JPH02289818A - eyeglass lenses - Google Patents

Abstract

(57) [Summary] This bulletin contains application data before electronic filing, so abstract data is not recorded.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field 1] The present invention relates to the surface shape of the front convex side of an off mirror lens, and particularly to the surface shape of a spectacle lens used for myopia correction. [Prior art 1] Conventionally, the refractive surface on the front convex side (hereinafter referred to as the front refractive surface) of a spectacle lens for the purpose of correcting myopia has been a spherical surface for ease of processing. Hereinafter, this lens will be referred to as a spherical lens. In general, the refractive power of a lens is
Hereinafter, it is expressed in the unit D), and the refractive power on the surface of the lens (surface refractive power) is the curvature ρ of that surface (unit: m-1).
and the refractive index n of the lens material, it is defined as the following formula. Surface refractive power "(n-1) x ρ The surface refractive power of the front refractive surface of the lens is especially called the 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 determined by the front and rear refractive power. Since it is determined by the refractive power of the two refractive surfaces, the base curve can take various values depending on how they are combined.However, in reality, the optical performance, especially when viewed through the side portion away from the optical axis of the lens, is determined by the base curve. In order to reduce the astigmatism that affects the eye when a lens is used, the base curve is limited to a specific range with respect to the power of the lens. Figure 2 shows an example of a lens with a refractive index of 1.50. It is
When the vertical axis is the base curve and the horizontal axis is the lens power, it shows the occurrence of astigmatism when looking 30 degrees to the side of the optical axis while wearing glasses. The solid line is the astigmatism when viewing at a distance, and the number attached to the line indicates the amount of astigmatism, with lines for astigmatism 0.3D on both sides of the no-astigmatism (OD) line. ing. The broken line similarly represents astigmatism in near vision (30 cm). As can be seen from this figure, the optimal base curve for zero astigmatism is different for distance vision and near vision. Therefore, in order to provide equally good distance vision and near vision, a base curve in the shaded range indicated by a in the figure is generally adopted. By the way, one drawback of lenses for myopia correction is that the edge thickness of the lens (thickness at the outer edge of the lens) increases as the degree of myopia increases. Figure 3 shows an example of this, and shows a cross section of a lens with a power of -6D and a lens diameter of 75mm. This lens is a commonly used plastic lens with a refractive index of 1.5, a base curve of 2.0D, and a center thickness of 2mm. In this example, the rim thickness of the lens is 11.7 mm, which results in an unsightly thick rim when used as eyeglasses. One way to solve this problem is to make the base curve smaller. Figure 4 shows the same striped lens as Figure 3, with a base curve of 1.0D. The edge thickness of this lens is 11.2mm, which allows for a reduction in edge thickness of 0.5mm. However, as mentioned above, the base curve is determined based on the optical performance, and as shown in Figures 5 and 6, when the base curve is set to 1.0, the optical performance deteriorates significantly.
Figures 5 and 6 are for base curve 2, respectively. OD and 1
．． It shows the astigmatism in the visual field when a 0D item is worn. The vertical axis is the angle of the visual field (unit: 0), and the horizontal axis is the astigmatism based on the refractive power in the direction of the spherical defect (unit: D). It represents. In the figure, the viewing distance is infinite (oo). 1m, 0
．． The astigmatism in each field of view for each case of 3 m is shown. On the other hand, in order to solve the defects in appearance of lenses for myopia correction, there are several methods of making the front refractive surface or rear refractive surface of the lens aspheric (including a combination of two or more spherical surfaces). Proposed. Below, we describe these methods and their problems. As for the front refractive surface made into an aspherical surface, JP-A-53-
94947, Special Publication No. 59-4 1 1 64 (US4,
279,480). In JP-A-53-94947, the front refracting surface is the central part (according to the example, the diameter is 40 mm).
