JPH0120723B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates generally to ophthalmic lenses, and more particularly to ophthalmic lenses with sequentially varying focal lengths.

Presbyopia is a term used to describe the reduced or incomplete elasticity of the eye's crystalline lens. It is a affliction that affects many people, usually in middle age, and is characterized by the loss of the eye's ability to focus sharply to see near objects.

Traditionally, the treatment of presbyopia has been to prescribe corrective spectacle lenses having two or more spherical surfaces or sections of different refractive index. In particular, these lenses, known as multifocal lenses, are designed so that the refractive index of one part of the lens allows for proper focus on nearby objects, while the other part corrects vision for seeing things further away. ing. Typically, people who develop presbyopia initially wear two-part lenses known as bifocals, and later as their vision deteriorates, they wear three-part lenses known as trifocals. This helps focus objects at intermediate distances.

Multifocal lenses have been used for many years and are generally quite acceptable as far as their ability to provide improved vision is concerned. However, these lenses suffer from several disadvantages. For one thing, a typical multifocal lens has sharp branching lines or discontinuities between the various parts of the lens, so that when the field of vision crosses this branching line, there is a jump in the image perceived by the wearer. It always happens. For many wearers, this feel is difficult to control.

Also, patients, especially those with a marked decrease in adaptability (the ability of the eye to automatically adjust to see objects at different distances, is called adaptability) may be able to use different parts of the lens at distances other than the one in focus. Objects between these distances cannot be brought into sharp focus.

Finally, people with reduced accommodation are reluctant to wear multifocal lenses. This is because they believe that wearing clothes will damage their appearance and give third parties an impression of how old they are. Although these people need corrective glasses, they do not wear them, or at least do not wear them all the time, thus not only sacrificing good vision but also creating safety issues, such as wearing them properly. This has created problems such as driving a car without proper glasses.

Recognizing the inconveniences of ordinary multifocal lenses, new types of lenses have recently appeared on the market. These lenses are lenses whose focal lengths vary sequentially, or more simply known as progressive lenses; It provides the functionality of a lens. In particular, such lenses are characterized by having a progressive portion located between and merged with the distance and reading portions of the lens. Additionally, the successively changing portion is a continuously changing focus that begins with a focus equal to the distance portion (where it merges with the distance portion) and ends with a focus equal to the reading portion (where it merges with the reading portion). It is designed to have.

These three sections, the distance section, the reading section and the progressive section, constitute the functional area of the lens, and this area provides corrective optical power depending on the prescription. The remaining area of the lens constitutes the peripheral area, which is usually subject to strong aberrations and does not provide adequate corrective magnification to the wearer.

The basic patent for this type of lens was issued in 1915 (U.S. Pat. No. 1,143,316), and a more sophisticated version was issued in 1924 (U.S. Pat. No.
No. 1518405). Both of the above two patents primarily relate to the functional area of the lens. A number of subsequently issued patents provided various prescriptions for the peripheral zone, some intended to reduce aberrations, some relating to manufacturing methods, or both. The introduction of numerically controlled surface forming machines in the last decade has removed many of the limitations imposed by manufacturing techniques, and as a result, most recent patents have focused on reducing aberrations in the peripheral zone. I've put it together.

Two aberrations in the peripheral zone that have a major effect on wearer comfort are horizontal and vertical astigmatism and distortion. The physical and mathematical properties of these two aberrations are well understood by those skilled in the art, and it is recognized that these aberrations cannot be completely eliminated due to the physical requirements to be met in the functional area. There is. This means limiting the design object to the development of a surface geometry with a specific distribution of aberrations in its peripheral area, within which it provides the best possible comfort for the wearer.

Particularly troubling is the distortion of horizontal and vertical lines in the temporary surrounding area. Also, the unavoidable astigmatism is particularly unpleasant in areas adjacent to the distance portion. This is because astigmatism adversely affects nearby peripheral vision when looking at distant objects. Another undesirable area for this aberration is the lower peripheral area. This is because the lower part tends to distort the true ground level. Typically, the most recent US patents such as US Pat. No. 3,687,528; US Pat. No. 3,711,191; US Pat.
Nos. 4,055,379 and 4,062,629 are all intended to provide the best solution for the above-mentioned conditions.

The present invention is intended for the same design object as mentioned above, namely to provide the best comfort to the wearer. In particular, the present invention reduces horizontal and vertical line distortion in the temporary peripheral area below the detection level, minimizes emergency aberrations in the area adjacent to the far field, and lowers the temporal peripheral area. We present a new mathematical model for the overall lens surface geometry that eliminates astigmatism in .

Additionally, the present invention provides a unique geometry that allows the lens to retain these properties after rotation to accommodate left or right eyes.
In particular, since the lens must be used for both distance and near vision, the optical centers of both the distance and reading portions cannot lie on the same vertical line. Instead, the optical center of the reading portion must be close to the nose for the left and right lenses for convergence of the eyeballs when viewing nearby objects (see Figure 4).

Essentially, this requires two different lenses for the left and right eyes, and in fact, certain prior art embodiments provide different lenses for each eye. An economical and more preferable solution to this problem would be to provide one common design for the left and right eyes, then rotate the lens about the center of the lens to displace the reading portion relative to the nose, and use other commercially available Prior art lenses are designed in this way. However, this approach creates other design difficulties. In detail,
If the lens is made to correct horizontal and vertical distortions in the peripheral area about one central direction, the lens loses its corrective power after being rotated to accommodate the left or right eye. According to the invention, this corrective force is not lost even after rotation.

Other specific features and advantages of the invention are set forth below, along with a detailed description of the best mode for carrying out the invention.

FIG. 1 schematically shows a progressive power lens according to the invention.

FIG. 2 schematically shows a progressive power lens according to the invention placed in the coordinates used to create a mathematical description of the lens surface. In particular, FIG. 2a shows a front view of the lens surface, and FIGS. 2b and 2c each show an arrow 2--2 in FIG. 2a.
3 shows a cross section of the lens surface viewed from the direction 3-3.

FIG. 3 schematically shows the lower half of the lens surface at the same coordinates as FIG. 2 to aid in understanding the invention. Figure 3a shows a front view of the lens surface, Figures 3b and 3c respectively
3A shows a cross section of the lens surface viewed from the direction of arrows 4-4 and 5-5 in FIG.

FIG. 4 schematically shows the progressive power lens of the present invention inserted into a pair of eyeglass frames.

Figures 5a and 5b depict the lens of Figure 4 placed on top of a grating pattern to illustrate the improved properties of the progressive power lens of the present invention.

FIG. 1 schematically illustrates a progressive power lens 10 for spectacles according to a preferred embodiment of the invention, and in particular the front convex surface 11 of such a lens. Lens surface 11 may be considered in at least four parts or zones. That is, the long distance portion 12,
Reading section 13, sequential corridor 14 and surrounding area 1
It is 6.

The distance portion 12 occupies substantially the upper half of the lens and is preferably a spherically curved surface of constant diopters and is used for viewing objects at a distance. The reading portion 13 is located near the bottom of the lens and is preferably also of constant magnification and has a spherically curved surface used to view objects at a normal reading distance.

The sequential corridor 14 is located between the long-distance section 12 and the reading section 13 and optically connects them. As is known in the art and as described in more detail below, this sequentially varying portion 14
extends from the long-distance portion 12 to the reading portion 13, and its magnification is equal to the magnification of the long-distance portion at the place where it joins the long-distance portion, and is equal to the magnification of the reading portion at the place where it joins the reading portion. It consists of corridors that are equally and gradually and continuously changing between them. As the eye scans this corridor from top to bottom, a clear vision of any object between infinity and reading distance is obtained.

