JPH10301065A - Multiple-focus spectacle lens - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multiple-focus lens with an excellent optical characteristic and a thin rim thickness by providing the lens with a pair of refraction faces of a front refraction face and a rear refraction face, composing it of the front refraction face of a basic lens part for far-looking and a small lens part for near-looking, providing the basic lens with a negative refractive power and making either of a basic lens or a smaller lens aspherical. SOLUTION: A front refraction face is comprised of a far-looking basic lens and a near-looking small lens, and refractive power of the basic lens is negative, and either of the basic lens or the small lens is made aspherical. When a meridian plane 1 curvature of the front refraction face of the basic lens is expressed by βm (m<-1> ), a sagittal plane curvature orthogonal to a meridian plane by β s (m<-1> ), a difference between. both curvatures by Z=βm-βs, the curvature difference Z increases within a range of 20 mm in the direction of outer circumference from the symmetrical axis of a rotary symmetry, and decreases outside of this range. Namely, in the neighborhood of the rotary axis, the lens has a same base curve curvature as a conventional spherical, lens 4 but is increased in the curvature as it goes to the outer circumference.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multifocal spectacle lens used for assisting accommodation of the eye, particularly for correcting presbyopia.

[0002]

2. Description of the Related Art A spherical lens is used as a first refracting surface of a spectacle lens used for correcting a refractive error of an eye in consideration of easiness of processing. On the other hand, in addition to the spherical surface, a toric surface is used as the second refraction surface for correcting astigmatism and the like. Hereinafter, in the present invention, the spherical lens and the toric surface lens are collectively referred to as a spherical lens.

The refractive power of a lens is a diopter (hereinafter, referred to as diopter).
"D"). The refractive power (surface refractive power) on the surface of the lens is the curvature ρ of the surface.
(Unit is m ⁻¹ , radius of curvature R = 1 / ρ) and refractive index n of the glass material of the lens, Is defined as The refractive power of the first surface of the lens is particularly called a base curve, and a curvature corresponding to the base curve is called a base curve curvature.

Since the power of a lens is mainly determined by the two refractive powers of the first surface and the second surface, the base curve required to obtain a constant power of the lens has various values depending on the combination of the refractive powers. Can be taken. However, in practice, the base curve is limited to a certain range with respect to the power of the lens, in order to reduce the optical performance, especially the astigmatism acting on the eye when viewed through the side part away from the optical axis of the lens. You. In general, a spectacle lens used to determine a value that minimizes the astigmatism is a so-called Chernning ellipse. The value obtained using the Chelning ellipse is the minimum solution of astigmatism in a thin lens, and since the actual lens has a center thickness, it is necessary to perform ray tracing instead of the Chelning ellipse to find a practical solution. I have. Although the solution obtained by the Chelning ellipse and the practical solution by ray tracing are slightly different, the practical solution does not deviate so much from the Chelning ellipse.

According to the Chelning's ellipse, the optimal base curve that minimizes astigmatism is different between far vision and near vision. That is, when designing an optical system, the optimum base curve differs depending on whether importance is placed on far vision or near vision. Therefore, in order to correct aberrations equally in far vision and near vision, a base curve near the middle between the far vision base curve and the near vision base curve is generally adopted.

[0006] As described above, as a lens design concept,
(1) When the aberration is reduced in the far vision, (2) When the aberration is reduced in the near vision, (3) The aberration is minimized in both the far vision and the near vision. In this case, three design goals can be considered.

Next, the multifocal lens will be described. One lens is used for the far vision part (distance part) and the near vision part (near vision part)
A lens having two different powers is referred to as a bifocal lens, and a lens having three types of powers for distance use, near use, and intermediate is referred to as a triple focus lens. A lens in which the refractive power is continuously changed from the distance portion to the near portion is called a progressive lens.

The types of currently used bifocal lenses can be broadly classified into a fusion type and a one-piece type. FIGS. 5A and 5B show the configuration of the fusion lens. In the fusion-type lens, small glass balls such as barium flint having a high refractive index are embedded and fused on the front surface of a lens serving as a crown glass ball. The fusion-type lens has a feature that there is no step in the boundary line of the lens, and the boundary between the base ball and the small ball is less noticeable.

