Free-form lenses Part 2 (C8065)

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The best form for an ophthalmic lens to be made in a higher refractive index material is, generally, more steeply curved than the form required for a normal index material. Normal index materials are defined as those whose refractive index is less than 1.54. When stock single vision lenses are supplied in higher refractive index materials one can assume that the manufacturer has employed best form curves for that refractive index. However, when higher refractive index lenses are made by completing the concave side of a semi-finished blank, there is no certainty that the new lens will duplicate the off-axis effects of the previous normal index design. An important advantage of free-form processing is the ability to produce lenses in higher refractive index materials, whose off-axis performance matches that of a form previously worn by the subject in a normal index material. Additionally, the former problem of the laboratory perhaps not having the correct smoothing and polishing tools for the chosen high-index material disappears with a cut-to-polish system, where the lens passes directly from the generator to the free-form polisher. The need for the traditional smoothing and polishing tools is eliminated.