Localized Refractive Changes Induced by Symmetric and Progressive Asymmetric Intracorneal Ring Segments Assessed with a 3D Finite-Element Model

To build a representative 3D finite element model (FEM) for intracorneal ring segment (ICRS) implantation and to investigate localized optical changes induced by different ICRS geometries, a hyperelastic shell FEM was developed to compare the effect of symmetric and progressive asymmetric ICRS designs in a generic healthy and asymmetric keratoconic (KC) cornea. The resulting deformed geometry was assessed in terms of average curvature via a biconic fit, sagittal curvature (K), and optical aberrations via Zernike polynomials. The sagittal curvature map showed a locally restricted flattening interior to the ring (Kmax -11 to -25 dpt) and, in the KC cornea, an additional local steepening on the opposite half of the cornea (Kmax up to +1.9 dpt). Considering the optical aberrations present in the model of the KC cornea, the progressive ICRS corrected vertical coma (-3.42 vs. -3.13 mu m); horizontal coma (-0.67 vs. 0.36 mu m); and defocus (2.90 vs. 2.75 mu m), oblique trefoil (-0.54 vs. -0.08 mu m), and oblique secondary astigmatism (0.48 vs. -0.09 mu m) aberrations stronger than the symmetric ICRS. Customized ICRS designs inspired by the underlying KC phenotype have the potential to achieve more tailored refractive corrections, particularly in asymmetric keratoconus patterns.

Automated summary

A hyperelastic shell finite element model was developed to investigate the optical changes induced by different intracorneal ring segment (ICRS) geometries. The results showed that customized ICRS designs have the potential to achieve more tailored refractive corrections, particularly in asymmetric keratoconus patterns.