Dislocations are known for their peculiar effects on the diffraction profiles. Each given dislocation type, produces specific anisotropic line broadening basically determined by the so-called contrast factor (CF). Owing to the lack of a suitable mathematical frame to deal with dislocations in crystal of any symmetry, CFs have been so far determined for high symmetry materials. In this work we present the main points of a general approach for determining CF, as well as a specific application to scheelite CaWO4.