MXPA00003343A - Ophthalmic lens - Google Patents

Abstract

A novel ophthalmic lens is provided. The lens includes an astigmatism subtracting surface that removes unwanted astigmatism caused by other elements of the lens.

Description

OPHTHALMIC LENSES FIELD OF THE INVENTION This invention relates to the correction of astigmatism errors in ophthalmic lenses. More specifically it relates to the correction of such errors in eyeglass lenses.

BACKGROUND OF THE INVENTION One of the problems encountered by lens designers is astigmatic error. This refers to astigmatic errors caused by the ophthalmic lenses themselves, contrary to an astigmatism that exists as part of an uncorrected vision of a patient. Astigmatic error can be found in almost any ophthalmic lens, including lenses for a single type of vision used to correct myopia. It is a particularly significant problem in multifocal lenses, including progressive addition lenses (PAL), which are a special case of such lenses. Progressive addition lenses to correct presbyopia have been the subject of extensive research and development over the past five decades, as reported in the patent literature. All optical materials for progressive lenses consist of two refractive surfaces. The anterior surface contains a non-spherical shape that provides the different regions of magnification, and the upper surface is either a pure sphere or a toric surface that provides the base magnification or provides the base magnification and correction of the user's astigmatism respectively. The geometry of the frontal surface is optimized to minimize unwanted astigmatism and other aberrations, to provide a first optical zone with the minimum of astigmatic aberrations to see distant objects, a second optical zone with a higher spherical increase to see objects close, and a third optical zone that connects the first two zones, of variable spherical increase to provide intermediate vision. In a previous design, shown in the patent E.U.A. No. 2,878,721, the unwanted astigmatism was disseminated through the total optical material, thereby reducing the maximum astigmatism. But the intermediate connection zone does not provide a smooth transition in the refractive increase, and the residual unwanted astigmatism in the near and distant vision zones remains unacceptably high. In the most recent progressive designs, the zones designed for distance vision and near vision remain spherical, while at the same time the unwanted astigmatism, which inevitably arises when connecting the remote vision and near vision zones with a continuous surface soft, it is (1) disseminated through an area as large as that of the optical material as much as possible in order to reduce astigmatism, (2) it is spread more evenly. See for example, patents E.U.A. We 4,056,311 and 4,315,673. In all cases, the posterior surface of the optical material is left spherical or toroidal, and is not designed to provide correction of the unwanted astigmatic error caused by a progressive lens surface on its own. As a result, even after fifty years of research and development, progressive addition lenses of the most advanced technique have numerous limitations, including high levels of peripheral astigmatism, significant peripheral refractive errors, narrow channel width, as well as insufficient widths of the zones of near and distance vision increase, limiting the peripheral vision. The design of optical materials for ophthalmic lenses avoids the optimization of the posterior surface, because the conventional method of manufacturing optical materials for progressive addition lenses prevents the development and specification of complex geometries for the posterior surface, as will become clear in the next section. In effect, the non-spherical correction provided to minimize the unwanted astigmatism inherent in lenses of a single type of vision, also it is confined to the front surface of the optical material. All these methods for dealing with unwanted astigmatic errors involve managing the error by distributing it in larger or more distant areas of the lenses or other such techniques. None really eliminates the astigmatic error. Previously known methods of manufacturing optical materials for ophthalmic lenses could have prevented designers of optical materials from providing non-spherical corrections to the back surface of the optical material, and also that they propose multilayer optical materials that incorporate intermediate or "hidden" surfaces. The method of manufacturing optical ophthalmic materials begins with the emptying of a semi-finished preform from an optical material incorporating the front (anterior) surface of the optical material in finished form, often coated with a scratch-resistant layer. This semi-finished preform is subsequently cut to size and polished at regional milling laboratories, or occasionally at retail locations to adjust a particular prescription. In this way the posterior surface becomes spherical or toroidal, depending on the prescription, adjusting the axis of correction of cylinder placing the main meridian that passes through the optical center of the area of remote augmentation and the optical center of the area of close increase in proper angular orientation by reference to marks on the mounting fixture used to hold the preform during the machining process. For the most part, the carving and polishing equipment used in finishing laboratories only allows to provide spherical or toroidal curves, therefore for optical materials to be widely available, the designer of optical materials can not rely on the rear surface be non-spherical or corrective. There is therefore a need to develop designs for optical materials for ophthalmic lenses in which the posterior surface of the optical material and / or intermediate surfaces are designed to eliminate as much as possible the undesired astigmatism induced by the continuous change Ü É », ^ of the radius of curvature of the front surface required for intermediate vision, and to provide methods for its fabrication.

