Patent Description:
Patent document <NUM> describes a technique of providing a progressive surface on an eye-side surface instead of on an object-side surface which is conventionally formed a progressive surface, in a progressive multifocal lens used for a spectacle lens suitable for correcting a vision such as presbyopia. Thus, the object-side surface can be formed into a spherical surface with a constant base curve, and therefore variation by a shape factor of magnification can be prevented, difference of magnification between the distance portion and the near portion can be reduced, and the variation of magnification in a progressive portion can be suppressed. Accordingly, swing or distortion of an image by the difference of magnification can be reduced, and the progressive multifocal lens capable of obtaining a comfortable visual field can be provided. Patent document <NUM> also describes a technique of combining a progressive surface and a toric surface for correcting astigmatism into an eyeball-side surface using a combining formula, and reducing a swing or distortion even in the progressive multifocal lens for correcting astigmatism.

Patent document <NUM> describes a technique of providing a multifocal lens for spectacles including visual field portions with different powers such as a distance portion and a near portion, and including a specific addition power by mathematically setting a difference between a mean surface power of the distance portion and a mean surface power of a near portion on the object-side surface, to be smaller than the addition power, and adjusting the mean surface power of the distance portion and the mean surface power of the near portion on the eyeball-side surface. The mean surface power on the object-side surface can be adjusted so that the difference of magnification between the distance portion and the near portion can be small, and also difference of mean surface power on the object-side surface can also be small. Accordingly, the multifocal lens with less swing or distortion by the difference of magnification, and capable of obtaining a suitable visual field with wide clear vision area, improved astigmatism, and less swing of an image, can be provided.

Patent document <NUM> describes a technique of providing a bi-aspherical surface progressive addition lens capable of reducing a difference of magnification of images between a distance portion and a near portion, correcting a vision satisfactorily based on a prescription value, and providing a wide effective visual field with less distortion in an as-worn state. Therefore, patent document <NUM> describes as follows: when a horizontal surface power and a vertical surface power at distance reference point F1 are respectively defined as DHf and DVf on a first addition surface on the object-side surface, and a horizontal surface power and a vertical surface power at near reference point N1 are respectively defined as DHn and DVn on the first addition surface, a relation formula is satisfied as follows: DHf + DHn < DVf + DVn and DHn < DVn, and a surface astigmatic component at F1 and N1 on the first addition surface is canceled by a second addition surface on the eyeball-side surface, thus providing a distance power and an addition power based on a prescription value by combining the first and second addition surfaces.

Patent document <NUM> describes a technique of providing a progressive addition lens capable of reducing a distortion or blurring of an image which is inevitably generated in a progressive addition lens, and improving a wearing feeling. Therefore, patent document <NUM> provides a both-side progressive lens in which both surfaces of an outer surface and inner surface are progressive surfaces, wherein the shape of the progressive surface is designed so that addition for the outer surface is minus, and a mean surface power distribution is similar in the outer surface and the inner surface.

The document <CIT> which has been cited under Art. <NUM>(<NUM>) EPC relates to a progressive power lens with less image sway. A method of designing a progressive power lens includes preferentially selecting a spectacle specification including a first condition if an average prescription power of a distance portion is equal to or greater than +<NUM> D, and preferentially selecting a spectacle specification including a second condition if the average prescription power is equal to or smaller than -<NUM> D. In a progressive power lens, at least a surface power OHPf in a horizontal direction of a distance portion on an object-side surface is greater than a surface power OVPf in a vertical direction, or a surface power OHPn in a horizontal direction of a near portion is greater than a surface power OVPn in a vertical direction.

The document <CIT> describes a bi-aspherical type progressive-power lens which provides visual acuity correction for prescription values and a wide effective visual field with less distortion in wearing, by reducing a magnification difference of an image between a distance portion and a near portion of a lens, and a method of designing the same.

The document <CIT> relates to a progressive power lens which includes a pair of an outer refractive surface and an inner refractive surface, at least one of the outer refractive surface and the inner refractive surface being a progressive surface.

Finally, the document <CIT> describes ophthalmic lenses having a first lens surface that is described by a continuous, gradual increase in optical power that proceeds without inflection points of discontinuities across substantially the entire useable optical area of this lens surface, and an opposite surface of the lens configured to cooperate with the power gradation of the first surface to provide a desired prescription, including at least one stabilized area of optical power. The power gradation of the first surface increases from one edge of the useable area to substantially the opposite edge, and may increase according to linear or non-linear relationships. In another preferred embodiment, the two lens surfaces cooperate to create two stabilized areas of optical power, for a prescription with near-viewing and distance-viewing values.

Although improvement of performance is achieved by these techniques, there is still a user who cannot be accustomed to the characteristic of the progressive addition lens and particularly to the swing, and also improvement is requested. In addition, in order to provide a lens having optimal parameter in accordance with a prescription, many kinds of lenses are required to be previously manufactured and prepared, or individually manufactured, and this is a factor of increasing a manufacturing cost.

In view of the above-descried problem, the present invention is provided, and according to several aspects of the present invention, there are provided a lens set, a method of designing a lens and a method of manufacturing a lens, with less swing of an image viewed through a lens and capable of suppressing a manufacturing cost.

Namely, the first lens and the second lens satisfy the following conditions. <MAT> <MAT> <MAT>.

The first lens and the second lens are progressive addition lenses including a toric surface (called a troidal surface) element along a vertical reference line or a principal sight line (both of them called a "principal meridian") passing through a fitting point on an object-side surface (outer surface). The toric surface element on the object-side surface is the element in which horizontal surface power OHPf1 (OHPf2) and surface power OHPn1 (OHPn2) are larger than vertical surface power OVPf1 (OVPf2) and surface power OVPn1 (OVPn2) in both of the distance portion and the near portion (conditions (<NUM>) and (<NUM>)). Namely, in both of the distance portion and the near portion, horizontal curvature (in horizontal direction) is larger than vertical curvature (in vertical direction) on the object-side surface in both of the distance portion and the near portion. Thus, the progressive addition lens with less swing can be provided.

Namely, a typical movement of a sight line (eye) when swing is generated in an image obtained through the first lens or the second lens, is caused by movement of an eyeball (sight line) with respect to a head, by vestibule-ocular reflex that compensates the movement of the head. A moving range of the sight line by the vestibule-ocular reflex, is generally wide in the horizontal direction (lateral direction). Accordingly, by introducing the toric surface element on the object-side surface in which a horizontal surface power is larger than a vertical surface power, variation of an angle formed when the sight line passes through the object-side surface of a spectacle lens, can be suppressed when the sight line moves in the horizontal direction.

Therefore, various aberrations of the image obtained through the first lens or the second lens can be reduced when the sight line is moved, and the first lens and the second lens with less swing of the image obtained through the first lens or the second lens, can be provided.

The first lens and the second lens are capable of reducing a difference of magnification between the image obtained through the distance portion and the image obtained through the near portion of the progressive addition lens, by including a degressive element in which the surface power of the near portion on the object-side surface is smaller than the surface power of the distance portion reversely to the addition power (condition (<NUM>)).

The degressive element on the object-side surface may be introduced by both of the vertical surface power and the horizontal surface power. However, a structure on the object-side surface becomes complicated. Therefore, the degressive element is preferably introduced on the object-side surface by such a small vertical surface power. Thus, the progressive addition lens with less swing of image, can be provided at a low cost.

