作者：杨广宇，管怀进
作者单位：214002中国江苏省无锡市第二人民医院眼科；226000中国江苏省南通市南通医学院附属医院眼科
【摘要】目的：探索人正常晶状体前表面的地形特征。
方法：使用三坐标测量仪扫描8只人离体眼球晶状体前表面，通过图形软件surfacer v10.0将扫描获得的数据重建晶状体前表面，计算获取晶状体前表面地形图。测量出晶状体前表面各处的曲率半径，并作两因素方差分析。计算离晶状体前表面中心点不同距离处的平均曲率半径，并和离中心点的距离作曲线回归。计算晶状体表面非对称性指数（Lens Surface Asymmetric Index, LSAI）。转换坐标系后，将晶状体前表面水平经线和垂直经线各点作圆、椭圆、抛物线、双曲线等的曲线拟合。
结果：人晶状体前表面地形图显示中央区较陡峭（中心曲率半径9.09±0.80mm），往周边区逐渐平坦（周边曲率半径17.05±2.20mm）。每个晶状体前表面各处的曲率半径作两因素方差分析均有统计学差异（P＜0.05）。离晶状体前表面中心点不同距离处的平均曲率半径和距离作曲线回归显示两者间为三次幂函数关系。LSAI从晶状体前表面中央(0.013± 0.005)至周边(0.184±0.065)逐渐增大。晶状体前表面水平经线和垂直经线作曲线拟合的决定系数为双曲线最大(0.99890.9999)。
结论：人晶状体前表面地形图近似为圆形,但并非完美的旋转对称，晶状体前表面越靠近中心对称性越好。晶状体前表面由中央区至周边区逐渐变平坦，而且曲率半径呈现加速变大趋势。人晶状体前表面曲线最接近于双曲线。
【关键词】 晶状体 表面地形 三坐标测量仪
INTRODUCTION
The human crystalline lens surface was universally regarded as a sphere in the research of the eye optical system to simplify the calculation.However the lens was a complex optical element of human eye.Some researchers took photographs of the lens slit image in vivo or removed the lens and took photograph of the lens section after cryofixation.Those photographs were analysed and lens surface was found to be aspherical [13]. But those measurements had the defect that only one meridian of the lens surface was measured,data of meridians in other directions couldnt been obtained.So whether the lens surface was rotational symmetric couldnt be confirmed and the topography of the lens surface couldnt be established .The purpose of our study was to use a new method to measure the radii of curvature over the lens surface to establish the topography and determine whether the lens surface was rotational symmetric and the best curve fit of the lens surface.
MATERIALS AND METHODS
Subjects Eight fresh human cadaver eyeballs were collected from eight subjects between 28 and 36 years of age (mean,32 years).The crystalline lens were all normal and eye axial lengths were between 22 and 25mm.All subjects hadnt had the histories of intraocular surgeries.All eyeballs were kept in balanced salt solution under 4℃ and measured within 24 hours after enucleation. Before measurement, the cornea and iris were removed and the crystalline lens,zonules,vitreous were kept intact.The entire anterior surfaces of crystalline lens were exposed.
Methods Threecoordinate measuring system (PFX MicroXcel,Brown & Sharpe company,UK) was used to scan the anterior surface of crystalline lens. The preset points interval was 0.2mm.The three dimensional coordinates of the points on the lens anterior surface were obtained and the computer models of the lens anterior surfaces were made using the program of Surfacer V10.0.Nine concentric circles were constructed on the lens surface with the center of anterior lens surface as the circle center.The radii of the circles were 0.5, 1.0, 1.5, 2.0, 2.5, 3.0, 3.5,4.0 and 4.5mm respectively.And eight meridians seperated by 45 degrees were made (Figure 1) .The radius of curvature topographies of lens anterior surfaces were established using Surfacer V10.0. The radii of curvature of lens anterior surface at the crossing points of every meridian and concentric circle were measured and analysed by two way analysis of variance. The data were analysed to determine whether the radius of curvature varied systematically with the position on the lens surface from which the calculation was made. LSAI was defined as the coefficient of variation of the radius of curvature in eight directions of a certain concentric circle on lens surface and calculated to show the rotational symmtricity of the lens surface.The bigger the value of LSAI was,the more asymmetric the surface was.The coordinate system was reconstructed with the center of lens anterior surface as the origin.The axis X.Y were tangent to the lens anterior surface.The new coordinate of the crossing points of the horizontal and vertical meridians with the circles were obtained.And horizontal and vertical meridians were fit to circle,ellipse and parabola.The point (0,0,1) was taken as a new origin with the direction of axis X.Y unchanged.The coordinate system was reconstructed and horizontal and vertical meridians were fit to hyperbola.
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