JPH0812339B2 - Eyeglass lens - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial field of application] The present invention relates to the front convex surface shape of a spectacle lens,
In particular, it relates to the surface shape of a spectacle lens used for myopia correction.

[Conventional technology]

BACKGROUND ART Conventionally, a spherical surface is adopted as a refracting surface on the front convex surface side (hereinafter, referred to as a front refracting surface) of a spectacle lens for the purpose of correcting myopia for easy processing. Hereinafter, this lens is referred to as a spherical lens. Generally, the refracting power of a lens is expressed in a unit called diopter (hereinafter, D), and the refracting power (surface refracting power) on the surface of the lens is a curvature ρ (the unit is m ^-1 ) of the surface.
And the refractive index n of the lens material are defined by the following equation.

Surface refracting power = (n−1) × ρ The surface refracting power of the lens front refracting surface is particularly called a base curve. Hereinafter, the curvature corresponding to the base curve is called the curvature of the base curve. The power of the lens is mainly 2 in the front and the rear.
Since it is determined by the refracting powers of the two refracting surfaces, the base curve can take various values depending on how they are combined. 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 that acts on the eye when viewed through the side part away from the optical axis of the lens. To be done. Fig. 2 shows an example with a refractive index of 1.50. When the vertical axis is the base curve and the horizontal axis is the lens power, the side of the optical axis is viewed at 30 ° with the glasses worn. The astigmatism generation situation in this case is shown. The solid line is the astigmatism at distance viewing, and the number attached to the line shows the amount of astigmatism. The line of astigmatism 0.3D is shown on both sides of the line with no astigmatism (0D). There is. The broken line similarly represents astigmatism in near vision (30 cm). As can be seen from this figure, the optimum base curve where the astigmatism is zero differs between far vision and near vision.
Therefore, the base curve in the shaded area indicated by a in the figure is generally adopted so that the distance vision and the near vision are equally improved.

By the way, a drawback of the myopic lens is that the edge thickness of the lens (the thickness at the outer peripheral edge of the lens) becomes thicker as the myopia becomes stronger. FIG. 3 shows an example thereof, and shows a cross section of a lens having a power of −6D and a lens diameter of 75 mm. This lens is a commonly used plastic lens with a refractive index of 1.5 and a base curve of 2.0.
D, lens center thickness is 2 mm. In the case of this example, the edge thickness of the lens is 11.7 mm, which makes the edge thick and unsightly when worn as eyeglasses. As a method of solving this, it is conceivable to reduce the base curve. FIG. 4 shows a lens under the same conditions as in FIG. 3 with a base curve of 1.0D. The edge thickness of this lens is 11.2 mm, and the edge thickness can be reduced by 0.5 mm. However, as described above, the base curve is determined from the optical performance, and as shown in FIGS. 5 and 6, when it is set to 1.0 base, the optical performance deteriorates remarkably. Figures 5 and 6 show the base curve, respectively.
The astigmatism in the field of view of the 2.0D and 1.0D ones is shown. The vertical axis represents the field angle (unit: O), and the horizontal axis represents the astigmatism based on the refractive power in the sagittal direction ( Unit: D). The figure shows infinity (∞), 1m, 0.3m
The astigmatism at each field in each case is shown.

On the other hand, as a method for solving such a defect in the appearance of the lens for correcting myopia, there are some methods in which the front refractive surface or the rear refractive surface of the lens is made aspherical (including a combination of two or more spherical surfaces). Proposed. Hereinafter, those methods and their problems will be described.

An example of an aspherical front refracting surface is disclosed in JP-A-53-
There are 94947 and Japanese Patent Publication No. 59-41164 (US 4,279,480). In JP-A-53-94947, the front refracting surface is divided into a central portion (diameter 40 mm according to the embodiment) and its outer peripheral portion, and the central portion is defined as one spherical surface. The outer peripheral portion is defined by the curvature of the central spherical surface. It is disclosed that it is configured by a toric surface having a large curvature. In this case, since there is a large spherical part in the center,
In order to prevent the optical performance of the outer peripheral portion from being significantly impaired, an extreme difference in curvature with respect to the central portion cannot be provided, so that a large thinning effect cannot be obtained. Japanese Patent Publication 59-41164
(US4,279,480) discloses a front refracting surface which is an aspherical surface given by a special function. in this case,
It is characterized in that the lens refraction surface projects from the center of rotation of the lens toward the peripheral direction to the front side and then faces rearward.
The problem with this lens is its unique shape, This is a point that is unfavorable in appearance because remarkably uneven reflection occurs on the front refracting surface of the lens.

