METHOD FOR DESIGNING VISION CORRECTION LENS, AND VISION CORRECTION LENS |
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申请号 | EP16922435.9 | 申请日 | 2016-11-25 | 公开(公告)号 | EP3467573A1 | 公开(公告)日 | 2019-04-10 |
申请人 | Itoh Optical Industrial Co., Ltd.; | 发明人 | MIYAJIMA, Yasushi; | ||||
摘要 | A corrective lens that can improve contrast sensitivity in a dark place, for example, at night is provided. When an axis in the anteroposterior direction passing through the geometric center of a lens is defined as the z-axis and a direction extending to the rear side of the lens is defined as the positive direction of the z-axis, a focal depth extension component represented by Ar 3 (where r is the distance from the z-axis and A is a constant) is added to the z-coordinate value of a refractive surface determined based on a prescription power to increase the focal depth. The focal depth that decreases (shallows) in a dark place is increased to facilitate focusing on a target object located in front of or behind the original focal point. This can improve contrast sensitivity in a dark place. | ||||||
权利要求 | |||||||
说明书全文 | The present invention relates to a corrective lens such as an eyeglass lens or contact lens and a design method for the corrective lens and, more particularly, to a corrective lens having a focal depth extension effect and a design method for the corrective lens. Patent Literature 1 cited below discloses an optical plate that can increase the optical depth, which is the optical plate of the second optical system disposed in front of the first optical system serving as an imaging optical system for incident light waves. It is described that this optical plate increases in thickness almost in proportion to a third-order power function of the distance from a base point in the optical plate. Patent Literature 1: Meanwhile, in a dark place with low illuminance, for example, in the evening or at night, a person whose accommodation ability of the eye has deteriorated due to aging or fatigue experiences difficulty in perceiving contrast, and experiences difficulty in seeing even with eyeglasses or contact lenses. The present invention solves the above problem and has its object to provide a design method for a corrective lens that can improve contrast sensitivity in a dark place and a corrective lens. A design method for a corrective lens according to the present invention is characterized in that when an axis in an anteroposterior direction passing through the geometric center of a lens is defined as the z-axis and a direction extending to the rear side of the lens is defined as the positive direction of the z-axis, a focal depth extension component represented by Ar3 (where r is the distance from the z-axis and A is a constant) is added to the z-coordinate value of a refractive surface determined based on a prescription power to increase the focal depth. A corrective lens prepared by this preparation method increases in focal depth, which decreases (shallows) in a dark place, to facilitate focusing on a target object located in front of or behind the original focal point. This makes it possible to improve the contrast sensitivity in a dark place. In this case, when the refractive surface is the rear surface of the lens and the constant A is a positive number or the refractive surface is the front surface of the lens and the constant A is a negative number, an edge thickness reduction component for a reduction in edge thickness of the lens is preferably added to the z-coordinate value. This is because adding the edge thickness reduction component will reduce the edge thickness that is increased by the addition of a focal depth extension component. The edge thickness reduction component is preferably represented by Dr10 (where D is a negative constant when constant A is positive, and is a positive constant when constant A is negative). This is because such setting increases the influence on the edge portion of the lens and can reduce the edge thickness. The constant A is preferably set such that the absolute value of the constant A falls within a range of 1.73 × 10-6 to 1.96 × 10-5. This is because when the absolute value of constant A for an eyeglass lens having a normal size falls within such a range, an appropriate focal depth extension effect can be obtained, and the occurrence of astigmatism can be suppressed. The constant A and the constant D are preferably set such that the absolute value of the constant A falls within a range of 1.73 × 10-6 to 1.96 × 10-5, the absolute value of the constant D falls within a range of 1.65 × 10-17 to 1.88 × 10-16, and the absolute value of the constant D increases with an increase in the absolute value of the constant A. This is because setting constant A and constant D for an eyeglass lens having a normal size in this manner can provide an appropriate focal depth extension effect and suppress the occurrence of astigmatism. In addition, this can make the edge thickness equal to that of the lens before the addition of a focal depth extension component. A corrective lens according to the present invention is characterized in that when an axis in an anteroposterior direction passing through the geometric center of a lens is defined as the z-axis and a direction extending to the rear side of the lens is defined as the positive direction of the z-axis, a focal depth extension component represented by Ar3 (where r is the distance from the z-axis and A is a constant) is added to the z-coordinate value of a refractive surface determined based on a prescription power to increase the focal depth. This lens increases in focal depth, which decreases (shallows) in a dark place, to facilitate focusing on a target object located in front of or behind the original focal point. This makes it possible to improve the contrast sensitivity in a dark place. In this case, when the refractive surface is the rear surface of the lens and the constant A is a positive number or the refractive surface is the front surface of the lens and the constant A is a negative number, an edge thickness reduction component for a reduction in edge thickness of the lens is preferably added to the z-coordinate value. This is because adding the edge thickness reduction component will reduce the edge thickness that is increased by the addition of a focal depth extension component. The edge thickness reduction component is preferably represented by Dr10 (where D is a negative constant when constant A is positive, and is a positive constant when constant A is negative). This is because such setting increases the influence on the edge portion of the lens and can reduce the edge thickness. The absolute value of the constant A preferably falls within a range of 1.73 × 10-6 to 1.96 × 10-5. This is because when the absolute value of constant A for an eyeglass lens having a normal size falls within such a range, an appropriate focal depth extension effect can be obtained, and the occurrence of astigmatism can be suppressed.
