Best Fit Sphere Back and Adjusted Maximum Elevation of Corneal Back Surface as Novel Predictors of Keratoconus Progression

Abstract

Purpose: To evaluate the Maximum Elevation of Corneal Back Surface adjusted to the same Best Fit Sphere Back between timeline measurements (AdjEleBmax) and the Best Fit Sphere Back (BFSB) radius itself as new tomographic parameters for documentation of ectasia progression and to compare them with the most recent and reliable parameters used on keratoconus (KC) progression. Results: We evaluated the performance and the ideal cut-off point of Kmax, D-index, posterior radius of curvature from the 3.0 mm centered on the thinnest point (PCR), EleBmax, BFSB and AdjEleBmax as isolated parameters to document KC progression (defined as a significant change in two or more variables), we found a sensitivity of 70%, 82%, 79%, 65%, 51% and 63%, and a specificity of 91%, 98%, 80%, 73%, 80% and 84% to detect KC progression. The area under the curve (AUC) for each variable was 0.822, 0.927, 0.844, 0.690, 0.695, 0.754, respectively. Conclusions: AdjEleBmax presented a greater specificity, larger AUC and better performance compared to EleBmax without any adjustment, with similar sensitivity. Although AdjEleBmax and BFSB demonstrated smaller AUC and specificities comparing with Kmax and D-Index, these back surface parameters still presented a good performance with a reasonable AUC. Considering the current knowledge that the posterior corneal surface may be the first interface to suffer changes in KC, we suggest the inclusion of these two parameters in the evaluation of KC progression in conjunction with other variables to increase the reliability of our clinical evaluation and early detection of progression.