A typical one-piece lens is a one-piece lens made of a plastic material.
FIGS. 6A and 6B show an example of a one-piece lens. The weight of the one-piece plastic lens is reduced, and the small balls protrude from the base ball, and there are steps at the boundary. Here, the difference between the refractive power of the distance portion and the refractive power of the near portion is generally referred to as an addition power.

For correcting presbyopia, a single focus lens, a bifocal (bifocal) lens, a progressive multifocal lens, or the like is used. Of these, progressive multifocal lenses are
Since there is no need to change or remove glasses during distance vision and near vision, and there is no boundary between lenses such as a bifocal lens, the demand has been considerably increased. However, the progressive multifocal lens still has so-called shaking distortion, the optical performance of which is not so excellent, not only takes time to get used to, but also some people are not used to it.

On the other hand, a multifocal lens such as a bifocal lens does not have an intermediate portion of a focal length unlike a progressive multifocal lens, but is only optically superior to a progressive multifocal lens. It is relatively easy to use because it has a wide field of view. However, there is a boundary between lenses in appearance.

Conventionally, various multifocal lenses have been manufactured and sold. As described above, the bifocal lens and the like have excellent optical performance as compared with the progressive multifocal lens. It cannot be said that it has performance. For example, even if the optical performance of the distance portion is excellent, the optical performance of the near portion may not be sufficient, or vice versa.

A disadvantage of a lens having a negative power, which is used mainly for correcting myopia (the refractive power of a base lens is negative) in a far vision portion, is that the edge thickness of the lens (the outer circumference of the lens) increases as the power of the lens increases. (Edge thickness).

FIG. 7 shows a conventional example of a lens having a far vision (infinity) correction design. The power of such a lens is -4.0 D, and the lens diameter is 70 mm. This lens is a commonly used plastic lens having a refractive index of 1.50, and has a base curve of 4.0 D and a center thickness of 1.0. 0 mm. In addition,
The refractive index is a refractive index for the d-line (λ = 587.56 nm). In the case of this conventional example, the edge thickness ED of the lens is 6.7.
mm, and the protrusion amount H is 11.7 mm. As is evident from FIG. 7, when the lens is a spectacle lens, the edge thickness becomes thick and the appearance becomes unsightly (poor appearance). As a method for solving this, it is conceivable to reduce the base curve. The lens shown in FIG. 8 is a lens having the same condition as that of FIG. 7 and having a base curve of 0.5D. The edge thickness ED of this lens is 6.0 mm, and the edge thickness can be reduced by 0.7 mm as compared with the lens of FIG. In addition, the protrusion amount H is 6.7 mm, which is similarly reduced by 5.0 mm.

On the other hand, since the base curve itself is originally determined from the optical performance as described above,
When a D base curve is used, the optical performance is significantly reduced as compared with a lens having a 4.0 D base curve. FIGS. 9 and 10 show the astigmatism in the visual field when the lenses having the base curves of 4.0D and 0.5D are worn, respectively. The vertical axis is the angle of the field of view (unit: degree), and the horizontal axis is astigmatism (unit is D, meridional (m
direction (m) and sagittal (sagi)
tal) direction (s) represents the difference (ms). )
It is. As is clear from FIGS. 9 and 10, the astigmatism is significantly larger when the base curve is 0.5D than when it is 4.0D. You can see how the selection of the base curve affects the optical performance.

Table 1 below shows the specification values of the above-mentioned conventional spherical lens. R1 and R2 are radii of curvature of the lens surface from the observation object side.

[0017]

Table 1 In the case of distance vision design / base curve 4.0D (FIG. 7) R1 = 125,000 ED = 6.7 R2 = 62.417 H = 11.7 For distance vision design / base curve 0.5D Case (FIG. 8) R1 = 10000.00 ED = 6.0 R2 = 111.107 H = 6.7

Further, as is apparent from the Chelning's ellipse, the optimal base curve in far vision is larger than the optimal base curve in near vision. In a multifocal lens such as a bifocal lens, by adding power in the lens to supplement the accommodation power of the eye to be examined,
It compensates for the lack of accommodation of the eye. In this case, the curve for the near portion is a curve obtained by adding the addition amount to the curve for the distance portion, and the curve for the distance portion is smaller than the curve for the near portion. For example, the base curve of the distance section is 5D
, When the addition is 2D, the base curve of the near portion is 7
D. Therefore, no matter how much the optical performance in far vision is improved, it will not only be optimal in near vision but rather worsen. Conversely, even if the optical performance for near vision is improved, the optical performance for far vision will deteriorate.

