  Light propagation is investigated in the context of local anisotropic
nonlinear dielectric media at rest with the dielectric coefficients
$\epsilon^\mu{}_\nu = \epsilon^\mu{}_\nu (\vec{E},\vec{B})$ and constant $\mu$,
in the limit of geometrical optics. Birefringence was examined and the general
conditions for its occurrence were presented. A toy model is exhibited, in
which uniaxial birefringent media with nonlinear dielectric properties could be
driven by external fields in such way that birefringence may be artificially
controlled. The effective geometry interpretation is also addressed.
