Ophthalmic spectacle lenses having a hyperbolic surface

Abstract

Ophthalmic spectacle lenses are provided with powers ranging from -20 to +7 diopters, for minus powered lenses, with a posterior surface of a hyperboloidal form and, for positive powered lenses with an anterior surface of a hyperboloidal form. Such hyperboloidal forms are computed by modifying the conventional formulae used for "Best Form" spherical lens surfaces from y.sup.2 =2000(n'-n).times./Fo-x.sup.2 to the formulae y.sup.2 =2000(n'-n).times./Fo-px.sup.2 ; where `p` has a value ranging from 0 to -4, Fo is the optical power of the lens at the intersection of the lens surface and the optic axis, Fo being given as follows: Fo=1000(n'-n)/ro where ro is the radius of the lens surface at the optic axis, and where (n'-n) is the difference between the refractive indices on opposite sides of the lens surface taken in the direction of light travel to the eye through the lens, all dimensions in the formulae being in millimeters and x and y being orthogonal co-ordinates.

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