Abstract Defect diffusion under irradiation is inherently anisotropic due to the non-cubic symmetry of the saddle point configurations. A technique is developed to compute the capture efficiency of a sink in an anisotropic diffusion field of point defects, drawing an analogy between the diffusion problem and the anisotropic dielectricity problem. Analytic expressions in terms of the sink capture efficiency and, alternatively, the effective capture radii are obtained for an edge dislocation. It is found that the effect of the point defect/dislocation interactions can be attributed to the shear polarizability and an effective relaxation volume of the defect. The latter includes both the size effect and the shape effect and is in most cases considerably larger than the isotropic relaxation volume. Values of the effective relaxation volume and the effective capture radii as well as the net bias between vacancies and interstitials are given for Al, Cu, Ni, Fe, and Mo. For self interstitials, the effective relaxation volume is estimated to be 2Ω in all cases. Anisotropic growth due to mechanisms of several similar origins is also predicted.