Further analysis of the predictability of corneal endothelial cell density estimates when polymegethism is present

Purpose:
To assess variability in endothelial cell density (ECD) estimates when polymegethism (variance in cell areas) is present.

Methods:
Using noncontact specular microscope images of the corneal endothelium, 4 sets of 20 cases were selected, which included 200 cells and had coefficient of variation values of less than 30% (group 1), 31%–40% (group 2), 41%–50% (group 3), and over 50% (group 4). A stepwise analysis was undertaken, 20 cells at a time, of the ECD estimates when using different numbers of cells for the calculations.

Results:
The net differences in ECD estimates when comparing sets of 20 cells with 200 cells were 5.0% ± 3.9%, 8.1% ± 7.3%, 11.3% ± 9.4%, and 14.5% ± 12.4% for groups 1 to 4, respectively. For measures on 100 cells per image, the predicted variances in ECD values were 5.6%, 8.8%, 11.1%, and 13.7% for the 4 groups.

Conclusions:
Higher values of corneal endothelial polymegethism result in predictable increases in the variability (uncertainty) in ECD estimates, thus reducing the “accuracy” of ECD values. There is no obvious utility in assessing more than 100 cells in such endothelia.