Nanoindentation Derived Mechanical Properties of the Corneoscleral Rim of the Human Eye

Abstract

The corneoscleral rim of the eye represents a region with unique anatomical properties due to its location between the cornea and sclera / conjunctiva. It further has unique functional properties due to the location of adult corneal epithelial stem cells in the rim structure (limbus) itself. These stem cells are essential for the regeneration of the corneal epithelium and for preventing the conjunctival epithelium from growing onto the corneal surface, which could result in blindness. Survival and self-renewal properties of stem cells are known to depend on specific biological and biomechanical properties of its niche environment. We therefore aimed to measure the local mechanical properties of the human corneoscleral rim using a novel nanoindentation device (Bioindenter CSM Instruments, Neuchâtel, Switzerland) developed for soft tissues evaluation. Nanoindentation was performed using a spherical indenter of 0,5mm radius, a maximal load ranging between 20 μN to 30 μN and a penetration depth of several μm to 60μm. The hold period at maximum load was 180 seconds. Youngs modulus (E) was calculated using a Hertzian fit to the loading data. E of the central cornea was in the range of 19 kPa, while in the scleral region we found 17 kPa and the limbal rim region 10 kPa. Considerable creep relaxation occurred during the hold period at maximum load, which scaled with the elastic modulus of the different structures. These results reveal biomechanical properties of the corneoscleral rim with distinct mechanical properties for the three anatomical regions.