Whole-surface characterization of progressive addition lenses.

PURPOSE: To characterize and compare progressive addition lens (PAL) surfaces in terms of the Zernike polynomials.

METHODS

We examine the spherocylindrical characteristics of PALs by performing a physical surface height measurement of three lenses. Surface shape is described as the sum of Zernike polynomials. These data were used to analyze and compare each surface, using the second derivatives of surface height. We compare PALs to each other and to a prototypical progressive surface, i.e., the Alvarez lens surface.

RESULTS

The high order freeform surfaces of PALs produce a gradient of spherical power across the lens aperture and also a profile of astigmatic power with high order aberration. Each lens is similar to the Alvarez surface, but each has characteristics that differentiate it from the others. Each high order Zernike term contributes sphere and/or astigmatism, and aberration, to the surface.

CONCLUSIONS

This approach to PAL analysis, in which the entire lens surface is defined and expressed as the sum of Zernike polynomial terms, is different from most previous approaches in which a lens is described as an array of subapertures. It is potentially an efficient and useful method for defining and designing PAL surfaces.