Prevalence of and risk factors for myopia among urban and rural children in Northeast China: protocol for a school-based cross-sectional study

Abstract

Introduction

The worldwide prevalence of myopia is high and continues to increase. In this study, a school screening programme for myopia will be implemented using the whole-process information method. The purpose of this study is to investigate the prevalence of myopia in urban and rural areas of Northeast China and to determine the factors related to myopia.

Methods and analysis

This is a school-based cross-sectional study. Our study population will include 6000 school-aged children from 2 urban and 2 rural schools in Jinzhou, China. The study will be conducted using our self-developed internet-based intelligent data collection, transmission, storage and analysis system. Examination parameters include uncorrected distance visual acuity, presenting distance visual acuity, non-cycloplegic autorefraction, height, weight, waist circumference, hip circumference, spinal curvature and dental caries. The examination report will be automatically sent to parents, who will complete the questionnaire, and appropriate statistical analysis will be performed. The main outcome is the prevalence of myopia, defined as an equivalent spherical degree ≤−0.5 D.

Ethics and dissemination

Ethical approval was obtained from the Third Affiliated Hospital of Jinzhou Medical University (number: JYDSY-KXYJ-IEC-2023-018). Findings will be published in a peer-reviewed journal. Subjects and their parents (or other authorised agents) give informed consent prior to study participation.

Trial registration number

ChiCTR2300072893.

STRENGTHS AND LIMITATIONS OF THIS STUDY.

• The protocol will include a significant diversity of factors that could influence the prevalence and severity of myopia.

• The use of an automated, whole-process approach for data collection will streamline the process and reduce error, enabling the development of new and more efficient screening procedures.

• This study incorporates feedback from multiple stakeholders, including students, parents, schools and government agencies. This codesign approach ensures that the developed procedures are more likely to be accepted and adopted in school-based myopia control programmes.

• The study will not include biochemical markers of the disease.

• The questionnaire response rate will be partially influenced by the internet capability and information technology literacy of the participants and their guardians.

Introduction

Myopia has reached epidemic proportions, and its global prevalence is still increasing; it is projected that by 2050, half of the world’s population will be myopic unless effective strategies against myopia are developed.^1–3 The prevalence of myopia and high myopia is particularly notable in certain regions of East and Southeast Asia, with a rate of approximately 50%, which is significantly higher than that in Europe (approximately 35%) and Africa (approximately 10%).⁴ Urbanised areas in East and Southeast Asia, such as Singapore, and urban cities in mainland China, Hong Kong, Taiwan, Japan, and South Korea, have the highest rates of myopia. These variations, together with the rapid increase in the prevalence of myopia (especially among children in Asia and higher income areas), suggest that environmental factors are important determinants of myopia and that this discrepancy in myopia prevalence might reflect a distinct genetic susceptibility to myopia between ethnicities.^{5 6}

The impact of myopia on children is significant. It not only increases the risk of pathological ocular changes, such as myopic macular degeneration and retinal detachment, which may result in permanent blindness, but also affects psychosocial well-being, potentially hindering education and future opportunities.^{7 8} According to recent studies, the occurrence of myopia in children is linked to various factors, including increasing age, sex, household income, parents’ education, residence in urban areas, type of school attended, anthropometric indicators and so on.^9–13 Certain factors that contribute to the risk of myopia development, such as sex and age, are unmodifiable and cannot be altered. Consequently, efforts have focused on identifying environmental or behavioural factors associated with myopia that can be modified to minimise the likelihood of its onset.¹⁴

Numerous studies have demonstrated varying rates of myopia among populations with comparable genetic backgrounds but varying degrees of urbanisation.¹⁵ For example, Wang et al reported myopia prevalence of 82.71% and 72.76% among students aged 6–18 years in urban Dalian city and rural areas of China, respectively.¹⁶ Similarly, Peng et al found that the prevalence of myopia in urban and rural regions in Anhui was 68.1% and 63.7%,¹⁷ respectively.

To date, no surveys have been conducted on refractive errors in Northeast China. This study protocol will aim to investigate the prevalence and risk factors of myopia among school-aged children in Jinzhou City. This research is based on the newly information collection platform developed by the Institute of Biomedical Engineering Technology of Chinese Academy of Sciences to realise the electronic and automatic data collection and transmission of the whole process.The main objective of this study is to determine the prevalence of myopia and high myopia. Secondary goals include exploring whether ocular data are associated with body stature and dental caries. Furthermore, this study includes a questionnaire survey to examine the living environment, mental health, dietary, physical activity, digital screen behaviour and eye health. Differences in the associated factors of myopia will be studied in future research.

