Design method for lenses for high myopia

Abstract

To provide a novel powerful short-sighted lens capable of reducing deterioration in visual appearance in a wearing state.SOLUTION: A powerful short-sighted lens 1 of -4.5 diopter in average power as prescription power comprises: a first region 12 which is set at the center part of the lens and has short-sightness correction power based upon the prescription power and a second region 14 which is a region set outside the first region 12, and has more plus-side powder than the prescription power by adding a spherical surface component to at least one refractive surface of a pair of front rear refractive surfaces. The powerful short-sighted lens 1 is less in thickness in the second region 14 than a spherical lens 1B which has the same prescription power with the powerful short-sighted lens 1 and has the same base curve and the same lens center thickness, and increases in difference in thickness from the spherical lens 1B radially outward.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to lenses for high myopia and methods for designing lenses for high myopia, and more specifically, to lenses for high myopia and methods for designing lenses for high myopia that are effective in reducing deterioration of appearance when worn. [Background technology]

[0002] One reason why people with high myopia avoid using strong prescription eyeglass lenses is the deterioration of their appearance when wearing them. Specifically, this includes the deformation of the face line as seen by others, total internal reflection around the lens, and the thickness of the lens edges that protrude from the frame. These problems become more pronounced as the lens prescription increases.

[0003] To mitigate the deterioration in appearance associated with the use of such high-presbyopia lenses, methods include using eyeglass frames with smaller lens frames, using lenses with a curved shape, and reducing the vertex distance when worn. However, when using eyeglass frames with small lens frames, the types of frames that can be selected are limited. Lenses with a curved shape have an unnatural appearance. Reducing the vertex distance can lead to new problems, such as a decrease in comfort and the inability to obtain the prescribed power.

[0004] Furthermore, as described in the patent document below, there are lenses in which an aspherical component is added to at least one of the refractive surfaces to suppress the thickness of the lens periphery. However, since this attempts to reduce the thickness while ensuring optical properties in the lens periphery, it has little effect in suppressing deterioration of appearance when worn. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-5966 [Overview of the project] [Problems that the invention aims to solve]

[0006] The present invention aims to solve these problems and provide a novel lens for high myopia that can reduce deterioration of appearance when worn. [Means for solving the problem]

[0007] The lens for high myopia of the present invention is a lens for high myopia in which the average prescription power is -4.5 diopters or less. A first region is set in the center of the lens and has myopia correcting power based on the prescribed power, A second region set outside the first region, wherein an aspherical component is added to at least one of the pair of refractive surfaces, and the power is set to be on the positive side of the prescription power, Equipped with, When compared to a spherical lens having the same prescription power, base curve, and center thickness as the aforementioned high myopia lens, the thickness in the second region is thinner than that of the spherical lens, and the difference in thickness from the spherical lens increases as it moves radially outward.

[0008] This invention relates to a lens for severe myopia in which the average prescription power is -4.5 diopters or less. Here, the average prescription power can be determined by S power + (C power ÷ 2) based on the spherical power (S power) and astigmatism power (C power) as prescribed powers. The aforementioned problem of deterioration in appearance when wearing such high-strength myopia lenses is caused by a rapid increase in lens thickness at the periphery due to the strong negative power. The high-strength myopia lens of the present invention ensures optical properties based on the prescription power in the central part of the lens (first region) while adding an aspherical component to the periphery of the lens (second region), thereby changing the power to the positive side of the prescription power and suppressing the thickness of the periphery of the lens, thus reducing deterioration in appearance when worn.

[0009] Here, the first region can include an area with dimensions of 6.72 mm to the left and right, 3.53 mm upward, and 5.33 mm downward from the optical center, and can be located inside a virtual circle with a radius of 25 mm from the optical center. The area defined here, extending 6.72 mm to the left and right, 3.53 mm upward, and 5.33 mm downward from the optical center, corresponds to the effective field of view of a lens with a vertex distance of 12 mm. By setting the first region to include this area, an object viewed directly through the lens can be clearly and instantly seen. However, if the first region is set too large, the second region, which is used to reduce the thickness of the lens periphery, becomes relatively narrower. Therefore, it is preferable that the outer edge of the first region be inside a virtual circle with a radius of 25 mm from the optical center. More preferably, it is inside a virtual circle with a radius of 10 mm.