and its outer peripheral part, with the center part as one spherical surface,
It has been disclosed that the outer peripheral part consists of a torus surface with a larger curvature than the curvature of the central spherical surface. In this case, since the center has a large spherical surface, in order not to significantly impair the optical performance of the outer periphery, it is not possible to create a very extreme difference in curvature with respect to the center, so there is no significant thinning effect. I can't get it. Special Publication No. 59-41164 (US
4,279,480) discloses that the front refractive surface is an aspheric surface given by a special function. In this case, the lens refractive surface is characterized by protruding at one end toward the front from the center of rotation of the lens toward the periphery, and then toward the rear. The problem with this lens is its unique shape, which causes extremely uneven reflection on the front refractive surface of the lens, making it visually undesirable. Next, as for the one in which the rear refractive surface is made aspherical, JP-A-53-8474 1. JP-A-53-84742, JP-A-58-195826 (IT48315/82). There is Japanese Patent Application Publication No. 60-60724. A common problem with these lenses with an aspherical rear refractive surface is that in lenses with astigmatism, the front refractive surface is a convex toric surface or a cylindrical surface, resulting in poor appearance when used in eyeglasses. In addition, the currently popular eyeglass lenses have a concave toric rear refractive surface, and lens processing machines are also made for this purpose, so in order to handle lenses with an aspheric rear refractive surface, There is also the problem of requiring major changes in equipment. As mentioned above, even in lenses using conventional aspherical surfaces,
There were various problems. [Problems to be Solved by the Invention] The present invention solves the above-mentioned problems with spectacle lenses for correcting myopia, and provides spectacle lenses with excellent optical performance and thin edges. [Means for Solving the Problems] 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 diagram for explaining the present invention and schematically shows the cross-sectional shape of a lens according to the present invention. 1 in the figure is a cross section (meridian II) of the front refractive surface according to the present invention. 2 is the rear refractive surface, and 3 is the axis of symmetry of the lens. In the present invention, the surface formed by rotating the non-circular meridian shown in 1 around the axis of symmetry 3 is used as the front refractive surface. 4 is the center of rotation of the front refractive surface 0
shows a circular cross section drawn by the radius of curvature (the radius of curvature is the reciprocal of the curvature). In other words, 4 shows the cross section of a conventional eyeglass lens whose front refractive surface is a spherical surface. Hereinafter, the present invention will be explained in detail with reference to Examples. [Example 11 Figures 7 and 8 show the first example of the present invention.
D. The present invention was applied to a base curve of 1 and OD. Figure 7 shows the change in curvature in the meridian of the front refracting surface, where the horizontal axis shows the distance from the axis of symmetry, and the vertical axis shows the amount of change in curvature from the base curve. The specific amount of change in curvature △C is shown in Table 1. As shown in Figure 7, the curvature of the meridian gradually increases as it moves away from the axis of symmetry, and the degree of increase becomes stronger as it moves away from the axis of symmetry.
The degree of increase begins to decline between 20 and 25 mm, and the increase reaches zero between 20 and 25 mm, and on the contrary, it begins to decrease. Expressing it mathematically, the function C is a curvature with respect to the distance r from the axis of symmetry.
(r), it gradually increases as it moves away,
It peaks between 10 and 15 mm and then decreases. By changing the curvature in this way, the shape of the front refractive surface moves toward the rear refractive surface of the lens as it moves away from the axis of symmetry with respect to the arc of the base curve as shown in Figure 1, and the edge thickness of the lens changes. can be made thinner. In this example, the edge thickness was 10.8 mm, which was 11.2 mm for the spherical one, and an additional 0.4 m.
m It is thinner. Therefore, the normal base curve (2.0
Compared to the spherical one shown in D), the edge thickness has been reduced by 0.9 mm. Figure 8 shows the astigmatism of the lens of this example.Compared to the conventional lens, which had a worse astigmatism due to the base curve being lower than usual as shown in Figure 6. , it can be seen that even with the same base curve, astigmatism is significantly improved by making the surface aspheric. Table 1 [Example 21] Figures 9 and 10 show a second example of the present invention, and like the first example, the lens power is -6D and the base curve is 1.0D.
The present invention was implemented in the following. FIG. 9 shows changes in the curvature of the front refractive surface, and the specific amount of change in curvature is shown in Table 2. As can be seen by comparing these with FIG. 7 and Table 1 of the previous embodiment, this second embodiment is completely the same as the first embodiment up to 15 mm from the axis of symmetry,
The curvature increases rapidly from there to the outer periphery. As a result, the meridian on the outer periphery of the lens moves further toward the rear refractive surface than in the first embodiment, so the edge thickness becomes even thinner than in the first embodiment. In this example, the edge thickness is 10.5 mm.
