Preoperative Topographic Characteristics of Eyes That Developed Postoperative LASIK Keratectasia

PURPOSE: To assess the suitability of corneal anterior and posterior surface aberrations and pachymetry profile data to discriminate between eyes that later developed postoperative LASIK iatrogenic keratectasia and eyes that remained stable. METHODS: Ten eyes of five patients that later developed iatrogenic keratectasia and 245 control eyes of 245 patients with a stable postoperative LASIK follow-up of 12 months or more were included. Zernike coefficients from anterior and posterior cornea, data from corneal pachymetry profiles, and output values of discriminant functions (input from Zernike coefficients, pachymetry data, and age) were assessed for their usefulness to discriminate between preoperative eyes with iatrogenic keratectasia eyes and controls using receiver operator characteristic (ROC) curve analysis. Furthermore, Randleman Ectasia Risk Scores were calculated for each eye. RESULTS: Anterior horizontal coma (C-3(1)) was the coefficient with highest discriminative ability (area under the ROC curve [A(Z)ROC] = 0.819). For posterior coefficients and pachymetry data, A(Z)ROC values were lower. Constructing discriminant functions increased A(Z)ROC values. The function containing anterior and posterior Zernike coefficients, pachymetry data, and age reached an A(Z)ROC of 0.991. The other functions ranged from 0.858 (pachymetry) to 0.981 (anterior and posterior Zernike coefficients and age). With the Randleman Ectasia Risk Scores, 80.4% were classified correctly if eyes with 4 points or more were excluded from treatment (87.1% for 3 points or more). CONCLUSIONS: Preoperative corneal topographic characteristics of eyes that developed iatrogenic keratectasia were different than those of eyes that remained stable. However, topography patterns were not identical with those found in eyes with subclinical keratoconus in previous studies. Discriminant functions from Zernike coefficients and pachymetry data were useful to discriminate between normal eyes and eyes with preoperative iatrogenic keratectasia.