−1.0 D), where ΔSE is the change in SE over the past 1 year.10

Investigation of risk factors

Myopia progression risk factors were identified and assessed based on the results of the questionnaire before the third eye examination. The collected demographic information included sex, the child’s area of residence, parental characteristics such as maternal education level and parental myopia status, the child’s lifestyle and reading habits, and the use of ‘cycloplegics’ as treatment for myopia. The questions about lifestyles and reading habits pertained to near work activities, outdoor activity participation outside of school and participation in an after-school tutorial programme, which contains mostly homework writing and reading. Near work questions asked about the age when the child began doing near work, the average time spent on near work each day, the distance from objects when doing near work, whether the child had a 10 min rest after doing 30 min of near work, and whether cellphones, computers and computer tablets were used during the past 1 year. A question about the average time spent playing outdoors after school on weekdays and on weekends was also part of the questionnaire. Instead of atropine, we asked if the children use ‘cycloplegics’ as a treatment for myopia in the questionnaire because some ophthalmologists in Taiwan prefer tropicamide or cyclopentolate to atropine as a treatment for childhood myopia, and not all parents knew the kinds of cycloplegics their children were using.

Statistical analysis

The distribution of baseline characteristics for second-grade students with myopia among three myopia progression groups is described in table 1. A multinomial logistic regression model was used to investigate the association between myopia progression speed (slow vs moderate and fast progression) and potential risk factors. OR and their 95% CI were calculated. In addition, simple and multiple linear regression models were applied to examine the association between the 1 year change in SE and risk factors. The standard coefficient beta and their 95% CI values were calculated. Statistical analysis was performed using Statistical Analysis System Software (SAS V.9.3). p Values <0.05 were considered statistically significant.

Table 1

Demographics and parental characteristics of myopic children with various 1-year progression speeds

Of the 19 374 eligible second graders in Taipei in 2013, the parents of 11 590 children provided consent and the children were evaluated using cycloplegic refraction. Among them, a total of 4214 (36.4%) children were myopic. One year later in 2014, 3297 (78.2%) of these myopic children received the third free eye examination and submitted the questionnaires completed by their parents. After excluding 41 children who were receiving orthokeratology for myopia during the interval, the data for a total of 3256 (77.3%) children with a mean age of 7.49 (±0.31) years were included in the analyses. When we compared these myopic children who completed the follow-up and those who did not, no significant differences in baseline demographic characteristics were noted.

Results

The average baseline SE was −1.43±1.1 D (range, −14.0 D to −0.5 D) in these children. The average 1-year change of SE (ΔSE) was −0.42±0.85 D, and 46.96%, 28.50% and 24.54% of the children showed slow (ΔSE=0.20±0.77 D), moderate (ΔSE=−0.67±0.14 D) and fast (ΔSE=−1.33±0.36 D) myopia progression, respectively. Dividing these myopic children by three different cycloplegics, the baseline SE was −1.45±1.2 D, −1.44±1.1 D and −1.40±1.0 D (p=0.55) and ΔSE was −0.39±0.9 D, −0.41±0.9 D and −0.46±0.8 D (p=0.10) in the 1% cyclopentolate, 1% tropicamide and 0.5% phenylephrine hydrochloride/0.5% tropicamide groups, respectively. The characteristics of all the study subjects and the speed of myopia progression for each category are shown in tables 1 and 2. The results of multinomial logistic regression analysis of the risk factors associated with the rate of myopia progression are shown in table 3; the fast myopia progression group was associated with more myopic SE at baseline (OR 0.67, 95% CI 0.61 to 0.72, p <0.001) and shorter visual distance when doing near work (OR 1.45, 95% CI 1.18 to 1.78, p <0.01) compared with the slow myopia progression group. More time spent doing outdoor activities after school on weekdays and weekends was not associated with the rate of myopia progression. Unexpectedly, treatment with ‘cycloplegics’ during the 1-year interval was not associated with a slower speed of myopia progression, but was more likely to be related to moderate myopia progression than slow myopia progression. The average ΔSE was −0.46±0.68 D (range, −1.39 to −1.85 D) for those receiving cycloplegic treatment and −0.40±0.95 D (range, −1.45 to −1.85 D) for those who were not treated.