In order to solve the problem of the appearance of the lens and the deterioration of the optical performance, the first refracting surface or the second refracting surface of the lens is made aspheric (two or more spherical surfaces). Various methods (including combinations) have been proposed.

[0020]

In order to solve the above-mentioned drawbacks in optical performance, the first refracting surface is made aspherical regardless of whether it is a single focus lens or a multifocal lens.
JP-A-53-94947, JP-B-59-4116
No. 4, for example, have been proposed.

JP-A-53-94947 discloses the first
Center part of the refracting surface (40 mm in diameter according to the embodiment)
And its outer peripheral part, with the central part as one spherical surface,
It is disclosed that the outer peripheral portion is constituted by a toric surface having a curvature larger than the curvature of the central spherical surface. In this case, since there is a large spherical portion in the center, in order not to significantly impair the optical performance of the outer peripheral portion, a very extreme difference in curvature cannot be given to the center, so that a large thinning effect is obtained. It is a problem without being obtained.

In Japanese Patent Application Laid-Open No. Hei 8-5966, the lens is made thinner and the optical performance is improved to some extent, but it is not suitable for a multifocal lens.

Japanese Patent Publication No. 59-41164 discloses the first
A refracting surface having an aspheric surface given by a special function is disclosed. In this case, the lens refracting surface is characterized in that the lens refracting surface protrudes from the center of rotation of the lens toward the peripheral direction toward the first surface side and then goes rearward. This aspherical lens has a problem in that, due to its unique shape, remarkably uneven reflection occurs on the refracting surface of the undulating lens first surface, which is undesirable in appearance.

Japanese Patent Application Laid-Open Nos. 53-84741 and 53-84741 disclose a second refracting surface having an aspherical surface.
JP-A-85742, JP-A-58-195826, and JP-A-60-60724. A common problem in the case where the second surface refraction surface is an aspherical surface is that, when a spectacle lens is used, in a lens with astigmatism, the first surface refraction surface is a convex toric surface or a cylindrical surface. The appearance is bad. Also,
At present, spectacle lenses that are widely used have the second refracting surface as a concave toric surface, and therefore a lens processing machine is also manufactured to process such a shape. Therefore, in order to manufacture a lens having the second surface refracting surface as an aspherical surface, there is also a problem that a large change in equipment such as a processing machine is required.

The present invention relates to a multifocal spectacle lens which is used for correcting presbyopia as an aid to the accommodation power of the eye as described above, and a problem with a multifocal lens having a negative refractive power for a base lens. It is an object of the present invention to provide a multifocal spectacle lens excellent in optical performance and having a small edge thickness.

[0026]

The multifocal spectacle lens of the present invention has a pair of refracting surfaces, a front refracting surface and a rear refracting surface, wherein the front refracting surface has a base portion for far vision, And a small ball portion for near vision, wherein the refractive power of the ball has a negative refractive power, and at least one of the ball portion and the small ball portion is an aspherical surface. .

As described above, in general, the optimal base curve for a spherical lens is a curve close to that obtained from the Chernning ellipse. When this curve is employed, satisfactory optical performance can be obtained. However, disadvantages are that the edge thickness of the lens increases as the dioptric power increases, and the curve of the second surface becomes tighter, so that the protrusion of the lens is reduced. It may be stronger and harder to see.

As long as the base ball has a spherical shape, the optimum base curve in terms of optical performance is uniquely determined, and when it is used as a spectacle lens, the edge thickness becomes thick and the appearance becomes unsightly. In order to eliminate the disadvantage that the edge thickness becomes thick and it becomes hard to see, it is necessary to adopt a base curve that is duller than the optimum base curve in optical performance. At this time, the optical performance deteriorates as described above.

In the configuration of the present invention, by adopting an aspherical surface, a base curve which is duller than an optimal base curve in terms of optical performance is adopted, and excellent optical performance can be realized while eliminating external defects.