The embodiments of the present invention will be described below with reference to the accompanying drawings. Note that, in the following description, the back and forth, right and left, and up and down of a person wearing eyeglasses using lenses respectively coincide with the back and forth, right and left, and up and down of each lens. <First Embodiment> As shown in As indicated by equation (i), for the rear surface 2, a third-order term Ar3 of r is added to the z-coordinate value of a refractive surface defined by equation (iii) given below based on a prescription power. Constant A is selected from a range of 1.73 × 10-6 to 1.96 × 10-5 for the following reason. When constant A for an eyeglass lens having a normal size (diameter: 50 mm to 80 mm) falls within this range, an appropriate focal depth extension effect can be obtained, and the occurrence of astigmatism can be suppressed. That is, with an increase in constant A, the focal depth extension effect increases, and the occurrence of astigmatism increases. The above range is determined in consideration of the balance between them. In this embodiment, A = 7.68 × 10-6 is provided. As indicated by (b) in A design method for the lens 1 will be described next. First, the refractive surface of the front surface 3 and the refractive surface of the rear surface 2 of the lens 1 are determined based on a prescription power. This determination method is well known, and hence a detailed description of the method will be omitted. A focal depth extension component represented by Ar3 (where r is the distance from the z-axis and A is a constant) is then added to the z-coordinate value of the determined refractive surface of the front surface 3 or the rear surface 2. In this embodiment, the refractive surface of the front surface 3 and the refractive surface of the rear surface 2 of the lens 1 were respectively determined, based on a prescription power, as spherical surfaces represented by equations (ii) and (iii) given above, and the focal depth extension component Ar3 (where A = 7.68 × 10-6) was added to the z-coordinate value of the refractive surface of the rear surface 2. A focal depth extension effect will be described next. In In The focal depth extension effect is high in a dark place with low illuminance, for example, at night. This phenomenon will be described below with reference to In In In Comparisons between Next, description will be given of the results obtained by preparing, for seven subjects, ordinary single-focus lenses, each having a front surface determined by equation (ii) given above and a rear surface determined by equation (iii) given above in accordance with a corresponding prescription power, and focal depth extension lenses, each having the focal depth extension component Ar3 (where A = 7.68 × 10-6) added to a corresponding rear surface, i.e., the lenses 1, and measuring contrast sensitivities upon letting the subjects wear the prepared lenses. Table 3 shows the ages of the respective subjects, the prescription powers, and the powers of the prepared lenses. Note that the prepared lenses are prototypes, and hence there are slight differences between the powers of the lenses and the prescription powers. R and L in Table 3 respectively represent a right eye and a left eye, and each lens has a refractive index of 1.60. The contrast sensitivities were measured by using vision contrast tester 6500 available from Vitech Corporation. Table 4 shows the measurement results. Vison contrast tester 6500 available from Vitech Corporation is designed to measure a contrast sensitivity depending on up to which index of a plurality of indices, arranged for each of indices A to E, it can identify. Table 4 shows up to which index each subject was able to identify for each of indices A to E. Note that in Table 4, lens A indicates an ordinary single-focus lens, and lens B indicates the lens 1. In addition, for each subject, measurements were conducted on the right eye, the left eye, and both eyes in bright and dark places. Table 4 includes illuminances in the respective measurement places. The distance from each subject to each index is 3.00 m. Contrast sensitivities are converted according to a predetermined conversion table such that, for example, measurement result "6" on index B is converted into contrast sensitivity "85," and measurement result "7" is converted into contrast sensitivity "170." The ratios of the contrast sensitivities obtained with the lenses 1 to the contrast sensitivities obtained with the ordinary single-focus lenses concerning the right eye, the left eye, and both eyes of each subject in each of the bright and dark places, i.e., (contrast sensitivities with lenses 1)/(contrast sensitivities with ordinary single-focus lenses), are obtained for each of indices A to E, based on the contrast sensitivities obtained from the measurement results in Table 4. Table 5 shows the averages of the obtained ratios