Therefore, it is 0.3 mm thinner than that of the first embodiment. Figure 10 shows the astigmatism of this example, with a field of view 30' corresponding approximately to 15 mm on the lens.
Up to this point, it is the same as the first embodiment shown in FIG. 8, but it can be seen that astigmatism increases rapidly on the outside.
This example is applied to a range that is frequently used and requires good optical properties in normal use, that is, 1 point from the axis of symmetry on the lens.
Within 5 mm, the optical characteristics are improved by a gradual increase in curvature as in the first embodiment, and outside of this, the curvature is increased more rapidly to achieve thinner edge thickness. be. [Example 31] Figures 11 and 12 show a third example of the present invention, in which the present invention was implemented on the aforementioned lens having a power of -6D, a base curve of 2, and an OD. Table In this example, as can be seen from FIG. 11 and Table 3, the curvature increases by one degree and then decreases, becoming smaller than the curvature of the base curve near the outer periphery of the lens. In this example, the edge thickness is 11.5 mm, which is 0.2 mm compared to the spherical one, so there is no thinning effect, but as shown in Figure 12, there is an improvement in optical performance. [Example 4J Figures 13 and 14 show the fourth example of the present invention, which has a radius of 5 mm in the center of the previous first example.
It has a spherical part. In this example, the first
As can be seen from Figure 3 and Table 4, the curvature is constant and does not change up to 5 mm, and then, as in the first example, it increases once toward the outer periphery and then decreases. As a result, as shown in Figure 14, there is an increase in astigmatism in the central spherical part due to the smaller base curve; As in the example, an improvement in astigmatism can be seen.
This temporary increase in astigmatism at the center can be as large as 0.1D to O. By adjusting the size of the base curve and the central spherical part so that it is within 15D,
It can be used visually without any problems. The edge thickness at this time is
lo. At 9 mm, the thinning effect is somewhat reduced compared to the first embodiment, but it still has a large thinning effect compared to the conventional one. Moreover, this embodiment has the following advantages compared to the previous three embodiments. First, stable measurement results can be obtained when measuring lens power.
In other words, since the three examples mentioned above have a completely aspherical surface without a spherical surface in the center, the measurement position will be slightly shifted when measuring power with a lens meter at its tip axis (which usually coincides with the axis of symmetry). However, by having a spherical surface in the center, the power may shift or cause astigmatic aberration due to the influence of the aspherical surface, but this can be eliminated by providing a spherical surface in the center.
(Comparing Figures 8 and 14, they appear to be opposites, but both figures show the astigmatism from the center to the outer periphery when the lens is worn. In power measurement, the passing angle of the light ray is different, so the results are opposite to those shown in Figures 8 and 14 as described above.) Table 4 Also, as in the case where the general front refracting surface is a spherical surface, the order of eccentricity is You can respond to In other words, as mentioned above, the central spherical part provides a more stable power than the fully aspherical part, so even if eccentric processing is performed within the length range, the specified power can be obtained unlike the fully aspherical part. In order to obtain the above advantages, a central spherical portion with a radius of at least 3 mm, preferably 5 mm or more is required. This is because the aperture diameter of the measuring section of a normal lens meter is 5 to 10 mm. [Embodiment 5] Figures 15 and 16 show a fifth embodiment of the present invention, in which the power of the lens is -6D, the same as in the previous embodiment, and the lens diameter and center thickness are also the same. However, the refractive index of the lens material is 1.60,
The number is 35, the base curve is 1, and the OD.
Figure 15 shows the change in curvature of the front refracting surface along the meridian, with the horizontal axis showing the distance from the axis of symmetry, and the vertical axis showing the amount of change in curvature from the curvature of the base curve. The specific amount of change ΔC is shown in Table 1. This example is based on the previous example 3.
Similarly, the curvature of the meridian is constant up to 5 mm from the axis of rotation, and increases as it moves away from the axis of symmetry, as shown in Figure 15. gradually increasing from 10 to 15
The rate of increase begins to decline between 25mm and 25mm, and the increase reaches zero and begins to decrease. Expressing this mathematically, astigmatism increases significantly by lowering the base curve's curvature relative to the distance r from the axis of symmetry as shown in function C diagram. By designing an aspheric surface with a change in curvature, astigmatism has been significantly improved. It is zero up to 65 mm from the symmetry axis, and from there it gradually increases as r becomes larger (away from the symmetry axis), and lO ~ 1
It peaks between 5mm and then decreases. In this example, the edge thickness is 9.0 mm, and the conventional spherical lens with a refractive index of 1.50 has a thickness of 11.7 mm or 11 mm.
