Method of generating virtual surface data of a progressive addition lens

A system comprising:

• an apparatus for generating virtual surface data of a progressive addition lens for a further operation of surfacing of a lens blank, the operation of surfacing being configured to transform the lens blank into a surfaced lens satisfying a prescription, the apparatus comprising processing circuitry configured to:
• acquire prescription data including at least a sphere value, a cylinder value, and an addition value,
• obtain a virtual base surface in a virtual base surface database storing at least one virtual progressive base surface so that the virtual base surface is obtained without reference to or reliance upon the prescribed addition value,
• process the selected virtual base surface according to the prescribed addition value to obtain a modified virtual base surface providing at least a part of the prescribed addition value,
• select a virtual adjusting surface in a virtual adjusting surface database storing a plurality of virtual adjusting surfaces at least on the basis of a value of a parameter relative to the modified virtual base surface, and
• combine the modified virtual base surface and the selected virtual adjusting surface to form a virtual progressive adjusted surface,
• wherein each virtual progressive base surface stored in the virtual base surface database corresponds to a virtual front progressive surface so that the virtual progressive adjusted surface formed from the combination of the virtual base surface with the virtual adjusting surface is a virtual progressive front surface;
• an apparatus configured to:
• perform a reversing operation to transform the virtual progressive front surface into a virtual reversed progressive adjusted surface;
• generate a virtual sphero-toric surface on the basis of the prescribed sphere value, the prescribed cylinder value and the finished front surface of the selected semi-finished lens;
• and
• combine the virtual reversed progressive adjusted surface with the virtual sphero-toric surface to form a final virtual progressive back surface;
• wherein the processing circuitry is configured to select a semi-finished lens in a semi-finished lens database on the basis of the prescribed sphere value and the prescribed cylinder value, the semi-finished lens having a first surface which is a finished surface and a second surface which is an unfinished surface;
• and
• a device configured to surface the second surface of the semi-finished lens on the basis of the virtual surface data so that the second surface of the semi-finished lens, after being surfaced by the device, corresponds to the virtual progressive adjusted surface.