AU650617B2 - Progressive addition spectacle lens - Google Patents

Description

FORM S F Ref: 114243 COMMONWEALTH OF AUSTRALIA PATENTS ACT 1952 COMPLETE SPECIFICATION

(ORIGINAL)

FOR OFFICE USE: Class Int Class Complete Specification Lodged: Accepted: Published: Priority: Related Art: Name and Address of Applicant: siti Address for Service: American Optical Corporation 14 Mechanic Street Southbridge Massachusetts 01550 UNITED STATES OF AMERICA Spruson Ferguson, Patent Attorneys Level 33 St Martins Tower, 31 Market Street Sydney, New South Wales, 2000, Australia r=JI Complete Specification for the invention entitled: Progressive Addition Spectacle Lens The following statement is a full description of this invention, including the best method of performing it known to me/us 5845/5 ROGRESSIVE ADDIIO SPECTACLE LENS Abstract of the Disclosure: Lenses are presented in occupational, dynamic activity and general purpose configurations, len lenses all being of compatible polar or bipolar progressive power design to form a series of progressive power lenses.

Reference to Related AnlicyAum: This application is a continuation-in-part of my co-pending application, Serial No. 131,987, filed December 10, 1907, which, in turn, was a continuation-in-part of my application Serial No.

10 944,702, filed December 19, 1986, now abandoned.

*logo: 0 Del -2bACKGROUND OF THE INVENTION Field of the Invention This invention relates to spectacle lenses, and, more particularly, to improvements in progressive lenses for the correction of presbyopia.

The subject of this application is occupational and dynamic activity progressive lenses to complement the general purpose lens of my prior application and a system of general purpose, occupational and dynamic activity progressive lenses.

Related Application This is an application for a patent of addition to Australian Patent No. 592484.

SUMMARY OF THE INVENTION There is disclosed herein a progressive power ophthalmic lens comprising a lens body having a progressive power surface with a near portion and a distance port-on, the near portion having a power different than the distance portion, at least one of said near and distance portions having an area of optical stability and a series of contours of successively different constant mean surface powers around a point, the power change in said area of optical stability being imperceptible, a meridian of continuous change of power between said distance portion and said near portion, and the form of the progressive power surface of the lens being effective to distribute surface astigmatism over substantially the entire surface of the lens from the distance portion to the near portion the meridional power law of said lens being effective to provide either an occupational lens having a relatively large and stable near viewing portion and a relatively small distance portion or a dynamic activity lens having a relatively large and stable far viewing portion and a relatively small near view portion.

There is further disclosed herein a series of progressive power lenses, including a general purpose progressive lens, an occupational progressive lens and a dynamic activity progressive lens, each of said lenses comprising a lens body having a progressive power surface with a near portion of relatively high power and a distance portion of relatively lower power, wherein constant power regions of the near portion and the distance portion comprise substantially two spaced points on the progressive power surface of the lens, each of said points being surrounded by an area of optical stability and an area of progressive power, said two spaced points being connected by an umbilic of LF/01251 -3progressive dioptric power, and the surface being shaped to distribute surface astigmatism over essentially the surface of the lens between said two spaced points, the meridional power law of said occupational lens being effective to provide a stable and large near portion relative to the near portion of the general purpose lens and a small distance portion relative to the distance portion of said general purpose lens, and the meridional power law of said dynamic activity lens being effective to provide a stable and large distance portion relative to the near portion of the general purpose lens and a small near portion relative to the near portion of the general purpose lens.

There is further disclosed herein a series of progressive power ophthalmic lens, including a general purpose progressive lens, an occupational progressive lens and a dynamic activity progressive lens, each of said lenses comprising a lens body having a progressive power S 15 surface with a near portion and a distance portion, the near portion having a different power than the distance portion, at least one of said 4near and distance portic.ns having an area of optical stability and a series of contours of successively different constant mean surface powers around a point, the power change in said area of optical stability being imperceptible, a meridian of continuous change of power between said distance portion and said near portion, and the form of the progressive power surface of the lens being effective to distribute surface astigmatism over substantially the entire surface of the lens from the distance portion to the near portion, the meridional power law of said 25 occupational lens being effective to provide a stable and large near Q* *portion relative to the near portion of the general purpose lens and a small distance portion relative to the distance portion of said general purpose lens, and the meridional power law of said dynamic activity lens being effective to provide a stable and large distance portion relative to the near portion of the general purpose lens and a small near portion relative to the near portion of the general purpose lens.

