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J. F. Bille, H. Zhang; Finite Element Modeling (FEM) of Intrastromal Presbyopia Treatment Procedures Using the Femtec Femtosecond Laser. Invest. Ophthalmol. Vis. Sci. 2009;50(13):2801.
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To develop a three-dimensional, non-linear, non-homogeneous finite element model of the human cornea to simulate customized femtosecond laser intrastromal surgical patterns for the correction of presbyopia and prediction of potential surgical outcomes.
In a new surgical procedure (IntraCOR) employing the FEMTEC (20/10 Perfect Vision AG, Heidelberg) femtosecond laser, an infrared femtosecond laser interacts directly with corneal stroma without damaging Bowman’s layer or endothelium. Customized surgical patterns are calculated according to the pre-surgical patient data and are applied to the stromal tissue within the cornea. Due to the biomechanical changes to the stroma induced by the plasma-mediated photodisruption laser-tissue interaction process and the existing intraocular pressure (IOP), the curvature of the cornea is reshaped in a defined manner. A finite element modeling (FEM) method is used to study the biomechanical properties of the cornea and to predict the surgical effects. Different parameters to describe the biomechanical properties are chosen to simulate epithelial, Bowman’s layer and stroma tissues. The intraocular pressure is homogeneously applied to the endothelium of the cornea. Customized intrastromal patterns are simulated with the FEM-model to calculate biomechanical changes and induced curvature alterations. Refractive power changes related to curvature alterations are further evaluated to estimate surgical outcomes.
The current finite element corneal model demonstrates that, after intrastromal presbyopic surgical patterns are applied, the refractive power of the central cornea is increased which results in improved near visual acuity. Distance visual acuity is minimally affected. The results are comparable with Pentacam observations of the eyes of patients who underwent IntraCOR presbyopic treatments.
A new three-dimensional, non-linear, heterogeneous finite element model of the human cornea has been established to study the biomechanics of the cornea and to predict surgical outcomes induced by the new femtosecond laser based, intrastromal presbyopic correction.
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