An optical element such as a reflector defining a differentiable fiducial surface having a first portion, with a flat region, that seamlessly adjoins, along a curved line, a second portion having a two-dimensionally curved region. The quality of optical imaging in the reflector is drastically improved by reducing the ratio of optical powers measured in two perpendicular directions along the two-dimensionally curved portion of the surface. The vehicular rearview assembly including such a reflector possesses a field-of-view (FOV) that is significantly higher than the FOV of a conventional flat mirror and facilitates visual access to a “blind spot” behind the vehicle.