US 20070216863 A1
The invention provides lenses produced by the adding of two or more surfaces, in which lenses both the length of the corridor is shortened and the maximum unwanted astigmatism is reduced.
33. A mark for a spectacle lens, comprising of: a) a location mark for measuring a distance power: b) a location mark for measuring a near power; c) a location mark for measuring a prism power; and d) a linear mark of at least about 1 mm in length along which a fitting point may be located.
34. A progressive lens, comprising a corridor having a length of less than about 12 mm and a maximum unwanted astigmatism of less than about 80% of a total add power of the lens.
35. The lens of
The present invention relates to multifocal ophthalmic lenses. In particular, the invention provides progressive addition lens designs with both a shortened corridor and reduced unwanted astigmatism.
The use of ophthalmic lenses for the correction of ametropia is well known. For example, multifocal lenses, such as progressive addition lenses (“PALs”) are used for the treatment of presbyopia. PALs have at least one progressive surface that provides far, intermediate, and near vision in a gradual, continuous progression of vertically increasing dioptric power from far to near focus, or top to bottom, of the lens.
PALs are appealing to the wearer because PALs are free of the visible ledges between the zones of differing dioptric power that are found in other multifocal lenses, such as bifocals and trifocals. However, an inherent disadvantage of PALs is the presence of unwanted astigmatism, or astigmatism that is undesirable and is introduced or caused by one or more of the lens' surfaces. Unwanted astigmatism can produce swim, image magnification, and motion effects for the lens wearer that disrupts the wearer's vision. In hard PAL lens designs, the unwanted astigmatism borders the lens channel and near vision zone. In soft designs, the unwanted astigmatism may extend into the distance zone.
Typical PALs have a 12 to 14 mm in length corridor between the fitting point and the point along the prime meridian of the lens at which the power reaches 85% of the lens' add power. Although such a corridor helps provide more gradual power changes and lower levels of unwanted astigmatism, the near viewing zone is often cut-off when lenses of these designs are mounted into standard frames.
Some PAL lenses have been designed with short corridors in the 9 mm to 12 mm range, but these PALs typically have much higher levels of unwanted astigmatism. If a PAL wearer has become accustomed to a particular design in a standard size frame and then chooses to switch to a smaller frame, typically the ECP must switch the patient into another PAL brand, which may result in wearer adaptation problems.
The present invention provides lenses, and methods for their design and manufacture, in which both the length of the corridor is shortened and the maximum unwanted astigmatism is reduced. The lenses of the invention are provided by adding two or more progressive surfaces.
In one embodiment, the invention provides a method for designing a progressive addition lens, comprising, consisting essentially of, and consisting of: a.) providing a first progressive addition surface having a first add power and a first corridor of a first length; b.) expressing the first surface as a first plurality of sag values; c.) multiplying the first plurality of sag values by a first blending function; d.) providing a second progressive addition surface having a second add power and a second corridor of a second length; e.) expressing the second surface as a first plurality of sag values; f.) multiplying the second plurality of sag values by a second blending function that may be the same or different from the first blending function; g.) adding the first and second plurality of sag values to produce a third progressive surface having the first add power, a third corridor wherein a length of the third corridor is at least about 1 mm less than either or both the first and second corridor lengths.
In a preferred embodiment, the invention provides a method for designing a progressive addition lens, comprising, consisting essentially of, and consisting of: a.) providing a first progressive addition surface having a first add power, a first corridor of a first length and a first unwanted astigmatism; b.) expressing the first surface as a first plurality of sag values; c.) multiplying the first plurality of sag values by a first blending function; d.) providing a second progressive addition surface having a second add power, a second corridor of a second length and a second unwanted astigmatism; e.) expressing the second surface as a first plurality of sag values; f.) multiplying the second plurality of sag values by a second blending function that may be the same or different from the first blending function; g.) adding the first and second plurality of sag values to produce a third progressive surface having the first add power, a third corridor wherein a length of the third corridor is at least about 1 mm less than either or both the first and second corridor lengths and a third maximum unwanted astigmatism wherein the third unwanted astigmatism is greater by about 0.2 or less diopters than one or both of the first and second maximum astigmatism.
By “lens” is meant any ophthalmic lens including, without limitation, a spectacle, contact, intraocular lens, and the like. Preferably, the lens of the invention is a spectacle lens. By “sag value” is meant the absolute value of the z-axis distance between a point on a progressive surface located at coordinates (x, y) and a corresponding point on a reference plane. For purposes of the invention, the z-axis is the axis orthogonal to the x-y plane.
By “progressive addition surface” or “progressive surface” is meant a continuous, aspheric surface having distance and near viewing zones, and a zone of increasing dioptric power connecting the distance and near zones. One ordinarily skilled in the art will recognize that, if the progressive surface is the convex surface of the lens, the distance vision zone curvature will be less than that of the near zone curvature and if the progressive surface is the lens' concave surface, the distance curvature will be greater than that of the near zone.
