MXPA00000778A - Progressive multifocal ophthalmic lens - Google Patents

Abstract

In a progressive multifocal ophthalmic lens having an aspherical surface comprising a far vision region (VL), a near vision region (VP), an intermediate vision region, a main meridian of progression passing through these three regions, and a mounting center (CM), the far vision region includes an angular sector with its apex at the mounting center and a central angle of 110 , within which values of sphere and cylinder are less than or equal to 0.50 diopters, and a region of the lens above the near vision reference point and extending substantially up to the middle of the intermediate vision region has a maximum variation in values of cylinder 20 mm to both sides of the meridian limited to less than or equal to 0.30 diopters, and to less than or equal to 10%of the power addition of the lens. The lenses obtained, generally of power addition greater than or equal to 2.50, have wider near and intermediate vision regions, as well as a distribution of sphere and cylinder which is as homogeneous as possible over the complete surface of the lens.

Description

PROGRESSIVE MULTIFOCAL OPHTHALMIC LENS BACKGROUND OF THE INVENTION The present invention relates to progressive multifocal ophthalmic lenses. These lenses are well known; they are suitable for users of corrective presbytic glasses, and consequently provide an optical power that is different between near vision and far vision, when mounted in a frame. Progressive ophthalmic lenses conventionally comprise a far vision region, a near vision region, an intermediate vision region, and a major meridian of progression that passes through these three regions. French Patent Application 2,699,294 the reference of which can be made for more details, dssions, in its introduction, various elements of a progressive multifocal ophthalmic lens, together with a work carried out by the applicant for the purpose of improving the comfort of the users of said lenses. In summary, the upper lens potion is called the far vision region and is used by the eyeglass user for distance vision. The lower portion of the lens is the near vision region that the spectacle wearer uses for closed work, for example for reading. The region that extend between these last two regions is called the intermediate vision region.

In practice, progressive multifocal lenses often comprise a spherical face, and a face that is spherical or toric, which is machined to adapt the lens to the prescription of the users. Consequently it is usual to characterize a progressive multifocal lens by means of surface parameters of the spherical surface, specifically an average sphere S and a cylinder, at each point thereof. The mean sphere S is defined by the following formula: S = n 1 ( where Ri and R2 are the minimum and maximum radius of the curvature, expressed in meters, and n is the refractive index of the lens material. The cylinder is given, using the same conventions, by the formula S = (n - 1) Now it is called the power addition to the difference in the middle sphere between the reference point in the far vision region and a reference point in the near vision region. These two reference points are usually chosen to be the main meridian of progression.