BRIEF DESCRIPTION OF THE DRAHINGS A preferred form of the present invention will now be described by way of example with reference to the accompanying drawings, wherein: RLF/01251 RLF/OI 251 4- Figs. 1A and 1B are views, in vertical elevation and cross section respectively, of a representative progressive power ophthalmic lens of a type known in the prior art; Fig. 2 sl a graphical representation illustrating the evolute of the meridional line of the lens of Figs. 1A and 1B; Fig. 3 is a graphical illustration showing the construction of a progressive surface of the lens of Figs. 1A and 1B; Fig. 4 is a vertical elevational view of the prior art progressive power ophthalmic lens showing various viewing zones thereof and a graphical representation of the associated power law; Figs. SA, 5B and 5C depict, respectively, contours of constant mean surface power, contours of constant surface astigmatism, and an isometric plot of surface astigmatism Scorresponding to the prior art lens of Fig. 4.

Fig. 6 is a vertical elevation view illustrating the location of the poles of the bipolar system of optical power characterizing a representative lens in accordance with the present invention; Figs. 7A and 7B are contour plots demonstrating a geometrical transformation from a prior progressive lens to one representative of the present invention; 25 Fig. 8 is a graphical representation schematically illustrating a development of cylindrical surfaces to satisfy the aims of the present invention; Fig. 9 is a graphical representation depicting the layout of a typical lens constructed according to the present invention and incorporating an eighth-order meridional power law; -43- Figs. 10A, 10B and 10C depict, respectively, contours of constant mean surface power, contours of constant surface astigmatism, and an isometric plot of surface astigmatism corresponding to the typical design of Fig. 9; Fig. 11 is a graphical representation depicting the layout of a typical lens constructed according to the principles of the invention and incorporating a linear meridional power law; Figs. 12A, 12B and 12C depict, respectively, contours of constant mean surface power, contours of constant surface astigmatism, and an isometric plot of surface astigmatism corresponding to the typical design of Fig. 11.

Figs. 13A, 13B and 13C depict, respectively, contours of constant mean surface power, contours of constant surface astigmatism, and an isometric plot of surface astigmatism for a lens according to the invention especially suited to intermediate and near working distances.

Figs. 14A, 14B and 14C depict, respectively, contours of constant mean surface power, contours of constant surface astigmatism, and an isometric plot of surface astigmatism for a lens according to the invention especially suited to dynamic outdoor activity.

DESCRIPTION OF PREFERRED EMBODIMENTS 4 Dipolar progressive power lenses in accordance with the present invention may be made of glass or plastic material having a uniform index of refraction. In the embodiments of the 0 invention described herein, the changing curvatures required for progressive power variation are confined to the convex side of 4* the lens, with the concave side being reserved for perscription grinding in the usual way and the convex side of the lens will hereafter be referred to as the "progressive surface". However, the invention is not limited to lenses having convex progressive surfaces and is applicable equally to lenses having concave progressive surfaces.

X^ N The lens design which comprises the present invention is an s 35A improvement over earlier designs, and for a better understanding Referring to Figs. IA and 1B of the drawings, a prior art lens 10 has a progressive surface 12 which is tangent to a vertical plane 14 at the geometrical center 0 and a second vertical plane 16 passes through the center 0 at right angles to the first vertical plane dividing the lens into two symmetrical halves. The second plane 16 Is called the principal vertical meridian, and Its curve of Intersection is designated M' in Fig. 2 In which the progressive surface Is represented by the meridian line 18.