By “corridor” is meant a channel of vision the width of which is the area of vision that is free of unwanted astigmatism of about 0.75, preferably about 1.00, diopters or greater when the wearer's eye is scanning through the intermediate vision zone to the near vision zone and back and the length is the area between the fitting point and the point along the prime meridian of the lens at which the power reaches 85% of the lens' add power.
By “unwanted astigmatism” is meant astigmatism that is undesirable and is introduced or caused by the lens surface. For purposes of the invention, the areas of unwanted astigmatism considered are those located on either side of the channel and preferably below the fitting point. By “fitting point” is meant the point on a lens aligned with the wearer's pupil in its distance viewing position when the wearer is looking straight ahead.
The method of the invention may be used to design any progressive lens. However, the method may find its greatest utility in the design of progressive lenses in which the corridor length is less than about 12 mm and which have a maximum unwanted astigmatism that is less than about 80% of the total add power of the lens. Thus, in yet another embodiment, the invention provides a progressive lens comprising, consisting essentially of, and consisting of a corridor having a length of less than about 12 mm and a maximum unwanted astigmatism of less than about 80% of a total add power of the lens.
In the first step of the method of the invention, a first progressive surface is provided by any convenient optical design method. The surface, U may be a single progressive surface or a surface that is the result of combining one or more progressive and regressive surfaces. By “regressive surface” is meant a continuous, aspheric surface having zones of distance and near vision and a zone of decreasing dioptric power connecting the distance and near zones. If the regressive surface is the convex surface of the lens, the distance zone curvature will be greater than that of the near zone and if the regressive surface is the lens' concave surface the distance curvature will be less than that of the near zone.
In carrying out the method of the invention, designing of the surface preferably is carried out using a method that divides the surface into a number of sections and provides a curved surface equation for each area as disclosed, for example, in U.S. Pat. No. 5,886,766 incorporated herein in its entirety by reference. Optimization of the surface may be carried out by any convenient method. Additional properties of a specific lens wearer may be introduced into the design optimization process including, without limitation, variations in the pupil diameter of about 1.5 to about 7 mm, image convergence at a point about 25 to about 28 mm behind the front vertex of the surface, pantoscopic tilt of about 7 to about 20 degrees and the like, and combinations thereof.
The distance and near vision powers for the surface design are selected so that powers of the lens are those needed to correct the lens wearer's visual acuity. The dioptric add power for the surfaces will typically be about +0.10 to about +6.00 diopters. Generally, the distance curvature of the progressive surfaces will be within about 0.25 to about 8.50 diopters. The near vision curvature will be about 1.00 to about 12.00 diopters.
The first progressive surface, U, is then expressed as a plurality of sag values. The sag values are calculated by subtracting U from a base spherical surface Uo, with a curvature equal to the distance curvature or base curvature, to yield the surface's sag values u(x,y). The steps of providing a progressive surface and expressing the surface as a plurality of sag values is repeated for a second progressive surface, V which yields the surface's sag values, v(x, y) by subtraction from a base spherical surface Vo. The second surface may be the same or, preferably, different from the first surface. In either case, the optical centers and distance measurement locations of the surfaces preferably are aligned to within manufacturing tolerances, typically between about ±0.25 mm to about ±0.5 mm, or unwanted changes in power and introduction of prism will result.
The first and second plurality of sag values are then each multiplied by a blending function and added to produce a third progressive surface. The blending function used for each surface may the same or, preferably, different from the function used for the other surface. In one embodiment, the added progressive addition surface may be expressed as sag departures from a reference sphere, Wo(x,y), as follows:
In another embodiment, the same blending function, F, is used and the added progressive addition surface may be calculated according to the equation:
Several types of blending functions may be used and selection of a blending function will be dependent upon its shape. Preferred functions will be equal to 1.0 at the optical center and decay to 0 at the edge of the lens.
One convenient form for F is
Surfaces U and V may be scaled to different add powers prior to the addition step. In the case in which the progressive surfaces to be added are the same, which is preferred, the surfaces will need to be scaled to two different values prior to adding. Scaling enables the corridor of the blended surface to be changed to achieve design objectives. The corridor length of each surface may be the same or, preferably, different. If different corridor lengths are chosen, the corridor lengths must be selected to ensure that the wearer's required distance and add powers are substantially maintained.
Additionally, the surfaces to be added may have areas of unwanted astigmatism that are aligned or preferably misaligned. By misaligned is meant that the location of the areas of unwanted astigmatism of one surface do no substantially coincide with the areas of unwanted astigmatism of the other surface. The latter option has the advantage in that the misaligning the astigmatism maxima of the surfaces reduces the overall maximum, unwanted astigmatism of the added surface.
In an optional, and preferred, final step of the method of the invention, the resulting surface may be smoothed by any suitable fitting technique to eliminate curvature discontinuities that result in localized power changes of greater than about 0.05 diopters. Any known technique may be used including, without limitation, fitting using polynomial, splines and the like. Preferably, the blending function is selected so that no discontinuities are introduced into the blended surface that cannot be smoothed.