Methods and analysis

Objective

Primary objective

This study aims to estimate the prevalence of myopia among children and adolescents aged 6–16 years in a multiethnic urban and rural region of Northeast China and to identify the associated risk factors.

Secondary objectives

• To assess the association of anthropometric indicators such as height, weight, waist circumference, hip circumference, spinal curvature and dental caries with myopia.

• To assess the association between different ethnic groups, such as Han, Mongolian and Manchu with myopia.

• To identify the main factors that could significantly influence the occurrence of myopia.

Study area and population

Jinzhou (figure 1), one of the major cities in Liaoning Province, has a permanent population of 3 435 000 according to 2020 data from China’s National Bureau of Statistics. Jinzhou was chosen because its population is relatively stable and it is a multiethnic integrated area, including Mongolians, Manchus and Hans. To determine how the environment affects the occurrence of myopia, we randomly selected four schools, including two urban schools and two rural schools. Primary and middle school students aged 6–16 years old will be recruited from urban (Taihe District and Linghe District, Jinzhou) and rural (Yixian County, Jinzhou) areas for school admission screening. This cross-sectional study will involve the entire population that fits the inclusion criteria.

Figure 1.

Location of this protocol and average years of education for population aged 15 and above in each county or district of Jinzhou.

Study design and data collection

This is a school-based, cross-sectional study. Considering the varying economic conditions in Jinzhou, we aimed to include schools from different districts for epidemiological research. Regarding sampling methods, two schools were randomly selected from Taihe District and Linghe District, which are urban areas in Jinzhou City. Additionally, two schools were randomly selected from Yixian County, a rural area. Data will be collected on ocular screening, anthropometric measurements, scoliosis, dental caries and questionnaires. The survey will be conducted in batches across four schools starting in 2023 and the study is expected to be concluded by 2026.

The data for this study are sourced from our developed Intelligent Health Information Collection and Management System, aiming to improve screening efficiency, reduce personnel input, ensure complete digital data collection, and avoid errors and losses. This system consists of a Health Information Management Platform, primarily used for establishing students’ digital health records. Health information includes but is not limited to anthropometric measurements data, ophthalmic examinations data, scoliosis measurements data and dental caries measurements data, among others. After processing and analysing this data, a comprehensive health report will be generated for each student. Additionally, the system includes an automatic data collection module that allows screening personnel to upload various instrument measurement data to the Health Information Management System via Bluetooth or WiFi. This feature greatly simplifies the data collection process and ensures the accuracy and timeliness of the data. We have also developed a parent interaction application specifically, which allows parents to fill out questionnaires on their mobile phones, receive their child’s examination reports, and receive intervention and referral suggestions. This enables parents to promptly understand their child’s health status and take corresponding measures based on the suggestions. The Health Information Management Platform also has the characteristic of open access, allowing government, schools and hospitals to access and use the data on the platform. Through this open access, we have achieved collaborative management among students, families, schools, government and medical institutions. This design makes student health management more efficient and convenient for all parties involved. Figure 2 provides a detailed description of the screening work plan, data collection, analysis and application process for this study.

Figure 2.

Framework of the study. Specifically, our data collection process will be as follows: (1) the school provides a student list; including basic information such as full name, personal ID, student ID, class, grade, school type, school name and administrative division; (2) relevant personnel will organise and import the list into the system; (3) student manuals will be created and printed with screening codes; including informed consent, project introduction and instructions for using the parent application; (4) the school will be contacted to determine the screening date and location; (5) the site will be surveyed and equipment deployed for screening preparation; (6) student manuals with screening codes will be distributed to provide the relevant education; (7) real-time screening will begin including anthropometric measurements data, ophthalmic examinations data, scoliosis measurements data and dental caries measurements data, with data automatically uploaded to the backend system and (8) data will be downloaded and further statistical analysis conducted.

Recruitment

We selected two schools from urban areas and two schools from rural areas, then contacted the local head of the district or county in charge of the Department of Education, who informed school principals about the project. Subsequently, the principals conveyed this information to the school doctors. The researchers will work with the school doctors to send text messages to parents and class teachers of elementary and middle school students, as well as post advertisements in school corridors, billboards and other public places to explain the purpose of this study, the testing project and the potential benefits for the participants.

