Prevalence of 'non-hexagonal' cells in the corneal endothelium of young Caucasian adults, and their inter-relationships.

The corneal endothelium is often described as a mosaic of hexagonal cells, despite numerous reports that the relative number of 'hexagonal' cells is often only around 65%. Such estimates also cannot define the relative area contribution to the cell mosaic of either these cells, or those that are not 6-sided. Specular micrographs were therefore taken of 20 healthy young Caucasian adults aged 21 to 34 years and the apical surface areas of at least 105 contiguous cells from each central corneal endothelium measured by planimetry. The numbers of each cell type and their surface areas were assessed so that the summated area occupied by each cell type could be calculated. The results reveal that endothelia that show only modest variance in cell areas are usually composed of 4-, 5-, 6-, 7- and 8-sided cells. Assessments of relative contribution of each cell type to the mosaic indicates that the 6-sided cells can be expected to constitute just over 60% of the total cell area. Increases in the variance in the areas across all the cells can be strongly correlated with a reduction in the 6-sided cells and increases in the 5- and 7-sided cells. Each cell type (4-, 5-, 6-sided etc) has a preferred area that is proportional to other cells. The results firmly indicate that the mosaic is not random and follows a specific order that is presumably dictated by the physics of cell packing. These methods of comparing endothelia should allow distinctions to be made between endothelia that are different, versus being abnormal (i.e. with disease).