Abstract
Purpose :
Optical coherence elastography (OCE) is a promising technique for high-resolution strain imaging in ocular tissues. We have recently developed an approach to capture corneal strain maps when subjecting the eye to intraocular pressure (IOP) changes in a range similar to diurnal physiological changes. The purpose of the current study was to assess local differences in corneal deformation and axial strain in ex vivo porcine corneas that have been treated with corneal cross-linking (CXL) treatment.
Methods :
6 freshly-enucleated whole porcine eye globes were obtained and prepared for CXL. First, the epithelium was removed and 0.1%-riboflavin instilled for 30min. Subsequently, half of each cornea was subjected to UV irradiation at either 3mW/cm2 for 30min or 9mW/cm2 for 10min, the non-irradiated part served as control. For strain imaging, eyes were mounted on a customized silicon mold and initial IOP was adjusted to 15mmHg by inserting a needle connected to a pressure control unit into the anterior chamber. Different levels of corneal strain were induced by first in- and then decreasing IOP by a total of 5mmHg, in steps of 1mmHg. Each IOP step was adjusted by a customized pressure system and controlled by a closed-loop routine written in LabView. 12 cross-sectional B-scans were recorded at each IOP step. The axial displacement maps were computed from magnitude and phase changes in the raw OCT signal. Strain maps were generated by computing the gradients in axial direction.
Results :
Differences between CXL and control tissue were not directly visible in axial strain maps, but became apparent when performing local comparisons: Mean overall elastic modulus was 1.1x higher (p=0.014) in cross-linked compared to control tissue (16.0±0.4 vs 14.5±0.4 kPa). A hysteresis between IOP increase and decrease was observed, which was lower after CXL than in controls (1.18 vs 1.47 Pa, p<0.022). Axial strain was higher in the posterior half compared to the anterior half cornea, both with CXL (factor 2.48±0.9) and in controls (factor 2.59±0.5).
Conclusions :
The derived corneal strain maps permit a localized comparison of biomechanical characteristics. A higher elastic modulus along with a smaller hysteresis after CXL indicates increased stiffness and reduced viscosity confirming previous literature.
This abstract was presented at the 2019 ARVO Imaging in the Eye Conference, held in Vancouver, Canada, April 26-27, 2019.