JPS6342764B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to the shape of a refractive surface of a progressive multifocal lens.

The purpose of the present invention is to minimize astigmatism and image distortion that inevitably exist in progressive multifocal lenses, and to provide a progressive multifocal lens that provides the most satisfaction to its users when used in various situations. It is about providing.

In order to facilitate understanding of the present invention, the use, structure, and optical characteristics of a progressive multifocal lens will be explained.

Progressive multifocal lenses are mainly used to correct the decline in the accommodative function of the crystalline lens of the eye in elderly people.
This lens has an area for seeing distant objects, an area for seeing near objects, and an intermediate distance lens with continuously changing power between the two areas. It has a field of view. These three areas are called a distance area, a near area, and an intermediate area, respectively.

Figures 1 to 4 are examples of general progressive multifocal lenses, and Figure 1 shows the general structure of a progressive multifocal lens, and is a perspective view of a convex refractive surface. . The concave surface on the opposite side (not shown) is a spherical or cylindrical curved surface, and is used to correct hyperopia, myopia, and astigmatism. 1 in the figure is the optical center axis (hereinafter referred to as the optical axis) of the lens, which passes through the geometric center O of the lens. Reference numeral 2 denotes a principal meridian curve that is an intersection between a perpendicular plane 5 including the optical axis 1 (hereinafter referred to as the principal meridian plane) and the refractive surface of the lens. Figure 2 shows the change in curvature of this principal meridian curve, and the vertical axis of the figure is the distance along the principal meridian curve.
The horizontal axis P is surface refractive power (value of refractive effect due to a convex refractive surface. Value of refractive effect as a lens including a concave surface is called refractive power). Both refractive powers along the principal meridian curve are constant above point A and below point B, and increase progressively from point A to point B. These points A and B are called the distance center and the near center, respectively, and the amount of change in both refractive powers (ADD in the figure) between them is called the addition power.
Since both refractive powers and curvature of the lens are proportional, this figure can be regarded as a change in curvature, and the locus of the center of curvature of the principal meridian curve is as shown by 3 in FIG. Also, the curvature in the direction orthogonal to the principal meridian curve on the refracting surface at each point on the principal meridian curve is equal to the curvature in the direction along the same curve, which is a so-called navel-shaped curve. The point aberration becomes zero. That is, the portion along the principal meridian curve has a substantially spherical shape. However, in order to connect spherical surfaces with different curvatures to form one smooth curved surface, the surface must become aspherical as it moves away from the principal meridian curve, and astigmatism will therefore occur in the periphery. Furthermore, since the magnification of the image differs in each part of the refractive surface, image distortion also occurs.

FIG. 3 shows an example of the astigmatism distribution of a general progressive multifocal lens. In the figure, the narrower the hatching pitch, the larger the aberration.
In other words, this means that the image becomes blurred. Generally, people perceive astigmatism and feel discomfort at 0.5
It is said to be more than 1.5D (hereinafter abbreviated as D), and the unhatched area in the figure is 0.5D.
The following areas are covered. This area above point A is called the distance clear vision area, this area below point B is called the near clear vision area, and this area between point A and B is called the intermediate clear vision area. This is the range in which objects are perceived as clearly visible.

FIG. 4 shows an example of image distortion when a lattice pattern (hereinafter referred to as a square lattice) drawn at equal pitches in the vertical and horizontal directions is viewed through a general progressive multifocal lens. In the image of the grid, due to the change in magnification, as shown in the figure, the vertical lines bulge downward with the line passing through the principal meridian curve (41 in the figure) as the center, and the horizontal lines also curve towards the periphery.

This image distortion is not only perceived as image distortion, but also when the user follows a moving object with their eyes.
When an object moves relative to the line of sight, such as by moving the head, this is perceived as image shaking, causing significant discomfort. Cases in which we see moving objects in this way are called dynamic vision, whereas cases in which there is almost no movement of the gaze and objects, such as when reading a book or gazing at a single point, are called static vision. As is clear from the above discussion, static vision is primarily affected by astigmatism. That is,
The smaller the astigmatism as a whole, the better distance vision,
The wider the near and intermediate clear vision ranges, the more comfortable vision can be obtained.

