MXPA98008609A - Multifo oftalmico lens - Google Patents

Abstract

A multifocal ophthalmic lens is provided comprising a far vision region, a near vision region, an intermediate vision region, and a main progress meridian passing through these three regions where a major length of progress, defined as a ratio between the addition of power and the maximum inclination of the middle sphere along the meridian is less than 16 millimeters, the sphere varies in a monotonous way as a function of the angle on a circle of a radius of 20 millimeters centered on a geometric center of the lens on both sides of the meridian, and wherein the far vision region, bounded in an upper portion of the lens by the lines formed from the points for which the cylinder equals half of the power addition, includes an angular sector that has its origin in the geometric center of the lens, with an included angle greater than 150ø. This provides a good distribution of the isocylinder and the ionosphere lines on the lens, ensuring that the progress is very smooth.

Description

MU LTIFOCAL OPHTHALMIC LENS BACKGROUND OF THE I NVENTION The present invention relates to a multifocal ophthalmic lens, having a spherical surface having a middle sphere and a cylinder at each point thereof. These lenses are well known; Among multifocal lenses one can distinguish lenses known as progressive lenses adapted to view 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 a main meridian of progress that passes through all three regions. The French patent application 2,699,294, describes, in its preamble, the different elements of a progressive multifocal ophthalmic lens (main meridian of progress, far vision region, near mink region, etc.), as well as the work carried out by the applicant to improve the user's comfort of said lenses. The applicant has also proposed, in order to better meet the visual needs of people with eyestrain and to improve the comfort of progressive multifocal lenses, to adapt the shape of the main meridian of progress, as a function of the power addition value A (application French Patent FR-A-2,683,642). For such lenses, the power addition value A is defined as the variation in the mean sphere between a reference point in the far vision region and a reference point in the near vision region. Such progressive lenses are usually prescribed as a function of the user's ametropia and the power needed for near vision. The lenses also exist that are dedicated more specifically to near vision; said lenses do not have a far vision region with a defined reference point as conventional progressive lenses do. These lenses are prescribed depending on the near vision power that the user needs, regardless of the far vision power. Said lens is described in an article in "Opticíen Lunetier" dated April 1988, and sold commercially by the applicant under the Essilor Delta brand; This lens is also as simple to use and easy to put on as a progressive lens, and is attractive to people with eyestrain not accustomed to progressive lenses. This lens is also described in French patent application FR-A-2,588,973. It has a central portion that is equivalent to the lenses of an approach that would normally be used to correct eyestrain, in order to ensure satisfactory near vision. In addition, it has a slight reduction in power in the upper portion, ensuring that the user has a sharp vision beyond the usual near field of vision. Finally, the lens has a point at a power value equal to the rated power for near vision, a higher power region in the lower portion of the lens, and a lower power region in the upper part of the lens. The existing multifocal lenses, either progressive or dedicated to near vision, can be further improved in terms of their foveal vision operation, in order to improve user comfort. Users of multifocal lenses do in fact sometimes feel uncomfortable with dynamic vision. Such lenses can also improve by conserving a near vision region that is high enough to ensure the comfort of the optimal user, along with wide visual fields in near, middle and far vision.

BRIEF DESCRIPTION OF THE INVENTION The present invention provides a multifocal lens that overcomes the disadvantages of the lenses of the prior art and which ensures improved peripheral vision, while maintaining good foveal vision performance, thereby facilitating the adaptation of users to their lenses. Nevertheless, the invention ensures the rapid progress of the middle sphere, so that the presence of a large near vision area is ensured. A balanced distribution of the isosphere and the indile indro lines is also achieved. The invention provides a multifocal ophthalmic lens comprising a spherical 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 main meridian of progress MM 'that passes through said three regions, where a main length of progress, defined as a ratio between the addition of power and the maximum inclination of the average sphere over the meridian is less than 16 mm, where the sphere varies monotonously as a function of the angle in a circle with radius of 20 mm centered on a geometric center of the lens on both sides of said meridian, and where the far vision region delimited in an upper portion of said lens by the lines formed of points for which the indro cylinder is equal to the power addition half includes an angular sector that has its origin in the geometric center of the lens with an included angle greater than 1 50 °. Advantageously, the primary programming meridian is made by midpoints of horizontal segments joining respective lines formed by points where the cylinder is 0.50 diopters. In one modality, the near vision region, delimited in an upper portion of said lens by the lines formed by the points where the cylinder is equal to the power addition half has a width that is greater than 12. mm at a reference point for near vision. In another embodiment, said included angle has a value comprised between 160 ° and 170 °, preferably of the order of 165 °. Preferably, the module of the derivative dS / d? of medium sphere with respect to the angle in said circle is between 0.005 and 0.01 5 when said angle? it is between [30 °; 1 00o] and [270 °; 325 °]. Advantageously, the module of the derivative dS / d? of medium sphere with respect to the angle in said circle is between 0.01 and 0.04 when said angle? is on the scale [125 °; 1 80o] and [200 °; 250 °]. In one embodiment, the lens is a multifocal lens dedicated to near vision and intermediate vision, said lens having a power addition defined as a difference between the maximum and minimum values of the average sphere in said meridian of progress, within a circle with radius of 20 mm centered on the geometric center of said lens. In another embodiment, the lens is a progressive multi-focal lens that has a reference point for a near vision region, a reference point for a far-vision region, and a power addition defined as a difference between the values of the middle sphere in these two points.

