"Wavefront correction" has become an often used concept in refractive surgery, even though it is not always uniquely defined. Clinical results, however, are lagging behind the original expectations.The physical items wavefront error, light ray, ray tracing and refraction error first have to be well defined, including demonstration of the applicability of the underlying model assumptions. In our simulations optical errors of the eye are expressed in three different ways: two-dimensional refraction error maps, error maps of optical path lengths, and blurred images on the retina.Optical errors are completely correctable only at the locations where they originally occur, i. e., corneal errors at the cornea, lens errors in the lens. Correction at another localization always introduces new errors. Other than in astronomical telescopes, the correction of optical path length errors in the human eye is already limited by short time-scale fluctuations of the relevant parameters which are two orders of magnitude beyond the tolerable error limits. Approximation of the optical path length error by a series expansion (e. g., Zernike polynomials) can induce additional errors.The worse the optical properties of an eye are, the less is the wavefront approach applicable for correction.