Progressive lens design by discrete shape modelling techniques

The free-form technologies, recently introduced in the manufacturing process of ophthalmic lenses, allow the production of high performance and custom progressive addition lenses (PALs). In this work a method for the parametric design and analysis of PAL, based on discrete shape modelling, is proposed. Both the optical (e.g. power and addition) and the geometrical (e.g. inset, corridor length, amplitude of the distance and near vision area) parameters have been taken into account. In addition the method developed for the analysis of surface optical properties, especially with regard to the astigmatic surface power, has proved an essential tool for the analysis of results. Moreover the exchange data formats for the CNC manufacturing process were described. The influence of different parameters on the optical properties are analyzed and discussed. In this context a key role on the resultant optical properties of the designed PAL is covered by the distribution of the curves in the intermediate area and by the curvature equation along the corridor. Surface power and astigmatic surface power show similar behaviour to other commercial progressive additional lens but, moreover, the designer can specify the distribution of astigmatism in the intermediate region. Compared to the methods proposed in literature, this one shows more opportunities in the design parameters definition and allows highly customized lens, designed on the main habits of the wearer. Finally the method was applied to the manufacturing process of glass mould for PAL and the results of optical parameters measurements are proposed.