[0010] Furthermore, in this invention, the thickness at the starting point of the addition of the aspherical component is t0, the thickness at any point radially outward from the starting point is t1, and the thickness t at the point corresponding to the arbitrary point in the spherical lens is t S In this case, the value of the thickness reduction coefficient Q calculated based on the following formula (1) at any point within the second region can be set to 0.6 or less. t1 = t0 + (t S -t0)×Q ...Formula (1)

[0011] In this invention, in the second region, the reduction of thickness is prioritized over optical properties. For example, the average frequency at a point in the second region located 5 mm radially outward from the boundary between the first and second regions can be set to be at least 1.0 diopter positive than the average frequency at the optical center, and the astigmatism at that point can be set to be at least 1.0 diopter positive than the astigmatism at the optical center.

[0012] The lens design method for high myopia of the present invention is a lens design method for high myopia in which the average refractive power as a prescription refractive power is -4.5 diopters or less, (a) a step of partitioning the lens into a first region that is set in the central portion of the lens and is given a myopia correction power based on the prescription refractive power, and a second region that is an outer region than the first region and to which an aspherical component for reducing deterioration of appearance is added; (b) When the thickness at the addition start point of the aspherical component is t0, the target thickness at an arbitrary point radially outside the addition start point is t2, and the thickness t S at the point corresponding to the arbitrary point in the spherical lens determined based on the prescription refractive power, and when the thickness reduction coefficient is Q, a step of calculating the target thickness t2 at an arbitrary point in the second region based on the following formula (2); t2 = t0 + (t S - t0) × Q … Formula (2) (c) obtaining an aspherical component corresponding to the difference between the target thickness t2 at an arbitrary point in the second region and the thickness t S at the corresponding point of the spherical lens, and adding the aspherical component to the coordinate values of the refractive surface determined based on the prescription refractive power; and is characterized by comprising the above. According to the lens design method for high myopia defined in this way, it is possible to suitably design the above-described lens for high myopia that can reduce deterioration of appearance in the wearing state.

Brief Description of Drawings

[0013] [Figure 1] (A) is a front view of a spherical lens for high myopia, and (B) is a cross-sectional view including the optical axis of the same lens. [Figure 2] (A) is a front view of a lens for high myopia according to an embodiment of the present invention, and (B) is a cross-sectional view including the optical axis of the same lens. [Figure 3] It is an explanatory diagram of the first region of the lens for high myopia in FIG. 2. [Figure 4] It is a view showing an enlarged upper half of the lens cross-section in FIG. 2(B). [Figure 5] It is an explanatory diagram of a method for designing a lens for high myopia in the same embodiment. [Figure 6] (A) is an average diopter contour map of the example lens, and (B) is an aberration contour map of the example lens. [Figure 7] (A) is a front view of the state in which a spherical lens of the comparative example is mounted, and (B) is a front view of the state in which the example lens is mounted.

Mode for Carrying Out the Invention

[0014] Hereinafter, embodiments of the present invention will be described based on the drawings. In the following description, the front-back, left-right, and up-down directions for a wearer wearing glasses using lenses are defined as the front-back, left-right, and up-down directions in the respective lenses.

[0015] First, a spherical lens for high myopia (reference example) will be described. The lens 1B in FIG. 1 is a spherical lens for high myopia with a spherical diopter of -4.5 diopters or less. The rear surface 2 is a concave surface defined by the following formula (3), and the front surface 3 is a convex surface defined by the following formula (4). The axis in the front-back direction passing through the optical center O of the lens 1B (base point O1 on the rear surface 2 and base point O2 on the front surface 3) is defined as the z-axis, and the direction toward the rear of the lens 1B is defined as the positive direction of the z-axis. The z-axis coincides with the optical axis of the lens 1B.

[0016] z = r 2 / (R1 + (R1 2 [[ID=3]]-Kr 2 ) 1 / 2 ) … Equation (3) z = r 2 / (R2 + (R2 2 -Kr 2 ) 1 / 2 ) … Equation (4)

[0017] In Equations (3) and (4), r is the distance from the z-axis. That is, when considering a rectangular coordinate system with the x-axis and y-axis being the axes in the left-right and up-down directions orthogonal to the z-axis centered on the base point O1 on the rear surface 2 and the base point O2 on the front surface 3, r = (x 2+y 2 ) 1 / 2 R1 and R2 are the radii of curvature at the vertices of the surface, and the coefficient K is 1. The radii of curvature R1 and R2 are determined by the prescription power (specifically, the S power, C power, and astigmatism axis AX). Lens 1B is a lens for high myopia for myopic people, therefore R1 <R2である。 With lens 1B, the larger the absolute value of the spherical power (S power), the more apparent problems become with the deterioration of appearance, such as deformation of the face line as seen by others, total internal reflection at the periphery of the lens, and the thickness of the lens edge that protrudes from the frame.

