US Patent 7210779 Double progressive spectacle lens

A double-progressive spectacle lens in which the progressive action is distributed over the front and rear surfaces of the double-progressive spectacle lenses and described by the quotient QQ=Addvfl/AddGesamtwhere Addvfl represents the increase in the surface dioptric power along the principal line on the front surface between the distance area and the near area, and ADDGesamt represents the increase in the total dioptric power along the principal line between the distance area and the near area, and the fraction Q increases with growing distance area effect F: