BRIEF DESCRITION OF THE FIGURES
FIG. 1 illustrates a prior art diffractive lens with blazed periodic structure forming different diffraction orders along which the light can only be channeled. The figure also include a description of a “geometrical model” of the diffractive lens through the relationship between the blaze ray defined by the refraction at the blaze and directions of the diffraction orders;
FIG. 2 illustrates a portion of aspheric multifocal diffractive lens of this invention with blazed periodic structure forming multifocal base surface for zero-order and (−1)-order diffraction for near focus along which the light is channeled. The diffractive structure is placed on the posterior surface of the lens but it can be placed on the anterior surface as a different embodiment. A multifocal asphere can be placed at the base surface as a different embodiment. The FIG. 2 incorporates also a description of a “geometrical model” of the diffractive lens through the relationship between the blaze ray defined by the refraction at the blaze and directions of the diffraction orders;
FIG. 3 is a plan view of a preferred embodiment of a lens made in accordance with the present invention, which has aspheric multifocal diffractive central zone;
FIG. 4 is a plan view of a preferred embodiment of a lens made in accordance with the present invention, which has aspheric multifocal diffractive zone as annulus;
FIG. 5 is a Power Profile of the lens described in the FIG. 3.
FIG. 6 is a Power Profiles of the lens described in the FIG. 4.
FIG. 7 shows Power Profiles of the lens described also on FIG. 4 but with different central zones.
FIG. 8A and 8B are profile views of aspheric multifocal diffractive zone.
FIG. 9 is a plan view of a preferred embodiment of a lens made in accordance with the present invention, which has multifocal diffractive central zone and aspheric refractive zone outside it that includes intermediate and far foci. The aspheric refractive zone may incorporate an enhancing DOF form. The aspheric multifocal refractive zone and diffractive zone may be on the same or opposite lens surfaces;
FIG. 10 is a plan view of a preferred embodiment of a lens made in accordance with the present invention, which has multifocal diffractive zone as annulus and aspheric multifocal refractive zone outside it with intermediate and far foci. The aspheric refractive zone may incorporate the enhancing DOF form. The aspheric refractive zone and diffractive zone may be on the same or opposite lens surfaces;
FIG. 11 is the example of an IOL Power Profile where the IOL is taken by itself The Power Profile includes the near power distribution and Base (Far) power distribution. The base surface manifests a multifocal surface covering intermediate and far powers as well as being aspherized.
FIG. 12 is the example of an Eye Power Profile where the IOL is part of the Eye optical system. The Power Profile includes the near power distribution of a single power and Base (Far) power distribution. The base surface manifests a multifocal surface covering intermediate and far powers as well as being aspherized.
FIG. 13 demonstrates a Modulus of the Optical Transfer Function for different focus positions, so called Through Focus Response (TFR). The TFR graph represents image quality of the eye with preferred embodiment of the aspherical diffractive multifocal lens.
DETAILED DESCRITION
FIG. 1 describes a portion of a prior art diffractive lens 10 with blazed periodic structure 50 creating different diffraction orders indicating by the directions 20a, 20b, 20c, etc. along which the light can only be channeled. The figure includes input light ray 20 refracted by the lens 10. It also shows the refractive base curve 40 that would refract the exiting ray corresponding to the input ray 20 along the direction of zero-order diffraction 20b. Direction of (+1)-order diffraction is shown by 20a and (−1)-order diffraction by 20c. Theoretically, there are infinite orders of diffraction.
The FIG. 1 incorporates a reference to the “geometrical model” of diffractive lens by including blaze ray 30 as the ray corresponding to the input ray 20 and refracted by the blaze. The direction of the blaze ray 30 differs from the direction of 0-order diffraction 20b due to the different refraction angles of the rays at the base curve 40 and blaze structure 50. The angle difference is created by the blaze material thickness (h).
