A skew ray trace through a toric surface is presented, starting from the data of a ray incident on the optical axis in a plane forming an arbitrary angle with the meridional. With these data and the constructional parameters the refracted ray data are found in a series of equations. This trace can be readily generalized to accommodate the case of a ray incident on any point of the toric surface from any direction.
ALLEN E. MURRAY, "A Toric Skew Ray Trace," J. Opt. Soc. Am. 44, 672-672 (1954)