Keratectasia after laser in situ keratomileusis (LASIK): evaluation of the calculated residual stromal bed thickness.

PURPOSE To report corneal histopathology associated with keratectasia after laser in situ keratomileusis (LASIK) and to evaluate the thickness of the calculated residual stromal bed in two cases and those in the literature. DESIGN Interventional case reports. METHODS Three eyes of two patients developed keratectasia after LASIK. Corneal specimens after penetrating keratoplasty in one eye of each patient were studied histopathologically, and the residual stromal bed was directly measured. For comparison, residual stromal bed thicknesses were calculated from published cases of keratectasia. RESULTS Two eyes of a 26-year-old woman and one eye of a 22-year-old woman developed keratectasia after LASIK. Calculated residual stromal bed thicknesses were 210, 213, and 261 microm. Histologic sections revealed focal scarring in the flap plane. The cornea specimens measured 75 and 118 microm thinner than calculated values immediately after LASIK. Transmission electron microscopy of one case revealed an average lamellar thickness of 0.94 microm. In 28 (49%) of 57 previous cases of keratectasia, the calculated residual stromal bed thicknesses were greater than 250 microm. CONCLUSIONS Both the flap and the stromal bed of the cornea may thin after LASIK. A residual stromal bed thickness of 250 microm does not preclude the development of keratectasia after LASIK.