The functional requirements of a progressive lens dictate that the surface along the meridian line and its partial derivatives, at least through second order and preferably through third order, must be continuous. To provide for progressive power variation, the curvature of the meridian line Increases continuously in a predetermined manner >~..from a minimum value in the upper half of the lens to a *1 maximum value In the lower half. This variation of curvature along the vertical meridian Is called the meridional power law.

The locus of the centers of curvature of the meridian line 18 shown In Fig. 2 comprises a continuous plane curve mm called the evolute of the meridian line. For each point Q of the mezidian line there exists a corresponding point q ,too*:on the evolute. The radius vector qQ connecting two corresponding points q) is perpendicular to the meridian line 0 18 at Q and tangent to the evolute mm' at q.

Fig. 3 illustrates the construction of a representative progressive power lens. The progressive surface Is generated by a circular arc C having a horizontal orientation and a variable radius which passes successively through each point Q of the meridian line 18. Specifically, the gener- 7 ator C through a given point Q is defined as the line of intersection formed between a sphere of radius Qq centered at q and a horizontal plane through Q. Thus, the complete progressive surface may be considered to be generated, or swept out, by the line of intersection C between a sphere of variable radius and a corresponding horizontal plane of variable height. In consequence of this construction, the principal curvatures at each point Q of the meridian line are equal, with the result that the surface is free of as- .tigmatism at the meridian line.

The progressive surface 12 of this prior art lens is readily described in algebraic terms. A rectangular coordinate system illustrated in Fig. 1 is defined whose origin coincides with 0, and whose x-y plane coincides with the S' 15 tangent plane at 0. The x-axis points downward in the di- 1 rection of increasing optical power. In this system, the z-axis is normal to the surface at 0, and the equation of the surface 12 may be written in the form z f(x,y).

Letting u denote thle x-coordinate of a point Q on the meridian line, the coordinates i, C) of the correspond- S* Ing point q on the evolute may be expressed as a function of the parameter u: u-r sin 0 Sn 0 (1) 25

U

r cos 9 J tanOdu I 0 where u sin o J df (2) 0 *r h -4and r r(u) qQ. It is to be noted that sin 0 0 when u 0, so that the progressive surface is tangent to the x-y plane at the origin 0.

The equation of the sphere of radius r(u) centered at Q expressed as an elevation with respect to the x-y plane may be written: z C(u) (r(u) 2 Ix 2 y2)2 (3) The equation of a horizontal plane through Q is: S= u (4) Equation represents a family of spheres, and equation a family of parallel planes. The members of each family are generated by the single parameter u. For each 2 value of u there exists a unique sphere and a plane that intersects it. The curve of intersection between the sphere 15 and plane surface is denoted C and is shown in Fig. 3. When u is varied between its maximum and minimum values, the curve C is caused to sweep out the complete progressive surface. By eliminating u between equations and a single, nonparametric algebraic equation of the surface is 20 produced: z where f(x,y) a 2_-y2 1 If the meridional power law of lens 10 has the conventional form illustrated in Fig. 4, then the DP and RP areas of the design are spherical and extend over the full width of the lens. Such a design provides full distance and reading utility but, as is well known, the astigmatism in the intermediate area is unacceptably strong. The surface 9 power and astigmatism characteristits of this prior art lens are depicted in Figs. SA, 58 and Many other design variations in the boundaries of the spherical DP and RP zones have been illustrated In the previously cited references, but in each of these the modified spherical DP and RP zones are of finite size and such lenses do not reduce the unwanted astigmatism to the maximum possible extent.

In accordance with the present invention, a progressive power spectacle lens with the smoothest possible distributionl of dioptric power and lowest possible level of unwanted astigmatism is achieved by reducing the areas occupied by the spherical DP and RP to zero. 11 other words, the DP and of the present Invention, stzictly speaking, are mathe- 215 matical points, not areas. This construction Is Illustrated schematically In Fig. 6 wherein the points F and N comprise the poles of a bipolar system of optical power.

