Wound healing response
There are complex interactions between the corneal epithelium and the stroma that occur as part of the wound healing response after refractive surgery. Both the corneal epithelial thickness and the corneal response to injury can greatly influence the post-operative course.
Møller-Pedersen et al demonstrated that activated keratocyte-mediated rethickening of the photoablated stroma was a key biological factor responsible for post-PRK regression of myopia. They demonstrated that the corneal rethickening causes myopic regression mediated almost solely by stromal rethickening.
Only a minor contribution appeared to originate from restoration of the postoperative epithelial thickness.9 In their study, they found a significant thickening in the posterior stroma between 1 week and 1 month after surgery. Meanwhile, the spheroequivalent refraction changed considerably to the myopic side between these time points (−0.34 versus −0.57), but the difference was not statistically significant.
It is possible that the posterior stromal rethickening seen 1 month after LASIK may be related to the activated keratocytes, since the highest value for the thickness of the activated keratocyte zone was found at the 1-week postoperative examination point, and it is well known that activated keratocytes are associated with the healing process after excimer laser treatment.
Normally, it would be expected that a 10- to 15-μm rethickening of the posterior stroma produced a 1-D myopic shift, but the much greater rethickening observed in their study created only a small amount of refractive change.
This finding may suggest that the cornea simply swells after LASIK treatment and anterior curvature does not change despite a high degree of thickening. However, pachymetry data or corneal curvature measurement is required to support this hypothesis.