Comparative observations on corneas, with special reference to bowman's layer and descemet's membrane in mammals and amphibians

Abstract

Corneas of tadpole, mouse, rat, guinea pig, rabbit, cat, cattle, and human were examined by TEM and SEM in a comparative study. The differences between species were noted mainly by using TEM. Bowman's layer showed a tendency to be well developed in higher mammals. Tadpoles lack a Bowman's layer, lower mammals have a thin Bowman's layer, and higher mammals have a thick Bowman's layer. The boundary between the substantia propria and Descemet's membrane was distinct in higher mammals. On the other hand, there are no differences in thickness of the collagen fibrils that constitute Bowman's layer and those of the substantia propria. NaOH digestion was utilized for SEM preparation. SEM imaging revealed a textured appearance of the epithelial side of Bowman's layer. In Descemet's membrane, fibrous long spacing (FLS) fiber-like structures, which are arranged in parallel to the endothelium, were observed by both TEM and SEM. To our knowledge, this is the first report of SEM observations of FLS fiber-like structures on the endothelial surface of Descemet's membrane. SEM at a plane normal to the plane of the cornea showed that Descemet's membrane has a piled laminar structure. Descemet's membrane is closely associated with the collagen layer of the substantia propria. Collagen fibrils invading from the substantia propria into Descemet's membrane were observed with both TEM and SEM.

Pattern recognition receptors in microbial keratitis

“…Examples include the fact that the blink rate in both mice and rabbits is lower than that in humans; 182,183 humans also have a much higher concentration of lysozyme in their tears. 184 Rabbits possess a nictitating membrane, and the structure of a human cornea is different in several ways to that of mice and rabbits: Bowman's layer and Descemet's membrane are thicker, 185 the orientation of the collagen is different 186 and the depth of each of the layers varies depending on species. 187 On a molecular level, examples of species differences include the fact that mice are known to use several NAIP accessory proteins to activate the NLRP4 inflammasome, whereas in humans only one type of NAIP has been found.…”

Stromal architecture and immune tolerance in additive corneal xenografts in rodents

“…Early work on the cornea showed that, unlike humans, the rat has no Bowman's layer (Jakus 1954). Recently, however, the somewhat disorganized anteriormost stroma extending a few fibrils beneath the lamina densa in the rat has been referred to as a very thin and indistinct Bowman's layer (Hayashi et al 2002). However, there are significant differences between the dense fibrillar meshwork that constitutes Bowman's layer in humans, which is up to 12 mm thick (Komai & Ushiki 1991), and the slightly disorganized stroma immediately beneath the epithelial basement membrane in the rat cornea (Fig.…”

Surgical outcomes of phototherapeutic keratectomy on Epithelial basement membrane dystrophy, and the characterisation of Bowman's Layer

“…Non-myelinated nerve axons penetrate BL irregularly across the cornea to ultimately provide epithelial innervation. Bowman's layer is well developed in higher mammals (cattle), lower mammals (rodents) have a thin BL and tadpoles completely lack BL [37]. BL does not regenerate after injury, but injuries to this layer are often replaced by disordered, collagenous scar tissue [38].…”

“…Previous measurements of human BL thickness have had widely varying results, ranging from 8 to 17.7µm, depending on the type of measurement (in vivo or ex vivo), tissue preparation method, and the measurement technique used. The techniques used to date include light microscopy (LM) [4], transmission electron microscopy (TEM) [37,40], tandem scanning confocal microscopy (TSCM) [41], and spectral domain optical coherence tomography (SD-OCT) [42] (Table 1). …”