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Multifocal birefringent lens system

  • US 4,981,342 A
  • Filed: 08/01/1988
  • Issued: 01/01/1991
  • Est. Priority Date: 09/24/1987
  • Status: Expired due to Fees
First Claim
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1. A multifocal non-achromatized birefringent lens system which comprises:

  • (a) a first lens component which is a first birefringent lens possessing two positive or negative powers Doa and Dea in which Doa is the value of the power of the lens associated with the ordinary rays of said lens and Dea is the value of the power of the lens associated with the extraordinary rays of said lens, the ratio Doa /Dea being determined by the indices of refraction and the orientation of the crystal optic axis of the lens; and

    ,(b) a second lens component adjacent to said first lens component, the curvatures of the opposed surfaces of the first and second lens components being substantially identical or complementary, said second lens component being selected from the group consisting of(i) a second birefringent lens possessing two different positive or negative powers Dob and Deb in which Dob is the value of the power of the lens associated with the ordinary rays of said lens and Deb is the value of the power of the lens associated with the extraordinary rays of said lens, the ratio Dob /Deb being determined by the indices of refraction and the orientation of the crystal optic axis of the lens, and(ii) an isotropic lens possessing a positive, negative, or zero power D,provided that in the case of the lens system comprising first birefringent lens (a) and second birefringent lens (b) (i), said first birefringent lens (a) and said second birefringent lens (b) (i) are shaped and positioned such that at least two out of the four resulting powers Doa +Dob, Doa +Deb, Dea +Dob and Dea +Deb of the lens systems are selectable independently from one another, andin the case of the lens system comprising first birefringent lens (a) and isotropic lens (b) (ii), said first birefringent lens (a) and said isotropic lens (b) (ii) are shaped and positioned such that both of the resulting powers Doa +D and Dea +D are selectable independently from one another,said lens system exhibiting no unwanted power or powers, andsaid lens system employed as a contact lens.

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