If the blaze material thickness h is zero than the blaze structure 50 coincides with the base curve 40 and the lens becomes pure refractive type. If the blaze material thickness (h) increases to refract the blaze ray 30 along (−1)-order of diffraction 20b the lens becomes a Kinoform with 100% efficiency at (−1)-order diffraction. The blaze ray 30 at the FIG. 1 is placed in the middle between 0-order and (−1)-order diffraction to equally channel the light between these two orders. The rigorous diffraction theory demonstrates that maximum 40.5% of light can be channeled along each of these orders for the given design wavelength with the rest of the light is spread out between the higher orders of diffraction. In the present multifocal diffractive designs 0-order diffraction is selected to coincide with the power for Far vision (Far power) and (−1)-order coincides with the power required for Near vision (Near power).
FIG. 2 describes a portion of diffractive lens 100 according to the present invention with blazed periodic structure 130 creating different diffraction orders indicating by the directions 200a (zero-order) and 200b (higher order), etc. along which the light can only be channeled. The figure includes input light ray 200 refracted by the lens 100. It also shows the aspheric refractive base curve 140 that would refract the exiting ray corresponding to the input ray 200 along the directions of zero-order diffraction 200a for the given lens segment. There is a range of directions due to underlying asphericity of the base curve. The shape of the base curve is such that the corresponding refractive lens enhances the depth of focus around far focus. Direction of (−1)-order diffraction is shown by 200b.
The corresponding aspheric shape may be applied to the other surface and the base curve of the multifocal diffractive zone may be conventional spherical shape. In either case if the enhancing DOF aspheric zone placed on the other surface or serves as the base curve of the diffraction zone, the lens zero-order diffraction forms a wavefront that enhances DOF around distant vision or have a combination of intermediate and far foci. There is a range of directions of zero-order diffraction 200a due to underlying asphericity of the enhancing DOF aspheric zone.
The FIG. 2 incorporates a reference to the “geometrical model” of diffractive lens by including blaze ray 160 as the ray corresponding to the input ray 200 and refracted by the blaze. The direction of the blaze ray 160 differs from the directions of 0-order diffraction 200a due to the different refraction angles of the rays at the base curve 140 and blaze structure 130. The angle difference is created by the blaze material thickness (h′).
If the blaze material thickness h′ is zero than the blaze structure 130 coincides with the base curve 140 and the lens becomes pure aspheric refractive type. If the blaze material thickness (h′) increases to refract the blaze ray 160 the light is split between 0-order and (−1)-order diffraction to channel the light between these two orders.
The blaze width and height does not follow now simple equations (1) and (2) but are such to compliment the sag variation of the aspheric base curve in order to result in the constructive interference at near focus by non-zero diffractive order.
FIG. 3 is a plan view of a preferred embodiment of the ophthalmic lens 100 made in accordance with the present invention which has multifocal diffractive central zone 120FIG. 3 demonstrates the central zone 120 with a spherical shape but other suitable shape may be utilized. For example, a multifocal diffractive zone 120 may be spherical shape or segment or variable radii. The enhancing DOF asphere can serve as base curve of the multifocal diffractive zone of on the other surface of the lens but with light passing though both enhancing DOF asphere multifocal diffractive zone to form multiple orders of diffraction, i.e. zero-order diffraction in both cases is of aspheric nature with intermediate and far foci and may be shaped to enhance DOF at distant vision.
FIG. 4 is a plan view of another preferred embodiment of an ophthalmic lens 150 made in accordance with the present invention which has multifocal diffractive zone 180 placed outside of the central refractive or diffractive zone 170. The enhancing DOF asphere can serve as base curve of the multifocal diffractive zone of on the other surface of the lens but with light passing though both enhancing DOF asphere multifocal diffractive zone to form multiple orders of diffraction, i.e. zero-order diffraction in both cases is of aspheric nature with intermediate and far foci and may be shaped to enhance DOF at distant vision.
The FIG. 4 demonstrates central zone 170 to be of a spherical shape but for generality it may be of any shape located centrally to the multifocal diffractive zone 180.
