Posters

Comparison of central corneal pachymetry between Fourier-domain optical coherence tomography, very high-frequency digital ultrasound and Scheimpflug imaging systems

Poster Details

First Author: T.Yap UK

Co Author(s):    D. Reinstein   T. Archer   M. Gobbe        

Abstract Details

Purpose:

To compare central corneal thickness (CCT) measurements between three different imaging systems.

Setting:

London Vision Clinic, London, UK

Methods:

This was a retrospective study of 204 pre-operative and 159 post-LASIK consecutive eyes. CCT was measured at the corneal vertex using RTVue Fourier-domain Optical Coherence Tomography (OCT), Artemis very high-frequency digital ultrasound (VHFDU) and Pentacam Scheimpflug Imaging System. CCT on RTVue was taken by manually reading off the central reading on the corneal map. Agreement between the methods was analysed by calculating the mean differences (OCT - VHFDU, OCT - Scheimpflug, VHFDU - Scheimpflug), Pearson's correlation coefficient (PCC) and Bland-Altman style analysis using 95% limits of agreement.

Results:

In pre-operative patients, mean±SD CCT was 510±34 µm (range: 428 to 588 µm) for OCT, 516±34 µm (range: 440 to 592 µm) for VHFDU, and 533±33 µm (range: 453 to 621 µm) for Scheimpflug. OCT and VHFDU showed the closest agreement with a mean difference of -6 µm, 95% LoA ±13 µm (p<0.001, PCC=0.98). The greatest difference was found between OCT and Scheimpflug with a mean of -23 µm, 95% LoA ±19 µm (p<0.001, PCC=0.96). The mean difference between VHFDU and Scheimpflug was -17 µm, 95% LoA ±17 µm (p<0.001, PCC=0.97). In post-operative patients, mean±SD CCT was 427±51 µm (range: 342 to 575 µm) for OCT, 434±50 µm (range: 348 to 571 µm) for VHFDU, and 439±47 µm (range: 359 to 580 µm) for Scheimpflug. The smallest mean difference was again between OCT and VHFDU (-8 µm, 95% LoA ±10 µm, p<0.001, PCC=0.98) with the largest difference between OCT and Scheimpflug (-19 µm, 95% LoA ±11 µm, p<0.001, PCC=0.97). The mean difference between VHFDU and Scheimpflug was -11 µm, 95% LoA ±19 µm (p<0.001, PCC=0.98). No relationship was observed between difference in CCT and mean CCT.

Conclusions:

Central corneal thickness was measured thinner by OCT and thicker by Scheimpflug compared to VHFDU in the majority of pre-operative and post-operative eyes. The consistent bias found suggests that pachymetry data from these three methods are not interchangeable. Mean CCT was found to have no effect on difference between CCT measurements using different methods. FINANCIAL INTEREST: One of more of the authors... has significant investment interest in a company producing, developing or supplying product or procedure presented