Elements of the dioptric power matrix and the concept of torsional power: a reinterpretation.

The elements of the dioptic power matrix have previously been interpreted in terms of power along particular meridians with the off-diagonal elements interpreted as a new form of dioptric power called torsional power. This paper shows that such new concepts are not necessary. Decomposition of the matrix provides an interpretation in terms that are quite familiar. The elements represent three component powers: the diagonal elements are two cylinders and the off-diagonal elements a crossed-cylinder with axes at 45 degrees and 135 degrees. The component crossed-cylinder obviates the need for the concept of torsional power. The concept of meridional power is avoided.