3.1 Subject characteristics
After excluding 34 eyes that did not meet the inclusion criteria (4 eyes had IOP > 21 mmHg, 5 eyes had strabismus or amblyopia, 4 eyes wearing corneal contact lens) or had low image quality (21 eyes), 349 (91.1%) children's right eyes were included in the final analysis. The mean age was 8.23 ± 1.06 years old (range, 6 to 11 years old) and 160 were girls (45.8%). The demographics were depicted in Table 1. Overall, the mean SER and AL were -0.10 ± 1.57D (range, -6.50 to 3.875 D) and 23.44 ± 0.95 mm (range, 21.52 to 26.51 mm), respectively.
Table 1 The demographic characteristics of the participants
Parameters
|
Boys (n = 189)
|
Girls (n = 160)
|
Total (n = 349)
|
P(age)
|
P(sex)
|
6-7y
|
8-9y
|
10-11y
|
6-7y
|
8-9y
|
10-11y
|
BMI (kg/m2)
|
17.11 ± 2.70
|
18.71 ± 3.66
|
20.60 ± 4.31
|
16.67 ± 3.10
|
17.43 ± 3.50
|
19.85 ± 4.32
|
18.10 ± 3.70
|
< 0.001
|
0.004
|
IOP (mmHg)
|
16.25 ± 2.90
|
16.91 ± 2.86
|
16.87 ± 2.54
|
16.92 ± 2.81
|
17.02 ± 2.90
|
17.05 ± 2.12
|
16.86 ± 2.80
|
0.575
|
0.417
|
SER (D)
|
0.40 ± 0.79
|
0.06 ± 1.47
|
-1.35 ± 1.93
|
0.72 ± 0.78
|
-0.35 ± 1.75
|
-1.02 ± 1.76
|
-0.10 ± 1.57
|
< 0.001
|
0.898
|
AL (mm)
|
23.30 ± 0.60
|
23.67 ± 0.91
|
24.36 ± 1.09
|
22.67 ± 0.66
|
23.23 ± 0.89
|
23.84 ± 0.77
|
23.44 ± 0.95
|
< 0.001
|
< 0.001
|
Values are presented as mean ± SD.
Gender differences were compared using independent samples t-test.
Age differences were compared using ANOVA.
Table 2 summarized the AC and ACA measurements. The mean ACD and ACW were 3.17 ± 0.24 mm and 11.69 ± 0.43 mm. By independent samples t-test, the AOD were 0.72 ± 0.25 mm, 0.63 ± 0.22 mm at N1, T1 (p < 0.001), and 0.98 ± 0.30 mm, 0.84 ± 0.27mm at N2, T2 (p < 0.001). The TISA were 0.24 ± 0.09 mm2, 0.22 ± 0.09 mm2 at N1, T1 (p < 0.001), and 0.46 ± 0.16 mm2, 0.40 ± 0.14 mm2 at N2, T2 (p < 0.001). Among the three age groups, participants aged 10-11 had the longest AL, the deepest ACD, and the widest ACA (all p < 0.001). All parameters except SER and IOP revealed significant gender differences. Girls have shorter AL, shallower AC, and narrower ACA than boys (all p < 0.05).
Table 2 The AC and ACA characteristics of the participants
Parameters
|
Boys
|
Girls
|
Total
|
P(age)
|
P(sex)
|
6-7y
|
8-9y
|
10-11y
|
6-7y
|
8-9y
|
10-11y
|
AC
|
ACD (mm)
|
3.14 ± 0.14
|
3.24 ± 0.23
|
3.27 ± 0.23
|
3.04 ± 0.21
|
3.11 ± 0.26
|
3.20 ± 0.33
|
3.17 ± 0.24
|
< 0.001
|
< 0.001
|
ACW (mm)
|
11.68 ± 0.36
|
11.75 ± 0.41
|
11.80 ± 0.43
|
11.67 ± 0.50
|
11.58 ± 0.42
|
11.87 ± 0.37
|
11.69 ± 0.43
|
0.068
|
0.022
|
ACA
|
AOD (mm)
|
N1
|
0.65 ± 0.16
|
0.81 ± 0.27
|
0.78 ± 0.24
|
0.62 ± 0.16