From a theoretical point of view, it is preferred that the successive galleries be astigmatic along their entire length. However, it should be recognized that from a physiological point of view the eye readily tolerates certain astigmatisms, especially at the beginning (top) of the gallery. This part of the gallery is very rarely used for viewing. This is because the residual flexibility allows the wearer to use the distance portion to see in this range. In the present invention, we have recognized that by introducing some tolerable astigmatism into the sequential corridors, significant improvements in the overall lens can be obtained. especially,
The curvature of substantially any vertical element of the gallery is always made flatter, or less diopter, than the curvature of the corresponding horizontal cross-section in that vertical element. Typically, the magnification difference between vertical and horizontal surfaces along a sequential corridor is about 20 of the additional magnification at the beginning of the corridor.
% and gradually decreases to zero at the end of the corridor. Since the vertical cross section of the sequential corridor designed according to the invention is flatter than in conventional designs, the entire reading section can be advanced closer to the sphere defining the distance section. As a result, the peripheral portion providing the junction between the distance portion and the reading portion is less distorted and thus results in less astigmatism. Another additional advantage of this approach is better uniformity of the lens layer thickness, so that for positive distance magnification, thinner lenses are required.

As previously mentioned, the distance section, the reading section and the sequential corridors constitute the functional areas of the lens which provide corrective optical power as determined by the wearer. The lens remainder, identified by reference numeral 16, constitutes the peripheral area of the lens surface. The function of these areas is simply to fill in the remaining areas of the lens and provide a continuous optical surface. As will be clear from what follows, it is in this area that aberrations are necessarily present and that the invention is primarily concerned in order to provide lenses with the best properties.

In this regard, it should be clearly understood that the divisions shown in FIG. 1 between the various portions of the lens surface are merely for ease of explanation. In reality, there are no lines or discontinuities, either physically or optically. Instead, each portion of the lens surface gradually merges with its adjacent portion. When the eye passes across the lens, for example from the reading section to the successive corridors, or from the successive corridors to the peripheral part, the wearer can see the exact area where the change from one part to the other takes place. or lines cannot be easily identified.

It should be understood that the present invention pertains only to the variable power surface of the lens that constitutes the convex front surface of lens 10 in the preferred embodiment shown in the drawings. The concave back surface of the lens may include a spherical or other surface specifically designed to adapt the lens to the wearer's particular eyeglass prescription.

As mentioned above, the distance and reading portions of the lens surface are typically spherical, each having a specific diopter. The difference in refractive index between the distance part and the reading part is, for example, from 1/2 diopter to 3 diopters or more. The particular refractive index of these parts of the lens is not particularly relevant to the present invention. But whatever these refractive indices may be, a sequential gallery has at its top an index of refraction equal to the distance section, at its bottom an index of refraction equal to the reading section, and continuously along its length. It goes without saying that the refractive index must change.

When the wearer wears progressively variable magnification lenses,
It is common to view objects through the distance, reading, or gallery portion of the lens. The peripheral area of the lens is also often viewed through as well, so it is important to put effort into its design. However, as previously mentioned, it is not possible to design this surface to be aberration-free, so the primary goal in many progressive power lenses currently on the market is to minimize errors in these parts of the lens surface. The goal was to design the product so that it would be accurate, or to ensure that errors would not cause discomfort to the wearer.

It has generally been found that it is desirable to eliminate vertical and horizontal distortion in the temporal peripheral area and to avoid strong astigmatism in areas adjacent to the distance section and at the bottom of the peripheral area. . This is because they are easily recognized when viewed through a lens with these characteristics.

As an aid to the description of the present invention, FIG. 2 schematically shows a three-dimensional x, y, z coordinate arrangement of the progressive power lens 10 to provide a mathematical description of the lens surface 11. Figure 2a shows a front view of the lens surface, and Figure 2b shows the arrow 2--2 in Figure 2a.
The cross section of the lens surface viewed from the direction of
The figure shows a cross-section of the lens surface taken in the direction of arrow 3--3 in figure 2a. For ease of explanation, only the front progressive surface 11 of the lens is shown in the figure.