On the other hand, dynamic vision is mainly affected by image distortion. In other words, the smaller the image distortion, the more comfortable vision can be obtained with less image shaking. The relationship between static vision and dynamic vision is not an independent relationship; if you widen the clear visual field to obtain good static vision,
Because the change in image magnification becomes rapid on the sides of the lens, image distortion becomes large and dynamic vision is impaired; There is a contradictory relationship in that the astigmatism increases in both directions, impairing static vision.

In this way, the present inventor has developed a lens that minimizes astigmatism and image distortion, which are inherent in progressive multifocal lenses, and provides the best dynamic vision under various static vision conditions. Developed a progressive multifocal lens as shown in 1971-171569.

5, 6, and 7 are diagrams for explaining the structure of the refractive surface of the progressive multifocal lens, with FIG. 5 being a front view and FIG. 7 being a perspective view of a part of the refractive surface.

In FIG. 5, C1 and C2 are distance center A and near center B, respectively, and are curves that intersect with the principal meridian curve M and divide the lens refractive surface into three,
The regions 51, 52, and 53 are respectively defined as a distance region, a near region, and an intermediate region. M1 is a cross-sectional curve on a plane parallel to the principal meridian, and curves C1,
Let the intersections with C2 be A1 and B1, respectively.

FIG. 6 shows changes in the angle between the normal to the lens refractive surface and the principal meridian at each point on the cross-sectional curve M1, which can be easily understood from the perspective view of FIG.

In FIG. 7, P1, P2, and P3 are points within the far, near, and intermediate regions on the cross-sectional curve M1, and the angle between the normals T1, T2, and T3 of each point and the principal meridian plane 71 is as follows: Indicated by K1, K2, and K3. One of the features of this lens is that this angle is the distance between the distance area (above A1) and the near area, as shown in Figure 6 (the vertical axis is the position on the curve M1, and the horizontal axis is the angle). (B1
In the lower part), each value is constant, and in the middle region (between A1 and B1), it changes continuously and smoothly, and the way it changes depends on the curvature on the principal meridian curve. It is the same as the law of change.

For example, if the curvature of the principal meridian curve in the intermediate region changes linearly, the above-mentioned angle also changes linearly, as shown in FIG. this is,
It is satisfied in all cross sections parallel to the principal meridian plane.

FIG. 8 is a diagram showing the above-mentioned angular changes in a plurality of cross sections, and represents the angular changes in the cross sections moving away from the principal meridian curve in the order of M1, M2, M3, and M4. Since the change in angle along this vertical cross-sectional curve is approximately proportional to the horizontal prism change along the cross-sectional curve, Figure 8 can be regarded as a distortion of the vertical line at each cross-section. . Distortion of the horizontal line is related to distortion of the vertical line; if there is no distortion in the vertical line, the horizontal line will not be distorted, and where the vertical line is distorted, the horizontal line will also be distorted. Therefore, the distance region and the near region have normal distortion in which the square lattice is deformed into a rectangular shape, and the intermediate region has skew distortion in which the square lattice is deformed into a parallelogram shape. This suppresses the shaking of the images in the distance vision area and the near vision area.

In addition, in the intermediate region, by making the way the vertical line is distorted the same as the law of change of curvature between the distance center and the near center on the principal meridian curve,
Astigmatism on the principal meridian curve is made zero, and the surrounding lattice is arranged, making it possible to suppress astigmatism and image distortion as much as possible.

The present invention provides visual improvements to the progressive multifocal lens based on such a basic idea.

Hereinafter, the present invention will be explained in detail with reference to Examples.

Fig. 9 is an example of the lens shown in Japanese Patent Application No. 171569/1982. In the figure, M is the principal meridian curve, M1 to M9
indicates a cross-sectional curve by a plane parallel to the principal meridian,
The spacing is equal. In this lens, a boundary line C1 between the distance region and the intermediate region and a boundary line C2 between the near vision region and the intermediate region are monotonous curves from the principal meridian curve to the lens outer periphery.

