In this paper a method has been developed to extend the use of the well-known expression of Clausius-Mosotti for inhomogeneous materials, considering their anisotropy through a series expansion based on the structural factor of nonsphericity. This is related to experimental results available from the ordinary and extraordinary refractive indices of a set of samples of low-density polyethylene films, where such phenomena are observed. Here results are obtained which are valid for the microscopic optical response, as it is shown by the linear fitting of these general expressions, with excellent correlation coefficients. Furthermore, if we apply the Bergman-Milton limits, we can theoretically confirm the existence of two neutral lines experimentally obtained.