JP7511864B2 - Single focus lens and its design method - Google Patents

Description

The present invention relates to a single-vision lens with astigmatism correction function, for example, used in spectacles and loupes, and a method for designing the same.

Astigmatism is one of the visual disorders caused by a distorted cornea. Astigmatism is a condition in which a point light source is not focused as a point, but as a circle, ellipse, or line, and thus cannot be clearly seen. When astigmatism occurs, it becomes difficult to see objects and can cause eye strain and headaches, so it is preferable to correct it unless it is very mild. The main prescription data for making a lens for correcting astigmatism in a single-focus lens are represented by the S power, C power, and astigmatism axis. The S power is a spherical power and indicates the degree of myopia or hyperopia. The C power indicates the degree of astigmatism and is the astigmatism correction power. Astigmatism is caused by distortion of the eyeball and can be corrected with a cylindrical lens. In reality, it is synthesized as a toric surface with a semi-cylindrical shape cut in the axial direction of a cylindrical lens. In addition, since the direction in which the eyeball is distorted varies from person to person, the astigmatism axis (the axial direction of the cylindrical lens) is set as information indicating the direction of the distortion.
An example of such a lens for correcting astigmatism is disclosed in Japanese Patent Application Laid-Open No. 2003-233696.

JP 2002-311397 A

If the astigmatism is relatively strong, correcting the astigmatism correctly may cause eye fatigue or make the wearer feel unsteady when walking. This is because the difference in image magnification between the weak and strong gaze directions, which are the axial directions, becomes too large on the toric surface for correcting astigmatism, causing spatial distortion. For this reason, in the past, for wearers with relatively strong astigmatism, the amount of astigmatism correction was sometimes adjusted to be weaker than the measured value, depending on the subjective opinion of the spectacles store or the request of the wearer.
for example,
Fully corrected power S-4.00 C-4.00
In this case, the amount of astigmatism correction is thinned out, for example, S-4.00 C-3.00.
Fully corrected power S-4.00 C-4.00
In this case, half the power of the amount of astigmatism correction to be thinned out is added to the spherical power (so-called equivalent spherical prescription), for example, S-4.50 C-3.00.
However, since neither of these methods uses the original measurement values, they cannot be said to be the optimal vision correction method for wearers with relatively strong astigmatism. In addition, it is difficult for opticians to determine how much deviation from the perfect correction power is necessary to obtain a prescription that is more suitable for the wearer without difficulty.
Therefore, there has been a demand for an astigmatism correcting lens that uses the wearer's perfect correction power, and that does not tire the wearer and makes the wearer feel unsteady when walking while wearing the lens, and a method for designing the same.

In order to solve the above problem, in Means 1, in an astigmatism correction lens to which astigmatism correction power for correcting astigmatism has been added, a predetermined astigmatism correction power is set in a central region of the lens including the center of the lens, and the predetermined astigmatism correction power is gradually decreased from the central region of the lens toward the periphery of the lens.
As a result, a specified astigmatism correction power is maintained near the center, making it possible to view with the prescribed perfect correction power or a power close to the perfect correction power, while at the periphery of the lens, the difference in image magnification between the weak principal gaze direction and the strong principal gaze direction is reduced or eliminated, making it difficult to sense distortion in space and reducing eye fatigue during use and the feeling of unsteadiness when walking.

"Astigmatism correction lenses with added astigmatism correction power" do not necessarily have to have S power (spherical power) set as long as C power (astigmatism correction power) is set. The surface for correcting astigmatism is a toric surface. A toric surface is a curved surface that is drawn when a circle is rotated around an axis of a straight line that does not pass through the center, and there are two types: "barrel type" and "donut type". Since the curvature of the vertical direction and the horizontal (circumferential) direction differs in a toric surface, astigmatism is corrected by setting a toric surface with a specified vertical and horizontal curvature.
The "central region of the lens including the center of the lens" is a region where the wearer has distance vision to near vision, and preferably includes at least the region for distance vision when facing forward.
Since it says that "the predetermined astigmatism correction power is gradually decreased from the central region toward the periphery of the lens," the astigmatism correction power becomes weaker as it moves from the central region toward the periphery.
In the calculation, the S power, C power, and AX (axis of cylinder cylinder) may be used, and these may be converted into standardized data of JCC (Jackson Cross Cylinder) for calculation.
In addition to being used in eyeglasses for vision correction, the lenses can also be used as magnifying glasses that can be used without holding the glasses, like eyeglasses with temples. In the case of magnifying glasses, the lenses are plus lenses.

In the second aspect, the predetermined astigmatism correction power is gradually decreased so as to form an equivalent spherical surface on the periphery of the lens.
As a result, although astigmatism correction is low around the entire periphery of the lens, this is covered by the spherical power, so that refractive correction is relatively good.
In conventional astigmatism lenses, it is highly likely that refractive correction is performed with a spherical equivalent without completely correcting astigmatism in order to prevent the user's eyes from getting tired or staggering when walking. In the lens of the present invention, although astigmatism is completely corrected at the center of the lens, the vision at the periphery of the lens is close to that of the spherical equivalent of conventional astigmatism lenses, so the overall wearing comfort is maintained and only the benefit of improved visual acuity at the center of the lens is enjoyed.
In the third aspect, the equivalent spherical surface is of mean power. The mean power also provides the same effects as those described above.