Further, the difference between surface power OVPf1 and surface power OVPn1 of the first lens, and the difference between surface power OVPf2 and surface power OVPn2 of the second lens are the same, irrespective of the addition power of the lens, and therefore the shape of the object-side surface (outer surface) can be easily formed in common. Thus, a plurality of kinds of lenses having different addition powers can be manufactured from a common semifinished lens, and therefore a manufacturing cost can be suppressed.

(<NUM>) According to an aspect not forming part of the invention, there is provided a method of designing a lens, which is a progressive addition lens for spectacles, including:.

According to the first lens and the second lens designed by this method, the variation of the angle formed when the sight line passes through the object-side surface of the first lens or the second lens, can be suppressed when the sight line moves in the horizontal direction, by introducing the toric surface element on the object-side surface in which the horizontal surface power is larger than the vertical surface power. Accordingly, various aberrations of the image can be reduced, the image being obtained through the first lens or the second lens when the sight line is moved, and the first lens and the second lens with less swing of image can be designed, the image being obtained through the first lens or the second lens.

Further, the difference between surface power OVPf1 and surface power OVPn1 of the first lens, and a difference between surface power OVPf2 and surface power OVPn2 of the second lens are the same, and therefore the shape of the object-side surface (outer surface) can be easily formed in common. Accordingly, a plurality of kinds of lenses having different addition powers can be manufactured from the common semifinished lens, and therefore the lens capable of suppressing the manufacturing cost can be designed.

(<NUM>) The method of manufacturing a lens not forming part of the invention includes manufacturing a progressive addition lens designed by the abovementioned method of designing a lens.

Thus, a plurality of kinds of lenses having different addition powers can be manufactured from the common semifinished lens, and therefore the manufacturing cost can be suppressed.

Preferable embodiments of the present invention will be described hereafter in detail, using the drawings. The embodiments described hereafter, don't unjustly limit the contents of the present invention described in the claims. Further, all of the structures described hereafter should not necessarily be taken as essential constituting features of the present invention.

The embodiments of the present invention will be described hereafter in the following order.

Main terms used for the description of the present invention will be described.

"An upper side" of a lens means a head top side of a wearer when wearing a spectacle by a user.

"A lower side" of a lens means a chin side of a wearer when wearing a spectacle by a user.

"An outer surface" of a lens means a surface opposed to an object when wearing a spectacle by a wearer, which is also called "an object-side surface" and "a convex surface".

"An inner surface" of a lens means a surface opposed to an eyeball of the wearer when wearing the spectacle by the wearer, which is also called "an eyeball-side surface" and "a concave surface".

"A distance portion" of a lens is a visual field part for viewing an object in a long distance (for a distance view).

"A near portion" of a lens is a visual field part for viewing an object in a short distance (for a near view), in which a diopter (power) is different from that of the distance portion.

"An intermediate portion" of a lens is an area for connecting the distance portion and the near portion so that the power is continuously varied, which is also called a portion for an intermediate view, a progressive portion, and an intermediate corridor.

"A distance portion on an outer surface (inner surface) " is an area on the outer surface (inner surface) corresponding to the distance portion of a lens.

"A near portion on an outer surface (inner surface) " is an area on the outer surface (inner surface) corresponding to the near portion of a lens.

"An intermediate portion on an outer surface (inner surface) " is an area on the outer surface (inner surface) corresponding to the intermediate portion of a lens.

"A distance reference point" means a coordinate on the outer surface or the inner surface of a lens in which a designing specification of the distance portion is used. Note that the distance reference point may also include a minute area, although the area is a "point".

"A near reference point" means a coordinate on the outer surface or the inner surface of a lens in which a designing specification in a near portion of a lens is used. Note that the near reference point may also include a minute area, although the area is a "point".

"A surface power of a distance portion" means a surface power at a distance reference point.

"A surface power of a near portion" means a surface power at a near reference point.

"Power" of a lens means an equivalent spherical power at the distance reference point.

"A base curve" means a curvature of the outer surface of a lens.

"A primary position" means a relative position of an eyeball with respect to a head of a wearer when facing up to an object in front at a height of an eyeball of a wearer.

"A fitting point" means a coordinate indicated by a designer of a lens, as an intersection point of a sight line of the wearer at the primary position and the outer surface of the lens.

"The same" power means a case that power is within an allowable range of an error, in addition to a case that two powers to be compared are completely equal to each other. Specifically, allowance of the progressive addition lens defined in "JIS T <NUM>: PROGRESSIVE ADDITION SPECTACLE LENS FOR POWER CORRECTION" (Japanese Industrial Standards Committee) is <NUM>. 25D as an absolute value, and therefore a value less than <NUM>. 25D is in a range of error.

<FIG> is a view schematically showing a lens set <NUM> according to an embodiment. The lens set <NUM> of this embodiment includes a distance portion and a near portion having different powers, and is the progressive addition lens for spectacles with plus equivalent spherical power of the distance portion, and includes a first lens 10a and a second lens 10b having mutually different addition powers. In an example shown in <FIG>, two lenses are included in the lens set <NUM>, but the lens set <NUM> may be constituted including three or more lenses. When the lens set <NUM> is constituted including three or more lenses, arbitrarily selected two lenses may correspond to the first lens 10a and the second lens 10b. Also, the lens set <NUM> may include two or more first lens 10a or second lens 10b.

<FIG> is a perspective view showing an example of a spectacle <NUM> using the lens included in the lens set <NUM>.

In this embodiment, explanation is given for a spectacle <NUM> in which a left side is left and a right side is right viewed from a user side (wearer side or eyeball side). The spectacle <NUM> has right and left pair of spectacle lenses <NUM> and 10R for right eyes and left eyes, and a spectacle frame <NUM> into which the lens <NUM> and the lens 10R are respectively settled. The lens <NUM> and the lens 10R shown in <FIG> are the lenses obtained by processing the first lens 10a or the second lens 10b to fit in a frame <NUM>. Additions of the lens <NUM> and the lens 10R may be the same or may be different from each other. However, it is general to set the same additions of the lens <NUM> and the lens 10R. Both of the lens <NUM> and the lens 10R of this embodiment are the first lens 10a. The lens <NUM> and the lens 10R are respectively a progressive multifocal lens (progressive addition lens). The lens <NUM> and the lens 10R are meniscus lenses whose basic shape is a convex to an object-side. Accordingly, the lens <NUM> and the lens 10R respectively include an object-side surface (convex surface, also called an outer surface) 19A and an eyeball-side (user side) surface (concave surface, also called an inner surface) 19B. Note that the lens <NUM> and the lens 10R are selected in accordance with a prescription of a user, and therefore prescription power and prism amount, etc., may be different.

<FIG> is a schematic view of the lens 10R for right eye viewed from the eyeball-side, and <FIG> is a view schematically showing a sectional surface of the lens 10R for right eye. The lens 10R includes a distance portion <NUM> in an upper side, and includes a near portion <NUM> in a lower side. Further, the lens 10R includes an intermediate portion <NUM> connecting the distance portion <NUM> and the near portion <NUM>. Also, the lens 10R includes a principal sight line <NUM> connecting positions on a lens, which are centers of a visual field in a case of a distance vision, an intermediate vision, and a near vision. A fitting point Pe is usually positioned almost at a lower end of the distance portion <NUM>, which is a reference point on a lens through which a sight line passes in a case of a distance horizontal front view (primary position) when an outer periphery of the lens 10R is molded to fit and settle in the frame. Hereafter, the fitting point Pe is set as a coordinate origin of a lens, and a coordinate in a direction along a horizontal reference line <NUM> is set as x-coordinate, and a coordinate in a direction along a vertical reference line is y-coordinate. The principal sight line <NUM> extends almost vertically in a direction of the near portion <NUM> from the distance portion <NUM>, and is curved to a nose side from a point passing through the fitting point Pe.

