Calculating through-focus characteristics of the human eye from a single objective measurement of wavefront aberration can be accomplished through a range of methods that are inherently computationally cumbersome. A simple yet accurate and computationally efficient method is developed, which combines the philosophy of the extended Nijboer–Zernike approach with the radial-basis-function-based approximation of the complex pupil function. The main advantage of the proposed technique is that the increase of the computational cost for a vector-valued defocus parameter is practically negligible in comparison to the corresponding scalar-valued defocus parameter.