The main characteristics of study participants were reported in Table 1. Of the 3256 school students, 33.42% is primary school students, 33.42% is middle school students and 33.17% is high school students. The average ages of three groups were 10.66, 13.59 and 16.59 years old, respectively. The proportions of male students were 53.77%, 50.37% and 46.20%, respectively. The situation of reading and writing posture was shown in Table 1 as well.
Table 1
Characteristics of all subjects included in the study.
Characteristics
|
Primary School
(N = 1088)
|
Middle School
(N = 1088)
|
High School
(N = 1080)
|
Age
|
10.66 ± 0.86
|
13.59 ± 0.92
|
16.59 ± 0.89
|
Gender (M / F)
|
585 / 503
|
548 / 540
|
499 / 581
|
Myopia prevalence
|
61.49%
(669 / 1088)
|
81.43%
(886 / 1088)
|
89.72%
(969 / 1080)
|
Male
|
58.63%
(343 / 585)
|
78.28%
(429 / 548)
|
87.17%
(435 / 499)
|
Female
|
64.81%
(326 / 503)
|
84.63%
(457 / 540)
|
91.91%
(534 / 581)
|
When you're reading and writing
|
The chest is more than one fist from the edge of the table
|
Never/ Sometimes/ Usually/ Always
|
135/ 340/ 321/ 290
|
78/ 408/ 322/ 279
|
92/ 434/ 330/ 218
|
The eyes are more than one Chi away from the book
|
Never/ Sometimes/ Usually/ Always
|
132/ 373/ 278/ 300
|
92/ 467/ 294/ 228
|
114/ 534/ 309/ 118
|
The finger is about one Cun away from the tip of the nose
|
Never/ Sometimes/ Usually/ Always
|
162/ 218/ 227/ 473
|
142/ 287/ 267/ 386
|
174/ 331/ 261/ 306
|
Does your teacher remind you that your reading and writing posture is not correct?
|
Never/ Sometimes/ Usually/ Always
|
181/ 302/ 227/ 372
|
191/ 419/ 231/ 243
|
357/ 488/ 158/ 72
|
Do your parents remind you that your reading and writing posture is not correct?
|
Never/ Sometimes/ Usually/ Always
|
91/ 272/ 253/ 467
|
97/ 274/ 326/ 387
|
140/ 419/ 357/ 159
|
Myopia prevalence of primary school students was 61.49%, 58.63% for male students and 64.81% for female students. Myopia prevalence of middle school students was 81.43%, 78.28% for male students and 84.63% for female students. Myopia prevalence of high school students was 89.72%, 87.17% for male students and 91.91% for female students (Fig. 1).
In the associations between reading and writing posture and myopia, we applied logistic regression analysis in different gender and different school types. As shown in Table 2, after adjusting for age and grade, the eyes are more than one Chi away from the book was identified as a protective factor in female students. And the more they choose to keep eyes are more than one Chi away from the book, the lower risk they will get myopic. Compared with the female students who choose "never" for "the eyes are more than one Chi away from the book", the ORs and 95% CIs for subjects who choose "sometimes", "usually", "always" were 0.522 (0.280, 0.974), 0.492 (0.253, 0.956) and 0.309 (0.150, 0.635), respectively. And in male students, the finger is about one Cun away from the tip of the nose turned out to be a protective factor as well. Compared with the male students who choose "never" for "the finger is about one Cun away from the tip of the nose", the OR and 95% CI for subjects who choose "sometimes" were 0.613 (0.390, 0.962). However, the chest is more than one fist from the edge of the table was a risk factor in female students for myopia (Usually: 1.894 (1.027, 3.494), Always: 2.005 (1.036, 3.882)). And in both male and female students, the more parents remind their reading and writing postures, they are more tend to be myopic.
Table 2
Logistic regression of myopia-related factors by gender.
Items
|
Male
|
Female
|
OR (95% CI)
|
P value
|
OR (95% CI)
|
P value
|
Age
|
1.209 (1.056, 1.383)
|
0.006
|
1.267 (1.087, 1.477)
|
0.002
|
Grade
|
1.319 (0.868, 2.007)
|
0.195
|
1.243 (0.770, 2.006)
|
0.373
|
The chest is more than one fist from the edge of the table
|
Never
|
Reference
|
Sometimes
|
1.271 (0.781, 2.069)
|
0.334
|
1.301 (0.729, 2.324)
|
0.373
|
Usually
|
1.273 (0.760, 2.131)
|
0.359
|
1.894 (1.027, 3.494)
|
0.041
|
Always
|
1.157 (0.672, 1.994)
|
0.598
|
2.005 (1.036, 3.882)
|
0.039
|
The eyes are more than one Chi away from the book
|
Never
|
Reference
|
Sometimes
|
1.514 (0.919, 2.494)
|
0.103
|
0.522 (0.280, 0.974)
|
0.041
|
Usually
|
1.491 (0.864, 2.575)
|
0.152
|
0.492 (0.253, 0.956)
|
0.036
|
Always
|
0.925 (0.522, 1.640)
|
0.790
|
0.309 (0.150, 0.635)
|
0.001
|
The finger is about one Cun away from the tip of the nose
|
Never
|
Reference
|
Sometimes
|
0.613 (0.390, 0.962)
|
0.033
|
1.010 (0.620, 1.646)
|
0.967
|
Usually
|
0.782 (0.489, 1.249)
|
0.303
|
0.673 (0.413, 1.094)
|
0.110
|
Always
|
0.871 (0.554, 1.370)
|
0.550
|
0.925 (0.574, 1.491)
|
0.748
|
Does your teacher remind you that your reading and writing posture is not correct?