The main meridian of progression is a line which is generally defined as being the intersection of the spherical surface of the lens and the user's gaze when the latter looks straight forward, at various distances. The principal meridian of progression is frequently in the umbilical line, in other words one of which all points have the cylinder of zero. The applicant has also proposed, in order to better meet the visual requirements of the users of presbytic glasses and improve the comfort of progressive multifocal lenses, to adapt the shape of the main meridian of progression, as a function of the power addition, and in this regard see French Patent Application 2,683,642. The existing progressive multifocal lenses can be further improved, notably those that have a higher power addition. For such lenses, the cylinder values reach high levels in view of the increase in lens power. This leads to disorders for dynamic vision and to a reduction in the width of the intermediate vision region and closed vision region. This is all altered when it is considered that, for the prescriptions of the power addition greater than 2.50, the user does not have more than the adaptation of the objective. In such cases, consequently it is better to provide the user with the addition of eyeglasses that he or she needs for good vision in closed vision along with wide and accessible visual fields for near or intermediate vision. Advantageously, the near vision region is also sufficiently large to ensure that the user enjoys optimum comfort. In the French Patent Applications 2, 683,642 and 2,683,643, the applicant has proposed improvements consisting of the variation of the meridian shape as a function of the addition of power and, consequently, the age of the user. The lateral displacement, to the nasal side, of the reference point of the closed vision took the vision of the closed movement of the reading plane as the age of the users advances. The applicant has also proposed to vary the position of the closed vision reference point not only as a function of the power addition, but also as an ametropia function, to take the version of the prismatic effects. In the French patent application 2,753,805, the applicant has described another improvement to determine the meridian. A method for using ray tracing makes it possible to determine the meridian, taking the version of closed motion for the reading plane as well as the prismatic effects. Therefore, for a given power addition, users suffering from different degrees of ametropia perceive the same power variations from the far vision region to the near vision region. The sphere and cylinder manager ensures broad fields of vision. COMPENDIUM OF THE INVENTION The present invention relates to improved lenses having an addition of power greater than or equal to 2.50. The obtained lenses have near and intermediate wide viewing regions, as well as a sphere and cylinder distribution that is as homogeneous as possible over the entire surface. This invention particularly proposes carefully master variations in the cylinder in the region that extend on both sides of the meridian, from the middle part of the intermediate vision region to the upper part of the near vision region. The present invention describes a multifocal lens that overcomes the disadvantages of the lenses of the prior art and that also ensures the user benefits of a near vision region extending from the top along with a good binocular effect, not only in static vision, but also in dynamic vision. - The invention provides a progressive multifocal ophthalmic lens, comprising a spherical surface having at each point thereof a middle sphere and a cylinder, and comprising a region of far vision with a reference point (CL), a region of vision close with a reference point (CP), a region of intermediate vision, a main meridian of progression passing through the three regions, and a center of assembly (CM), characterized in that: - the addition of power A, is defined as the difference in the mean sphere between the reference point of the near vision region and the reference point of the far vision region is greater than, or equal to 2.50 diopters, - a difference between the average sphere in the assembly center and the middle sphere at the reference point of the far vision region is less than, or equal to 0.25 diopter; - the far vision region includes at least one angular sector with its vertex in the center of assembly and a central angle of 110 °, within which the values of the sphere and the cylinder are less than, or equal to 0.50 diopters; - in a region of the anterior lens, the near vision reference point, and which substantially extends to the center of the intermediate vision region: - the differences between the maximum cylinder values over a distance of 20 mm on both sides of the meridian have an absolute value less than, or equal to 0.30 diopters; and - on each side of the meridian, an absolute value of the difference between the maximum and minimum values of the cylinder that is less than, or equal to the product k * A obtained by multiplying the power addition by a constant k having a value of 0.10.

Preferably, the anterior region of the lens above the near vision reference point extends over 7 mm, below the horizontal line it locates 11 mm below the mounting center. Advantageously, a near vision region has a lower limit in the upper portion of the lens formed by the isosphere lines A / 6, where A is the power addition. In one embodiment, the lens has a major progression length less than or equal to 15 mm, the length of progression being defined as a superior difference between the mounting center and a point on the meridian that has a sphere value of 85. % of the power addition greater than the sphere to the far vision reference point. Preferably, a rule of the gradient of the sphere at each point on a surface thereof is less than, or equal to the product k '* A resulting in the multiplication of addition of power A by a constant k' of the value 0.1 mm- 1. Advantageously, a higher value of the cylinder does not exceed the power addition by more than 10%. A rule of the cylinder gradient on the isocylinder lines representing half the value of the lens power addition, to the top of the near vision reference point, is preferably less than, or equal to, the point k "* A results from the multiplication of the addition of power A by a constant k "that has a value of 0.14 mm-1.

The distance between the isocilynd lines that represent half of the lens power addition to the near vision reference point is preferably equal to, or greater than 15 mm. Preferably, in the intermediate vision region, a distance between the isocylinder lines representing half of the lens power addition, to each top part, is greater than, or equal to 40% of the distance between the socilindrical lines that they represent half of the lens power addition to the top of the near vision reference point. In a preferred embodiment, in the region of the lens above the point of near vision, an absolute value of the difference between the maximum value for the cylinder over a distance of 20 mm on both sides of the meridian is less than, or equal to, 0.10 diopters. The additional features and advantages of the invention will become clearer from the following description of a modality thereof, provided by the form of the example and with reference to the accompanying drawings. BRIEF DESCRIPTION OF THE DRAWINGS FIGURE 1 is a diagrammatic view of the spherical surface of a progressive multifocal lens. FIGURE 2 shows the values for the cylinder on the lines of FIGURE 1, for a lens according to the invention; FIGURE 3 is a diagram similar to that in FIGURE 2.