[0018] In the above explanation, a lens in which both the front surface 3 and the rear surface 2 are spherical was defined as a spherical lens. However, in order to achieve the prescribed power, a toric surface for astigmatism correction may be used on one of the surfaces. In the following explanation, in addition to the case where both the front surface 3 and the rear surface 2 are formed as spherical surfaces, lenses in which one surface is spherical and the other surface is toric will also be referred to as spherical lenses.

[0019] Figure 2 shows a lens 1 according to one embodiment of the present invention. This lens 1 has an aspherical component added to the peripheral part of the lens, excluding the central part of the spherical lens 1B. This ensures optical properties based on the prescription power in the central part of the lens while significantly reducing the thickness in the peripheral part of the lens, thereby resolving the problem of poor appearance in lenses for high myopia.

[0020] As shown in Figure 2(A), lens 1 has a first region 12 formed in the center of the lens, and a second region 14 formed outside the first region 12.

[0021] The first region 12 is a region that has myopia correcting power based on the prescription power, and the wearer can clearly see objects through the first region 12. The refractive surface shape of the front surface 3 of the first region 12 is defined by the above formula (4), and the refractive surface shape of the rear surface 2 is defined by the above formula (3).

[0022] Generally speaking, the central visual field, which offers superior visual acuity and color discrimination and allows for highly accurate information reception, is considered to be within 5 degrees of the human field of vision. This area is called the discriminative field of vision. Furthermore, the area in which information can be instantaneously received solely through eye movements is considered to be approximately 30 degrees horizontally (±15 degrees to the left and right) and approximately 20 degrees vertically (8 degrees upward and 12 degrees downward). This area is called the effective field of vision. Assuming a vertex-to-vertex distance of 12 mm, the lens region corresponding to the effective field of view is, as shown in Figure 3, an area measuring 6.72 mm to the left and right, 3.53 mm upward, and 5.33 mm downward from the optical center. In this example, the first region 12 is set to include this lens region corresponding to the effective field of view. However, if the first region 12 is excessively large, the second region 14 will become relatively narrower. Therefore, the outer edge of the first region 12 is set to be inside a virtual circle with a radius of 25 mm from the optical center O. More preferably, it is inside a virtual circle with a radius of 10 mm.

[0023] The second region 14 is a region set outside the first region 12. In this example, an aspherical component is added to the posterior surface 2b of the lens belonging to the second region 14, and the power in the second region 14 is set to a positive power compared to the prescription power.

[0024] In Figure 2(B), the dashed line shows the lens shape of a spherical lens 1B having the same prescription power, base curve, and center thickness as lens 1 for high myopia. As shown in the figure, the thickness of lens 1 in the second region 14 is thinner than that of spherical lens 1B shown by the dashed line, and the difference in thickness between lens 1 and spherical lens 1B increases towards the radially outward direction.

[0025] Figure 4 is a magnified view of the upper half of the lens cross-section shown in Figure 2(B). In the figure, P is the distance from the optical center at the starting point of the addition of the aspherical component (the boundary between the first region 12 and the second region 14), and t0 is the thickness at the starting point. r is the distance from the optical center at any point radially outside the starting point, t1 is the thickness at that point, and t is the thickness at the point corresponding to that point in the spherical lens 1B. SThis is the case. In this lens 1, these thicknesses t1, t0, t S When the relationship is shown by equation (1) above, the value of the thickness reduction coefficient Q in equation (1) is set to 0.6 or less. The smaller the value of this thickness reduction coefficient Q, the thinner the lens becomes at the periphery, and the effect of reducing deterioration of appearance when worn can be enhanced. A preferred value of the thickness reduction coefficient Q is 0.4 or less, more preferably 0.3 or less.

[0026] Next, we will explain the design method for lens 1. First, the refractive surfaces of the front surface 3 (see equation (4)) and the rear surface 2 (see equation (3)) of the spherical lens 1B are determined based on the prescription power. Since this determination method is well-known, it will not be described in detail here. Next, as shown in Figure 2, the lens is divided into a first region 12 which is a circle with radius P from the optical center O, and a second region 14 which is located radially outward from the first region 12 and extends to the edge of the lens. In this example, this determines the shape of the first region 12 which has myopia correcting power based on the prescription.

