Diffractive lens with a composite profile

0001The present invention relates to the field of ophthalmic lenses.

0002It particularly relates to contact lenses and intraocular implants. The unifocal contact lenses are intended to be placed on the cornea of ​​the eye and they make it possible to compensate for the ametropia of the eye (myopia or hyperopia). On the other hand, intraocular implants are intended to replace the lens inside the eye.

0003We have sought, for many years, to develop bifocal or multifocal contact lenses placed in front of the cornea, making it possible to compensate for the accommodation of subjects with presbyopia and giving the possibility of correcting both a defect of far vision and of assist the lens in near vision.

0004Many types of bifocal or multifocal contact lenses have already been proposed. However, none of these multifocal lenses hitherto proposed is entirely satisfactory.

0005The document FR-A-1 423 908 evokes, as schematically illustrated in FIGS. 1A and 1B appended corresponding respectively to a front view and to a side section view, a contact lens 10 formed of two regions 11, 12 having on at least one face with different radii of curvature and therefore with different refractive properties adapted respectively to near vision and to far vision. The use of the lens described in the document FR-A-1 423 908 requires a relative displacement between the lens and the eye when switching from far vision to near vision thanks to the support of the lens on the lower eyelid, so that the axis of vision OO passes alternately through one or the other of the two regions 11, 12. In the appended FIGS. 2A and 2B, the theoretical relative position of the lens 10 and of the eye are illustrated schematically in far vision and in near vision. In these figures 2A and 2B a distant object is referenced 13, a close object is referenced 14, while the retina, the natural lens and the lower eyelid are referenced 15, 16 and 17 respectively. Such a type of lens is not entirely satisfactory. It will be noted in particular that this type of lens in theory requires a significant displacement of the lens 10 relative to the eye so that the axis of vision OO passes alternately through one or the other of the two regions 11, 12 Therefore, the essential support of the lens 10 on the lower eyelid 17, combined with the relative movement of the lens / eye make these lenses difficult to bear. If, moreover, the two types of correction are used simultaneously, the optical axis OO being close to the junction between the two regions 11, 12, an unacceptable image jump is obtained.

0006It will be noted that, as illustrated in FIGS. 3A, 3B and 4A, 4B respectively in front view and in side section view, the documents US-A-1 647 721 and US-A-1 735 758 refer to lenses 20, 30, intended to be mounted on spectacle frames which, similarly to document FR-A-1 423 908, regions 21, 22; 31, 32, having different refractive properties; however, according to documents US-A-1 647 721 and US-1 735 758 the different refractive properties are not obtained by variation of radius of curvature, but by variation of index. More precisely, the different refractive properties are obtained by inclusion, in the body 22, 32 of the lens formed of a material of determined index, of an element 21, 31, formed of a material of different index. The lenses defined in documents US-A-1 647 721 and US-A-1 735 758 have the same drawbacks as the lens presented in document FR-A-1 423 908.

0007The contact lenses of the prior art which have been succinctly described above with reference to FIGS. 1 to 4 are intended to allow alternating vision. These lenses generally require a ballast to maintain their orientation and prevent their rotation on the eye, ballast which constitutes an extra thickness very troublesome for the comfort of the wearer.

0008In addition, it is necessary that the movement of the lens is perfectly controlled to ensure correct alternating vision. However, due to different variations, independent of the geometry of the lens, such as eyelid pressure, flow of the film of tears, etc., this displacement can become irregular and uncontrolled.

0009To overcome these drawbacks, other contact lenses have been proposed and use the concept of simultaneous far and near vision.

0010As illustrated diagrammatically in FIGS. 5A and 5B appended respectively in front view and in side section view, the documents EP-A-1 184 490, EP-A-0 232 191, US-A-4 636 049 evoke a lens contact 40 formed of two concentric regions 41, 42, having on at least one face different radii of curvature and therefore different refractive properties, adapted respectively to near vision and far vision. These lenses no longer require relative movement between the lens and the eye to switch from one type of vision to another. However, there is a superposition of images at the transition between the two regions. In addition, the component is very sensitive to variations in the pupillary diameter and the latter may experience large variations depending on the luminance and the patient. For example, if the central region 41 of the lens is assigned to near vision, when the opening of the lens is such that it covers only the central region 41, the user cannot correctly see a distant object.