Explanation is given hereafter mainly for the lens 10R for right eyes as a lens. However, the lens may be the lens <NUM> for left eyes, and basically the lens <NUM> for left eyes has a right and left symmetric structure with respect to the lens 10R for right eyes, excluding a difference of a spectacle specification between right and left eyes. Further, hereafter, the lens 10R for right eye and the lens <NUM> for left eye are called a lens <NUM> in common. Also, hereafter, the surface power of the lens <NUM> is expressed as OVPf, OVPn, OHPf, OHPn, IVPf, IVPn, IHPv, and IHPn respectively.

A range of the visual field in optical performances of the lens <NUM> can be known by an astigmatism distribution view and an equivalent spherical power distribution view. The swing felt by a user when wearing the lens <NUM> and moving a head, is important and given as one of the performances of the lens <NUM>, and a difference is sometimes generated in the swing, even if the astigmatism distribution and the equivalent spherical power distribution are almost the same. Explanation is given hereafter for an evaluation method of the swing in "<NUM>. Evaluation method of swing", and a result of comparing the example of the present application and the comparative example using the evaluation method, is shown in "<NUM>.

In the first lens 10a of the lens set <NUM>, an object-side surface 19A includes a toric surface element in which when a horizontal surface power in a distance portion <NUM> along a principal sigh line <NUM> (or a vertical reference line passing through a fitting point Pe (a vertical reference line (called a "vertical reference line" hereafter)) is defined as OHPf1, and a vertical surface power in the distance portion <NUM> along the principal sight line (or the vertical reference line) is defined as OVPf1, and a horizontal surface power in a near portion <NUM> along the principal sight line <NUM> (or the vertical reference line) is defined as OHPn1, and a vertical surface power in the near portion <NUM> along the principal sight line <NUM> (or the vertical reference line) is defined as OVPn1, OVPn1 is smaller than OVPf1, and OHPf1 is larger than OVPf1, and OHPn1 is larger than OVPn1, and the eyeball-side surface 19B along the principal sight line <NUM> (or the vertical reference line) includes an element for canceling the toric surface element.

In the second lens 10b of the lens set <NUM>, the object-side surface 19A includes a toric surface element in which when a horizontal surface power in the distance portion <NUM> along the principal sigh line <NUM> (or the vertical reference line) is defined as OHPf2, and a vertical surface power in the distance portion <NUM> along the principal sight line (or the vertical reference line) is defined as OVPf2, and a horizontal surface power in the near portion <NUM> along the principal sight line <NUM> (or the vertical reference line) is defined as OHPn2, and a vertical surface power in the near portion <NUM> along the principal sight line <NUM> (or the vertical reference line) is defined as OVPn2, OVPn2 is smaller than OVPf2, and OHPf2 is larger than OVPf2, and OHPn2 is larger than OVPn2, and the eyeball-side surface 19B along the principal sight line <NUM> (or the vertical reference line) includes an element for canceling the toric surface element.

Namely, the first lens 10a and the second lens 10b satisfy the following conditions. <MAT> <MAT> <MAT>.

The first lens 10a and the second lens 10b are bi-aspherical addition lenses including the toric surface (also called a troidal surface) element along the principal sight line on the object-side surface 19A. The toric surface element on the object-side surface 19A is the element in which horizontal surface power OHPf1 (OHPf2) and horizontal surface power OHPn1 (OHPn2) are larger than vertical surface power OVPf1 (OVPf2) and vertical surface power OVPn1 (OVPn2) in both of the distance portion <NUM> and the near portion <NUM> (Conditions (<NUM>) and (<NUM>)).

Therefore, the intermediate portion <NUM> also includes a similar toric surface element. Namely, horizontal (horizontal direction) curvature is larger than vertical (vertical direction) curvature on the object-side surface 19A in both of the distance portion <NUM> and the near portion <NUM>. Thus, the progressive addition lens with small swing can be provided. Note that the intermediate portion <NUM> may also include the similar toric surface element as the distance portion <NUM> and the near portion <NUM>.

A typical movement of a sight line (eye) when generating the swing in an image obtained through the first lens 10a or the second lens 10b, is caused by the movement of the eyeball (sight line) with respect to a head by vestibule-ocular reflex for compensating the movement of the head. Such a visual movement range by the vestibule-ocular reflex is generally wider in the horizontal direction than the vertical direction. Accordingly, by introducing the toric surface element on the object-side surface 19A in which the horizontal surface power is larger than the vertical surface power, a variation of angles formed when the sight line passes through the object-side surface 19A of the first lens 10a or the second lens 10b, can be suppressed when the sight line moves in the horizontal direction.

Therefore, various aberrations of the image obtained through the first lens 10a or the second lens 10b can be reduced when moving the sight line, and the first lens 10a and the second lens 10b with less swing of image obtained through the first lens 10a or the second lens 10b, can be provided.

The first lens 10a and the second lens 10b are capable of reducing a difference of magnification between the image obtained through the distance portion <NUM> and the image obtained through the near portion <NUM>, by introducing a degressive element for making the surface power in the near portion <NUM> smaller than the surface power in the distance portion <NUM> on the object-side surface 19A, in such a manner as being reverse to addition (condition (<NUM>)).

The degressive element on the object-side surface 19A may be introduced by both of the vertical surface power and the horizontal surface power. However, the structure on the object-side surface 19A is complicated. Generally, a spectacle lens is manufactured in accordance with a prescription of a wearer, by previously manufacturing a lens (semifinished lens) in which one surface (usually an outer surface) is completed, and thereafter edging and grinding the other surface (usually an inner surface) in accordance with a design. If the structure on the object-side surface 19A is complicated, many man-hours are required for ensuring an edging accuracy of the semifinished lens, and therefore the degressive element is preferably introduced on the object-side surface 19A by small vertical surface power which allows easy edging with high precision. Thus, the progressive addition lens with less swing of image can be provided at a low cost.

Further, addition powers of the first lens 10a and the second lens 10b can be ensured by setting a difference between the surface power in the distance portion <NUM> and the surface power in the near portion <NUM> on the eyeball side surface 19B, to be larger than the difference between the surface power in the distance portion <NUM> and the surface power in the near portion <NUM> on the object-side surface 19A. Namely, when a vertical surface power in the distance portion <NUM> is defined as IVPf1, and a vertical surface power in the near portion <NUM> is defined as IVPn1 on the eyeball-side surface 19B along the principal sight line <NUM> (or the vertical reference line) of the first lens 10a, and when a vertical surface power in the distance portion <NUM> is defined as IVPf2, and a vertical surface power in the near portion <NUM> is defined as IVPn2 on the eyeball-side surface 19B along the principal sight line <NUM> (or the vertical reference line) of the second lens 10b, the following condition is satisfied.

Wherein, surface powers IVPF1, IVPf2, IVPn1, and IVPn2 in condition (<NUM>) are absolute values.