Next, as the aspherical rear refracting surface, there are JP-A-53-84741, JP-A-53-84742, and JP-A-58-195826 (IT
48315/82), and JP-A-60-60724. A common problem in the case where these rear refracting surfaces are made aspherical is that, in a lens with astigmatism, the front refracting surface is a convex toric surface or a cylindrical surface, so that the appearance is bad when it is used as eyeglasses. In addition, the spectacle lenses that are currently in widespread use have a backward refracting surface that is a concave toric surface, and a lens processing machine is also made for that. However, there is also the problem of having to make major changes in equipment.

As described above, the conventional lens using the aspherical surface has various problems.

[Problems to be Solved by the Invention]

The present invention solves the above-mentioned problems in the spectacle lens for correcting myopia, and provides a spectacle lens having excellent optical performance and a thin edge.

[Means for solving the problem]

The present invention solves the above-mentioned problems by forming the front refractive surface of the lens into a special aspherical shape. FIG. 1 is a view for explaining the present invention and schematically shows the shape of a lens cross section according to the present invention. In the figure, 1 is a cross section of a front refracting surface (meridian) according to the present invention, 2 is a rear refracting surface, and 3 is an axis of symmetry of a lens. In the present invention, the surface formed by rotating the non-circular meridian shown by 1 around the symmetry axis 3 is the front refracting surface. 4 is the center of rotation of the front refracting surface 0
3 shows a circular cross section drawn by the radius of curvature (the radius of curvature is the reciprocal of the curvature). That is, 4 shows a cross section of a conventional spectacle lens having a spherical front refracting surface. Hereinafter, the present invention will be described in detail with reference to Examples.

[Embodiment 1] Figs. 7 and 8 show a first embodiment of the present invention, in which the above-mentioned frequency-
The present invention is applied to a 6D and a base curve of 1.0D. FIG. 7 shows the change in curvature on the meridian of the front refracting surface, where the horizontal axis represents the distance from the axis of symmetry and the vertical axis represents the amount of change in curvature from the curvature of the base curve. The specific amount of change in curvature ΔC is as shown in Table 1. As shown in Fig. 7, the curvature of the meridian gradually increases with increasing distance from the symmetry axis, and the increasing degree begins to fall between 10 and 15 mm, and the increasing value becomes zero between 20 and 25 mm. And, on the contrary, it has started to decrease. Mathematically expressing it, when the curvature is a function C (r) with respect to the distance r from the axis of symmetry,
The first-order differential coefficient dc / dr starts from zero on the axis of symmetry and gradually increases with distance, reaches a peak between 10 and 15 mm, and then decreases. By giving such a change in curvature, the shape of the front refracting surface becomes a shape that moves to the lens rear refracting surface side as it moves away from the axis of symmetry with respect to the arc of the base curve as shown in FIG. Can be thinned. In this example, the edge thickness is
It was 10.8 mm, which was 0.4 mm thinner than the spherical one, which was 11.2 mm. Therefore, the edge thickness is 0.9mm, which is thinner than the normal base curve (2.0D) spherical one.

FIG. 8 shows the astigmatism of the lens of this example. Compared with the conventional one, the astigmatism increased by setting the base curve lower than usual as shown in FIG. It can be seen that, even with the same base curve, astigmatism is remarkably improved by asphericalization.

[Embodiment 2] FIGS. 9 and 10 show a second embodiment of the present invention. Similar to the first embodiment, the present invention is applied to a lens power of -6D and a base curve of 1.0D. . FIG. 9 shows the change in the curvature of the front refracting surface.
Shown in. As can be seen by comparing these with FIG. 7 and Table 1 of the previous embodiment, in the second embodiment, from the axis of symmetry
Up to 15 mm, it is exactly the same as in the first embodiment, and the curvature sharply increases from there to the outer circumference. As a result, the meridian on the outer circumference of the lens moves further to the rear refracting surface side than that of the first embodiment, so that the edge thickness becomes thinner than that of the first embodiment. In this embodiment, the edge thickness is 10.5 mm, which is 0.3 mm thinner than that of the first embodiment. FIG. 10 shows the astigmatism of this embodiment, which is the same as the first embodiment of FIG. 8 up to a field of view of 30 °, which corresponds approximately to 15 mm on the lens, but sharply outside of that. It can be seen that the astigmatism increases. This embodiment is frequently used in normal use, and within a range where good optical characteristics are required, that is, within 15 mm from the axis of symmetry on the lens, the optical characteristics change due to the gradually increasing curvature as in the first embodiment. The edge thickness is further improved by increasing the curvature more sharply outside the edge.