DETAILED DESCRIPTION OF THE INVENTION 5 The present invention provides a lens with a front surface that provides or contributes to the desired visual correction (such as a PAL lens). The anterior surface can be designed to achieve this correction without taking into account any possible astigmatic error that can be produced. Lenses in accordance with this invention have a back surface that is configured so that the optical properties of the lens reduce these astigmatic errors. The term "reduce" encompasses significant reductions in unwanted astigmatism, not just the complete elimination of astigmatism. 15 If the lens has a homogeneous composition, this astigmatism reducing surface is the posterior surface of the lens. In a multi-layered lens, the astigmatism reducing surface may be the posterior surface or one of the intermediate surfaces that are posterior to the anterior surface of the lens. A design as such implies the incorporation of one or more intermediate surfaces, separating each surface to two optical materials with different refractive index. The higher the difference in the refractive indices on both sides of a surface, the more useful will be its role as a design element to minimize the unwanted astigmatism. The design may also be associated with the use of a non-spherical toroidal posterior surface designed to reduce peripheral astigmatism introduced by the anterior surface, without using any intermediate layer, or two different optical materials. The present invention can be used in lenses having an astigmatism producing surface. The shape of the astigmatism reducing surface will necessarily be dictated by the shape of the astigmatism producing surface. There are too many surfaces that produce astigmatism and therefore a large number of reducing surfaces. astigmatism. No astigmatism reducing surface alone encompasses the full range of this invention. Furthermore, although this invention is described with reference to an anterior astigmatism producing surface, and a posterior surface reducing astigmatism, it easily encompasses other such arrangements. Those skilled in the art of lens designs follow a set of generally known procedures for designing a lens surface having the desired properties. These are generally applicable to the design of an astigmatism reducing surface that will be used in the present invention. See for example, "Geometrical Optics and Optical Design," P. Pouroulis and J. MacDonald, Oxford Univ. Press (1997). An application of these methods can be described as follows. The design procedure starts with the description three-dimensional front surface, the progressive surface. The front surface can be described in the form of a camber frame (the x, y, z coordinates of a large number of points chosen to provide a high level of optical resolution, typically 1000 to 10,000 dots in a 80 mm projection of " bowl diameter "). Alternatively, the front surface can be described as a bicubic slot surface which is suitable for describing arbitrary shapes or alternatively by a differentiable analytical expression, such as those to be presented: the radially symmetric polynomial, the two-dimensional polynomials or the imperfect anamorphic sphere. The design procedure continues by choosing a type of surface for the back surface and if present, and for the intermediate surface. These surfaces are described or assigned parameters by a set of coefficients which, when varied, generate a family of surfaces. The desired lens performance is specified: this includes but is not necessarily limited to specifying the desired magnification and astigmatism as a function of the field angles, the desired image quality and the construction parameters such as the minimum thickness of the optical materials. A quality function is defined for the lens which generally includes non-negative terms which calculate how close the lens is to the desired lens performance. The quality function typically includes summations of RMS (average root square) spot sizes for images in various fields and wavelengths or similar image measurements. The quality function may also include functions of aberration coefficients (such as astigmatism) and functions of the lens construction parameters and other desired constraints on the geometry and performance of the lens. 5 The next step in the design procedure is to select an appropriate starting point design to send it to an optimization program. An optimization routine will take a prescription of optical system and will vary a list of coefficients to try to minimize the quality function to give a well-corrected lens in terms of aberrations which meets the specifications. If the final quality function is small enough, and the designer determines that the resulting lens performance is close enough to the specifications, then the lens design procedure is completed and the final lens is specified. However, an optimization program will only produce good final lens performance for a limited range of input surface coefficients. The definitive design of the lens is achieved by testing various combinations of coefficients and understanding their individual effects. This procedure is guided by the experience of the lens designer and careful observation. 20 The functions used to represent surfaces are either rotationally symmetric functions, including imperfect spheres of the 20th order, or non-rotationally symmetric functions which include toroids, non-spherical toroids or imperfect anamorphic spheres. The The posterior surface may also be non-spherical, toroidly non-spherical, or anamorphically non-spherical to provide uniform additional astigmatic compensation and to accommodate the intrinsic astigmatism of the user. The selection of an appropriate surface type for the posterior astigmatism corrective surface 5, and an intermediate surface if used, depends on the type of progressive surface on the frontal surface. Three such types of astigmatism corrective surfaces are presented, (1) a radially asymmetric imperfect sphere, (2) a dimensional polynomial, and (3) an imperfect anamorphic sphere. The radially symmetric imperfect sphere is usually the best choice to correct the astigmatism of progressive surfaces with radially symmetric increase prescriptions. For lens with a progressive "channel" the dimensional polynomial or imperfect anamorphic sphere are appropriate and experimentation will determine what kind of surface yields a superior correction of astigmatism. Besides, the The posterior surface, and possibly the intermediate surface, will be composed of several sectors with different surface equations within each sector. Therefore, a surface area of the lens is described by an equation different from that of the other areas. The non-sequential trajectory tracing technique is then used to plot the trajectory of a surface described by various sectors. When it is desired that the surface of the lens be smooth and continuously differentiable, the lens designer must ensure that the bulges and slopes of the surface are properly matched along all the boundaries of sectors by the . ^^^^^. ^. ^^^^ a ^. ^ ... more appropriate choice of coefficients in each sector. A rotationally symmetric non-spherical surface can be represented by an equation of the general form: h2c Z (h) = + A 3 + A? h4 + A? 5 + ... + A h "l + (l - (\ + k) c ¿2hí ¿2) 2 + A, h In this equation, z is the bump height of the surface, h is the distance from the mechanical axis of the surface, c is the base curvature, k is the conical constant, and the An values are the rotationally symmetric polynomial coefficients. One such particularly useful equation is the shape of the 20th order of the equation, shown below: Z (h) = ch2. { 1 + (1 - [1 + k] c2h2) 1/2} + Ah4 + Bh6 + Ch8 + Dh10 + Eh 2 + Fh14 + Gh16 + 15 Hh18 + Jh20. where: z is the camber in the z direction. c is the radius of curvature at the pole of the surface, k is the conical constant. 20 h2 = x2 + y2 An anamorphic surface is a non-spherical surface with bilateral symmetry in both x and y but not necessarily with symmetry aa &fcjs «- ij i rotational. A surface as such is described by an imperfect anamorphic sphere equation. An equation as such is of the general form: z (x, y) = x2cux + v2cuv 1 + (1 - (1 + kx) x2cux2- (1 + ky) y2cuy2) v2 + AR. { (1 -AP) x2 + (1 + AP) f + BR. { . { ? -BP) ^. { + Bp) y2} 2 + CR. { -CP) x2 + (1 + CP) y2} 3 + DR. { (1-DP) x2 + (1 + DP) /} 4 In this equation, the surface sag, z, is calculated at each point, (x, y), with cux defined as the base curvature in the x, k direction and defined as the conic constant in the x direction, which is defined as the base curvature in the y direction, and ky defined as the conical constant in the y direction. The terms AR, BR, CR, DR, and any of the higher R terms define the rotationally symmetric coefficients of the higher order non-spherical terms, and the terms AP, BP, CP, DP, and any of the higher P terms define the non-rotationally symmetric coefficients for the higher-order non-spherical terms.