0011Document US-A-3,726,578 mentions a lens which, similarly to documents EP-A-0 184 490, EP-0 232 191 and US-A-4 636 049, concentric regions having different refractive properties. However, according to document US Pat. No. 3,726,578, the different refractive properties are not obtained by variation of radius of curvature, but by variation of index, that is to say by inclusion, in the body of the lens formed of a material of determined index, of an element formed of a material of different index.

0012The document US-A-3,339,997 mentions a lens very close to those mentioned above but which, however, using the chromatic aberration of the eye, has two concentric regions or not, of different chromatism in order to present different refractive properties according to The wavelength.

0013Documents US-A-3,004,470, US-4,162,122, US-A-4,210,391 and US-4,340,283 refer to lenses 50, 60 schematically illustrated in front view in attached FIG. 6A and in side sections in FIGS. 6B and 6C, no longer presenting two concentric regions only as recommended by documents EP-A-0 184 490, EP-0 232 191 and US-A-4 636 049, but a series of concentric zones in a crown 51 , 52; 61, 62, having alternately radii of curvature of a first and a second value 53, 54, 63, 64, to work alternately in near vision and in far vision. The alternation of the zones makes it possible to overcome the sensitivity to the variation of the pupillary diameter, (this is a definite advantage compared to the subject of documents EP-A-0 184 490, EP-AO 232 191 and US-A- 4,636 O49). However, the lenses mentioned in documents US-A-3 OO4 47O, US-A-1 162 122, US-A-4 210 391 and US-A-4 340 283 do not mention the diffractive properties of such alternating profiles .

0014The documents EP-AO O64 812 and US-A-4 637 697 mention another type of lens, intended to achieve bifocal correction of the eye without zone separation. For this, the lens proposed in documents EP-AO O64 812 and US-A-4 637 697 has a posterior surface and an anterior surface of medium curvatures adapted to the correction necessary for the distance vision of the wearer, the lens having in in addition to a hologram which provides the lens with additional diffraction power, such that the image of a close object is correctly focused on the retina. According to the aforementioned documents, the hologram can be generated within the lens or on the surface thereof. The hologram can be generated by holographic recording. It can be generated mechanically in the form of a hologram in relief on the surface of the lens, as illustrated in FIG. 7 appended, that is to say in the form of a zoned network inspired by the optical system known from skilled in the art, under the name of SORET network.

0015More precisely still, the holograms in relief according to the document US-A-4 637 697 are formed of zones 70, 71, 72, 73, 74, concentric of the same surface, that is to say whose external rays evolve according to a geometric progression in <maths id="math0001"><math display="inline"><mrow><msqrt><mtext>K</mtext></msqrt></mrow></math><img file="EP0343067B1_D0001.tif" /></maths> r₁ or r₁ denotes the external radius of the central zone 70, and K denotes the integers. The phase profile of the hologram in relief is identical for all the zones 70, 71, 72, 73, 74 and asymmetrical to favor the +1 diffraction order. By way of example, the phase profile of each zone 70, 71, 72, 73, 74 can be defined by a series of A concentric levels of different thicknesses to obtain differences in optical delay of 2π / A. According to document EP-AO 064 812, the hologram can be provided over all or only a part of the optical zone of the lens. In addition, the lens can be produced with several holograms generated separately, possibly superimposed, providing different diffraction powers. In the case of holograms in relief forming a zoned network, obtaining different diffraction powers is materialized by zones consisting of concentric sub-zones whose external rays respond to different geometric progressions from one zone to another . The use of lenses of the type mentioned in documents EP-O O64 812 and US-A-4 637 697 poses problems of perception of contrasts under certain vision conditions.

0016Note that the document GB-A-802 918 previously described the association, in a sighting system for a firearm, on the one hand of optical means allowing the user to clearly see a distant target, on the other hand a zoned network allowing the user to observe the handlebars of the weapon. According to document GB-A-802 918, the zoned network can be formed either of a transparent lens, one of the faces of which is formed of concentric zones of the same surface, alternately transparent and opaque, or of a transparent lens formed of concentric rings of the same radial surface but alternately having one or the other of two optical thicknesses.

0017The object of the present invention is to propose a new type of bifocal or multifocal lens which eliminates the drawbacks of previous lenses.

0018The ophthalmic lens according to the present invention is of the known type comprising concentric diffractive components, and it is characterized in that it comprises at least two concentric regions having diffractive components which have phase profiles different from one region to the other in order to use different diffraction orders.

0019As will be explained below, the lens according to the present invention, because it has diffractive components of different phase profiles distributed over concentric regions, has a diffraction efficiency ratio in far vision and in near vision respectively which evolves according to the diameter of the pupillary opening. The lens according to the present invention can therefore be better adapted to the conditions of use.

