European Journal of Anatomy

Official Journal of The Spanish Society of Anatomy
Cover Volume 24 - Number 5
Eur J Anat, 24 (5): 399-406 (2020)

The microanatomy of Bowman’s layer in the cornea of the pig: Changes in collagen fibril architecture at the corneoscleral limbus

Greg M. Hammond1, Robert D. Young1, Duncan D. Muir2, Andrew J. Quan-tock1

1Structural Biophysics Group, School of Optometry & Vision Sciences, Cardiff University, Maindy Road, Cathays, Car-diff, CF24 4HQ, Wales, UK, 2School of Earth and Ocean Sciences, Cardiff University, Main Building, Park Place, Car-diff, CF10 3AT, Wales, UK

ABSTRACT In most animals, Bowman’s layer is a feature of the cornea of the eye, and lies between the sur-face epithelium and the stromal extracellular matrix that makes up the bulk of the cornea. It is com-prised of a condensation of disorganised collagen fibrils. However, it has been conjectured that not all species possess Bowman’s layer, and pigs are a species that has classically been stated to lack this anatomical structure, although there is disa-greement in the published literature. Here, we studied the porcine cornea using transmission and scanning electron microscopy (TEM and SEM) to ascertain whether Bowman’s layer existed. TEM identified a thin band of disorganised collagen fi-brils between the epithelial basement membrane and corneal stroma. SEM images of the central and peripheral corneal surfaces, following removal of the corneal epithelium by cell maceration, re-vealed a disorganised meshwork of collagen fibrils, with a highly aligned annulus of collagen at the limbus. In between the peripheral cornea and lim-bus, a “transition zone” is observed where collagenfibrils start to align. Quantification of fibril alignment demonstrates a significant increase in collagen alignment from 0.08 ± 0.04 to 0.33 ± 0.07 (p < 0.001; n = 60; 0 = no alignment, 1 = full alignment) with increasing distance from the corneal centre. These data together lead us to conclude that the porcine cornea does include Bowman’s layer, though it is thin (contributing roughly 0.2% of cor-neal thickness), and thus, reaffirms the porcine cornea’s similarity to its human counterpart and usefulness as a model system.

Keywords: Bowman membrane – Cornea – Scanning electron microscopy – Transmission electron microscopy – Collagen – Porcine

European Journal of anatomy
ISSN 2340-311X (Online)