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

BRIEF DESCRIPTION OF THE DIAMETERS Figure 1 is a diagrammatic front view of a multifocal prog resive lens. Figure 2 shows graphically the variation in power over the meridian of the lens according to the invention. Figure 3 is a front view of the lens in Figure 2, showing the main meridian of progress and the lines indicating the level of the middle sphere. Figure 4 is a front view of the lens in Figure 2, showing the main meridian of progress and the lines indicating the level of the cylinder. Figure 5 is a three-dimensional view of the sphere inclinations in the lens of Figure 2. Figure 6 shows, in diagram, the sphere in the circle with radius of 20 mm at the geometric center of the lens, as a function of the angle for the lens in figure 2 and for the lens in figures 7 and 12. Figures 7 to 9 are views similar to those in figures 2 to 4, for a power addition of 2 d ioptrias.

Figures 1 to 1 are views similar to those in Figures 2 to 4, for a power addition of 3 diopters.

DETAILED DESCRIPTION OF THE PREFERRED MODALI DAD Later, an orthonormal coordinate system will be used where the x axis corresponds to the horizontal axis 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 6 show the optical characteristics of the lens according to the invention, this lens having a diameter of approximately 60 mm. In Figures 2 to 6, a lens having a power addition of one diopter is described. Figures 7 to 1 2 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. Said lens generally has a spherical face shown in Figure 1 and a second face which may be spherical or toroidal. For each point on the spherical surface, an average sphere D is defined from the formula: D = G (1 + 1) 2 R, R2 where: Ri and R2 are the maximum and minimum radii of curvature expressed in meters, and n is the refractive index of the lens material. Cylinder C is defined by the formula: C = (n - 1) | 1 - 1 | The lines of the isosphere are lines formed by the projection in a plane tangential to the progressive surface at the geometric center O of the points on the surface of the lens that has the same value of the middle sphere. Similarly, the lines of the isocylinder are lines constituted by the projection in this same plane of points that has e | same lindro. Conventionally, the 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 reference point 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, no corresponding reference point is defined for the far vision region.

In FIG. 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 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 substantially vertically from the top of the lens, passing through the point L, to a point D, referred to as the center of adjustment, and located between the point of far vision control L and geometric center O. 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 near vision reigon 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 sphere values are measured in the meridian thus defined within the limits of a circle with a radius of 20 mm centered on the geometric center of the lens . The power addition is now the difference between three minimum and maximum values of the sphere; this definition is substantially equivalent, for progressive lenses, to the conventional definition of power addition and the difference in 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 isocylinder lines of a value equal to half the power addition. Similarly, the boundary of the near mink region in the lower portion of the lens is established by isocylinder lines of a value equal to half the power addition. The inner circle shown in Figure 1 represents the region detected by the eye when performing everyday tasks. The size and position of this portion, known as the foveal vision region, has been determined by several series of measurements carried out in the applicant's laboratories; reference can be made to IEEE, portable eye movement recorder by T. Bonnin and N. Bar, Proceedings of the 14th annual international conference of the Society of Engineering in Medicine and Biology of I EEE 1992, part 4, pages 1668 to 1669, to AAO 1993, for "Optimization of ophthalmic spherical 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 once again to ECEM 93, "The use of visual space", a poster by N Bar. region covers a disk with a diameter of 30 mm centered on the assembly center.

