How to treat a decentering post LASIK?
A shift is defined as a shift towards the Visual axis which is sufficient to cause Visual symptoms (double vision, halos, permanent gene with the impression that the view is never clear, especially when the ambient brightness is reduced)- see the page Aberrometry and shift post LASIK. The management of a shift is based on the respect of the following points:
(1) one must always exclude the possibility of a post ectasia LASIKwhich can give the same table clinical and topographic, especially before a greater shift. For this, the inspection of the preoperative maps looking for one aspect of Keratoconus frustrated unnoticed is desirable, as well as the repetition of a differential topography with map. A shift appears immediately after LASIK or PKR, and never topographically, progresses to the opposite of an ectasia.
(2) aberrometrique examination is necessary to confirm the presence of optical aberrations induced by the shift. An image of topographical shift is not enough. When the angle kappa is pronounced, the pupil is located frankly nasal, and case of constitutive horizontal asymmetry of the cornea in preoperative, an aspect of horizontal shift can be observed on the topography, but instead translate a proper focus on the Visual axis. Simply, the intersection of the Visual axis with the cornea is relatively remote from its geometric center or the vertex. The symptoms of the shift are often pupil-dependent: they increase when the pupil expands, what is happening in low light conditions so-called "mesopiques conditions".
(3) when considering a trade-in, please make sure that the residual cornea thickness is sufficient. This can achieve an optical product and an OCT to measure the respective flap of LASIK and the posterior residual wall thicknesses.
(4) the prognosis of a reprocessing is best when the shift is accompanied by a myopic correction. Indeed, the complementary photoablation induces a 'hypermetropique shift' (consumes the correction laser of the shift of the corneal tissue in the center of the optical box, which "removes" the myopia).
(5) in LASIK, please make sure that the component is centered and of sufficient size. A significant proportion of the tilt is related to a mismanaged decentering of the stromal component (this can be seen especially with mechanical microkeratomes for femtosecond lasers allow to check and adjust the centering before cutting). It is best not to proceed to the excimer ablation photo if the flap is biased. If the surgeon makes a photoablatif treatment under a biased viewpoint, this causes a shift of the photoablation. If there is a shift but that the flap is bad, it is unfortunately not possible to perform a reprocessing in good conditions.
The treatment can be medical, surgical or contactologique
-medical treatment: decentering moderate case, responsible of tolerable discomfort for the patient except for certain activities such as night driving, prescription eyedrops like Alphagan® may be indicated. This eye drops which the first indication is the hyper ocular pressure (it is prescribed in some forms of glaucoma) induced a reduction in the expansion of the pupil. This effect tends to diminish over time. We can also propose to the patient to drive with a light ceiling light lit, to induce a slight pupillary constriction, which reduces the gene, halos, etc.
-contactologique treatment: it is stated in case of important shift for which it is not possible to achieve a reprocessing (too thin cornea, flap biased, etc.). To use a large diameter lens, which will "absorb" the asymmetry of the corneal surface and restore a good optical regularity
-recovery and photoablation excimer treatment: this is an elective indication to custom laser treatment. Rather than empirical and ineffective methods (reprocess de-centralized in the opposite direction, etc.), it is possible to use topographic data or aberrometriques, if you benefit from a laser platform allowing the coupling between topographer, aberrometer and excimer laser (and to control the realization of these treatments 'tailor-made'). In the case of aberrometriques data usage, please check that they are of good quality. The use of topographic data is done on a diameter of broader analysis, and their accuracy is often better in this context.
Commented images of management of a post LASIK shift example: