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Paul Lang, Praneetha Thulasi, Sumitra Khandelwal, James Bradley Randleman; Comparing Change in Anterior Curvature after Corneal Cross-Linking Using Placido and Scheimpflug Imaging. Invest. Ophthalmol. Vis. Sci. 2018;59(9):4398.
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© ARVO (1962-2015); The Authors (2016-present)
To evaluate the correlation for anterior axial curvature difference maps following corneal crosslinking (CXL) for keratoconus between Scheimpflug-based tomography and Placido-based topography.
Corneal imaging was collected pre-operatively and 1, 3, 6, and 12 months post-operatively using Scheimpflug-based tomography (Pentacam, Oculus Inc., Lynnwood, WA) and Placido-based topography (Orbscan II, Bausch & Lomb, Rochester, NY) in patients with progressive keratoconus receiving standard protocol CXL (3mW/cm2 for 30 minutes). Regularization index, absolute maximum keratometry (KMax), and change in KMax were compared between the two imaging devices at each time point. Analysis was then conducted separately on patients with pre-operative KMax <60D and ≥60D to assess the impact of disease severity on device measurements.
Absolute KMax differed pre-operatively [60.1±8.9D Pentacam vs. 57.0±6.3D Orbscan (p=0.02)], at 1, and 3 months, but not at 6 or 12 months [57.4±8.8D Pentacam vs. 54.8±7.1 Orbscan (p=0.11)]. Regularization index differed at 1 month only. Absolute KMax values were correlated at all time points (pre-op r=0.88, p<0.001; 12 month r=0.91, p<0.001). Regularization index was correlated at 12 months only (r=0.59, p<0.001). The devices did not differ in the <60D group, while the ≥60D group differed in absolute KMax at pre-op, 1, and 3 months, and in regularization index at pre-op and 1 month. Absolute KMax values were correlated at all time points for both the <60D group (pre-op r=0.92, p<0.001; 12 month r=0.90, p<0.001) and ≥60D group (pre-op r=0.49, p<0.01; 12 month r=0.80, p<0.001). Change in KMax was correlated in the <60D group at 1, 6, and 12 months (r=0.47, p=0.02), compared to only 12 months for the ≥60D group (r=0.69, p<0.001). Regularization index was correlated for the <60D group at 1, 3, 6, and 12 months (r=0.61, p<0.001). Regularization index was correlated for the ≥60D group at 6 and 12 months (r=0.64, p<0.001).
Measurements made using Scheimpflug or Placido systems on absolute KMax were interchangeable for patients with Kmax<60D but were more weakly correlated with KMax≥60D. The devices were weakly correlated in both <60D and ≥60D groups when measuring change in KMax and regularization index, although interchangeability was better with measurements on the <60D group, particularly when earlier in treatment course.
This is an abstract that was submitted for the 2018 ARVO Annual Meeting, held in Honolulu, Hawaii, April 29 - May 3, 2018.
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