The cornea is the transparent dome at the front of the eye that is essential to maintaining clear vision. In humans, the cornea is comprised of five layers, but in many other species there are only four. Bowman’s layer is a disorganised band of collagen, beneath the surface epithelium of the cornea, which is missing in many species. However, they still possess fully functional corneas, causing the exact function of this layer to remain a mystery.

Pigs are one of the species classically stated not to have a Bowman’s layer, though there are contradictory reports. This new research uses high-resolution electron microscopy to image the microstructure of the collagen fibrils of the pig’s corneal surface and demonstrates the remarkable similarity to human Bowman’s layer. Image analysis software was also used to quantify the alignment of the collagen fibrils and shows how they become more aligned towards the edge of the cornea, where Bowman’s layer terminates, a sign that there is a structure here distinct from the surrounding collagen.

This paper offers robust support that the pig cornea does include Bowman’s layer, though it is very thin. This further demonstrates the similarity of the pig cornea to the human and supports its continued use as an accessible model, however the function of Bowman’s layer still remains to be realised.

Greg Hammond, SWBio DTP student

Paper: “The microanatomy of Bowman’s layer in the cornea of the pig: Changes in collagen fibril architecture at the corneoscleral limbus” by Greg M. Hammond, Robert D. Young, Duncan D. Muir and Andrew J. Quantock in European Journal of Anatomy.