The molecular basis of corneal transparency

Keratocyte and fibroblast phenotypes in the repairing cornea.

AIM—To analyse the human corneal stroma in extreme hydration to discover if its structure is responsible for corneal stability.
METHODS—Corneas in several hydration states were used: postmortem control corneas (PM; n=3), corneas left for 1 day in phosphate buffered saline (PBS; n=4), and corneas left for 1 day (n=4), 2 days (n=4), 3 days (n=2), and 4 days (n=4) in deionised water. All corneas were fixed under standardised conditions and processed for light and electron microscopy. In addition, two fresh corneas from the operating theatre were studied which were processed 6 months after storage in sodium cacodylate buffer.
RESULTS—After 1 day in deionised water maximal stromal swelling was reached which did not change up to 4 days. The stroma of deionised water corneas (1400 µm) was much thicker than that of PBS corneas (650 µm) and PM corneas (450 µm). Deionised water treatment led to disappearance of all keratocytes leaving only remnants of nuclei and large interlamellar spaces. In these specimens the distance between the collagen fibres had increased significantly, but the diameter of the collagen fibres did not seem to be affected. A remarkable observation was that the most anterior part of the stroma (100-120 µm) in all deionised water specimens and those stored for 6 months in buffer was not swollen, indicating that the tightly interwoven anterior lamellae are resistant to extreme non-physiological hydration states.
CONCLUSIONS—The rigidity of the most anterior part of the corneal stroma in extreme hydration states points to an important role in maintenance of corneal curvature. Since a large part of this rigid anterior part of the stroma is either removed (PRK) or intersected (LASIK), it is possible that in the long run patients who underwent refractive surgery may be confronted with optical problems.

https://bjo.bmj.com/content/bjophthalmol/85/4/437.full.pdf

The specific architecture of the anterior stroma accounts for maintenance of corneal curvature

Human Corneal Anatomy Redefined: A Novel Pre-Descemet's Layer (Dua's Layer)

The last 5 years have seen a marked increase in research on keratan sulfate (KS) and a concomitant increase in our understanding of the range of molecules that carry this adaptable polysaccharide. More than 15 KS-linked proteins have been identified and many of the genes encoding these have been cloned. KS-containing molecules have been identified in numerous epithelial and neural tissues in which KS expression responds to embryonic development, physiological variations, and to wound healing. A corneal cell culture system has been developed in which long-term KS biosynthesis is maintained. Progress has been made toward identification of the glycosyl- and sulfotransferases responsible for KS biosynthesis. A mouse knockout of a corneal KS-proteoglycan has provided the first experimental support for the role of KS in corneal transparency. Evidence has also been presented supporting functional roles of KS in cellular recognition of protein ligands, axonal guidance, cell motility, and in embryo implantation. These findings have served to expand the concept of what keratan sulfate is and the potential roles it may play in the cellular biology of diverse tissues.

/pdf/mini-review-keratan-sulfate-structure-biosynthesis-and-wycdlz9l15.pdf

MINI REVIEW Keratan sulfate: structure, biosynthesis, and function

The hydration of proteoglycans of bovine cornea

Keratan sulfate was isolated from bovine cornea. The water vapor sorption isotherms were obtained on both sodium and calcium salts of keratan sulfate at different temperatures. Deuterated water sorption isotherms were obtained on sodium keratan sulfates. The infrared spectra of the keratan-sulfate was monitored as a function of water and D2O uptake. The results are discussed in terms of an open polymer matrix that exists in the solid state of keratan sulfate.

Boake Plessy

Papers

The hydration of proteoglycans of bovine cornea

Water vapor sorption of keratan sulfate.