MXPA98008610A - Multifo oftalmico lens - Google Patents

Abstract

A multifocal ophthalmic lens is provided which comprises a far vision region, a near vision region, and an intermediate vision region, which has a high near vision region and a broad field of view in the near vision region, in the intermediate vision region, and in the far vision region. Progress is slight, although the distance between a mounting center on the lens and the point where the power addition is 85% higher than the power addition at a far vision control point is less than 16 millimeters, while simultaneously, the maximum cylinder within a circle of a radius of 20 millimeters centered on a geometric center of the lens, is maintained at a value of

Description

MULTIFOCAL OPHTHALMIC LENS BACKGROUND OF THE INVENTION The present invention relates to a multifocal ophthalmic lens, having an aspheric surface, having an average sphere, and a cylinder at each point thereof. These lenses are well known; Among the multifocal lenses, we can distinguish lenses known as progressive lenses adapted to vision at all distances, and lenses that are more specifically dedicated to near vision and intermediate vision. Progressive multifocal ophthalmic lenses comprise a far-vision region, a near-vision region, an intermediate-vision region, and an average meridian of progress that passes through all three regions. French Patent Application Number 2,699,294 which is incorporated herein by reference, describes, in its preamble, the different elements of a progressive multifocal ophthalmic lens (medium meridian of progress, far vision region, near vision region, etc.), as well as the work done by the applicant to improve user comfort with these lenses. The applicant has also proposed in order to better meet the visual needs of long-distance people, and to improve the comfort of the lenses progressive multifocals, adapt the shape of the medium meridian of progress, as a function of the power vision value A (French Patent Application FR-A-2, 683, 642). For these lenses, the power addition value A is defined as the variation in the average spherical between a reference point in the far vision region and a reference point in the near vision region. These progressive lenses are generally prescribed as a function of the user's ametropia, and the power needed for near vision. There are also lenses that are more specifically dedicated to near vision; These lenses do not have a far vision region with a defined reference point like conventional progressive lenses. These lenses are prescribed depending on the near vision power that the user needs, regardless of the far vision power. This lens is disclosed in an article in "Opticien Lunetier" dated April 1988, and is sold commercially by the applicant under the registered trademark Essilor Delta; This lens is also simple and easy to use as a progressive lens, and is attractive to long-distance people who do not adapt with progressive lenses. This lens is also described in French Patent Application Number FR-A-2, 588, 973. It has a central portion that is equivalent to the lens of a single focus that normally it would have been used to correct the long view, in order to ensure a satisfactory close vision. Additional entity has a slight decrease in power in the upper portion, ensuring that the user also have a clear vision beyond the usual near field of vision. Finally, the lens has a point at a power addition value equal to the rated power for near vision, a higher power region at the lower portion of the lens, and a lower power region at the upper portion of the lens . The existing multifocal lenses, either progressive or dedicated to near vision, can still be further improved with respect to the functioning of their foveal vision, in order to improve user comfort. Multifocal lens users do in fact sometimes feel uncomfortable with dynamic vision. These lenses can also be improved by conserving a near vision region that is sufficiently high to ensure optimal user comfort; finally, it is important that broad visual fields are provided in near, middle, and far vision.

