  We extended a previous study of the Eaton lens at specific refraction angles
to the Eaton lens at any refraction angle. The refractive index of the Eaton
lens is complicated and has not analytical form except at a few specific
angles.
  We derived a more accessible form of the refractive index for any refraction
angle with some accuracy by retroreflector approximation. The finding of this
study will be useful for a rapid estimation of the refractive index, and the
the design of various Eaton lenses.
