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Kara Maki, David Ross; Understanding Contact Lens Mechanics. Invest. Ophthalmol. Vis. Sci. 2014;55(13):6057.
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The purpose of this study is to better understand how the design of contact lenses can be optimized for patient comfort and ocular fit. To do so, we present a new approach to computing the suction pressure under a soft contact lens. When a contact lens is placed on an eye, it is subjected to forces from both the tear film in which it is immersed and the blinking eyelid. In response, the lens bends and stretches. These forces center the lens, and they produce the suction pressure that keeps the lens on the cornea.
We couple fluid and solid mechanics to determine the most prominent forces acting on the lens. We find that the important mechanical property of the contact lens for producing suction pressure is stretching, i.e., elastic tension. We assume the contact lens must conform to the shape of the eye. This perspective allows us to derive a terse system of ordinary differential equations to determine the suction pressure under the contact lens. We solve this system numerically for various eye shapes and contact lens shapes.
We probe how the different contact lens design parameters, such as shape, thickness, and material properties, influence the suction pressure. Our numerical results indicate for a fixed eye shape that the suction pressure at the center of the lens increases in magnitude as the radius of curvature of the lens is increases, whereas the positive suction pressure at the edge decreases; the negative pressure generated in the transition region also increases in magnitude with increasing radii of curvature. In addition, we found that thinner contact lenses produced smaller suction pressures.
We developed a mathematical model to characterize the suction pressure under the contact lens. The system of ordinary differential equations captures the basic physics, the elastic tension, needed to begin to understand a “working” contact lens. Therefore, we can begin to create “rules of thumb” for contact lens design.
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