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.

Repeatability and Comparison of Corneal Tomography in Mild to Severe Keratoconus Between the Anterior Segment OCT MS-39 and Pentacam HR.

PURPOSE: To detect keratoconus progression, accuracy of tomographic measurements is crucial. The impoved axial resolution of optical coherence tomography (OCT) compared to Scheimpflug photography serves as the motivation to investigate and compare the repeatability of the anterior segment OCT MS-39 (CSO) to Pentacam HR (Oculus Optikgeräte GmbH) in patients with keratoconus. METHODS: One hundred twenty-three eyes of 123 patients with keratoconus were enrolled and subdivided in four groups by maximum keratometry (Kmax): Kmax < 48.00 diopters (D), Kmax of 48.00 to 53.01 D, Kmax of 53.00 to 58.00 D, and Kmax > 58.00 D. Three consecutive measurements per eye were acquired with the MS-39 and compared to the Pentacam HR. Kmax, thinnest pachymetry, anterior asphericity, and posterior elevation data were compared. Within-subject standard deviation (Sw), coefficient of variation (CoV), test-retest repeatability (TRT), and the intra-class correlation (ICC) were calculated and evaluated. Bland-Altman plots were also analyzed. RESULTS: The Pentacam HR measures significantly higher Kmax values than the MS-39, with a more pronounced difference for severe cases of keratoconus (0.57 D for all cases; 1.88 D for cases with Kmax > 58.00 D). Thinnest pachymetry was approximately 5 µm thinner when measured by the Pentacam HR than the MS-39, independently of keratoconus stage. A further progressed keratoconus stage was significantly associated with increased measurement errors and resulted in worse repeatability (Kmax < 48.00 D: Sw = 0.18 D, TRT = 0.50 D, CoV = 0.39%, ICC = 0.989; Kmax > 58.00 D: Sw = 0.53 D, TRT = 1.48 D, CoV = 0.90%, ICC = 0.984). The behavior was similar for other tomographic parameters. CONCLUSIONS: The Pentacam HR and the MS-39 have an overall good agreement for keratoconus; however, the Pentacam HR measures steeper and thinner than the MS-39. The association between the magnitude of topographic and tomographic parameters and their measurement errors suggests that the diagnosis of keratoconus disease progression should be based on the stage and the test-retest repeatability rather than on a fixed value (eg, 1.00 D). [J Refract Surg. 2022;38(4):250-255.].