AIM: To investigate the difference, correlation, and consistency of corneal thickness and the thinnest point position detected by Pentacam HR corneal topography map and RTVue optical coherence tomography(OCT)in patients with keratoconus.

METHODS: Cross-sectional comparative study. The corneal curvature map, corneal thickness map, thinnest point position, and thinnest point thickness were detected by Pentacam HR and RTVue OCT. Paired sample t-test was used for data consistent with normal distribution, and paired sample rank sum test was used for data inconsistent with normal distribution. Spearman correlation analysis and Bland-Altman analysis were used for the correlation and consistency of the two measurement methods.

RESULTS: A total of 63 patients(105 eyes)with keratoconus were included in this study, including 49 males(77.8%)and 14 females(22.2%), aged 22.24±6.19 years; among them, relevant data of Pentacam HR topographic map: Km was 47.85±4.73D and Kmax was 55.43±8.72D. In measuring central corneal thickness and the thinnest point thickness of keratoconus, the Pentacam HR was 4.70μm and 19.46μm thicker than the mean value measured by RTVue OCT(P<0.05). There was no significant difference between the horizontal and vertical coordinates of the thinnest points measured by the two devices(P>0.05). The central corneal thickness and the thinnest point thickness measured by the two devices were highly correlated, the horizontal coordinate of the thinnest point was moderately correlated, and the vertical coordinate of the thinnest point was weakly correlated. Bland-Altman analysis showed that the central corneal thickness, the thinnest point thickness, the horizontal coordinate of the thinnest point, and the vertical coordinate of the thinnest point were 95.2%(100/105)and 93.3%(98/105), 95.2%(100/105), 95.2%(100/105)respectively, which were within the 95% consistency limit, while the consistency ranges were -36.00～+26.62μm, -42.27～+3.36μm, -0.80～+0.84mm, and -1.95～+1.06mm, respectively.

CONCLUSION: In keratoconus, the central corneal thickness and the thinnest point thickness measured by Pentacam HR were higher than those measured by RTVue OCT. It is not recommended that the central corneal thickness and the thinnest point thickness measured by the two instruments be interchangeable in clinical use because of the wide range of consistency between the two instruments' results. The position of the thinnest corneal point measured by the two instruments is similar and consistent, so it could be considered to replace the measured values of the two instruments in clinical use.