A special case of an equation as such is the form of the order of the equation, shown below: . ^ Jtf JL ** * ^^ - ^^ z = (cxx2 + cyy2) / (1 + { 1 - [1 + k?] Cx2x2- [1 + ky] cy2y2.}. / 2) + AR [(1-AP) x2 + (1 + AP) y2] í BR [(1 -BP) x2 + (1 + BP) y2] 3 + CR [(1 -CP) x2 + (1 + CP) y2] 4 + DR [(1-DP) x2 + (1 + DP) y2] 5 in which: cx, Cy are the curvatures in x and y kx, ky are the conic coefficients in x and y AR, BR, CR and DR are the rotationally symmetric portions of the deformations of? , 62, 8- and 10s the order of the cone and AP, BP, CP, DP represent the non-rotationally symmetric portions of the deformations of 4-, 6-, 8Q and 10s the order of the cone. Finally, a two-dimensional polynomial equation can be used. This has the following form: Z (x, y) = A0 + Awx + A0? Y + A3oX3 + A2? X2y + A 12xy2 + A03y3 = S? Anm ?? ym n m Again, the sag height, z, is calculated at each point (x, y) of the surface. The values of the Anm coefficients determine the figure of the surface. It can be shown that a surface generated by any of the The non-spherical equation rotationally symmetric or the non-spherical anamorphic equation can be represented exactly by the polynomial equation given sufficient terms for the polynomial equation. The order of a term is equal to m + n. It is well understood by those skilled in the art that surfaces can be described in many functional forms or nearly equivalent equations. Such alternative surface equations may be exactly equal to one another or differ by such a small amount that the optical performance of such surfaces could not be distinguished within the tolerances of the human eye. Therefore, a radially symmetrical non-spherical surface within a specified aperture can be very well approximated by a two-dimensional Fourier series, a sum of Zernike polynomials, by a set of bicubic groove surfaces; or through many other functions. Similarly, the imperfect anamorphic sphere can also be approximated very closely by these and other functions. The purpose of the astigmatism correction surface applied to the posterior or intermediate surface of a progressive lens is to reduce the unwanted, noticeable astigmatism of the progressive surface. In addition, the eye is sensitive to changes of approximately 0.2 diopters of magnification and astigmatism in an ophthalmic lens. Therefore if a surface is specified with a shape which closely conforms to a non-spherical anamorphic surface in such a way that the increase is the same within 0. 2 diopters over all 3 mm openings to this non-spherical anamorphic surface, and the magnitude of astigmatism and orientation are the same within 0.2 diopters and 15 degrees over all 3 mm openings to this same imperfect anamorphic sphere, then the surface 5 will be understood as being quite similar to the anamorphic non-spherical surface as equivalent for purposes of the present invention. If a surface has an increase within 0.2 diopters, a magnitude of astigmatism within 0.2 diopters and an orientation of astigmatism that is within 15 degrees of a radially symmetric polynomial over all 3 mm openings within the opening of the surface used in the ophthalmic lens, then the specified surface and the radially symmetric polynomial are equivalent for purposes of the present invention. Similar tolerances apply to lenses that use other surface forms, such as the two-dimensional polynomial surface, to reduce astigmatism. As mentioned above, one embodiment of this invention is an optical ophthalmic material with a front surface comprising a zone of increased distance, an area of increased aggregation and a third optical zone in which there is a progression of increase, a layer intermediate which is an anamorphic spherical surface designed to reduce the peripheral astigmatism of the anterior surface, and a posterior surface which is a non-spherical surface designed to provide toric correction required by a specific prescription and to further minimize the residual astigmatism of the general design.