Further, in the first lens 10a and the second lens 10b of this embodiment, the difference between surface power OVPf1 and surface power OVPn1 of the first lens 10a, and the difference between surface power OVPf2 and surface power OVPn2 of the second lens 10b are the same.

<FIG> is a view showing the lens set of this embodiment. The vertical axis indicates a spherical power (Sph) in the distance portion, and the horizontal axis indicates a prescription addition power (Add) of the lens <NUM>. Generally, the progressive addition lens is divided into a plurality of groups in an allowable range regarding an optical performance such as astigmatism and a mechanical performance such as a thickness, etc., based on a prescription (at least spherical power and addition power in the distance portion). The lens included in each lens set is edged from a common semifinished lens. In this embodiment, G4 to G11 respectively indicates the lens set manufactured from the common (the same-shaped) semifinished lens. Namely, degressive elements (condition (<NUM>)) of the first lens 10a and the second lens 10b included in each lens set are the same. For example, lens set G5 includes the first lens 10a satisfying Sph:+<NUM>. 50D, and Add: <NUM>. 00D, and the second lens 10b satisfying Sph: +<NUM>. 00D and Add: <NUM>. 00D, wherein difference between OVPf1 and OVPn1 and difference between OVPf2 and OVPn2 are the same.

Here, if the addition power of the first lens 10a is assumed to be smaller than the addition power of the second lens 10b, the swing of the image in the first lens 10a and the second lens 10b can be suppressed in a certain degree of range by setting an amount of the degressive element for the second lens 10b to be larger than a size of the degressive element for the first lens 10a. Meanwhile, in the lens <NUM> of this embodiment, if the amount of the degressive element for the second lens 10b is set to be smaller than the degressive element for the first lens 10a, the curvature of the object-side surface 19A of the second lens 10b can be prevented from being relatively large. Namely, a protrusion degree of the object-side surface 19A of the second lens 10b can be reduced, and therefore an outer appearance as a spectacle can be improved. Namely, swing or the outer appearance of the lens can be improved by including the degressive element for a different amount in response to the addition power.

However, if the degressive element is varied in response to the addition power, the curvature of the object-side surface 19A is varied in response to the addition power, and the common semifinished lens cannot be used. Accordingly, the lens set in <FIG> is required to be further finely divided for each prescribed addition power (Add).

Meanwhile, in the lens set of this embodiment, the difference between surface power OVPF1 and surface power OVPn1 of the first lens 10a, and the difference between surface power OVPf2 and surface power OVPn2 of the second lens 10b are the same, irrespective of the addition power of the lens. Therefore, the shape of the object-side surface 19A can be easily formed into a common shape. Thus, a plurality of kinds of different lenses having different addition powers and different spherical powers can be manufactured from the same kinds of semifinished lenses as the inner surface progressive lens in which the object-side surface 19A is formed into a spherical surface. Therefore, a manufacturing cost can be suppressed to the same as the manufacturing cost of the conventional lens.

Further, in the lens sets G4 to G11 as a whole, the degressive element may be the same. In this case, the whole body of <FIG> can be regarded as one lens set, and this lens set is divided into a group of G4 to G11 (having different semifinished lens) based on the prescription. For example, one lens set may be constituted by the first lens 10a having Sph of +<NUM> and Add of <NUM>. 00D (included in the lens set G5), and the second lens 10b having Sph of +<NUM>. 50D and Add of <NUM>. 25D (included in the lens set G6). Thus, there is no necessity for considering the difference of the degressive element in designing and manufacturing the lens <NUM>, and therefore generation of a defective product can be suppressed, which is caused by design error or edging calculation error during manufacture, or selection error of a jig, etc. Accordingly, the manufacturing cost can be suppressed.

<NUM> is a flowchart for describing a method of designing a lens and a method of manufacturing a lens wherein, explanation is given for an example of designing and manufacturing the first lens 10a and the second lens 10b described in "<NUM>.

The method of designing a lens includes the steps of: including a toric surface element in an object-side surface of the first lens 10a in which surface power OVPn1 is smaller than surface power OVPf1 (step S100), and surface power OHPf1 is larger than surface power OVPf1 and surface power OHPn1 is larger than surface power OVPn1 (step S102); and including an element for canceling the toric surface element in the eyeball-side surface 19B of the first lens 10a along the principal sight line <NUM> (or the vertical reference line) (step S104), also including a toric surface element in an object-side surface of the second lens 10b in which surface power OVPn2 is smaller than surface power OVPf2 (step S106), and surface power OHPf2 is larger than surface power OVPf2 and surface power OHPn2 is larger than surface power OVPn2 (step S108), and including an element for canceling the toric surface element in the eyeball-side surface 19B of the second lens 10b along the principal sight line <NUM> (or the vertical reference line) (step S110), and setting the difference between surface power OVPf1 and surface power OVPn1 and the difference between surface power OVPf2 and surface power OVPf2 to be the same (step S112). Note that an order of each step of step S100 to step S112 is arbitrarily selected.

According to the first lens 10a and the second lens 10b designed by this method, by introducing the toric surface element on the object-side surface 19A in which the horizontal surface power is larger than the vertical surface power, the variation of the angle formed when the sight line passes through the object-side surface 19A of the first lens 10a or the second lens 10b can be suppressed when the sight line moves in the horizontal direction. Accordingly, various aberrations of the image obtained through the first lens 10a or the second lens 10b can be reduced when the sight line moves, and the first lens 10a and the second lens 10b with less swing of image obtained through the first lens 10a or the second lens 10b, can be designed.

Further, the difference between surface power OVPf1 and surface power OVPn1 of the first lens 10a, and the difference between surface power OVPf2 and surface power OVPn2 of the second lens 10b, are the same, and therefore the object-side surface 19A can be easily formed into a common shape. Accordingly, a plurality of kinds of different lenses having different addition powers can be manufactured from the common semifinished lens and therefore the lens capable of suppressing the manufacturing cost can be designed.

The method of manufacturing a lens includes the step of manufacturing a progressive addition lens designed by the abovementioned method of designing a lens (step S100 to step S112) (step S102).

<FIG> is a view showing an equivalent spherical power distribution (unit is dioptre (D)) of a typical progressive addition lens (lens <NUM>), <FIG> is a view showing an astigmatism distribution (unit is dioptre (D)), and <FIG> is a view showing a state of distortion when viewing square grids through the lens <NUM>. In the lens <NUM>, a specific power is added along the principal sight line <NUM>. A large astigmatism is generated in the side part of the intermediate portion <NUM> by addition of the power, and therefore an object is blurred in the side part of the intermediate portion <NUM>. In the equivalent spherical power distribution, power is increased by a specific amount in the near portion <NUM>, and the power is sequentially reduced toward the intermediate portion <NUM> and the distance portion <NUM>. In the lens <NUM> shown in <FIG>, power (distance power, Sph) is <NUM>. 00D (dioptre), and addition power (Add) is <NUM>. 00D in the distance portion <NUM>.

The magnification of the image becomes large in the near portion <NUM> having a large power, compared with the image in the distance portion <NUM>, depending on the difference of powers by the position on the lens <NUM>, and the image of each square grid is deformed in the side part of the intermediate portion <NUM> to the near portion <NUM>. This is the cause of the swing of the image when moving the head.

