Variation in central and vertical corneal endothelial cell density in normal subjects

Twenty normal subjects, aged 20 to 50, who had never worn contact lenses underwent determinations of central, inferior and superior corneal endothelial cell density using the Heyer-Schulte specular microscope. Analysis of variance revealed that superior cell density was significantly larger than central cell density, and that central cell density was significantly larger than inferior cell density (P less than 0.00001). In addition, 4 of these subjects had measurements taken on 4 separate sessions. Analysis of variance revealed that central and vertical cell density determinations were reproducible across measurement sessions. The finding of a vertical gradient in cell density was in contrast to 2 published reports which found no vertical differences in the normal cornea. Consequently, those data were re-analyzed using correct statistical procedures and similar vertical differences were obtained for one series of patients. The finding of a vertical gradient in endothelial cell density challenges the appropriateness of relying upon measurement of the central corneal field as an indicator of the pre-operative endothelial cell density.