Numerical modeling and characterization of eye deformation response to an air-puff with varying corneal and scleral moduli

Abstract

Purpose : The purpose of this study is to characterize biomechanical impact of corneal and scleral stiffness on eye deformation response during air-puff test.

Methods : Human eye comprising cornea, sclera, vitreous, and fat was generated using a two-dimensional axisymmetric model (Figure 1A). A Finite Element Analysis (FEA) framework was developed using ABAQUS 6.1 software to evaluate the effect of corneal and scleral moduli reduction on the maximum apical deflection of the cornea as well as maximum displacement of the whole eye. The pressure profile of an air-puff was taken from previous experimental study¹ using hot wire anemometry. Cornea, sclera, and fat material properties were defined based on literature² as Hyperelastic, whereas vitreous and fat were defined as linear elastic with viscoelastic material properties. The following four conditions were modeled in this study: 1) control case with nominal corneal and constant IOP = 10 mmHg applied to the posterior cornea and sclera.; 2) 15% reduction in corneal modulus; 3) 30% reduction in corneal modulus; 4) 30% reduction in both corneal and scleral moduli.

Results : FEA results predicted increase in maximum apical deflection of the cornea and decrease in maximum whole eye motion in experiments 2, 3, and 4. Figure 1B shows the impact of each experiment on corneal and whole eye response.

Conclusions : Biomechanical markers such as corneal deflection and whole eye motion have been used to assess the cornea and ocular biomechanical state in diseases such as glaucoma and keratoconus. Therefore, it’s important to recognize that whole eye motion is affected by both the properties of the cornea and sclera, without changing the properties of the orbital contents. The findings of this study indicate that without any changes to vitreous and fat characteristics and by decreasing corneal and scleral moduli, whole eye motion decreased while corneal deflection increased. These results can be furthered characterized to improve clinical biomechanical assessment methodologies using air-puff techniques.
¹C. J. Roberts et al., J Refract Surg, 2017.
²Liu, et al. J Biomech, 2013.

This is a 2020 ARVO Annual Meeting abstract.

 

Figure 1: A) Whole eye model consist of Cornea (yellow), Sclera (red), Vitreous (blue), and Orbital fat (grey); B) Results of the four experiments showing effect of each factor on Maximum Apical Deflection of Cornea and Maximum Whole Eye Motion.