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

The purpose of this work is to assess the reliability of endothelial cell-density (ECD) estimates in corneas with different severity pseudoguttata. Specular microscopy was undertaken on grade 1, 2, or 3 pseudoguttata patients and age-matched controls aged 52-83 years. On high magnification prints of central cornea, areas of complete cells (all sides visible) and partial 'cells' (one or more sides obscured) were measured manually. Sets of 45 complete cells were selected, as well as 75 cells that were a mixture of complete and partial cells on guttate endothelia. ECD was calculated by a progressive averaging technique. Each group comprised 12 patients with similar range of ECD values (1,230-4,587 cells/mm(2)). Based on 40 complete cells, ECD could be estimated to within +/- 3.1% for grade 3 pseudoguttata versus +/- 2.0% for controls. If a mixture of complete and partial cells were measured, ECD could be estimated to within +/- 2.8% for grade 3 pseudoguttata images (n = 70 cells) and +/- 1.1% for controls. The estimated variability increases to substantial levels of +/- 20% if only ten cells were measured. No statistical differences in ECD were noted between guttate and normal endothelia if only complete cells were measured, but could be different if partial 'cells' were included. Providing adequate numbers of complete cells are measured and in the absence of obvious polymegathism, ECD estimates can be made to within around +/- 3% in the presence of typical but significant pseudoguttata.