Multi-Modal Evaluation of Corneal Biomechanics Integrating Optical Coherence Elastography, Nanoindentation, and Uniaxial Tensile Testing

Abstract

Purpose : A comprehensive biomechanical characterization of the human cornea is essential to better understand the structural architecture of corneal tissue. It is also important to quantify the effects of treatment modalities that alter the biomechanical properties of the cornea. The aim of this study was to experimentally quantify biomechanical properties before and after UVA-Crosslinking (CXL) using optical coherence elastography (OCE), nanoindentation (NI), and uniaxial tensile testing (UTT).

Methods : Prior to the experiments, five human donor corneas that were not suitable for transplantation were dehydrated for 24 hours in a cell culture medium supplemented with 15% dextran. To perform OCE and NI, the corneas were clamped in an artificial anterior chamber and exposed to an adjustable retro-corneal fluid pressure (RCP) during the measurements. All corneas were measured before and after CXL (Dresden Protocol) using OCE (via pressure modulation ΔRCP=2mmHg) and NI (RCP=15mmHg). Subsequently, laser-cut corneal tissue strips (6x2x0.15mm) were subjected to UTT.

Results : The mean age of the donors was 75 ± 5.39 years (range 66 - 80 years; 3 females, 2 males). High-resolution OCE analysis showed more positive strain amplitudes in post-CXL tissue when compared to pre-CXL strain maps (-5.9±0.9‰ vs 1.1±2.9‰; p=0.06, respectively for pre- and post-treatment). After CXL, NI showed a significantly increased elastic modulus in the central cornea (mean △183kPa; p<0.01). The corneal tissue exhibited a stiffer, but statistically non-significant behavior under UTT after CXL, which was reflected by an increase tangent modulus (124±77kPa vs 164±70kPa; p=0.12).

Conclusions : This approach allows for quantitative uni - and multiaxial investigation of human corneal biomechanics by optical imaging (OCE) across low strains, absolute force measurements (NI) with moderate strains and confirmation via UTT at high strains. All three measurement methods indicate a stiffening effect of the CXL treatment. This methodology enables a calibration of non-invasive OCE with more traditional methods (NI & UTT).The data obtained here contribute to a better understanding of corneal architecture and can serve as a basis for numerical modeling of corneal tissue.

This abstract was presented at the 2024 ARVO Annual Meeting, held in Seattle, WA, May 5-9, 2024.

 

Fig. 1:CXL effect. A axial strain by OCE; B elastic modulus by NI; C tangent elastic modulus by UTT.