COMPENDIUM OF THE INVENTION The present invention provides a multifocal lens that overcomes the drawbacks of the lenses of the art above, and that ensures the user a good visual comfort, a high region of near vision, and a broad field of vision in the near vision region, in the intermediate vision region, and in the far vision region. It also ensures that the user enjoys light progress in all regions of the lens. The invention provides a multifocal ophthalmic lens comprising an aspherical surface having at each point thereof, a middle sphere and a cylinder, and comprising a far vision region VL, a near vision region VP, an intermediate vision region VI, a mean meridian of progress MM 'passing through these three regions, where a main length of progress as defined in the present, is shorter than 16 millimeters, 1 and where the maximum cylinder Cma? inside a circle of a radius of 20 millimeters centered on a geometric center of the lens, it is defined by the following relation: Cma? / d < 0.50. Pmer where d is a distance between the geometric center of the lens and a point inside the circle, where the cylinder is at a maximum value, and Pmer is a maximum inclination of the middle sphere along the medium meridian of progress. In accordance with a preferred embodiment, the principal progress meridian is formed by midpoints of the horizontal segments that join the respective lines formed by the points where the cylinder is 0.50 diopters. In one embodiment, the lens is a multifocal lens dedicated to near vision and intermediate vision, the lens having a power vision defined as a difference between maximum and minimum values of the middle sphere on the meridian of progress, inside a circle of a radius of 20 millimeters centered on the geometric center of the lens. In this case, the main length of progress of preference is defined as a ratio between the addition of power and the maximum inclination of the average sphere on the meridian, and the cylinder inside the circle of a radius of 20 millimeters centered on a geometric center of the lens, is less than the power addition, and preferably less than 80 percent power addition. According to another embodiment, the lens is a progressive multifocal lens having a reference point for a near vision region, a reference point for a far vision region, and a power addition defined by a difference between the values of the middle sphere in these two points. In this case, the main length of progress can be defined as a vertical distance between a mounting center and a point on the meridian where the average sphere it is 85 percent higher than the average sphere at the reference point for far vision, and the cylinder inside the circle of a radius of 20 millimeters centered on a geometric center of the lens, is smaller than the addition of power, and preference less than 80 percent of the power addition. In a further preferred embodiment of both lenses, a difference between the maximum cylinder on both sides of the meridian, inside the circle of a radius of 20 millimeters centered on a geometric center of the lens, is less than 0.05 diopters, and preferably less than 0.03. diopters. According to a further preferred embodiment, an angle between the median lines originating from a geometric center of the lens, and passing through the points of intersection of the circle, and the lines formed from the points where the cylinder is equal at half of the power addition in the near vision region, it is greater than 45 °. According to still a further preferred embodiment, the far vision region defined in an upper portion of the lens by the lines formed by the points where the cylinder is equal to half of the power addition, contains an angular sector formed by two middle lines originating in a geometric center of the lens, and having an included angle greater than 130 °, and preferably comprised between 160 ° and 165 °.

Other features and advantages of the present invention will become clearer from the following description of an embodiment of the invention provided by way of non-limiting example, with reference to the accompanying drawings.

BRIEF DESCRIPTION OF THE DRAWINGS Figure 1 is a diagrammatic front view of a multifocal progressive lens. Figure 2 shows graphically the variation in power along the meridian of the lens according to the invention. Figure 3 is a front view of the lens of Figure 2, showing the principal meridian of progress and the lines indicating the level of the middle sphere. Figure 4 is a front view of the lens of Figure 2, showing the main meridian of progress and the lines indicating the level of the cylinder. Figure 5 is a view similar to that of Figure 2, for a power addition of two diopters. Figure 6 is a view similar to that of Figure 3, for a power addition of two diopters. Figure 7 is a view similar to that of Figure 4, for a power addition of two diopters. Figure 8 is a view similar to that of the Figure 2, for a power addition of 3 diopters. Figure 9 is a view similar to that of Figure 3, for a power addition of three diopters. Figure 10 is a view similar to that of Figure 4, for a power addition of three diopters.

DETAILED DESCRIPTION OF THE PREFERRED MODALITY Later we will use an orthonormal coordinate system, where the X axis corresponds to the horizontal axis of the lens, and the Y axis corresponds to the vertical axis; center 0 of the reference frame is the geometric center of the lens. Figure 1 is a diagrammatic front view of a known progressive ophthalmic lens, showing the different elements thereof. Figures 2 to 4 show the optical characteristics of the lens according to the invention, this lens having a diameter of approximately 60 millimeters. In Figures 2 to 4, we have described a lens that has a power addition of one diopter. Figures 5 to 10 show a similar view, for lenses having a power addition of 2 or 3 diopters. With reference to Figure 1, the different elements of a multifocal ophthalmic lens will now be described.

This lens generally has an aspherical face shown in Figure 1, and a second face which may be aspherical or toroidal.