[Embodiment 3] FIGS. 11 and 12 show a third embodiment of the present invention in which the present invention is applied to a lens having a lens power of −6D and a base curve of 2.0D.

In this embodiment, as can be seen from FIG. 11 and Table 3, the curvature increases, then decreases, and becomes smaller than the curvature of the base curve in the portion near the outer circumference of the lens. In this embodiment, the edge thickness is 11.5 mm, and the effect of thinning the spherical surface is only 0.2 mm, but the improvement in optical performance is observed as shown in FIG.

[Embodiment 4] FIGS. 13 and 14 show a fourth embodiment of the present invention, which is the same as the first embodiment, except that a spherical portion having a radius of 5 mm is provided in the central portion. In this embodiment, as can be seen from FIG. 13 and Table 4, the curvature is constant and does not change up to 5 mm, and thereafter, as in the first embodiment, the curvature increases once toward the outer circumference and then decreases. There is. As a result, the astigmatism is reduced in the central spherical part as shown in Fig. 14,
Although the astigmatism is increased by making the base curve smaller, the astigmatism is improved on the outer side by making the aspheric surface similar to the first embodiment. The temporary increase in the central part of this astigmatism is 0.1D.
By adjusting the size of the base curve and the central spherical surface so that it is within 0.15D, it can be used visually without any problems. The edge thickness at this time is 10.9 mm, which is slightly smaller than that of the first embodiment, but still has a greater thinning effect than the conventional one.

Further, this embodiment has the following merits as compared with the above-mentioned three embodiments.

First, stable measurement results are obtained when measuring the lens power. That is, in the above-mentioned three examples, since the entire surface is an aspherical surface having no spherical surface at the center, the measurement position is slightly shifted in the diopter measurement with the lens meter on the optical axis (usually coincident with the axis of symmetry). However, the power may be deviated or astigmatism may be caused by the influence of the aspherical surface, but this can be eliminated by providing the spherical surface in the central portion. (Comparing Fig. 8 and Fig. 14 seems to be the opposite,
Both figures show the astigmatism from the center to the outer circumference when the lens is worn, and as shown in FIGS. The result is the opposite of the figure. ) In addition, it is possible to meet the order of eccentricity in the same manner as a general front refracting surface having a spherical surface. That is, as described above, a more stable power is obtained in the central spherical portion than that of an aspherical surface, so even if eccentricity processing is performed within that range, a designated frequency different from that of an aspherical surface can be obtained.

In order to obtain the above merits, a central spherical portion having a radius of 3 mm, preferably 5 mm or more is required. This is because the aperture diameter of the measurement part of a normal lens meter is 5 to 10 mm.

[Embodiment 5] FIGS. 15 and 16 show the fifth embodiment of the present invention, in which the lens power is the same as in the previous embodiment -6D, and the lens diameter and center thickness are the same. However, the lens material has a refractive index of 1.60 and Abbe number
35 and the base curve is 1.0D. FIG. 15 shows the change in curvature at the meridian of the front refracting surface, where the horizontal axis represents the distance from the axis of symmetry and the vertical axis represents the amount of change in curvature from the curvature of the base curve. The specific amount of change ΔC is as shown in Table 1. This embodiment has a spherical surface at the center as in the case of the third embodiment, and as shown in FIG. 15, the curvature of the meridian is constant up to 5 mm from the axis of rotation, and symmetric after 5 mm. It gradually increases while increasing the degree of increase as it moves away from the axis, and the degree of increase begins to fall between 10 and 15 mm,
At around 25 mm, the increase has become zero and has started to decrease. Mathematically speaking, when the curvature with respect to the distance r from the axis of symmetry is expressed by the function C (r), its first derivative dc / dr is zero up to 5 mm from the axis of symmetry, and r increases from that point. Increasing gradually (away from the axis of symmetry), 10-15mm
It has decreased after reaching its peak during the period. In this example, the border thickness is 9.0 mm, and the conventional refractive index described above is 1.50.
While the spherical lens of was 11.7mm or 11.2mm, it was 2.7mm (23%) and 2.2mm (20%) thinner, respectively. Further, as compared with Example 4 having a similar change in curvature, the effect of increasing the refractive index of the material is 10.9 mm to 9.0 mm.
It has a thinning effect of 1.9 mm (17.4%).

