Computation of unwanted sphere and cylinder in the periphery of a spectacle lens.

The author discusses practical issues relating to optometrists ordering and laboratories supplying ophthalmic lenses that meet the ANSI Z80. 1 Standard (1972) for minimizing unwanted spherical and cylindrical power in the periphery of lenses. He spells out the optical principles and formulas needed to develop a computer program that can be used by optometrists and opticians for designing lenses that meet the Z80. 1 Standard.