A second preferred embodiment of this invention is an ophthalmic optic material with a front surface comprising a distance enhancing zone, an aggregate increase zone and a third zone in which there is an increase progression, and a back surface which is a non-spherical surface designed to reduce the peripheral astigmatism of the frontal surface. The refractive index of the material with which the lenses are manufactured is preferably above 1.50. The manufacture of ophthalmic lenses of the design described in the present invention begins with the manufacture of a lens preform, which consists of a front surface of specific geometry and a back surface whose geometry is that specified for the intermediate layer. The optical material may be a melt processable thermoplastic, such as a bisphenol-A polycarbonate, or a thermosetting resin, such as diethylene glycol bisalkyl carbonate. The material can be injection molded or compacted, or cast molded using thermal or photochemical polymerization initiation modes, or a combination thereof. Preferably, the optical material has a refractive index greater than 1.57. In a preferred manufacturing process, such as the forming, the optical preform is designed to provide the exact distance and the correction of aggregate increase for a particular prescription, ie, the preform can either be molded according to the prescription, or this it can be elaborated in advance, in quantity, covering a wide range of distance combinations and aggregate increases. For example, the number of different types of Feiperfused optical preform to cover a prescription range of + 6.00D to -6.00D and an aggregate increase range of 1.00D to 3.00D is 468. The preform may be coated in the anterior surface, (convex) with any number of optical coatings, such as a scratch resistant coating, an anti-reflective coating, photochromic or hydrophobic coating, such coatings being applied by a thermal or photochemical curing process. Then, the preform is placed with its concave surface in juxtaposition to an O-mold with a molding surface designed to provide a non-spherical toroidal optical quality surface after emptying, the space between the two surfaces (the back surface of the preform and the molding surface of the mold) is filled with a polymerizable resin, then the resin is polymerized to form a rigid adherent layer attached to the preform, and permanently adhered thereto. The angular orientation between the main meridian on the convex surface of the preform and the toric axis of the mold is carefully adjusted before starting the polymerization of the resin, so that the toric axis is formed in the desired orientation. In the preferred manufacturing method, this layer does not provide any spherical increase, but provides the toric correction necessary for a particular prescription. However, it should be noted that it is possible to add both a spherical and toric increase by emptying the addition surface to the concave surface.

