Considerations in Contact Lens Use Under Adverse Conditions Proceedings of a Symposium (1991) / Chapter Skim
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Mechanical Aspects of Soft Contact Lenses
Mechanical Aspects of Soft Contact Lenses
Pages 44-50
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From page 44... ...
In any case, following a blink the lens is deformed and displaced slightly; it then recovers its original position in the period between blinks. The way it recovers this centered position is essentially by balancing the forces associated with the elastic deformation against the viscous resistance of the fluid in the tear film behind it.
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From page 45... ...
These forces, in conjunction with the action of the lid, permit a tear film of greater thickness behind the lens; consequently, there is much more movement of the hard lens on the eye. In modeling the soft lens, the central portion is taken to be an elastic sheet that resists stretching, and the region near the edge is considered to be an elastic shell that resists bending.
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From page 46... ...
Figure 2 shows the evolution of shape as the pressure decreases. This is a prediction based typical lens material and a realistic thickness.
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From page 47... ...
. We have predicted the deformed configuration of the soft lens, the pressure distribution applied to its back, and the tear film thickness beneath it.
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From page 48... ...
This would be the case if there were a minimum of energy. Unfortunately, as the lens contacts the cornea on the center line and this central contact begins to spread, the energy decreases further.
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From page 49... ...
normalized by the cube of the central radius a of the lens and Young's modulus versus the normalized tear film pressure. purely mechanical analysis predicts that the configuration with the least energy is that with the lens in complete conformity with the eye.
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From page 50... ...
Holden 1986 Forces developed beneath hydrogel contact lenses due to squeeze pressure. Physics in Medicine and Biology 30~6~:635-649.
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