A comparative study of the corneal endothelium in vertebrates

Abstract

INTRODUCTION: In vertebrates, a corneal endothelium is essential for the maintenance of corneal transparency in a variety of environments, including aerial, terrestrial and aquatic. Knowledge of the surface structure of the corneal endothelium may assist our understanding of this unique tissue and its evolutionary development. Except for humans and some mammals, there have been few studies of other vertebrates, particularly the unique Australian species. METHODS: The field emission scanning electron microscope was used to study the corneal endothelium in representatives of four vertebrate classes: Teleostei (five species), Reptilia (two species), Aves (four species) and Mammalia (three species), including Marsupialia (two species). Endothelial cell densities were calculated from micrographs using computer-based image analysis. RESULTS: The cell densities varied considerably from 1,900 +/- 197 cells per mm(2) for the bream to 11,734 +/- 1,687 cells per mm(2) for the emu. Most of the corneal endothelia were similar to those reported for mammals. However, in some species such as the koala, the pattern was irregular. Some endothelial cells in birds possessed cilia. CONCLUSIONS: The shape of the corneal endothelial cells of vertebrates is typically a mixture of hexagonal and pentagonal cells, in which the cell borders are irregular and interdigitating. An exception is the koala, in which the cells were markedly irregular. Many of the cells have surface microvilli but only in the birds are cilia found in the centre of many endothelial cells. In spite of the range of corneal environments, there are no systematic differences in the cell densities of the various classes and species.

Morphology of endothelial cells from different regions of the equine cornea

“…The high cost of specular microscopes and the difficulty in obtaining good images in injured endothelial areas are common challenges or barriers to the use of this technique (ANDREW et al, 2001;PIGATTO et al, 2005a;SAAD et al, 2008). SEM has been widely used to compare the endothelial ultrastructure of vertebrates and to evaluate the effects of medications, chemicals, or surgical procedures on the endothelium (COLLIN & COLLIN, 1998;PIGATTO et al, 2004;PIGATTO et al, 2005a;PIGATTO et al, 2005b;PIGATTO et al, 2009). Changes in endothelial cell dimensions can occur as a result of processing the cornea for SEM and the data obtained with regard to endothelial cell density cannot be compared with those obtained using specular microscopy (SCHUTTEN & VAN HORN , 1980).…”

Effects of intracameral brilliant blue on the corneal endothelium of swine: in vitro study

“…Humans and rabbits have twenty to thirty microvilli in the cell superficies, and these structures react to tox- ic substances changing their sizes (Collin & Collin 1998). Both the endothelium control and experimental groups presented almost the same morphological characters in scanning electron microscopy analyses, and the microvillus and interdigitation were evident in all sample images.…”

“…The results observed in this study show that normal swine corneal endothelium consisted of a continuous monolayer with mainly hexagonal cells, but were also found cells with five sides and with seven sides. Previous studies conducted involving vertebrate animals have shown that there is predominance of cells with hexagonal shape and, in lower proportion, there is presence of five-and seven-sided cells (Collin & Collin, 1998, Pigatto et al 2005, Gum et al 2007, Tamayo-Arango et al 2009, Bercht et al 2015, Coyo, et al 2015.…”

“…The endothelial cellular membranes' integrity for scanning electron microscopy evaluation depends on adequate tissue preservation and fixation from the time after the death of the animal until the use of the tissue samples (Collin & Collin 1998). In humans, corneal tissues for transplants must be used within six hours of the donor's death and need to be safely maintained to avoid endothelial damage (Franzen et al 2010).…”

“…Both the endothelium control and experimental groups presented almost the same morphological characters in scanning electron microscopy analyses, and the microvillus and interdigitation were evident in all sample images. The cilia in swine corneal endothelial cells are described by Tamayo The cilia absence or the presence of a few numbers of them in swine endothelium research is due to their fragility during sample production (Collin & Collin 1998, Tamayo-Arango et al 2009). …”