An approximate solution to the problem of a light wave propagating through a lens is obtained by systematically replacing the integrals required to solve the problem by their stationary-phase approximation. This approach is shown to yield (1) geometrical optics in its eikonal form, and (2) a diffraction theory of image formation applicable to lenses with large apertures and fields.
A. WALTHER, "Lenses, Wave Optics, and Eikonal Functions," J. Opt. Soc. Am. 59, 1325-1331 (1969)