Referring to FIG. 2, the origin of this coordinate is at vertex 21 of the lens surface. This apex coincides with the starting point of the apex of the sequential corridor portion of the lens surface (the first
(see figure). The x-axis of the coordinates coincides with the protrusion of the vertical centerline 24 of the successive corridors, as shown more clearly in Figure 2b. This center line, also called the central line, runs successively along the entire length of the corridor.

Figures 3a, 3b and 3c show the same arrangement of lenses as in Figures 2a, 2b and 2c, respectively, but only the lower half of the lens surface is shown for easier explanation. be. Specifically, Figure 3a shows a front view of the lens surface;
Figure b shows a cross-sectional view taken in the direction of arrow 4--4 in Figure 3a, and Figure 3c shows a cross-sectional view taken in the direction of arrow 5--5 of Figure 3a, for example.

The upper half of the lens represents the distance portion 12 (see FIG. 1) and is preferably spherical as described above. In the following description of the lens surface, only the lower half of the lens surface will be discussed, so all references to the lens surface should be understood to refer to the lower half of the lens surface.

The geometry of the lens surface (ie, the lower half) is defined in terms of parameters. In detail, yz
Each cross-section of the surface in a plane parallel to the surface (e.g. perpendicular to the plane of the paper in Figure 3a and y
The planes 31 and 32) parallel to the axis are described as quadratic curves by equations containing numerical parameters that vary as a function of the x-axis. Furthermore, these quadratic curves have two parts, namely coordinates −y ₁ and +y ₁ (3rd a
and a peripheral portion located outside the -y ₁ and +y ₁ boundaries. In other words, −y ₁ and +
y ₁ defines the inner boundary of the peripheral portion 16 of the lens surface, and although it is shown as a straight line, these −
The y ₁ and +y ₁ boundaries can obviously have any shape to indicate the inner boundaries of the peripheral portion.

The central part of the curve (i.e. the part between −y ₁ and +y ₁ ) is defined by the function Z _n(x,y) , and the central part of the curve is defined by Z _o(x,y). Ru. The constant expressed as a parametric variable in both functions basically depends on the value of x.

The function Z _n(x,y) is defined by the following equation (1).

Z _n(x,y) =Z _np(x) +1/B _(x) (√ ² _(x) + _(x) ²
−ρ _(x) )−1/n _(x) C _(x) y ⁿ (x) (1) The various parameters of this function are defined as follows.

Z _np(x) is a function that describes the geometry of the center line 24 (see Figure 3b). The shape of this curve is governed by the rate of refractive index change in the successive corridors and by the refractive index of the reading portion of the lens.

B _(x) is the conic constant for the conic component of the function. It assumes a value that continuously transforms the conic section from a circle at the start of the successive corridor (adjacent to the distance part) to a circle at the end of the successive corridor and then back to a circle towards the center of the reading part. There is. This function is intended to improve the surface geometry in the transition area between the sequential corridor and the reading section.

ρ _(x) are the y, z components of the local radius R _n(x) of the centerline curve defined by Z np(x ₎ (denote these functions for a particular cross-sectional curve x ₁ 3rd b
(see diagram).

The exponential component of function (1) provides a smooth transition to the Z _o(x) function.

The parameter C _(x) is a very small value to suppress the contribution of this component in the center of the curve. Typically, it varies from a value of 10 ^-4 at the point x=0 to a value of about 10 ^-10 at x=max.

The parameter n _(x) is for ensuring smooth joining of the curve Z _{n (x, y)} to Z _{o (x, y)} at _one point -y and _one point +y. This condition is satisfied if the first derivative of the function Z _{n (x, y)} is equal to the first derivative of the function Z _{o (x, y)} at +y ₁ or −y ₁ point. in the end,
The value of n _(x) is found by solving the following equation (2).

dZ _n(x,y) /dy=dZ _o(x,y) /dy (2) (for y=±y ₁ ) The peripheral curve Z _o(x,y) is defined by the following function (3) be done.