<FIG> is a view showing an outline of the vestibulo-ocular reflex (VOR). When a head is moved in viewing an object <NUM>, the visual field is also moved. At this time, an image on a retina is also moved. However, if an eyeball <NUM> moves (rotation (turn) of an eye) so as to cancel the movement of the head (rotation (turn) of a face, and rotation of a head) <NUM>, a sight line <NUM> is stabilized (is not moved), and the retina image is not moved. Such a reflective eyeball movement having a function of stabilizing the retina image, is called a compensatory eye movement. The vestibule-ocular reflex is one of the compensatory eye movements, in which a reflection is generated, with the rotation of the head as a stimulant. A neural mechanism of the vestibule-ocular reflex by horizontal rotation (horizontal turn) is clarified to some extent as follows. Namely, it can be considered that rotation <NUM> of the head is detected by a horizontal semicircular canal, and input from the horizontal semicircular canal adds inhibitory and excitatory action on extraocular muscles, to thereby move the eyeball <NUM>.

When the head rotates, the eyeball is also rotated by the vestibule-ocular reflex, but the retina image is not moved. Then, the lens <NUM> provided in spectacle <NUM> is rotated in conjunction with rotation of the head as shown by broken line and one dot chain line of <FIG>. Therefore, the sight line <NUM> passing through the lens <NUM> by the vestibule-ocular reflex, moves on the lens <NUM> relatively. Accordingly, if there is a difference of an imaging performance of the lens <NUM> in a range in which the eyeball <NUM> moves by the vestibule-ocular reflex, namely in a range through which the sight line <NUM> passes by the vestibule-ocular reflex, the retina image sometimes swings.

<FIG> is a graph showing an example of observing a movement of a head position (primary position) when searching an object. The horizontal axis indicates an angle formed by a front direction of an examinee and a gaze point (object), and the vertical axis indicates a rotation angle of the head. A graph shown in <FIG> shows a degree of the rotation of the head, to recognize the object that moves by a certain angle from the gaze point in the horizontal direction. In a fixation state for focusing the object <NUM>, the head is rotated together with the object <NUM> as shown in graph <NUM>. Meanwhile, in a state of a discriminating view for simply recognizing the object, as shown in graph <NUM>, the movement of the head becomes smaller (reduced) by about <NUM> degrees than the angle (movement) of the object. Owing to such an observation result, a limit of a range of recognizing the object <NUM> by the movement of the eyeball can be set to about <NUM> degrees. Accordingly, it can be considered that a rotation angle of the head in the horizontal direction when viewing the object <NUM> by the vestibule-ocular reflex while moving a human head in a natural state, is about <NUM> degrees in maximum in right and left (a maximum horizontal angle θxm formed by the movement of the eyeball <NUM> by the vestibule-ocular reflex).

Meanwhile, in a case of the progressive addition lens, there is a variation in powers in the intermediate portion <NUM>, and therefore if the rotation of the head is maximum in the vertical direction when viewing the object <NUM> by the vestibule-ocular reflex, power is not fitted to a distance of the object due to a large movement, thus blurring the image. Therefore, it can be considered that the maximum rotation angle of the head in the vertical direction when viewing the object <NUM> by the vestibule-ocular reflex, is smaller than the maximum rotation angle in the horizontal direction. As described above, the rotation angle of the head which is a parameter in a case of performing a simulation of the swing, is about <NUM> degrees in the horizontal direction in right and left, and is smaller than the horizontal maximum rotation angle in the vertical direction, and is about <NUM> degrees vertically for example, and such a rotation angle of the head is preferably used. Further, a typical value of the range in which the sight line moves by the vestibule-ocular reflex, is about ±<NUM> degrees in the horizontal direction in right and left of the principal sight line <NUM>.

<FIG> shows a state that simulation is performed for a vision in consideration of the vestibule-ocular reflex when rotating the head to the object <NUM> disposed on a virtual surface <NUM> in a virtual space. In an example shown in <FIG>, the object <NUM> is a rectangular pattern <NUM> (sign of the object <NUM> is not shown in <FIG>). The z-axis is set in a horizontal front direction, with rotation center Rc of the eyeball <NUM> as an origin, and the x-axis is set in the horizontal direction and the y-axis is set in the vertical direction in the virtual space. The x-axis, y-axis, and z-axis are orthogonal to each other. The rectangular pattern <NUM> is formed on the virtual surface <NUM> across distance d in a direction of angle θx with respect to y-z plane and angle θy with respect to x-z plane.

In an example shown in <FIG>, the rectangular pattern <NUM> is vertically bisected square grid, including central vertical grid line <NUM> passing through geometrical center <NUM> and right and left vertical grid lines <NUM> which are bilaterally symmetrical with respect to the central vertical grid line <NUM>, central horizontal grid line <NUM> passing through the geometrical center <NUM>, and upper and lower horizontal grid lines <NUM> which are vertically symmetrical with respect to the central horizontal grid line <NUM>. In the rectangular pattern <NUM> of the square grid, distance d between the virtual surface <NUM> and the eyeball <NUM> is adjusted so that a pitch (interval of the adjacent vertical grid lines <NUM> (horizontal grid lines <NUM>)) is set on the lens <NUM> at a viewing angle. Note that the pitch is expressed by an angle (unit°) in the horizontal direction or in the vertical direction, with a straight line connecting the rotation center Rc and the geometrical center <NUM> as a reference.

In the example shown in <FIG>, the lens <NUM> is disposed in front of the eyeball <NUM> at the same position and in the same posture as an actual as-worn position and posture of the lens <NUM>, and the virtual surface <NUM> is set so as to view the vicinity of the maximum horizontal angle θxm in which the eyeball <NUM> moves to the gaze point by the vestibule-ocular reflex, namely, so as to view the right and left vertical grid lines <NUM> and the upper and lower horizontal grid lines <NUM> at ±<NUM> degrees with respect to the gaze point.

The size of the rectangular pattern <NUM> of the square grid can be defined by the viewing angle, and can be set in accordance with a viewed object. For example, the pitch of the grid is small on a screen of a mobile computer, and the pitch of the grid is large on the screen of a desktop computer.

Meanwhile, it is appropriate to set the distance d to the virtual surface <NUM>, as a long distance of several meter or more in the distance portion <NUM>, as a near distance of about <NUM> to <NUM> in the near portion <NUM>, and as an intermediate distance of about <NUM> to <NUM> in the intermediate portion <NUM>, because there is a variation in the distance of the object <NUM> estimated by the distance portion <NUM>, the intermediate portion <NUM>, and the near portion <NUM>. However, there is no necessity for strictly setting the distance d in accordance with distance, intermediate, and near areas on the lens, because the rectangular pattern <NUM> in a distance of <NUM> to <NUM> is supposed to be observed in the intermediate portion <NUM> and the near portion <NUM>, when walking.

The rectangular pattern <NUM> is observed by refraction of the lens <NUM>, in a direction of the viewing angle deviated from a viewing direction (θx, θy). An observation image of the rectangular pattern <NUM> at this time, can be obtained by a normal ray tracing method. If the head is rotated by +α° in the horizontal direction with this state as a reference, the lens <NUM> is also rotated by +α° together with a face. At this time, the eyeball <NUM> is reversely rotated by α°, namely -α° by the vestibule-ocular reflex, and therefore the sight line <NUM> views the geometrical center <NUM> of the rectangular pattern <NUM> on the lens <NUM> using a position moved by -α°. Accordingly, a transmission point of the sight line <NUM> through the lens <NUM> and an incident angle on the lens <NUM> are varied, and therefore the rectangular pattern <NUM> is observed in a form different from an actual form. Such a deviation in the form is a factor of causing the swing of the image.

