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Typically, a progressive surface is a free-form surface. Thus one could describe any progressive lens as a free-form lens. However, a laboratory which finishes a convex side semi-finished progressive blank with traditional surfacing equipment (toric or spherical generator, followed by traditional smoothing and polishing) would be foolish to claim that they are manufacturing a free-form lens.
The real advantage of free-form technology is that it allows the designer to better compensate for the aberrations of the lens when working the concave side of the semi-finished blank. This, of course, demands software which can calculate the optimum form of the surface upon receipt of individual prescriptions from the eye care practitioner. Only the major manufacturers, with their in-house design teams, really have the ability to produce these ‘double free-form surface’ lenses.
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