[0027] Next, the step of calculating the target thickness t2 along the radial direction within the second region 14 is performed. Specifically, as shown in Figure 5, t0 is the thickness at the starting point of the addition of the aspherical component (the boundary between the first region 12 and the second region 14), t2 is the target thickness at any point radially outside the addition starting point, and t0 is the thickness at the point corresponding to the arbitrary point in the spherical lens determined based on the prescription power. S When the thickness reduction coefficient is Q, the target thickness t2 at any point along the radial direction within the second region 14 is calculated based on the following equation (2). t2 = t0 + (t S -t0)×Q …Formula (2) The thickness reduction coefficient Q can be appropriately determined within the range of 0 to 1, and the smaller the value of the thickness reduction coefficient Q, the thinner the lens ends can be. For example, it is preferable to set the value of the thickness reduction coefficient Q to 0.4 or less.

[0028] Then, the target thickness t2 at any point in the second region 14 and the thickness t at the point corresponding to the aforementioned point on the spherical lens 1B, which is determined based on the prescription power. S The aspherical component δ, which corresponds to the difference, is calculated, and the aspherical component δ is added to the coordinate values ​​of the refractive surface S0 of the rear surface 2 of the spherical lens 1B, which was determined based on the prescription power. The aspherical component δ can be expressed, for example, using the following equation (5). The target thickness t at the refractive surface of the rear surface 2. S The optimal aspheric coefficients B, C, D, and E for obtaining a thickness (or an approximate thickness) can be determined by ray tracing simulations. δ = B(rP) 4 +C(rP) 6 +D(rP) 8 +E(rP) 10 …Equation (5) Here, r is the distance from the z-axis, P is the distance from the z-axis to the starting point of the addition of the aspherical component, and B, C, D, and E are constants (aspherical coefficients).

[0029] By adding the aspherical component δ obtained in this way to the coordinate values ​​of the refractive surface S0 of the posterior surface 2 of the spherical lens 1B, which is determined based on the prescription power, the shape of the second region 14 can be identified, and a lens 1 for high myopia with a high effect in reducing deterioration of appearance can be designed.

[0030] [Examples] Based on the lens data below, lenses for high myopia were fabricated, and their average power distribution, astigmatism distribution, and appearance were evaluated. The lens data is as follows: Refractive index n 1.738 Front curve K 0.69 Spherical power S -8.50D (diopter) Astigmatism power C -2.00D Astigmatism axis direction Ax 175° Outer diameter Φ75mm Center thickness CT 1.1mm Radius P of the first region: 6 mm Design thickness reduction factor Q 0.4 Aspherical coefficient BCDE Rear -1.98E-05 4.423E-08 -4.223E-11 1.449E-14 Furthermore, in the aspherical coefficients B, C, D, and E, E and the number to the right of E represent a power with base 10 and the number to the right of E as the exponent.

[0031] Figure 6(A) is an average power contour plot for the example lens, showing the average power, which is the average of the refractive power in the radial direction (meridional direction) and the refractive power in the circumferential direction (sagittal direction), as a contour plot with a step width of 1.0D. The dotted lines in the figure indicate a grid with a pitch of 5 mm. According to Figure 6(A), in this example lens, the average power within the first region (within 6 mm from the optical center O) is in the range of -10.0D to -9.0D. The average power changes positively as it moves radially outward, and the average power at point r1 (11 mm from the optical center O), which is 5 mm radially outward from the boundary between the first and second regions (6 mm from the optical center O), is in the range of -8.0D to -7.0D. In other words, the average frequency at a point 5 mm radially outward from the boundary between the first region 12 and the second region 14 is more than 1.0 diopter positive than the average frequency at the optical center O.

[0032] Figure 6(B) is an astigmatism contour plot for the example lens, showing astigmatism, which is the difference between the refractive power in the radial direction (meridional direction) and the refractive power in the circumferential direction (sagittal direction), as a contour plot with a step width of 1.0D. The dotted lines in the figure represent a grid with a pitch of 5 mm. According to Figure 6(B), in this example lens, the astigmatism in the first region including the optical center O is in the range of 1.1D to 2.1D. Furthermore, the astigmatism at point r1 (11 mm from the optical center O), which is 5 mm radially outward from the boundary between the first and second regions, is in the range of approximately 4.1D to 5.1D, although it differs in the circumferential direction. In other words, the astigmatism at the point 5 mm radially outward from the boundary between the first region 12 and the second region 14 is more than 1.0 diopter positive than the astigmatism at the optical center O. In this embodiment, the lens ensures optical properties based on the prescription power in the central part of the lens (first region 12), while tolerating a deterioration in optical properties in the peripheral part of the lens (second region 14). This is because, in the peripheral part of the lens, thickness reduction is prioritized over optical properties.