Eligibility criteria

Inclusion criteria are as follows:

• School students aged 6–16 years.

• Have lived in the corresponding residence in the survey area for more than 3 years.

• Volunteer to participate in this study and sign the informed consent.

There are no exclusion criteria.

Sample size

According to data from the National Health Commission of the People’s Republic of China,¹⁸ the estimated incidence of myopia in this age group is 52.7%. With α=0.05 and tolerance error of 3.5%, the sample size calculated using the PASS V.15 software (NCSS) to be n=808. Considering the impact of case shedding, an additional 13.5% increase in the sample size is needed. Therefore, theoretically, this study would need to include a minimum of 921 students. This epidemiological investigation aims to explore the prevalence of myopia among students in the northeastern region of China. Therefore, we believe that by including a larger sample size, we can more accurately reflect the actual situation. In April 2023, we collaborated with the Health Commission of Liaoning Province and Jinzhou Municipal Education Bureau to conduct school physical examinations at Yi County Jurui Primary School and Yi County Yizhou Primary School in Yixian County, Jinzhou City. During the examination process, we collected data from 1648 and 1797 individuals in each school, respectively. Hence, in the subsequent data collection process, while ensuring the reliability and avoiding resource waste, we aim to collect data from at least 1500 individuals in each school. Apart from these two schools, we will also conduct school physical examinations at Jinzhou Experimental School (Lingnan) in Taihe District, Jinzhou City and Jinzhou Experimental School (Desheng) in Linghe District, Jinzhou City. As a result, the total number of samples collected from the four schools will be no less than 6000 individuals. In this study, the target sample size is 6000 individuals, which exceeds the minimum requirement to ensure the fulfilment of sample size needs.

Examinations

Ophthalmic examinations

Distance visual acuity examination

The electronic visual acuity metre (EyeVision, EV160301, China) is used to measure uncorrected distance visual acuity (UDVA) and presenting distance visual acuity (PDVA) at 5 m, based on the E Standard Logarithmic Visual Acuity Chart (GB 11533-1989). If participants wear prescription glasses, both UDVA and PDVA will be measured. Otherwise, only UDVA will be measured. Participants unable to identify any optotype will be classified as having low vision. The electronic visual acuity metre will automatically transmit the values to the database.

Non-cycloplegic autorefraction

After the distance visual acuity examination, every participant will undergo non-cycloplegic autorefraction using autorefractometry (Change, ARK7800L, China), which will automatically transmit the values to the database. Each eye will be measured three times. The spherical equivalent (SE) of the refraction is calculated as the sum of the spherical refractive error and half of the negative cylindrical refractive error. Myopia will be defined as SE <−0.5 dioptres (D), high myopia as SE≤−6.0 D¹⁰ and low myopia as SE between − 0.50 D and − 6.00 D.

Anthropometric measurements

Anthropometric measurements will be performed according to the methods described by Peng et al.¹⁹ The examination’s aim is obtaining height, weight, waist circumference and hip circumference data according to standard techniques by trained investigators. The participants will be measured by removing heavy clothing and standing barefoot on a calibrated electronic height and weight metre (YIHEZHILIAN, EY-1560, China), with the investigators holding the measuring scale firmly over the subject’s head and recording height and weight readings in centimetres (cm) and kilograms (kg), respectively, after stabilisation. Waist circumference is measured at the midpoint between the lower margin of the last rib and top of the iliac crest. Hip circumference is measured around the widest portion of the buttocks with a tape parallel to the floor. Each measurement is performed in duplicate. If the measurements are within 1 cm of each other, an average is calculated. Otherwise, two additional measurements are performed. The waist–hip ratio (WHR) is the ratio of the circumference of the waist to that of the hip. Body mass index (BMI) is calculated as weight/height and recorded in kilograms per square metre (kg/m²). According to the American Academy of Pediatrics, childhood obesity is defined as having a BMI≥the 95th percentile for age and sex. Severe obesity was defined as BMI≥120% of the 95th percentile for age and sex.²⁰ The measurement data are recorded by the screener via mobile phone or tablet, and the data are automatically uploaded to the database.

