1 Basic characteristics of children in the three groups: Two children in FPALs group could not adapt to the glasses after 1 month and were re-allocated to the SVL group while maintaining the masking, after decision of the PACT investigator committee, resulting in 74 children in the SVL group, 66 children in the FPALs group and 71 in the PPALs group. Table 2 shows the basic data of the 211 children included in the three groups. There was no significant difference in the components between the three groups.
Table 2 basic characteristics of the children in the three groups
Total(211) / PPAL
(71) / FPAL
(66) / SVL
(74) / Comparison between three groups
Age (y) / 9.7 ± 1.1 / 9.7 ± 1.1 / 9.8 ± 1.1 / 9.6 ± 1.1 / F=0.66, p=0.52
male / 115 (52%) / 39 (55%) / 36 (55%) / 40 (54%) / X2=0.01, p=1.0
female / 96 (48%) / 32 (45%) / 30 (45%) / 34 (46%)
Age of first glasses (y) / 8.5 ± 1.1 / 8.6 ± 1.2 / 8.7 ± 1.1 / 8.5 ± 1.0 / F=0.31, p=0.73
Numbers of myopic parents / 1.1 ± 0.8 / 1.0 ± 0.8 / 1.0 ± 0.8 / 1.1 ± 0.7 / F=0.54, p=0.59
SE of cycloplegic autorefraction (right eye, D) / -2.36 ± 0.64 / -2.35 ± 0.70 / -2.36 ± 0.61 / -2.38 ± 0.62 / F=0.026,p=0.97
Axial length (mm) / 24.58 ± 0.74 / 24.6 ± 0.71 / 24.6 ± 0.73 / 24.6 ± 0.78 / F=0.001,p=1.0
Vitreous chamber depth (mm) / 17.25 ± 0.73 / 17.25 ± 0.75 / 17.25 ± 0.70 / 17.23 ± 0.75 / F=0.013, p=0.99
Anterior chamber depth (mm) / 3.28 ± 0.20 / 3.30 ± 0.22 / 3.25 ± 0.18 / 3.29 ± 0.20 / F=1.25, p=0.29
Lens thickness (mm) / 3.33 ± 0.13 / 3.30 ± 0.14 / 3.14 ± 0.13 / 3.33 ± 0.12 / F=0.52, p=0.59
AL/CR / 3.14 ± 0.06 / 3.14 ± 0.07 / 3.13 ± 0.05 / 3.15 ± 0.06 / F=1.60, p=0.21
Phoria at near (pd) / 0.97 ± 5.0 / 1.0 ± 5.1 / 0.89 ± 4.7 / 0.99 ± 5.2 / F=0.012, p=0.99
Phoria at near (No. subjects) / esophoria / 89 (42%) / 30 (42%) / 28 (42%) / 31 (42%) / X2=0.96,
p=0.92
orthophoria / 52 (25%) / 20 (28%) / 15 (23%) / 17 (23%)
exophoria / 70 (33%) / 21 (30%) / 23 (35%) / 26 (35%)
Accommodative Lag (D) / 1.40 ± 0.50 / 1.37 ± 0.52 / 1.44 ± 0.39 / 1.39 ± 0.58 / F=0.33, p=0.72
Accommodative lags with near addition lenses (D) / 0.77 ± 0.69 / 0.38 ± 0.53 / 0.48 ± 0.38 / 1.39 ± 0.58 / F=87.9,
p < 0.001
FA/Ph with near addition lenses / 6.00 ± 7.67 / 5.35 ± 10.01 / 5.10 ± 5.63 / 6.27 ± 6.63 / F=0.50, p=0.63
2 Refractive data: There was no significant difference between the SE of right and left eyes measured by cycloplegic autorefraction (t=0.80, p=0.47) or subjective refraction (t=1.40, p=0.17). Therefore, we analyzed and present the data of right eyes only. Figure 2 shows the distribution of SE determined by cycloplegic autorefraction in right eyes of the 211 children, with a mean of -2.36 ± 0.64 D (table 2). Most of the subjects (191, 90.2%) had a SE between -1.5D and -3.5 D. Cycloplegic autorefraction SE was not correlated to age (r=0.09, p= 0.21) and was similar in males (-2.38 ± 0.68 D) and females (-2.35 ± 0.61 D) (t=0.33, p=0.74).