On the other hand, FIG. 16 shows the astigmatism of the lens of this example, and the astigmatism of the conventional spherical design is remarkably increased by lowering the base curve as shown in FIG. On the other hand, even if the base curve is the same, astigmatism is remarkably improved by designing the aspherical surface with the above-mentioned change in curvature.

It should be noted that, in the above-described examples, the design is aimed at making astigmatism almost zero when viewing a subject at a distance of 1 m (design corresponding to intermediate vision), and it can be seen that this is achieved. (However, in Example 2, the improvement was made by limiting the viewing angle to within 30 °.) In addition to this, a design aiming at zero astigmatism when looking at a distance (design corresponding to distance vision) and 30
A design aiming at zero astigmatism when viewing a short distance of about cm (design for near vision) is also possible. In all cases, the basic change in curvature is the same as that of this embodiment, but the amount of change in curvature is larger in the case of adjusting for distance vision than in the present embodiment, and in the case of adjusting for near vision, The amount of change in curvature is smaller than that of the example. In that case, the border thickness is thinner than that of the present embodiment in the design for distance vision, and the border thickness is thicker than that of this embodiment in the design for near vision (however, it is larger than that of the spherical surface. Is thin). Regarding the distance to which the improvement of this astigmatism is adjusted, according to the research by the present inventor, the correction power in the lens side portion becomes insufficient when it is adjusted to the distance vision, and when it is adjusted to the intermediate distance of 1 m, the side is corrected. It has been known that the correction power in the lateral part is almost the same as that in the center or slightly undercorrected, and that the lateral power is slightly overcorrected when it is adjusted to near vision.
Therefore, depending on the purpose of use of the lens, the design distance may be decided in balance with the thinning effect mentioned above, but in daily use, the one with an intermediate distance of about 1 m gives good results. Has been obtained.

〔The invention's effect〕

As described above, according to the present invention, in the spectacle lens for correcting myopia, it is possible to reduce the edge thickness and at the same time improve the optical performance. In particular, gradually increasing the curvature of the meridian within 15 mm from the axis of symmetry is effective in both reducing the edge thickness of the lens and improving the optical performance. Further, it was found that it is effective to improve the optical performance by increasing the first derivative of the curvature C (r) from the symmetry axis of the lens and then decreasing it. In addition, a base curve (curve value in the vicinity of the axis of symmetry in the present invention) that cannot be used in optical performance with the curvature change as described above and an ordinary spherical lens, for example, regarding the equivalent spherical power S of the lens, a) −6 ≦ When S ≦ −2 (n−1) × ρ ₀ ≦ 0.5 × (S + 6) +1.5 b) When S <−6 (n−1) × ρ ₀ ≦ 1.5 (where n is the refraction of the lens material) The ratio, ρ ₀ is the curvature near the axis of symmetry, that is, the curvature of the base curve). By combining this with a low base curve, the spectacle lens is excellent in optical performance and the edge thickness is greatly reduced. Is possible.

Further, as shown in the examples, a high refractive index (a plastic spectacle lens having a refractive index of more than 1.55 as compared with a normal refractive index of 1.50 is called a medium refractive index or a high refractive index).
When combined with the above materials, a large thinning effect can be obtained.

In general, high refractive index materials have a small Abbe number (for plastic materials, the Abbe number is approximately 40 or less at a refractive index of 1.55 or more), and the prism function of the lens when looking at an object through the periphery of the lens. This causes a defect called chromatic aberration in which light is dispersed into color components and color bleeding occurs in the ring portion. However, when the aspherical surface design according to the present invention is performed, the wedge shape formed by the front refracting surface and the rear refracting surface at the peripheral portion becomes smaller than that of the spherical lens, that is, the prism action becomes smaller, as shown in FIG. Thereby, the chromatic aberration is improved.

Another effect is that the change in curvature between the rotation axis and 5 mm is zero, that is, when a spherical portion of 10 mm is provided in the center of the lens, the lens on the optical axis (usually coincides with the rotation axis) 1 in processing in frequency measurement with a meter
Even if the optical axis is deviated by ~ 2 mm, stable power can be obtained without being affected by the aspherical surface. Also, from this, if it is within 2 to 3 mm, it is possible to accept special orders for eccentricity (where the optical axis is intentionally shifted).