To ensure maximum visual comfort for the user, the disc with a diameter of 40 mm centered on the geometric center of the lens, covering the foveal vision region, is considered and it has been established to limit the tangential variations in the sphere on this circle. The control of the variations in the sphere on this circle makes it possible to dominate the deformations in the optical characteristics of the multifocal surface; in this way it improves the peripheral vision of the user. It is also desired to overcome defects such as the cylinder within the 40 mm circle, as much as possible, acute vision within the foveal region. This circle is shown in figure 1. In 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. In order to improve the fragility of the progress of the lenses, and to facilitate the user to adapt to the lens, the present invention considers a new definition of the characteristics of the lens surface, explained with reference to the following figures. The figures cover the case of progressive multifocal lenses; The invention applies mutatis mutandis to multifocal lenses dedicated to near vision. Figure 2 is a graph showing the power over 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 mm on the y-axis on 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 middle sphere is 5.2 diopters and the cylinder is 0; the point that has a value of the axis and 14 mm in the meridian is the reference point P for near vision; at this point, the average sphere is 6.22 diopters and the cylinder is 0.02 diopters. A main length of progress is defined as the ratio between the addition of power A as defined above and the maximum value of the average sphere inclination on the meridian; this relation is written as: Lpp - A / H m ßr For a progressive multifocal lens, we have: where SVP and SL are respectively the values of medium sphere in the near and far vision control points and Pmer is the maximum value of the inclination of the sphere on the meridian; this inclination of sphere corresponds to the maximum modulus of the sphere gradient with respect to x or a and. For a progressive multifocal lens dedicated to near and intermediate vision, we have: Lpp - (tnax - m¡n) / r me r where Smax and Smi p are respectively the maximum and minimum values of sphere in the meridian, and Pmer is as defined before. This ratio is equivalent to a length, and represents the length over which the average sphere increases by a value corresponding to the addition of power. Figure 2 shows that, at the beginning, the sphere remains substantially constant in the far vision region above point L. It also shows that the sphere remains substantially constant in the near vision region, around point P. Finally, it shows that the Main length of progress, equal to 12.50 mm, is low, and is notably less than 16 mm. This ensures satisfactory near vision in a region that extends over the near vision control point, making obvious the need for the user to move their head. Close and comfortable close vision is assured. The maximum inclination of sphere in the meridian is 0.08 diopters per mm. Figure 3 is a front view of the lens in Figure 2, showing the principal meridian of progress and the equal mean sphere lines. Those elements shown in Figure 2 will also be found in Figure 3 with the addition of isosphere lines. The isosphere lines in figure 3 are the lines 1 1, 12, 13 and 14 that represent respectively the average sphere that is greater by 0.25, 0.5, 0.75 or 1 diopter to the middle sphere at the far vision control point L Finally, a circle with a diameter of 40 mm centered on the geometric center of the lens is shown.

Figure 4 is a front view of the lens in Figure 2, showing the principal meridian of progress and the equal cylinder lines. Those elements shown in figure 2 are also present in figure 4. Since the cylinder is low on the main meridian of progress, there are two isocylinder lines for each cylinder value. The isocylinder lines in Figure 4 are lines 16 and 16 ', and 17 and 17', which represent, respectively, a cylinder of 0.25, and 0.50 diopters. As indicated above, in the upper portion of the lens the limit of the far vision region is constituted substantially by lines 17 and 17 'of the isocylinder of 0.5. The lens of the invention in this manner has a wide far vision region that extends over almost the entire upper half of the lens. Quantitatively, the far vision region includes an angular sector defined by two median lines 20 and 21 'originating from the geometric center of the lens with an included angle greater than 130 °; in figure 4, the angle between the middle lines 20 and 20 'is of the order of 160 °. In the lower portion of the lens, the limit of the near vision region is also substantially constituted by lines 17 and 17 'of the isocylinder of 0.5. Figure 5 is a three-dimensional representation of sphere inclinations in the lens of Figure 2; Figure 5 shows the average sphere inclination, in diopters per mm, as a position function in the lens, in the frame of reference defined above.

