Abstract
Purpose :
Contact lens-assisted cross-linking (CACXL) is designed for thin corneas to protect them from endothelial cell apoptosis by introducing extra thickness. However, depth-dependent biomechanical changes caused by CACXL stay unknown due to lack of proper methods. With the help of non-contact Brillouin microscopy, mechanical properties along depth direction are achieved before and after CACXL. Experiments are conducted to determine the impact of CACXL on regional corneal stiffness as compared to the standard protocol using Brillouin microscopy.
Methods :
Standard cross-linking (CXL) and CACXL were performed on intact fresh porcine eyes. Depth profile of stiffness variation and averaged elastic modulus of anterior, middle and posterior stroma were determined by analyzing Brillouin maps. Corneas were cut into strips to conduct mechanical stress-strain tests after Brillouin microscopy to verify stiffness difference between CXL and CACXL. Each eye served as its own control.
Results :
Based on Brillouin maps, CACXL introduces an average stiffness increase of 7.03% in the anterior region, 2.67% in the middle region and 0.14% in the posterior region. Comparing with standard CXL, the corresponding values in these three regions are 9.81% (P<0.001), 3.70% (P<0.001) and 0.60% (P<0.01). When considering Brillouin stiffness gradient, CACXL introduces a gradient of 0.28 MPa/μm from posterior to anterior stroma. In comparison, the Brillouin stiffness gradient of standard CXL is 0.38 MPa/μm (P<0.001). Stress-strain tests show that at 10% strain averaged Young’s modulus for CACXL is 3.41 MPa and that for standard CXL is 4.50 MPa (P<0.001).
Conclusions :
CACXL leads to less stiffening results compared with standard CXL. For depth-dependent stiffness variation, stiffening effect of CACXL exists primarily in the anterior third of the cornea. Attenuating but continuous stiffening effect can be observed through the whole cornea for both CACXL and standard CXL, though CACXL has a smaller stiffness gradient.
This abstract was presented at the 2019 ARVO Annual Meeting, held in Vancouver, Canada, April 28 - May 2, 2019.