Title : Repeatability and agreement of total corneal astigmatism measured in keratoconic eyes using four current devices
Purpose: To evaluate repeatability and agreement of measurements of total corneal astigmatism (TCA) in keratoconic (KC) eyes, obtained by two swept-source (SS) optical coherence tomography (OCT)-based devices (Anterion and Casia SS-1000), one SS-OCT combined with reflectometry (IOLMaster 700) and one spectral-domain (SD) OCT combined with Placido imaging (MS-39).
Methods: Three consecutive measurements were acquired with each of the four devices in 136 eyes. TCA values were transformed into power vector components (J0/J45). The acquisitions from the Anterion and the IOLMaster 700 also provided Axial length (AL) measurements. The repeatability was calculated using pooled within-subject standard deviation (Sw). The agreement between the four devices was assessed by Repeated-measures ANOVA, Bland–Altman plots, and Double-angle plots for vector difference in astigmatism.
Results: The repeatability of TCA measurements showed Sw ≤ 0.23 D for cylinder magnitude, ≤ 0.14 D for J0, and ≤ 0.12 D for J45, for all four devices. There were statistically significant differences in cylinder magnitude for each pair, except when comparing IOLMaster 700 to MS-39 and Anterion to MS-39. There were no statistically significant differences in J45 for any pairs, but there were statistically significant differences in J0 when comparing Anterion to MS-39 and Anterion to MS-39. The smallest mean magnitude of vector difference in astigmatism was between Anterion and Casia SS-1000 (0.55 ± 0.43 D), while the largest was between Anterion and MS-39 (1.36 ± 1.32 D). Both Anterion and IOLMaster 700 showed high repeatability in AL measurements (Sw: 0.007 mm for Anterion and 0.009 mm for IOLMaster 700). The difference in AL between the two was 0.015 ± 0.033 mm (p< 0.001).
Conclusion: All four devices showed good repeatability in measurements of TCA in KC eyes, but there were statistically significant variations in cylinder magnitude. Anterion and IOLMaster 700 showed good repeatability and agreement in AL measurements. Future studies are warranted to evaluate the use of the four devices in refractive procedures.
Audience Take Away Notes:
- All four devices showed good repeatability in the measurements of TCA in KC eyes, Anterion being the best.
- For the measurements of TCA, the SS-OCT-technology-only devices should not be used interchangeably with SS-OCT combined with telecentric keratometry (Anterion and Casia SS-1000 vs. IOLMaster 700) or with SD-OCT combined Placido devices (Anterion and Casia SS-1000 vs. MS-39).
- Devices using different hybrid technologies (IOLMaster 700 and MS-39) should not be used interchangeably.
- For AL measurements, Anterion and IOLMaster 700 showed good repeatability and agreement and may be used interchangeably.