Multifocal lens

Abstract

The invention relates to a multifocal lens (1) with a refractive focus (F.sub.r) and with a diffractive structure (5) which, in the radial direction (r) of the lens (1), plotted across the squared radius (r.sup.2), has a periodic profile (6, 7, 8, 9), wherein the profile (6, 7, 8, 9) per period has four adjoining portions (6, 7, 8, 9) which are not differentiable at their connection sites (10, 11, 12, 13), wherein a first portion (9) has a monotonically falling function and the three further portions (6, 7, 8) have a monotonically rising function or vice versa, and wherein the further portion (7), which does not adjoin the first portion (9), has a greater pitch than the other further portions (6, 8).

Claims

1. A multifocal lens with a refractive focal point (F.sub.r) and a diffractive structure, the structure having a periodic profile in the radial direction (r) of the lens plotted over the squared radius (r.sup.2), and the profile having four mutually adjacent portions per period which cannot be differentiated at their junctions, the four portions including a first portion, a second portion, a third portion and a fourth portion, wherein the first portion is adjacent to the fourth portion and the second portion, and the third portion is adjacent to the second portion and fourth portion, wherein the first portion falls monotonically and the second portion, the third portion, and the fourth portion each rise monotonically, or a first portion rises monotonically and the second portion, the third portion, and the fourth portion each fall monotonically, and wherein the third portion has a steeper gradient than the second portion and the fourth portion, and wherein the period (p) of the profile, plotted over the squared radius, amounts to 0.5 mm.sup.2 to 1 mm.sup.2 and the profile depth (T) to 2 μm to 10 μm.

2. The multifocal lens according to claim 1, wherein the first portion, the second portion, the third portion, and the fourth portion each are linear when plotted over the squared radius (r.sup.2).

3. The multifocal lens according to claim 1, wherein the first portion is substantially vertical.

4. The multifocal lens according to claim 1, wherein the third portion is substantially vertical.

5. The multifocal lens according to claim 1, wherein the second portion and the fourth portion have substantially the same gradient.

6. The multifocal lens according to claim 1, wherein the multifocal lens is an intraocular lens or contact lens.

Description

BRIEF DESCRIPTION OF THE FIGURES

(1) The invention is explained in greater detail below on the basis of exemplary embodiments shown in the appended drawings, in which:

(2) FIG. 1 is a schematic plan view of the lens according to the invention;

(3) FIG. 2 is a schematic side view of the lens of FIG. 1;

(4) FIG. 3 shows an enlarged half section of the lens of FIG. 1;

(5) FIG. 4 shows the profile of the diffractive structure of the lens of FIGS. 1-3, plotted over the squared radius of the lens; and

(6) FIG. 5 shows a comparison of the intensity distribution of the lens according to the invention with that of a lens according to the prior art.

DETAILED DESCRIPTION OF THE DISCLOSURE

(7) FIGS. 1 and 2 show a lens 1 with a front face 2, a back face 3 and an optical axis 4. The lens 1 has a central zone Z.sub.1 and an annular zone Z.sub.2, which are explained in further detail below. The described lens 1 is used in particular as an intraocular lens or contact lens, but may also be used in optical equipment.

(8) The lens 1 has a refractive focal point F.sub.r located on the optical axis 4, which focal point may be used, as described below, for distance or near vision and is also described hereinafter as a zeroth order focal point. A diffractive structure 5 is incorporated into the back or front 2, 3 of the lens 1, see FIGS. 3 and 4, in order to adapt the lens 1 both to near and to intermediate and distance vision.

(9) The diffractive structure 5 generates a plurality of further focal points F.sub.i (i= . . . , −2, −1, 1, 2 etc.) located on the optical axis 4 which are distributed symmetrically around the refractive focal point F.sub.r, wherein the refractive focal point F.sub.r is provided by the shape of the lens 1, irrespective of the plotted diffractive structure 5. The diffractive focal points F.sub.1, F.sub.2 are described as positive first or second order focal points respectively of the diffractive structure 5 and lie on the optical axis 4 between the lens 1 and the refractive focal point F.sub.r. The diffractive focal points F.sub.−1, F.sub.−2 are described as negative first or second order focal points respectively of the diffractive structure 5 and lie on the side of the refractive focal point F.sub.r remote from the lens 1.

(10) Although the (position) distribution of the focal points F.sub.i is symmetrical around the refractive focal point F.sub.r, the intensity distribution assigned to the respective focal points F.sub.i is not intended to be symmetrical. For instance, in the case of a trifocal lens in particular three maximum intensities are intended to form, namely for distance, intermediate and near vision. This is achieved by forming the diffractive structure 5 according to FIG. 4.

(11) According to FIG. 4 (x-axis: squared radius r.sup.2 [mm]; y-axis: profile depth T [μm]) the diffractive structure 5 comprises a periodic profile in the radial direction r of the lens 1, plotted over the squared radius r.sup.2, which has four mutually adjacent portions 6, 7, 8, 9 per period p which cannot be differentiated at their junctions 10, 11, 12, 13. The phrase “plotted over the squared radius” means, with regard to periodicity, that the period intervals p diminish on the lens 1.

(12) In an intraocular or contact lens, for example, the period p may lie in the range from 0.5 mm.sup.2 to 1 mm.sup.2 and the profile depth T in the range from 2 μm to 10 μm.