FIGURE 4 is a diagram similar to that of FIGURE 3, for a prior art lens. FIGURE 5 shows, a graphical form, the middle sphere along the meridian of a lens according to the invention. FIGURE 6 shows the iso-sphere lines for the lens in FIGURE 5. FIGURE 7 shows the iso-cylinder lines for the lens in FIGURE 5. DETAILED DESCRIPTION OF A PREFERRED MODALITY In the rest of this description we must Consider, by the form of the example, a lens having a spherical surface directed towards the lens of the lens space and a toric or cylindrical surface facing the lens of the spectacle wearer. In the rest of the description, a lens tried for the right eye should be considered. The lens for the left eye can be supplied obtained by symmetry with respect to this lens. We must use a coordinated ortho-normal system in which the x axis corresponds to the horizontal axis of the lens and the axis for the vertical axis of the same; the center, 0, of the reference frame is the geometric center of the spherical lens surface. The axes are graduated in millimeters. FIGURE 1 is a diagrammatic view of the spherical surface of a progressive multifocal lens or, more accurately, of the projection of the surface in the plane (x, y); on the diagram, the reference frame is therefore defined to be recognizable along with the progression meridian shown in thick letter in FIGURE 1. In the example in FIGURE 1, the main meridian of the progression is essentially It has two portions. In the first portion, the main meridian of progression has a vertical segment that fails on the y-axis. This terminal segment, in its inferred portion, at a point known as the assembly center. This point has the coordinates (0, 4), in other words this point is located four millimeters above the center of the spherical surface of the lens. The assembly center is used by the eye doctors to mount the lens in the frame that corresponds to a horizontal direction of the look, when the user has his head straight. At this point, one should preferably take a condition that the average sphere does not exceed the value of the average sphere at the near vision reference point by more than 0.24 diopters. This ensures that the user has 0.25 diopters of tolerance at this point with respect to the prescription value. The second portion of the beginning of the meridian in the center of the assembly. If it extends from the nasal side of the lens, it passes through the intermediary and the near vision regions and passes through the near vision reverence point. The position of the meridian can be calculated by plotting the ray to ensure the optical foveal binocular vision enjoyed by the user without taking into account the addition of lens power. For more detail on the calculation of the meridian, the reference can be made according to French Patent 2,753,805. The far vision reference point, called VL in FIGURE 1, is a point that has the coordinates (0, 8), in other words it is symmetric from the center of the lens with respect to the mounting center. The near vision reference vision point, marked by the VP reference on the drawing, is located on the meridian with a y-axis coordinate of -14 mm. Its value of the x axis, for a power addition of 2.50 to 3.40 varies from 2.0 to 5.0 m. The dashed line in FIGURE 1, which passes through the mounting center CM and which is convexly ascending, substantially corresponds to the lower limit of the far vision region, in the upper portion of the lens. This limit substantially corresponds, as shown in FIGURE 6, to the isosphere lines of 0.50 diopters, or A / 6 in the case that the lens has an addition of power A = 3 shown in the drawings. Similarly, the dashed line in FIGURE 1, which crosses the lower portion of the meridian, and which is descendingly convex, substantially corresponds to the upper limit of the region of vision near, in the lower portion of the lens. As can be seen in FIGURE 6, this line more or less corresponds, to the lateral portions, to the isosphere lines of 5A / 6 or 2.50 diopters.

FIGURE 1 additionally shows the segments of horizontal straight line in the coordinates of the x-axis included between 11 mm above the center of the assembly and 18 mm below the center of the assembly, in 1 mm steps. Each segment extends over a distance of 20 mm on each side of the meridian. The y-axis coordinates are 18 mm below the center of assembly corresponding to the y-axis coordinate of the near-vision reference point; the axis coordinate y at 11 mm below the mounting center substantially corresponds to the middle part of the intermediate vision region. In FIGURE 1, with a mounting center having a y-axis coordinate of 4 mm, the segments extend between y-axis coordinates from -7 to -11 mm. In this form, vertically, the segments materially represent an area corresponding to the swept region by the eye of a spectacle user whose sight is directed to objects in the object space at distances varying substantially between 60 and 40 cm, for a power addition of 2.50 diopters, and 50 to 33 cm for a power addition of 3.00 diopters. Horizontally, the segments in FIGURE 1 materially represent an area of the lens where the aberration is much better. A particular effort can be made for the main aberration in this area. To improve the comfort of the user, the invention is directed to the limit of horizontal variations in the cylinder in the area covered by the segments in FIGURE 1. More precisely, the invention proposes to limit, for all segments, a difference between the maximum value of the cylinder on one side of the meridian and the maximum value of the cylinder on another side of the meridian. Advantageously, the absolute value of the difference is less than or equal to 0.30 diopters; if it is preferably less than, or equal to, 0.10 diopters. For the right and left symmetric lenses, this coercion applied to the cylinder is made possible to limit the variations in the cylinder between the homologous points that correspond to a given point in the separation of the object. In this form, the invention also makes possible the comfort of the improved user in binocular vision, in the upper part of the near vision region and in the lower part of the intermediate vision region. In order to improve the comfort of the user in the dynamic vision, the invention also proposes to limit the horizontal and vertical variations in the cylinder on both sides of the meridian. More precisely, the invention proposes to limit, on one side of the meridian, the difference between a maximum value of the cylinder and a minimum value of the cylinder, measured on all the segments. This difference is advantageously smaller than, or equal to the product k * A resulting from the multiplication of the addition of power A by a constant k; k has, for example, a value of 0.1, and the product k * A is 0.30 diopters in the case of a power addition lens of 3 diopters.