Scoliosis measurements

Orthopaedic professionals on the detection team will screen for abnormal curvature of the spine. The scoliosis tester (AYMS, yds11, China) designed by Bunnell²¹ will be used to examine spinal curvature. We have developed an intelligent transmission application on this method that automatically transmits the values measured by the scoliosis tester to the database. In the forward-bending experiment, decibels are used to measure each segment of the subject’s back (chest, thoracolumbar and lumbar segments), and the maximum deviation angle and location are recorded. Scoliosis is suspected if the most severe back asymmetry exceeds 5%. The size of the trunk rotation angle measured by the scoliometer correlates with the severity of scoliosis, with an inclination >5°, including nearly all scoliosis cases with a Cobb angle >10°. The degrees of the thoracolumbar and lumbar segments will be collected for subsequent statistical analyses.

Dental caries measurements

Dental examinations will be performed under fiber-optic lighting by dental professionals in the inspection team using a dental probe and a plane mouth mirror. Disposable oral instruments will be used for all oral examinations (Dongbei, 2S-1, China). We will use a standardised code approach based on the WHO Standards for Dental Caries screening 2013.²² The subjects of our examination are students aged 6–16 years, the roots of the teeth will not be examined and the examination will be performed in the order of quadrants. Considering that a diagnosis can only be made after probing, the points, spaces, fossa, furrows and other common sites of caries will be examined using a probe. The codes for the diagnostic criteria are shown in online supplemental appendix A. Based on the tooth notation system jointly developed by the WHO and FDI (previously called Fédération Dentaire Internationale, now World Dental Federation), the diagnostic results will be recorded in the corresponding squares in terms of primary teeth and permanent teeth (see online supplemental appendix A). The total number of caries, tooth losses and fillings will be calculated automatically using our self-developed system. The measurement data are recorded by the screener via mobile phone or tablet, and the data are automatically uploaded to the database.

Online questionnaires

The health questionnaire consists of two parts. The first part is filled out by parents themselves, while the second part is completed with the assistance of parents for the students. The first part includes general information about the students and their family members, as well as a psychological health survey for the students (parent version). The second part includes a dietary survey, physical activity survey, electronic screen usage behaviour survey and eye health survey for the students. The questionnaire is completed using a mobile application on the parents’ smartphones. Details of the questionnaire can be found in online supplemental appendix B.

Data quality control and analysis plan

The data downloaded from the health information management system will be filtered using quality control procedures before analysis. Statistical analyses will be performed using the statistical package R V.4.1.0 (http://www.R-project.org, The R Foundation, Vienna, Austria) and the Free Statistics platform V.1.8. The right eye of each student will be included in the data analysis. If data for the right eye are unavailable, the left eye will be included in the analysis.

Categorical variables will be represented as proportions (%), while continuous variables will be described as the mean (SD) or median (IQR), as appropriate. To compare differences across the groups, the one-way analysis of variance (normal distribution), Kruskal-Wallis tests (skewed distribution) and χ² tests (categorical variables) will be performed. Logistic regression models will be used to determine the ORs and 95% CIs for the relationships between BMI, WHR, spinal curvature type, and ethnic group, and myopia. We will select appropriate examination indicators and questionnaire information as covariables.

In addition, restricted cubic spline regression will be performed with four knots at the 5th, 35th, 65th and 95th percentiles of examination indicators and different ethnic groups to assess linearity and to examine the dose–response curve between BMI and WHR, and myopia after adjusting for covariates. If there is a non-linear relationship, we will use a two-piecewise logistic regression model with smoothing to analyse the association threshold between BMI and WHR, and myopia. The likelihood ratio test and bootstrap resampling method will be used to determine inflection points.

Subgroup analyses will be performed using stratified logistic regression models. Interactions across the subgroups will be tested using a likelihood ratio test.

Screening personnel

The screening personnel will include ophthalmology, optometry, orthopaedics, stomatology professionals and graduate students involved in the project. The training task will be undertaken by Suzhou Institute of Biomedical Engineering and Technology of the Chinese Academy of Sciences and The Third Affiliated Hospital of Jinzhou Medical University. Among them, The Third Affiliated Hospital of Jinzhou Medical University is responsible for training in the medical field, including ophthalmology, physique, spinal curvature, oral screening knowledge learning and clinical operations. Suzhou Institute of Medical Engineering of the Chinese Academy of Sciences is responsible for software installation, commissioning, training, calibration and use of instruments, registration, upload, storage and application of data, etc. Each screener is required to study all screening programmes, including theoretical courses and practical exercises, and will take an exam at the end of the study. To be considered a screener for the study, each professional screener is required to score an A grade in both the theoretical and practical assessments, respectively.