With the DP and RP zones having been reduced to mathemaical points, the proper form of the progressive surface that surrounds them must be determined. This Is accomplished conceptually by applying a geometrical transforma- I tion from the prior art, the nature of which in Illustrated In Flns. 7A and 7B. In Fig. 7A a prior art lens is Illuistrated showing the Intersections of members of the family of planes x u with the x-y plane. These Intersectio'ns form a tool *0 family of parallel straight lines, which are, in turn, parallel to the straight-line OP and RP' boundaries. As Fig. 78 Indicates, In passing to an embodiment of the present Invention, in which the OP and RP' are points, the family of parallel straight lines transforms into a family of circular arcs of varying radii. The circular arcs of the lens 3428 illustratci in Sig. 7B represent the interscitions of a one-parameter family of ci cular cylinders with the x-y plane. For each member of the original family of planes, there exists a corresponding member of the family of cylinders. Corresponding members of the families of intersecting spheres and cylinders intersect in a generating curve C.

Moreover, these corresponding members are identified by the same parameiter u, where u is the x-coordinate of a point Q on the meridian line of either lens. By varying the parameter u between its maximum and minimum values, the curve C is caused to sweep out the complete progreasive surface of the invention.

An algebraic equation for the new surface analogous to equation is readily obtained. The equation of any mem- 15 ber of the family of cylindrical surfaces may be written in the form: x g(y,u) (6) This equation may be solved for the, parameter u, giving an equation of tho forms a a 20 u h(x,y) (7) S as s t which reduces to equation in the case of the prior art lens. The equation of the progressive surface of the new lens is obtained by eliminating the parameter u between 'a equation and Explicitly, 0 0 f(x,y) 2 y2)1/2 (8) The detailed form of the resulting progressive surface will naturally depend on the form of the progression of If power along the umbilic meridian line, and on the spacing of the circular cylinders represented by equation To satisfy the aims of the Invention, meridional power progression and the spacing of the cylindrical surfaces must be chosen so as to produce a gently curving surface, thereby ensuring a smooth optical effect.

As stated above, t1.a form of the progression of power along the curve FN4 Is determined by two factors: optical stability requirements near points F and N4, and the requirement that the progression k(u) be a smooth function of the parameter u.

An area of optical stability is one in which the tdloptric power does not char'ge appreciably. The requirced size of the stable area surrounding F or N will naturally on the Intended application of the spectacle. For example, a spectacle lens intended for general use will require a larger'stable far-viewing area, and a smaller 2 stable near-viewing area, than will an occupational lens specifically designed for close work.

The size of the stable area surrounding F In the prest* ent invention depends essentially on the rate of growth of the curq'ature k(u) as a function of distance from F. The slower the rate of growth, the larger the stable far-viewing Similarly, the slower the rate of growth of k(u) as a function of distance from N, the larger the stable nearviewing area.

Let k(u) possess derivatives to all orders. Then the rates of growth of k(u) at F and N can be related to the orders of the first non-vanishing derivatives at those points. (In the series au 4+ bu 5, the first non-vanishing derivative at u 0 Is the 4th order derivative.) The I2.

higher the order of the first non-vanishing derivative, the slower the rate of growth. For instance, a function k(u) whose first non-vanishing derivative at F is d k/du will exhibit a slower rate of growth than will one whose first non-vanishing derivative is d 2 k/du 2 By appropriately selecting the orders of the first non-vanishing derivatives at F and N, one controls the sizes of the stable Ear- and near-viewing areas.

To satisfy the aims of the invention, the function k(u) is to be the smoothest function of u consistent with the behavior of the function and its derivatives at F and N.

As a criterion of smoothness, one might reasonably demand that the mean square gradient of k(u) be a minimum; or in other words, that k(u) minimize the Dirichlet integral:

N

I k' 2 du, (9)

F

where k' dk(u)/du, subject to the conditions k(F) k and k(N) k 2 This integral is of the form:

N

I ff(u,k,k')du,

F

1 which is rendered a minimum by a function k(u) satisfying the Euler-Lagrange equation, 25 8f/ k (d/du)(8 0, (11) S which, since e 2 reduces tos k" 0. (12) 13 Hence k(u) c 0 c 1 u (13) where c 0 and c 1 are constants determined by the values of k at F and N. Thus the function corresponding to the smoothness criterion is a linear function of u. Criterion (9) does not apply to functions whose first non-vanishing derivatives at F and N are of order 2 or higher. A more general smoothness criterion is required.