Further, in the multifocal spectacle lens of the present invention, the front refracting surface of the base lens or the small ball has a rotationally symmetric aspherical shape, and the meridional surface of the front refracting surface has a curvature of βm (m ⁻¹ ), When the curvature of the spherical surface that is perpendicular to the meridian plane is βs (m ⁻¹ ), and the difference between the two curvatures is Z = βm−βs, It is characterized in that the value of the curvature difference Z increases within a range of at least 20 mm in the outer peripheral direction, and thereafter decreases.

In a spectacle lens, it is necessary that astigmatism be minimized. The use of a base curve that is duller than the optimum base curve in terms of optical performance increases astigmatism. It goes without saying that an aspheric surface that minimizes such astigmatism is desirable. In order to minimize astigmatism, an aspherical surface may be used in which the curvature in the meridional direction (m) and the curvature in the sagittal direction (s) are different. The amount depends on the generated astigmatism and the height on the lens surface. Therefore, when the curvature of the meridional surface of the front refraction surface is βm (m ⁻¹ ) and the curvature of the sphere lacking surface perpendicular to the meridian surface is βs (m ⁻¹ ), Z = βm−βs from the center to the outer periphery. Value and its change are important. This is true for both the distance portion and the near portion.

According to the present invention, in order to correct the astigmatism caused by dulling the curve of the refraction surface of the first surface of the lens of the lens, the surface is formed with an aspherical shape. Has adopted. Further, in the present invention, a multifocal lens having a thin appearance and excellent optical performance is realized by adopting an aspheric surface while making the first refraction surface of the small ball dull.

Further, in the present invention, the front refraction surface of the base ball or the small ball has a rotationally symmetric aspherical shape, the curvature of the meridional surface of the front refraction surface is βm (m ⁻¹ ), and is orthogonal to the meridian surface. Is the curvature of the missing spherical surface, βs (m ⁻¹ ), the difference between the two curvatures is Z = βm−βs, and the curvature of the base ball or the small ball on the rotational axis symmetry axis is ρ.
(M ^-1 ), the d-line (λ = 587.5)
6 nm) and n (m) the distance from the axis of symmetry of the rotational axis symmetry, at least 20 mm from the axis of symmetry of the rotational axis symmetry toward the outer periphery of the baseball or small ball. In the range, (n−1) × ρ × h <| Z | <(n−1) × ρ × h × l
It is desirable to satisfy the condition of 000.

In the present invention, while the curve of the refracting surface of the base lens of the first surface of the lens is made dull, an aspherical surface is employed to correct astigmatism caused by making the curve dull. ing. By satisfying these conditions,
Even if the edge thickness of the lens becomes strong, the edge thickness does not become too thick, and the curve of the second surface becomes dull, so the protrusion of the lens is reduced, and a lens having a shape that is not visually unsightly has been realized. However, it is possible to provide an optical element having excellent optical performance. This becomes remarkable as the near portion area (the shape of the small ball) becomes wider.

[0035]

Embodiments of the present invention will be described below with reference to the accompanying drawings.

FIG. 1 is a diagram showing a lens configuration of a baseball portion. In FIG. 1, a small ball portion is omitted.

In this embodiment, the frequency shown in FIG.
The aspheric surface of the present invention is applied to a spherical lens having an infinity design of 4.0D and a base curve of 0.5D. In FIG. 1, 1 is a first refraction surface, 2 is a second refraction surface, and 3 is an axis of symmetry of the lens. A broken line 4 indicates a conventional spherical lens, and is an arc having a curvature corresponding to a base curve. Cross section (meridional plane) 1 of the first surface of the lens according to the present embodiment 1
Has the same curvature of the base curve as 4 near the rotation axis, but the curvature increases toward the outer periphery (radius of curvature decreases), and as a result, the outer periphery is behind the circular arc of the base curve. (Observed side).

FIGS. 2 (a) and 2 (b) show that the curvature of the meridional surface of the front refracting surface is βm (m ⁻¹ ), and the curvature of the spherical surface perpendicular to the meridional surface is βs (m ⁻¹ ). Sometimes, a change in the difference Z = βm−βs between the two curvatures from the center to the outer periphery, and an astigmatism when the spectacles according to the present invention are worn are shown. The horizontal axis indicates the distance h from the symmetry axis 3 and the vertical axis indicates the value of Z. Table 2 shows specific values of Z.