In the fourth aspect, the lens central region is an area located inside the lens with a radius of 15 mm from the center.
The central region may extend from the center to an area with a radius of more than 15 mm outside, but the area inside the radius of 15 mm is an area where the line of sight is particularly focused on an object to enable the user to see it clearly, and in that area the user can use the lens with the astigmatism correctly corrected. On the other hand, the area outside the radius of 15 mm is a peripheral area of the visual field that is not focused on, and therefore it is an area where there is not much problem even if the astigmatism is not correctly corrected, and therefore by gradually reducing the astigmatism correction power, eye fatigue and unsteadiness when walking are suppressed.
In addition, in Means 5, under the condition that the distance from the virtual center of rotation when the wearer's eyeball rotates to the center of the back surface of the lens is 25 mm, when the line of sight is rotated 30° from the center of the lens to the periphery of the lens, the cylindrical power in the effective refractive power at the lens surface through which the line of sight passes is smaller by 0.25D to 1.00D than the cylindrical power in the prescription value for the wearer at the lens center.
The lens surface through which the line of sight passes when the line of sight is rotated 30° is approximately 15 mm from the center of the lens. This is approximately the shortest distance from the center of the lens to the frame in a "smaller" eyeglass frame among the various eyeglass frames available, and it is anticipated that if a correction of 0.25 D or more is applied within this range, the lenses of almost all users will be able to enjoy the effects of the present invention.
Furthermore, in practical evaluations, it was confirmed that even with corrections of around 0.75 to 1.00 D, there was no discomfort due to changes in power, and the lenses were worn in a good condition.

In addition, in the sixth aspect, the spherical power is made to be positive.
An example of a magnifying glass with a positive spherical power is a magnifying glass for correcting farsightedness, or a magnifying glass for glasses that has a frame like glasses and is worn by hanging the temples on the ears without using the hands.
In the seventh aspect, the spherical power is negative.
An example of a case where the spherical power is negative is when correcting myopia.
In addition, in the eighth aspect, the spherical power is set to zero.
For example, a user is assumed to have no myopia or hyperopia power, but only astigmatism power.

In addition, Means 9 is a method for processing a single-focus lens in which a predetermined astigmatism correction power is set in a central region of the lens including the lens center, and the predetermined astigmatism correction power gradually decreases from the central region of the lens toward the periphery of the lens, and a curved surface of an astigmatism correction surface is synthesized in which, relative to a base surface configured as a reference spherical or aspherical surface, the direction in which the curvature of the cross-sectional curve formed by the intersection of a plane including the center of the lens body and perpendicular to the lens surface with the lens surface is maximum and minimum, and the curved surface of a correction surface in which the curvature of the cross-sectional curve is uniform from the central region of the lens including the lens center toward the periphery is synthesized.
This makes it possible to produce a single-focus lens in which a predetermined astigmatism correction power is set in the central region of the lens, including the center of the lens, and the predetermined astigmatism correction power gradually decreases from the central region to the periphery of the lens.

The idea of this means 9 is to combine a toric surface with a lens surface that is to be a spherical or aspherical surface, and further combine the combined surface with a correction surface that reduces the toric surface toward the periphery. However, the order of combination does not matter, and in processing, processing may be performed in the order of spherical or aspherical surface → toric surface → correction surface, or processing may be performed simultaneously based on the combined data obtained by combining the three data.
In the astigmatism correction surface, the direction in which the curvature of the cross-sectional curve is minimum (i.e., the axis of astigmatism) and the direction in which the curvature of the cross-sectional curve is maximum are basically designed to be perpendicular to each other. However, since there is no problem in terms of the astigmatism correction ability in actual wear, it is acceptable for the directions to be approximately perpendicular to each other. More specifically, for example, if the directions are in the range of 70 to 110 degrees, they are included in the range of approximately perpendicular to each other, and there is no problem in actual wear.
In addition, the rate of change in the shape when gradually decreasing the astigmatism correction power from the lens central area to the lens periphery is preferably such that the toric surface is gradually corrected and there is no toric surface or the rate of change is very gradual in the peripheral area. Therefore, it is preferable to set the rate of change as a linear or quadratic expression in which the functional relationship is not likely to become abrupt so that the rate of change is not abrupt.
The present invention is not limited to the configurations described in the following embodiments. The components of each embodiment and modification may be arbitrarily selected and combined. Any component of each embodiment or modification may be arbitrarily combined with any component described in the Summary for Solving the Problems of the Invention or any component that embodies any component described in the Summary for Solving the Problems of the Invention. The present invention also intends to obtain rights to these by amending the present application or filing a divisional application, etc.
In addition, the applicant intends to obtain rights to the overall design or partial design by filing a conversion application to a design application. The drawings show the entire device in solid lines, but they also include partial designs claimed for a portion of the device as well as the overall design. For example, a partial design may include a portion of the device as a partial design, regardless of the portion. A portion of the device may be a portion of the device, or may be a part of that portion.

In the present invention, a specified astigmatism correction power is maintained near the center, making it possible to see with the prescribed full correction power or a power close to the full correction power, while at the periphery of the lens, the difference in image magnification between the weak and strong gaze directions is reduced or eliminated, making it difficult to sense distortion in space and reducing eye fatigue during use and the feeling of unsteadiness when walking.

