JPS6029724A - Progressive multi-focus lens - Google Patents

Abstract

PURPOSE:To easily improve the astigmatism of a progressive multi-focus lens which has a longsighted part area and a shortsighted part area by performing such simple work that a prism with a 90 deg. basic direction which is not for squint correction is added to the progressive multi-focus lens. CONSTITUTION:Prisms for squint corrections are not incorporated like a normal prism formula, and prisms having a 90 deg. basic direction are added equally to both right and left lens; and the astigmatism distribution of a one-side half part obtained by cutting the progressive multi-focus lens having a center A for longsight and a center B for short-sight along its main meridian shows a great decrease in astigmatism, specially, in a shortsighted area by adding the prism having the bases in a 90 deg. direction. The amount of added prisms is preferably set the best prism amount in a range from 1.0 to 6.0 prism diopter.

Description

[Detailed description of the invention] The present invention relates to the shape of a progressive multifocal lens.

An object of the present invention is to improve the astigmatism distribution of a progressive multifocal lens.

Before entering into the details of the present invention, the characteristics of the progressive multifocal lens will be described. Progressive multifocal lenses compensate for presbyopia, a decline in the accommodative power of the eye's crystalline lens.The upper half of the lens has an area for seeing far away (distance area), and the lower part of the lens has an area for seeing near objects. There is an area for seeing (near area), and between these ranges there is an area for seeing things at intermediate distances (intermediate area). Each region is smoothly connected to form a single aspherical lens refractive surface. FIG. 1 shows the structure of a general progressive multifocal lens. This figure shows the front refractive surface of a progressive multifocal lens, and the rear refractive surface, which is located on the back side and cooperates to form one lens, is omitted.

M in the figure is a curve that runs almost vertically through the center of the lens and is called the principal meridian. Above point A, which is approximately the center of this principal meridian Mix lens, the radius of curvature r is almost the same, and below point B, which is about 10 mm below point A, the radius of curvature rt (rt 〈rt), and the radius of curvature r(r, <r<r□)'f, which varies continuously between dimensions A and B,
have. 4 in the figure is a curve indicating a change in the position of the center of curvature of the principal meridian, that is, an evolute line. Approximately the upper half of the lens above lA (1 in the figure) is the distance vision area, and the part below B (2 in the figure) is the near vision area.
The area between them (3 in the figure) is the intermediate area. When used as eyeglasses, the glasses are fitted so that when viewed from the front, the line of sight passes through a point in the distance region near point A. Therefore, the near vision area is located at the lower lens periphery of the glasses. Single-focal lenses, which are used to correct myopia and farsightedness, use the central part of the lens when looking far away, and when looking at objects close up (even when reading, the central part of the lens is 5
This is one of the characteristics of a progressive multifocal lens. Other characteristics include astigmatism and image distortion, which occur when the refractive power of a progressive multifocal lens partially changes. It is perceived as image shaking, and how to suppress it is a problem for progressive multifocal lenses.For this purpose, much research and development has been carried out in the United States and commercialized.The inventor of the present invention filed a patent application in
5-171569 and patent application 1982-. 1756011
A progressive multifocal lens that satisfactorily suppresses astigmatism and image distortion has been proposed. It divides the lens refractive surface into a distance area, an intermediate area, and a near area by a curve passing through the center of distance vision and a curve passing through the center of near vision, and calculates the arbitrary lens refraction when cut parallel to the principal meridian. It is characterized in that the angle formed between the normal of each point on the cross-sectional curve of a surface and the plane containing the principal meridian changes according to the same law as the law of change of curvature on the principal meridian curve. This makes the distribution of astigmatism gentle and the distortion of the image changes gradually. Furthermore, in the distance and near vision regions, the central portion and the vicinity of the principal meridian are made spherical or nearly spherical, and the curvature perpendicular to the principal meridian is increased and decreased at the outer periphery, respectively, from the central portion. This suppresses image distortion and reduces lateral astigmatism at the intermediate portion.

Now, what determines the shape of a progressive multifocal lens is the pace curve, in addition to the method of configuring the curved surface shape over each region as described above. In the case of progressive multifocal lenses, the pace curve is defined as the main partial optical power (unit: ζ dioptre) in the distance vision region. Once this base curve is determined, the curve of the near vision area is automatically determined by adding the base curve VC's degree of human strength, and by adding the change in curvature in the water direction as described above. The final curved shape of the lens refractive surface is determined.

