The work presents a study about dielectric lenses designed to correct the aperture phase and amplitude of horn antennas. Based on Geometrical Optics (GO) principles, it has been developed a computational tool that synthesizes a dielectric lens that transforms the aperture fields of horn into a specified aperture distribution. Besides the synthesis, the tool also presents a GO approximated analysis of the horn antenna radiation pattern, by considering the losses due to the reflection not accounted in the synthesis. It is performed by applying the ray tracing from the feed to a virtual aperture in front the lens, and by applying the Aperture Method to calculate the radiation pattern. The design performances are compared with studies found in the technical literature and with a rigorous analysis performed in Microwave Studio CST. The first part of the study, presents design examples to correct the aperture fields of corrugated horns that radiates approximated circular radiation pattern, leading to circular symmetric lenses. Finally, in the second part, it has been considered the case where the feed is a conic horn, which requires asymmetric lenses.