(a) is an end view of a single focal minus lens of an embodiment of the present invention, cut in the direction of the astigmatism axis, (b) is an end view of the same single focal minus lens cut in a direction perpendicular to the astigmatism axis, (c) is an end view of a single focal plus lens of an embodiment of the present invention, cut in the direction of the astigmatism axis, and (b) is an end view of the same single focal plus lens cut in a direction perpendicular to the astigmatism axis. 1 is an explanatory diagram illustrating the angle through which a wearer's line of sight passes when the wearer rotates his or her line of sight from the center of the lens to the periphery of the lens. FIG. 2 is a cylindrical power distribution diagram showing changes in power focusing only on the cylindrical power of the lens of Example 1. 13A and 13B are graphs showing a simulation of the change in power of the lens of Example 1 with the movement of the line of sight. 11 is a distribution diagram for confirming distortion aberration from the degree of distortion of a grid when passing through the lens of Example 1. FIG. FIG. 11 is a cylindrical power distribution diagram showing the change in power focusing only on the cylindrical power of the lens of Example 2. 13A and 13B are graphs showing a simulation of the change in power of the lens of Example 2 with the movement of the line of sight. FIG. 11 is a distribution diagram for confirming distortion aberration from the degree of distortion of a grid when passing through the lens of Example 2. FIG. 11 is a cylindrical power distribution diagram showing the change in power focusing only on the cylindrical power of the lens of Example 3. 13A and 13B are graphs showing a simulation of the change in power of the lens of Example 3 with the movement of the line of sight. FIG. 13 is a distribution diagram for confirming distortion aberration from the degree of distortion of a grid when passing through the lens of Example 3. 1 is a cylindrical power distribution diagram showing changes in power focusing only on the cylindrical power of the lens of Comparative Example 1. 6A and 6B are graphs simulating the change in power of the lens of Comparative Example 1 with the movement of the line of sight. 11 is a distribution diagram for confirming distortion aberration from the degree of distortion of a grid when passing through the lens of Comparative Example 1. 13 is a cylindrical power distribution diagram showing the change in power focusing only on the cylindrical power of the lens of Comparative Example 2. 13A and 13B are graphs simulating the change in power of the lens of Comparative Example 2 with the movement of the line of sight. 13 is a distribution diagram for confirming distortion aberration from the degree of distortion of a grid when passing through the lens of Comparative Example 2. FIG. 11 is a cylindrical power distribution diagram showing the change in power focusing only on the cylindrical power of the lens of Example 4. 13A and 13B are graphs showing a simulation of the change in power of the lens of Example 4 with the movement of the line of sight. FIG. 13 is a distribution diagram for confirming distortion aberration from the degree of distortion of a grid when passing through the lens of Example 4. 13 is a cylindrical power distribution diagram showing the change in power focusing only on the cylindrical power of the lens of Comparative Example 3. 13A and 13B are graphs simulating the change in power of the lens of Comparative Example 3 with the movement of the line of sight. 13 is a distribution diagram for confirming distortion aberration from the degree of distortion of a grid when passing through the lens of Comparative Example 3. 13 is a cylindrical power distribution diagram showing the change in power focusing only on the cylindrical power of the lens of Comparative Example 4. 13A and 13B are graphs showing a simulation of the change in power of the lens of Comparative Example 4 with the movement of the line of sight. 13 is a distribution diagram for confirming distortion aberration from the degree of distortion of a grid when passing through the lens of Comparative Example 4.

A specific embodiment specialized for a single focal length lens will be described below.
In the design of this embodiment, a specific lens design is performed by a lens characteristic calculation computer (not shown). The lens characteristic calculation computer is composed of a CPU (Central Processing Unit) and its peripheral devices. The CPU designs lens shape data with a predetermined power distribution and astigmatism distribution based on various programs and input lens characteristic data (S power data, C power data, astigmatism axis data, eye point data, prism data, etc.). In addition to various programs for creating lens shape data, the storage device stores basic programs such as a program for controlling the operation of the CPU and an office automation processing program for managing functions that can be commonly applied to multiple programs (e.g., Japanese input function, printing function, etc.).
A material block having a sufficient thickness, called "semi-finished," is processed by a computer aided manufacturing (CAM) device (not shown) based on the lens shape data designed by the lens characteristic calculation computer to produce a lens. However, the CAM device may be integrated with the lens characteristic calculation computer.

In this embodiment, the back surface of the material block is machined by a CAM device. Specifically, the axial direction parallel to the optical axis passing through the lens center is defined as the Z direction, and two directions perpendicular to this are defined as the X and Y directions, and three-dimensional shape data is determined. The planar position of the back surface is determined by X and Y, and the Z direction at each planar position is defined as the cutting amount (sag amount). The cutting part (not shown) of the CAM device cuts (machines) the material block while moving toward and away from the material block that rotates relative to the cutting part.
In this embodiment, the shape data is designed so that a first curve shape that serves as the reference for the back surface is designed based on the S power data and C power data of the user's (wearer's) lens information, and a second curve shape is designed so that the C power of the first curve shape is canceled at the periphery, and the CAM device performs processing based on the combined shape data.