FIG. 5 demonstrates a Power graph of the lens described in the FIG. 3 where the power profile of the base curve includes far and intermediate foci. This power profile might be continuously varied as shown on the FIG. 5 or a combination of discrete intermediate and far powers. FIG. 5 shows the base curve power profile modulate between power in the intermediate and far power ranges. The combination of powers for intermediate and far powers could be of different forms but with the outcome to produce the enhanced depth of focus around far focus. The groove widths, heights and profiles are such that the corresponding wavefront shifts together with the contribution of base curve sags create contractive interference at the (−1)-order of diffraction corresponding to near focus with substantial diffraction efficiency to produce near vision in addition to far and intermediate vision produced by the aspheric base curve.
FIG. 6 is a Power graph of the lens described in the FIG. 4 where the power distribution along the central zone is represented of the variety of forms of single power or variable power profiles.
FIG. 7 is a Power graph of the lens described in the FIG. 4 where the power distribution along the central zone inside of the aspheric diffractive annulus is a combination of refractive zone of varying power profiles and single focus diffractive annulus (Kinoform) for near focus.
FIG. 8A is a profile view of the multifocal diffractive portion of lens 150a of width l1 and posterior surface 250. The width l1 is about from 0.4 mm to 2.5 mm. The figure demonstrates groove height h′m that is continually reduced but in general they may be have the height reduction in steps. “Geometrical model” of the diffractive optic explains the reduction in grove height in order to direct the blaze ray in between the diffraction orders associated with far-intermediate zero-order and near foci non-zero order to split the light between aspheric multifocal 0-order and single focus (−1)-order though a rigorous diffraction theory is required to provide a fully quantitative solution for the groove widths, profile and heights meeting the specific transmittance requirements for far, intermediate and near foci.
FIG. 8B is a profile view of multifocal diffractive zone of lens 150b similar to those described by FIG. 8A with both zones being recessed by the depth 295, which is at least as deep as the groove height (h′m). This construction is particularly useful when involve soft material when the diffractive surface can be pressed against an ocular tissue and deform its shape. For instance, for placement at the posterior surface of the intraocular lens or contact lens that may interface with the ocular tissue and deform the groove shapes.
FIG. 9 is a plan view of a preferred embodiment of the ophthalmic lens 300 made in accordance with the present invention which has multifocal diffractive central zone 320FIG. 9 demonstrates the central zone 320 with a spherical shape but other suitable shape may be utilized. For example, a multifocal diffractive zone 320 may be spherical shape or segment or variable radii. The refractive aspheric zone 330 is placed outside of the multifocal diffractive zone either on the same or opposite lens surface.
FIG. 10 is a plan view of another preferred embodiment of an ophthalmic lens 350 made in accordance with the present invention which has multifocal diffractive zone 380 placed outside of the central refractive or diffractive zone 370 of a single power. A refractive aspheric zone 360 is placed outside of the multifocal diffractive zone either on the same or opposite lens surface. The refractive aspheric zone 360 is placed outside of the multifocal diffractive zone either on the same or opposite lens surface.
FIG. 11 is the example of an IOL Power Profile where the IOL is taken by itself. The Power Profile includes the near power distribution and Base (Far) power distribution. The Zero axis is taken at the power of best distant focus defined as the best image quality in terms of modulation transfer function. The vertical axis is scaled in IOL diopters or so called reduced diopters defined at the IOL plane.
The lens of the particular example was made of PMMA with spherical anterior surface of radius 12.3 mm, 0.8 mm thickness and aspheric multifocal posterior surface. Later consists of three aspheric zones: (1) refractive aspheric central zone of 1.5 mm diameter, (2) diffractive aspheric annular zone with 3.8 mm peripheral diameter and (3) refractive aspheric zone of 6 mm peripheral diameter.
Each zone is described by standard aspheric format:
- Where z(r)=surface sag; r=distance to the lens center; c=1/R=surface vertex curvature (R=surface vertex radius); Ai=aspheric coefficients.
