cisis

Special case: Keratoconus after LASIK

One complication of LASIK surgeries which are used as a therapy of normal myopia is a keratoconus referred to as post-LASIK keratectasia. During this surgery the cornea is weakened to a high degree, because of the flap which never grows back as well as given the removal of tissue by laser which strongly affects the cornea’s stability and, consequently, damages it. Thus, the cornea starts bulging and thinning exactly the same way which can be observed in normal cases of keratoconus. In this very specific case, CISIS / MyoRing therapy is clearly the first choice of treatment

Why?

Most frequently, given the lack of available alternatives, surgeons tend to recommend Crosslinking. While Crosslinking can stop the progression of a “normal” keratoconus, this does not apply in the same way to post-LASIK keratectasia. This difference in therapy options is caused by the flap which is created during LASIK treatment and which does, biomechanically, not grow back anymore. Thus, the biomechanical and the anatomic corneal thickness do not correspond to one another after a LASIK treatment as the loose flap does not contribute to the corneal biomechanical stability any longer. Merely the remaining fraction of the cornea under the flap (residual stromal bed = anatomic corneal thickness without the thickness of the flap) adds to the cornea’s stability. However, during Crosslinking mainly the anatomic frontal section of the cornea, in the case of post-LASIK keratectasia the biomechanically ineffective flap is hardened. This does not make any sense as the mechanically relevant part of the cornea, this is the residual stromal bed, is, practically, not treated. Thus, CISIS / MyoRing is, in fact, the only available therapy capable of stopping the progression of post-LASIK keratectasia. Moreover, based on their margins, ring segments do have a rather high rate of complications, as in up to 40% of the treated cases extrusions (growing out of the cornea) occur even if “normal” cases of keratoconus are concerned. In contrast, in CISIS/MyoRing the rate of complications is practically inexistent as the pressure forces on the tissue are distributed along the entire ring structure and are not merely concentrated towards its margins. However, it has to be mentioned that given the short distance to the biomechanical surface which applies in post-LASIK keratectasia (boarder area between the flap and the residual stromal bed), extrusions might also occur if a MyoRing is used, especially if thick flaps and a thin residual stromal bed are concerned.

Conclusion: CISIS/MyoRing is the first choice as far as post-LASIK keratectasia is concerned.

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