Method for determining a radial refractive-index profile of a cylindrical optical object which has a cylinder longitudinal axis around which at least one layer k with a layer radius r k and with a layer refractive index n k extends radially symmetrically, wherein a deflection angle distribution Ψ(y) is measured and the refractive index profile is reconstructed therefrom on the basis of a model, wherein the deflection angle Ψ is defined as the angle between an exit beam from the optical object and an entry beam into the optical object in a plane perpendicular to the longitudinal axis comprising the exit beam and the entry beam, and wherein "y" in the plane comprising the exit beam and the entry beam is defined as the distance between the entry point of the entry beam into the optical object and a line parallel to the entry beam passing through the longitudinal axis, said model comprising the following measures: (a) preparing the measured deflection angle distribution Ψ(y), including an extreme value determination of the deflection angle distribution, wherein a prepared deflection angle distribution Ψ'(y) is obtained, (b) transforming the prepared deflection angle distribution Ψ'(y) into a prepared refractive-index profile n'(r), (c) evaluating the prepared refractive-index profile n'(r) for the fixation of orientation values, comprising an orientation value r* k for the layer radius and an orientation value n* k for the layer refractive index of a hypothetical refractive-index profile n*(r), (d) generating a simulated deflection angle distribution Ψ"(y) on the basis of the hypothetical refractive-index profile n*(r) with the orientation values r* k and n* k , and transforming said deflection angle distribution into a simulated refractive-index profile n"(r), and (e) fitting the simulated refractive index profile n"(r) to the prepared refractive-index profile n'(r) by iterative adaptation of the parameters r* k and n* k , wherein a fitted, simulated refractive-index profile n*(r) fit is obtained, which is defined by adapted parameters r* k,fit and n* k.fit , and (f) obtaining the refractive index profile as the hypothetical refractive-index profile with the adapted parameters r* k,fit and n* k,fit . (a) preparing the measured deflection angle distribution Ψ(y), including an extreme value determination of the deflection angle distribution, wherein a prepared deflection angle distribution Ψ'(y) is obtained, (b) transforming the prepared deflection angle distribution Ψ'(y) into a prepared refractive-index profile n'(r), (c) evaluating the prepared refractive-index profile n'(r) for the fixation of orientation values, comprising an orientation value r* k for the layer radius and an orientation value n* k for the layer refractive index of a hypothetical refractive-index profile n*(r), (d) generating a simulated deflection angle distribution Ψ"(y) on the basis of the hypothetical refractive-index profile n*(r) with the orientation values r* k and n* k , and transforming said deflection angle distribution into a simulated refractive-index profile n"(r), and (e) fitting the simulated refractive index profile n"(r) to the prepared refractive-index profile n'(r) by iterative adaptation of the parameters r* k and n* k , wherein a fitted, simulated refractive-index profile n*(r) fit is obtained, which is defined by adapted parameters r* k,fit and n* k.fit , and (f) obtaining the refractive index profile as the hypothetical refractive-index profile with the adapted parameters r* k,fit and n* k,fit . <EOS>