Microstructure Characteristics of the Cornea in Birds and Mammals

Abstract

ABSTRACT. In this study, the microstructure of the cornea was compared among chickens (Gallus gallus), jungle crows (Corvus macrorhynchos), rats (Rattus norvegicus) and rabbits (Oryctolagus cuniculus). The density of keratocytes in the mammals was over 3 times that in the birds. The size of the keratocytes in the birds and rat were significantly lower than those in the rabbit. Using scanning and transmission electron microscopy, the bundles of collagen fibers in the birds were found to be well arranged, while those in the mammals were arranged randomly. The collagen lamellae of the birds were significantly thicker than those of the mammals, and the numbers of collagen lamellae in the birds were significantly smaller than in the mammals. The center-to-center distances between the collagen fibrils of the chicken and rabbit were significantly larger than those of the crow and rat. The densities of collagen fibrils in the chicken and rabbit were significantly less than those of the crow and rat.

Lateral Growth Limitation of Corneal Fibrils and Their Lamellar Stacking Depend on Covalent Collagen Cross-linking by Transglutaminase-2 and Lysyl Oxidases, Respectively

“…The values of the larger population reasonably agree with reported diameter values determined from transmission electron micrographs for typical corneal collagen fibrils in many adult vertebrate species. Diameter values range from 25 to 40 nm (23,24), depending on the exact tissue embedding conditions and, more specifically, on the extent of dehydration. X-ray diffraction of fully hydrated corneas yielded diameter values close to 40 nm (25).…”

Analysis of the corneal endothelium in eyes of chickens using contact specular microscopy

“…The choice of chickens was due to the wide applicability of this species in ophthalmic research (KAFARNIK et al, 2007;NICKLA et al, 1998;PRASHAR et al, 2007;SCHMID et al, 2003;TSUKAHARA et al, 2010;WAGGONER, 1978). The chicken has been used extensively as a myopia model (WAGGONER, 1978).…”

Functional morphology of the cornea of the Little PenguinEudyptula minor(Aves)

“…There have been very few studies of the functional morphology of the cornea in birds. Using scanning electron microscopy (SEM), there appear to be only six publications (Collin & Collin, 1998a, 2000a, 2000b, 2006; Pigatto et al, 2005; Tsukahara et al, 2010) that investigate the surface ultrastructure of the cornea in birds with only three of these studies including some data on at least 1 of the 17 species of penguin (Collin & Collin, 2000a, 2006; Pigatto et al, 2005). In a large comparative study of the epithelial surface in a range of vertebrates, Collin and Collin (2000a, 2006) described an epithelial cell density of 13,220 cells per mm 2 with an average width of microridges of 87 nm in the central cornea of the Little Penguin Eudyptula minor .…”

“…At the level of the transmission electron microscope, there are only two published studies of the ultrastructure of the cornea in birds with both concentrating on the corneal stroma with little or no reference to the other corneal structures (Craig & Parry, 1981; Tsukahara et al, 2010). The collagen lamellae in chickens Gallus gallus and Jungle Crows Corvus macrorhynchos were found to be significantly thicker but fewer in number than in rabbits Oryctolagus cuniculus and rats Rattus norvegicus (Tsukahara et al, 2010). However, a comparative study of five species of birds and nine species of mammals reveals that the diameter of the collagen fibrils is relatively consistent (24–25 nm, Craig & Parry, 1981).…”