Study On Simulation Method And Optimization Design Of Ophthalmic Freeform Lenses

With the demands of lightweight, functionality, comfortability and novelty of theophthalmic lenses, traditional ophthalmic lenses cannot meet the needs any more. Thefreeform technology based on digital surface treatment is overturning traditionalmanufacturing industry of the ophthalmic lenses. For larger degrees of freedom, freeformsurface could control the power and astigmatism distribution as needed. The application offreeform surface in ophthalmic design is a hot topic in the recent years.Aspheric astigmatism lenses and progressive addition lenses (PALs) are the mainrepresentatives of ophthalmic freeform lenses (OFLs). In this paper, we start from thenovelty and market demand of PALs. By analyzing the existing problems ofmeasurement/evaluating methods and design methods, we propose a comprehensivesimulation method which could give out the astigmatic axis of OFLs. A global optimizationdesign method by pointwise directional curvature compensation is proposed to reduce theundesirable astigmatism. Moreover, a simulation method upon the eye-plus-lens model isalso put forward to evaluate double OFLs.First of all, this paper overviews in detail the state of art of research about OFLs homeand abroad. It is point out that vigorous development of personalized design is urgent inour large populous country. Through analysis of the surface characteristics includingprincipal curvature, principal direction and mean curvature, a theoretical foundation is laidfor the study on simulation method and optimization design method of OFLs.Then, a comprehensive simulation method which could give out the astigmatic axis ofOFLs is proposed. The evaluation principles and steps are clearly introduced and theevaluation results are explicitly displayed. Our investigations show that the evaluatingaccuracy of the comprehensive simulation method completely depends on the samplinginterval which is related to the computing time. The smaller sampling interval wouldcontribute more accurate results, but would take more computing time. The proposed comprehensive simulation method and the conventional simulation method are compared.We also present a simplified simulation method used for evaluating a certain range ofOFLs with comparatively less computing time.Based on the derived equation of computing the normal curvatures of the freeformsurface at arbitrary direction, a global optimization design by pointwise directionalcurvature compensation is put forward to reduce the undesirable astigmatism. The detailedsteps and the example are clearly introduced. It is shown that the optimization designmethod, which isn’t related with the initial design process and design method, applies tooptimize different designs of PALs.At last, in order to consider the wearer performance of OFLs, the idea of evaluatingdouble OFLs upon the eye-plus-lens model is first proposed. The positions of each ray onthe front and rear surfaces are computed by performing the ray tracing. It is more accurateand sound to characterize the double OFLs with the contour plots of wearer power andastigmatism with astigmatic axis, which can be obtained by computing each combinednormal curvatures at arbitrary direction on the respective positions of the front and rearsurfaces. The factors affecting the evaluating results are discussed.