．． 2mm, respectively, 2.7mm (
23%) and 2.2mm (20%) thinner.
Also, compared to Example 4, which has a similar change in curvature, the effect of increasing the refractive index of the material is that 10.9 mm becomes 9.0 mm.
It has a thinning effect of 1.9mm (17.4%). On the other hand, Fig. 16 shows the astigmatism of the lens of this example, and the lens of the conventional spherical design is shown in Table 6.5. The design aims to reduce the distance to almost zero (designed to suit intermediate vision), and it can be seen that this goal has been achieved. (However, in Example 2, the improvement was limited to a viewing angle of 30 cm or less.) In addition to this, there is also a design aimed at zeroing out astigmatism when looking into the distance (a design tailored to long distance vision), and a design that aims to reduce astigmatism to around 30 cm It is also possible to design a lens that aims to eliminate astigmatism when viewing objects at close distances (a design tailored to near vision). In any case, the basic change in curvature is the same as that in this example, but the amount of change in curvature in the case adapted to distance vision is larger than in this example, and the amount of change in curvature is greater in the case adapted to near vision than in this example. The amount of change in curvature is smaller than in the example. In that case, a design suited for far vision will have a thinner edge thickness than the one in this example, and a design suited for near vision will have a thicker edge thickness than the one in this example (however, the edge thickness will be thicker than the one in this example). is thin). Regarding the distance at which this astigmatism should be improved, according to the research of the present inventor, if it is adjusted to distance vision, the correction power at the side part of the lens will be insufficient, and if it is adjusted to the intermediate distance of lm, the correction power will be insufficient at the side part of the lens. It is known that the corrected power in the lateral areas is almost the same as that in the center or slightly undercorrected, and that when adjusted to near vision, the corrected power in the lateral areas becomes slightly overcorrected. Therefore, depending on the intended use of the lens, the design distance should be determined by taking a balance with the aforementioned thinning effect, but in daily use, a lens with an intermediate distance of about 1 meter will give good results. It has been obtained. [Effects of the Invention] As described above, according to the present invention, it is possible to reduce the edge thickness of an ocular rust lens for myopia correction and to improve optical performance at the same time. 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 optical performance. It was also found that increasing the first-order differential coefficient of the curved skewer C (r) by one step from the axis of symmetry of the lens and then decreasing it is effective for improving optical performance. In addition, regarding the above-mentioned curvature change and the base force curve (in the present invention, the curve value near the axis of symmetry) that cannot be used with a normal spherical lens due to optical performance, for example, the equivalent spherical power S of the lens, a) - When 6≦S≦-2 (n-1)xρa≦0.5x (S+6)+1.5
b) When S<-6, (n-1)Xρ. ≦1.5 (where n is the refractive index of the lens material, and ρ is the curvature near the axis of symmetry, that is, the curvature of the base curve).By combining this with a low base curve that satisfies This enables eyeglass lenses with significantly thinner edges. Furthermore, as shown in the examples, materials with a high refractive index (for plastic eyeglass lenses, those with a refractive index exceeding 1.55 compared to the usual 1.50 are called medium refractive index or high refractive index). When combined with this, a significant thinning effect can be obtained. Additionally, in general, high refractive index materials have a small Abpe number (in the case of plastic materials, when the refractive index is 1.55 or more, the Appe number is approximately 40 or less), which means that when an object is viewed through the periphery of the lens, the Abbe number is small. Due to the prism effect, light is split into color components, resulting in a defect called chromatic aberration, where color blur appears in the infrared region. However, by designing an aspherical surface according to the present invention,
For example, as shown in Figure 1, the wedge shape formed by the front and rear refractive surfaces at the periphery is smaller than that of a spherical lens, that is, the prism effect is reduced, and chromatic aberration is improved. Another effect is to make the curvature change zero within 5 mm from the rotation axis, that is, if a 10 mm spherical part is provided in the center of the lens, the optical axis (usually coincident with the rotation axis)
When measuring power using a lens meter, even if the optical axis shifts by 1 to 2 mm during processing, a stable power can be obtained without being affected by the aspheric surface. Furthermore, we can also accept special orders for eccentricity (intentionally shifted optical axis) within 2 to 3 mm. In addition, according to the present invention, there is no problem in appearance or processing as seen in conventional aspherical lenses for myopia correction, and the lens for myopia correction has sufficient thinning effect and excellent optical performance. Glasses. can be provided. In the embodiments of the present invention, the curvature of the front refractive surface is shown to be continuously changing.45 In other cases, for example, as shown in FIG. The present invention includes those in which the curvature changes in minute steps, and those that show changes substantially as shown in the embodiments of the present invention even if there is slight variation.

