The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Jan. 20, 1987
Filed:
Oct. 19, 1983
Michael H Freeman, Wales, GB;
Pilkington P.E. Limited, , GB;
Abstract
A bifocal contact lens has diffractive power added to the basic refractive power provided by the material of the lens and the basic curvature of its front and rear surfaces. The diffractive power arises from concentric zones, each providing an asymmetric retardation of light across the zone width to direct design wavelength light predominantly into a required order and sign of diffraction, while other wavelength light is predominantly transmitted at zero order. Design wavelength light from an object at one distance can then be focused by way of diffraction of that order and sign, and other wavelength light from an object at another distance can be focused by way of zero order transmission. Preferably the zones are defined, and the asymmetric retardation provided, by a rear surface contour having steps but which approximates to the required basic curvature.