Table 2

Lifestyle and reading habits of myopic children with various 1-year progression speeds

Table 3

Associations between the rate of myopia progression (compared with slow progression) and possible risk factors

The associations between various potential risk factors and the 1-year ΔSE of the study eyes are shown in table 4. In short, the less eye–object distance for near work and the no 10-min rest period after 30 min of near work were associated with greater myopic progression of SE after 1-year follow-up. If myopic children receiving cycloplegic treatment were excluded from the analysis (n=1903), the factor of less eye–object distance for near work remained significantly associated with faster myopic progression.

Table 4

Associations between the change in spherical equivalent and possible risk factors

Discussion

The rate of myopia progression in children without treatment has been approaching 1 D per year in East Asia.16 Atropine, pirenzepine (an M1 muscarinic receptor selective antagonist) and orthokeratology contact lenses are treatments that are effective in slowing down the progression of myopia.17 Among them, pirenzepine is not commercially available in Taiwan. This article aimed to identify modifiable environmental factors that are related to myopia progression in juvenile primary school children. Myopic children treated with orthokeratology contact lenses were excluded from this study because of its proven effect in myopia treatment and its implementation is unlikely to be subject to recall bias.

In this citywide study, we found the average rate of 1-year myopia progression in eyes noted to have myopia at baseline was −0.42±0.85 D. This is slower than that reported by Donovan and colleagues (−0.82 D) in one meta-analysis study of urban children in Asia.7 The slower progression speed of myopia found in our study might be due to the fact that 41.6% of our study participants received cycloplegia treatment during the 1-year interval. However, our finding that the use of cycloplegics was not associated with a slower speed of myopia progression, using a variety of statistical analytic methods, makes this argument less convincing. Although variables such as genetic composition, environmental factors, lifestyle patterns and socioeconomic levels may influence myopia progression, the slower progression in our study could be attributed, at least in part, to the impact of case manager-led telecoaching and the large-scale eye care education programme implemented after the first eye examination.

When evaluating the risk factors of myopia progression, we found that, compared with slow myopia progression, fast myopia progression was associated with greater myopic SE at baseline and a shorter eye–object distance (<30 cm) while doing near work. Using multiple linear regression analysis, the amount of myopia progression was associated with a shorter distance for doing near work and the lack of a 10-min rest period after 30 min of near work. These findings were in line with those reported by Pärssinen and Lyyra in a 3-year follow-up randomised clinical trial of myopia treatment that included 238 school children with a mean age of 10.9 years.6 The importance of a break after a period of near work has been reported to prevent myopia.18 19 Our study results implicate that keeping a proper eye–object distance and a short rest between periods of prolonged near work might be helpful in decreasing the speed of myopia progression in young children.

Interestingly, Pärssinen and Lyyra also found that myopia progression was significantly faster among girls than boys, and this might be explained by the faster maturation and body growth in girls at the age of their study population.6 Our study participants were younger than those in the abovementioned study, and we did not identify sex as a risk factor for myopia progression. Thus, the role sex plays in myopia progression remains unclear.

Numerous studies have demonstrated that time spent doing outdoor activities is associated with a lower incidence of myopia.20 21 In the present study, we found time spent in outdoor activities was not associated with myopic progression in these primary school children. Our findings are in agreement with previous studies.6 18 19 Recently, Wu et al and Jones-Jordan et al found that outdoor activities had a significant effect on lessening myopic shift in non-myopic children, but had no impact in myopic children.19 22 Wu et al speculated that the myopic children in their study did not spend enough time outdoors despite study intervention, and more outdoor time may be needed to prevent myopia progression than to prevent myopia onset.19 These findings signify the importance of spending more time doing outdoor activities to prevent the early onset of myopia and lessen myopia progression in young children.

We found the overall 1-year myopia progression was not significantly different between those with and without self-reported ‘cycloplegic treatment’. This finding may be explained by several reasons. First, the cause–effect relation cannot be ascertained using association analyses. It was possible that children who were identified to have faster myopia progression on the second follow-up examination (6 months after the first examination) were more prone to start ‘cycloplegic treatment’ for the rest of the follow-up period. This reasoning is supported by the finding that cycloplegic treatment is more likely to be related to moderate myopic progression than slow progression. Second, this was not a randomised controlled clinical study and we could not monitor participants’ compliance with cycloplegic treatment. Third, the follow-up period was short, and the participants were exposed to manager-led telecoaching and a large-scale eye care educational programme after the first eye examination, and these factors might confound the study results. Finally, not all ophthalmologists in Taipei use atropine as the drug of choice in myopia treatment out of fear that blurred near vision and photophobia may lead to incompliance and treatment failure. Instead, they might prescribe short-acting cycloplegics such as tropicamide or cyclopentolate, but these agents have no proven effects on myopia control.17 23

This study has several strengths. First, the sample size is relatively large. Second, it is a population-based study and all second-grade children in Taipei were invited to participate without using a sampling strategy, so the potential selection bias was minimised. Third, the parents of all of the 3256 children included in the analysis completed the questionnaire, and all of the children were evaluated using cycloplegic refraction 1 year apart. These data facilitated us to comprehensively assess the risk factors associated with myopia progression in such a young myopic population.