[0039]

Table 2 h (mm) Z 0.0 0.0 5.0 0.144 10.0 0.508 15.0 0.917 20.0 1.166 25.0 1.161 30.0 1. 104 35.0 1.727

As shown in FIG. 2A, the value of Z increases away from the axis of symmetry and toward the outer periphery, and thereafter changes from an increase to a decrease around 25 mm from the axis of symmetry 3. Originally, it is advantageous that the value of Z should continue to increase without changing from increasing to decreasing only in order to reduce the edge thickness. That is, if the design philosophy is to maintain sufficient optical performance up to a distance of about 30 mm from the axis of symmetry 3 and not to consider optical performance in the vicinity of 30 mm or more, there is no need to turn from increase to decrease in this way. In the present embodiment, the value of Z is changed from increase to decrease in order to maintain sufficient optical performance up to a range where the distance from the symmetry axis 3 is about 35 mm.

In this embodiment, in order to attain both sufficient optical performance and elimination of the unsightly appearance (thickness of the edge thickness), a range of at least 20 mm from the symmetry axis of the rotational axis toward the outer peripheral direction of the lens. In this case, the value of Z is increased. By giving such a change in curvature, the shape of the first refracting surface becomes as shown in FIG. 1, and the edge thickness can be reduced as compared with the conventional one. In the present embodiment, the edge thickness ED is 5.
4 mm and the protrusion amount H is 6.7 mm. Compared with the conventional spherical lens shown in FIG. 7, the edge thickness is 1.3 mm and the protrusion amount is 5.0 mm. ing. Further, looking at astigmatism, a large astigmatism was generated in the spherical lens having the base curve of 0.5D (FIG. 8) as shown in FIG. However, as shown in FIG. 2B, the astigmatism of the present embodiment is significantly improved while the base curve is 0.5D.

As described above, in this embodiment, the first lens
In order to correct astigmatism generated by making the curve of the refraction surface dull while making the curve dull, an aspheric surface is adopted for the surface. As a result, a lens having a thinner lens, improved appearance, and excellent optical performance is realized. In this embodiment, FIG.
As is clear from the astigmatism diagram of FIG. 3B, the design is such that the astigmatism when an object at a distance in far vision (infinity) is viewed is zero.

The above embodiment is designed to make astigmatism zero in far vision (infinity). Apart from such a far vision correction design of the distance portion, a design aiming at zero astigmatism when viewing the near portion at a distance of near vision (about 30 cm) is also possible. is there. Hereinafter, another embodiment based on the near vision correction design of the near portion will be described.

FIG. 3 is a lens configuration diagram of another embodiment in which an aspherical surface is used for a small lens portion of a spectacle lens. The refractive power of the small ball is obtained by adding +2 diopter as an addition to the distance portion described above, the refractive power of the near portion is -2D, and the front base curve of the near portion is 2.5D. The present invention is applied to a design emphasizing near vision (30 cm).

In FIG. 3, reference numeral 1 denotes a first refracting surface, 2 denotes a second refracting surface, and 3 denotes an axis of symmetry of the lens of the small lens portion. Broken line 4
Is an arc having a curvature corresponding to a base curve in a conventional spherical lens. The refractive surface cross section (meridional surface) 1 of the first surface of the lens according to the present invention is made to have a base curve and an aspherical base ball and a small ball, so that the outer periphery of the lens is smaller than the base curve arc of the conventional spherical lens at the outer periphery. Also, the base ball portion is located forward and the small ball portion is located rearward.

FIG. 4A shows the curvature of the meridional surface of the front refracting surface as βm (m ⁻¹ ), and the curvature of the spherical surface perpendicular to the meridional surface as β.
FIG. 6 is a diagram showing a change in the difference Z = βm−βs from the center to the outer periphery when s (m ⁻¹ ), where the vertical axis represents the value of Z, and the horizontal axis represents the distance from the symmetry axis 3. h.

Table 3 shows specific values of Z.

