高负值度数镜片设计

作者：GREGORY L. STEPHENS and JOHN K. DAVIS      

译者： Lisa Huang                                                            

原文出处：http://www.eyecalcs.com/DWAN/pages/v1/v1c051b.html#ato

负值度数特别高的处方（大于约10.00D）镜片边缘很厚，影响美观，且在某些镜架上很难安装。这个问题可以通过尽可能为患者提供可行的小镜架来缓解，同时，高指数塑料也可以帮上忙。虽然会有离轴横向色差，大部分患者还是可以忍受这种色差的，因为镜片更厚更轻了。高负值度数镜片一般两面都是凹的，因为光学实验室很难把度数全部铣磨在镜片的一个面上。轻薄的上色和防反射镀膜可以减弱镜片边缘附近的多环反射（近视环）。

高负值度数镜片偶尔会用凸镜的形式制作（图17）。从本质上来说，它是在镜片后表面切割掉较厚的边缘，使外缘载体不再有光学作用，同时直径40mm的中心碗状部分可以做到折射矫正。当镜片的前表面较平时，载体的后表面也会平，这样的镜片被称为myodisk。载体的连接处和负值凸透镜镜片的碗状部分可以混合在一起，从而使它不那么明显，也没有了锋利的边缘。这个过程通常被称为myothinning（见图17）。由于它们脆弱的外形，所有高负值度数镜片必须小心使用。

图17为负值凸透镜和通过myothinning的负值凸透镜的正视图和横截面图。

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