Correlation of corneal elevations measured by Scheimpflug corneal imaging with severity of keratoconus

To evaluate the correlation of corneal elevation and difference elevation with severity of keratoconus. Methods: Anterior and posterior corneal elevations with both conventional and enhanced best-fit spheres (using rotating Scheimpflug camera) were measured. Front and back difference elevation were extrapolated from difference map of Belin/Ambrỏsio Enhanced Ectasia Display of the Scheimpflug system. Data from corneal elevations and difference elevations were correlated with maximum keratometry, minimal corneal thickness, and severity of keratoconus as assessed by Amsler-Krumiech classification of keratoconus. Results: Ninety eyes of 55 keratoconus patients of different clinical stages were evaluated. There was a significant positive correlation between keratoconus severity and corneal elevations (anterior and posterior elevation as measured with both conventional and enhanced best-fit spheres) and also between keratoconus severity and corneal elevation differences (P < 0.001 and r > 0.625 for all). Maximum keratometry (Kmax), mean keratometry (Kmean), and all corneal elevations and difference elevations were highly correlated (P < 0.001 and r > 0.840 for all). A significant negative correlation was found between minimum corneal thickness and all corneal elevations and difference elevations (P < 0.001 and r < 0.711 for all). Receiver operating characteristic (ROC) curve analyses showed that anterior and posterior difference elevations have the best predictive accuracy for grading keratoconus severity. Conclusion: Evaluation of corneal elevation and difference elevation data obtained from Scheimpflug corneal imaging is useful for grading severity of keratoconus.