Abstract
Purpose :
Previous studies have demonstrated that corneal keratocyte differentiation, motility and mechanical behavior are influenced by extracellular matrix (ECM) stiffness and mechanical stress. Most biomechanical models of the surgical techniques used to treat keratoconus or to correct for refractive errors focus on predicting corneal shape. Here, we have created finite element (FE) models to predict how these procedures impact the spatial distributions of mechanical stress to which keratocytes are exposed.
Methods :
A 2D axisymmetric FE model was developed in ANSYS to simulate the re-distribution of mechanical stress within the cornea following corneal cross-linking (CXL), photorefractive keratectomy (PRK) or phototherapeutic keratectomy (PTK). The cornea was modeled as a Mooney-Rivlin hyperelastic material, as described previously. To simulate CXL, the stiffness of the anterior 50% of the cornea was doubled in a central, circular region (8 mm diameter). For PTK and PRK, standard clinical ablation profiles were incorporated. We also evaluated how altering the surgical parameters (e.g. size and stiffness of CXL area, PRK ablation depth), IOP or stromal material properties impacted the stress distribution in the cornea.
Results :
We found that each surgical procedure substantially re-distributes mechanical stresses within the cornea (Figure 1). In the central cornea, following CXL, the stress in the anterior cornea increases, whereas the stress in the posterior cornea decreases. In contrast, stress in both the anterior and posterior cornea increase following PTK or PRK. In the corneal periphery, the stress distribution generally remained similar to the control (unoperated) cornea. Altering the simulated surgical parameters, IOP or material properties changed the magnitude of the responses, but the overall patterns of stress were similar. Because of the nonlinear stress-strain relationship, increases in stress also increase the effective tissue stiffness.
Conclusions :
In addition to altering corneal shape, corneal surgical procedures can have a profound impact on the regional stress distribution within the stroma and its response to fluctuations in IOP. These factors may influence keratocyte wound healing responses and long term stromal physiology.
This is a 2021 ARVO Annual Meeting abstract.