There was little astigmatism in this group of children: J0 and J45 were mostly close to zero within a ± 0.25 D range (90% for J0 and 85% for J45, figure 3). The axis of the cylinder was classified according to a previous study: with the rule (WTR) was defined as between 0° and 22.5° or between 157.5° and 180°, against the rule (ATR) as between 67.5° and 112.5°, and oblique as the intermediate values.23 Eighty-one percent of the astigmatism was WTR, 14% with oblique and 5% was ATR in the right eyes of our sample.
The mean difference between the SE of the distance prescription determined by subjective refraction and the cycloplegic autorefraction was minor (0.10 ± 0.29 D, with 95% limits of agreement of 0.06 to 0.14 D) but significant (t=5.1, p0.001), with the distance prescription being slightly more positive. Figure 4 shows the good correlation between the distance prescription and cycloplegic autorefraction (r=0.90, p0.001).
3 Ocular components: Axial length of the right eyes (24.58 ± 0.74 mm) was similar to left eyes (24.58 ± 0.75 mm) in the 211 children (t=0.27, p=0.79). Boys had longer axial length, anterior chamber depth, vitreous chamber depth, and thinner lenses than girls (table 3). Vitreous chamber depth was the main cause of the axial length difference and was significantly correlated with axial length (r=0.95, p0.001). Both Axial length (figure 5, r=0.25, p0.01) and vitreous chamber depth (r=0.23, p0.001) were positively correlated to age. However, lens thickness and age were not significantly correlated (r=0.03, p=0.73).
Table 3 Comparison of ocular components between genders
Male(n=115) / Female
(n=96)
Axial length (mm) / 24.89 ± 0.67 / 24.22 ± 0.64 / t=7.4, p<0.01
Anterior chamber depth (mm) / 3.31 ± 0.19 / 3.25 ± 0.21 / t=2.5, p=0.015
Lens thickness (mm) / 3.31 ± 0.12 / 3.35 ± 0.14 / t=2.3, p=0.025
Vitreous chamber depth (mm) / 17.54 ± 0.68 / 16.89 ± 0.63 / t=7.2, p<0.01
4 Corneal radii: There were small but significant differences of corneal radii between right (42.7 ± 1.3 D) and left eyes (42.6 ± 1.3D) in K2 (t=2.37, p=0.018), but not in K1 (OD: 43.6 ± 1.5 D, OS: 43.7 ± 1.5D, t=1.77, p=0.078). Girl’s eyes had significantly steeper corneas in both meridians in the right eyes (K1: 44.3 ± 1.3 D, K2: 43.2 ± 1.2 D) compared to boys (K1: 43.1 ± 1.1 D, K2: 42.3 ± 1.3 D) (K1: t=6.0, p0.01, K2: t=5.3, p0.001). Keratometry was negatively correlated to age (figure 6, r=-0.18, p=0.01).
There was no significant difference in AL/CR ratio (axial length over corneal radius) between right and left eyes (t=0.67, p=0.51). Average AL/CR ratio was 3.14 ± 0.06, with 99.5% larger than 3.0 in right eyes of the 211 children. No significant difference in AL/CR ratios was found between girls (3.14 ± 0.06) and boys (3.15 ± 0.07) (t=1.3, p=0.20). The correlation between the age and AL/CR ratio was not significant (r=0.088, p=0.20).
. 5 Near addition, FA/Ph and accommodative lag. Figure 7 shows the near addition values of the 71 children in the PPAL group, which ranged from 0.75 D to 3.0 D (2.19 ± 0.73 D). In 82.5% of the subjects, lags of accommodation were higher than 1.0D when measured with their distance prescription (table 2). When measured with their near addition lenses, lags of accommodation were significantly lower in the two PAL groups compared to SVLs, with no difference between the two PAL groups (table 2, t=0.18, p=0.86). FA/Ph was similar between the three groups.
Figure 2 Baseline distribution of cycloplegic refraction SE in right eyes.
Figure 3 Baseline distribution of J0 (left) and J45 (right) in right eyes
Figure 4 SE of distance prescription in right eyes as a function of cycloplegic autorefraction (r=0.90, p<0.001).
Figure 5 Axial length in right eyes as a function of age (r=0.25, p<0.001).
Figure 6 Mean keratometry in right eyes as a function of age (r=-0.178, p=0.01).
Figure 7 Distribution of addition values in children with PPALs as a function of near phoria.