[0033] Table 1 below shows the radial thickness of the example lens, along with the thickness of a spherical lens (a spherical lens with the same prescription, base curve, and center thickness) as a comparative example. According to Table 1, the example lens is thinner at the periphery than the comparative spherical lens, and the difference in thickness from the spherical lens increases as you move radially outward.

[0034] [Table 1]

[0035] Next, Figure 7(A) is a front view of the comparative example with the spherical lens worn, and Figure 7(B) is a front view of the example lens worn. Note that in Figures 7(A) and (B), the lens is fitted into the frame only on the left eye side. In both Figures 7(A) and (B), deformation of the face line is observed on the left eye side. However, in the example lens in which the increase in thickness at the periphery of the lens is significantly reduced, as shown in Table 1 above, when compared with a spherical lens (see Figure 7(A)) having the same prescription, the same base curve, and the same lens center thickness, the deformation of the face line as seen by others is significantly improved, as shown in Figure 7(B). This is because the prism effect that causes deformation of the face line is well suppressed in the example lens.

[0036] As described above, the high myopia lens of this embodiment ensures optical properties based on the prescription power in the central part of the lens (first region 12) while adding an aspherical component to the peripheral part of the lens (second region 14). This changes the average power to a more positive side than the prescription power, and reduces the thickness of the peripheral part of the lens. With the high myopia lens of this embodiment, deterioration of appearance when worn can be reduced.

[0037] The embodiments of the present invention have been described in detail above, but these are merely examples. For example, in the above embodiment, an aspherical component is added to the refractive surface on the rear side of the lens to suppress the increase in lens thickness at the periphery of the lens. However, the aspherical component can also be added to the front side of the lens, or to both the front and rear sides. Furthermore, in the above embodiment, the aspherical component is defined using aspherical coefficients of the fourth, sixth, eighth, and tenth order, but in some cases, it is also possible to define the aspherical component using aspherical coefficients of a different order. Furthermore, although the first region is defined as circular in the above embodiment, it is also possible to define the first region as non-circular. Furthermore, although the above embodiment provides the second region around the entire circumference, it is also possible to provide it only in a specific region (for example, the region on the ear side) in some cases. In short, the present invention can be implemented in various modified forms without departing from its spirit. [Explanation of symbols]

[0038] 1. Lens (for high myopia) 1B Spherical Lens 2 Rear 3 Front 12 First area 14 Second area δ Aspherical component

Claims

[Claim 1] A lens for severe myopia with an average prescription power of -4.5 diopters or less, A region set in the center of the lens, in which a pair of front and rear refractive surfaces are composed of the refractive surfaces of a spherical lens based on the prescribed power, and a first region having myopia correcting power, A second region set outside the first region, wherein an aspherical component is added to at least one of the pair of refractive surfaces, and the power is set to be on the positive side of the prescription power, Equipped with, In a comparison between the aforementioned high-strength myopia lens and a spherical lens having the same prescription power, the same base curve, and the same lens center thickness, the thickness at the boundary between the first region and the second region, which is the starting point for the addition of the aspheric component, is t 0 , the thickness at any point radially outward from the starting point of addition is t 1 The thickness of the point corresponding to any point in the spherical lens is t S In this case, the value of the thickness reduction coefficient Q calculated based on the following formula (1) at any point within the second region is set to 0.6 or less. t 1 = t 0 + (t S - t 0 )×Q...Equation (1) The thickness in the second region is thinner than that of the spherical lens, and the difference in thickness from the spherical lens increases as it extends radially outward. A method for designing a lens for high myopia, wherein the first region includes an area measuring 6.72 mm to the left and right, 3.53 mm upward, and 5.33 mm downward from the optical center, and the outer edge of the first region is inside a virtual circle with a radius of 10 mm from the optical center. (a) A step of dividing the lens into a first region set in the center of the lens and to which myopia correcting power based on the prescription is applied, and a second region which is outside the first region and to which an aspherical component is added to reduce deterioration of appearance, (b) The thickness at the starting point of the addition of the aspherical component is t 0 , the target thickness at any point radially outward from the starting point of the addition is t 2 , the thickness of the point corresponding to any point in the spherical lens determined based on the prescription power is t S When the thickness reduction coefficient is Q, the target thickness t at any point within the second region is 2 The steps are to calculate based on the following formula (2), t 2 =t 0 + (t) S -t 0 )×Q …Formula (2) (c) The target thickness t at any point in the second region 2 And the thickness t of the spherical lens corresponding to this. S The steps include: determining the aspherical component corresponding to the difference between the two values, and adding the aspherical component to the coordinate values ​​of the refractive surface determined based on the prescription power; A method for designing lenses for severe myopia, characterized by having the following features.

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