For each point on the aspheric surface, an average sphere D is defined from the formula: n • -, 1 11 + II DD == R. where: Rl R2 are the maximum and minimum curvature of the curves expressed in meters, and n is the refractive index of the lens material. Cylinder C is defined by the formula: C = (n - 1) ¡1 -? | Rl R2 The lines of the isosphere are lines formed by the projection on a plane tangential to the progressive surface at the geometric center 0 of the points on the surface of the lens that have the same value of the middle sphere. In a similar way, the lines of the isocylinder are lines constituted by the projection on this same plane of the points that have the same cylinder. Conventionally, lens 1 comprises in its upper portion, a far vision region VL, in its lower portion a near vision region VP, and between these two regions, an intermediate region VI. For a progressive lens, a reference point P is defined in the near vision region, where near vision is measured, and a point of reference L where far vision is measured. For a lens dedicated to near vision, a reference point P is defined in the near vision region to measure near vision; however, a corresponding reference point is not defined for the far vision region. In Figure 1, the principal meridian of progress 2 of the lens is shown, which passes through the far vision region, the intermediate vision region and the near vision region. This meridian is defined as the place of the midpoints of the horizontal segments delimited by the isocylinder line of 0.50 diopters. In the example of Figure 1, the meridian is essentially composed of three segments, the first extending in a substantially vertical manner from the top of the lens, passing through the point L, down to a point D, referred to as the center of adjustment, and located between the point of far vision control L and geometric center 0. The second segment extends from point D obliquely towards the nasal side of the lens, and the third segment starts from the C end of the second segment, and passes through the control point near vision P. Other meridian forms are possible. In the case of progressive multifocal ophthalmic lenses, a power addition is defined in a manner known per se, this being the difference in the average sphere between a reference point P in the region of vision close, and a reference point L in the region of far vision. For multifocal lenses dedicated to near vision and intermediate vision, the minimum and maximum values of the sphere are measured on the meridian thus defined within the limits of a circle of a radius of 20 millimeters centered on the geometric center of the lens. The power addition is now the difference between these minimum and maximum values of the sphere; this definition is substantially equivalent, for progressive lenses, to the conventional definition of power addition, and that is the difference in the sphere between the reference points for near and far vision. With these definitions, it is generally considered that the limit of the far vision region in the upper portion of the lens is formed by the isocylinder lines of a value equal to half of the power addition. In a similar way, the limit of the near vision region in the lower portion of the lens is established by the isocylinder lines of a value equal to half of the power addition. In the lenses of the prior art, and in particular in the case of the applicant's lenses, the vision in the region around the main meridian of progress is completely satisfactory. The inner circle shown in Figure 1 represents the region explored by the eye when performing daily tasks. The size and position of this portion, known as the foveal region of vision, has been determined by numerous series of measurements made in the applicant's laboratories; for example, reference can be made to IEEE, Portable Eye Movement Recorder by T. Bonnin. and N. Bar, memoirs of the 14th annual international conference of the Society of Engineering in Medicine and Biology of IEEE, 1992, part 4, pages 1668 to 1669; to AAO 1993, to "Optimization of ophthalmic aspherical lenses: recording of eye movement for daily tasks" N. bar, T. Bonnin and C. Pedreno, Optometry and vision science 1993, No. 12s, volume 70, page 154, or still again to ECEM 93"The use of visual space", a poster by N. Bar. This region covers a disk with a diameter of 30 millimeters centered on the assembly center. To ensure maximum visual comfort for the user, we consider the disc with a diameter of 40 millimeters centered on the geometric center of the lens, which covers the region of foveal vision, and as explained in detail later, a condition is made in which, inside the circulating, the quantity Cma? / d can be less than 0.50 -Pmer- The defects, such as cylinder, are dominated in this way inside this region, ensuring for the same, as far as possible, a vision clear in the foveal vision region.

In order to improve the softness of progress of the lenses, and the comfort in the foveal vision region, the present invention sets out to consider a new definition of the characteristics of the lens surface, explained with reference in the following figures. The figures cover the case of progressive multifocal lenses; the invention responds mutatis utandis to multifocal lenses dedicated to near vision. Figure 2 is a graph showing the power along the meridian of the lens according to the invention, the power addition of this lens being one diopter. The coordinates of the y-axis of the graph of Figure 1 are the coordinates of the y-axis of the lens; the coordinates of the x axis give the difference in power, in diopters, from the reference point in the far vision region. The point that has the value y = 8 millimeters on the y axis along the meridian, corresponds to the reference point L for far vision, which, in the case of Figure 2, is the point of the minimum sphere; at this point, the average sphere is 5.2 diopters, and the cylinder is 0; the point that has a value of the axis and of 14 millimeters on the meridian, is the point of reference P for near vision; at this point, the average sphere is 6.22 diopters, and the cylinder is 0.02 diopter. In the case of a progressive multifocal lens, the difference between the value of the axis and the assembly center and the value on the y-axis of a point on the meridian where the average sphere is equal to the sum of the average sphere at the reference point for the far-vision region 85 percent of the power addition is called the main progress length Lpp. In the example of Figure 2, the average sphere is 85 percent higher than the power addition for the medium sphere at the far vision reference point, at a value on the y-axis of y = 10.8 millimeters; for a mounting center with an axis coordinate of y = 4 millimeters, the main progress length is 14.8 millimeters. In the case of multifocal lenses dedicated to near vision and intermediate vision, the main progress length is the ratio between the addition of power as defined above, and the inclination of the middle sphere along the meridian; this proportion is written as: PP = max ~ smin ^ 'pmer where Smax and Sm; _n are respectively the maximum and minimum values of the sphere on the meridian, and Pmer is the maximum value of the inclination of the sphere along the meridian; this inclination of the sphere corresponds to the maximum modulus of the inclination of the sphere with respect to x or y. This Lpp ratio is equivalent to a length, and is representative of the length over which the average sphere is increased by value corresponding to the addition of power. In both cases, the main progress length is for a position along the meridian corresponding to a variation in the mean sphere. Figure 2 shows that, at the beginning, the sphere remains substantially constant in the region of far vision above point L. It shows that the sphere remains substantially constant in the near vision region, below point P. Finally, it shows that the length of main progress, equal to 14.8 millimeters, is low, and, notably, is less than 16 millimeters. Accordingly, this ensures the possibility of using close vision in an extensive way, with considerable comfort. Figure 3 is a front view of the lens of Figure 2, showing the principal meridian of progress and the lines of the equal mean sphere. These elements shown in Figure 2 will also be found in Figure 3 with the addition of the lines of the isosphere. The lines of the isosphere of Figure 3 are lines 11, 12, 13, and 14, which represent respectively the average sphere that is greater by 0.25, 0.5, 0.75, or 1 biop for the average sphere at the control point of far vision L. Figure 4 is a front view of the lens of the Figure 2, showing the main meridian of progress and the equal cylinder lines. These elements shown in Figure 2 are also present in Figure 4. Since the cylinder is low along the main progress meridian, there are two isocylinder lines for each cylinder value. The lines of the isosphere of Figure 4 are lines 16, and 16 ', 17, and 17', 18 and 18 ', which represents, respectively a cylinder of 0.25, 0.50, 0.75, diopters. As indicated above, in the upper portion of the lens, the edge of the far vision region is constituted substantially by the isocylinder lines 0.5, 17 and 17 '. The lens of the invention, therefore, has a wide far vision region that extends over the entire upper half of the lens. In the lower portion of the lens, the edge of the near vision region is also constituted substantially by the isocylinder lines 0.5, 17, and 17 '. Figure 4 shows the lens of the invention, having a width of the near vision region, measured between the isocylinder lines 17 and 17 'at the point P, which is greater than 13 millimeters. If we consider the disc of diameter of 40 millimeters centered on the geometric center of the lens, the maximum value of the cylinder inside this disc is of 0.741 diopters; This maximum value is reached at a point with the coordinates x = -16, y = -12, located at a distance of 20 millimeters from the center of the lens. The lens of Figures 2 to 4, therefore, ensures very light progress while still having a short progress length, and therefore, a high near vision region. In a quantitative way, this is expressed through the following relationship: where Cmax is the maximum value, in diopters, of the cylinder inside the disc of diameter of 40 millimeters centered on the geometric center of the lens; d is the distance in millimeters between the geometric center and the point on the disk where this maximum value is reached; Pmer is the maximum value of the inclination of the middle sphere along the meridian, in diopters per millimeter. Therefore, the value of 0.50 has no dimension. The reaction (1) reflects the fact that the rapid progress in the sphere along the meridian does not introduce defects that are too significant in the foveal lens vision region: the Pmer value expresses the maximum inclination value of the sphere; a large value represents a pronounced progress. The value Cma? reflects the alterations induced on the surface of the lens, within the limits of disc diameter of 40 millimeters, for a high progressiveness; this value is measured by the 1 / d coefficient that reflects the fact that the alteration causes fewer problems in the periphery of the lens than in its center. The relation (1) is not satisfied by any of the progressive ophthalmic lenses of the prior art tested by the applicant. The lens of the prior art that most closely accords with this criterion, is one of the applicant's own lenses, for which the amount Cma? / D .Pmer, measured on the lens, 'reaches a value of 0.55. Consequently, the lens ensures, for the first time, a compromise between pronounced progress, and particularly well-controlled alterations in the foveal region. Figures 5 to 7 show views similar to those of Figures 2 to 4, but for a lens having a power addition of 2 diopters; Figures 8 to 10 show views similar to those of Figures 2 to 4, but for a lens having a power addition value of 3 diopters. Figures 6 and 9 show the isosphere lines in steps of 0.25 diopters; in Figures 8 and 10, the isocylinder lines are also shown in steps of 0.25 diopters. For each lens, the relationship is satisfied, with the following values: The invention discloses other features Convenient that, in combination with the relation (1), make it possible to improve the operation of the lens according to the invention. As mentioned above with reference to Figure 2, the main progress length is conveniently less than 16 millimeters; its value is 14.8 millimeters for the lens of a power addition of 1; the main progress length is substantially identical for a lens of a power addition of 2, and for a lens of a power addition of 3. This low length of progress is represented in practice by a near vision region extending high on the lens. Conveniently, the maximum cylinder inside the diameter circle of 40 millimeters is smaller than the power addition, and preferably less than 80 percent of the power addition. As an example, considering a power addition of 1 diopter, the maximum cylinder inside the circle is 0.741 diopter; this value is 1.52 diopters for a power addition of 2 diopters, and 2.28 diopters for a power vision of 3 diopters. A provision can be made for the difference between the maximum cylinder on both sides of the meridian, inside a circle of a radius of 20 millimeters centered on the geometric center of the lens, to be less than 0.05 diopters, and preferably less than 0.03 diopters .

In a convenient way, the angle between the middle lines that originate from the geometric center of the lens, and that pass through the points of intersection of the circle of a radius of 20 millimeters, and the lines formed by the points for which the cylinder is equal to half the power addition, inside the near vision region, it is greater than 45 °. In the embodiment of Figures 2 to 4, the included angle of these middle lines, bearing the references 21 and 21 'is of the order of 45 °. Its value is substantially identical for the lenses of a power addition of 2 and 3 of Figures 5 and following; the corresponding median lines are also shown in Figures 7 and 10. The invention further proposes that the maximum value of the cylinder be substantially equal to the nasal and temporal sides of the lens; this value is conveniently of the order of 75 percent of the power addition defined above; in the lens of a power addition of 1 according to the present invention, the maximum cylinder on the nasal side is 0.734 diopter, and is obtained at a point having the coordinates x = 17 millimeters and y = -10 millimeters. On the temporary side, the maximum value of the cylinder is 0.741 diopters, and it is reached at the point that has the coordinates x = -6 millimeters, and y = -12 millimeters. This maximum value is reached at points located at distances of 19.7 and 20 millimeters from the geometric center of the lens. This ensures that the point of the maximum cylinder is located in the periphery of the region used for foveal vision. In one embodiment of the invention, the far vision region comprises at least one sector formed by two half lines intersecting the geometric center of the lens, giving the included angle between them towards the upper portion of the lens, which is at least 130 ° C. This value is conveniently between 160 ° and 165 °. As can be seen in Figure 4, in the case of a power addition of one diopter, the angle between the middle lines, identified by references 20 and 20 ', is 163 °. The angle is substantially the same for a power addition of two or three diopters, and the corresponding midlines are also shown in Figures 7 and 10. Now we will give the details of the different characteristics to make it possible to provide the different compliance lenses. with the invention As you know for yourself, the surface of the lenses is continuous, and you can derive continuously three times. As is known to those skilled in the art, the surface of progressive lenses is obtained by digital optimization using a computer, establishing the limiting conditions for a number of lens parameters. One or more of the criteria defined above can be used as limiting conditions.

