Secondhand smoke (SHS) exposure is associated with an increased risk of developing myopia among nonmyopic children in China

Table 1 Baseline demographic and other characteristics between SHS group and control group

Characteristic		Mean (SD)
Characteristic		SHS group (n = 128)	Control group (n = 104)	P value
Age, y		6.83 (1.32)	6.90 (1.42)	0.676
Sex, No. (%)
	Male	64 (50.0)	50 (48.1)	0.771
	Female	64 (50.0)	54 (51.9)	0.771
Height, cm		127.21 (9.78)	127.94 (10.98)	0.593
Weight, kg		27.50 (7.87)	28.18 (9.44)	0.546
Spherical equivalent, D^a		0.72 (0.56)	0.78 (0.51)	0.389
Axial length, mm^b		22.94 (0.75)	22.95 (0.72)	0.922
Average corneal K-reading, D^c		43.52 (2.23)	43.72 (1.40)	0.427
Intraocular pressure, mmHg^d		16.14 (2.21)	16.07 (2.61)	0.812
Central corneal thickness, um^e		544.7 (32.99)	542.16 (28.32)	0.537
Anterior chamber depth, mm^f		3.03 (0.22)	3.06 (0.23)	0.245
Crystalline lens thickness, mm^g		3.65 (0.23)	3.68 (0.24)	0.390
Pupil size, mm
	Photopic^h	3.15 (0.59)	3.09 (0.58)	0.433
	Mesopicⁱ	6.14 (0.91)	6.12 (0.77)	0.845
Subfoveal choroidal thickness, um^j		260.79 (55.05)	267.00 (47.17)	0.364
Outdoor activity, h/d^k		1.09 (0.88)	0.88 (0.55)	0.044
Near work after school, h/d^l		1.91 (0.81)	1.86 (0.85)	0.626
Parents with myopia, No. (%)
	0	36 (28.1)	32 (30.8)	0.317
	1	65 (50.8)	58 (55.8)
	2	27 (21.1)	14 (13.5)
Mother ‘s education level, No. (%)
	College degree and below	66 (51.6)	62 (59.6)	0.220
	Bachelor’s degree and above	62 (48.4)	42 (40.4)	0.220
Father’s education level, No. (%)
	College degree and below	90 (70.3)	54 (51.9)	0.004
	Bachelor’s degree and above	38 (29.7)	50 (48.1)	0.004

a. Spherical equivalent is calculated as spherical power plus half of the cylinder power
b. Axial length is the distance from the anterior surface of the cornea to the retinal pigment epithelium
c. Average corneal K-reading represents the average curvature of the cornea
d. Intraocular pressure refers to the fluid pressure inside the eye
e. Central corneal thickness is the thickness of the central cornea
f. Anterior chamber depth refers to the distance between the posterior surface of the cornea and the anterior surface of the iris
g. Crystalline lens thickness indicates the size and condition of the crystalline lens within the eye
h. Photopic pupil size is measured in a environment with an intensity of 500 lx
i. Mesopic pupil size is measured in a environment with an intensity of 4 lx
j. Subfoveal choroidal thickness is the thickness of the choroidal beneath the foveal
k. Outdoor activity includes outdoor exercise plus outdoor leisure activity
l. Near work after school includes doing homework, reading, playing cell phone, using computer, playing video game, watching television and so on

ISSN: 1471-2415