The typical shape of the single-focus lens processed in this way is as shown in Figures 1(a) and 1(b) for the minus lens 1, and as shown in Figures 1(c) and 1(d) for the plus lens 2. The surface curve shape of these lenses 1 and 2 appears the same in cross section in any direction, and the back curve shape is a curve close to the prescribed spherical power or equivalent spherical power toward the periphery in the astigmatism axis direction, while the power of the prescribed astigmatism correction power is the direction perpendicular to the astigmatism axis in the central region, and is formed more gently from the central region to the periphery as shown by the dashed line than the curve of the solid line prescription value. In other words, the astigmatism power is gradually decreased in the direction of decreasing power (the plus side for the minus lens 1, and the minus side for the plus lens 21). The dashed line correction shape is given largest in the direction perpendicular to the astigmatism axis and increases or decreases depending on the phase between the astigmatism axis direction. The correction shape may be designed to extend to the astigmatism axis direction, or may be designed not to correct in the astigmatism axis direction.
It is preferable that the lens has the same spherical power all around with no astigmatism power at the outermost position, but if the astigmatism power is reduced at the periphery, it is not necessary to have the same spherical power all around. For example, it may be designed so that some astigmatism power remains in the direction perpendicular to the astigmatism axis. This is because it is better to reduce the distortion aberration of the lens as a whole. Also, as an example of a shape that is not typical as described above, for example, in the case of minus lens 1, depending on the shape of the surface curve, the minus power in the astigmatism axis direction may be strengthened to reduce the astigmatism power.

In addition, in the minus lens 1 and plus lens 2 thus constructed, the astigmatism correction power is gradually decreased from the lens central region toward the lens periphery, so that when the line of sight is rotated 30° from the center of the lens toward the periphery of the lens, the astigmatism correction power in the effective refractive power at the lens surface through which the line of sight passes is designed to be 0.25D to 1.00D less than the astigmatism correction power in the prescription value for the wearer at the lens center, under the condition that the shortest distance (vertex of the lens back surface) from the virtual center of rotation O when the wearer's eyeball L rotates to the center P1 of the lens back surface is 25 mm as shown in FIG. 2.

An example in which the single focal length lens of the present invention is simulated will now be described.
Example 1
Example 1 is an example of a single-focus minus lens. The lens parameters of Example 1 are as shown in Table 1.
The lens surface of Example 1 is spherical, and the back surface of the lens is shaped based on the prescription for the S power, C power, astigmatism axis direction, and radius of curvature of the back surface of the lens (in the 0° and 90° directions) with the powers shown in Table 1.
The shape of the lens back surface in the first embodiment is defined by the formula 1. The formula 1 will be explained. The formula 1 is a formula that indicates the total sag amount of the lens in the first embodiment, which is a combination of two formulas for the amount of sag, A shown in the formula 2 and B shown in the formula 3. The formula A is a general formula that defines the shape of the back surface of a spherical lens with a cylindrical power for a wearer with a cylindrical power. The formula B is a formula that cancels the cylindrical power of the lens periphery by combining with the formula A.
In each formula, X indicates the horizontal coordinate (0° direction) of the lens surface, and Y indicates the vertical coordinate (90° direction) of the lens surface. Cx is the lens horizontal curvature (0° direction), and Cy is the lens vertical curvature (90° direction). Cx is the reciprocal of Rx, and Cy is the reciprocal of Ry. In formula B, the coefficient is the curvature of S-5, which is the equivalent sphere (average diopter) of S diopter and C diopter shown in Table 1. This is the target diopter of the lens periphery.
The constant (-6.282E- ^7h2 + 2.699E- ^10h3 - 1.116E- ^13h4 + 3.133E- ^17h5 ) added to the formula 1 is the amount of sag given to make an aspheric lens with improved aberration of a spherical lens. The coefficient of the term h in this constant is the condition that minimizes the aberration for h when the radius of curvature of the lens front surface and the radius of curvature of the lens back surface are Rx (0° direction) and Ry (90° direction) shown in Table 1, and is found by optimization calculation using, for example, the least squares method.
Also, h=X ² +Y ^2. That is, the first embodiment is designed so that the aspheric lens cancels the cylindrical power toward the periphery.
g is a variable that is a coefficient for allocating formula A and formula B according to the distance from the lens center. In the first embodiment, g = sqrt(0.01875X ² + 0.0375Y ² ) is used as an example. Formula A has a coefficient (1-g), and formula B has a coefficient g. Since A and B have a linear function relationship with respect to g and the amount of change is linear, the astigmatism power does not decrease suddenly. Therefore, the closer to the center, formula A dominates, and the closer to the periphery, the greater the influence of formula B. In other words, the astigmatism power gradually decreases (decreases) toward the lens periphery. In the first embodiment, the coefficient is set so that (1-g) does not become negative according to the lens diameter and the cancellation degree of the astigmatism power. In addition, the coefficient of Y ² is increased (doubled here as an example) relative to X ² so that the sag on the thick side (vertical direction (90° direction)) in formula A is reduced.

