Direct (GL)and reverse (GLR)indices of linear polarization for an optical system are presented. These parameters have been calculated using the
concept of the degree of linear polarization for the light beam emerging from the system and they are expressed as a function of the elements of the corresponding Mueller matrix. Values of GL and GLR for pure and combinations of polarization elements have been calculated. Real examples
such as the human eye and an in vitro cornea are also shown.