This pace curve is related to the optical properties of the lens.
There is a close relationship with the IB. That is, when the power of the lens is specified, the optically optimal pace curve is limited. Many studies have been conducted for a long time on the relationship between lens power and base curve, including the famous Czerning ellipse. Figure 2 shows the vertical astigmatism when looking at an angle of 60° from the optical axis (hereinafter referred to as the viewing angle) with all single focus spherical lenses installed.
iIVC pace curve (Dl), horizontal axis shows lens power (p
w). The large line in the figure shows that when looking into the distance (hereinafter referred to as far vision) [representing astigmatism,
Line a represents the relationship between the pace curve and the power at which the astigmatism becomes zero. The broken line is when looking close (hereinafter referred to as near-mansight)
The dashed line represents the total astigmatism, and the astigmatism is zero. The + and - signs in the figure indicate the directions of the two principal refractive powers (maximum refractive power and minimum refractive power. The difference between these two refractive powers becomes astigmatism). There is. +1J means that the maximum refractive power is in the radial direction of the lens, -2 means that it is in the circumferential direction of the lens. In an area where the lens power is negative, the area below the zero line is one, and in an area where the lens power is positive, the area above the zero line is -. The magnitude of astigmatism increases as the distance from the zero line increases. In general single vision lenses, in order to reduce astigmatism when looking far and near, the line is between the zero astigmatism line a for distance vision and the zero astigmatism line a for near vision. The base curve is set according to the lens power.

Now, in the case of a progressive multifocal lens, the setting of the base curve is more complicated than that of the above-mentioned single focus spherical lens. This is because when using a progressive multifocal lens as mentioned earlier, the distance between the lens area and the object being viewed is fixed, so it is necessary that astigmatism be small when viewing from a distance in the distance area. In the near vision region, the condition is that astigmatism when viewing near is small.

FIG. 6 shows the relationship between lens power and base curve regarding astigmatism in the case of a progressive multifocal lens. The representation of the figure is the same as in Figure 2. In a progressive multifocal lens, distance vision is the same as a single vision spherical lens, but in near vision, the center of curvature of the near vision area is not on the lens optical axis as shown in Figure 1, so the zero line of astigmatism However, as shown in the figure, compared to a single focus spherical lens, it is lower on the negative power side and upward on the positive power side. In this figure, the eccentricity of the center of curvature of the near vision region with respect to the optical axis is k 3 ng, and as the eccentricity increases, this tendency also increases. It should be noted here that with progressive multifocal lenses, near vision occurs only in the near vision area, so the base curve of the vertical axis in Figure 0 in the case of near vision and the horizontal narrow The dioptric power refers to the dioptric power and dioptric power in the near vision region, respectively, and is different from the so-called base curve and dioptric power of a progressive multifocal lens. For example, base curve 4.5
D (D stands for diopter), Katana Ujindo ZOD, degree!
, X-6D progressive multifocal lens has a partial optical power in the near vision area of i6.5D and a dioptric power of -4.5D. In this example, the astigmatism in the 30° visual angle direction is represented by 71 in the common area and E in the near river area in the figure.

From this figure, it can be seen that with this lens, astigmatism is small and good in the far vision region, but astigmatism is very large in the near vision region. - Even if a progressive multifocal lens has a refractive surface of the same shape with a base curve of 4.5D and an addition power of 2.0D, when the lens power is CLOD, the distance area is F/, and the near area is above 1. The active area is E', and it can be seen that astigmatism is small in both cases. This is concretely shown in FIGS. 4 and 5.

Figures 4 and 5 are the patent application filed in 1975-175, 1960 mentioned above.
1 lens, base curve 4.5D, add power 2.
This lens has the same 0D refractive surface shape as the front refractive surface. Figure 4 shows the lens power -6, OD, sp.
'j! J is the lens power αOD.

In both figures, (a) shows the astigmatism distribution s of one half of the lens cut from the principal meridian. (b) A shows the direction of the maximum refractive power of the astigmatism in the same half (hereinafter referred to as the direction of astigmatism) and its direction. It shows the size, and the coordinate axis is the viewing angle.

((b) figure omits the upper part and part of the side) A in the figure.

Bl) Distance center and near center kawasu, respectively.

