A treatment apparatus comprising at least one ophthalmologic laser for the laser-induced refractive index change of a cornea of a human or animal eye, wherein the treatment apparatus further comprises a control device and a polarization device, wherein the polarization device is configured to adjust a polarization property of a laser beam of the ophthalmologic laser, wherein the control device is configured to determine an expected orientation of collagen fibers in the cornea at predetermined treatment positions in the cornea of the eye that are intended to be changed by the laser-induced refractive index change on the basis of predetermined collagen fiber data of the cornea, and the polarization device is configured to adjust the polarization property depending on the expected orientation of the collagen fibers at the respective treatment position during irradiation with the ophthalmologic laser.