Therefore, in the evaluation method of the swing described in this section, an image of the rectangular pattern <NUM> is obtained at both end positions of maximum or specific rotation angle θ × <NUM> at the time of repeated right and left, or upper and lower rotation of the head, and the obtained image is overlapped on the geometrical center <NUM>, to thereby geometrically calculate the deviation of the form of both images. Maximum horizontal angle (about <NUM> degrees) in which the eyeball <NUM> moves by the vestibule-ocular reflex, is given as an example of the horizontal angle θ × <NUM>.

In the evaluation method of the swing described in this item, swing index IDs is given as the index used for evaluating the swing. Swing index IDs is the index indicating a moving area of the vertical grid line <NUM>, vertical grid line <NUM>, horizontal grid line <NUM> and horizontal grid line <NUM>.

<FIG> shows an example of the image of the rectangular pattern <NUM> when moving the eyeball <NUM> and the rectangular pattern <NUM> in right and left at first horizontal angle (shaking angle) θ × <NUM> (<NUM> degrees) with respect to the gaze point. A state shown in <FIG> corresponds to a state of viewing the rectangular pattern <NUM> so that the sight line <NUM> does not move from the geometrical center <NUM> of the rectangular pattern <NUM>, when the head moves in right and left in an as-worn state of the lens <NUM> at <NUM> degrees of the horizontal angle (shaking angle) θ × <NUM>. The rectangular pattern 50a (broken line) is an image (right rotation image) observed at shaking angle of <NUM>° through the lens <NUM> by the ray tracing method, and the rectangular pattern 50b (solid line) is an image (left rotation image) similarly observed at shaking angle of -<NUM>°. In <FIG>, the rectangular patterns 50a and 50b are shown in a state of being overlapped on each other so that the geometrical centers <NUM> coincide with each other. Note that the image of the rectangular pattern <NUM> observed at shaking angle of <NUM>° is positioned almost in a middle of them (not shown). An image observed when setting the shaking angle vertically (upper rotation image and lower rotation image) can also be similarly obtained.

The rectangular patterns 50a and 50b correspond to the image of the rectangular pattern <NUM> which is actually recognized by a user when shaking a head while viewing the rectangular pattern <NUM> through the lens <NUM>. A difference between the rectangular patterns 50a and 50b corresponds to the movement of the image actually recognized by the user when shaking the head.

<FIG> and <FIG> are views for describing the swing index IDs. Swing index IDs is the index indicating the moving area of the vertical grid line <NUM>, vertical grid line <NUM>, horizontal grid line <NUM> and horizontal grid line <NUM>. Namely, swing index IDs is the index corresponding to the magnitude of the deformation of the entire shape of the rectangular pattern <NUM>. As shown in <FIG> and <FIG>, twelve numerical values can be obtained as the swing index IDs by geometrically calculating each moving amount of the vertical grid line <NUM>, vertical grid line <NUM>, horizontal grid line <NUM> and horizontal grid line <NUM> of the rectangular pattern <NUM> as an area. <FIG> shows the moving amount (shaded part) of the horizontal grid lines <NUM> and <NUM>, and <FIG> is a view showing the moving amount of the vertical grid lines <NUM> and <NUM> (shaded part). It can be considered that "flickering" is expressed by the moving amount of the vertical grid line <NUM> and the vertical grid line <NUM> out of these gird lines, and "swell (waving)" is expressed by the moving amount of the horizontal grid lien <NUM> and the horizontal gird line <NUM>. Accordingly, if the moving amounts of the vertical grid line <NUM> and the vertical grid line <NUM> are added-up, the swing can be quantitatively evaluated as the "sense of flickering". Further, if the moving amounts of the horizontal grid line <NUM> and the horizontal grid line <NUM> are added-up, the swing can be quantitatively evaluated as a "sense of swell (waving)". Also, when the lens <NUM> has a large variation of magnification at a point near an evaluation point, for example when deformation such as expansion and contraction occurs in the horizontal direction, the swing index IDs is the index including such an element.

The unit of the swing index IDs is the square of degree (°) because the swing index IDs indicates the area on the viewing angle coordinate. Note that a value obtained by dividing the moving area of the vertical grid line <NUM>, the vertical grid line <NUM>, the horizontal grid line <NUM>, and the horizontal grid line <NUM>, by the area of the rectangular pattern <NUM> before the head is caused to rotate (<NUM> degree) and expressed by ratio (for example percentage), can also be used as the swing index IDs.

Regarding the swing index IDs, sum of moving areas of the vertical grid line <NUM> and vertical grid line <NUM> is defined as "vertical L", and sum of the moving areas of horizontal grid line <NUM> and horizontal grid line <NUM> is defined as "horizontal L", and sum of the "vertical L" and "horizontal L" may be indicated by an index s "total L".

"Horizontal L" and "vertical L" can be said as the indexes close to the sense of a user, from a fact that movement of an outline of the object grasped as a form is simultaneously sensed when a human such as a "user" actually feels the swing. Further, the user feels horizontal and vertical swings simultaneously, and therefore total swings of them, namely, "total L" can be a most appropriate index. However, there is a possibility that sensitivity to the "sense of flickering" and "sense of swell (waving)" is different depending on the user, or regarding a use of the sight line in the individual living environment, the following cases can be considered. Namely, movement of the sight line occurs frequently in the horizontal direction, and therefore what matters here is the "swell (waving)" or reversely the "flickering". Accordingly, it is also useful to index and evaluate the swing by each direction component. The merit of the swing index IDs is a point that the variation of magnification is taken into consideration. Particularly, in the case of the progressive addition lens, power is added in the vertical direction. Therefore, when viewing an object by vertically shaking a neck, the following phenomena are generated. Namely, the image is expanded or contracted, or viewed swinging back and forth, depending on the variation of powers. Further, even when the addition power is large, there is a remarkable phenomenon that the magnification is reduced in the side part of the near portion <NUM>. Therefore, expansion/contraction of the image occurs in the lateral direction of the image. Since these variations can be indicated by values, the swing index IDs is useful as the evaluation method.

<FIG> is a table showing parameters in examples and comparative examples described hereafter. The unit of the values in <FIG> is dioptre (D). Values of power Sph[D], example number (No.), vertical base curve (BC(vertical))[D], horizontal base curve (BC(horizontal))[D], toric surface element [D], and degressive element (degression)[D], are respectively shown sequentially from the left. Note that the vertical base curve corresponds to surface power OVPf. Horizontal base curve corresponds to surface power OHPf.

The progressive addition lens of examples and comparative examples shown below, is designed so that a corridor length of <NUM> as a spectacle specification applied to the progressive addition lens produced by SEIKO OPTICAL PRODUCTS CORPORATION, LTD. "SEIKO P-1SYNERGY <NUM>. 67AS(power: <NUM>)". The lens (finished lens not subjected to edging) has a diameter of <NUM>, and does not include an astigmatic power. The progressive addition lens of examples and comparative examples are fabricated by varying the degressive element in each combination of power Sph and addition power Add.