These limits of constraint, towards the meridian, variations in the cylinder when the gaze of spectacle wearers is in motion from the region of vision close to the intermediate vision region, in other words when the wearer of glasses is looking at a point in the space of the object at the distance of which varies between 50 and 33 cm by a prescription of power addition glasses of 3 diopters. This coercion improves the user's comfort in dynamic vision; and minimizes deformation as perceived by the spectacle wearer. FIGURE 2 shows the measurements of the cylinder in the lines shown in FIGURE 1, for a lens according to the invention; the horizontal axis represents the coordinates of the x-axis graduated in mm and the vertical axis, the cylinder expressed in diopters. FIGURE 2, shows, for each of the segments in a straight line in FIGURE 1, the value of the cylinder; This is reduced to the minimum on the meridian where it has a value of zero or practically zero. It increases on each side of the meridian. The distance of 20 mm on each side of the meridian on which the segments in FIGURE 1 that extend are also shown. The coordinate of the X axis, Xm represents the average value of the coordinate of the x-axis of the meridian in the scale of the coordinates of the y-axis between -7 and -14 mm, which, for the lens shown in the drawings, is 3.92 mm. FIGURE 2 additionally shows, on the temporary side, the maximum value of the cylinder that is marked max_t on FIGURE 2.

Here, its value is 3.07 diopters and is reached on the segment in a straight line with the y axis coordinate, y = -7; the minimum value of the cylinder on the temporary side marked min_t in FIGURE 2, is equal to 2.80 diopters, is reached on the segment in a straight line that has a Y axis coordinate of y = -7; the difference, 3.07 -2.80 between these two values is 0.282 diopters; as proposed by the invention, this is less than, or equal to 0.30 diopters, in other words in the product k * A, with k = 0.1 and A = 3 diopters. On the nasal side, the maximum value, max_n, of the cylinder is 3.12 diopters and is reached on the segment in a straight line of the y-axis coordinate, y = -7 mm. The minimum value, min_n of the cylinder reached on the segment in a straight line of the y-axis coordinate, y = -7mm and is equal to 2.90 diopters. As proposed by the invention, the difference between these two values, which is 0.22, is less than or equal to 0.30 diopters, in other words the product k * A, with k = 0.1 and A = 3 diopters in the case of our example. The invention also proposes to consider the difference between the maximum value ct of the temporary side of the cylinder and the maximum value cn of the cylinder of the nasal side and more precisely, to consider the absolute value |? C | of the difference between these two values. In the example of FIGURE 2, the maximum value of the nasal-side cylinder is 3.12 diopters, and the maximum value of the temporary side cylinder is 3.07 diopters; the difference between these two values is 0.05 diopters; the difference between these two values is 0.05 diopters and consequently they are inferior or mainly equal to the value of 0.30 diopters and even the preferred value is 0.10 diopters. FIGURE 3 is a diagram similar to that in FIGURE 2 but without several articles in the text. FIGURE 4 shows, by way of comparison, a diagram similar to that of FIGURE 3 for a prior art lens having the same power addition of 3 diopters; the comparison of FIGURES 3 and 4 shows that in the case of the lens of the prior art, the difference between the minimum and maximum cylinder values on each side of the meridian is greater than 0.30 diopters. On the temporary side, this difference is 0.67 in the lens of the prior art of FIGURE 4. On the nasal side, this difference is 0.36 for the same lens. The difference between the maximum values of the cylinder on both sides of the meridian is 0.24 diopters. FIGURE 5 shows, a graphic form, the sphere measured along the meridian of the lens according to the invention; the vertical axis in FIGURE 5 is graduated in mm and represents the coordinates of the y axis: on the surface of the lens, the horizontal axis is graduated in diopters, with a displacement of 5 diopters. The solid line shows the middle sphere and the dashed lines the values n / R1 and n / R2 the difference of which is given in the cylinder. FIGURE 5 shows that the values n / R1 and n / R2 are substantially identical that the cylinder means on the meridian is substantially at zero. The values of the sphere and the cylinder at the distant vision reference point, with a Y-axis coordinate of 8 mm on the meridian, are, respectively, 5.19 and 0.01 diopters. At the near-vision reference point, the axis coordinate and -14 mm on the meridian, these values are 8.23 and 0.01 diopters. The value of the average sphere in the assembly center, of the y-axis coordinate of 4 mm, is 0.12 diopters. This