Corneal higher-order aberrations measurements: Comparison between Scheimpflug and dual Scheimpflug–Placido technology in keratoconic eyes

Purpose To compare the difference and agreement of corneal higher-order aberrations (HOAs) in keratoconic eyes using Scheimpflug and dual Scheimpflug–Placido imaging systems. Setting Emory University, Atlanta, Georgia, and the University of Southern California, Los Angeles, California, USA. Design Retrospective between-devices reliability and agreement study. Methods Patients diagnosed with keratoconus were evaluated sequentially by Scheimpflug and dual Scheimpflug–Placido devices. Differences, correlations, and agreement between values for total root mean square (RMS), trefoil, coma, and spherical aberration were analyzed, and Bland-Altman plots were generated. Results Fifty eyes from 50 patients (31 men, 19 women) were evaluated. Trefoil at 30 degrees, spherical aberration, and total RMS were significantly different between groups ( P r  = 0.228), and a moderate positive correlation for trefoil at 30 degrees ( r  = 0.473), horizontal coma ( r  = 0.430), and for total corneal RMS ( r  = 0.637). Vertical coma ( r  = 0.816) and spherical aberration ( r  = 0.874) showed a strong positive correlation. The 95% limits of agreement (LoA) for absolute values were 1.963 μm for trefoil at 30 degrees, 2.449 μm for trefoil at 0 degrees, 3.530 μm for horizontal coma, 2.145 μm for vertical coma, 1.242 μm for spherical aberration, and 10.527 μm for RMS. Conclusion Significant differences were found between measurements of corneal HOAs generated by Scheimpflug and dual Scheimpflug–Placido devices in patients with keratoconus, with generally limited correlations and wide LoA. HOAs measurements from these devices should not be considered equivalent.