Abstract
Aim or Purpose: To describe the effect of varying scleral stiffness on the biomechanical deformation response of the cornea under air-puff loading via a finite-element (FE) model.Methods: A two-dimensional axisymmetric stationary FE model of the whole human eye was used to examine the effects varying scleral stiffness and intraocular pressure (IOP) on the maximum apical displacement of the cornea. The model was comprised of the cornea, sclera, vitreous, and surrounding air region. The velocity and pressure profiles of an air-puff from a dynamic Scheimpflug analyzer were replicated in the FE model, and the resultant profile was applied to deform the cornea in a multiphysics study (where the air-puff was first simulated before being applied to the corneal surface). IOP was simulated as a uniform pressure on the globe interior. The simulation results were compared to data from ex vivo scleral stiffening experiments with human donor globes.Results: The FE model predicted decreased maximum apical displacement with increased IOP and increased ratio of scleral-to-corneal Young's moduli. These predictions were in good agreement (within one standard deviation) with findings from ex vivo scleral stiffening experiments using human donor eyes. These findings demonstrate the importance of scleral material properties on the biomechanical deformation response of the cornea in air-puff induced deformation.Conclusion: The results of an air-puff induced deformation are often considered to be solely due to IOP and corneal properties. The current study showed that the stiffer the sclera, the greater will be the limitation on corneal deformation, separately from IOP. This may have important clinical implications to interpreting the response of the cornea under air-puff loading in pathologic conditions.
Highlights
It has been shown that the biomechanical response of the cornea under air-puff deformation is significantly affected by its boundary properties (Elsheikh, 2010; Metzler et al, 2014)
Metzler et al showed that the human cornea behaves more stiffly in the case of a corneoscleral button mounted on a rigid artificial anterior chamber as opposed to a cornea that remains connected to an intact whole globe at physiologically normal values of intraocular pressure (IOP)
Because traditional methods for biomechanical evaluation are limited to ex vivo studies, finite-element (FE) models have been explored as a way to evaluate in vivo properties and response (Elsheikh, 2010; Girard et al, 2015; Pandolfi and Boschetti, 2015; Ariza-Gracia et al, 2016)
Summary
Biomechanical markers are being explored to improve screening, diagnosis, and management of diseases such as keratoconus and glaucoma (Liu and Roberts, 2005; Elsheikh et al, 2009; Ruberti et al, 2011; Coudrillier et al, 2012; Tang and Liu, 2012; Hon and Lam, 2013; Metzler et al, 2014; Girard et al, 2015; Sinha Roy et al, 2015; Ariza-Gracia et al, 2016; Roberts, 2016). Metzler et al showed that the human cornea behaves more stiffly in the case of a corneoscleral button mounted on a rigid artificial anterior chamber (simulating stiffer scleral material properties) as opposed to a cornea that remains connected to an intact whole globe at physiologically normal values of IOP. Their results suggest that the scleral properties have an important impact on the deformation response of the cornea under air-puff loading (Metzler et al, 2014)
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