[0048]

Table 3 h (mm) Z 0.0 0.0 0.5 0.031 10.0 0.108 15.0 0.191 20.0 0.239 25.0 0.229 30.0 0. 129 35.0 -0.267

As is clear from FIG. 4A, the curvature difference Z
Increases from the symmetry axis 3 toward the outer periphery, and then changes from increase to decrease within a range of 20 to 25 mm from the symmetry axis. Originally, if only the edge thickness is to be reduced, it is advantageous to keep increasing without changing from increasing to decreasing. For example, maintain sufficient optical performance up to a distance of about 25 mm from the axis of symmetry, and thereafter (after 25 mm)
If the optical performance is not a problem in the range, there is no need to switch from increasing to decreasing in this way. However, in this embodiment, the value of Z is changed from increasing to decreasing in order to maintain sufficient optical performance up to a distance of about 35 mm from the symmetry axis toward the outer periphery.

Further, in the present embodiment, in order to achieve both sufficient optical performance and elimination of the unsightly appearance (thickness of the edge thickness), at least 20 mm from the symmetric axis of rotation axis symmetry to the outer peripheral direction of the lens. In the period between, the value of the curvature difference Z is increased. By giving such a change in the curvature, the shape of the first refraction surface of the lens of this embodiment becomes as shown in FIG. As is apparent from FIG. 3, the protrusion amount of the small ball portion is reduced due to the effect of the aspherical surface and the decrease of the base curve of the near portion accompanying the decrease of the base curve of the distance portion.

FIG. 4B shows astigmatism in near vision when the lens of this embodiment is worn.

Table 4 shows the specification values of the embodiment of the present invention.
Signs are the same as in Table 1.

[0053]

Table 4 In the case of a far-sight part design (FIG. 1) R1 = 1000.000 (0.50D) ED = 5.4 R2 = 111.107 H = 6.7 In the case of a near-sight part design (FIG. 3) R1 = 200.000 (2.5D) R2 = 111.107

As described above, in this embodiment, in order to correct the astigmatism caused by making the curve of the refracting surface of the first surface of the lens dull while making the curve dull, the aspherical surface is used for the distance portion. And for near use. As a result, a spectacle lens having excellent optical performance can be realized while improving the lens rim and the amount of protrusion that are not good in appearance.

The above embodiment is directed to a spectacle lens having a pair of front and rear refracting surfaces, wherein at least one of the two refracting surfaces is mainly a ball portion used for far vision and a near lens portion for near vision. Is composed of
The multifocal lens has a base lens having a negative refractive power, and the base ball portion and the small ball portion are aspherical. In addition,
The edge thickness of the lens becomes slightly thicker as the power increases,
At the expense of the external appearance, in which the amount of protrusion of the lens increases, the refracting surface of the base ball may have a spherical shape with an optimum base curve, and the small ball portion may have an aspherical shape.

When the area of the small ball portion is small, the field of view is narrowed. Therefore, the surface shape of the small ball portion may be spherical.

Although the embodiments are described for a bifocal lens, it goes without saying that the present invention can be applied to a trifocal lens.

Further, in each embodiment, the design in which the distance vision is emphasized in the design of the base portion is taken up. However, a design in which the intermediate vision between the distance vision and the near vision is emphasized is also included in the present invention. Needless to say,

[0059]

According to the present invention, the thickness of the edge can be reduced and the protrusion of the first refractive surface can be reduced (flattened), and at the same time, the optical performance can be improved. Furthermore, not only can astigmatism at any specific distance from far vision to near vision be controlled in good condition over the entire lens range according to each purpose, but in combination with a low base curve, optical performance can be improved. It is possible to realize a spectacle lens which is excellent in appearance, has a thin edge and is flat and has a good appearance. Needless to say, when combined with a material having a high refractive index, a greater effect can be obtained.

[Brief description of the drawings]

FIG. 1 is a diagram showing a lens shape of a spectacle lens according to an example of the present invention.

FIGS. 2A and 2B are diagrams respectively showing a curvature difference Z and astigmatism of the multifocal spectacle lens shown in FIG.

FIG. 3 is a diagram showing a lens shape of a spectacle lens according to another embodiment of the present invention.

4A and 4B are diagrams respectively showing a curvature difference Z and astigmatism of the multifocal spectacle lens shown in FIG.