Figure 6 shows the variation in average sphere in the 40 mm diameter circle centered on the geometric center of the lens for various power addition values; the y-axis is graduated in diopters and the x-axis shows the angle? in a system of polar coordinates the center of which is the geometric center of the lens and the angles of which are measured starting from an upright vertical line directed upwards that originates from the geometric center of the lens; in other words; the x axis represents the angle? between, first, an upright vertical middle line that originates from the geometric center of the lens and, second, a half line that originates from the geometric center of the lens and passes through the point in said circle where the sphere is measured . The lower curve in figure 6 corresponds to the variation in sphere in the circle with diameter of 40 mm for the power addition lens of a diopter shown in figures 2 to 5; the middle and upper curve in Figure 6 show respectively these same variations for power addition lenses of two and three diopters. Figure 6 shows that the variations in sphere in the circle with radius of 20 mm centered on the geometric center of the lens are monotonous, when one moves in the circle from a point of intersection with the meridian to another point of intersection of the circle with the meridian. In other words, in figure 6, the point of the value of the axis x 0o or 360 ° corresponds to the point that has the coordinates x = 0 mm, y = 20 mm in the orthonormal reference defined above, and also corresponds substantially to the point intersection of the meridian and the circle, in the upper portion of the lens. The point on the x axis where? = 1 87 ° in Figure 6 is the point for which the sphere has a maximum value; this point corresponds to the intersection of the circle with the meridian in the lower portion of the lens, and has, in the orthonormal reference frame defined above, the coordinates x = 3.47 mm and y = - 1 9.70 m. When one moves around the circle from the angle point? = 0o towards the point of the angle? = 1 87 °, the sphere is a function of increasing angle; when one moves around the circle from the point of the angle? = 187 ° to the angle of the angle? = 0o, the sphere is a function of decreasing angle. This condition with respect to the monotonic variation of sphere over the circle on both sides of the meridian ensures that it is a very careful and uniform progress of the optical characteristics of the lens, both inside the foveal region and outside it. The lens in Figures 2 to 6 thus ensures the progress which is very careful, ensuring a much easier adaptation on the part of the user of the lenses. Quantitatively, this is reflected by the following conditions: (1) the far vision region comprises an angular sector with its origin at the geometric center of the lens, with an incl angle of at least 1 50 °; (2) the main length of progress, that is, the ratio between the addition of power and the maximum inclination of the medium sphere in the meridian is less than 16 mm, and (3) the variation in sphere in the circle with radius of 20 mm centered in the geometric center of the lens is monotone on both sides of the meridian. The relationship (1), as explained above, establishes a lower limit for the surface area of the far vision. The relation (2) reflects the fact that the main length of progress of the lens is low, and in this way the fact that the near vision region is sufficiently high in the lens to ensure optimal comfort for the user in near vision. The third relationship ensures, through the monotony of variations in the middle sphere at the edge of the foveal region, and considering the continuity and derivation properties of the progressive surfaces, well known to those skilled in the art, good mastery of variations in optical parameters inside and outside this region. The combination of these three conditions ensures a good distribution of the isosphere and isocylinder lines on the surface of the lens, thus ensuring very careful progress. The combination of these three conditions is not satisfied by any prior art multifocal ophthalmic lens tested by the applicant. The invention provides, for the first time, said distribution of isosphere and isocylinder lines.

Figures 7 to 9 are views similar to those in Figures 2 to 4 but for a power addition lens of 2 diopters; Figures 10 to 12 are views similar to those in Figures 2 to 4, but for a power addition lens of 3 diopters. The isosphere lines with a step of 0.25 diopters are shown in figures 8 and 11; the isocylinder lines in steps of 0.25 diopters are shown in figures 9 and 12. These diagrams also show the mean lines tangential to the isocylinder lines A / 2, in the far vision region. For each of these lenses, all three conditions are satisfied. In the case of the lens in Figures 2 to 5, there is, as indicated above: angle in the center of the angular sector included in the far vision region: 163 °; Lpp = 12.50 mm. For power addition lenses of 2 and 3 diopters, the values of the angle at the center and the main length of progress are the same. The invention provides additional advantageous features, which, combined with these three conditions, make it possible to improve the operation of the lens according to the invention. According to the invention, the near vision region has, at the reference point level for near vision, a width of at least 12 mm, and preferably a width greater than 13 mm; this width is measured in the y-axis coordinate of point P, between the isocylinder lines A / 2, where A is the power addition as defined above. As can be seen in figure 3, in the case of power addition of a diopter, the width of the near vision region is 13.5 mm. For a power addition of two or three diopters, this value remains substantially the same. In one embodiment of the invention, the angle at the center of the angular sector contained in the far vision region is between 160 and 170 °, and preferably close to 165 °; in the example shown in the figures, this angle at the center is substantially 163 ° for the power addition lens of one diopter, and is the same for power addition lenses of two or three diopters. Advantageously, limits are also imposed on the average sphere inclination in the 20 mm radius circle; this inclination is in fact the derivative dS / d? of the function represented in the curves in Figure 6. The table below gives average values for the absolute value of inclination for different angles and for different power additions.

