Myopia has become a major global public health problem, particularly in East Asia [
In recent years, Chinese scientific research institutions have carried out large-scale epidemiological survey on myopia in the northern and southern areas. Numerous cross-sectional studies have provided information on the pattern of prevalence and risk factors for myopia. Although the exact pathogenic mechanism of myopia is still unclear, most scholars believe that myopia is the result of a combination of genetic and environmental factors. Recent epidemiological surveys have shown that the prevalence of myopia varies widely, depending on age, gender, geography, and ethnicity [
The Childhood Errors of Refraction Study was a cross-sectional epidemiological study investigating the prevalence of refractive error in 10–15-year-old school-aged children conducted from December 2015 to January 2016. The sample calculation formula
The study was approved by the Ethics Committee of the Review Board of the Qingdao Economic and Technological Development Area First people’s Hospital and adhered to the Declaration of Helsinki. Written informed consent was obtained from parents or guardians.
The children underwent a comprehensive eye examination, including measurement of visual acuity, color vision, assessment of ocular motility, slit-lamp examination, autorefraction, cycloplegic autorefraction, and fundus examination using a direct ophthalmoscope (YZ6E; Six Six Vision Corp., Suzhou, China). The cycloplegic autorefraction was measured by a binocular open-field autorefractor (RM-8000A, Topcon, Japan) with a measurement range of −25 to +22 diopters (D). Cycloplegia was induced in each eye by instillation of three drops of 0.5% tropicamide 5 min apart. Extra tropicamide (1 or 2 drops) was also used in some children to obtain adequate mydriasis (a minimum pupil diameter of 6 mm and disappearance of papillary light reflex).
A standardized myopia questionnaire, which was modified from the Sydney Myopia Study (SMS) group, was adapted and applied to this study. The questionnaire was translated by ophthalmologists, an epidemiologist, and a statistician in our study group. It is composed of two parts: the parental version and the children’s version. A pilot study in the Anyang Childhood Eye Study (ACES) proved that this questionnaire is valid and reliable [
The equipment was checked and calibrated daily. All examiners were senior clinical ophthalmologists. Data entry was completed by well-trained staff.
Spherical equivalent (SE) was calculated with the following equation: SE = spherical diopter +0.5 × cylinder diopter. Myopia, emmetropia, and hyperopia was defined as the SE < −0.50 D (low myopia < −0.5 to >−3.0 D, moderate myopia ≤ −3.0 to >−6.0 D, and high myopia ≤ −6.0 D), −0.50 D ≤ SE ≤ +0.50 D, and SE > + 0.50 D, respectively [
The mean refractive error was −1.62 (±1.82) D, and the overall prevalence of myopia was 52.02%. The prevalence of myopia in students increased with age (
The prevalence of myopia in different age groups.
Age (years) | Number ( |
Myopia ( |
Myopia (%) |
---|---|---|---|
10 | 690 | 156 | 22.61 |
11 | 678 | 222 | 32.74 |
12 | 671 | 307 | 45.75 |
13 | 685 | 390 | 56.93 |
14 | 1080 | 716 | 66.30 |
15 | 1086 | 753 | 69.34 |
Total | 4890 | 2544 | 52.02 |
The prevalence of myopia of different genders in different age groups.
Age (years) | Male | Female | ||
---|---|---|---|---|
|
Myopia (%) |
|
Myopia (%) | |
10 | 361 | 94 (26.0) | 329 | 62 (18.8) |
11 | 348 | 119 (34.2) | 330 | 103 (31.2) |
12 | 351 | 156 (44.4) | 320 | 151 (47.2) |
13 | 344 | 199 (57.8) | 341 | 191 (56.0) |
14 | 560 | 346 (61.8) | 520 | 370 (71.2) |
15 | 565 | 387 (68.5) | 521 | 366 (70.2) |
Total | 2529 | 1301 (51.4) | 2361 | 1243 (52.6) |
In addition, we found that low myopia was still the main form of adolescent myopia. The proportion of high myopia increased with age (
The prevalence of low, moderate, and high myopia in different age groups.
Age (years) | No myopia | Low myopia | Moderate myopia | High myopia | ||||
---|---|---|---|---|---|---|---|---|
|
% |
|
% |
|
% |
|
% | |
10 | 534 | 77.39 | 130 | 18.84 | 17 | 2.46 | 9 | 1.30 |
11 | 456 | 67.26 | 162 | 23.89 | 50 | 7.37 | 10 | 1.47 |
12 | 364 | 54.25 | 192 | 28.61 | 89 | 13.26 | 26 | 3.87 |
13 | 295 | 45.07 | 226 | 32.99 | 117 | 17.08 | 47 | 6.86 |
14 | 364 | 33.70 | 380 | 35.19 | 247 | 22.87 | 89 | 8.24 |
15 | 333 | 30.66 | 388 | 35.73 | 266 | 24.49 | 99 | 9.12 |
Total | 2346 | 47.98 | 1478 | 30.22 | 786 | 16.07 | 280 | 5.73 |
Near work and outdoor activity time (hours per day) of the students.
Age (years) |
|
Near work (h/d) | Outdoor activity (h/d) |
---|---|---|---|
(Mean ± SD) | (Mean ± SD) | ||
10 | 562 | 3.32 ± 1.32 | 2.28 ± 1.21 |
11 | 559 | 3.42 ± 1.56 | 2.24 ± 1.26 |
12 | 536 | 3.41 ± 1.82 | 2.06 ± 1.32 |
13 | 561 | 3.78 ± 1.42 | 1.88 ± 1.12 |
14 | 752 | 4.32 ± 1.84 | 1.64 ± 1.14 |
15 | 783 | 4.62 ± 1.26 | 1.42 ± 0.96 |
|
|
|
The results of univariate and multivariate analyses of factors associated with myopia are shown in Table
Associations between myopia and possible risk factors.
