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Nandor Bekesi, Carlos Dorronsoro, Susana Marcos; Biomechanical properties and IOP reconstruction from air-puff corneal deformation imaging: validations in model and porcine eyes. Invest. Ophthalmol. Vis. Sci. 2016;57(12):2398. doi: https://doi.org/.
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© ARVO (1962-2015); The Authors (2016-present)
Keratoconus is a disease that alters the mechanical behavior of the cornea. Air-puff corneal dynamic deformation depends on the corneal biomechanical properties, corneal thickness and Intraocular Pressure (IOP). The aim of the study is to estimate both mechanical properties and IOP by means of inverse Finite Element modeling.
Corneal deformation of artificial hydrogel corneal models and enucleated porcine eyes (n = 8) to an air puff were measured by high speed Scheimpflug imaging (Corvis ST) at different IOPs (15 to 45 mmHg). A computational optimization incorporating inverse modeling was utilized in order to obtain mechanical properties from Corvis deformation images. Corneal Finite Element Models were programmed in ANSYS software, using Scheimpflug-based corneal geometry measurements, and literature values for the sclera. Air-puff pressure dynamics was measured in a previous study (Kling et al PLOS One 2014). The parameters of the hyperelastic material model and the IOP were changed in an iterative simulation to fit the simulated deformed shape and the deformation history of the corneas with the measured ones.
The maximum deformation amplitudes (DA) of the artificial corneal model were 0.69, 0.52 and 0.47 mm at IOP of 15, 30 and 45 mmHg, respectively. Simulations resulted in Young's moduli of 0.475, 0.465 and 0.478 MPa for the three IOP levels respectively. DA of porcine corneas were 1.25, 0.869 and 0.624 mm at IOP of 15, 30 and 45 mmHg, respectively. Resulting Young's moduli of the cornea were 0.462, 0.436 and 0.454 MPa. The simulated IOP values matched the nominal IOP values within the step size (1 mmHg) of the optimization.
High speed imaging together with numerical optimization allows simultaneous accurate reconstruction of both corneal mechanical properties and IOP, as validated with models ex vivo. This study extends previous work where the reconstructed mechanical parameters were obtained ex vivo with fixed, known IOP. The proposed method can be useful to monitor corneal mechanical parameters in patients (i.e. keratoconus and cross-linking treatment). Also, it allows absolute estimates of IOP, independent of mechanical parameters, of high relevance to monitoring of glaucoma.
This is an abstract that was submitted for the 2016 ARVO Annual Meeting, held in Seattle, Wash., May 1-5, 2016.
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