Abstract
Experimental inflation tests, conducted on 90 pig corneas before and after corneal collagen crosslinking (CXL) treatment, are simulated with the finite element method. The experimental sample consists of five groups of corneas treated with different UV-A irradiation times (2.5, 5, 10, 15, and 20 min) at constant irradiance 9 mW/cm2. The linear elastic shell theory is used to estimate the equivalent material stiffness of the corneas, revealing that it increases with the exposure time in CXL corneas. In the view of numerical simulations, a simple mechanical model assuming piecewise constant elastic modulus across the corneal thickness is introduced, to estimate the effective increment of the material stiffness in the anterior stroma and the effective depth of the stiffness increment. The two effective quantities are used in the finite element models to simulate the post-CXL tests. Numerical models are able to describe the mechanical effects of CXL in the cornea. The increment of equivalent material stiffness has to be ascribed to a localized increment of the material stiffness in the anterior layers of the cornea, while the posterior layers preserve the original material stiffness. According to the simplified model, the increment of the material stiffness of the anterior cornea increases with the irradiation dose, while the effective reinforcement depth decreases with the irradiation dose. This trend, predicted by a simple mechanical model by imposing equilibrium and compatibility, has been verified by the numerical calculations that captured the global mechanical response of the corneas in untreated and post-CXL conditions.
Highlights
The cornea is organized into five principal layers: the epithelium, the Bowman lamina, the stroma, the Descemet lamina, and the endothelium, in order from anterior to posterior surfaces [1]
Acknowledged outcomes of CXL are the stabilization of ectasia and the halting of the keratoconus evolution
CXL can be performed according to several protocols. Both riboflavin dose and time interval between sequential imbibition are important during the intervention, but, according to the clinical observations, the most relevant parameter for the cornea stiffening is the irradiation dose, i.e., the total amount of energy irradiated during the entire procedure
Summary
The cornea is organized into five principal layers: the epithelium, the Bowman lamina, the stroma, the Descemet lamina, and the endothelium, in order from anterior to posterior surfaces [1]. The stroma, the carrying structure of the cornea, is composed of a matrix of elastin and proteoglycans embedding collagen fibrils, organized into a highly specialized hierarchical architecture enabled by chemical bonds (crosslink) able to provide the necessary mechanical stiffness and to shape the curvature of the lens [2]. From the geometrical point of view, the topography and the pointwise thickness are the most relevant parameters; from the material point of view, fundamental are the composition, the microstructure, and the mechanical properties (material stiffness, material strength, time dependence) of the single constituents [5]. The quasi-spherical shape of the cornea is the optimal mechanical response of the structure to the action of the uniform intraocular pressure (IOP) exerted by the aqueous humor [2, 6]. Typical diseases of the cornea are keratoconus and post-laser assisted in situ keratomileusis (LASIK) ectasia
Sign-in/Register to view highlights & summary Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a callDisclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.
