Higher-order aberration measurements: Comparison between Scheimpflug and dual Scheimpflug–Placido technology in normal eyes

Purpose To compare higher order aberrations (HOAs) in normal eyes between a Scheimpflug imaging system (Pentacam HR) and dual Scheimpflug–Placido imaging system (Galilei G4). Setting Emory University, Atlanta, Georgia, and the University of Southern California, Los Angeles, USA. Design Retrospective case series. Methods Eyes screened for refractive surgery were evaluated sequentially using a Scheimpflug device and a dual Scheimpflug–Placido device. 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 One hundred five eyes of 105 patients (44 men, 61 women) were evaluated. Total RMS, coma, and trefoil were significantly different between groups (all P r  = 0.475 to 0.652), coma ( r  = 0.574 to 0.651), and spherical aberration ( r  = 0.483) and a strong correlation for total cornea RMS ( r  = 0.817). There was no directional bias between groups. The 95% limits of agreement for absolute values was 0.039 μm for trefoil at 30 degrees, 0.405 μm for trefoil at 0 degree, 0.553 μm for horizontal coma, 0.545 μm for vertical coma, 0.318 μm for spherical aberration, and 0.617 μm for RMS. Conclusions A Scheimpflug imaging device and dual Scheimpflug–Placido imaging device generated statistically different values for total cornea HOAs; however, the correlation between devices was moderate to strong and there was reasonable agreement in all measures for normal eyes. Based on these findings, the devices appear functionally equivalent for clinical use, although caution is warranted for outcomes-based research protocols that report HOAs.