In an attempt to bridge the gap between theory and applications, this paper brings together a few diverse subjects, and presents them as much as possible in self-contained form. A general perturbation method is developed for calculating the first order effects in quite general bi-anisotropic materials. The advantage of this approach is the feasibility of generating solutions of the Maxwell equations for the complicated media, in terms of well-known solutions for simple media. Specifically, the present study was motivated by a need to provide a theoretical framework for polarimetric glucometry methods, presently under investigation, in the hope of gaining better understanding of the systems and their limitations, as well as suggesting new configurations for acquiring better data. To that end, we chose to analyze gyromagnetic effects in lossless magneto-optical systems. Some representative examples have been chosen, and the obtained results, for various situations involving plane and spherical waves, are discussed. It is shown that the specific configuration of the magnetic fields affect the solutions. Generally speaking, the magnetic fields create new multipoles in the resultant wave fields. Another interesting feature of the present approach is the fact that we get the elementary Faraday rotation effect without resorting to a pair of two oppositely oriented circularly polarized waves, as usually done. Consequently we are able to discuss explicitly complicated situations involving non-planar waves and various external magnetic fields. The penalty is of course the restricted validity of the model to small non-isotropic effects.