A comparison of two methods for estimating polymegethism in cell areas of the human corneal endothelium

Abstract

To compare the outcome measures from two different methods for estimating the coefficient of variation (COV) in cell area for human corneal endothelia. A single non-contact specular micrograph was obtained from the central region of the corneal endothelium of 100 healthy non-contact lens-wearing white European subjects, aged from 32 to 62 years. The captured image file was either assessed using a machine-based algorithm in which 21 cells were marked and their areas reported (designated as the TOPCON 'centre-dot' method), or by an overlay and semi-automated computer-based image analysis system of the entire image of around 200 cells (designated as the AUTO method). The average cell area values were used to calculate the endothelial cell density (ECD), while the COV was calculated from the standard deviation of the cell area measures. The TOPCON and AUTO methods yielded comparable data for average cell area (395 vs 391 microm(2)) and estimated ECD (2566 vs 2575 cells mm(-2)) that were not statistically different (p > or = 0.351), although there was a slight bias between the two methods. However, the mean COV values were very different at 43.5 and 31.4% (p < 0.001). The overestimation of the COV was related to the difference in the largest cell area domain identified by the two methods (p < 0.001, r = > or =0.748). A centre-dot method using a small number of cells generates useful data on cell area and ECD, but it should be used cautiously for estimates of COV.