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Grace Lytle, Marc Friedman, Peter Hersh, David Muller; Use of Zonal Km vs Point Kmax for Analysis of Corneal Cross-linking Pentacam Topography. Invest. Ophthalmol. Vis. Sci. 2013;54(15):5276.
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To determine whether analysis of topography in a 2 or 3 mm zone centered over Kmax provides a more sensitive measure of change in corneal curvature in eyes with keratoconus following corneal cross-linking than the use of a point Kmax value.
The Pentacam software module (Version 6.03r19, Oculus Inc.) was used to retrospectively analyze a randomly selected subset of 28 eyes with a diagnosis of keratoconus treated with corneal cross-linking as part of a clinical trial in 2008 through 2009. Cross-linking was performed by removing the corneal epithelium and then pretreating the cornea for 30 minutes with 0.1% Riboflavin Ophthalmic Solution to saturate the corneal tissue with the riboflavin photosensitizer. The cornea was then irradiated with UVA (365 nm) at 3 mW/cm2 for 30 minutes for a total radiant exposure of 5.4 J/cm2. Pentacam scans were obtained pre-operatively, and at 1, 3, 6 and 12 months following corneal cross-linking. Kmax values and their corresponding coordinates were identified by the software and were recorded for each eye at each time point. The Pentacam software module was used to manually define a 3mm zone centered over the coordinates of the Kmax value in each eye at each time point on sagittal curvature maps. This procedure was repeated for a 2mm zone centered over the same coordinates. A number of software generated parameters from this analysis were recorded, including the mean (Km) of the values contained within this zone. A statistical analysis of these values was conducted.
Analysis of the 3mm zonal Km using a two tailed t-test demonstrated statistically significant improvement in sagittal curvature from baseline at 3 months (P< 0.15, 85% confidence interval). Improvement in Kmax and 2mm zonal Km were not significant at this time point, (P=0.635 and P=0.229). All three measurements were statistically significant at 12 months (P <0.05, 95% confidence interval)
The analysis of a 3mm zone centered on Kmax may allow for earlier detection of the efficacy of corneal cross-linking in halting the progression of disease in eyes with keratoconus than the use of a point Kmax value alone. A larger sample size needs to be analyzed to determine statistical validity of using the 3 mm zonal Km as an early predictor of 12 month stabilization or improvement in Kmax.
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