Let m and n denote the orders of the first non-vanish- Ing derivatives of k at F and N, respectively. Let p m n. Then, in place of one requires that R minimize the Integrals

N

I f[IdP-k/duP- 1

I

2 du. (14)

F

The function k that renders (14) a minimum is given by the Euler-Lagrange equations dPk/du P 0, the solution of which is the p-l order polynomials cal 20 P-1un 0 k(u) I cnu~ n(16) n=O in which the p coefficients are determined by the p endpoint

I"I"I

conditions. If kF and k denote the curvatures at F and N, respectively, and if F is located at u L as shown in .Fig. 9, equation (16) may be rewritten in the form: Ip-I k(u) kF (k k) 1 c(u L) n (17) 1%n_1 r-p.

1+- [The c n In this equation are n the same as those in Equation (17) defines the smoothest curvature function k(u) consistent with the given endpoint conditions.

Having defined the far- and near-viewing "areas" by the points F and N, and having specified the form of the power law k(u) between those points, it remains to specify the form of the progressive surface over the remainder of the lens. To satisfy the aims of the invention, the power and astigmatism are to be distributed as smoothly as possible over the area of the lens. To accomplish this, it seems at first reasonable to identify the curves of intersection C between corresponding members of the intersecting spheres and cylinders with curves of constant mean surface curvature, and to Zix their spacing by demanding, as in the case of the meridional power law, that k minimize the Dirichlet integralt I-fR,2 jR2 Idxdy (8 "where the subscripts x and y denote partial derivatives with 2 respect to those variables. This approach, however, is not 20 mathematically feasible. Instead, it is convenient to work, not with the mean curvature k, but with the auxiliary functhee tLion 4(xy).

As illustrated in Fig. 8, the auxiliary function f(x,y) is defined on the x-y plane. The function does not represent the progressive surface itself, but is used to define the spacing of the cylindrical surfaces. This function takes on the following boundary values: S I f(x,y) c when DP pole, F M C wheh (xy) RP pole, N 0 at infnity, (19) Is- -4;3where c I and c 2 are constants. The smoothest function f(x,y) consistent with these boundary conditions is deduced from the following considerations: If the problem were one-dimensional, rather than twodimensional, it would be obvious that if f(x) has tl'o boundary values 4(0) c I and f(1) c 2 then the smoothest function between x 0 and x 1 would be the linear function 4(x) c 1 (c2 cl)x. This function satisfies the differential equation: d 2 d4 0 dx Thus, the required function in the two-dimensional case satisfies the two-dimensional Laplace equation: (i 2 j 2 j) (xy) 0 (21) which is to be solved'subject to the boundary conditions Functions satisfying equation (21) are called harft *0 monic functions. 'Ifs o 4 The preceding result may be deduced in a more rigorous 20 way. A criterion for smoothness is to require that the average values of the moduli of the derivatives ak/3x and *9 aei/3y be a minimum. Alternatively, if the average sum of the squares of these quantities is considered, the Dirichlet integral

S.

I* 25 2 25c) l dx dy, (22) then, according to the Euler-Lagrange variational calculus, mls equation (22) is minimized when satisfies Laplace's C i

I

Ii equation, equation The fact that equation (22) is minimized by a function satisfying Laplace's equation is known as Dirichlet's principle, or the principle of minimum potential energy. The Dirichlet principle accounts for the distribution of electrical potential around a charged electrical conductor, as well as the steady-state distribution of temperature in a thermal conductor. Such naturallyoccurring distributions are smooth in the sense that the fields defining them minimize the Dirichlet integral. As will be demonstrated, a progressive lens whose surface derives from the Dirichlet principle likewise exhibits the property of smoothness.

To make use of the auxiliary function one forms the so-called level curves, f(x,y) c const., (23) which are curves of constant -value. These curves may be expressed in the form given by equations or and therefore may be taken to represent the req iced farily of cylinders.

