Abstract
Purpose :
To elucidate the hierarchical deformation mechanisms of human corneal collagen under controlled inflation of physiological and pathological magnitudes.
Methods :
6 human donor corneas with scleral rim were mounted onto a bespoke sealed cell, which was connected via two pressure regulators and an expansion vessel to a source of compressed nitrogen. The cell included a window transparent to X-rays and was connected to translation and rotation stages inside beamline I22 at the Diamond Light Source synchrotron, UK. Images were acquired naso-temporally across the cornea from limbus to limbus at intraocular pressures of 5.5 mmHg, 17.5 mmHg and 40 mmHg. These increments were chosen for comparison with previous static results in the literature and to mimic the normal physiological state and ocular hypertension.
Results :
The inflation apparatus was able to maintain pressure to an accuracy better than 0.1 mmHg. Features corresponding to collagen fibril diameter, spacing, D-period and orientation as well as tropocollagen spacing and orientation were measured simultaneously. Preliminary analysis revealed a radial distribution of strain (manifested as a change in D-period) across the cornea, which was accentuated in the outer periphery and limbus. In general, the interfibrillar spacing in the periphery and limbus (where collagen fibrils are arranged circumferentially) was found to increase with pressure.
Conclusions :
The trends in D-period strain are indicative of bulging under increased pressure, which is pronounced at the limbus and the outer periphery. This agrees with the general consensus that the outer periphery and limbus act as a buffer zone, which takes up most of the strain under changes in intraocular pressure, and thus minimises changes in focussing power of the cornea. Further in-depth analysis of this data will allow us to calculate the supramolecular twist (which gives rise to a spring-like stretch in collagen fibrils) and examine in more detail the hierarchical response of corneal collagen to changes in intraocular pressures.
This abstract was presented at the 2022 ARVO Annual Meeting, held in Denver, CO, May 1-4, 2022, and virtually.