These criteria apply both to a conventional progressive multifocal lens with a reference point in the far vision region and a reference point in the near vision region, as well as to a multifocal lens that is dedicated to near vision. Conveniently you can start by defining, for each lens of the family, a principal meridian of progress. For this, the teachings of French Patent Application FR-A-2, 683, 642, mentioned above, are used, which is hereby incorporated by reference in its entirety. Any other definition of the principal meridian of progress can be used to apply the teaching of the invention. Obviously, this invention is not limited to what has been described: among other things, the aspheric surface could be the surface that faces the wearer of the lenses. Additionally, although it was not mentioned in the description of the lenses that may be different for each of the eyes, of course, this obviously applies.

Claims (10)

1. A multifocal ophthalmic lens comprising an aspherical surface having at each point thereof, a middle sphere and a cylinder, and comprising a far vision region VL, a near vision region VP, an intermediate vision region VI, a average meridian of progress MM 'passing through these three regions, where a main length of progress as defined herein, is shorter than 16 millimeters, a ratio between (a) the maximum cylinder in a circle of a 20 mm radius centered on a geometric center of the lens, and (b) a distance between a geometric center of the lens and a point inside the circle, where the cylinder is at a maximum value, is less than, or equal to, the half of a maximum inclination of the average sphere Pmer along the principal meridian of progress, whereby:

2. The lens according to claim 1, characterized in that the main meridian of progress is formed by the midpoints of the horizontal segments joining the respective lines formed by the points where the cylinder is 0.50 diopters.

3. The lens according to claim 1 or 2, characterized in that the lens is a multifocal lens dedicated to near vision and intermediate vision, this lens having an addition of power defined as a difference between the maximum and minimum values of the average sphere of the progress meridian inside a circle of a radius 20 mm centered on the geometric center of the lens. The lens according to claim 3, characterized in that the main length of progress is defined as a ratio between the addition of power and the maximum inclination of the middle sphere on the meridian. The lens according to claim 1 or 2, characterized in that the lens is a progressive multifocal lens having a reference point for a near vision region, a reference point for a far vision region, and an addition of power defined as a difference between the values of the average sphere in these two points. The lens according to claim 5, characterized in that the main length of progress is defined as a vertical distance between a mounting center and a point on the meridian where the middle sphere is 85 percent higher than the sphere average at the reference point for far vision. The lens according to one of claims 3 to 6, characterized in that the cylinder inside the circle of a radius of 20 millimeters centered on a geometric center of the lens is less than the power addition, preferably less than 80 percent of the power addition. The lens according to one of claims 1 to 7, characterized in that a difference between the maximum cylinder on both sides of the meridian, inside the circle of a radius of 20 millimeters centered on a geometric center of the lens, is less than 0.05 diopters, and preferably less than 0.03 diopters. The lens according to one of claims 3 to 8, characterized in that an angle between the median lines originating from a geometric center of the lens, and passing through the points of intersection of the circle, and the lines formed of the points where the cylinder equals half of the power addition in the near vision region, is greater than 45 °. The lens according to one of claims 3 to 9, characterized in that the far vision region defined in an upper portion of the lens by the lines formed by the points where the cylinder is equal to half of the power addition. , contains an angular sector formed by two middle lines originating in a geometric center of the lens, and having an included angle greater than 130 °, and preferably comprised between 160 ° and 165 °.