In 1604 Kepler published Astronomiae Pars Optica, the work that transformed optics from the science of vision into the geometry of light. Kepler analyzed how the eye forms an image on the retina, explained image inversion, and established the principle of point-to-point ray tracing from object to image. The work served as a bridge between Alhazen's Kitāb al-Manāẓir — which described vision correctly but without the mathematics of image formation — and Newton's experimental optics. Kepler also explained why magnifying instruments work, giving theoretical grounding to telescopes and microscopes before a theory of light existed.