Optimization of the added surface may be accomplished by the establishment and maximization of a merit function weighing distance, intermediate and near vision, corridor length and width, distortion and swim. One such merit function is the Corridor Factor, Cf which is defined as:
The resulting added and smoothed surface will not change substantially from the first surface in the distance, near or prism powers provided the blending is performed within the constraints outlined above. However, if significant changes do occur, appropriate compensations in power may be incorporated into a complementary surface of the lens to offset the changes. Accordingly, other surfaces designed to adapt the lens to the ophthalmic prescription of the lens wearer may be used in combination with, or addition to, the optimized progressive addition surface. Additionally, the individual surfaces of the lens may have a spherical or aspherical distance vision zone. The corridor may be closer to the distance or near viewing zone. Further, combinations of any of the above variations may be used.
In a preferred embodiment, the lens of the invention has as its convex surface the surface of the invention and a complementary concave surface, which concave surface corrects the wearer's astigmatism and prism. The convex surface preferably is of a symmetric, soft progressive design produced by combining two convex progressive surfaces, each of which surfaces has a channel length of about 10 to about 22 mm. One surface has an aspherical distance viewing zone and the maximum, localized unwanted astigmatism is located closer to the distance than the near viewing zone preferably on either side of the upper two thirds of the channel. The distance zone preferably is aspherized to provide additional plus power to the surface of up to about 2.00 diopters, preferably up to about 1.00 diopters, more preferably up to about 0.50 diopters. Aspherization may be outside of a circle centered at the fitting point having a radius of about 10 mm, preferably about 15 mm, more preferably about 20 mm. The other surface has no aspherical distance viewing zone and the maximum, localized unwanted astigmatism is located closer to the near viewing zone than the distance viewing zone, preferably on either side of the lower two thirds of the corridor.
Because the shortened corridor surface of the invention may be achieved with a low level of unwanted astigmatism, a lens produced by this design method may be either fit at the optical center, y=0 mm, or some distance above the optical center to improve distance vision. The range of fitting location may be raised between about 1 mm and 5 mm, preferably between about 2 mm and 3 mm from the optical center. This range provides greater flexibility in addressing the wearer's visual needs than conventional lens designs.
In order to facilitate such a flexibility, the present invention also provides PAL markings. The markings may be placed on the lens surface or a film that is affixed to the lens surface. Prior art markings typically have a single point location for the fitting point demarcated, as illustrated in
Thus, in another embodiment the invention provides for a marking comprising, consisting essentially of, and consisting of: a) a location mark for measuring the distance power; b) a location mark for measuring the near power; c) a location mark for measuring the prism power; and d) a linear mark of at least 1 mm in length along which the fitting point may be located.
The lenses of the invention may be constructed of any known material suitable for production of ophthalmic lenses. Such materials may be constructed of any known material suitable for production of ophthalmic lenses. Such materials are either commercially available or methods for their production are known. Further, the lenses may be produced by any conventional lens fabrication technique including, without limitation, grinding, whole lens casting, molding, thermoforming, laminating, surface casting, or combinations thereof.
The invention will be clarified further by a consideration of the following, non-limiting examples.
A contour map for a commercially available short corridor progressive lens, AO Compact™, Lens 1, was created using a coordinate measuring machine and using the sag values obtained in a ray trace program to obtain power and cylinder profiles.
A first progressive surface was designed using a material with a refractive index of 1.515. The lens' base curve was 104.3 mm and the add power was 2.04 diopters. This surface had a standard length corridor of 12.3 mm and maximum unwanted astigmatism is 1.56 diopters. The corridor factor Cf was 9.40 mm. The surface U was scaled with the following scaling factor: u(x,y)=1.019 *U(x,y).
A second progressive surface having the same refractive index, base curve, add power, corridor length, corridor factor and maximum unwanted astigmatism as the first surface was also designed. The second surface was scaled to a lower add power with the following scaling factor v(x,y)=1.045 *U(x,y) according to the design methodology of the invention.
The first and second surfaces were added using the blending function F of Equation. III with a=−0.001466 and b=0.018. The addition and blending result in the following equation for the resulting progressive surface w(x,y):
The optical data for the resultant progressive surface (W) is shown in Table 1. The power and cylinder contour plots are shown in
The surface (W) of Example 2 was shifted vertically so that the fitting point was located at y=+2 mm. The optical data for the resulting progressive surface (W) is shown in Table 1. The power and cylinder contour plots are shown in
Example 1 demonstrates that, beginning with a surface with a standard corridor length and using the method of the invention, a surface with a shorter corridor length than the prior art lenses, but without the high unwanted astigmatism results. In Example 2, a lens wearer may be fit higher, by about 2 mm, to lengthen the corridor to as standard length without changing the unwanted astigmatism.