[Brief explanation of drawings]

FIG. 1 is a diagram showing a meridian cross section of a lens according to the present invention.
1 is the front refractive surface of the lens of the present invention, 2 is the rear refractive surface, and 3
is the axis of rotational symmetry, and 4 is the spherical front refractive surface of the conventional lens. Figure 2 is a diagram showing astigmatism caused by the combination of the lens power and pace curve of a conventional spherical lens. Figures 3 and 4 are cross-sectional views of conventional spherical lenses. Figure 3 shows the power -6D. Base carp 2.0D thing. Figure 4 shows the degree -
6D, base curve 1, OD. Figures 5 and 6 are diagrams showing the amount of astigmatism depending on the viewing angle of the conventional spherical lens shown in Figures 3 and 4, respectively. 7 and 8 show the first embodiment of the present invention. FIG. 7 is a diagram showing changes in meridian curvature, and FIG. 8 is a diagram showing the amount of astigmatism depending on the viewing angle. Figure 9 and IO are the second embodiment of the present invention, and Figure 9 is a diagram showing changes in the curvature of the meridian,
Figure 1O is a diagram showing the amount of astigmatism depending on the angle of view. 11 and 12 show a third embodiment of the present invention, and FIG. 11 is a diagram showing changes in meridian curvature, and FIG. 12 is a diagram showing the amount of astigmatism depending on the viewing angle. 13 and 14 show a fourth embodiment of the present invention, and FIG. 13 is a diagram showing changes in meridian curvature, and FIG. 14 is a diagram showing the amount of astigmatism depending on the viewing angle. 15 and 16 show a fifth embodiment of the present invention, and FIG. 15 is a diagram showing changes in meridian curvature, and FIG. 16 is a diagram showing the amount of astigmatism depending on the viewing angle. FIG. 17 is a sixth embodiment of the present invention, and is a diagram showing changes in meridian curvature. Applicant Seiko Epson Co., Ltd. Agent Patent Attorney Kisaburo Suzuki (and I others) Figure 3 Toin (transition) L solid Figure Z name and ri 3 ) Mebth

Claims (1)

[Claims] 1. A spectacle lens having a pair of front and rear refractive surfaces, in which the front refractive surface is symmetrical about the rotational axis, and the curvature of the meridian of the front refractive surface is symmetrical about the rotational axis. A spectacle lens characterized by increasing substantially within at least 15 mm from the axis of symmetry in the direction of the outer circumference of the lens. 2. The curvature of the meridian is at least 15 mm from the axis of symmetry.
The spectacle lens according to claim 1, characterized in that the lens increases monotonically in a direction away from the axis of symmetry within a range of mm. 3. When the curvature of the meridian is expressed as C(r) as a function of the distance r from the axis of rotation, the first derivative coefficient dc/dr of the function C changes at least once as the distance from the axis of symmetry increases. The spectacle lens according to claim 1 or 2, characterized in that the lens increases and then decreases. 4. The value of the curvature of the front refractive surface near the axis of symmetry is ρ_0[m^-^1], and the equivalent spherical power of the lens is S[
A) When -6≦S≦-2 (n-1)×ρ_0≦0.5×(S+6)+1.5B)
The spectacle lens according to claim 1, characterized in that when S<-6, (n-1)×ρ_0≦1.5 is satisfied. Here, n is the refractive index of the lens material. 5. The curvature of the meridian of the front refractive surface is constant for at least 3 mm or more, preferably 5 mm or more in the outer circumferential direction from the axis of symmetry, and then increases. The spectacle lens according to claim 3 or 4. 6. The spectacle lens according to claim 1, 2, 3, 4, or 5, wherein the material has a refractive index of 1.55 or more and an Abbe number of 40 or less.