Table 2 Magnitude of cylinder power and prevalence rate of astigmatism by characteristics of students (N = 4804)

Age (years)

P < 0.0001

P < 0.0001

P = 0.02

P = 0.81

  ≤ 6

0.69 (0.61)

25 (8.5%)

3 (1.0%)

2.17 (0.97)

 7

0.64 (0.57)

25 (7.3%)

6 (1.7%)

2.19 (0.79)

 8

0.73 (0.76)

27 (7.5%)

5 (1.4%)

2.24 (0.94)

 9

0.73 (0.58)

30 (8.1%)

5 (1.4%)

2.17 (0.72)

 10

0.71 (0.59)

24 (6.8%)

6 (1.7%)

2.26 (1.07)

 11

0.78 (0.85)

40 (10.4%)

5 (1.3%)

2.08 (0.65)

 12

0.96 (0.93)

54 (15.3%)

12 (3.4%)

2.37 (0.94)

 13

0.89 (0.62)

56 (15.0%)

7 (1.9%)

2.04 (0.62)

 14

0.90 (0.63)

56 (15.3%)

4 (1.1%)

2.05 (0.64)

 15

1.02 (0.78)

67 (18.1%)

14 (3.8%)

2.36 (0.82)

 16

1.09 (1.03)

93 (25.8%)

5 (1.4%)

2.17 (1.48)

 17

1.07 (0.86)

76 (20.5%)

11 (3.0%)

2.27 (0.88)

 18

1.07 (0.87)

85 (23.0%)

15 (4.1%)

2.26 (1.04)

  ≥ 19

1.06 (0.79)

22 (17.5%)

5 (4.0%)

2.36 (0.95)

Gender

P < 0.0001

P < 0.0001

P = 0.001

P = 0.04

 Male

0.92 (0.89)

427 (16.1%)

73 (2.8%)

2.27 (1.06)

 Female

0.82 (0.80)

253 (11.8%)

30 (1.4%)

2.13 (0.78)

Grade

P < 0.0001

P < 0.0001

P = 0.02

P = 0.88

 Kindergarten

0.67 (0.58)

29 (7.6%)

3 (0.8%)

2.16 (0.91)

 Grade 1

0.66 (0.65)

27 (8.2%)

8 (2.4%)

2.33 (0.95)

 Grade 2

0.74 (0.71)

26 (7.1%)

5 (1.4%)

2.14 (0.79)

 Grade 3

0.73 (0.57)

30 (8.1%)

4 (1.1%)

2.16 (0.69)

 Grade 4

0.72 (0.62)

28 (7.6%)

7 (1.9%)

2.27 (1.11)

 Grade 5

0.82 (0.84)

41 (10.9%)

4 (1.1%)

2.03 (0.56)

 Grade 6

0.93 (0.92)

56 (15.0%)

12 (3.3%)

2.35 (0.96)

 Grade 7

0.91 90.61)

57 (15.2%)

6 (1.6%)

2.05 (0.55)

 Grade 8

0.94 (0.71)

58 (16.1%)

7 (1.9%)

2.17 (0.85)

 Grade 9

1.01 (0.75)

68 (19.7%)

12 (3.5%)

2.25 (0.73)

 Grade 10

1.10 (1.02)

96 (25.1%)

6 (1.6%)

2.22 (1.48)

 Grade 11

1.09 (0.89)

83 (22.3%)

14 (3.8%)

2.29 (0.86)

 Grade 12

1.06 (0.83)

82 (20.4%)

15 (3.7%)

2.26 (1.06)

Grade levels

P < 0.0001

P < 0.0001

P = 0.03

P = 0.66

 Kindergarten

0.66 (0.58)

29 (7.6%)

3 (0.8%)

2.16 (0.91)

 Elementary school (grade 1–6)

0.75 (0.63)

207 (9.5%)

40 (1.8%)

2.22 (0.86)

 Middle school (grade 7–9)

0.95 (0.69)

183 (16.9%)

25 (2.3%)

2.16 (0.72)

 High school (grade 10–12)

1.08 (0.90)

261 (22.5%)

35 (3.0%)

2.25 (1.18)

School location

P < 0.0001

P = 0.0001

P = 0.29

P = 0.64

 Urban

0.91 (0.76)

427 (15.9%)

63 (2.3%)

2.20 (1.00)

 Rural

0.82 (0.69)

253 (12.0%)

40 (1.9%)

2.24 (0.91)

Spherical equivalent of more astigmatic eye (diopters)

P < 0.0001

P < 0.0001

P < 0.0001

P = 0.008

  ≤ −6

1.67 (1.26)

174 (49.6%)

33 (9.4%)

2.46 (1.36)

  > −6, ≤ −5

1.23 (0.81)

75 (28.1%)

12 (4.5%)

2.21 (0.87)

  > −5, ≤ −4

1.07 (0.66)

90 (21.7%)

10 (2.4%)

2.05 (0.61)

  > −4, ≤ −3

0.96 (0.68)

84 (16.5%)

10 (2.0%)

2.12 (0.84)

  > −3, ≤ −2

0.78 (0.61)

54 (9.3%)

7 (1.2%)

2.18 (0.93)

  > −2, ≤ −1

0.75 (0.61)

67 (8.7%)

14 (1.8%)

2.26 (0.79)

  > −1, ≤ −0.5

0.68 (0.47)

35 (6.3%)

3 (0.5%)

1.96 (0.52)

  > −0.5, < 0.5

0.62 (0.47)

48 (4.5%)

6 (0.7%)

2.05 (0.78)

  ≥ 0.5, < 1.0

0.69 (0.56)

20 (11.7%)

0 (0.0%)

1.87 (0.42)

  ≥ 1.0

1.23 (0.92)

33 (32.0%)

8 (7.8%)

2.32 (0.72)