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

Abstract

To determine whether ectasia after laser in situ keratomileusis (LASIK) is related to residual corneal bed thickness. Retrospective noncomparative case series. Thirty-two eyes of 16 patients with refractive errors of -4.00 to -18.00 diopters were examined. LASIK was performed. The topography of the posterior corneal surface was examined with the Orbscan slit scanning corneal topography/pachymetry system. The difference in the elevation of posterior corneal surface regarding the best-fit sphere was measured. After surgery, mean bulge of 17.2 +/- 7.2 microns was found in eyes with residual corneal bed of 250 microns or greater, whereas 41.0 +/- 22.1 microns was seen in eyes with bed thickness less than 250 microns (t = 4.29; P = 0.000). 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 microns.