The results of simulating the characteristics of the lens of Example 1 will be described with reference to FIG. 3 and FIGS. 4(a) and (b).
FIG. 3 is a distribution diagram of astigmatism power obtained by simulating the change in power (power) focusing only on the astigmatism power of the lens. The angle in the XY direction indicates the angle of the line of sight with the origin being the center direction of the lens back surface when the lens from the center of the gyrus to the center of the lens back surface is 25 mm. In FIG. 3, the central region is set to -2.00 D set for the lens of this Example 1, and a negative contour line indicates a decrease in power. According to FIG. 3, the central region has the prescribed astigmatism power in both the horizontal and vertical directions, but the astigmatism power decreases gradually and relatively balanced toward the periphery and evenly according to the distance toward the periphery, and the astigmatism power is reduced to around -0.75 D, that is, -1.50 to -1.25 D, in the vicinity of 20 to 30 degrees.
4(a) and (b) are graphs simulating the change in power with the movement of the line of sight when the lens is set to 25 mm from the center of the gyrus to the center of the lens back surface. First, in FIG. 4(a) showing the change in the horizontal direction, which is the astigmatism axis direction, the astigmatism is corrected in the vertical direction indicated by the thick line, and the power is -6.00D near the center (near 0°). Due to the nature of the minus lens, this power of -6.00D tends to increase as the line of sight approaches the lens periphery, but in this embodiment 1, the power of the astigmatism is gradually reduced toward the lens periphery, so the power is offset and the power of -6.00D is maintained. On the other hand, in the horizontal direction indicated by the thin line, the power is -6.00D, but tends to increase toward the lens periphery due to the nature of the lens.
On the other hand, in Fig. 4(b), which shows the change in the vertical direction, which is the direction perpendicular to the axis of astigmatism, the power of astigmatism decreases in the vertical direction indicated by the thick line. This is a result that closely reflects Fig. 3. In the horizontal direction indicated by the thin line, the power of -4.00D is almost maintained.

FIG. 5 is a diagram for confirming the distortion aberration from the degree of distortion of the grid when it is passed through the single focus lens of Example 1, and is a simulation of how a grid appears on a plane perpendicular to the front line of sight at a distance of 4 m from the lens surface. The size of one grid is 60 cm x 60 cm, and the overall size is 600 cm x 600 cm. In this figure, the aspect ratio (horizontal / vertical) when the four central grids (120 cm x 120 cm) are viewed through the lens is 1.056 (the closer the aspect ratio is to 1, the smaller the sense of spatial distortion). On the other hand, the aspect ratio when the entire lens, including the peripheral part, is viewed is 1.042 in Example 1. In other words, the distortion in the peripheral part is smaller. As can be seen from this, it can be seen that the distortion of the peripheral part is improved compared to the center. This improvement is a reflection of the cancellation of the astigmatism power.
When a wearer wears the single focus lens of Example 1, astigmatism is corrected based on the prescription near the central area, and the prescribed astigmatism power is canceled across the entire area toward the periphery, thereby reducing eye fatigue and the feeling of unsteadiness when walking.

Example 2
Example 2 is also an example of a single-focus minus lens. The lens parameters of Example 2 are also as shown in Table 1.
The lens surface of Example 2 is also spherical, and the back surface of the lens is shaped based on the prescription for the S power, C power, astigmatism axis direction, and radius of curvature of the back surface of the lens (in the 0° and 90° directions) with the powers shown in Table 1.
The shape of the lens back surface in the second embodiment is defined by the formula 4. The formula 4 will be described. The formula 4, like the formula 1, is a formula that indicates the total sag amount of the lens in the second embodiment, which is a combination of two formulas for the sag amount, A shown in the formula 2 and B shown in the formula 3. The formulas A and B are the same as those in the first embodiment, so their explanations will be omitted. The constant added to the formula 3 is also the same as the formula 1 in the first embodiment, so their explanations will be omitted. g is a variable that is a coefficient for allocating the formulas A and B according to the distance from the lens center, and is the same as that in the first embodiment, but a coefficient different from that in the first embodiment is adopted in the second embodiment. That is, g=sqrt(0.0125X2 + 0.025Y2).

The results of simulating the characteristics of the lens of Example 2 will be described with reference to FIG. 6 and FIGS. 7(a) and 7(b).
Fig. 6 is a distribution diagram of cylindrical power obtained by simulating the change in power (power) focusing only on the cylindrical power of the lens, as in Example 1. As can be seen from Fig. 6, in Example 2, the area in which the prescribed cylindrical power remains in the central area is wider than in Example 1, but in the periphery, the area in which the cylindrical power is reduced by -0.75 is wider and is designed to decrease more gradually.
7(a) and (b) are graphs simulating the change in power with the movement of the line of sight, similar to Example 1. It can be seen from Fig. 7(b) that the design is such that the power gradually decreases more gently than in Example 1.
FIG. 8 is a simulation of the appearance of a lattice on a plane perpendicular to the line of sight 4 m away from the lens surface, as in Example 1. In Example 2, the aspect ratio (horizontal/vertical) of the four central lattices (120 cm x 120 cm) when viewed through the lens is 1.056. On the other hand, the aspect ratio when the lens is viewed as a whole, including the peripheral part, is 1.046 in Example 2. In other words, the distortion in the peripheral part is small. In the single-focus lens of Example 2, astigmatism correction based on the prescription is performed near the central area when the lens is worn by a wearer, and the prescribed astigmatism power is canceled in the entire area near the periphery, so eye fatigue and unsteadiness when walking are reduced.

Example 3
Example 3 is also an example of a single-focus minus lens. The lens parameters of Example 3 are also as shown in Table 1.
The lens surface of Example 3 is also spherical, and the back surface of the lens is shaped based on the prescription for the S power, C power, astigmatism axis direction, and radius of curvature of the back surface of the lens (in the 0° and 90° directions) with the powers shown in Table 1.
The shape of the lens back surface in the third embodiment is defined by the formula 5. The formula 5 will be explained. The formula 5 is a formula that indicates the total sag amount of the lens in the third embodiment, which is a combination of two formulas for the sag amount, A shown in the formula 2 and B shown in the formula 3. The formulas A and B are the same as those in the first embodiment, so their explanations will be omitted. In addition, the constant added to the formula 3 is the same as the formula 1 in the first embodiment, so their explanations will be omitted. g is a variable that is a coefficient for allocating the formulas A and B according to the distance from the lens center, and is the same as the formula in the first embodiment, but in the third embodiment, a coefficient different from that in the first embodiment and the second embodiment is adopted. That is, g=sqrt(0.0214X2 + 0.0357Y2). In addition, in the third embodiment, the formula format for allocating the value of g to A and B is a quadratic formula of g.

