Refractive changes of a new asymmetric intracorneal ring segment with variable thickness and base width: A 2D finite-element model

Abstract

Purpose To evaluate the local geometric effects of a unilateral intrastromal ring segment with a combined variation of ring thickness and base width in a finite element simulation, and to compare it against the isolated effect of thickness or base width variation alone. Methods A two-dimensional finite-element model of a transversely isotropic cornea was created assuming either axisymmetric stress or plane strain condition. The model geometry was composed of a three-layered corneal tissue (epithelium, anterior and posterior stroma) fixed at the limbus. The implantation of a triangular-shape asymmetric ring segment with varying ring thickness (150 to 300 μm) and base width (600 to 800 μm) was simulated. Also, changes induced by thickness or base width alone were studied and compared their combined effect in the asymmetric ring segment. Geometrical deformation of the simulated cornea and sagittal curvature were the main parameters of study. Results Increasing ring thickness and base width along the arc of the asymmetric ring segment produced a more pronounced flattening in this part of the ring. The asymmetric design did find a good balance between maximizing corneal flattening at one end and minimizing it at the other end, compared to the isolated effect of ring thickness and width. Ring thickness was the most robust parameter in flattening both, the central and peripheral cornea. Conclusion The finite-element model permitted a theoretical study of corneal deformation undergoing implantation of realistic and hypothetical ring geometries. Intracorneal asymmetric ring segments with varying thickness and base width can be a good alternative in corneas with asymmetric keratoconus phenotypes.

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

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Ex vivo, in vivo and in silico studies of corneal biomechanics: a systematic review

“…However, starting from the experimental-derived evidence, novel promising approaches can be introduced by computational modelling, in particular finite element methods (FEMs), that are applied successfully in several surgical fields [ 35 – 39 ] and are spreading also in ophthalmic research [ 40 , 41 ]. Reliable FEMs require to be validated by means of strong comparisons with physical reality, by implementing healthy and pathological conditions, simulating the experimental set-ups and obtaining numerical results able to correctly report what has happened in clinics or labs.…”

High post-penetrating keratoplasty astigmatism can be mitigated using specialized intrastromal corneal ring segment implants

“…Recently, a finite element simulation study demonstrated that the use of an 800-µm base while maintaining the same ring thickness resulted in the strongest peripheral and central flattening. [ 3 ]…”