Further, according to the present invention, there is no problem in appearance and processing as seen in the conventional aspherical lens for myopia correction, and for myopia correction having a sufficient thinning effect and excellent optical performance. A spectacle lens can be provided.

In the embodiment of the present invention, the curvature of the front refracting surface is shown to change continuously, but other than that, for example, as shown in FIG. 17, it becomes stepwise as it moves away from the axis of symmetry. The present invention includes the one in which the curvature changes in a minute step, and the one in which even if there is a minute variation, the curvature substantially changes as shown in the embodiments of the present invention.

[Brief description of drawings]

FIG. 1 is a diagram showing a meridional section of a lens according to the present invention.
1 is a front refracting surface of the lens of the present invention, 2 is a back refracting surface, 3
Is a rotationally symmetric axis of symmetry, and 4 is a front refracting surface formed by a spherical surface of a conventional lens. FIG. 2 is a diagram showing astigmatism caused by a combination of a lens power and a base curve of a conventional spherical lens. 3 and 4 are sectional views of conventional spherical lenses. Figure 3 shows a frequency of -6D and a base curve of 2.0D. Figure 4 shows a frequency of -6D and a base curve of 1.0D. FIGS. 5 and 6 are diagrams showing the amount of astigmatism depending on the field angle of the conventional spherical lens shown in FIGS. 3 and 4, respectively. 7 and 8 show the first embodiment of the present invention, FIG. 7 is a view showing the change of the curvature of the meridian, and FIG. 8 is a view showing the amount of astigmatism depending on the angle of the visual field. 9 and 10 show a second embodiment of the present invention. FIG. 9 is a diagram showing a change in curvature of meridian, and FIG. 10 is a diagram showing the amount of astigmatism depending on the angle of the visual field. FIGS. 11 and 12 show the third embodiment of the present invention, FIG. 11 is a view showing the change in the curvature of the meridian, and FIG. 12 is a view showing the amount of astigmatism depending on the angle of the visual field. 13 and 14 show a fourth embodiment of the present invention, FIG. 13 is a view showing a change in curvature of a meridian, and FIG. 14 is a view showing an amount of astigmatism depending on an angle of a visual field. FIGS. 15 and 16 show the fifth embodiment of the present invention, FIG. 15 is a view showing the change in the curvature of the meridian, and FIG. 16 is a view showing the amount of astigmatism depending on the angle of the visual field. FIG. 17 is a sixth embodiment of the present invention and is a diagram showing changes in the curvature of the meridian.

Claims (6)

[Claims] 1. A spectacle lens having a pair of front and rear refracting surfaces, wherein the front refracting surface has a rotationally symmetric shape.
The spectacle lens, wherein the curvature of the meridian of the front refracting surface increases substantially within at least 15 mm in the lens outer peripheral direction from the axis of symmetry of the rotational axis symmetry. 2. The spectacle lens according to claim 1, wherein the curvature of the meridian increases monotonically in a direction away from the axis of symmetry within at least 15 mm from the axis of symmetry. 3. When the curvature of the meridian is expressed as C (r) as a function of the distance r from the rotation axis, the first derivative coefficient dc / dr of the function C is at least 1 as it goes away from the axis of symmetry. The spectacle lens according to claim 1 or 2, wherein the spectacle lens increases once and then decreases. 4. A curvature value near the symmetry axis of the front refracting surface is ρ ₀ [m ⁻¹ ], and an equivalent spherical power of the lens is S.
When [Diopter] is set: a) When -6≤S≤-2 (n-1) x ρ ₀ ≤0.5 x (S + 6) +1.5 b) When S <-6 (n-1) x ρ The spectacle lens according to claim 1, 2 or 3, wherein ₀ ≤ 1.5 is satisfied. Where n is the refractive index of the lens material. 5. The curvature of the meridian of the front refracting surface is at least 3 mm or more, preferably 5 mm in the outer peripheral direction from the axis of symmetry.
Claim 1 or Claim 2 or Claim 3 or Claim 4 which is constant during the above period and increases thereafter.
The spectacle lens according to. 6. The spectacle lens according to claim 1, wherein the material has a refractive index of 1.55 or more and an Abbe number of 40 or less.