Purpose. We sought to determine the variance in endothelial cell density (ECD) estimates for human corneal endothelia.
Methods. Noncontact specular micrographs were obtained from white subjects without any history of contact lens wear, or major eye disease or surgery; subjects were within four age groups (children, young adults, older adults, senior citizens). The endothelial image was scanned, and the areas from ≥75 cells measured from an overlay by planimetry. The cell-area values were used to calculate the ECD repeatedly so that the intra-and intersubject variation in an average ECD estimate could be made by using different numbers of cells (5, 10, 15, etc.).
Results. An average ECD of 3,519 cells/mm2 (range, 2,598–5,312 cells/mm2) was obtained of counts of 75 cells/endothelium from individuals aged 6–83 years. Average ECD estimates in each age group were 4,124, 3,457, 3,360, and 3,113 cells/mm2, respectively. Analysis of intersubject variance revealed that ECD estimates would be expected to be no better than ±10% if only 25 cells were measured per endothelium, but approach ±2% if 75 cells are measured.
Conclusion. In assessing the corneal endothelium by noncontact specular microscopy, cell count should be given, and this should be ≥75/endothelium for an expected variance to be at a level close to that recommended for monitoring age-, stress-, or surgery-related changes.