Patient and public involvement

This study is conducted by the research committee, composed of the Health Commission of Liaoning Province, Jinzhou Municipal Education Bureau, Suzhou Institute of Biomedical Engineering and Technology of the Chinese Academy of Sciences and the Third Affiliated Hospital of Jinzhou Medical University. The committee is responsible for organising, coordinating and overseeing the myopia survey. Members of the research team, including experts, doctors and engineers, participated in the development of the study protocol. In addition to the school screening that students are required to complete, students and their guardians are required to complete a set of online questionnaires. Students, their parents, schools and the government are informed of the results of the screening programme in real time at various levels, both quantitative and qualitative. At the same time, students suspected of myopia will be referred to the hospital for further examination through special channels and appropriate measures will be taken.

Ethics and dissemination

This study was approved by the Medical Ethics Committee of the Third Affiliated Hospital of Jinzhou Medical University (approval number: JYDSY-KXYJ IEC-2023-018) and was registered in the Chinese Clinical Trial Registry (approval number: ChiCTR2300072893). Students and their parents (or other authorised surrogates) will provide informed consent before participation. The scientific research will comply with the principles of the Declaration of Helsinki and its regulations applicable to research and human participants. Study investigators should protect the participants’ privacy and be responsible for the confidentiality of all private information. The principal investigator is responsible for informing the ethics committee about any amendments to the study protocol. The results will be published in a peer-reviewed journal.

The datasets will be maintained at Jinzhou Medical University. No public reports of the results will disclose personal information. The data will be deidentified before being passed on to the study statisticians. Data will be kept with strict confidence and will only be assessed by the study investigators and authorised personnel. All data documents will be password protected and stored on a secure server. If the study plan is modified, the ClinicalTrials.gov registry record will be updated to reflect any changes, and any deviations from the published protocol will be reported alongside the study results.

Discussion

Myopia, a form of distance vision impairment, is a global public health problem with a high incidence rate in young people and is particularly serious in China. Myopia incurs a wide range of costs. In 2015, the global productivity loss due to uncorrected myopia was estimated to be approximately US$244 billion.²³ In Singapore, the annual cost of treating myopia is estimated to be around US$755 million. In the USA, the direct cost of correcting distance vision caused by refractive errors, including myopia, is within US$3.8–US$7.2 billion annually.^{24 25} In urban China, the extrapolated annual cost of myopia in individuals aged 5–50 years is approximately CNY173.6 billion (equivalent to US$26.3 billion).²⁶ With the occurrence and development of myopia, simple myopia may progress to pathological myopia, and patients may have other complications, leading to a further increase in medical costs. The persistence of myopia can be a lifelong burden; thus, the medical costs of treating myopia are enormous, resulting in a significant burden on the global economy.

Prevention of myopia is more important than treatment. In this protocol, we described the design and methodology of the screening system. During the process, Health Commission of Liaoning Province, Jinzhou Municipal Education Bureau, the Third Affiliated Hospital of Jinzhou Medical University, Suzhou Institute of Biomedical Engineering Technology, Chinese Academy of Sciences came together to ensure the integrity and implementability of this protocol. We have developed an intelligent health information collection and management system which can provide automated data collection, cloud data transmission, automated data processing and automated data feedback capabilities for schools, families, government and medical institutions. Therefore, this study can not only obtain the baseline situation of myopia of urban and rural children in Northeast China but also present the results of student screening to parents, schools and the government in real time, and parents will also receive intervention and referral recommendations and connect with corresponding medical institutions. Schools and governments receive different levels of statistical data that can help develop myopia prevention and control strategies.

At present, this study has not considered the collection of students’ biological samples, so it is unable to discuss the genetic factors influencing myopia. Considering that the prevention and control of myopia are mainly from the perspective of students’ behaviour, the current stage mainly focuses on the environmental impact of children’s myopia. Additionally, the current questionnaire is primarily filled out by parents and students through their mobile phones. Without professional surveyors, the survey results will be determined by parents’ cognitive level and proficiency in using electronic products. In this study, we will use non-cycloplegic autorefraction. Although cycloplegia is the gold standard for refractive error measurement in young children, it is difficult to achieve in large-scale screening for myopia. Time and resources are difficult to coordinate, and parents show great resistance to cycloplegia. These problems will continue to be discovered, summarised and improved in the course of subsequent experiments and statistical analysis.

Ethics statements

Patient consent for publication

Not applicable.