In FIG. 4, large astigmatism is seen in the near vision region (approximately below 30°), and the direction of the astigmatism is approximately vertical. There is also large astigmatism on the sides of the intermediate region. -1 In FIG. 5, astigmatism is small in all regions. The difference in astigmatism between these two lenses is explained as follows. The astigmatism of an aspherical lens can be considered separately into two factors. One of them is astigmatism, which the refractive surface of the lens itself has, and is caused by the fact that the refractive surface of the lens is an aspherical surface. This will be called the aspherical factor. Of course, this factor does not apply to spherical refractive surfaces. Another factor arises from the relationship between the base curve and lens power mentioned above. We will call this the Wobase Carp factor. Figures 2 and 3 above show the base curve factors. These two factors explain the difference in astigmatism between the two lenses of FIG. 4 and FIG. 1. That is, in both lenses, the aspherical shape of the front refractive surface is the same and the rear refractive surface is also spherical, so the aspherical factors are the same. Therefore, the difference in astigmatism between both lenses is due to the base curve factor. This is proven by the fact that the difference in base curve factors of both lenses shown in FIG. 6 and the difference in astigmatism shown in FIGS. 4 and 5 correspond well. To explain in detail, in the case of the 50th lens power αOD, the base curve factor is very small as shown in Fig. 3, and the astigmatism is mostly due to the aspherical factor. Fig. 5 ( In b), the direction of astigmatism is horizontal in the lateral part of the distance vision area, and the direction of astigmatism is vertical in the lateral part of the near vision area. The shape for suppressing distortion and intermediate lateral astigmatism, that is, the shape of the horizontal cross section of the lens, increases in curvature in the distance region and increases in the near vision region. This is because the shape has a decreasing curvature.The lenses in Figure 4 are the addition of the base curve factors F and E in Figure 3 to such aspherical surface factors, and the distance vision area is In the near vision area, a small astigmatism in the ten directions, that is, astigmatism in the direction toward the center of the lens, is added, and in the near vision area, a large astigmatism in the ten directions is added.This can be seen in Figure 4 (
b) is confirmed by Especially in the near vision area,
It can be seen that because the direction of the astigmatism due to the aspherical surface placement and the direction of the astigmatism due to the base curve factor are almost the same, the astigmatism at the side portions increases rapidly.

Now, it is clear that this fourth lens has a large astigmatism in the near vision region and is not suitable for use.

Therefore, it is natural to consider changing the base curve. From the diagram of base curve factors in Figure 3, all 4 base curves
．． It is easy to guess that it would be better if it was lower than 5D to 2.5DK. However, it is not so easy to disappear. Figure 6 shows the base curve i2.5DE of the lens in Figure 4. In this lens, the aspherical factors are the same as those in FIG. Comparing the astigmatism distribution shown in FIG. 4 with that shown in FIG. 4, the astigmatism in the near vision region remains large and has hardly been improved.

This may seem to contradict the change in base curve factors shown in FIG. 6, but this is not the case. The astigmatism in near vision shown by the broken line in Fig. 6 is for a case where the eccentricity of the center of curvature in the near vision region is 3 mm, and as the base curve becomes smaller, the eccentricity increases even with the same addition power. In the case of this lens, where the astigmatism changes to the + side compared to the one in Figure 3, +c[
+l 2 D is added to the one in FIG. For this reason, the astigmatism in the near region of the lens shown in FIG. 6 is almost the same as that of the lens shown in FIG. 4. On the other hand, in the upper side of the distance region, where the aspherical factor of astigmatism has a horizontal direction, the base curve factor acts in one direction, that is, in the circumferential direction with respect to the lens center. Both factors are added together, and the astigmatism becomes large.

As mentioned above, the setting of the base curve for progressive multifocal lenses is very complicated, unlike that for single-focal spherical lenses, and it is not possible to be satisfied with simply setting the base curve as in the previous example. In some cases, full performance may not be achieved. The present invention aims to improve astigmatism in such a progressive multifocal lens by a simple method without designing a resulfurized lens.

Hereinafter, the present invention will be explained in detail including Examples.

FIG. 7 shows one embodiment of the present invention. The front aspherical refractive surface of this lens is the same as shown in Figure 4. Therefore, the base curve is 4.5D and the addition i2. OD'tl'
Al. The lens power is also -6, o D? There is the same L type, but a prism with a base in the 90° direction (2.0-degree prism) is added to the 2.0 prism diagonal. The feature of the present invention is to attach a prism with a base direction of 90°.The C prism is attached equally to both the left and right lenses of glasses, and can be used for the purpose of correcting strabismus like a normal prism prescription, or for the purpose of correcting strabismus on both sides. Lens Ki% bottom direction 2
This is different from the case where a 7o0 prism is inserted to make the plus lens thinner.

Now, if we compare Figure 4 with Figure 7, the effects of the present invention will become clear. In the object of the present invention, astigmatism is significantly reduced in the near vision region, and astigmatism is also reduced and improved on the sides of the intermediate region.

In the distance area, the astigmatism is slightly worse in the upper part, but in the side part, the area with small astigmatism is
As shown in the figure, it is lowered downwards.

Considering that the top of the lens is cut when inserting the lens into the frame, this is an improvement.

The effects of the present invention can be explained with reference to FIG. Figure 8 shows a prism with a base direction of 90' as a 2.0 prism diopter) U
- Distance vision and near vision when added (both visual angles are 5
0' (same as the 2nd and 5th curves), the relationship between the lens power and astigmatism. ) Also, as in FIG. 3, the eccentricity of the near vision region is set to 3IfIl. From this figure, it can be seen that by adding a prism in the base direction 90', astigmatism shifts to the + side in the case of far vision, and shifts to one side in the case of near vision. Therefore, in the near vision region, astigmatism in ten directions, which was the cause of large astigmatism, is reduced, and in the distance vision region, the astigmatism in the lateral regions is offset by the aspherical factor. The above-mentioned effect can be obtained by increasing the astigmatism in the ten directions.

