Progress in the spectacle correction of presbyopia. Part 2: Modern progressive lens technologies.

The first installment of this two-part series reviewed the fundamental optical principles and early development work associated with progressive lenses. Recent progress made in advancing the state of the art in progressive lenses will now be presented, with particular emphasis on 'free-form' progressive lenses and the application of 'wavefront' technology in progressive lens design. Because several fundamental concepts were developed in the first paper that will serve as the basis for discussions presented in this paper, including the basic optics and mathematics of progressive lens surfaces, the reader is strongly encouraged to review the companion paper.