We consider using toroidal curved detectors to improve the performance of imaging optical systems. We demonstrate that some optical systems have an anamorphic field curvature. We consider an unobscured reimaging three-mirror anastigmat as an example (f'=960 mm, F/5.3, ωx×ωy=4°×4°). By assuming that the image is focused on a toroidal detector surface and performing reoptimization, it becomes possible to obtain a notable gain in the image quality-up to 40% in terms of the spot root mean square radius. Through analytic computations and finite-element analysis, we demonstrate that this toroidal shape can be obtained by bending of a thinned detector in a relatively simple setup.