In part three of this six-part series, Professor Mo Jalie continues his discussion of the development of progressive lenses from the second to the fourth generation designs
In 1972, Essilor introduced its second generation progressive design, the Varilux 2 lens.1 Like the original Varilux design, the principle of the progressive surface can be understood by comparing it with the surface of an elephant’s trunk, but in this case, one whose sagittal sections are no longer circular. Imagine that near the top of the trunk the horizontal sections are shaped like ellipses with one end of the minor axis lying along the meridian line, DN, as shown in figure 1.
Figure 1: Evolving conic sections of the progressive surface of the Varilux 2 design
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