Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Patent
1992-08-25
1995-10-03
Sugarman, Scott J.
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
G02C 706
Patent
active
054556422
DESCRIPTION:
BRIEF SUMMARY
BACKGROUND OF THE INVENTION
The present invention relates to a configuration of a progressive power lens for correcting presbyopia, and particularly relates to a progressive power lens which is capable of reducing in weight and thickness as well as providing an excellent field of view by improving aberration thereof.
BACKGROUND ART
As typically shown in Japanese examined patent publication No. 52(1977)-20271, conventional progressive power lenses consist of a region used for seeing relatively distant objects (hereinafter referred to as distant portion), a region for seeing relatively near objects (hereinafter referred to as reading portion), and a region, located between the distance portion and the reading portion, for seeing objects which are at intermediate distances. These portions are arranged as shown in FIG. 9A. Here, in FIG. 9A the reference numeral 1 designates a distance portion, 2 a reading portion, and 3 an intermediate portion. The distance portion 1 and the intermediate portion are imaginally separated by the boundary line 5 whereas the intermediate portion and the reading portion 2 the boundary line 6. In practical lenses, regions are however smoothly joined to each other, and there is no clear boundary line. Furthermore, each of the regions is substantially and horizontally divided by the principal gazing line. The principal gazing line is an imaginary line along the movement of the line of sight when the spectacles are put. In progressive power lenses, objects are often watched in the vicinity of the principal gazing line, and this portion is particularly carefully designed in view of optical performance.
In a single progressive power lens, there are three different regions; a distance portion 1, a reading portion 2 and an intermediate portion 3, and thus importance of design is conventionally placed on how to smoothly join these regions. For this reason, many inventions are made to smoothly connect the regions by forming refracting surfaces into complicated aspherical shapes.
FIG. 11 illustrates a section of this progressive power lens taken along the vertical principal gazing line which passes substantially centrally each of the regions previously described. In the sectional shape of each of conventional progressive power lenses, the object side refracting surface 8 has a feature such that the lower portion of the lens is more bent toward the eyeball than the upper portion. For this reason, a lens which is thin in the reading portion and thick in the distance portion is, as indicated by the broken line 11 in FIG. 11, produced when the lens is produced according to the ordinary method without any prescription for prismatic power. To improve the thickness of this distance portion, a prism which has no object to correct squint of the base in the direction of 270.degree. is put or provided, and processing is made as shown in the solid line 12, so that reduction in thickness is achieved not only in the distance portion but also in the whole lens.
In Japanese examined patent publication No. 2(1990)-39769, improvement of chromatic aberration in the reading portion and reduction in thickness are achieved by providing a prism with the base in the direction of 90.degree. in the case where the distance portion region 1 has a prescription for correcting myopia.
In general lenses, there are defects in optical performance called aberration, and in portions which are away from the optical axis 7 substantially at the center of the lens, these often produce problems which appear as fuzziness and distortion of images. Particularly, large refractive power lenses are necessary to improve aberration. In conventional progressive power lenses, there has been no attempt to improve in aberration since emphasis has been placed on how to smoothly join three regions as previously described. Accordingly, the present invention provides a progressive power lens which is capable of obtaining a good visual field by improving aberration thereof as well as smoothly joining the three regions.
In the case where in a len
REFERENCES:
patent: 4606622 (1986-08-01), Fueter
patent: 4729651 (1988-03-01), Kitani
Sieko Epson Corporation
Sugarman Scott J.
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