20 For the bipolar configuration depicted in Figs. 6 and 9, the solution of Laplace's equation, subject to coaditions is particularly simple. The curves of constant coincide precisely with the circular coordinate lines of a I 25, cylindrical bipolar coordinate system. Let the poles of the coordinate system be separated by the distance h, with the DP pole displaced a distance L above the origin 0, as shown in Fig. 9. If the level curve through an arbitrary point intersects the x-axis at the point then, after calculation, it is found that 17 u h L g (sgn p) (g2 h 2 )1/ 2 (24) 2 4 where g (p v 2 h 2 /4) p and p x h L (26) 2 This expression for when inserted in equation provides a complete algebraic specification of the progressive surface of a bipolar lens according to the invention.

Different embodiments are generated by varying the form of the meridional power law r r(u).

In summary, the bipolar progressive surface f(x,y) is specified by the following set of equations: z f(x,y) (r(u) 2 (x 21/2 where 4 S(u) u r(u) sin O(u),

U

c(u) r(u) cos O(u) J tan O(u) du, 0

*O

2sinO(u) J I 25 o r(u) u L g (sgn p) (g 2 h2/4)1/ I 6

C

9 g (p 2 2 p p x 11 L, 2 h vertical distance between DP and RP poles, L vertical displacement of DP pole above origin 0, and the meridional power law is an Nth order polynomial,

N

1 i I Cn(U L)n, r(u) r D r R r D n=l r D radius of curvature of the progressive surface at the DP pole, r R radius of curvature of the progressive surface at the RP pole, and c n constant coefficients.

FIRST NUMERICAL EXAMPLE A typical example of a lens constructed according to the above principles in accordance with the invention, and suitable for general use, will now be given.

The lens Is characterized by an eighth-order polynomial power law, depicted in Fig. 9, and defined by the equations 2. '4 8n Ul_ L_ Cn(u (27) U' r(u) r

D

r R rD n=l where 4 C =c 2 c 3 c 4 0, 4 c 5 56/h -140/h 6 (28) 4 4 1 Io, II a c7= 120/h 7 ca Ni:hte that 1/r i/r D when u -L (DP pole), and 1/r 1 /rR when u -L h (RP pole). The quantity A r R r D(29) where n Is-the Index of refraction of the lens material, represents the "addition power" of the multifocal lens.

This particular power law provides gradually varying surface power In the neighborhoods of the DP and RP poles. The lens thus pr 3vldes adequate focal stability for the distant and near visual fields.

The progressive surface defined by the power law of equation (27) will now be evaluated for a lens having a -reading addition of 2.00 diopters. The lens Is assumed to have an Index of refraction of 1.498, and the following values of the parameters are assumedi Oct.h =37.71 mm t.l £=10.65 mm rD) 83.00 mm r S0R 62.25 mm Figures 10A, l0B and hOC show the results of an electronic computer evaluation of the equations, using the given values of the parameters. Fig. 10A gives the contours of constant mean surface power; Fig. lOB gives the contours of *constant surface astigmatism; and Fig. 1oC provides a *ili~T z0 three-dimensional view of the distribution of surface astigmatism. Inspection of these diagrams shows that the power and astigmatism characteristics of the lens are smooth and slowly varying. The minimum progressive corridor width, as measured between lines of 1.0 diopter astigmatism, is about 9 mm. In addition, the surface astigmatism reaches a maximum value of just 1.51 diopters; this is about 0.4 diopter less astigmatism than that of any other 2.00 diopter addition progressive lens presently available. This example thus meets the goals of the invention.

SECOND NUMERICAL EX APLE The next example is that of a lens possessing what may be the lowest level of astigmatism possible in a progressive lens with umbilio vertical meridian. Because astigmatism is generated by power gradients, such a lens must exhibit the lowest possible power gradient between the poles of the bipolar construction. This is provided by a linear power law, depicted in Fig. 11, and defined by the equation

C,

20 r(u) rD rR r D The surface defined by the linear power law will now be evaluated utilizing the values of the parameters given in equation Figure 12A shows the contours of constant mean surface power; Fig. 12B the contours of constant surface astigmatism; and Fig. 12C a three-dimensional representation oi the surface astigmatism. The maximum surface "astigmatism is just 0.66 diopters, or 1/3 the add power.

