Prevention of corneal ectasia in laser in situ keratomileusis

PURPOSE: Ectasia after laser in situ keratomileusis (LASIK) is a rare but serious complication. Prevention includes proper patient selection with detection of those at particular risk. Causes of ectasia include predisposition, excessive ablation with less than 250 μm of residual stromal bed, thicker than normal flap, irregular corneal thickness, and different ablation rates. METHODS: We evaluated corneal curvature patterns and their relationship to corneal topography and pachymetry maps. RESULTS: Corneal topography (axial, tangential, and altimetric) and pachymetry map characteristics of normally astigmatic corneas, keratoconus, false-positive and false-negative cases, as well as contact lens-induced warpage are discussed. CONCLUSIONS: Preoperative pachymetry maps for LASIK surgery allow accurate case selection through detection of borderline cases, and provide important documentation of preoperative status, as well as useful information for improving surgical strategy. Another important parameter is the asphericity index.