Z _o(x,y) =Z _op(x) +R _p(x) −√ ² _p(x) − ₂ (3) This function lies on the curve defined by the parametric representation function Z _op(x). Define a circle with vertices located at (see Figure 3c).

The parametric representation function Z _op(x) is given by the following conic equation.

Z _op(x) = 1/BL(√ ² _L + _L(x) ² −R _L ) (4) The constants B _L and R _L provide the desired width of the reading section and are adjacent to the distance section. chosen to minimize emergency aberrations in the area.

The parameter R _p(x) indicates the deformation distance between the point x ₁ y ₁ on the curve and a line parallel to the x-axis and intersecting the center line of the long distance portion C _d (see Figure 3b). It is the following formula
(5).

R _p(x) = R _(x) (1−A _(x) ) (5) where R _(x) is the exact value of the above distance (see Figure 3b) and A _(x) is the deformation factor. Typically, it takes a value of 0.2 when x=maximum and zero when x=minimum.

As is clear from the description below, this deformation component is used to correct the distortion of horizontal and vertical lines on the temple side of the peripheral area after rotating the lens to adapt it to the left or right eye. is necessary.

By designing a lens according to the parametric equations described above, it is possible to provide a lens that eliminates astigmatism in the lower part of the temporal periphery while at the same time substantially reducing horizontal and vertical distortion. It becomes possible. This design accomplishes this without the need for desphericalization of the distance portion as is found in some prior art techniques. Also, there is no need to provide very strong astigmatism concentration in a very narrow area as is done in other designs.

A particularly important feature of the invention is that its design makes it possible to correct horizontal and vertical line distortions on the temple side of the peripheral area after rotating the lens to adapt it to the right or left eye. There is a particular thing.
Specifically, FIG. 4 schematically shows successive change lenses 41 and 42 inserted into a pair of front surfaces 43 of eyeglass frames. As seen in the illustration of the sequential corridor and reading portion of the lens, both lenses are slanted inward, which is necessary for convergence of the eye when viewing nearby objects. Typically these lenses are tilted 8-10 degrees from vertical.

Although many prior art designs allow lenses to be corrected for horizontal and vertical distortion in peripheral bands for one central array,
It eliminates post-rotation correction. The present invention provides a unique geometry that allows correction of horizontal and vertical distortions in the temporal periphery during left-right rotation of the lens to keep them below the detection level. This is illustrated by Figures 5a and 5b.
In these figures, a pair of lenses 51 and 52, rotated to accommodate the left and right eyes, are placed on a grid pattern. Specifically, these lenses have a distance index of zero and an add index of 2 diopters. These figures clearly show that horizontal and vertical line distortions are practically undetectable in the temporal peripheral bands of the lens.

It should be noted that contours 53 and 54 in FIGS. 5a and 5b are the contours of the spectacle frame showing the shape of the lens after the frame is provided with a lip for insertion.

Progressive change lenses according to the invention can be made from glass or plastic as is well known in the art. However, plastic lenses made from CR-39, a resin commonly used in the manufacture of plastic ophthalmic lenses, are preferred. Such lenses can be cast in a mold defined by two mold members separated from each other by suitable gaskets. One of the mold members has a gradation surface on its concave surface, which allows the gradation surface to be transferred to the opposing concave surface of the plastic lens molding.

Sequential template surfaces can also be created in a variety of ways well known in the art. Preferably, it is formed by recessing a circular piece of glass into a block of refractory material or metal with a machined graduated surface. The refractory material can of course be used multiple times for producing castings, and the mold parts can also be used multiple times for lens casting.

Although the foregoing constitutes the most preferred embodiments of the invention, it should be understood that various changes and modifications are possible. It is, therefore, to be understood that the invention is limited only by the scope of the claims appended hereto.

