Comparison of Corneal Thickness Measurements After Customized Corneal Crosslinking Using High-Resolution Optical Coherence Tomography and Scheimpflug Tomography.

Purpose: The aim of this study was to compare the evolution of corneal pachymetry after customized corneal crosslinking (CXL) between Scheimpflug-based and optical coherence-based corneal tomography (OCT).

Methods: In this retrospective study, central corneal thickness (CCT), thinnest corneal thickness, and epithelial thickness of 33 eyes of 33 patients with keratoconus were measured preoperatively and 1, 3, and 12 months after customized CXL using the Pentacam HR and the MS-39. The mean pachymetry values of measurements were compared with a paired sample t test. Bland-Altman plots and 95% limits of agreement (LoA) were used to assess the agreement between the measurements of the 2 devices.

Results: The mean age of the participants was 29.7 ± 11.4 years. At baseline, the mean CCT measurements were equal with Pentacam HR (478.30 ± 36.77 μm) and MS-39 (478.46 ± 38.01 μm). After CXL, CCT obtained by Pentacam HR was 460.65 ± 38.69 μm, 464.65 ± 44.45 μm, and 476.77 ± 39.85 μm, and by MS-39 was 478.18 ± 39.50 μm, 472.89 ± 40.92 μm, and 479.51 ± 39.20 μm at 1, 3, and 12 months, respectively. Pentacam HR measured significantly lower CCT ( P < 0.05) at months 1 and 3 after CXL. The agreement was smallest between both devices at month 1 (95% LoA -59 to 24 μm) followed by month 3 (95% LoA: -41 to 23 μm). Epithelial thickness, measured with OCT alone, increased significantly at 1 month and regained preoperative levels at 3 months and thereafter.

Conclusions: After CXL, corneal pachymetry significantly differs between OCT-based and Scheimpflug-based corneal tomography. Pentacam HR seems to underestimate pachymetry when haze is present.