FIG. 10 shows changes in the angle K between the normal to the lens refractive surface and the principal meridian plane in each cross section. In this lens, the shape of the cross-sectional curve (hereinafter referred to as the cross-section), which is the line of intersection between the plane perpendicular to the principal meridian curve and the lens refractive surface, changes as the distance from the principal meridian curve increases in the distance region. It has a shape in which the curvature increases, and in the near region, the curvature decreases as it moves away from the principal meridian curve. M to M9
Since the amount of increase ΔK in the angle K between each section up to is approximately proportional to the size of the curvature between them,
As shown in the figure, in the distance vision region, the angular increase amount ΔK between each section from M to M9 gradually increases (that is, the interval becomes wider), and in the near vision region, on the contrary, the angular increase amount ΔK gradually decreases. (i.e., the interval becomes narrower). By using the relationship between this curvature and the amount of angular increase, it is possible to know the change in the curvature of the cross section of the intermediate region from this figure. In other words, the curvature change of the cross section is such that the horizontal line (for example, S1-S1') at the position corresponding to the cross section in the same figure changes from M1 to M1.
This is approximately equal to the change in the spacing between each line when cutting each line up to 9.

Figure 11 shows S1-S1', S2- in Figure 10.
It shows the change in curvature of each cross section of S2', S3-S3', and S4-S4'. The vertical axis represents the curvature ρ, and the horizontal axis represents the distance x from the principal meridian curve. From the figure, the shape of the cross section in the intermediate region shows that the curvature increases monotonically as it moves away from the principal meridian curve on the distance vision region side (S1-S in the figure).
1'), it can be seen that on the near vision region side, it first decreases and then increases (S4-S4' in the figure).

FIG. 12 shows an embodiment of the present invention, and the shape determining factors of the lens refractive surface other than how to divide the distance region, intermediate region, and near region are the same as the conventional example shown in FIG. 9. It's the same. In the figure, in order to clearly show the difference in the method of division, the method of division in the conventional example is shown by broken lines. The features of the present invention are the above-mentioned three
The curve C1 and the curve C2, which are the boundary lines of the regions, have portions that are convex toward the distance region and the near region, respectively, from the principal meridian curve to the outer periphery of the lens.

Similar to the prior art example described above, changes in the angle K on each cross section from M to M9 are shown in FIG. 13, and changes in the curvature of the cross section in the intermediate region are shown in FIG. 14. The broken line in FIG. 13 indicates the angle K in the conventional example in FIG.
As can be seen, in the present invention, the boundary lines C1 and C2 of the intermediate region
Cross section M of the part that bulges upward and downward in a convex shape
3. The angles K of M4, M5, and M6 change more slowly than in the conventional case, and the rates of change are almost equal. The curvature of the cross section of the intermediate region at this time is
As shown in Fig. 14, on the far vision side, as it moves away from the principal meridian curve, it increases once and then decreases;
After that, the change increases again (S1-S in the figure).
1'), on the near region side, the change decreases and then increases as the distance from the principal meridian curve increases (S4-S4' in the figure). Furthermore, once the curvature of the cross section on the distance vision region side increases, a portion W is created at an intermediate position from the principal meridian curve to the outer periphery of the lens, where the change in curvature of the cross section is approximately equal.

These facts explain the effects of the present invention. In other words, the distortion of the image seen through the lens is
Since it is almost equal to the change in angle K shown in Fig. 13,
According to the present invention, image distortion on the sides of the intermediate region can be reduced, and image shaking can be improved. In addition, astigmatism is also leveled out in the area indicated by W in FIG. 14, resulting in a gentler distribution than in the past, and it is possible to alleviate the feeling that the image suddenly blurs on the sides of the intermediate region.

Next, a second example will be shown. In this embodiment, the method of dividing the distance, intermediate and near regions and the law of curvature change on the principal meridian curve are the same as in the conventional example shown in FIG. This embodiment differs from the conventional example in the manner in which the curvatures of the cross sections of the distance vision region and the near vision region change.