[Brief explanation of drawings]

FIG. 1 schematically shows a progressive power lens according to the invention. FIG. 2 schematically shows a progressive power lens according to the invention placed in the coordinates used for the mathematical description of the lens surface, FIG. 2a shows a front view of the lens surface, and FIG. Figures 2b and 2c show cross sections of the lens surface viewed from the directions of arrows 2-2 and 3-3 in Figure 2a, respectively. FIG. 3 schematically shows the lower half of the lens surface at the same coordinates as FIG. 2, FIG. 3a shows a front view of the lens surface, and FIGS. 3b and 3c are respectively shown in FIG. 2 shows a cross section of the lens surface viewed from the directions of arrows 4-4 and 5-5. FIG. 4 schematically shows the progressive power lens of the present invention inserted into a pair of eyeglass frames. Figures 5a and 5b depict the lens of Figure 4 placed on top of a grating pattern to demonstrate the improved properties of the progressive power lens of the present invention. 10...Lens, 11...Front convex surface, 12...
Long-distance portion, 13...Reading portion, 14...Successive magnification portion, 16...Peripheral area, 21...Vertex of lens surface, 24...Vertical center line, 31 and 32...In Figure 3a perpendicular to the paper and y
planes parallel to the axis, 41 and 42...lens, 43
... Glasses frame, 51 and 52 ... Lens, 53
and 54...the outline of the glasses frame.

Claims (1)

[Scope of Claims] 1. A lens with a progressively changing focus having a progressively changing surface consisting of a distance portion, a reading portion, a sequentially changing corridor, and a peripheral portion, wherein at least a portion of the surface refers to three-dimensional coordinates. The origin of the coordinate axes is at the vertex of the lens surface, the z-axis is perpendicular to the surface at the vertex, the x-axis is perpendicular to the surface, and the y-axis is an axis is horizontal with respect to the surface;
Central part and function where each cross section of the part parallel to the yz plane is defined by the parametric representation function Z _n(x,y)
Z _{n (x,y)} = Z _np(x) + 1/B _(x) (√ ² _(x) + _(x) ² − _(
x) ) −1/n _(x) C _(x) y ⁿ (x) and Z _o(x,y) =Z _op(x) +R _p(x) −√ ² _p(x) − ² [Above formula , Z _np(x) is a function that describes the geometry of the center line of the lens surface; B _x is the conic constant of the conic component of the function; ρ _(x) is defined by the function Z _np(x) . C _(x) is the exponential function at the center of the curve -1/n _{(x )} C _(x) y ⁿ It is a very small auxiliary variable to suppress the contribution of (x); n _(x) is a curve
It is a parameter that guarantees a smooth connection of Z _o(x,y) ,
Assuming that the values of y are equal at the junction, the equation
Its value can be found by solving dZ _n(x,y) /dy=dZ _o(x,y) /dy; Z _op(x) =1/BL(√ ² _L + ² _{L (x)} −R _L ) (where B _L and R _L are values chosen to provide the desired width of the reading portion of the lens surface) R _p(x) = R _(x) (1 − A _{( x)} ) (where R _(x) is equal to the distance between the point x _i y _i on the curve and the line that is parallel to the x axis and intersects the central curve of the long distance portion of the lens surface; A _(x) is a deformation coefficient for correcting distortion of horizontal and vertical lines on the temple side of the peripheral part after rotating the lens to adapt it to the left eye or the right eye)]. A lens with a focal point. 2. A lens according to claim 1, in which the lower half of the lens surface comprises a peripheral portion constituting a progressively changing corridor, a reading portion and a portion of the surface defined by a parameter representation. 3. The lens according to claim 2, wherein the long-distance portion substantially constitutes the upper half of the lens and has a spherical curved surface. 4. Any one of claims 1 to 3, wherein the progressive corridor is designed such that along its length the curved surface of its vertical element has a diopter that is weaker than the curved surface of the corresponding horizontal cross section. Lenses listed in section. 5. Claims in which the diopter difference between the curved surface of the vertical element of the corridor and the curved surface of the corresponding horizontal cross-section is equal to approximately 20% additional diopters at the top of the corridor and gradually decreases to zero at the bottom of the corridor Lens according to item 4.