Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-05-09
2002-07-02
Sugarman, Scott J. (Department: 2873)
Optics: eye examining, vision testing and correcting
Spectacles and eyeglasses
Ophthalmic lenses or blanks
C351S177000
Reexamination Certificate
active
06412948
ABSTRACT:
This application claims the benefit of Japanese Patent application No. 2000-137730 which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
The present invention relates to a progressive power multifocal lens, and more specifically, to a progressive power multifocal lens which is used to assist an accommodation power of an eye.
2. Related Background Art
In order to correct presbyopic eyes, a single focal lens, a bifocal lens, a progressive power multifocal lens, and the like, are conventionally used. Especially with respect to a progressive power multifocal lens, out of these lenses, the glasses which use the progressive power multifocal lenses are not required to be replaced or removed for looking at a distant point and for looking at a near point. For the outward looks, a progressive power multifocal lens has no border line, unlike in the case of a bifocal lens. As a result, a demand on progressive multifocal lenses is considerably increasing recently.
A progressive multifocal lens is a spectacle lens to assist an accommodation power of an eye when the accommodation power of the eye becomes weak so that a near vision is difficult to see clearly. In general, a progressive multifocal lens has a far vision correction portion which is positioned in an upper part of the lens when the lens is worn (hereinafter called “the far portion”), a near vision correction portion which is positioned in an lower part of the lens when the lens is worn (hereinafter called “the near portion”), and a progressive power portion in which the refracting power is continuously changed between the both portions (hereinafter called “the intermediate portion”). Note that the terms “upper”, “lower”, “horizontal” and “vertical” in the present invention are used to refer to positional relations in the lens when it is worn. For instance, the lower part of the far portion indicates an area which is inside the far portion and close to the intermediate portion.
FIG. 1
is a view for showing an outline of the divided regions of a progressive power multifocal lens which is designed symmetrically. The progressive power multifocal lens shown in
FIG. 1
comprises a far portion F which is located in an upper part of the lens when it is worn, a near portion N located in a lower part, and an intermediate portion P located between the far portion and the near portion in which the refracting power is continuously changed. As for the shape of a lens surface, an intersecting line MM′ of a cross section along the meridian passing through approximately the center of the lens surface and extending vertically from top to bottom and the lens surface on the object side (the side opposite to the eyes) is used as a reference line for expressing lens specifications such as the addition power of the lens and is also used as a significant reference line in the lens design. In the progressive power multifocal lens thus symmetrically designed, the center OF of far portion of the far portion F, an eyepoint E serving as a fitting point, the geometric center OG of the lens surface, and the center ON of the near portion are located on the center line MM′ serving as the reference line.
FIG. 2
is a view for showing an outline of the divided portions of a progressive power multifocal lens in which the near portion N is asymmetrically located in consideration of the fact that the center of the near portion ON comes close to the nasal side when the lens is worn (hereinafter called an “asymmetrical type progressive power multifocal lens”). Also in such an asymmetrical type progressive power multifocal lens as shown in
FIG. 2
, the center line MM′ which comprises the intersecting line of the cross section which passes through the center of distance vision portion OF of the far portion F, the eyepoint E for the distance portion, the geometric center OG of the lens surface, and the center of near vision portion ON and the object-side lens surface is used as the reference line.
In the present invention, these reference lines are collectively called the “principal meridian”. The center of the far portion F and the center of the near portion N are used as the reference positions for measuring lens powers. The reference point for measuring the lens power of a far portion is called the center of distance vision portion OF, while the reference point for measuring the lens power of a near portion is called the center of near vision portion ON. Furthermore, the mean surface refracting power of the center of distance vision portion OF is defined as a base curve, and the mean dioptric power of a transmitting light beam which passes through the center of distance vision portion OF is defined as the reference mean dioptric power in the far portion (hereinafter called “the distance dioptric power”). Normally, the center of the near portion is coincident with the eyepoint for the near vision. The terms “the center of distance vision portion” or “the center of near vision portion” does not indicate the geometric center in each of the portions, but indicates the functional center when the lens power is measured or the lens is worn.
According to the present invention, the mean surface refracting power (hereinafter called “the refracting power”) and the surface astigmatism (hereinafter called “the astigmatism”) can be respectively expressed by the following equations (a) and (b), where the maximum main curvature is &phgr;max and the minimum main curvature is &phgr;min at an arbitrary point on the progressive power multifocal surface:
the refracting power=(&phgr;max+&phgr;min)×(
n−
1)/2 (a);
and
the astigmatism=(&phgr;max−&phgr;min)×(
n−
1) (b).
Also according to the present invention, the mean dioptric power and the astigmatism can be respectively expressed by the following equations (c) and (d), where the maximum dioptric power and the minimum dioptric power in a light beam transmitted through an arbitrary point on the progressive power multifocal surface are defined as Dmax and Dmin, respectively:
the dioptric power=(
D
max+
D
min)/2 (c);
and
the astigmatism=(
D
max−
D
min) (d).
Furthermore, according to the present invention, the mean surface additional refracting power (hereinafter called “the surface additional refracting power”) is a refracting power which is obtained by subtracting the base curve from the refracting power at an arbitrary point on the progressive power multifocal surface. On the other hand, the mean additional dioptric power (hereinafter called the “additional dioptric power”) is a dioptric power which is obtained by subtracting the distance dioptric power from the mean dioptric power (hereinafter called the “dioptric power”) of a light beam passing through an arbitrary point on the progressive power multifocal surface power.
It is noted that, in the progressive power multifocal lens, a positive refracting power (or dioptric power) is continuously imparted from the center of distance vision portion OF toward the center of near vision portion ON on the principal meridian MM′ which approximately passes through the geometric center of the lens, and a value which is obtained by subtracting the refracting power (or dioptric power) of the center of distance vision portion OF from the additional refracting power (or additional dioptric power) of the center of near vision portion ON at which this addition refracting power (or additional dioptric power) approximately reaches the maximum is called the additional power of the progressive power multifocal lens. A progressive power multifocal lens which has wide clear vision ranges of all of the far vision portion F, the intermediate portion P, and the near portion N are wide, small fluctuation, distortion, and the like of an image, and is easily worn is an ideal progressive power multifocal lens.
Incidentally, as for a conventional progressive power multifocal lens, generally the optical characteristics of the progressive p
Miles & Stockbridge P.C.
Nikon-Essilor Co., Ltd.
Sugarman Scott J.
LandOfFree
Progressive power multifocal lens does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Progressive power multifocal lens, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Progressive power multifocal lens will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2817608