TABLE 1
|
|
Base Surface Zone parameters
|
Para-
|
meters
Zone 1
Zone 2
Zone 3
|
|
R (mm)
−20.80
−22.00
−26.65
|
Ai
A4 = 0.0066461
A4 = 0.0015878
A4 = 0.0001176
|
−0.000160836
A6 = 0.00003538346
|
A8 = −0.0000009912011
|
|
The diffractive structure is placed within the second zone to produce near power in addition to distant and intermediate powers of the base surface. The near power distribution is elevated over the base power by Add Power and spread out within 3.1 D and 3.7 D range. The groove width of the diffractive structure is about 0.17 mm at the internal zone diameter to about 0.08 mm at the periphery. The groove radii square do not follow the linear function of formula 1. The phase coefficients per the formula 3 of the diffractive structure measured in radians are:
α1=0.191405; α2=18.525067; α4=1.783861 and α6=−0.290676
FIG. 12 is the example of an Eye Power Profile where the IOL is part of the Eye optical system. The IOL is the same as one described on the FIG. 11. The Zero axis is taken at the power of best distant focus defined as the best image quality in terms of modulation transfer function. The vertical axis is scaled in diopters at corneal plane. The reciprocal of the corresponding dioptric power defines a distance to the viewing object in meters. The eye system is taken with typical corneal surfaces: Anterior surface of 7.8 mm of vertex radius and conic constant of −0.21 and posterior surface of 6.5 mm radius and conic constant of −0.23.
The remarkable outcome of the Power Profile with the described above IOL was that the Near Power was presented by a single power of 2.78 D for near viewing, i.e. the near object at around 0.36 m˜14″ from the eye is in focus. A single level of near power profile points out that the diffractive structure creates a spherical wavefront to channel all designated by the structure light to Near Focus thus maximizing the near focus efficiency. The explanation is that the interaction of the diffractive structure with the wavefront of the total optical system is such that it creates a spherical wavefront for near focus. As far as distant focus is concern, the multifocal structure of the base surface results in intermediate focus and broad depth of focus at distant focus.
FIG. 13 demonstrates a Modulus of the Optical Transfer Function for different focus positions, so called Through Focus Response (TFR). The TFR graph represents image quality of the eye with preferred embodiment of the aspherical diffractive multifocal lens per FIG. 12 and transmittance function of its apodized diffractive bifocal zone per Table 2 below.
The diffractive structure of the annular zone of radii between 0.75 mm and 1.0 mm is for near vision as 100% of light is transmitted to near focus. The diffractive bifocal zone occupies the width between 1.0 and 1.9 mm radii. The design includes the groove apodization defined by the transmittance to Far and Near foci: T=T0·(1−T1·r−T2·r2−T3·r3−T4·r4).
TABLE 2
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|
Efficiency/Transmittance
|
T0
T1
T2
T3
T4
|
|
Far focus
2.508375
3.010962
−2.98324
1.074313
−0.13188
|
Near focus
−16.4189
3.593128
−4.31017
2.167969
−0.3942
|
|
Thus, the apodization of the grooves within the diffractive bifocal zone is such that it starts with the height to direct all light along the diffraction order associated with near focus and then the heights are reduced to create the transmittance described by Table 2 until reaching close to zero to direct all light along the diffraction order associated with far focus.
The TFR of the preferred aspherical multifocal diffractive lens is compared with TFR of the multifocal diffractive lens where light is equally split between far and near foci (40.5% at each focus for the design wavelength with the rest of light is distributed between higher diffraction orders) for 3 mm lens aperture. The graphs demonstrate the remarkable advantage of the preferable aspherical multifocal diffractive lens over the multifocal diffractive lens by manifesting Intermediate vision capability in addition to the improved Near and Far vision capabilities as well as broad Depth of Focus to reduce sensitivity to a small refractive error.
Patent Application
20070258143
