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Factors affecting the forward shift of posterior corneal surface after laser in situ keratomileusis
Purpose:
To evaluate the anteroposterior movement of the corneal back surface after laser in situ keratomileusis (LASIK).
Design:
Retrospective noncomparative case series.
Participants:
One hundred ninety-six eyes of 120 subjects with myopic refractive errors of -2.0 to -12.5 diopters.
Intervention:
LASIK was performed. Corneal topography of the posterior corneal surface was obtained with the scanning slit topography system before and 1 month after surgery.
Main Outcome Measures:
The amount of forward shift of the posterior corneal surface was determined. Multiple regression analysis was used to assess the factors that affect the forward shift of the posterior corneal surface.
Results:
After surgery, the posterior corneal surface displayed mean forward shift of 40.9 +/- 24.8 micrometer. Explanatory variables relevant to the forward shift of corneal posterior surface were, in the order of magnitude of influence, the amount of laser ablation (partial regression coefficient B = 0.561, P < 0.0001), preoperative corneal thickness (B = -0.176, P = 0.00096), and preoperative intraocular pressure (B = 1.676, P = 0.0053). Preoperative refraction and achieved myopic correction showed collinearity with the amount of laser ablation.
Conclusions:
LASIK induces a forward shift of the cornea. Eyes with thinner corneas, higher intraocular pressure, and higher myopia requiring greater laser ablation are more predisposed to the anterior shift of the cornea.