In all cases, the absolute inclination value is between 0.005 and 0.015 for angle values? in [30 °; 100 °] or [270 °; 325 °]; is between 0.01 and 0.004 for angle values? in [125 °; 180 °] or [200 °; 250 °]. Now details of the different characteristics that make it possible to provide the different lenses according to the invention will be given. As it is known per se, the surface of the lenses is continuous and can be continuously derived three times. As is known to those skilled in the art, the surface of progressive lenses is obtained by digital optimization when using a computer, establishing boundary conditions for a certain number of lens parameters. Combinations of the three conditions defined above may be used as boundary conditions, together, if appropriate, with one or more of the criteria defined above as limiting conditions. These criteria apply 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 for a multifocal lens dedicated to near vision. One can begin favorably by defining, for each lens of the family, a principal meridian of progress. For this, the teachings of the French patent application FR-A-2,683,642 mentioned above, is used. 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 spherical surface may be the surface facing the wearer of the lenses. In addition, although it is not mentioned in the description of lenses that may be different for both eyes, it certainly applies obviously.

Claims (8)

RECIPE N D ICACIO NES

1 .- A multifocal ophthalmic lens comprising a spherical 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 main meridian of progress MM 'that passes through these three regions, where a primary length of progress, defined as a relation between the addition of power and the maximum inclination of the average sphere on said meridian is less 16 mm; wherein the sphere varies monotonously as a function of angle in a circle with a radius of 20 mm centered on a geometric center of the lens in both sides of said meridian, and wherein the region of far vision of the i in a portion its upper part of said lens by lines formed of points for which the indro cylinder is equal to the power admission half includes an angular sector that has its origin in the geometric center of the lens with an included angle greater than 1 50 °.

2. The lens according to claim 1, wherein said main meridian of progress is made by midpoints of horizontal segments joining respective lines formed by points where the core is 0.50 diopters.

3. - The lens according to claim 1, wherein said region of near vision, delimited in an upper portion of said lens by lines formed by points where the cylinder is equal to the power addition half has a width that is greater than 12 mm at a reference point for near vision.

4. The lens according to claim 1 or 2, wherein said included angle has a value comprised between 160 ° and 170 °, preferably of the order of 165 °.

5. The lens according to one of claims 1 to 4, where the module of the derivative dS / d? of medium sphere with respect to the angle in said circle is between 0.005 and 0.015 when said angle? is on the scales [30 °; 100 °] and [270 °; 325 °].

6. The lens according to one of claims 1 to 5, where the module of the derivative dS / d? of medium sphere with respect to the angle in said circle is between 0.01 and 0.04 when said angle? is on the scales [125 °; 180 °] and [200 °; 250 °].

7. The lens according to one of claims 1 to 6, wherein the lens is a multifocal lens dedicated to near vision and intermediate vision, said lens having a power addition defined as a difference between maximum and minimum values of medium sphere in said meridian of progress, within a circle with radius 20 mm centered on the geometric center of said lens.

8. - The lens according to one of claims 1 to 6, wherein said 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 average sphere in these two points. SUMMARY A multifocal ophthalmic lens is provided comprising a far vision region, a near vision region, an intermediate vision region, and a main progress meridian passing through these three regions, wherein a major length of progress, defined as a ratio between the addition of power and the maximum inclination of the middle sphere along the meridian, it is less than 16 millimeters; the sphere varies in a monotone form as a function of the angle on a circle of a radius of 20 millimeters centered on a geometric center of the lens on both sides of the meridian, and where the far vision region, bounded on an upper portion of the lens by the lines formed from the points for which the cylinder is equal to half the power addition, it includes an angular sector originating in the geometric center of the lens, with an included angle greater than 150 °. This provides a good distribution of the isocylinder and the ionosphere lines on the lens, ensuring that the progress is very smooth.