不同屈光状态儿童角膜前表面非球面特性分析及建模

doi:10.3760/cma.j.issn.1674-845X.2013.07.002

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Abstract

Objective To calculate the Q-value of the anterior corneal surface of children by using the tangential radius of curvature； to analyze the distribution of horizontal Q-values and the relationship between Q-value and different refractions. The vertical Q-values were calculated by curve fitting， and the Q-values of the 360° semi-meridians were then obtained， to complete the mathematical model of the anterior corneal surface. Methods The Ft-values of the 360 semi-meridians from the 84 right eyes of the children （12 cases of myopia， 45 cases of hyperopia， and 27 cases of emmetropia） were calculated by Orbscan Ⅱ topography using a linear regression equation to calculate the Q-values of the semi-meridians and analyze the nasal and temporal distribution of the Q-values and the effect of refractive state. MATLAB R2009b （Matrix Laboratory） was used for curve fitting calculations of the right eye data from 62 children （10 myopes， 25 hyperopes and 27 emmetropes） to obtain Q-values of 360 semi-meridians and to analyze the distribution of the Q-values. Results ①All of the coefficients of determination （R2） were greater than or equal to 0.5. The Q-values of the nasal and temporal distributions were between 1 and 0. The mean Q-values of the nasal distribution of 84 right eyes was -0.42±0.16， and the temporal distribution was -0.23±0.08. The difference was statistically significant （t=-9.527， P<0.05）. The mean r0 of the nasal distribution of 84 right eyes was 7.85±0.24 and the temporal distribution was 7.83±0.24. The difference was statistically significant （t=3.213， P<0.05）. No statistical correlation was found between Q-values and r0 in this study （nasal distribution r=-0.077， P=0.487， temporal distribution r=0.001， P=0.992）. ②The Q values of a one-way ANOVA analysis of emmetropes， myopes and hyperopes showed that the differences between the nasal corneas of myopes and emmetropes and of myopes and hyperopes were statistically significant （P<0.05）. No significant difference was found between the emmetropes and hyperopes （P>0.05）. The differences between the temporal distributions were not statistically significant （P>0.05）. ③The coefficient of determination （R2） of the curve fitting by MATLAB was greater than 0.9.④Fitting the vertical Q-values of the 48 eyes： the mean Q-values of the nasal distribution of the semi-meridian before and after curve fitting were -0.45±0.16 and -0.45±0.16 and the temporal distributions were -0.21±0.08 and -0.20±0.10. There were no significant differences before and after curve fittings （nasal distribution， t=2.009， P>0.05， temporal distribution， t=2.009， P>0.05）. The mean vertical Q-values of the superior and inferior distributions after curve fitting were -0.24±0.10 and -0.17±0.08. Conclusion ①The method of using linear regression to calculate the Q-value of the anterior corneal surface by the tangent radius of curvature proved to be stable and reliable. Corneal asphericity was represented by a prolate ellipse and a trend toward a more prolate Q-value was found in the nasal and horizontal distributions. The Q-value had a weak correlation to ametropia. ?②The distribution of 360 semi-meridians of the Q-value calculated from the curve fits were in the form of a double hump and the two peaks were above and below the vertical semi-meridinans. ③After curve fitting calculations， the horizontal semi-meridians had more asphericity than the vertical meridians， which were more round.④The method using the Curve Fitting Toolbox of the MATLAB System to fit the Q-values proved to be stable and reliable. It solves the problem of calculating Q-values， and enables the creation of a digital model of the corneal anterior surface to become a reality

Key words： Myopia Hyperopia Emmetropia Orbscan Ⅱ Topography Tangential radius of curvature Q-value Curve fitting calculation

Received: 05 June 2012

Corresponding Authors: SHI Ming-guang

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LIN Cheng-min,WANG Bo,SHI Ming-guang. An analysis of corneal asphericity and modeling of the anterior corneal surface in children with different refractive states[J]. Chinese Journal of Optometry Ophthalmology and Visual Science, 2013, 15(3): 131-136.

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https://www.cjoovs.com/EN/10.3760/cma.j.issn.1674-845X.2013.07.002 OR https://www.cjoovs.com/EN/Y2013/V15/I3/131

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