value only differs slightly from the value of the far-vision reference sphere. The invention consequently ensures that the experienced eyeglass user, when looking horizontally, the power that is closed at the power of the far vision reference point. Preferably, the difference between the sphere at the mounting center and the sphere at the far vision control point is less than, or equal to, 0.25 diopter. This invention consequently ensures that the user can enjoy good vision in the near vision region and in the far vision region together with the wide fields in the near vision region and in the intermediate vision region. The term progression length is used, in a progressive multifocal lens, to express that length, or more exactly the reading on the lens in which the main part of the power addition is achieved. One can consider remarkably, starting from the assembly center, the reading at which the average sphere is increased to a heat which is 85% power addition. In the case of the power addition lens 3 considered here, the main length of progression is defined as the difference between the y-axis coordinate of the far-vision reference point and the y-axis coordinate of the point at which the main wait is of 0.85 * 3 = 2.55 diopters greater than the average sphere at the far vision reference point. In the lens considered here, an average sphere of 5.19 plus 2.55 = 7.74 diopters is achieved at a point on the meridian that has an axis value of -8.55 mm. The length of progression consequently 12.55 mm. The invention proposes that this length of progression is preferably less than or equal to 15.0 mm. Said value ensures that the length of progression on the lens remains low and that the near vision region is sufficiently closed in the far vision region on the lens to assist the wearer of eyeglasses having the head movements formed, upper and lower or vice versa. FIGURE 6 shows the lines of the isosphere for the lens in FIGURE 5; these lines are made by points on the spherical surface that have the same value of the middle sphere. This value is indicated on the lines of FIGURE 6. In FIGURE 5, the lines of the isosphere for the value of the sphere at the far vision reference point, the solid line passing through the vision reference point far, and the lines of the isosphere for the values of 0.50, 1.00, 1.50, 2.00, 2.50 and 3.00 diopters greater than the value of the average sphere at the reference point of far vision that has been shown. The solid line around the reference point of near vision is on the line of the isosphere for 3 diopters above the value of the sphere at the far vision reference point. As shown in FIGURE 6, the groove of the middle sphere on the surface of the lens is advantageously smaller than, or equal to the product k '* A resulting from the multiplication of the power addition a by a constant k' of 0.1 mm "1, that is, in the case of the lens in FIGURE 6, less than, or equal to 0.30 diopters / mm In this context, the slot of the middle sphere is in the norm of the sphere gradient at a given point on the spherical surface, the gradient of the sphere is a vector that has the coordinates (dSIdx, dSIdy) in the frame of reference (x; y), the respective values of the partial derivatives of the sphere being respect to y with respect to y FIGURE 7 shows the isocylinder lines for the lens in FIGURE 5. These lines are defined in a similar way in the isosphere lines of FIGURE 6. The isocylinder line that corresponds to a cylinder value of zero substantially fails in the meridian, also the isocilynd lines rich for 0.50, 1.00, 1.50, 2.00 and 2.50 diopters are shown on FIGURE 7. As shown, and as a result of the presence of a zero cylinder meridian in the middle portion of the lens, this is an existing aspect of two Socilindrical lines for each cylinder value, one on each nasal side and the other on each temporal side. FIGURE 7 also shows that the maximum cylinder value on the lens surface, within a radius of 30 mm, is close to the power addition value, equal to 3 diopters in the example being considered. The maximum value is an aspect of 3.12 diopters on the nasal side, and reaches a point that has the coordinates (x = 15; y = -7). Advantageously, the cylinder value is limited on the surface of the lens by an upper limit which is closed in the power addition and preferably in an upper limit which differs from the power addition by less than or equal to 10%. Said restriction makes it possible to avoid deformations for the lens. As explained before, the isosphere lines of 0.50, or the A / 6 lines in the case of FIGURE 3 for the 3-diopter power addition lens, substantially represents the lower limit of the far vision region. . FIGURE 6 also shows two straight lines that originate from the assembly center and that are substantially tangential in these isosphere lines of 0.50 diopters. The angle between these two lines, on the upper portion of the