Repeatability and agreement of total corneal astigmatism measured in keratoconic eyes using four current devices.

Background: To evaluate repeatability and agreement in measurements of total corneal astigmatism (TCA) in keratoconic eyes, using four optical coherence tomography (OCT)-based devices: Anterion, Casia SS-1000, IOLMaster 700, and MS-39.

Methods: Three consecutive measurements were taken with each device in 136 eyes. TCA values were converted into components J₀ and J₄₅. The Anterion and the IOLMaster 700 also provided axial length (AL) measurements. The repeatability was calculated using pooled within-subject standard deviation (S_w). The agreement among the four devices was assessed by pairwise comparisons and Bland-Altman plots.

Results: For all devices, the repeatability of TCA measurements showed S_w ≤0.23 D for TCA magnitude, ≤0.14 D for J₀, and ≤0.12 D for J₄₅. There were statistically significant differences in TCA magnitude for each pair, except for IOLMaster 700 with MS-39, and Anterion with MS-39. The repeatability (S_w) of axis measurements had a statistically significant negative correlation with the TCA magnitude (p < 0.001 for all devices). Both Anterion and IOLMaster 700 had high repeatability in AL measurements (S_w: 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).

Conclusions: All four devices showed good repeatability in TCA measurements in keratoconic eyes, the agreement for TCA measurements between the tested devices was generally low. Anterion and IOLMaster 700 showed good repeatability and agreement in AL measurements.