The refractive index of the cast layer may be adjusted to be significantly less than that of the material constituting the preform, in which case, the intermediate surface may be designed to provide the optical benefit. In a second method the voided layer can be designed to have a refractive index closely equal to the refractive index of the preform, in which case, the intermediate surface does not provide optical benefit. It should be noted that both design methods have their advantages and disadvantages, and may be appropriate for use at different prescription intervals. The first method, which emphasizes The contribution of the intermediate layer leads to a more complete neutralization of the peripheral astigmatism, but produces a thicker lens at the edges, since the toric correction is provided by the relatively low refractive index material. Such a method could not be appropriate for prescriptions above -3.00D of toric correction. The first The method may be appropriate for low to intermediate toric gain corrections, and especially for prescriptions specifying high aggregate increases since the magnitude of peripheral astigmatism increases with the aggregate increase. The second method may also be appropriate for lenses provided for non-toric prescriptions, which constitute approximately 20% of all prescriptions. Any of the design methods described above as well as any of the manufacturing methods outlined above can be used to provide a superior lens of a single type of vision wherein both surfaces and, where desired, an intermediate layer, can be used to form an aberration-free optical material, in which the usable optical zone is larger than is currently available. The following non-limiting example may be used to illustrate this invention.

EXAMPLE A progressive addition surface was designed such as that shown in Figure 1, which is characterized by a zone of remote augmentation (11), an intermediate zone (12), and an area of added increase. (13) The areas of aggregate and distance increase are spherical, while the zone of intermediate increase is non-spherical. The distance gain was selected to be 0.0D, while the aggregate increase was 3.00D. The diameter of the zone of the aggregate increase was 26.0 mm, while the width of the ring was maintained at 15.0 mm. The refractive index of the material from which the preform could be manufactured was considered to be 1.59. The back surface of the perfoma that could constitute the intermediate layer in the finished design was designed to be a rotationally symmetric imperfect sphere with higher order terms. This design shows the properties of a circularly symmetric progressive magnifying lens with an intermediate corrective surface, m ^ u ^ áM? í m Using an independent equation for each sector of the lens surface to represent the entire surface. The materials used in this design have a refractive index of 1595 for the material of the anterior surface and 1495 for the material of the posterior surface. Since the lens itself can be described as having a distance portion, a progressive portion and an aggregate portion, it is natural to allow each of these portions to be described by its own mathematical function, and then to unite these equations together in their limits to form an individual surface without union marks. This method can produce more complex surface shapes which can more easily correct the residual astigmatism in these lenses. The design is for a distant region of zero diopter increase with a region of progressive magnification which changes the increase linearly with the radius from zero to three diopters from 30 mm in diameter to 15 mm in diameter, then it has a constant increase of three diopters for the central diameter of 15 mm of the aggregate region. Therefore, there are three sectors defined by this prescription: the zero increase sector, the progressive sector and the constant addition sector. Each sector in this particular design has three surfaces associated with it. There is an interior surface, the intermediate surface and the back surface. In this design, the surface area of zero magnification are all purely rotationally symmetrical spheres with curvatures of 0.018397 mm-1, 0.01843 mm-1 and 0.018519? Mm-1 for the inner surface, intermediate and subsequent, respectively. To model the region of progressive increase, a rotationally symmetric function was selected since the addition zone has rotational symmetry. Because the addition zone is in the lower half of the lens, a non-spherical equation of 202 non-centralized order was selected and tilted for both the anterior and intermediate surfaces, but only the terms of uniform order are used. The parameters of the previous surface are: c = 0.023254 mrt? 1 0 k = 4.037618 A4 = -0138653x10"5 mm" 3 A6 = -0.113202x10"5 mm-5 A8 = 0.326801x10" 5 mm-7 A10 = -0 -161103x10"5 mm" 9 5 A12 = -0.172200X10"5 mrt? 11 A14 = -0.116407x10" 5 mm "13 A16 = 0.140865x10" 5 mrt? 15 A18 = 0.161848x10"5 mm-17 A20 = -0.38862 x10"5 mrt? 19 0 with the origin at the offset coordinate -15 mm in the transverse direction and, 1.7 mm in the longitudinal direction ze inclined 15.701 degrees. The parameters for the intermediate surface are: c = 584.795322 mm-1 m¡ * k = -40.770451 t »A4 = 0.177311x10" 5 mm "3 A6 = -0100372x10" 5 mm "5 A8 = 0.186359x10" 5 mm "7 all others An = 0.0 with the origin to the coordinated displaced - 15 mm in the transverse direction and, 0.695 mm in the longitudinal direction ze inclined 15.701 degrees. The parameters for the back surface are: c = 0.018519 mm "1 k = An = 0.0 These equations are valid for the surface shape in the ring of internal diameter 30 mm and outer diameter 15 mm, centered 15 mm below the mechanical center of the lenses and inclined 15701. To model the region of constant added magnification, rotationally symmetric functions were again selected since the addition zone has rotational symmetry, because the zone of addition is in the lower half of the lens and is a constant increase, a decentralized and inclined sphere was used for the anterior, intermediate and posterior surfaces with curvatures of 0.023178 mm "1, 0.018431 mm" 1 and 0.018519 mm "1 respectively. Therefore, to describe each sector of a lens surface, three independent equations were used, and since there are three surfaces, 9 sets of parameters are required to specify the full prescription of the lens. Therefore, to describe each sector of the lens surface, three independent equations were used, and because there are three surfaces, 9 sets of parameters were required to specify the full prescription of the lens. The lenses according to this invention have unique advantages. The progressive addition ophthalmic lenses according to this invention can be free from astigmatism to a degree that could not previously be achieved. The unwanted astigmatic error in such lenses can easily be reduced to 60% or 50% of the nominal aggregate magnification of the lenses. It is even possible, as shown above, to reduce unwanted astigmatism until it is within the range of 40% to 20% of the nominal added magnification of the lenses. This invention will be defined below by the following claims. ti ^ á ^ i ¡m ^^^ g ^ _j