The results of simulating the characteristics of the lens of Example 3 will be described with reference to FIG. 9 and FIGS. 10(a) and 10(b).
Fig. 9 is a distribution diagram of cylindrical power obtained by simulating the change in power (power) focusing only on the cylindrical power of the lens, as in Example 1. According to Fig. 9, in Example 3, the area in which the cylindrical power of the central area is left is wider than in Example 2, and the distribution of the formula g given to the formula A and the formula B for gradually decreasing the power is a quadratic formula, so that the amount of decrease increases rapidly at the periphery.
10A and 10B are graphs simulating the change in power with the movement of the line of sight, similar to Example 1. It can be seen that the cylindrical power decreases rapidly at the periphery, particularly in the vertical power.
FIG. 11 is a simulation of the appearance of a lattice on a plane perpendicular to the line of sight 4 m away from the lens surface, as in Example 1. In Example 3, the aspect ratio (horizontal/vertical) of the four central lattices (120 cm x 120 cm) when viewed through the lens is 1.056. On the other hand, the aspect ratio when the lens is viewed as a whole, including the peripheral part, is 1.054 in Example 2. In other words, the distortion in the peripheral part is small. In the single-focus lens of Example 3, astigmatism correction based on the prescription is performed near the central area when the lens is worn by a wearer, and the prescribed astigmatism power is canceled in the entire area near the periphery, so eye fatigue and unsteadiness when walking are reduced.

<Comparative Example 1>
For comparison with Examples 1 to 3, a single-focus minus lens of Comparative Example 1 is presented, which was simulated under the same conditions as those in Table 1. The single-focus lens of Comparative Example 1 is a spherical lens with astigmatism correction. In the single-focus lens of Comparative Example 1, the shape of the lens back surface is defined only by the formula A in Equation 1.
The simulated lens characteristics of the single focal length lens of Comparative Example 1 will be described with reference to FIG. 12 and FIGS. 13(a) and 13(b).
12 is a cylindrical power distribution diagram of the lens of Comparative Example 1, which is a simulation of the change in power (power) focusing only on the cylindrical power of the lens, as in Examples 1 to 3. Compared to Examples 1 to 3, a uniform cylindrical power of -2.00D in the central region is widely obtained. In the left-right direction of the lens, the cylindrical power tends to gradually decrease from about 20°, but in the up-down direction of the lens, the cylindrical power already increases at a stage of 20° or less, and when viewed in the up-down direction in particular, the cylindrical power is greater than the prescribed level, which is not preferable.
In Figures 13(a) and 13(b), the degree of astigmatism increases in both the horizontal and vertical directions, with the vertical direction indicated by the thick line. Due to the nature of minus lenses, the line of sight increases toward the periphery of the lens, so the increase in the degree of astigmatism is slight in the horizontal direction, but in the vertical direction the degree of astigmatism increases significantly. This design causes eye fatigue and makes the wearer feel unsteady when walking.
14 is a simulation of how a lattice appears on a plane perpendicular to the line of sight 4 m away from the lens surface, as in Example 1. In Comparative Example 1, the aspect ratio (horizontal/vertical) of the four central lattices (120 cm x 120 cm) when viewed through the lens is also 1.056. On the other hand, the aspect ratio when the lens is viewed as a whole, including the periphery, is 1.066 in Comparative Example 1, which is worse. In other words, the lens of Comparative Example 1 has the same degree of distortion near the center as, for example, Examples 1 and 2, but the degree of curvature is greater overall than Examples 1 to 3.

<Comparative Example 2>
For comparison with Example 2, a single-focus minus lens of Comparative Example 2, which was simulated under the same conditions as those in Table 1, is presented. The single-focus lens of Comparative Example 2 is an aspheric lens with astigmatism correction. In the single-focus lens of Comparative Example 2, the shape of the lens back surface is defined by adding the constant (-6.282E- ^7h2 + 2.699E- ^10h3 - 1.116E- ^13h4 + 3.133E- ^17h5 ) of Equation 1 to A of Equation 1.
The simulated lens characteristics of the single focal length lens of Comparative Example 2 will be described with reference to FIG. 15 and FIGS. 16(a) and 16(b).
15 is a cylindrical power distribution diagram of the lens of Comparative Example 2, which is a simulation of the change in power focusing only on the cylindrical power of the lens, as in Examples 1 to 3. Compared with Examples 1 to 3, the uniform cylindrical power of -2.00 D in the central region is greatly expanded in the horizontal direction, and the horizontal aberration is greatly improved compared to Comparative Example 1, but the cylindrical power increases in the vertical direction, unlike Examples 1 to 3.
As shown in Fig. 16(a), the horizontal power is good in Comparative Example 2, but the astigmatism power increases in the vertical direction shown by the thick line in Fig. 16(b). Therefore, the design causes eye fatigue in the vertical direction and makes the wearer feel unsteady when walking.
17 is a simulation of how a lattice appears on a plane perpendicular to the line of sight 4 m away from the lens surface, as in Example 1. In Comparative Example 2, the aspect ratio (horizontal/vertical) of the four central lattices (120 cm x 120 cm) when viewed through the lens is also 1.056. On the other hand, the aspect ratio when the lens is viewed as a whole, including the periphery, is 1.064 in Comparative Example 2, which is worse. In other words, the lens of Comparative Example 1 has the same degree of distortion near the center as, for example, Examples 1 and 2, but the degree of curvature is greater overall than Examples 1 to 3.

