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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:

 

Image obtained by convolution of the Point Spread Function (PSF) retinal calculated in a patient complaining of poor visual quality after LASIK, with impression of vertical duplication of bright lights (under titles, etc.). This gene appeared immediately after LASIK.

The rate of optical aberration of high degree is higher than normal: it is of type coma aberration that predominates. The PSF (bottom left), has a "Comet Tail" appearance (where the origin of the term "coma" to describe this aberration).

The topographical map in refractive mode (left) suggests the presence of a lower shift, but it's the aberrometrique (right) map that says there is a refractive power gradient from the top to the bottom of the pupil of about 4 diopters (corroborating the optical origin of the patient's symptoms, and the shift of the optical zone). Stability of the topography in time and the lower the shift direction allow to Exxx_xxx_5197r the presence of photoablative recovery treatment is decided, because the existence of a slight correction and sufficient corneal residual wall thickness allow the realization. With the Nidek platform, it is even possible to select or exclude some high-level aberrations (pyramid of the Zernike polynomials). In the present case, the treatment aims to expand the functional optical area in superior.

Card differential after reprocessing which consisted in the uprising of the former flap and the issuance of a custom photoablation guided by corneal topography: it shows the magnification of the topographic otpique area, and the further flattening of the upper hemicornee.

After the recovery performed by lifting the LASIK flap monocular diplopia disappeared. The map in refractive mode confirms the magnification of the optical zone. map aberrometrique reveals the almost total disappearance of the vertical gradient of power, and the restoration of a refractive profile "location".

6 responses to "how to treat a LASIK post decentrement?"

  1. Bismuth says:

    Hello
    I would like to know the causes of a decentrement and whether he can be warned. What is the probability that this will happen during a surgery by PKR?
    Thanks in advance,

  2. Dr. Damien Gatinel says:

    It is difficult to know the cause of a shift, after LASIK or PKR. With the recent lasers, and in hands tested for refractive surgery, the occurrence of a shift is a unique complication. Poor positioning of the patient's head may sometimes produce a shift.

  3. John says:

    Hello

    I was operated in June 2016 of a refractive surgery for a strong hyperopia-astigmatism.

    This first intervention was not enough.
    She completely suppressed the hyperopia but I remained sufficiently astigmatism to completely blur the view from 1 meter.

    Last month, June 2017, I underwent a laser retouch, which went very well.
    My view was exceptional after the retouching.

    However, a month later, I observed a degradation of vision sharpness, while the day after surgery and for a week it was perfect.

    I have to force my eyes to improve sharpness.
    I also noticed that when I drop my head down, and I raise my eyes, my eyesight becomes perfect again.
    As soon as I straighten my head, the blur comes back.

    I'm afraid it's a decentralized treatment.
    But why gradually while for a week everything was perfect?

    I did all that was asked level post-op eye drops. I didn't miss anything.

    Thank you for your future response

  4. Dr. Damien Gatinel says:

    A decentering causes immediate and permanent visual symptoms. In your case, it is a priori to rule out that a decentering can explain your symptoms. These are more likely phenomena that combine the regression of the effect of surgery (scarring) and/or dryness of the eye.

  5. Amine says:

    Hello doctor,
    I was operated at the PKR of a myiopie OG-5 and OD-4.
    a J + 35 I see (maybe) a monocular diplopia, indeed when I close the left eye (which has a clear vision) I see a split vision on the other eye.
    I also noticed that when I drop my head down, and I raise my eyes, my eyesight becomes perfect again.
    As soon as I straighten my head, the blur comes back
    is this normal after a PKR? could this phenomenon fade over time? or should I plan a retouching?
    Thank you for your answer
    Kind regards

  6. Dr. Damien Gatinel says:

    It all depends on the importance of the phenomenon. Does the diplop concern only the lights on dark background, or any pattern in any bright ambience? Small duplications are often noted on contrasting lights after PKR. PKR patients are often "excluded" from LASIK because their corneas are fine and too irregular. These irregularities can be discovered in the weeks following the PKR. Time (epithelial resurfacing) often makes it possible to improve the quality of vision. Finally, if you rub your eyes (allergy, fatigue, dryness), it is urgent to stop, because this can also cause a slight duplication. If the duplication is strong, it may of course be a decentralization. The pronounced decentrements are quite annoying and responsible for a reduction in visual acuity. It is important to discuss this with your surgeon, and perform a aberrométrique examination (not just a corneal topography) to quantify it all.

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