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Zhaolong Han, Cynthia Roberts; Investigation of corneal vibration during air puff deformation using numerical approaches with clinical validation. Invest. Ophthalmol. Vis. Sci. 2013;54(15):1628.
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© ARVO (1962-2015); The Authors (2016-present)
To investigate cornea dynamics under air pulse deformation and relate vibration amplitude to corneal elasticity.
The phenomenon of in vivo cornea dynamic vibration under air pulse deformation is predicted using a nonlinear dynamic model based on a simplified kinematic differential equation describing corneal motion, y(t), as a function of equivalent external forces, corneal mass (m), damping constant (c) representing the viscoelastic capacity of the cornea, and the coefficient of corneal elasticity, (k). Corneal vibration is validated clinically with two keratoconic subjects and two normal subjects greater than 50 years of age with acquired measurements using the CorVis ST, a Scheimpflug system capturing approximately 140 images of a single horizontal corneal meridian during a 30ms air puff at greater than 4,000 frames/s, as well as the Ocular Response Analyzer (ORA) to provide corneal compensated intraocular pressure (IOPcc). In addition a 3D finite element (FE) cornea model is constructed in the environment of ANSYS 11.0 to simulate the results produced.
Modeling predicts greater vibration amplitude with lower coefficient of elasticity, as seen in Figure (a), which is validated with clinical measurements. Keratoconic subjects demonstrated greater vibration amplitude than older normal subjects. An example of vibration data from one keratoconic subject is shown in Figure (b) which represents corneal surface motion of a single point through the time course of the air puff. Also shown are two meshes from finite element modeling with high and low elasticities in Figure (c), which demonstrate greater depth of deformation with lower elastic modulus at consistent IOP.
Both numerical methods and clinical measurements show that softer corneas demonstrate larger vibration amplitude and greater depth of deformation compared to stiffer corneas. Future work will investigate the influence of IOP on corneal elasticity and vibration amplitude, as well as increase the complexity of the numerical modeling.
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