As shown in Figure 8, the change in astigmatism due to the addition of a 90° prism in the base direction, that is, the change in the base curve factor, is related to the amount of prism. Visually, it shifts to one side. Therefore, the amount of prism to be added can be selected from eight i&appropriate prisms depending on the base curve, lens power, design of lens refractive surface, etc. According to the inventor's research, if the amount of added prism is less than 11'ls'0 prism diopter, there will be no effect, and if it exceeds &0 prism diopter, the above-mentioned base curve factor will be affected. This will result in too many changes, which will actually impair the lens performance.In addition, adding a large prism will also affect the appearance of the lens, so take this into consideration when setting the axis of the 1.0 to 6.0 prism diopter. It is desirable to set the optimum amount of prism for the surface.

Another effect of the present invention is a reduction in the number of types of lenses. In other words, normal progressive multifocal lenses have lenses with different base curves depending on the power of the lens, but by inserting a prism at 90° in the Ki base direction as in the present invention, the amount of prism can be reduced. By making various changes, it is possible to cover a wide range of dioptric power with a single base curve (-2), thereby reducing the amount of space required for the lens. This is advantageous for mass production of lenses.

As described above, according to the present invention, it is possible to improve the astigmatism of the passenger by simply adding a prism of 90° in the base direction.

In addition, in the embodiments of the present invention, the description has been made assuming that 7" IJ sum fz Even if the principal meridian is tilted several degrees in consideration of the above, the effect of the present invention remains unchanged.

In addition, although a negative power lens was given as an example, the above-mentioned change in the B1 nosm W factor due to the addition of a prism in the base direction is the same for a positive power lens, so a positive power lens also has the same effect;・( 4) I'm happy. Furthermore, even if the base direction force of the prism is slightly deviated by 590 degrees, it does not fall outside the scope of the present invention.

[Brief explanation of the drawing]

FIG. 1 shows the -ff shape of the refractive surface of a progressive multifocal lens. 1
...Distance area 2...Near vision area 5...Medium 1
Tabe area 4...Evolute line of main meridian A...Far ID
Middle Ic? B... Near r19 M... Principal meridian r
, ... radius of curvature of the principal meridian in the distance part 1IiA region r
,...Radius of curvature of the principal meridian in the near area r...
Radius of curvature at one point on the principal meridian in the intermediate region Figure 2 shows the relationship between the base curve □ of a single focus spherical lens and the astigmatism at a visual angle of 30 degrees. Vertical axis D1...Base curve Horizontal II411pw...
Lens power Solid line: Isoastigmatism line for far vision Broken line: Isoastigmatism line for near vision a: Line of zero astigmatism for far vision b: Line of zero astigmatism for near vision Astigmatism zero line 3rd
The figure is a diagram showing the relationship between base curve lens power, visual angle, and astigmatism in the 30° direction in a progressive multifocal lens. In Fig. 4, □ base curve 4.5D, addition power 2. O.D. FIG. 3 is an astigmatism distribution diagram and an astigmatism direction diagram of a conventional progressive multifocal lens having a lens power of -6.0D. (a) Astigmatism distribution diagram (b) Direction diagram of astigmatism Figure 5 shows 1 pace curve 4. ．． 5 I), 71
0 people degree 2. O.D. Lens power (LOD) of conventional progressive multifocal lens astigmatism distribution diagram (a) and astigmatism direction diagram (b). Figure 6 shows base curve 2.6D1 addition power 2.OD Luns summer number -&OD Fig. 7 shows an astigmatism distribution diagram (a) and an astigmatism direction diagram (b) of a conventional progressive multifocal lens. Aberration distribution diagram (a) and astigmatism direction diagram (
b). FIG. 8 is a diagram showing the relationship between the base curve, V-lens power, and astigmatism at a visual angle of 30° of a progressive multifocal lens to which the present invention is applied. Above Figure 1 (0L) Cb) Figure 5 (α) (b) Figure 6 (a) Figure 7 (b)

Claims (1)

[Scope of Claims] (1) A distance vision region where the curvature of the horizontal section of the refractive surface of the lens is greater at the sides than at the center, and a near vision region where the curvature of the horizontal section is smaller at the sides than at the center. What is claimed is: 1. A progressive multifocal lens having at least 10,000 partial regions, characterized in that it has a prism with a base direction of 90 degrees that is not intended for strabismus correction. (2) The progressive multifocal lens according to claim 1, wherein the size P (unit: a prism diopter) of the prism satisfies 1.0≦P≦6.0.