Any gravitating system can, in principle, refocus the light from stars behind them so that you would see a ring surrounding the object if you looked at it, but so far, these Einstein Rings have only been detected by radio astronomers looking at distant quasars and radio galaxies. No one has ever seen such a thing around neutron stars although they are predicted by general relativity to occur there and around black holes. For more on this, have a look at Christopher Miller's black hole website. Also, have a look at R. Nemiroff's Journey to a Neutron Star computer simulation to look at the optical distortions that can occur there.