Aberration corrected ophthalmic progressive power lenses

Claim 1

- A concavo-convex ophthalmic lens with a progressively varying focal power for correcting high ametropia, comprising two refractive surfaces formed on opposite sides of a block of refringent material, the one of said two opposite refractive surfaces being a simple surface and the other of said two opposite refractive surfaces being a progressive surface, said simple surface and said progressive surface determining therebetween, when the lens is in use, an upper single focus lens portion for far vision having a first focal power and the optical center of which coincides with the optical center of the whole lens, a lower single focus lens portion for near vision having a second higher focal power and which is located around a point socalled the near vision center, and an intermediate progressive power lens portion extending from the optical center of the lens to the near vision center and on either side of the meridian plane of the lens containing said near vision center, the focal power in said intermediate lens portion progressively increasing from said first focal power at said optical center to said second higher focal power at said near vision center according to a predetermined law of progression along said meridian plane containing said near vision center and so-called meridian plane of progression, wherein said progressive surface is corrected for aberration and comprises: an upper surface portion corresponding in position to said upper far vision lens portion, and which is identical to the corresponding upper surface portion of a first aspheric aberration correcting surface operative to correct aberrations for far vision of a firsT single focus lens having the same focal power as the upper far vision lens portion, said upper surface portion having at the optical center a tangential radius of curvature of a first value and a sagittal radius of curvature of a second value, a lower surface portion corresponding in position to said lower near vision lens portion, and which is identical to the corresponding lower surface portion of a second aspheric abberation correcting surface operative to correct aberrations for a vision distance of 0.33 m of a second single focus lens having the same focal power as the lower near vision lens portion, said lower surface portion having at said near vision center a tangential radius of curvature of a third value and a sagittal radius of curvature of a fourth value, said second aspheric aberration correcting surface being such that said second single focus lens exhibits neither astigmatism nor field curvature at a point having a location on said second aspheric aberration correcting surface corresponding to the location of the near vision center on said progressive surface, whereby the ophthalmic lens exhibits neither astigmatism nor field curvature at said near vision center, and an intermediate surface portion corresponding in position to said intermediate progressive power lens portion, of which the intersection with said meridian plane of progression is a curve so-called meridian curve of progression of which the radius of curvature (tangential radius) increases or decreases according as the progressive surface is the concave or convex refractive surface of the lens, respectively, from said first value of the tangential radius of the upper surface portion at the optical center to said third value of the tangential radius of the lower surface portion at the near vision center, so that the tangential focal power in the intermediate lens portion progressively increases according to the predetermined law of progression from the value of the tangential focal power at said optical center to the value of the tangential focal power at said near vision center, and of which the intersection with a plane perpendicular to said meridian curve of progression at a point thereof travelling from the optical center to the near vision center is a curve of which the radius of curvature (sagittal radius) at said travelling point increases or decreases according as the progressive surface is the concave or convex refractive surface of the lens, respectively, from said second value of the sagittal radius of the upper surface portion at the optical center to said fourth value of the sagittal radius of the lower surface portion at the near vision center, so that the sagittal focal power in the intermediate lens portion progressively increases according to the same predetermined law as the tangential focal power from the value of the sagittal focal power at the optical center to the value of the sagittal focal power at the near vision center, the increasing or decreasing rate of the value of the tangential radius being always smaller than the increasing or decreasing rate, respectively, of the value of the sagittal radius.