Optics: eye examining – vision testing and correcting – Spectacles and eyeglasses – Ophthalmic lenses or blanks
Reexamination Certificate
2001-05-08
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
06412947
ABSTRACT:
This application claims the benefit of Japanese Patent application No. 2000-137731 which is hereby incorporated by reference.
BACKGROUND OF THE INVENTION
1. Field of the Invention
This invention relates to a progressive-power multifocal lens, and more particularly to a progressive-power multifocal lens used to assist the ability of accommodation of the eye.
2. Related Background Art
Single-vision lenses, bifocal lenses or progressive-power multifocal lenses are used to correct presbyopia. Of these lenses, in particular, the progressive-power multifocal lenses make it unnecessary to put on and put off spectacles between those for far vision and those for near vision, and also have an external appearance having no boundary line like that of bifocal lenses. Accordingly, in recent years, there is a reasonably increasing demand for the progressive-power multifocal lenses.
The progressive-power multifocal lenses are spectacle lenses for assisting the ability of accommodation of the eye when it grows weak to make the near vision difficult. The progressive-power multifocal lenses commonly have a far-vision correction portion and a near-vision correction portion which are positioned at the upper part and the lower part, respectively, of a lens at wear of spectacles (hereinafter, the former is often “far-vision portion” and the latter often “near-vision portion”), and a progressive-power portion where the refracting power changes continuously, positioned between the both portions (hereinafter often “intermediate portion”). Incidentally, in the present specification, terms “upper part”, “lower part”, “horizontal” and “vertical” describe the positional relationship of a lens at wear of spectacles. For example, the lower part of the far-vision portion is meant to be the portion close to the intermediate portion within the region of the far-vision portion.
FIG. 1
illustrates an outline of regional sections of a progressive-power multifocal lens which are designed symmetrically. The progressive-power multifocal lens shown in
FIG. 1
has a far-vision portion F and a near-vision portion N which are positioned at the upper part and the lower part, respectively, of the lens at wear of spectacles, and an intermediate portion P where the refracting power changes continuously, positioned between the both portions. With regard to the shape of lens surface, a line of intersection M-M′ where a cross section along the meridian which runs vertically through substantially the middle of lens surface from the upper part to the lower part intersects with the object-side (the side opposite to the eye) lens surface is used as a reference line for representing specification such as additional power of lenses. In the progressive-power multifocal lenses thus designed symmetrically, the center of far-vision portion, OF, of the far-vision portion F, the far-vision eyepoint E which is a fitting point, the geometric center of lens surface, OG, and the center of near-vision portion, ON, are positioned on the center line M-M′ serving as a reference.
FIG. 2
illustrates an outline of regional sections of a progressive-power multifocal lens which are designed asymmetrically, taking account of the fact that the center of near-vision portion, ON, of a lens comes close to the nasal side in wear of spectacles (this lens is hereinafter “asymmetrical progressive-power multifocal lens”). In the asymmetrical progressive-power multifocal lens shown in
FIG. 2
, too, the center line M-M′ consisting of a line of intersection where a cross section which passes along the center of far-vision portion, OF, of the far-vision portion F, the far-vision eyepoint E, the geometric center of lens surface, OG, and the center of near-vision portion, ON, intersects with the object-side lens surface is used as a reference line.
In the present specification, these reference lines are generically called “principal meridian curve”. The center of the far-vision portion F and the center of the near-vision portion are positions used as references when lens dioptric power is measured. A distance (far-vision) portion measurement reference point is called the center of far-vision portion, OF, and a near-portion measurement reference point is called the center of near-vision portion, ON. Also, mean surface refracting power at the the center of far-vision portion, OF, is regarded as a base curve, and mean dioptric power in respect of a light ray which passes through the center of far-vision portion, OF, is regarded as reference mean dioptric power at the far-vision portion (hereinafter “far-vision portion dioptric power). Usually, the center of near-vision portion, ON, is in agreement with the near-vision eyepoint. Note, however, that the center of far-vision portion and the center of near-vision portion which are herein referred to are meant not to be geometric centers in the respective portions but to be functional centers in the measurement of lenses and at wear of spectacles.
In the present specification, mean surface refracting power (hereinafter often “surface refracting power”) and surface astigmatism are expressed by the following equations (a) and (b), respectively, where a maximum main curvature at an arbitrary point on the progressive-power multifocal surface is represented by &psgr;max, a minimum main curvature by &psgr;min, and a refractive index of a lens by n.
Surface refracting power=(&psgr;
max+&psgr;min
)×(
n−
1)/2 (a)
Surface astigmatism=(&psgr;
max−&psgr;min
)×(
n−
1) (b)
In the present specification, mean dioptric power and astigmatism are expressed by the following equations (c) and (d), respectively, where maximum dioptric power in respect of a light ray having passed through an arbitrary point on the progressive-power multifocal surface is represented by Dmax, and minimum dioptric power by Dmin.
Mean dioptric power=(
Dmax+Dmin
)/2 (c)
Astigmatism=(
Dmax−Dmin
) (d)
In the present specification, mean surface additional refracting power (hereinafter often “surface additional refracting power”) refers to surface refracting power found by subtracting the base curve from the surface refracting power at an arbitrary point on the progressive-power multifocal surface. Also, mean additional dioptric power (hereinafter often “additional dioptric power”) refers to dioptric power found by subtracting far-vision portion dioptric power from the mean dioptric power (hereinafter often “dioptric power”) in respect of a light ray which passes through an arbitrary point on the progressive-power multifocal surface.
In the progressive-power multifocal lens, a plus surface refracting power (or dioptric power) is continuously added toward the center of near-vision portion, ON, from the center of far-vision portion, OF, on the principal meridian curve M-M′ which passes substantially the geometric center of the lens. The value found by subtracting the surface refracting power (or dioptric power) of the center of far-vision portion, OF, from the surface refracting power (or dioptric power) of the center of near-vision portion, ON, at which this surface additional refracting power (or additional dioptric power) comes to be maximum is called additional power of the progressive-power multifocal lens. In the progressive-power multifocal lens, what is ideal is a lens having distinct vision in a wide range and less crooked or distorted view in all regions of the far-vision portion F, the intermediate portion P and the near-vision portion N.
Now, in conventional progressive-power multifocal lenses, discussion has been made chiefly on optical characteristics of the progressive-power multifocal surface (refracting surface). More specifically, the performance of progressive-power multifocal lenses has often been evaluated on, e.g., their distribution of surface refracting power (or distribution of surface additional refracting power) and distribution of astigmatism at the progressive-power multifocal surface. According
Miles & Stockbridge P.C.
Nikon-Essilor Co., Ltd.
Sugarman Scott J.
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