基于Placido盘法的角膜地形图仪成像系统优化设计

Optimization Design of Corneal Topographer Imaging System Based on Placido Disk Method

现有的基于Placido盘的角膜地形图仪成像系统采用对称式消色差结构,其视场角小、角膜覆盖面积小,分辨率和检测精度不高。为实现角膜形貌的高覆盖率采集,根据人眼角膜的特点以及所选用的CCD相机,在传统的成像系统基础上利用ZEMAX软件对其进行优化设计。优化后系统由5片镜片组成,有效焦距为25mm,后工作距离为17mm,相对孔径为1/3,全视场为15°,光学总长为55mm。在镜头分辨率145lp/mm处,所有视场的调制传递函数值均接近0.4,场曲在全视场下小于0.1。优化系统角膜覆盖率大、成像质量更好,对实现高分辨率角膜地形图仪工程化生产具有实际意义。

A symmetric achromatic structure was adopted in the existing Placido disk-based corneal topographer imaging system,which has a small field of view angle,small corneal coverage area,and low resolution and detection accuracy.According to the characteristics of the human cornea and being selected CCD camera,the design based on the traditional imaging system was optimized by using the ZEMAX software in order to achieve high coverage of corneal topography. The optimized system consists of 5 lenses with an effective focal length of 20 mm,a rear working distance of17 mm,a relative aperture of 1/3,a full field of view of 15° and an optical total length of 55 mm. The modulation transfer function values for all fields of view are close to 0.4 at a lens resolution of 145 lp/mm;and the field curvature is less than 0.1 at full field of view. The optimized system has large corneal coverage and better imaging quality,which has practical significance for realizing high-resolution corneal topographer engineering production.