The limitations of this study are as follows. First, the 1-year follow-up period is short, and studies with longer follow-up are warranted. Second, although the MIT organising committee had formulated a standard operation procedure, variations in eye examination procedures across different MIT-associated medical facilities could not be completely avoided. Third, each MIT-associated medical facility chose one of three agents for cycloplegic refraction. Although 1% tropicamide and 0.5% phenylephrine hydrochloride/0.5% tropicamide are considered effective cycloplegic agents for Asian children,24 25 the cycloplegic effect of these two agents might differ from that of 1% cyclopentolate. This might result in an inadequate cycloplegic effect in some children and overestimate the prevalence of myopia, but was unlikely to significantly affect the study results regarding myopia progression as the baseline SE and the rate of myopia progression were not statistically different among these three drug groups. Fourth, among the 4214 myopic children identified on the first eye examination in 2013, only 3256 (77.3%) children completed the third eye examination 1 year later and were included in the final analysis. As no significant differences in baseline demographic characteristics were noted between the study subjects and all the eligible subjects, this might not influence the study outcome in a meaningful way. Finally, the age of myopia onset and age receiving first spectacles may be associated with myopia progression.6 Because it is hard to exactly know the age of myopia onset and subject to recall bias about time receiving first spectacles, we did not include these variables in our study. Although excluding children wearing spectacles from our study analysis might provide a more homogeneous data set for analysis and longer follow-up,26 we might also falsely negate possible associations by doing so because these children might be just those with risk factors of myopia progression.

In conclusion, this citywide population-based 1-year follow-up study found more myopic SE at baseline and shorter eye–object distance for near work were risk factors of fast myopia progression (ΔSE≤−1.0 D) in second-grade children. Considering the issue of vision-threatening ocular morbidities associated with high myopia and the increasing prevalence of myopia in young children in Asia, it is important to raise public awareness about risk factors associated with the onset and progression of myopia in young school children.

Acknowledgments

Data analysed in this study were retrieved from the Taipei City Public Health Database provided by the Department of Health, Taipei City Government, and verified by the Databank for Public Health Analysis. The interpretation and conclusions contained herein do not represent those of the Department of Health, Taipei City Government, or Databank for Public Health Analysis. The authors would like to express great thanks to Dr Chi-Hung Lin, Dr Allen Wen-Hsiang Chiu, and Dr Shiow-Wen Liou for their administrative support for this myopic investigation study in Taipei.

References

View Abstract

Footnotes

  • Contributors Substantial contributions to the conception or design of the work, or the acquisition, analysis or interpretation of data for the work: C-CH, NH, P-YL, S-YF, D-CT, S-YC, C-YT, L-CW, S-HC, CJ-LL. Drafting the work or revising it critically for important intellectual content: C-CH, NH, P-YL, S-YF, D-CT, S-YC, C-YT, L-CW, S-HC, CJ-LL. Final approval of the version to be published: C-CH, NH, P-YL, S-YF, D-CT, S-YC, C-YT, L-CW, S-HC, CJ-LL. Agreement to be accountable for all aspects of the work in ensuring that questions related to the accuracy or integrity of any part of the work are appropriately investigated and resolved: C-CH, NH, P-YL, S-YF, D-CT, S-YC, C-YT, L-CW, S-HC, CJ-LL.

  • Competing interests None declared.

  • Ethics approval Taipei City Hospital.

  • Provenance and peer review Not commissioned; externally peer reviewed.

  • Correction notice This article has been corrected since it was published Online First. The affiliation of Professor Lin-Chung Woung hs changed to “4,8” not “8”.

Request Permissions

If you wish to reuse any or all of this article please use the link below which will take you to the Copyright Clearance Center’s RightsLink service. You will be able to get a quick price and instant permission to reuse the content in many different ways.