|
0.68 ± 0.24
|
0.68 ± 0.32
|
0.72 ± 0.25
|
< 0.001
|
< 0.001
|
N2
|
0.90 ± 0.21
|
1.10 ± 0.32
|
1.06 ± 0.30
|
0.92 ± 0.29
|
0.90 ± 0.21
|
0.92 ± 0.37
|
0.98 ± 0.30
|
< 0.001
|
< 0.001
|
T1
|
0.59 ± 0.17
|
0.69 ± 0.25
|
0.69 ± 0.22
|
0.56 ± 0.16
|
0.58 ± 0.21
|
0.57 ± 0.27
|
0.63 ± 0.22
|
0.030
|
< 0.001
|
T2
|
0.80 ± 0.20
|
0.93 ± 0.28
|
0.93 ± 0.27
|
0.74 ± 0.19
|
0.79 ± 0.26
|
0.75 ± 0.32
|
0.84 ± 0.27
|
0.014
|
< 0.001
|
TISA (mm2)
|
N1
|
0.22 ± 0.05
|
0.28 ± 0.10
|
0.26 ± 0.09
|
0.21 ± 0.07
|
0.23 ± 0.09
|
0.23 ± 0.11
|
0.24 ± 0.09
|
0.001
|
< 0.001
|
N2
|
0.41 ± 0.10
|
0.52 ± 0.18
|
0.49 ± 0.15
|
0.39 ± 0.11
|
0.43 ± 0.15
|
0.44 ± 0.20
|
0.46 ± 0.16
|
< 0.001
|
< 0.001
|
T1
|
0.20 ± 0.06
|
0.24 ± 0.10
|
0.26 ± 0.08
|
0.19 ± 0.06
|
0.20 ± 0.08
|
0.20 ± 0.10
|
0.22 ± 0.09
|
0.012
|
< 0.001
|
T2
|
0.38 ± 0.10
|
0.44 ± 0.16
|
0.45 ± 0.14
|
0.35 ± 0.10
|
0.38 ± 0.14
|
0.37 ± 0.18
|
0.40 ± 0.14
|
0.015
|
< 0.001
|
3.2 AC and ACA parameters in different groups
Table 3 shows the differences in ACD, ACW, AOD, and TISA among different SER groups. The myopic group presented the deepest ACD (F = 25.53, p < 0.001). However, there was no significant difference in ACW among the three groups (F = 0.996, p = 0.371). Figure 3 shows that AOD and TISA increased sequentially at all locations in the hyperopic, emmetropic, and myopic groups.
Table 3 Comparison of AC and ACA parameters in subjects according to different refractive status
Variables
|
Hyperopia
(n = 146)
|
Emmetropia
(n = 98)
|
Myopia
(n = 98)
|
F
|
p value
|
AC
|
ACD (mm)
|
3.07 ± 0.23
|
3.20 ± 0.24
|
3.27 ± 0.21
|
25.53
|
< 0.001
|
ACW (mm)
|
11.71 ± 0.45
|
11.72 ± 0.46
|
11.65 ± 0.36
|
0.996
|
0.371
|
ACA
|
AOD (mm)
|
N1
|
0.63 ± 0.20
|
0.73 ± 0.24
|
0.83 ± 0.27
|
21.93
|
< 0.001
|
N2
|
0.87 ± 0.260
|
0.98 ± 0.29
|
1.11 ± 0.31
|
21.41
|
< 0.001
|
T1
|
0.55 ± 0.19
|
0.65 ± 0.21
|
0.71 ± 0.25
|
17.97
|
< 0.001
|
T2
|
0.74 ± 0.23
|
0.88 ± 0.26
|
0.94 ± 0.28
|
19.93
|
< 0.001
|
TISA (mm2)
|
N1
|
0.21 ± 0.07
|
0.24 ± 0.09
|
0.28 ± 0.10
|
18.82
|
< 0.001
|
N2
|
0.40 ± 0.13
|
0.46 ± 0.15
|
0.53 ± 0.17
|
20.55
|
< 0.001
|
T1
|
0.19 ± 0.07
|
0.23 ± 0.08
|
0.24 ± 0.10
|
12.99
|
< 0.001
|
T2
|
0.35 ± 0.12
|
0.42 ± 0.14
|
0.45 ± 0.16
|
15.99
|
< 0.001
|
Comparison underwent ANOVA.
We further compared the AC and ACA parameters in eyes with different axial lengths. Table 4 presents the eyes with the longest AL had the deepest ACD (F = 53.87, p < 0.001), the widest ACW (F = 32.63, p < 0.001), the largest AOD and TISA (all p < 0.001). Figure 4 presents that the nasal angle width grew more significantly with AL than the temporal angle.
