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Jia Huang, Xingtao Zhou, Xiaomei Qu; Refractive Astigmatism and the components of Astigmatism in preschool children of China. Invest. Ophthalmol. Vis. Sci. 2013;54(15):2336. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
To report the prevalence of refractive (RA), corneal (CA), and internal astigmatism (IA) in a population of preschool children in China, we also examine the contribution of corneal and internal astigmatism components to total refractive astigmatism by power vectors.
We examined refraction and eye health in 14116 cases of 3-6 years old children (7310 boys, 51.8%) in Yangpu District, Shanghai, China. Cycloplegic refractive and keratometri measures using autorefractor (Canon RK-F1,Japan) and IOL master( Carl Zeiss, Germany). Of 13080 eligible children, all the data from right eyes were analyzed. Measures of total and corneal cylinder were transposed into J0 and J45 components, where positive and negative J0 values quantified with-the-rule (WTR) and against-the-rule(ATR) astigmatisms, respectively, and J45 quantified oblique astigmatism. The difference of RA and CA is IA. We divided the sample into high RA group (total cylinder≥1 D; mean, 1.56±0.73 D; n =2899) and normal RA group (0.25D≤total cylinder≤0.75 D; mean, 0.54±0.20 D; n= 4264).
Overall prevalence of RA (≥1.0 diopter [D]) was 22.16%, CA (≥1.0 D) 64.21%, IA (≥1.0 D) 40.28%. In high RA group, RA axis was mainly WTR(81.54%), followed by oblique axis(17.00%), then ATR(1.46%); in normal RA group, RA axis was also mainly WTR(61.92%), then oblique axis(31.06%), ATR(7.02%). CA axis was mainly with the rule (85.69%), while IA axis was mainly against the rule (76.54%). Regression analysis showed J0 component of CA was positively correlated with RA only in high WTR astigmats’ group(R2=0.684; P<0.001 ). In all groups, the mean J0 component of CA were always positive; the mean J0 component of IA are always negative.
In 3-6 years old preschool children of China, astigmatism axis is mainly with the rule, especially in the high astigmatism group, followed by the oblique axis astigmatism and against the rule astigmatism. Corneal astigmatism is mainly with the rule, while internal astigmatism is mainly against the rule. J0 components of CA and IA counteract each other in all groups, J45 components of CA and IA also counteract each other in high RA group, however, J45 components of CA and IA are superimposed on each other in normal RA group.
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