A comparative study of corneal thickness measurements with the RTVue, Casia-2, and Pentacam devices in patients with mild to moderate keratoconus

Abstract

PurposeTo explore the characteristics of the RTVue, Casia-2, and Pentacam instruments for measuring the corneal thickness in patients with mild to moderate keratoconus.MethodsWe recruited patients diagnosed with mild to moderate keratoconus at our hospital from January to March 2022; 46 eyes (46 patients) were enrolled (35 men [76.09%], 30 right eyes [65.22%], mean age 24.3 ± 6.2 years). Central corneal thickness (CCT) and thinnest corneal thickness (TCT) were measured using two optical coherence tomography (OCT) instruments (RTVue and Casia-2) and the more conventional Pentacam. Then, differences and correlations between the CCTs and TCTs based on the device and factors influencing those differences were explored.ResultsThe CCTs were 488.9 ± 41.44 µm, 488.7 ± 42.52 µm, and 489.3 ± 44.17 µm for the RTVue, Casia-2, and Pentacam, respectively. The TCT results were 465.5 ± 39.78 µm, 466.5 ± 39.39 µm, and 480.5 ± 41.27 µm for the RTVue, Casia-2, and Pentacam, respectively. The CCTs were highly consistent among the groups and correlated with one another. The TCTs measured by the RTVue and Casia-2 were thinner than the Pentacam, but all three devices were highly correlated. The RTVue and Casia-2 thinnest point location measurements significantly differed from the Pentacam (p < 0.001). Bland-Altman plots demonstrated a significant agreement between the three instruments (p < 0.001); the 95% limits of agreement were − 16.19 µm to + 17.32 µm for Pentacam and RTVue and − 15.78 µm to + 15.47 µm forPentacam and Casia-2. Multivariate analysis identified that the TCT measurement difference between the RTVue and Pentacam were related to the difference between the CCT and TCT (b = 0.532, 95% confidence interval [CI]: 0.04 to 1.024, p < 0.001), whereas the difference between the Casia-2 and Pentacam were related to the anterior radius for curvature (A) grade (b = 3.9, 95% CI: 1.753 to 6.074, p = 0.001), corneal pachymetry at the thinnest (C) grade (b = − 7.875, 95% CI: − 11.404 to − 4.346, p < 0.001), and the difference between the CCT and TCT (b = 0.425, 95% CI: 0.1 to 0.751, t = 0.012).ConclusionsThe CCTs in patients with mild to moderate keratoconus were similar among all three devices, but the TCTs and thinnest point locations were not. Furthermore, the TCT measurement differences between the OCT instruments and the Pentacam were more pronounced in keratoconus cases with a steeper anterior surface, thicker TCTs, and a larger difference between the CCT and TCT.Trial registrationRegistration number: 2021118-1. Retrospectively registered: 01 September 2021.