Table 4 Comparison of AC and ACA parameters in subjects with different axial length
Variables
|
AL < 22.5mm, n = 62
|
22.5mm ≤ AL < 23.5mm, n = 129
|
AL ≥ 23.5mm, n = 158
|
F
|
p value
|
AC
|
ACD (mm)
|
2.97 ± 0.23
|
3.11 ± 0.21
|
3.29 ± 0.20
|
58.58
|
< 0.001
|
ACW (mm)
|
11.35 ± 0.35
|
11.67 ± 0.41
|
11.86 ± 0.39
|
39.15
|
< 0.001
|
ACA
|
AOD (mm)
|
N1
|
0.59 ± 0.18
|
0.67 ± 0.22
|
0.81 ± 0.26
|
23.52
|
< 0.001
|
N2
|
0.81 ± 0.24
|
0.92 ± 0.27
|
1.09 ± 0.30
|
26.41
|
< 0.001
|
T1
|
0.55 ± 0.18
|
0.57 ± 0.20
|
0.70 ± 0.23
|
19.15
|
< 0.001
|
T2
|
0.75 ± 0.23
|
0.78 ± 0.24
|
0.93 ± 0.27
|
19.22
|
< 0.001
|
TISA (mm2)
|
N1
|
0.19 ± 0.07
|
0.23 ± 0.09
|
0.27 ± 0.10
|
20.46
|
< 0.001
|
N2
|
0.37 ± 0.12
|
0.43 ± 0.14
|
0.51 ± 0.16
|
23.99
|
< 0.001
|
T1
|
0.19 ± 0.07
|
0.20 ± 0.07
|
0.24 ± 0.09
|
14.76
|
< 0.001
|
T2
|
0.35 ± 0.12
|
0.37 ± 0.13
|
0.45 ± 0.15
|
17.31
|
< 0.001
|
Comparison underwent ANOVA.
3.3 Associations between AC (ACD, ACW) and SER, AL
Figure 5 depicts the relationship between ACD, ACW and SER, AL. SER was found to be negatively correlated with ACD (r = 0.32, p < 0.0001, Figure 5A), but not with ACW (r = 0.06, p = 0.004, Figure 5C). AL had a significant positive correlation with ACD (r = 0.49, p < 0.0001, Figure 5B) and ACW (r = 0.39, p < 0.0001, Figure 5D). A larger AL implied a deeper and wider AC.
3.4 Associations between ACA (AOD, TISA) and SER, AL
Figure 6 demonstrates the correlation between AOD, TISA and SER, AL. SER was revealed to be significantly negatively correlated with AOD and TISA (all p < 0.0001, Figures 6A, C). AL had a strong positive correlation with AOD and TISA (all p < 0.0001, Figures 6B, D). The correlation of SER and AL with nasal angle was stronger than that with temporal angle.
3.5 Multiple linear regression
In multiple linear regression analysis, all variables (age, gender, BMI, SER, AL, IOP, ACD, ACW) were included in the initial model of exploratory testing to gradually determine the best predictors of angle parameters. The final regression model was presented in Table 5. All angle parameters were significantly associated with deeper ACD and narrower ACW. In addition, female gender was only significantly associated with AOD-T2 and TISA-T2. ACD was found to explain 30.9% and 36.3% of the variability in AOD-N1 and AOD-N2. It was also found to explain 24.3% and 29.2% of the variability in TISA-N1 and TISA-N2.
Table 5 Multiple regression analysis between AOD, TISA and other factors
Parameters
|
Significant factor
|
Standardized regression coefficient beta
|
Variance inflation
factor
|
p value
|
R2
|
AOD
(mm)
|
N1
|
ACD
ACW
AL
|
0.595
-0.245
0.143
|
1.438
1.310
1.375
|
< 0.001
< 0.001
0.005
|
0.361
|
N2
|
ACD
ACW
AL
|
0.638
-0.207
0.136
|
1.438
1.310
1.375
|
< 0.001
< 0.001
0.006
|
0.401
|
T1
|
ACD
ACW
AL
|
0.553
-0.256
0.131
|
1.438
1.310
1.375
|
< 0.001
< 0.001
0.014
|
0.301
|
T2
|
ACD
ACW
Gender
|
0.622
-0.256
0.122
|
1.294
1.240
1.059
|
< 0.001
< 0.001
0.007
|
0.356
|
TISA
(mm2)
|
N1
|
ACD
ACW
AL
|
0.514
-0.221
0.158
|
1.438
1.310
1.375
|
< 0.001
< 0.001
0.003
|
0.289
|
N2
|
ACD
ACW
AL
|
0.567
-0.227
0.153
|
1.438
1.310
1.375
|
< 0.001
< 0.001
0.004
|
0.339
|
T1
|
ACD
|
0.543
|
1.239
|
< 0.001
|
0.238
|
ACW
|
-0.232
|
1.239
|
< 0.001
|
T2
|
ACD
ACW
Gender
|
0.567
-0.243
-0.103
|
1.294
1.240
1.059
|
< 0.001
< 0.001
0.029
|
0.292
|