Example 4
Example 4 is a single-focus plus lens. The lens parameters of Example 4 are as shown in Table 2.
The lens surface of Example 4 is spherical, and the back surface of the lens is shaped based on the prescription of the S power, C power, astigmatism axis direction, and radius of curvature of the back surface of the lens (0° direction and 90° direction) with the powers shown in Table 2.
The shape of the lens back surface in Example 4 is defined by the formula 6. Formula 6 will be explained. Formula 6 is an equation showing the total sag amount of the lens in Example 4, which is a combination of two sag amount equations, A shown in Formula 2 and B shown in Formula 7. Formula A is the same as in Example 1, so its explanation is omitted. Formula B is an equation that cancels the cylindrical power of the lens periphery by being combined with formula A.
The constant (+1.437E- ^6h2 - 1.370E- ^9h3 + 9.998E- ^13h4 - 3.511E- ^16h5 ) added to the formula 6 is the amount of sag given to make an aspherical lens with improved aberration of a spherical lens. The coefficient of the term h in this constant is the condition for h to be the smallest aberration when the lens surface curvature radius and the lens back surface curvature radius Rx (0° direction) and Ry (90° direction) are shown in Table 2, and is obtained by optimization calculation using, for example, the least squares method. In the fourth embodiment, h = ^Y2 . If h is set as a rotationally symmetric aspheric surface as in the first to third embodiments, it is difficult to obtain a value suitable for the present invention, so the correction is given under the condition of only the Y direction.

The results of simulating the characteristics of the lens of Example 4 will be described with reference to FIG. 18 and FIGS. 19(a) and 19(b).
Fig. 18 is an astigmatism power distribution diagram simulating the change in power (power) focusing only on the astigmatism power of the lens, as in Example 1. As can be seen from Fig. 18, in Example 4, the prescribed astigmatism correction power of +2.00D is provided in the central region of a radius of about 10 to 15 mm, and the astigmatism power decreases gradually and relatively balanced toward the periphery according to the distance, and the astigmatism power is reduced to about -0.75D, that is, about +0.25D, at around 30°. Furthermore, the astigmatism power is gradually reduced outside 30°.
19(a) and (b), in particular, in FIG. 19(b), which shows the change in the vertical direction, which is the direction perpendicular to the axis of astigmatism, the degree of astigmatism decreases in the vertical direction indicated by the thick line. This is a result that closely reflects FIG. 18.
FIG. 20 is a diagram for confirming the distortion aberration from the degree of distortion of the grid when it is passed through the single focus lens of Example 4, and is a simulation of how the grid appears on a plane perpendicular to the front line of sight at a distance of 4 m from the lens surface. The size of one grid is 30 cm x 30 cm, and the overall size is 300 cm x 300 cm. In this figure, the aspect ratio (horizontal / vertical) when the four grids (60 cm x 60 cm) in the center are viewed through the lens is 0.940. On the other hand, the aspect ratio when the entire lens including the peripheral part is viewed is 0.949 in Example 4 (the closer the aspect ratio is to 1, the smaller the sense of distortion of space). In other words, the distortion is smaller in the peripheral part. As can be seen from this, it can be seen that the distortion of the peripheral part is improved compared to the center. This improvement is a reflection of the cancellation of the astigmatism power.
When a wearer wears the single focus lens of Example 4, astigmatism is corrected based on the prescription near the central area, and the prescribed astigmatism power is canceled across the entire area toward the periphery, thereby reducing eye fatigue and the feeling of unsteadiness when walking.

<Comparative Example 3>
For comparison with Example 4, a single-focus plus lens of Comparative Example 3 is presented, which was simulated under the same conditions as those in Table 2. The single-focus lens of Comparative Example 3 is a spherical lens with astigmatism correction. In the single-focus lens of Comparative Example 3, the shape of the lens back surface is defined only by the formula A in Equation 1.
The simulated lens characteristics of the single focal length lens of Comparative Example 3 will be described with reference to FIG. 21 and FIGS. 22(a) and 22(b).
21 is a cylindrical power distribution diagram of the lens of Comparative Example 3, which is a simulation of the change in power focusing only on the cylindrical power of the lens, as in Example 4. Compared to Example 4, a uniform cylindrical power of +2.00D in the central region is widely obtained. Although the cylindrical power tends to gradually decrease from about 20° in the left-right direction of the lens, the cylindrical power in the up-down direction of the lens is already increasing at a stage of 20° or less, and when viewed in the up-down direction in particular, the cylindrical power is more than the prescribed level, which is not preferable.
22(a) and 22(b), the astigmatism increases especially in the vertical direction indicated by the thick line in the vertical power, which results in eye fatigue and unsteadiness when walking.
23 is a simulation of the appearance of a lattice on a plane perpendicular to the line of sight 4 m away from the lens surface, as in Example 4. In Comparative Example 3, the aspect ratio (horizontal/vertical) of the four central lattices (60 cm x 60 cm) when viewed through the lens is also 0.940. On the other hand, the aspect ratio when the lens is viewed as a whole, including the peripheral portion, is 0.923 in Comparative Example 2, which is worse. In other words, in the lens of Comparative Example 1, the degree of distortion near the center is the same as in Examples 1 and 2, for example, but the degree of curvature is greater overall than in Example 4.

