Posterior corneal surface topographic changes after laser in situ keratomileusis are related to residual corneal bed thickness

Objective: To determine whether ectasia after laser in situ keratomileusis (LASIK) is related to residual corneal bed thickness, Design: Retrospective noncomparative case series Participants: Thirty-two eyes of 16 patients with refractive errors of -4.00 to -18.00 diopters were examined. Intervention: LASIK was performed. The topography of the posterior corneal surface was examined with the Orbscan slit scanning corneal topography/pachymetry system. Main Outcome Measures: The difference in the elevation of posterior corneal surface regarding the best-fit sphere was measured. Results: After surgery, mean bulge of 17.2 +/- 7.2 mu m was found in eyes with residual corneal bed of 250 mu m or greater, whereas 41.0 +/- 22.1 mu m was seen in eyes with bed thickness less than 250 mu m (t = 4.29; P = 0.000), Conclusion: Posterior corneal bulge is correlated with the residual corneal bed thickness. The risk of ectasia may be increased if the residual corneal bed is thinner than 250 mu m.