Further assessment of the size, shape and surface features of superficial cells of the bovine corneal epithelium, using scanning electron microscopy

Abstract

Purpose. To qualitatively and quantitatively assess the size and shape of the surface cells of the bovine corneal epithelium as assessed by scanning electron microscopy. Methods. After quality-control measures on recent postmortem bovine eyes obtained from a slaughterhouse, the ocular surface was aggressively washed with 0.97% saline and then fixed for scanning electron microscopy (SEM) by a dropwise application, in 37°C moist chamber, of a 2% glutaraldehyde solution (in 80 mM cacodylate, pH 7.2 to 7.4). A set of images were taken from the central region of the surface of the corneal epithelium. The cell areas, perimeter and dimensions of 25 to 30 cells from 18 different samples were measured with a digitiser pad or rule, and number of bordering cells (sides) counted manually. Cell shape was assessed by comparing the longer and shorter dimensions (LS ratio) and calculation of the figure coefficient (FC, 4?A/P 2) . Results. With the washing protocol, surface cells were evident that displayed a range of electron reflexes (light, medium and dark) and that were decorated with microplicae and some crater-like features. These features were generally not evident if the surface was only rinsed with saline. The cell surface areas ranged from 58 to 6444µm 2 (mean 1748 ± 1169µm 2) , and increased as the number of sides increases. Cells with a higher number of sides (n = 10) tended to be more rounded (LS ratio averaging 1.24) while cells with small number of sides (n = 3) were more elongated (LS ratio 1.94). Shape (FC) values ranged from 0.379 to 0.967, and increased as the number of cell sides increases. Assessment of cell shape in relation to the number of cell sides identified only a small proportion of surface cells with unusually low FC values. Conclusions. With an appropriate preparative procedure (aggressive washing with saline), bovine corneal epithelial surface (squamous) cells can be shown to have a similar appearance by SEM to that previously observed for rabbit and human corneas. The cell sizes are however substantially greater than those seen in rabbits, presumably because of the much larger corneal diameter (c. 28 mm vs. 13 mm). Based on detailed analysis of cell size and shape, the results indicate that the squamous cells have reasonably predictable characteristics.