<Comparative Example 4>
For comparison with Example 2, a single-focus minus lens of Comparative Example 4, which was simulated under the same conditions as those in Table 2, is presented. The single-focus lens of Comparative Example 4 is an aspheric lens with astigmatism correction. In the single-focus lens of Comparative Example 4, the shape of the lens back surface is defined by adding a constant (4.224E- ^7h2 - 3.612E- ^10h3 + 2.1114E- ^13h4 - 5.828E- ^17h5 ) to A in Equation 1. h = ^X2 + ^Y2 .
The simulated lens characteristics of the single focal length lens of Comparative Example 4 will be described with reference to FIG. 24 and FIGS. 25(a) and 25(b).
24 is a cylindrical power distribution diagram of the lens of Comparative Example 2, which is a simulation of the change in power focusing only on the cylindrical power of the lens, as in Example 4. Compared with Example 4 and Comparative Example 3, the uniform cylindrical power of +2.00D in the central region is greatly expanded in the horizontal direction, and the aberration in the horizontal direction is greatly improved compared to Comparative Example 2, but unlike Example 4, the cylindrical power increases in the vertical direction.
25A, the astigmatism power increases in the vertical direction, as indicated by the thick line, particularly in the vertical power, although not as much as in Comparative Example 3. Therefore, this design causes eye fatigue in the vertical direction and unsteadiness when walking.
26 is a simulation of the appearance of a lattice on a plane perpendicular to the line of sight 4 m away from the lens surface, as in Example 4. In Comparative Example 4, the aspect ratio (horizontal/vertical) of the four central lattices (60 cm x 60 cm) when viewed through the lens is 0.940. On the other hand, the aspect ratio when the lens is viewed as a whole, including the peripheral portion, is 0.921 in Comparative Example 2, which is worse. In other words, in the lens of Comparative Example 1, the degree of distortion near the center is the same as in Examples 1 and 2, for example, but the degree of curvature is greater overall than in Example 4.

The above embodiment is merely described as a specific embodiment for illustrating the principle and concept of the present invention. In other words, the present invention is not limited to the above embodiment. The present invention can be embodied in the following modified forms, for example.
In each of the above embodiments, various conditions such as the S power, the C power, and the cylinder axis direction can be changed arbitrarily.
In the above embodiment, the aspheric lens is designed to be modified to reduce the astigmatism power toward the periphery, but it is also possible to use a spherical lens as a base and reduce the astigmatism power at the periphery.
The specific coefficients (values) calculated for the above aspheric design are just an example. Naturally, these coefficients will change depending on other calculation methods and prescription conditions.
The coefficients (values) in the formula for g may be appropriately changed depending on the simulation results to provide suitable coefficients.
The present invention is not limited to the configurations described in the above-mentioned embodiments. The components of each of the above-mentioned embodiments and modifications may be arbitrarily selected and combined. Any component of each of the embodiments and modifications may be arbitrarily combined with any component described in the Summary for Solving the Problems of the Invention or any component that embodies any component described in the Summary for Solving the Problems of the Invention. We intend to obtain rights to these as well through amendments to this application or divisional applications, etc.
In addition, the applicant intends to obtain rights to the overall design or partial design by filing a conversion application to a design application. The drawings show the entire device in solid lines, but they also include partial designs claimed for a portion of the device as well as the overall design. For example, not only can a portion of the device be a partial design, but a portion of the device can also be included as a partial design regardless of the portion. A portion of the device may be a portion of the device, or a part of that portion.

1... A minus lens that is a single focal length lens, 2... A plus lens that is a single focal length lens.

Claims (7)

In a single-focus lens for spectacles to which astigmatism correction power for correcting astigmatism has been added,
A single focus lens for spectacles, characterized in that a predetermined astigmatism correction power is set in a lens central region including the lens center, and that the predetermined astigmatism correction power is gradually decreased from the lens central region toward the lens periphery so that astigmatism is less corrected , and that when the line of sight is rotated 30° from the center of the lens toward the lens periphery under the condition that the distance from the virtual center of rotation of the wearer's eyeball to the center of the back surface of the lens is 25 mm, the astigmatism power in the effective refractive power on the lens surface through which the line of sight passes is 0.25D to 1.00D less than the astigmatism power in the prescription value for the wearer at the lens center. 2. The single focus lens for spectacles according to claim 1, wherein the predetermined astigmatism correction power is gradually tapered to form an equivalent sphere at the periphery of the lens. 3. The single focus lens for spectacles according to claim 2, wherein the spherical equivalent surface is an average power. 4. The single focus eyeglass lens according to claim 1, wherein the central region of the lens is a region located inside the lens and having a radius of 15 mm from the center. 5. The single focus lens for spectacles according to claim 1 , characterized in that the spherical power is plus . 5. The single focus lens for spectacles according to claim 1 , characterized in that it has a negative spherical power. 5. The single focus lens for spectacles according to claim 1 , characterized in that the spherical power is zero .

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