Finite Element Model of Human Cornea to Investigate the Impact of Keratoconus and Crosslinking on Optical Quality
Elizabeth Diaz PhD Defense, Advised by Professors Paul Funkenbusch and Amy Lerner
Friday, August 19, 2022
This work is focused on developing a finite element model (FEM) of the cornea to investigate the impact of keratoconus (KC) and crosslinking (CXL) on the cornea through optical aberrations. First, we developed a finite element model of the human cornea that can capture the biomechanics of keratoconus and crosslinking through localized material property changes to test the impact of different input variables. We concluded that input variables such as degree of asymmetry of the natural geometry, depth dependence of material properties, and fibers' degree of dispersion play a key role in the outcomes of the model. All the variables deemed most important were incorporated into the model following their most realistic settings while variables with less impact were treated through a simpler approach based on the principles of design of experiments (DOE) and analysis of variance (ANOVA).
The KC model captures the thinning and bulging typical of the early stages of the ectatic disorder, by altering material properties locally. In addition, optical features associated with KC were observed in our model of KC such as the increment in curvature (+4 D), as well as the significant increments in higher order aberrations (HOAs), such as vertical coma. Clinical references confirmed the trend observed in aberrations computed from our model agreed with the observed in KC. Especially, the increment in vertical coma (and total coma), as well as HOAs which percent relative to the total aberrations increases considerably for KC corneas. In addition, crosslinking treatment was simulated on the keratoconic cornea models. The stiffening effect was confirmed through curvature flattening, reduction of strain and stresses, particularly the concentrated stresses in the limits of the KC region, as well as changes in optical aberrations.