Multifocal lens for eyeglass and eyeglass lens

Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks

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Details

351169, 351176, G02C 706, G02C 702

Patent

active

059262508

DESCRIPTION:

BRIEF SUMMARY
BACKGROUND OF THE INVENTION

1. Field of the Invention
The invention relates to a multifocal lens for vision-corrective eyeglass and an eyeglass lens therewith.
2. Description of Related Art
Because a multifocal lens provided with multiple visual field areas having different refractive powers, for example, a distance-vision area and a near-vision area, can obtain visual fields having different refractive powers with a single lens, it can be used as an eyeglass lens for correcting vision such as aging vision, and the like. Furthermore, one type of multifocal lens is a progressive multifocal lens provided with visual field areas in which the refractivity changes progressively. Because there are no boundaries in the visual field areas, a progressive visual field can be obtained. Furthermore, because it is superior also in external view, it is widely used as an eyeglass lens. FIGS. 11A and 11B show the general structure of a conventional progressive multifocal lens which is widely used as an eyeglass lens. FIG. 11A is an elevational view that shows the progressive multifocal lens 1 is provided with a distance-vision area 11 for viewing objects at a far distance, and a near-vision area 12 for viewing objects at a near distance, the refractive power of which is different from that of distance-vision area 11. The near vision area 12 is provided below distance-vision area 11. Also, the distance-vision area 11 and near-vision area 12 are connected smoothly by a progressive area 13, which is a visual field area for viewing objects at an intermediate distance. The progressive area 13 is endowed with a refractive power that changes continuously.
FIG. 11B is a sectional view and shows that in a one-piece lens 1 used for an eyeglass, there are two surfaces, being a refractive surface 3 on the side of the eye and a refractive surface 2 on the side of the viewed object. It is necessary to provide these surfaces with all the performance required for an eyeglass lens, for example, a vertex power meeting the user's prescription, a cylinder power for correcting astigmatism, an addition power for correcting aging vision, and furthermore a prism power for correcting skew. Therefore, a conventional multifocal lens 1 includes a distance-vision area 11 and near-vision area 12, and the surface power is adjusted by changing the curvature of refractive surface 2 on the side of the object. A progressive multifocal lens further includes a progressive area 13. Also, a toric surface is provided on the refractive surface 3 on the side of the eye when correction of astigmatism is necessary. For simplicity, the explanation is given below, assuming a progressive multifocal lens that does not perform correction of astigmatism.
The astigmatic aberration obtained with a conventional progressive multifocal lens is shown in FIG. 12. The progressive refractive surface 5 provided on the surface 2 on the side of the object is a non-spherical surface so as to change continuously the surface refractive power. Thus, curvature changes according to each area of the surface. For example, a schematic configuration of a progressive multifocal lens in which the refractive power of distance-vision area 11 is 0.00D and the addition power Add is 3.00D. However, when the average surface power D11 of distance-vision area 11 is set to 4.00 diopters (D), the average surface power of near-vision area 12 becomes 7.00D. Consequently, on surface 2 on the side of the object, an astigmatic aberration is caused because a difference of curvature is created between the x direction (the direction that is horizontal when the eyeglass is worn) and the y direction (the direction that is vertical along the lens perpendicular to the x direction), crossing from distance-vision area 11 to near-vision area 12. Meanwhile, surface 3 on the side of the eye may be a spherical surface having a constant curvature. The progressive multifocal lens 1 of the present example may include a spherical surface endowed with an average surface power D21 which is the same as the average surface power

REFERENCES:
Guilino, G. H., "Design Philosophy for Progressive Addition Lenses" Applied Optics, vol. 32, No. 1, Jan. 1, 1993, pp. 111-117.

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