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A. Sinha Roy, W. J. Dupps, Jr.; Influence of Non-Linear Anisotropy on Corneal Biomechanical Behavior in a 3-Dimensional Whole-Globe Finite Element Model. Invest. Ophthalmol. Vis. Sci. 2008;49(13):669.
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To study the influence of anisotropy on corneal shape before and after LASIK flap creation using 3-D finite element modeling.
A 3-D finite element model (Fig. 1a) of the whole eye was constructed from human MRI images detailing the cornea, sclera, iris, zonules, lens, choroid, retina, and optic nerve head region. Simulations at IOP of 10 mmHg were performed to compare models that incorporated (a) isotropic elastic properties of the cornea and (b) non-linear anisotropic elastic properties culled from ex vivo experimental data (El Sheik et al, personal communication). The combined effect of LASIK flap creation and anisotropy was also evaluated. Retrocorneal structures were modeled as linear elastic materials.
At IOP of 10 mmHg, the isotropic cornea (Fig. 1b) showed peak and minimum displacements in the paracentral and limbal regions, respectively. Displacement along each meridian was uniform. The anisotropic cornea (Fig. 1b) showed peak displacements near the limbus in the diagonal meridian (45-degree axis) as this zone is less stiff than the vertical and horizontal meridia. Sharp displacement gradients are seen at transitions between vertical, horizontal and oblique meridia. These gradients indicate stress concentrations in the paracentral cornea. A flap of 100 microns depth in the anisotropic model redistributes the cornea displacement with peak values near the limbus and center in the diagonal meridian. The sharp displacement gradient among the meridians is reduced after flap creation.
Corneal anisotropy in a whole-eye biomechanical model greatly influences corneal stresses and displacements both before and after LASIK flap creation. Corneal material anisotropy leads to meridional differences in corneal curvature change that may account for astigmatic effects of lamellar disruption.
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