Variables | Univariate analysis | Multivariate analysis | ||||
---|---|---|---|---|---|---|
Odds ratio | 95% CI |
|
Odds ratio | 95% CI |
|
|
Age | 1.43 | 1.34–1.52 | 0.012 |
1.23 | 1.18–1.27 | <0.001 |
Sex | ||||||
Boys | 1 | 1 | ||||
Girls | 1.64 | 0.48–2.21 | 0.14 | 1.68 | 0.42–1.92 | 0.12 |
Parental myopia | ||||||
None | 1 | 1 | ||||
One myopic | 1.47 | 1.24–1.96 | 0.01 |
1.62 | 0.71–2.34 | 0.12 |
Two myopic | 2.32 | 1.72–3.28 | <0.001 |
2.58 | 1.76–3.46 | <0.001 |
Near work distance (cm) | ||||||
>30 | 1 | 1 | ||||
20–30 | 1.27 | 1.02–1.54 | <0.001 |
1.12 | 0.69–1.38 | 0.23 |
10–20 | 2.46 | 1.52–4.76 | <0.001 |
1.76 | 0.49–2.74 | 0.18 |
0–10 | 1.29 | 1.08–1.54 | 0.04 | 1.21 | 0.84–1.41 | 0.32 |
Trend test | 0.16 | 0.21 | ||||
Near work time (h/d) | 1.28 | 1.04–1.86 | <0.001 |
1.42 | 0.79–2.04 | 0.16 |
Outdoor activity time (h/d) | 0.67 | 0.46–0.78 | 0.03 |
0.74 | 0.53–0.92 | <0.001 |
5 min rest after continuous near work time (min) | ||||||
0–15 | 1 | 1 | ||||
15–30 | 0.94 | 0.72–1.12 | 0.24 | 1.02 | 0.92–1.08 | 0.12 |
30–45 | 1.19 | 1.02–1.31 | 0.02 |
1.24 | 1.14–1.32 | <0.001 |
45–60 | 1.36 | 1.12–1.49 | <0.001 |
1.34 | 1.28–1.38 | 0.03 |
>60 | 2.12 | 1.76–2.72 | <0.001 |
2.48 | 1.92–3.24 | <0.001 |
Trend test | <0.001 |
<0.001 |
The prevalence of myopia around the world has increased recently. Previous studies have shown that 9 to 16 years of age is the fastest growing period for adolescent myopia [
Consistent with previous studies, we found that the prevalence of myopia in students persistently increased as the age increased. Interestingly, this result is lower than that in urban areas in Guangzhou [
At present, there is no unified conclusion about the prevalence of myopia among male or female. The current results revealed that girls were no more likely to suffer from myopia than boys. This is consistent with many previous studies [
Previous studies showed that parental myopia, in even only one parent, leads to an increased risk for juvenile myopia. In Australia, in six-year-old children, there was 3.16- and 3.33-fold increased risk of incident myopia than no parental myopia, respectively [
Previous numerous cross-sectional studies had reported that schoolchildren engaged in near work were more likely to have myopia than those who spent less time on near work [
Consistent with previous study [
In Singapore, a cross-sectional study was conducted to analyze the effect of outdoor activities on 1249 teenagers aged 11–20 years. They found a significant negative association between myopia and outdoor activities. Adjusting for the confounders, for each hour increase in outdoor activities per day, SE increased by 0.17 D and the axial length decreased by 0.06 mm [
In addition, it should be particularly pointed out that the questionnaire used in this study was similar to that of ACES. As the latest study on children myopia in China, the Anyang Childhood Eye Study has completed a series of horizontal and longitudinal studies on myopia. Therefore, we made a comparison of the two studies. At age 12 years, our children had similar level of near work time (3.41 versus 3.70 h/d) and outdoor activities time (2.06 versus 2.08 h/d) with the Anyang cohort [
Although there are several important findings in our study, the results of our analyses were tempered by some limitations. First, the data about near work, outdoor activities, and its related parameters was obtained from questionnaires. Although this method was predominant in previously reported studies, it could be subjected to recall bias. Second, the whole cycloplegic autorefraction data collection process lasted about 2 months, so there might be measurement bias. Third, there are some examples of using tropicamide for cycloplegia, but there are more international research examples of using cyclopentolate in recent years. As we all know, tropicamide is not as strong as cyclopentolate for paralyzing ciliary muscle. We finally chose tropicamide as cycloplegic agent mainly because we found some parents worried about the possible or potential side effects, and they also worry about that mydriasis for three days will affect children’s learning. If cyclopentolate is used, majority of parents will refuse to attend the study. Therefore, there may be some errors in the results of cycloplegic autorefraction. Lastly, this was only a cross-sectional survey; thus, we could not draw any conclusion about the incidence and progression for myopia.
In conclusion, the prevalence of myopia in adolescent students increased as the grade increased. Age, two myopic parents, and continuous near work time without 5 min rest were risk factors for myopia. Longer time spent on outdoor activities was significantly associated with a lower risk of myopia. These associations may indicate that low intensity near work and more outdoor activities may be important for future trials of intervention on myopia.
The authors declare that they have no conflicts of interest.