Example <NUM>-<NUM> to example <NUM>-<NUM> and comparative example <NUM> are the examples and comparative examples in the case that power Sph is <NUM>(D), and addition power Add is <NUM>(D). The surface power of the object-side surface 19A is called an outer surface power, and the surface power of the eyeball-side surface 19B is called an inner surface power hereafter. The inner surface power is originally a negative value, but shows an absolute value in this embodiment.

<FIG> is a graph showing vertical and horizontal outer surface powers on the principal sight line of example <NUM>-<NUM>, and <FIG> is a graph showing vertical and horizontal inner surface powers on the principal sight line of example <NUM>-<NUM>. <FIG> is a graph showing vertical and horizontal outer surface powers on the principal sight line of example <NUM>-<NUM>, and <FIG> is a graph showing vertical and horizontal inner surface powers on the principal sight line of example <NUM>-<NUM>. <FIG> is a graph showing vertical and horizontal outer surface powers on the principal sight line of example <NUM>-<NUM>, and <FIG> is a graph showing vertical and horizontal inner surface powers on the principal sight line of example <NUM>-<NUM>. <FIG> is a graph showing vertical and horizontal outer surface powers on the principal sight line of comparative example <NUM>, and <FIG> is a graph showing vertical and horizontal inner surface powers on the principal sight line of comparative example <NUM>. In each case, the horizontal axis corresponds to the coordinate on the principal sight line.

The progressive addition lens of example <NUM>-<NUM> to example <NUM>-<NUM> includes the abovementioned conditions (<NUM>) to (<NUM>). Namely, horizontal surface power OHPf is larger than vertical surface power OVPf in the distance portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19A (condition (<NUM>)). Also, horizontal surface power OHPn is larger than vertical surface power OVPn in the near portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19A (condition (<NUM>)). Also, vertical surface power OVPf in the distance portion <NUM> is larger than vertical surface power OVPn in the near portion <NUM>, in a degressive state (condition (<NUM>)). Also, in the progressive addition lens of example <NUM>-<NUM> to example <NUM>-<NUM>, horizontal surface power OHPm is also larger than vertical surface power OVPm in the intermediate portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19A.

Further, the object-side surface 19B includes the element for canceling the toric surface element included in the object-side surface 19A under condition (<NUM>) and condition (<NUM>). Namely, horizontal surface power IHPf is larger than vertical surface power IVPf in the distance portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19B. Also, horizontal surface power IHPn is larger than vertical surface power IVPn in the near portion <NUM> of the area long the principal sight line <NUM> on the eyeball-side surface 19B.

Further, the difference between vertical surface power IVPf in the distance portion <NUM> and vertical surface power IVPn in the near portion <NUM> of the area along the principal sight line <NUM> on the eyeball-side surface 19B, is larger than the difference between vertical surface power OVPf in the distance portion <NUM> and vertical surface power OVPn in the near portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19A, so that addition can be realized on the eyeball-side surface 19B with respect to the degression on the object-side surface 19A (Condition (<NUM>)).

Meanwhile, the progressive addition lens of comparative example <NUM> is a conventional inner surface progressive lens not including the abovementioned conditions (<NUM>) to (<NUM>).

Note that the variation of the surface power shown in <FIG> is briefly shown simply for understanding a basic structure. In an actual design, aspheric correction is added thereto, aiming at correcting an aberration in a lens circumferential view. A power variation is slightly generated in the vertical direction and the horizontal direction in the upper part of the distance portion <NUM> and the near portion <NUM>.

<FIG> is a view showing an astigmatism distribution when observing it through each position on the lens of the progressive addition lens of example <NUM>-<NUM> (through outer surface and inner surface of the lens, the same applies hereafter) , <FIG> is a view showing an astigmatism distribution when observing it through each position on a lens of the progressive addition lens of example <NUM>-<NUM>, <FIG> is a view showing an astigmatism distribution when observing it through each position on a lens of the progressive addition lens of example <NUM>-<NUM>, and <FIG> is a view showing an astigmatism distribution when observing it through each position on a lens of the progressive addition lens of comparative example <NUM>. As shown in <FIG>, the astigmatism distributions of the progressive addition lenses of example <NUM>-<NUM> to example <NUM>-<NUM> are approximately the same as the astigmatism distribution of the progressive addition lens of comparative example <NUM>.

Vertical and horizontal straight lines shown in <FIG> show a vertical reference line and a horizontal reference line passing through a geometrical center of a circular lens, and a shape image is also shown at the time of mounting the lens in a spectacle frame with the geometrical center as a fitting point Pe, which is an intersection point of the reference lines. The same thing can be said for <FIG>, <FIG>, <FIG>, <FIG>, and <FIG>.

<FIG> is a view showing an equivalent spherical power distribution when observing it through each position on a lens of the progressive addition lens of example <NUM>-<NUM>, <FIG> is a view showing an equivalent spherical power distribution when observing it through each position on a lens of the progressive addition lens of example <NUM>-<NUM>, <FIG> is a view showing an equivalent spherical power distribution when observing it through each position on a lens of the progressive addition lens of example <NUM>-<NUM>, and <FIG> is a view showing an equivalent spherical power distribution when observing it through each position on a lens of the progressive addition lens of comparative example <NUM>. As shown in <FIG>, the equivalent spherical power distributions of the progressive addition lenses of example <NUM>-<NUM> to example <NUM>-<NUM>, are approximately the same as the equivalent spherical power distribution of the progressive addition lens of comparative example <NUM>.

Accordingly, it is found that the progressive addition lens of example <NUM>-<NUM> to example <NUM>-<NUM> is the progressive addition lens having almost the same performance as the performance of the progressive addition lens of comparative example <NUM> in the astigmatism distribution and the equivalent spherical power distribution, by effectively using the aspheric correction.

<FIG> is a graph showing the swing index IDs of example <NUM>-<NUM> to example <NUM>-<NUM> and comparative example <NUM>. The horizontal axis indicates a vertical viewing angle corresponding to the coordinate on the principal sight line, and the vertical axis indicates the value corresponding to "total L" in the swing indexes IDs. The pitch of the rectangular pattern <NUM> is <NUM> degrees, and the swing of the head is <NUM> degrees horizontally in right and left respectively.

In each lens, the fitting point Pe is a primary position, namely, an intersection point of the sight line of a wearer and an outer surface of the lens in a horizontal front view in which the vertical viewing angle and the horizontal viewing angle are <NUM> degree. The distance portion <NUM> is a range from the fitting point Pe to <NUM> degrees upward, the intermediate portion <NUM> is a range from the fitting point Pe to the vicinity of -<NUM> degrees downward, and the near portion <NUM> is a range below the intermediate portion <NUM>.

As shown in <FIG>, in any one of the example <NUM>-<NUM> to example <NUM>-<NUM>, swing index IDs becomes smaller over the range from the distance portion <NUM> to the near portion <NUM>, compared with comparative example <NUM>. Accordingly, the progressive addition lenses of example <NUM>-<NUM> to example <NUM>-<NUM> are the lenses with less swing of image viewed through the lens, compared with the progressive addition lens of comparative example <NUM>.

Example <NUM>-<NUM> to example <NUM>-<NUM> and comparative example <NUM> are the examples and comparative example when power Sph is <NUM>(D) and addition power Add is <NUM>(D). Example <NUM>-<NUM> is shown in the figure hereafter, representing example <NUM>-<NUM> to example <NUM>-<NUM>.

