The authors conducted this study to determine whether the flex-center method of endothelial cell analysis agreed with the standard corner method and whether it could be used interchangeably with the center method. The flex-center method analyzes a larger number of cells than the center method, which is important in corneas with few cells, such as those that have undergone penetrating keratoplasty.
Using each of the three methods, the authors analyzed identical cells in endothelial images of 10 normal corneas and 10 corneas after penetrating keratoplasty. The center method of corneal endothelial cell analysis is a rapid and common technique that requires digitization of the center of each cell in a contiguous group of cells but excludes the outermost digitized cells of a contiguous group from analysis. The flex-center method is a modification that includes analysis of the outermost cells.
They found that in normal corneas, there were small but clinically insignificant differences among the three methods for mean endothelial cell density (ECD) (P < 0.001) (flex center, 2846 cells/mm2; center, 2870 cells/mm2; and corner, 2892 cells/mm2), coefficient of variation of cell area (CV) (P < 0.001) (flex center, 33 percent; center, 30 percent; and corner, 30 percent), and hexagonal cells (HEX) (P = 0.004) (flex center, 60 percent; center, 60 percent; and corner, 58 percent). In post-PK corneas, the methods agreed for ECD (P = 0.06) (flex center, 908 cells/mm2; center, 912 cells/mm2; and corner, 929 cells/mm2) but disagreed for CV (P = 0.02) (flex center, 35 percent; center, 30 percent; and corner, 35 percent) and HEX (P = 0.02) (flex center, 56 percent; center, 54 percent; and corner, 43 percent).
The authors conclude that the flex-center method of endothelial analysis can be used interchangeably with the center and corner methods when measuring ECD in normal or transplanted corneas. It can reduce analysis time and increase the number of cells analyzed. However, with the flex-center method morphometric data are not accurate when endothelial cell morphology becomes very abnormal in transplanted corneas.