(13) In the embodiment of FIG. 4, an arbitrary “first” portion of the profile 5, here the portion 9, falls monotonically and the three further portions 6, 7, 8 of the profile rise monotonically. The expression “first” used herein does not relate to the order of the portions 6-9, but rather serves merely to draw a distinction from three “further” portions. The order of the portions 6-9 within a period p may thus be freely selected or defined, whereby for example each of the portions 6, 7, 8, 9 may be selected as the “starting” portion and/or the “first” portion 9 does not necessarily lie at the start of the period p.

(14) In the embodiment shown in FIG. 4, the refractive focal point F.sub.r is designed for distance vision and the three monotonically rising further portions 6, 7, 8 and the monotonically falling first portion 9 result in two positive order diffractive focal points F.sub.1, F.sub.2 for near and intermediate vision (see FIG. 5). Alternatively, the refractive focal point F.sub.r may for example also be designed for near vision, to which end three monotonically falling further portions 6, 7, 8 and one monotonically rising first portion 9 are then used, resulting in two negative order diffractive focal points F.sub.−1, F.sub.−2 for intermediate and distance vision (not shown).

(15) The further portion which does not adjoin the first portion 9, i.e. in FIG. 4 the middle further portion 7, has a steeper gradient than the other two further portions 6, 8. The term “gradient” is defined herein as the total gradient covered by a portion 6, 7, 8, 9, i.e. as the gradient between the starting point of a portion 6, 7, 8 or 9 and the end point of the same portion 6, 7, 8 or 9.

(16) The portions 6-9, plotted over the squared radius r.sup.2, may be linear, whereby a monotonically rising portion 6, 7, 8 on the lens 1 gives rise to a flank rising quadratically with r.

(17) According to FIG. 4, moreover, the first portion 9 and the further portion which does not adjoin the first portion 9, i.e. here the middle further portion 7, are substantially vertical, i.e. they have a gradient of +/−∞. Alternatively, these two portions 7, 9 may also each mutually independently have a finite gradient (not shown).

(18) The two further portions 6, 8 which each adjoin the first portion 9 have substantially the same gradient, plotted over the squared radius r.sup.2. In the case of an intraocular or contact lens, the gradient may for example lie in the range from 1 μm/mm.sup.2 to 10 μm/mm.sup.2. The two portions 6, 8 may also comprise mutually different gradients (not shown).

(19) The diffractive structure 5 may either be applied to the entire surface of one side 2, 3 of the lens 1 or merely in a central region Z.sub.1 or an annular region Z.sub.2 of the lens 1, as shown in FIG. 1. Alternatively or in addition, the structure 5 may be apodised. This means that the profile depth T of the structure 5 decreases as the lens radius r increases.

(20) To produce the lens 1, the diffractive structure 5 may for example be incorporated directly into a lens blank, for example by turning on a lathe. The lens blank could however also merely be a processable starting material for a 3D printer, with incorporation of the structure into the lens blank then proceeding by 3D printing of the starting material to yield the multifocal lens 1.

(21) Alternatively, the diffractive structure 5 could initially also be incorporated as a negative into a moulded blank, for example again by means of a lathe or a 3D printer Then, a lens material is brought into contact with the moulded blank in order in this way to produce the multifocal lens 1. The lens material may for example already have been prefabricated into a lens blank, into which the structure 5 is pressed or impressed by means of the moulded blank acting as a “punch”. Alternatively, the lens material may be present in a liquid or viscous state and be cast onto the moulded blank, for example in a mould. The lens material is then hardened, for example by the input of light or heat.

(22) FIG. 5 shows a comparison of the intensity profile 14 (shown by a solid line) of the lens 1 presented here with the intensity profile 15 (shown by a broken line) of a lens according to the prior art (x-axis: distance D from the lens [mm]; y-axis: relative intensity I [1]).

(23) The lens 1 used for this comparison with the diffractive structure 5 presented herein had a period p, plotted over the squared radius r.sup.2, of 0.65 mm.sup.2, wherein the profile depth T was 4.4 μm. The two further portions 6, 8 which in each case adjoined the first portion 9 had, plotted over the squared radius r.sup.2, a gradient of 4.3 μm/mm.sup.2.

(24) In contrast, the comparison line relating to the prior art had a periodic profile which within one period had four portions which successively rose, fell, rose and fell monotonically.

(25) As is clear from the diagram of FIG. 5, the result is a similar intensity distribution profile in the region of the refractive focal point F.sub.r. It is however readily apparent from FIG. 5 that the lens 1 according to the prior art had greater intensity values in the region of the second negative focal point F.sub.−2 of the diffractive structure 5. In contrast, in the case of the lens 1 presented here, non-usable, negative order intensities are shifted into usable positive orders, as is apparent from the markedly increased intensities of the profile 10 at the focal points F.sub.1 and F.sub.2, and the markedly reduced intensity of the profile 14 at the focal point F.sub.−2. A more intensely coloured and higher contrast image is thus obtained for the user of the described lens 1 than with lenses according to the prior art

(26) The invention is accordingly not limited to the embodiments shown but rather comprises all variants, modifications and combinations thereof which fall within the scope of the appended claims.