This may well represent the minimum value possible in a ,roessive lens with umbilic vectical meridian, although no proof of the conjecture exists Figure 10A shows that the power distribution in the neighborhoods of the DP and RP poles is relatively unstable. For this reason, despite its low level of astigmatism, the lens may not be desirable for general use.

It is in fact beat suited to visual tasks requiring only a narrow visual field, for example, the computer work stations, comprising a keyboard and video-display terminal.

~Iifl~~R~AL EXAMPLE The third example to a lens specifically designed for near and intermediate working distances. it is to be considered an occupational lens, rather than a general-purpose lens. The meridional power law for this lens provides a large, stable near-viewing area and a relatively small, distance-viewing area. The power law is a 4th order polynomial with coeffiencts c 1 O, c 2 6/h 2 c 3 -8h 4 3 /14s (32) The progressive surface defined by these coefficients will be evaluated numerically for a lens having a reading addition of 2.00 diopt~ers. The inder of refraction is 1.498 and the *followin., values of the parameters are assumed: h =43'.03 ima, L -20.29 mm, r D -83.00 jean, -62.25 mm. (33) The results of the computer evaluation of thG equations are presented in Figs. 13A, 13B and 13C. Figs. 13A and 1313 depict.

*respectively, contours of constant mean surface power and constant surface astigmatism; Fig. 13C provides a toll It 30 three-dimensional viqw of the distribution of surface 4/ astigmatism. Inspection of Figs. 13A and 13B reveals that (1) the near-viewing area of the occupational lens is significantly wider than that of the general-purpose lens depicted in Figs.

and 10B; the distance-viewing area of the occupational lens is significantly narrower than that of the general-purpose lens; and the intermediate-viewing zone is wider than that of the general purpose lens. The maximum astigmatism of the occupational lens is even less than that of the general-purpose lens: 1.10 vs. 1.51 diopters in a 2.00 add lens. Moreover, the maximum aimof the occupational lens is located above the 0-180 0 line of the lenc, where it cannot interfere with Lhe neir-vision function. Fig. 13C exhibits the characteristic smoothness of lenses designed on the bipolar principle.

The occupational lens represents a kind of inversion of the general-purpose lens; it achieves improved near utilit:- at the expense of distance utility. Consequently, the occupational lens is suitable for those visual tasks in which intermediate and near working distances predominate. This lens works particularly well in the computer work environment computer terminal, personal computer or word processor terminal). in this application, the lens is mounted in the frame so that the optical power 15~ below the horizontal at the usual center of the video monitor) equals three-fourths the add power of the lens. This power is appropriate for typical screen distances The reading center of the lens will then occur 33 0 below the horizontal, 16 mm below the point where the horizontal intersects the *lens, and the distance center 25 0 above the horizontal, i.e., 12 mm above the point where the horizontal intersects the lens.

:30 The height of the distance center, while not convenient for *130 2 prolonged distance viewing, since the head must be tipped slightly to use it, is nonetheless perfectly functional for normal office F;'#.ivities.

23 -34- FOURTH NUMERICAL EXAMPLE The fourth and final example is a lens that emphasizes distance vision at the expense of near vision. This lens can be considered a dynamic-activity lens for sports activities). The meridional power law provides a large, stable distance-viewing area and a relative small reading area. The power law is a polynomial of 8th order wieh "-affiencts c I c 2 c 3 c 4 c 5

