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 < .05), whereas trefoil at 0 degrees and total coma values were not statistically different. There was a weak positive correlation between devices for trefoil at 0 degrees (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.

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 < .001), while spherical aberration values were not. There was moderate correlation between devices for trefoil (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.