Assessment of the Reliability of Calculations of the Coefficient of Variation for Normal and Polymegethous Human Corneal Endothelium

On the regional variability of averaged cell area estimates for the human corneal endothelium in relation to the extent of polymegethism

“…Assessments of published images indicated that measuring this number of cells (i.e. 75/image) should give reasonably reliable data in terms of predicted variability in cell areas [5].…”

“…For the COV estimates themselves, a later retrospective analysis of published endothelial images indicated that the reliability of any COV calculations would be predictably less if cell area heterogeneity appeared to be present, i.e. whether images were subjectively considered to be normal (homogeneous) or showing some evidence of heterogeneity (polymegethism) [5]. The analysis was, however, limited by the fact that relatively few images were available for analysis and some included somewhat fewer cells than others, often less than 100/image.…”

“…Stated another way, from a theoretical perspective it could be that parts of an endothelial image could be largely normal with only small regions (or portions) of the mosaic showing larger or smaller cells. The overall estimates of COV have been reported to be dependent on the number of cells measured and therefore included in the calculations [5,7].…”

Assessment of the reliability of endothelial cell-density estimates in the presence of pseudoguttata

“…Previous specific studies on this issue have not only led to the development of guidelines as to how many cells should be measured [6,8,9] but, far more importantly, show that there is a finite limit to the so-called repeatability or accuracy of such measures. One particular feature relates to whether the endothelium was uniform or non-uniform [8]; the latter condition is also widely known as endothelial polymegathism.…”

“…Such studies have indicated that the variability in ECD estimates tends to decrease as the number of cells measured gets smaller. From such studies, recommendations have been made that some 75 to 100 cells would be a reasonable target number for cells measured in corneal endothelial morphometry [6,8], and that that a more robust outcome is likely if the set of cells forms a contiguous (tessellated) group [8,9].…”