The present paper reanalyzes the problem of the refractive properties of the physical vacuum and their modification under the action of the gravitational field and the electromagnetic field. This problem was studied in our previous works and in the subsequent works of the researchers: Leuchs, Urban, Mainland and their collaborators. By modeling the physical vacuum as a particle-antiparticle system, we can deduce with a certain approximation, in a semiclassical theory, the properties of the free vacuum and the vacuum modified by the interaction with a gravitational field and an electromagnetic field. More precise calculation of permittivities of free vacuum and near a particle can lead to a non-point model of the particle. This modeling can follow both the quantum and the general relativistic path as well as the phenomenological path, the results complementing each other.