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L. A. Bachman, S. V. Patel, J. W. McLaren, W. M. Bourne; Comparison Between the Flex-Center and Center Methods of Corneal Endothelial Cell Analysis. Invest. Ophthalmol. Vis. Sci. 2009;50(13):618.
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© ARVO (1962-2015); The Authors (2016-present)
The Center method of corneal endothelial cell analysis is rapid and provides morphometric data for a contiguous region of cells, but the outermost cells are not included for analysis, which limits the number of cells analyzed when few cells are present. The Flex-Center method is similar to the Center method but includes analysis of the outermost identified cells. In this study, we compared these two methods of endothelial cell analysis by using the Konan Storage System KSS-400 (Konan Medical USA, Inc. Torrance, CA).
Endothelial images of 10 normal corneas (10 subjects) and 10 corneas (10 patients) after penetrating keratoplasty (PK) were first analyzed by using the Center method; one observer marked the center of each cell and saved the image with the marks. These images were then analyzed by using the Flex-Center method; the same observer traced the area around the marked endothelial cells, in such a way that the same cells were analyzed by both methods. Endothelial cell density (ECD), coefficient of variation of cell area (CV), and the percentage of hexagonal cells (HEX), measured by each method were compared by using paired tests, and agreement was assessed by determining mean differences and the limits of agreement (mean difference ± 2 standard deviations of the difference).
For normal corneas, the difference between analysis methods (Center minus Flex-Center) for ECD was 25 ± 17 cells/mm2 (mean ± standard deviation, p=0.002; limits of agreement: -9 to 59 cells/mm2), for CV was -2.7 ± 1.5 % (p<0.001; limits of agreement: -5.7 to 0.3%), and for HEX was 0.0 ± 2.1 % (p=1.0; limits of agreement: -4.2 to 4.2%); the mean total number of cells counted was 106 for the Center method and 105 for the Flex-Center method. For PK corneas, the difference between analysis methods for ECD was 1 ± 29 cells/mm2 (p=0.91; limits of agreement: -57 to 59 cells/mm2), for CV was -5.1 ± 6.0 % (p=0.03; limits of agreement: -17.1 to 6.9%) and for HEX was 0.0 ± 11.7 % (p=1.0; limits of agreement: -23.4 to 23.4%); the mean total number of cells counted was 25 for Center method and 25 for Flex-Center method.
The differences between endothelial cell density measured by the Flex-Center and Center methods are clinically insignificant for corneal endothelial images with large or small numbers of cells. Because the Flex-Center method includes more cells for analysis, it is preferable over the Center method when analyzing images with small numbers of cells, such as after corneal transplantation. The difference in CV between methods requires further investigation.
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