Figure 15 shows the difference. In the figure, ρ ₁ indicates a change in curvature of the cross section in the distance vision region, ρ ₂ indicates a change in curvature of the cross section in the near vision region, and the broken line is that of the conventional example. The feature of this embodiment is that, as shown in this figure, the change in curvature ρ ₂ of the cross section in the distance region is not simple, but ρ ₁ changes from the principal meridian curve to the outer circumference of the lens.
has a convex portion upward, and ρ ₂ has a convex portion downward. Expressing this mathematically, each curvature change can be expressed as a function of the distance x from the principal meridian curve ρ ₁
(x), ρ ₂ (x), 2 of ρ ₁ and ρ ₂ for x between the principal meridian curve and the outer circumference of the lens.
This means that the differential values each have negative and positive parts. FIG. 16 shows the change in angle K in this example. The broken line in the figure represents the angle change in the conventional example shown in FIG. From this figure, it is clear that the same improvements as in the previous embodiment are made in the intermediate region in this embodiment as well.
It goes without saying that the change in curvature of the cross section of the intermediate region at this time has the same shape as that of the previous embodiment shown in FIG.

As described above, according to the present invention, the distortion of the image on the sides of the intermediate region is reduced, and the distribution of astigmatism is smoothed, so that the progressive multifocal lens has good dynamic vision and static vision. lenses can be provided.

Note that even if some of the methods for improvement shown in the two embodiments of the present invention are used, or some of them are combined, commensurate effects can be obtained, and even in that case, the scope of the present invention does not fall within the scope of the present invention. not exceed.

[Brief explanation of the drawing]

Figures 1, 2, 3, and 4 show the structure of a general progressive multifocal lens, changes in surface refractive power on the principal meridian curve,
FIG. 3 is a diagram illustrating astigmatism distribution and distortion of a grating image. Figures 5, 6, 7, and 8 are diagrams for explaining the present invention, and are respectively a front view of the lens refractive surface, a change in the angle between the normal on the cross-sectional curve and the principal meridian, and a part of the lens refractive surface. FIG. 2 is a perspective view showing changes in the angle between the normal and the principal meridian on multiple cross-sectional curves. No. 9, 1
Figures 0 and 11 show the conventional lens shown in Japanese Patent Application No. 55-171569, and are respectively a front view of the refractive surface of the lens and
It shows changes in the angle between the normal and the principal meridian on multiple cross-sectional curves, and changes in the curvature of the cross section in the intermediate region.
Figures 12, 13, and 14 show examples of the present invention, respectively, showing a front view of the lens refractive surface, changes in the angle between the normal line on the multi-sectional curve and the principal meridian plane, and a cross-sectional view in the intermediate region. Shows changes in curvature. Figures 15 and 16
The figure shows a change in the curvature of the cross section in the distance region and near vision region, and a change in the angle between the normal line on the multi-section curve and the principal meridian plane, in another embodiment of the present invention. show. 2, M...principal meridian curve, A... distance center, B
... Center for near vision, C1... Boundary curve between the distance vision region and the intermediate region, C2... Boundary curve between the intermediate vision region and the near vision region, M1 to M9... Cross-sectional curves parallel to the principal meridian plane.

Claims (1)

[Claims] 1. On the principal meridian curve, the curvature changes according to a predetermined law between the distance center and the near center on the principal meridian curve, giving addition power, and at the distance center, the curvature changes between the distance center and the near center. A curve C1 on the refractive surface of the lens that intersects with a curve C2 on the refractive surface of the lens that intersects with the principal meridian curve at the center of the near vision center allows the refractive surface of the lens to be divided into a distance region, an intermediate region, and a near vision region. Divide into three areas,
In each arbitrary cross-sectional curve that is an intersection line between an arbitrary plane parallel to the plane containing the principal meridian curve and the refractive surface of the lens, the normal to the refractive surface at each point on the cross-sectional curve and the The angle formed with the plane containing the principal meridian curve is constant in the distance region and the near region, and the curvature between the distance center and the near center on the principal meridian curve is constant in the intermediate region. In a progressive multifocal lens that changes according to the same law as the law of change of a curvature that increases on the side of the region, and a curvature that decreases on the side of the region in the near vision region, and in the intermediate region, when the cross-sectional curve is on the side of the distance vision region; It has a curvature that increases and then decreases as it moves away from the main meridian curve, and then increases again, and the cross-sectional curve decreases and then increases as it moves away from the main meridian on the near region side. A progressive multifocal lens characterized by having a curvature.