Cubic zirconia, an elastically anisotropic material, has been irradiated with 300 keV Cs + ions and the irradiation-induced elastic strain has been measured using X-ray diffraction (XRD). In order to highlight the influence of the elastic properties on the strain level, two different cases have been investigated: (i) {100} vs. {111}-oriented zirconia single crystals and (ii) {100} zirconia vs. {100} strontium titanate. In the former case, raw experimental results show that {100} planes deform less than {111} planes. However, with a modelling that takes into account the effect of the elastic properties, it is demonstrated that the strain due to irradiation defects only is the same for both orientations (with a maximum value of ~0.8%). Combined use of this modelling and of a dedicated computer program for fitting XRD data allowed determining both defect concentration (~1%) and relaxation volume (~0.5 atomic volume). In the latter case, it is shown that elastic properties affect the measured strain in irradiated zirconia and strontium titanate. However, a difference between the two materials remains even taking into account this effect, confirming that different compounds of a same class of materials (namely ceramic oxides) can exhibit a different response to ion irradiation.