O,

c 6 28/h 6 c 7 -48/h 7 Cg 21/h 8 (34) The progressive surface defined by these coefficients will now be evaluated numerically for a lens having a reading addition of 2.00 diopters. The index of refraction iu 1.498 and the following values of the parameters are assumed: h 44.14 mm, L 19.30 mm, rD 83.00 mm, rR 62.25 mm. The computer-generated curves of constant mean power and surface astigmatism for this lens are presented in Figs. 14A and 14B, respectively; a three-dimensional plot of the surface 0*Ui astigmatism is given in Fig. 14C. From Figs. 14A and 14B it is evident that the distance-viewing area of the dynamic-activity lens is larger than that of the general-purp6oe lens depicted in Figs. 10A and 10B; the reading area o the dynamic activity lens is narrower than the reading area of the 0 general-purpose lens; and the progressive corridors of the two lenses are roughly equal in length (17 mm) and width (10 mm minimum between lines of 1,0 diopters astigmatism). The maximum a i surface astigmatism of the dynamic-activity lens is equal to that of the general-purpose lens (1.51 diopters), but it is located lower in the lens body, where it presents less of an obstacle to far and far-intermediate viewing. Fig. 14C exhibits again the smoothness characteristic of lenses based on the bipolar principle.

The dynamic-activity lens is intended for use in those visual situations in which far 'and far-intermediate distances predominate, and where freedom from distortion is required.' Thus it is a special purpose lens appropriate for, for example, the professional driver and the sports-minded person.

For ease of exposition, the general invention as well as the four example lenses have been described as having a vertical line of symmetry. This line runs down the middle of the progressive corridor and divides the lens into two symmetrical halves. In actual practice, however, the symmetry line of the lens must be rotated from the vertical to provide an effective mm Inset of the near viewing portion. This rotation, which of course is applied to both lenses of a spectacle, ensures that the lines of sight- can pass along the progressive corridors for clear vision at all distances.

An important consequence of the low astigmatism .hracterizing the invention is that binocular vision is not impaired by the reading-inset rotation. in the case of most prior art lenses, the astigmatism levels are so high that the 04 rotation adversely affects the binocular function, In some cases necessitating the introduction of an asymmetrical design.

However, in the case of the present invention, the astigmatism bee levels are so low, and astigmatism so smoothly distributed, that I'll the incorporation of asymmetry to counteract the effects of the 4 o reading-inset rotation is entirely unnecessary.

-43- The various embodiments of the invention described above and exemplified in examples 1-4 comprise a system of progressive lenses. The general-purpose lens (Example the occupational lens (Example and the dynamic-activity lens (Example 4) are functionally complementary. The system thus provides optimum utility for each viewing requirement. Moreover, because each of the lens designs is based on the same bipolar design principle, the lenses are mutually compatible. This ensures ease of switching from one progressive design to the other. Indeed, experience with the general-purpose and occupational lenses shows that it is often difficult to tell which spectacle one is wearing.

There are on the market today many general-purpose progressives and a few occupational progressives. While these two types of lenses are functionally complementary, they do not provide compatibility of design, and so do not comprise a system of lenses in the sense defined above. Thus, the present invention provides a system of progressive lenses having both e* t functional and design compatibility.

tIs It is to be understood that the term "lens" as used herein is intended to include the ophthalmic product in any and all forms common to the art, including lens blanks requiring second side (concave or convex) finishing as well as lenses finished on both sides and "uncut" or "cut" (edged) to a size 25 and shape required for spectacles frame glazing. The present lenses may be formed of glass or any one of the various known and used ophthalmic plastics. If second side finished, on the side opposite that having the progressive power surface, the i 0098 second side may have prescription surface curvatures applied 30 with the lens RP decentered in usual fashion.

i Those skilled in the art will readily appreciate that there are many forms and adapta~tions of the invention not discussed herein which may be mades to suit particular requirements. This include, without limitation, the use of meridional power laws that do not minimize the Dirichiet integral of equation (14), non-polynomial power laws; or spacings that depart from those spacinigs dictated by the Dirichlet Integral of equation Accordingly, all such forms and adaptations are included within the scope of the invention as defined by the following claims.

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Claims (1)

1. 22. A progressive power ophthalmic lens substantially as hereinbefore described with reference to Figs. 13A, 138, 13C, 14A, 14B and 14C of the accompanying drawings. DATED this TWENTY-NINTH day of APRIL 1994 American Optical Corporation Patent Attorneys for the Applicant SPRUSON FERGUSON 4I 4 2-3 RLF/01251