surface, advantageously is at least 110 °. In the angular sector defined by these two lines, in the upper portion of the lens, the value of the cylinder remains less than or equal to 0.50 diopters; preferably, the value of the sphere is also less than or equal to 0.50 diopters. A value as indicated above for the angle these straight lines made to ensure the presence of a broad field of far vision; forcing larger values of the cylinder to push on the lateral edges of the lens surface. This, particularly in the case of high-power additions, usually additions of power above 2.50 diopters, constitute a good balance between the desired to have a wide region of near vision and the desired to distribute the middle sphere and cylinder so uniformly as possible on the lens surface. The limitation of the lower part of the far vision region with respect to the lines of the isosphere described above. As regards the intermediary and the regions of near vision, the limitation field can be determined in place with respect to the isocillar lines. It is necessary, in these regions, that the cylinder have higher values than in the region of far vision. Additionally, while a power defect can be corrected by accommodating the surface of the cylinder that automatically creates discomfort for the user. Consequently it is preferable, in the near and intermediate vision regions, to refer to the isocylinder lines when they are determined in the width of the field. The A / 2 lines, or the 1.5 diopter lines in the case of the lens considered here, substantially represent the lateral limits of the intermediate vision region just similar to the near vision region. The distance between these isocilyndrical lines consequently represents substantially the width of the near vision region or the width of the intermediate vision region. In the lens considered here, at a value of the y-axis of -14 mm from the near vision reference point, the horizontal distance between the isocilideric lines A / 2, that is, the difference between the coordinates of the x-axis of the two points on the isocilíndricas line A / 2 that have a coordinate of the axis and of - 14 mm equal to the reference point of the near vision, is of 15.5 mm. The invention proposes that this near vision region width, therefore, measured between the isocylinder lines A / 2 at the reading of the near vision reference point, can advantageously be greater than or equal to 15 mm. Said width of the field assures the user that he can have a wide enough field for comfortable closed vision. This width of the field covers notably, a sheet of paper or a book of conventional size. One can also consider the closed cylinder slot at the limit of the near vision region. This cylinder groove is representative of the local variations in the cylinder. If defined, I similarly slot the sphere, by the cylinder gradient standard, to a given point. The fact to maintain such small variations is made possible to help certain deformations in dynamic vision at the edge of the near vision region. In the lens of FIGURE 7, in the reading of the reference point of the near vision region, ay = -14 mm, the cylinder groove on the isocylinder lines A / 2 is 0.38 diopters / mm on a temporary side and 0.38 diopters / mm to one nasal side. Advantageously, the invention proposes that the groove of the cylinder, on the isocylinder lines A / 2 in the reading of the reference point of the near vision region can be less than, or equal to the product k "* A resulting from the multiplication of addition of power A by a constant k ", which has a value of 0.14 mm" 1; for the power addition lens 3 considered here, this corresponds to a limit of 0.42 diopters / mm. By exposing said limit, a dynamic view of users is provided not only in the region of near vision but also on the edges thereof. In the intermediate vision region, the width can be measured between the isocylinder lines A / 2. This width is preferably always greater than 40% of the width of the near vision region at the height of the reference point of the near vision region. In the case of the lens described herein, the width of the intermediate vision between the isocylinder lines A / 2 was reduced to a minimum for an axis coordinate of the order of -4 mm, and then equal to 6.75 mm. This value is above 40% of the 15.5 mm width of the near vision region at the height of the near vision reference point. Now details of various features that make it possible to provide several lenses according to the invention should be given. The surface of the lens is, as it is known by itself, continuous and can continuously be derived three times. For those with experience in the field it is well known that the surface of progressive lenses is obtained by digital optimization using a computer, setting the limiting conditions for a certain number of lens parameters. One or more of the criteria defined above can be used as limiting conditions.

