Systems, methods, and devices for determining an aberration in an optical tissue system of an eye are provided. Techniques include inputting optical data from the optical tissue system of the eye, where the optical data includes set of local gradients corresponding to a non-circular shaped aperture, processing the optical data with an iterative Fourier transform to obtain a set of Fourier coefficients, converting the set of Fourier coefficients to a set of modified Zernike coefficients that are orthogonal over the non-circular shaped aperture, and determining the aberration in the optical tissue system of the eye based on the set of modified Zernike coefficients.