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KMID : 1159320070090010017
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Korean Journal of Vision Science
2007 Volume.9 No. 1 p.17 ~ p.30
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Asphericity and corneal shape according to the change of spherical equivalent for schoolchildren in Ilsan city
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Chang Bong-Soon
Kim Jeong-Mi
Oh Hyun-Jin
Won Chan-Hee
Bae Hyun-Ju
Mah Ki-Choong
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Abstract
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The present study conducted cycloplegic auto-refraction and corneal topography(Oculus Co., Keratograph V 1.65, Germany) for 325 eyes of 163 students living inIlsan and analyzed changes for a year by age and refractive error in order to obtain reference data for contact lens fitting in clinics and for the design and manufacturing of contact lens fit for Koreans.
For a year, the spherical equivalent of refractive error changed significantly (-0.368±0.413D) toward myopia(t = 16.068, p = 0.000), and the mean difference in the 1st and 2nd measurements was significantly in both elementary school students and middle school students(1st measurement : t = -3.696, p = 0.000, 2nd measurement : t = -3.016, p = 0.003), but the mean change was higher in elementary school students than in middle school ones and the difference was significant(t = 2.698, p = 0.007). In addition, the mean change was higher in the myopic group than in the non-myopic group(t = 2.703, p = 0.007). In the elementary school students the myopic group showed a larger change(t = 3.002, p = 0.003), and in the middle school students the myopic group showed a larger change but the difference was not significant(t = 1.586, p = 0.115).
As to 30° radius asphericity, no significant difference was observed between elementary school students and middle school students in the 1st measurement(t = 1.117, p = 0.265) and in the 2nd measurement(t = 0.084, p = 0.933). The mean change was slightly higher toward the negative (-) in middle school students but not significant(t = -1.711, p = 0.088). The mean change was slightly higher in the myopic group than in the non-myopic group(t = 1.873, p = 0.062). In elementary school students as well, the myopic group showed a larger change(t = 2.273, p = 0.024), and in middle school students the non-myopic group showed a larger change but not significant(t = -0.508, p = 0.613).
The corneal shape was mostly that of a prolate ellipse, flattening from corneal apex to periphery. When asphericity(Q) range of -0.4 ≤ Q < 0 was assumed to be the average corneal shape, 88.9% fell within the range in the 1st measurement and 85.5% in the 2nd measurement. The largest number of eyes were within the range of -0.4≤Q<-0.2, and concentration in the range was particularly high in the myopic group of middle school students. Asphericity was slightly more positive (+) in the non-myopic group than in the myopic group, and no correlation was observed between the change of sphericity and the change of the spherical equivalent of refractive error(r = -0.035, p = 0.526).
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KEYWORD
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corneal shape, corneal topography, asphericity, spherical equivalent
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