One can advantageously start by defining, each of the lenses in the family, a principal meridian of progression. For this, the teachings of French Patent 2,683,642 refers to that it can be used before. Any other definition of the principal meridian of progression can also be employed by applying the teachings of the invention. The two examples of the meridian should be observed, given with reference to FIGURE 1, and with reference to FIGURES 5-7. Obviously, the present invention is not limited to what has been just described: among other techniques, the spherical surface could be the surface directed towards the lens of the spectacle wearer. Additionally, it has not been insisted, in this description, on the presence of lenses that may be different from one eye to the other. Finally, if this description covers the example of a lens having a power addition of 3, the invention also applies to lenses having other power additions.

Claims (10)

1. CLAIMS 1. A progressive multifocal ophthalmic lens, comprising a spherical surface that has at each point thereof a middle sphere and a cylinder, and which comprises a far vision region with a reference point (CL), a region of near vision with a reference point (CP), an intermediate vision region, a main meridian of progression passing through the three regions, and a mounting center (CM), characterized in that: - the addition of power A, define as the difference in the average sphere between the reference point of the near vision region and the reference point of the far vision region is greater than, or equal to 2.50 diopters, - a difference between the middle sphere in the center of assembly and the middle sphere at the reference point of the far vision region is less than or equal to 0.25 diopters; - the far-vision region includes at least one angular sector with its vertex at the center of assembly and a central angle of 110 °, within which the values of the sphere and the cylinder are less than or equal to 0.50. diopters; - in a region of the anterior lens, the near vision reference point, and which substantially extends to the center of the intermediate vision region: - the differences between the values of the maximum cylinder over a distance of 20 mm on both sides of the meridian have an absolute value less than, or equal to 0.30 diopters; and - on each side of the meridian, an absolute value of the difference between the maximum and minimum values of the cylinder that is less than, or equal to the product k * A obtained by multiplying the power addition by a constant k having a value of 0.10. The lens according to claim 1, characterized in that the region of the front lens of the near vision reference point extends over 7 mm, below a horizontal line located 11 mm below the mounting center. The lens according to claim 1, 2 or 3, characterized in that the far vision region has a lower limit in the upper portion of the lens formed by the lines of the isosphere A / 6 where A is the addition of power. The lens according to claim 1, 2 or 3, characterized by a measured length of progression of less than or equal to 15 mm, the length of progression being defined as the height difference between the mounting center and a point on the meridian that has the value of the sphere of 85% of the power addition greater than the sphere of the far vision reference point. 5. The lens according to one of the claims 1-4, characterized in that a norm of the sphere gradient at each point on a surface thereof is less than, or equal to the product k '* A resulting from the multiplication of power addition A by a constant k 'of value 0.1 mm "1. The lens according to one of claims 1-5, characterized in that a higher value of the cylinder does not exceed the addition of power by more than 10%. The lens according to one of the claims 1-6, characterized in that a standard of the cylinder gradient on the isocylinder lines representing half the value of the lens power addition, in the reading of the reference point of closed vision is less than, or equal to, the product k "* A resulting from the multiplication of power addition A by a constant k" having the value of 0.14 mm "1. The lens according to one of claims 1-7, characterized in that a distance between the lines of the isocylinder that represent half of the power addition of the lens to the near vision reference point is equal to, or greater than 15 mm. The lens according to one of claims 1 to 8, characterized in that, the intermediate vision region, a distance between the isocylinder lines that represent half of the lens power addition., at each height, is greater than, or equal to, 40% of the distance between the isocylinder lines that represent half of the lens power addition at the height of the near vision reference point. The lens according to one of claims 1 to 9, characterized in that, in the region of the lens above the near vision reference point, an absolute value of the difference between the maximum value for the cylinder over the distance 20 mm on both sides of the meridian is less than or equal to 0.10 diopters.