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 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).

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 microns.