In the last few years, interest in research and development into new ways of creating gradient index optics has increased dramatically. One approach revisited was to employ diffusion, governed by Fick’s law, to generate both axial and radial index gradients. However, Fick’s law of diffusion tends to yield index gradients that are mathematically uncommon in optical engineering and lens design. The impact of these new gradients on lens aberrations and image quality are not well understood. We will examine index gradients that can be described by (makeable by) solving Fick’s diffusion laws but limited by the assumptions made to simplify the mathematics, the most significant of these being a diffusion coefficient of 1 on both sides of the boundary (implying a concentration change only) and that the change in concentration yields a one-to-one change in refractive index.