|
Never
|
Reference
|
Sometimes
|
1.029 (0.705, 1.501)
|
0.882
|
1.011 (0.677, 1.508)
|
0.959
|
Usually
|
0.808 (0.516, 1.266)
|
0.353
|
0.840 (0.519, 1.359)
|
0.478
|
Always
|
0.617 (0.370, 1.028)
|
0.064
|
0.919 (0.538, 1.568)
|
0.757
|
Do your parents remind you that your reading and writing posture is not correct?
|
Never
|
Reference
|
Sometimes
|
1.106 (0.701, 1.744)
|
0.666
|
1.431 (0.839, 2.441)
|
0.189
|
Usually
|
1.215 (0.740, 1.995)
|
0.440
|
2.032 (1.143, 3.614)
|
0.016
|
Always
|
2.222 (1.276, 3.867)
|
0.005
|
1.903 (1.051, 3.445)
|
0.034
|
The associations between reading and writing posture and myopia in different school types were similar (Table 3). After adjusting for gender and age, the eyes are more than one Chi away from the book was identified as a protective factor in both primary school (Always: 0.545 (0.300, 0.989)) and middle school (Always: 0.371 (0.154, 0.897)). And compared with the middle school students who choose "never" for "the finger is about one Cun away from the tip of the nose", the OR and 95% CI for subjects who choose "sometimes" were 0.411 (0.212, 0.794). Still, the chest is more than one fist from the edge of the table was a risk factor in middle school students and parents remind of reading and writing postures was a risk factor in primary school students.
Table 3
Logistic regression of myopia-related factors by school type.
Items
|
Primary School
|
Middle School
|
High School
|
OR (95% CI)
|
P value
|
OR (95% CI)
|
P value
|
OR (95% CI)
|
P value
|
Gender
|
1.320 (1.021, 1.707)
|
0.034
|
1.330 (0.963, 1.838)
|
0.084
|
1.499 (0.985, 2.282)
|
0.059
|
Age
|
1.546 (1.327, 1.801)
|
< 0.001
|
1.154 (0.968, 1.375)
|
0.111
|
0.817 (0.651, 1.027)
|
0.083
|
The chest is more than one fist from the edge of the table
|
Never
|
Reference
|
Sometimes
|
1.251 (0.762, 2.053)
|
0.376
|
1.931 (0.948, 3.935)
|
0.070
|
0.496 (0.168, 1.470)
|
0.206
|
Usually
|
1.540 (0.912, 2.600)
|
0.107
|
3.600 (1.663, 7.795)
|
0.001
|
0.365 (0.122, 1.093)
|
0.072
|
Always
|
1.703 (0.968, 2.996)
|
0.065
|
2.792 (1.246, 6.257)
|
0.013
|
0.329 (0.106, 1.021)
|
0.054
|
The eyes are more than one Chi away from the book
|
Never
|
Reference
|
Sometimes
|
0.777 (0.463, 1.304)
|
0.339
|
1.015 (0.467, 2.204)
|
0.970
|
1.858 (0.811, 4.258)
|
0.143
|
Usually
|
0.969 (0.549, 1.709)
|
0.913
|
0.575 (0.252, 1.309)
|
0.187
|
1.799 (0.736, 4.400)
|
0.198
|
Always
|
0.545 (0.300, 0.989)
|
0.046
|
0.371 (0.154, 0.897)
|
0.028
|
1.169 (0.425, 3.218)
|
0.762
|
The finger is about one Cun away from the tip of the nose
|
Never
|
Reference
|
Sometimes
|
1.001 (0.625, 1.603)
|
0.996
|
0.411 (0.212, 0.794)
|
0.008
|
0.855 (0.418, 1.745)
|
0.666
|
Usually
|
0.721 (0.447, 1.164)
|
0.181
|
0.634 (0.322, 1.248)
|
0.187
|
0.790 (0.375, 1.666)
|
0.536
|
Always
|
0.960 (0.610, 1.509)
|
0.858
|
0.659 (0.336, 1.293)
|
0.225
|
1.232 (0.590, 2.576)
|
0.578
|
Does your teacher remind you that your reading and writing posture is not correct?
|
Never
|
Reference
|
Sometimes
|
0.928 (0.604, 1.424)
|
0.731
|
1.026 (0.617, 1.705)
|
0.921
|
1.150 (0.683, 1.938)
|
0.599
|
Usually
|
0.885 (0.542, 1.444)
|
0.625
|
0.863 (0.472, 1.581)
|
0.634
|
0.549 (0.278, 1.086)
|
0.085
|
Always
|
0.729 (0.435, 1.223)
|
0.231
|
0.925 (0.470, 1.817)
|
0.820
|
0.647 (0.202, 2.077)
|
0.464
|
Do your parents remind you that your reading and writing posture is not correct?
|
Never
|
Reference
|
Sometimes
|
1.308 (0.764, 2.239)
|
0.328
|
1.336 (0.710, 2.513)
|
0.369
|
0.905 (0.464, 1.764)
|
0.770
|
Usually
|
1.560 (0.869, 2.801)
|
0.137
|
1.386 (0.706, 2.722)
|
0.343
|
1.517 (0.723, 3.182)
|
0.271
|
Always
|
1.958 (1.073, 3.574)
|
0.029
|
1.911 (0.933, 3.916)
|
0.077
|
2.489 (0.875, 7.079)
|
0.087
|