Claims (24)

NOVELTY OF THE INVENTION CLAIMS

1. - An ophthalmic lens comprising (1) a first surface that causes unwanted astigmatism (2) a second surface that includes at least a portion that is configured to reduce the unwanted astigmatism caused by the first surface, characterized in that the shape of the the portion of surface that reduces unwanted astigmatism is an imperfect anamorphic sphere, an imperfect radially symmetric sphere, or is defined by a two-dimensional polynomial.

2. A lens according to claim 1, further characterized in that the lens is a homogeneous lens having an aggregate nominal increase and the unwanted astigmatism caused by the first surface is reduced to 60% of the nominal added magnification of the lens.

3. The lens according to claim 2, further characterized in that the first surface is the anterior surface and the second surface is the posterior surface.

4. The lens according to claim 3, further characterized in that the front surface is that of a progressive addition lens.

5. The lens according to claim 1, further characterized in that the first surface is the front surface and the second surface is the rear surface.

6. - An Information lens with claim 5, further characterized in that the front surface is that of a progressive addition lens.

7. A lens according to claim 6, further characterized in that the anterior surface comprises a progressive channel and the shape of the surface portion that reduces unwanted astigmatism is an imperfect anamorphic sphere.

8. A lens according to claim 7, further characterized in that the imperfect anamorphic sphere is defined by an equation in the following way: z (x, y) = x2cux + v2cuv 1 + (1 - (1 + kx) x cwx2- (1 + ky) y2cu /) V2 +? ? { (1 -AP)) C + + Bpy2} 2 + CR. { (1 -CP) x2 + (1 + CP) y2} 3 + DR. { (1-DP) x2 + (1 + DP)} 4 where s is the surface sag, cux is the base curvature in the direction in the x direction, kx is the conical constant in the x direction, cuy is the base curvature in the y direction, and ky is the conical constant in the direction y, and the terms AR, BR, CR, DR, and any of the higher R terms define the rotationally symmetric coefficients for the higher order non-spherical terms, and the terms AP, BP, CP, DP, and any of the terms P The upper ones define the non-rotationally symmetric coefficients for the non-spherical terms of

9. A lens according to claim 8, further characterized in that the equation is of the order or of the lower order.

10. A lens according to claim 6, further characterized in that the progressive surface comprises a radially symmetric increase prescription and the shape of the surface portion that reduces unwanted astigmatism is an imperfect sphere. radially symmetrical

11. A lens according to claim 10, further characterized in that the radially symmetric imperfect sphere is defined by an equation in the following way: Z (h) = + Alh + A2h3 + A4h4 + A5h5 + ... + Anh "l + (l - (l + k) c¿h¿) where z is the bump height of the surface, h is the distance from the mechanical axis of the surface, c is the base curvature, k is the conical constant, and each of the numbers Ah are the rotationally symmetric polynomial coefficients .