<FIG> is a graph showing vertical and horizontal outer surface powers on the principal sight line of example <NUM>-<NUM>, and <FIG> is a graph showing vertical and horizontal inner surface powers on the principal sight line of example <NUM>-<NUM>. <FIG> is a graph showing vertical and horizontal outer surface powers on the principal sight line of comparative example <NUM>, and <FIG> is a graph showing vertical and horizontal inner surface powers on the principal sight line of comparative example <NUM>. In each case, the horizontal axis corresponds to the coordinate on the principal sight line.

The progressive addition lens of example <NUM>-<NUM> to example <NUM>-<NUM> includes the abovementioned conditions (<NUM>) to (<NUM>). Namely, horizontal surface power OHPf is larger than vertical surface power OVPf (condition (<NUM>)) in the distance portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19A. Also, horizontal surface power OHPn is larger than vertical surface power OVPn in the near portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19A (condition (<NUM>)). Also, vertical surface power OVPf in the distance portion <NUM> is larger than vertical surface power OVPn in the near portion <NUM>, in a degressive state (condition (<NUM>)). Also, in the progressive addition lens of example <NUM>-<NUM> to example <NUM>-<NUM>, horizontal surface power OHPm is larger than vertical surface power OVPm in the intermediate portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19A.

Further, difference between vertical surface power IVPf in the distance portion <NUM> and vertical surface power IVPn in the near portion <NUM> of the area along the principal sight lien <NUM> on the eyeball-side surface 19B, is larger than difference between vertical surface power OVPf in the distance portion <NUM> and vertical surface power OVPn in the near portion <NUM> of the area along the principal sight line <NUM> on the object-side surface 19A, so that addition can be realized on the eyeball-side surface 19B with respect to the degression on the object-side surface 19A (condition (<NUM>)).

<FIG> is a view showing an astigmatism distribution when observing it through each position on the lens of the progressive addition lens of example <NUM>-<NUM>, and <FIG> is a view showing an astigmatism distribution when observing it through each position on a lens of the progressive addition lens of comparative example <NUM>. As shown in <FIG>, the astigmatism distribution of the progressive addition lens of example <NUM>-<NUM> is approximately the same as the astigmatism distribution of the progressive addition lens of comparative example <NUM>. Further, as estimated from the results shown in <FIG> and <FIG>, the astigmatism distributions of the progressive addition lenses of example <NUM>-<NUM> and example <NUM>-<NUM> are also approximately the same as the astigmatism distribution of the progressive addition lens of comparative example <NUM>.

<FIG> is a view showing an equivalent spherical power distribution when observing it through each positon on a lens of the progressive addition lens of example <NUM>-<NUM>, and <FIG> is a view showing an equivalent spherical power distribution when observing it through each position on a lens of the progressive addition lens of comparative example <NUM>. As shown in <FIG>, the equivalent spherical power distribution of the progressive addition lens of example <NUM>-<NUM> is approximately the same as the equivalent spherical power distribution of the progressive addition lens of comparative example <NUM>. Also, as estimated from the results shown in <FIG> and <FIG>, the equivalent spherical power distributions of the progressive addition lenses of example <NUM>-<NUM> and example <NUM>-<NUM> are also approximately the same as the equivalent spherical power distribution of the progressive addition lens of comparative example <NUM>.

<FIG> is a view showing an equivalent spherical power distribution when observing it through each positon on a lens of the progressive addition lens of example <NUM>-<NUM>, and <FIG> is a view showing an equivalent spherical power distribution when observing it through each position on a lens of the progressive addition lens of comparative example <NUM>. As shown in <FIG>, the equivalent spherical power distribution of the progressive addition lens of example <NUM>-<NUM> is approximately the same as the equivalent spherical power distribution of the progressive addition lens of comparative example <NUM>. Also, as estimated from the results shown in <FIG> and <FIG>, the equivalent spherical power distribution of the progressive addition lenses of example <NUM>-<NUM> and example <NUM>-<NUM> are also approximately the same as the equivalent spherical power distribution of the progressive addition lens of comparative example <NUM>.

Accordingly, it is found that the progressive addition lenses of example <NUM>-<NUM> to example <NUM>-<NUM> are the progressive addition lenses having almost the same performance as the performance of the progressive addition lens of comparative example <NUM> in the astigmatism distribution and the equivalent spherical power distribution, by effectively using the aspheric correction.

From the abovementioned result, it is found that each example presents a lens with less swing of image viewed through a lens, compared with corresponding comparative examples, irrespective of magnitude of the addition power Add, and irrespective of the degressive element.

Note that the abovementioned embodiment and each modified example are given as an example, and the present invention is not limited thereto.

The present invention is not limited to the abovementioned embodiments and examples, but can be variously modified within the scope of the claims.

For example, the present invention includes substantially the same structure as the structure described in the embodiment (for example, the structure in which functions and methods are same, or the structure in which objects and effects are same). Also, the present invention includes a structure in which no-essential portion of the structure described in the embodiment is replaced. Also, the present invention includes a structure capable of exhibiting the same effect as the effect of the structure described in the embodiment, or a structure capable of achieving the same object. Also, the present invention includes a structure in which a publicly-known technique is added to the structure described in the embodiment.

Claim 1:
A lens set (<NUM>), comprising:
a plurality of progressive addition lenses for spectacles,
wherein
the plurality of progressive addition lenses have a distance portion (<NUM>) and a near portion (<NUM>) having different powers,
an equivalent spherical power of the distance portion (<NUM>) is plus,
the plurality of progressive addition lenses have common shapes as a shape of an object-side surface (19A),
the plurality of progressive addition lenses are lenses of plus prescription having different addition powers from each other by having different shapes from each other as the shape of an eyeball-side surface (19B);
the plurality of progressive addition lenses comprising a first lens (10a) and a second lens (10b), wherein the common shape of the object-side surface (19A) satisfies formulas (<NUM>) to (<NUM>): <MAT> <MAT> <MAT> <MAT> <MAT> wherein
OHPf1,<NUM>: a horizontal surface power of the distance portion (<NUM>) on the object-side surface (19A) along a vertical reference line or a principal sight line passing through a fitting point in the first, second lens (10a, 10b);
OHPn1,<NUM>: a horizontal surface power of the near portion (<NUM>) on the object-side surface (19A) along the vertical reference line or the principal sight line passing through the fitting point in the first, second lens (10a, 10b):
OVPf1,<NUM>: a vertical surface power of the distance portion (<NUM>) on the object-side surface (19A) along the vertical reference line or the principal sight line passing through the fitting point in the first, second lens (10a, 10b);
OVPn1,<NUM>: a vertical surface power of the near portion (<NUM>) on the object-side surface (19A) along the vertical reference line or the principal sight line passing through the fitting point in the first, second lens (10a, 10b);
wherein the fitting point is positioned at the geometric center of the first, second lens (10a, 10b);
wherein the eyeball-side surface (19B) along the vertical reference line or the principal sight line of the first lens (10a) and the second lens (10b) includes an element for cancelling the toric surface element defined in formulas (<NUM>) and (<NUM>); and
wherein an aspheric correction is added to the surface for correcting an aberration in a lens circumferential view, and wherein a power variation is generated in the vertical direction and the horizontal direction in the upper part of the distance portion (<NUM>) and in the near portion (<NUM>).