The corneal endothelium in the blowfish (Torquigener pleurogramma)

Purpose. In vertebrates, a corneal endothelium is essential for the mainten ance of corneal transparency in a variety of environments. Knowledge of the surface structure of the corneal endothelium may assist our understanding of this unique tissue and its evolutionary development. Although there have been many studies of the corneal endothelium of humans and some mammals, t here have been few in other vertebrates. Methods. The field emission scanni ng electron microscope was used to study the surface structure of the corne al endothelium in the blowfish, Torquigener pleurogramma (Tetraodontidae, T eleostei), and to examine cell density. Cell areas were measured by using i mage-analysis software. Results. The endothelium is composed of a sheet of interdigitating hexagonal and pentagonal cells with a mean area of 154 mu m (2) and a density of 6,486 cells/mm(2). Two types of surface features are i dentified; primary cilia and microvilli. The cilia are cylindrical, protrud e from either a pore or circular indentation in the cell center, and posses s a knob-like ending. The microvilli are button-like protrusions with a den sity of similar to 3.5 x 10(5) microvilli/mm(2) or 54 microvilli/cell in ce ntral cornea. Conclusion: The results show that the surface structure of te leost endothelial cells is similar to those described for other vertebrates and indicate that cell density varies across classes, with the presence of cilia a more widespread occurrence than previously believed.