This paper presents an effective approach to alleviate the cat-eye effect by inserting a freeform single lens into the original optical system. By shifting the image of the given optical system transversely on the original image plane, the reflected beams originating from the sensor are subsequently blocked by the optical aperture, substantially eliminating retroreflections from the system. The influence of incident angle on retroreflected beams is analyzed in detail, and the optimal image translation distance for completely eliminating the cat-eye effect is also proposed via numerical simulations. According to the translation requirement, a freeform single lens comprised of two different freeform surfaces is designed for the given system as the only translation element. The design recipe is elaborated on the basis of phase pupil function. Furthermore, a design example is demonstrated to verify the feasibility of our proposal. After optimization with optical design software, the modulation transfer function (MTF) of the modified system after translation is close to the diffraction limit, and the cat-eye reflected beam could be eliminated thoroughly.