Table 1 Characteristics of all participants

Age

P < 0.001**

  6–8 years

333

268 (80.48%)

65 (19.52%)

  9–12 years

253

92 (36.36%)

161 (63.64%)

Sex

P = 0.001**

  Female

273

148

(54.21%)

125

(45.79%)

  Male

313

212

(67.73%)

101

(32.27%)

Duration of electronic device use per week

P = 0.078

  0–7 h

328

213

(64.94%)

115

(35.06%)

  7–14 h

184

110

(59.78%)

74

(40.22%)

  14–21 h

50

27

(54.00%)

23

(46.00%)

  >21 h

24

10

(41.67%)

14

(58.33%)

Duration of watching television per week

P = 0.594

  0–7 h

416

250

(60.10%)

166

(39.90%)

  7–14 h

126

84

(66.67%)

42

(33.33%)

  14–21 h

30

18

(60.00%)

12

(40.00%)

  >21 h

14

8

(57.14%)

6

(42.86%)

Duration of near work per week

P < 0.001**

  0–25 h

189

136

(71.96%)

53

(28.04%)

  25–38 h

311

182

(58.52%)

129

(41.48%)

  >38 h

86

42

(48.84%)

44

(51.16%)

Near-work distance

P = 0.017**

  >33 cm

283

188

(66.43%)

95

(33.57%)

  <33 cm

303

172

(56.77%)

131

(43.23%)

Times of eye exercise per week

P = 0.280

  1–5 times

285

183

(64.21%)

102

(35.79%)

  5–10 times

246

140

(56.91%)

106

(43.09%)

  10–20 times

52

35

(67.31%)

17

(32.69%)

  >20 times

3

2

(66.67%)

1

(33.33%)

Times of visual fatigue per week

P = 0.021*

  0 time

338

221

(65.38%)

117

(34.62%)

  1–5 times

231

134

(58.01%)

97

(41.99%)

  5–10 times

12

4

(33.33%)

8

(66.67%)

  > 10 times

5

1

(20.00%)

4

(80.00%)

Reading posture

P = 0.022*

  Sitting

365

235

(64.38%)

130

(35.62%)

  Prone

175

93

(53.14%)

82

(46.86%)

  Supine

46

32

(69.57%)

14

(30.43%)

Distance between fingertip and nib

P = 0.082

  <1.5 cm

218

124

(56.88%)

94

(43.12%)

  >1.5 cm

368

236

(64.13%)

132

(35.87%)

Head angle

P = 0.233

  Vertical 0°

44

26

(59.09%)

18

(40.91%)

  Left 0°–45°

217

128

(58.99%)

89

(41.01%)

  Left 45°–90°

250

165

(66.00%)

85

(34.00%)

  Right 0°–45°

57

30

(52.63%)

27

(47.37%)

  Right 45°–90°

18

9

(50%)

9

(50%)

Light environment in classroom

P < 0.001**

  Closed curtains

92

39

(42.39%)

53

(57.61%)

  Open curtains

516

335

(64.92%)

181

(35.08%)

Outdoor time per week

P = 0.026*

  0–7 h

268

150

(55.97%)

118

(44.03%)

  7–14 h

257

166

(64.59%)

91

(35.41%)

  >14 h

61

44

(72.13%)

17

(27.87%)

Parents with myopia

P = 0.002*

  0

133

96

(72.18%)

37

(27.82%)

  1

253

158

(62.45%)

95

(37.55%)

  2

200

106

(53.00%)

94

(47.00%)

Parents with high myopia

P = 0.532

  0

422

257

(60.90%)

165

(39.10%)

  1

130

79

(60.77%)

51

(39.23%)

  2

34

24

(70.59%)

10

(29.41%)

Vegetable intake per day

P = 0.852

  < 75 g

179

113

(63.13%)

66

(36.87%)

  75–150 g

312

189

(60.58%)

123

(39.42%)

  > 150 g

95

58

(61.05%)

37

(38.95%)

Fruit intake per day

P = 0.545

  <75 g

295

177

(60.00%)

118

(40.00%)

  75–150 g

244

156

(63.93%)

88

(36.07%)

  >150 g

47

27

(57.45%)

20

(42.55%)

Percentage of grains in staple foods

P = 0.052

  <25%

362

213

(58.84%)

149

(41.16%)

  25–50%

179

112

(62.57%)

67

(37.43%)

  >50%

45

35

(77.78%)

10

(22.22%)

School type

P = 0.107

  Public schools

560

348

(62.14%)

212

(37.86%)

  Private schools

26

12

(46.15%)

14

(53.85%)