throughout the respective indices. Table 5 indicates that when, for example, subject A sees with both eyes in a bright place, the contrast sensitivity obtained with the lenses 1 is 100% with respect to the contrast sensitivity obtained with the ordinary single-focus lenses. That is, the contrast sensitivity remains the same with the use of either the lenses 1 or the ordinary single-focus lenses. In contrast, when subject A sees with both eyes in a dark place, the contrast sensitivity obtained with the lenses 1 is 220% with respect to the contrast sensitivity obtained with the ordinary single-focus lenses. That is, the contrast sensitivity obtained with the use of the lenses 1 is increased more than twice that obtained with the use of the ordinary single-focus lenses. As described above, in the dark place (illuminance: 50 Ix or less), increases in contrast sensitivity were observed in 12 eyes out of 16 eyes. That is, it is understood that the lens 1 improves the contrast sensitivity in a dark place where a decrease in contrast is observed, for example, in the evening or at night, and exhibits a high contrast sensitivity improving effect in a dark place especially for middle-aged and elderly persons whose contrast sensitivities rapidly deteriorate. Moreover, selecting constant A from a range of 1.73 × 10-6 to 1.96 × 10-5 makes it possible to obtain an appropriate focal depth extension effect and suppress the occurrence of astigmatism. That is, this increases the focal depth while suppressing peripheral distortion, and hence assists the accommodation of the eyes, thereby allowing the eyes to experience a comfortable feeling and hardly experience fatigue. <Second Embodiment> The second embodiment will be described next. The same reference numerals denote constituent elements common to those of the first embodiment, and a description of them will be omitted as appropriate. A lens according to the second embodiment is also an eyeglass lens. Like the lens 1, a front surface 3 is a convex surface defined by equation (ii) given above, but a rear surface 2 is obtained by adding an edge thickness reduction component Dr10 (where D is a negative constant) for reducing the edge thickness of the lens to the z-coordinate value of the rear surface 2. That is, the rear surface 2 of the lens according to the second embodiment is a concave surface defined by equation (iv) given below. As described in the first embodiment, constant A is preferably selected from a range of 1.73 × 10-6 to 1.96 × 10-5. When constant A is selected from this range, constant D is preferably selected from a range of -1.88 × 10-16 to -1.65 × 10-17, and is also preferably selected such that the absolute value of constant D increases with an increase in constant A. This is because selecting constant D in this manner will make the edge thickness of the lens equal to that of an ordinary single-focus lens. Note that the range of constant D was calculated according to D = Δ/a10 (where a = 37.5 mm and the unit of Δ: mm) by calculating, as an increase Δ, an increase in edge thickness of the lens 1 according to the first embodiment relative to the ordinary single-focus lens (an increase in edge thickness when the lens 1 is a 75 mm diameter lens which is often used as an eyeglass lens) when constant A falls within the above range. Table 6 shows the edge thicknesses of the lenses 1 according to the first embodiment, the lenses according to the second embodiment, and ordinary single-focus lenses (each having a lens diameter of 75 mm) calculated while the S power is changed when A = 1.73 × 10-6 and D = -1.65 × 10-17, and Table 7 shows those when A = 1.96 × 10-5 and D = -1.88 × 10-16. As is understood from Tables 6 and 7, adding the edge thickness reduction component Dr10 makes the edge thickness of the lens according to the second embodiment equal to that of the ordinary single-focus lens. Like the lens 1, the lens according to the second embodiment improves the contrast sensitivity in a dark place, especially the contrast sensitivity of middle-aged and elderly persons in a dark place, and can make the edge thickness of the lens equal to that of an ordinary lens. <Third Embodiment> The first and second embodiments are each a single-focus lens (distance lens) for a myopic person. The third embodiment is a single-focus lens (near lens) for a hyperopic person. The third embodiment will be described below. The same reference numerals denote constituent elements common to those of the first embodiment, and a description of them will be omitted as appropriate. The lens according to the third embodiment also has a rear surface 2 defined by equation (i) given above and a front surface 3 defined by equation (ii) given above, and a focal depth extension component Ar3 is added to the concave surface (rear surface 2) of the lens, with constant A being a negative number and selected from a range of -1.96 × 10-5 to -1.73 × 10-6. This