Progressive power lenses - part 4

Fifth generation progressive designs

In 1995 there was a major breakthrough in progressive lens design. A patent¹ was granted to Carl Zeiss for a new concept in which a progressive lens could be optimised for each individual prescription by combining a concave aspherical or atoroidal surface with a convex progressive surface in order to restore the optical performance to all powers within the range for which the convex surface had been designed. As an example, the prescription, +5.00 add +2.50 D might be made as a progressive lens with a convex progressive surface whose base curve, +8.25 D, has been specifically designed for this power, with the result that a contour plot of the iso-astigmatism lines is as shown in figure 1(a). The iso-astigmatism plot shows that the design has a wide distance area, a central corridor which is free from Minkwitz astigmatism leading to a fairly wide near zone.