FIGS. 5A and 5B are diagrams respectively showing a front surface and a cross section of a conventional fusion type bifocal lens.

FIGS. 6 (a) and (b) show a conventional one-piece type 2
It is a figure which shows the front and cross section of a bifocal lens, respectively.

FIG. 7 is a diagram showing a lens surface shape of a conventional spherical spectacle lens (base curve 4.0D) designed with emphasis on far vision.

FIG. 8 is a diagram illustrating a lens surface shape when the base curve is set to 0.5D at the same frequency as in FIG. 7;

9 is a diagram illustrating astigmatism in a wearing state of the lens illustrated in FIG. 7 having a base curve of 4.0D.

10 is a diagram illustrating astigmatism in a wearing state of the lens illustrated in FIG. 8 whose base curve is 0.5D.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 1st refraction surface 2 2nd refraction surface 3 Symmetry axis 4 Conventional spherical lens

Claims (7)

[Claims] 1. A multifocal spectacle lens having a pair of refracting surfaces, a front refracting surface and a rear refracting surface, wherein the front refracting surface is composed of a base ball for far vision and a small ball for near vision. The multifocal spectacle lens, wherein the refractive power of the base ball has a negative refractive power, and at least one of the base ball and the small ball is an aspheric surface. 2. The front refracting surface of the base ball has an aspherical shape symmetrical with respect to the rotation axis, the meridional surface of the front refracting surface has a curvature of βm (m ⁻¹ ), When the curvature is βs (m ⁻¹ ) and the difference between the two curvatures is Z = βm−βs, the curvature is within a range of at least 20 mm from the axis of symmetry of the rotational axis toward the outer periphery of the ball. The multifocal spectacle lens according to claim 1, wherein the value of the curvature difference Z increases, and the value of the Z decreases outside the range. 3. The front refracting surface of the base ball has an aspherical shape symmetrical with respect to a rotational axis, the curvature of the meridional surface of the front refracting surface is βm (m ⁻¹ ), The curvature is βs (m ⁻¹ ), the difference between the two curvatures is Z = βm−βs, the curvature on the symmetrical axis of rotation of the ball is ρ (m ⁻¹ ), and the d-line (λ = 587.56 nm), where n is the refractive index with respect to the rotational axis symmetry and h (m) is the distance from the symmetry axis with respect to the rotational axis toward the outer periphery of the ball. Within the range of 20 mm or less, (n-1) × ρ × h <| Z | <(n−1) × ρ × h × 1
The multifocal spectacle lens according to claim 1, which satisfies a condition of 000. 4. The multifocal spectacle lens according to claim 2, wherein the front refracting surface of the small ball has a spherical shape. 5. The front refracting surface of the small ball has an aspherical shape symmetrical with respect to the rotation axis, the curvature of the meridional surface of the front refracting surface is βm (m ⁻¹ ), and the curvature of a spherical segment perpendicular to the meridional surface. Is βs (m ⁻¹ ), and the difference between the polarities is Z = βm−βs. The curvature is within a range of at least 20 mm from the axis of symmetry of the rotational axis toward the outer periphery of the small ball. 2. The multifocal spectacle lens according to claim 1, wherein the value of the difference Z of the lens increases, and the value of Z decreases outside the range. 6. The front refracting surface of the small ball has an aspherical shape symmetrical with respect to the rotational axis, the curvature of the meridional surface of the front refracting surface is βm (m ⁻¹ ), and the curvature of a spherical segment perpendicular to the meridional surface. Is βs (m ⁻¹ ), the difference between the two curvatures is Z = βm−βs, the curvature on the axis of symmetry of the small ball on the rotational axis symmetry is ρ (m ⁻¹ ), and the d-line of the small ball (λ = 587. When the refractive index with respect to 56 nm) is n and the distance from the axis of symmetry of the rotation axis symmetry is h (m), a range within at least 20 mm from the axis of symmetry of the rotation axis symmetry to the outer peripheral direction of the small ball. In (n-1) × ρ × h <| Z | <(n−1) × ρ × h × l
The multifocal spectacle lens according to claim 1 or 5, wherein the following condition is satisfied. 7. The multifocal spectacle lens according to claim 5, wherein the front refracting surface of the base ball has a spherical shape.