12. A lens according to claim 11, further characterized in that the equation is of the order 20s or of a lower order.

13. A lens according to claim 6, further characterized in that the progressive surface comprises a channel "» - ^ < ™ MayMa a ^ MM »att» ... ^ i **** »-" i "^^^ 'progressive and the shape of the surface portion that reduces astigmatism is defined by a polynomial Two-dimensional as follows: Z (x, y) = A00 + Awx + A0? Y + A3oX3 + A2? X2y + A pxZ + A8y n m where z is the bump height of the surface and each Anm is a coefficient.

14. An ophthalmic lens comprising (1) at least two layers, each of which has a different refractive index, (2) a front surface, (3) a back surface and (4) an interface surface between the layers, characterized in that at least one of the anterior surface, the posterior surface and the interface surface causes unwanted astigmatism and at least one of the other surfaces reduces unwanted astigmatism characterized by the shape of the surface that reduces Unwanted astigmatism is an imperfect anamorphic sphere, an imperfect radially symmetric sphere, or is defined by a two-dimensional polynomial.

15. A lens according to claim 14, further characterized in that the astigmatism is caused by the interface surface.

16. A lens according to claim 14, further characterized in that the astigmatism is caused by the anterior surface.

17. A lens according to claim 14, further characterized in that the front surface is that of a progressive surface.

18. A lens according to claim 17, further characterized in that the shape of the surface portion that reduces the astigmatism is defined by a two-dimensional polynomial of the following form: (x, y) = A0 + Awx + Ao + A20x2 + A 1 ixy + Ao ^ + A30x3 + A21x2y + A 12x + AQ3y3 = S? Anmxnym n m where z is the bump height of the surface and each Anm is a coefficient.

19. A lens according to claim 17, further characterized in that the progressive surface comprises a channel ^ ¡^^^^ ¡^ ... ^^^^^^^^ ^ ^ 3 ^^^^^! ^ ^ ^ ^ S & ^ ¿^^^ 9? ^ ¡^^ progressive and the shape of the surface that reduces unwanted astigmatism is an imperfect anamorphic sphere.

20. A lens according to claim 19, further characterized in that the imperfect anamorphic sphere is defined by an equation in the following way: z (x, y) = x2cux + v2cuv 1 + (1 - (1 + kx) x2cux2- (+ ky) 2cu /) 2 + AR. { (1 -AP) x2 + (1 + AP) y2? + BR. { . { -BPx2 +. { + Bp /} 2 + CR. { ('\ -CP) x2 + (1 + CP) y2} 3 + DR. { (1-DP) x2 + (1 + DP) Z} 4 where s is the camber of the surface, where is the base curvature in the x direction, kx is the conical constant in the x direction, which is the base curvature in the y direction, and ky is the conical constant in the y direction , and the terms AR, BR, CR, DR and any of the higher R terms define the rotationally symmetric coefficients for the higher order non-spherical terms, and the terms AP, BP, CP, DP and any of the higher P terms define the non-rotationally symmetric coefficients for the higher-order non-spherical terms.

21. A lens according to claim 20, further characterized in that the equation is of the order or of the lower order.

22. A lens according to claim 19, further characterized in that the progressive surface comprises a prescription of radially symmetric magnification and the shape of the surface that reduces unwanted astigmatism is a radially symmetric imperfect sphere.

23. A lens according to claim 22, further characterized in that the radially symmetric imperfect sphere is defined by an equation in the following manner: Z (h) = h C,,, ,, + A, h + A2h3 + A.h4 + A5h5 + ... + A h "1 'i + a - a + A c2 /, 2) 1'2 - 2 4 5 10 where z is the bump height of the surface, h is the distance from the mechanical axis of the surface, c is the base curvature, k is the conical constant, and each of the numbers Ah is the rotationally symmetric polynomial coefficients 15

24. A lens according to claim 23, further characterized in that the equation is of the order 20Q or of the lower order.