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R. Stupplebeen, I. Cox, T. Green, C. Pinto, C. Schoof, A. Vogt, J. Zuba; Finite Element Analysis Conformation Model of Soft Contact Lenses. Invest. Ophthalmol. Vis. Sci. 2009;50(13):5622.
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Soft contact lenses are designed to conform to the eye, taking on a new shape based on the underlying topography of the cornea and sclera. The relationship of the original design and shape of the eye governs the clinical fitting and optical performance of the lens. To aid in the design of new soft contact lenses, a finite element model (FEM) of soft contact lenses that conform to the human cornea/sclera was developed and validated.
Soft contact lenses were designed in a CAD program and imported into a FEM of a rigid cornea/sclera. In the model, the contact lens was conformed to the cornea using a negative pressure normal to the posterior surface of the lens. The tear film between the lens and the cornea was not modeled. The conformed lens surface shapes were exported from the FEM and imported into a ray tracing model where the impact of lens conformation on the wavefront error of the lens was calculated and represented as Zernike coefficients. Comparisons to models of the unconformed lens demonstrated the change in optical performance of the lens due to conformation to the eye. Single vision spherical (SVS) and multifocal (MF) spherical lenses of differing powers were modeled and measured experimentally.
Conformations of negative power SVS lenses to corneas of varying curvature showed a slight, non-clinically significant, negative change in spherical aberration magnitude with steeper corneas and a positive shift when conformed to flatter corneas. However, conformations of MF lenses to an aspheric cornea showed that across sphere powers, primary, and secondary spherical aberration all became more negative. The change in primary spherical aberration of approximately 0.08 µm is clinically significant and could result in a perceptible change in optical performance if not accounted for in the lens design.
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