is because when constant A for an eyeglass lens having a normal size falls within this range, an appropriate focal depth extension effect can be obtained, and the occurrence of astigmatism can be suppressed. In addition, R1 > R2. Table 8 shows an example of lenses according to the third embodiment which respectively have S powers of +1.00D, +2.00D, and +3.00D. Constant A was set to - 7.68 × 10-6. As in the third embodiment, setting constant A to a negative number will extend the focal depth to a position in front of a focal point before focal depth extension. Because the edge thickness of the lens becomes smaller than that before focal depth extension, there is no need to add an edge thickness reduction component. The lens according to the third embodiment is configured such that the height from the original spherical surface S decreases in proportion to a third-order power function of a distance r from a base point O1. Accordingly, the focal point is shifted forward toward the edge of the lens. This increases the extension depth and improves the contrast sensitivity in a dark place. In addition, there is no need to add any edge thickness reduction component. <Fourth Embodiment> The fourth embodiment is a single-focus lens (near lens) for a hyperopic person, and differs from the third embodiment in that constant A is a positive number. The fourth embodiment will be described below. The same reference numerals denote constituent elements common to those of the first embodiment, and a description of them will be omitted as appropriate. The lens according to the fourth embodiment also has a rear surface 2 defined by equation (i) given above and a front surface 3 defined by equation (ii) given above, and a focal depth extension component Ar3 is added to the concave surface (rear surface 2) of the lens, with constant A being a positive number and selected from a range of 1.73 × 10-6 to 1.69 × 10-5. This is because when constant A for an eyeglass lens having a normal size falls within this range, an appropriate focal depth extension effect can be obtained, and the occurrence of astigmatism can be suppressed. In addition, R1 > R2. When constant A is set to a positive number, the focal depth is increased to the rear side of a focal point before focal depth extension. Table 9 shows an example of lenses according to the third embodiment which respectively have S powers of +1.00D, +2.00D, and +3.00D. Constant A was set to 7.68 × 10-6. Note that setting constant A to a positive number will extend the focal depth to the rear side of a focal point before focal depth extension. In addition, because the edge thickness increases, an edge thickness reduction component Dr10 may be added to the lens. When constant A is selected from a range of 1.73 × 10-6 to 1.96 × 10-5, constant D is preferably selected from a range of -1.88 × 10-16 to -1.65 × 10-17, and is also preferably selected such that the absolute value of constant D increases with an increase in constant A. The lens according to the fourth embodiment is configured such that the height from an original spherical surface S increases in proportion to a third-order power function of a distance r from a base point O1. Accordingly, the focal point is shifted backward with a reduction in distance to the edge of the lens. This increases the extension depth and improves contrast in a dark place.
That is, the focal depth extension component may be added to the rear surface 2 in one case, or may be added to the front surface 3 in another case. In either case, constant A is set to a positive number or a negative number. Moreover, in each of the cases shown in (a) and (b), an edge thickness reduction component may be added to the lens because the edge thickness increases. In each of the cases shown in (c) and (d), no edge thickness reduction component needs to be added because the edge thickness decreases. Assume that an edge thickness reduction component is added. In this case, when constant A is a positive number as indicated by (a), constant D is set to a negative number, whereas when constant A is a negative number as indicated by (b), constant D is set to a positive number. In addition, when the absolute value of constant A falls within the range of 1.73 × 10-6 to 1.96 × 10-5, the absolute value of constant D is preferably set within a range of 1.65 × 10-17 to 1.88 × 10-16, and the absolute value of constant D is preferably set so as to increase with an increase in the absolute value of constant A. This is because it is obvious in terms of calculation that determining constant A and constant D for an eyeglass lens having a normal size in this manner can provide an appropriate focal depth extension effect and suppress the occurrence of astigmatism, and in addition, the edge thickness can be set to be equal to that of the lens before the addition of a focal depth extension component.
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