0020Other characteristics, aims and advantages of the present invention will appear on reading the detailed description which follows, and with reference to the appended drawings given, by way of non-limiting examples and in which:<ul id="ul0001" list-style="dash"><li>FIGS. 1 to 7 previously described illustrate the state of the art,</li><li>FIG. 8 represents a schematic side section view of a lens according to the present invention,</li><li>FIGS. 9A and 9B show in enlarged view the profile of the reliefs of the diffractive components of a region of the lens,</li><li>FIG. 10 shows in enlarged view the profile of the reliefs of the diffractive components of another region of the lens,</li><li>FIG. 11 represents a section view of another variant of the lens according to the present invention,</li><li>FIGS. 12 and 13 represent the efficiency of the diffractive components represented respectively in FIGS. 8 and 11, as a function of the opening of the pupil, and</li><li>Figures 14, 15, 16 and 17 show the effectiveness of lenses according to 4 exemplary embodiments of the present invention.</li></ul>

0021As indicated above, according to an essential characteristic, a lens 100 in accordance with the present invention comprises at least two concentric regions 110, 120, having diffractive components having different phase profiles in order to favor different diffraction orders.

0022The diffractive components can be formed of phase holograms by modulation of the relief or of the index, hereinafter called relief or incide holograms.

0023In addition, the diffractive concentric regions of the lens 100 according to the present invention can be associated with a refractive component determined by the geometry of the lens. The refractive component is formed by the difference in radius of curvature between the two main surfaces 130, 140, of the lens. More specifically, the refractive component may have an identical refractive power over the entire extent of the lens, or may have two different refractive powers, respectively opposite the two concentric regions 110, 120, of diffractive components. It is also possible to envisage using a refractive component having different refractive powers with respect to a single concentric region 110, 120, of diffractive components.

0024According to a preferred characteristic of the present invention, the two concentric regions 110, 120, of the lens having different phase profiles, are adapted to work respectively one in the order n = +1, the other in the orders n = +1 and n = -1.

0025In the case where the diffractive components are formed of index holograms, these diffractive components are formed of concentric annular zones each having an index variation in the radial direction, the index profile of the various annular zones being identical, for a region considered 110 or 120 but differing from one region to another.

0026The external radius of the above-mentioned concentric annular zones, considered with respect to the optical axis of the lens, evolves according to a geometric progression of the type <maths id="math0002"><math display="inline"><mrow><msqrt><mtext>K</mtext></msqrt></mrow></math><img file="EP0343067B1_D0002.tif" /></maths> r₁ where K denotes the integers, and r₁ denotes the external radius of the central ring.

0027In the case where the diffractive components are formed of a hologram in relief, one of the faces 130 or 140 of the lens is formed of concentric annular relief structures. Each region 110, 120 is formed of at least one annular structure in relief centered on the axis of the lens. Each region 110, 120, can be formed of a large number of concentric relief structures referenced 110a, 110b, 110c ... for the central region 110 and 120a, 120b, 120c ... for the peripheral region 120 in FIGS. 8 and 11.

0028These structures 110a, 110b; 120a, 120b, have the same profile for the same region 110 or 120 but the relief structures 110a, 110b; 120a, 120b, have different profiles from one region to another. The different structures 110a, 110b; 120a, 120b, all have the same surface. The external rays of the different structures evolve according to a geometric progression of the type<maths id="math0003"><math display="inline"><mrow><msqrt><mtext>K</mtext></msqrt></mrow></math><img file="EP0343067B1_D0003.tif" /></maths> r₁ where r₁ denotes the external radius of the central structure 110a, as illustrated in FIGS. 8 and 11 and K denotes successive integers.

0029The focal lengths f_not of the diffractive component thus formed are equal to f_not = r₁² / 2nλ where r₁ denotes the external radius of the central structure 110a, n denotes the diffraction order and λ designates the wavelength considered.

0030The number N₁ of structures 110a, 110b ... included in the central region 110 of diameter D₁ equal:<maths id="math0004"><math display="block"><mrow><mtext>N₁ = D₁² / 4 r₁².</mtext></mrow></math><img file="EP0343067B1_D0004.tif" /></maths>

0031The number N₂ of structures 120a, 120b ... included in the peripheral region 120 of diameter D₂ equal:<maths id="math0005"><math display="block"><mrow><mtext>N₂ = (D₂² - D₁²) / 4r₁².</mtext></mrow></math><img file="EP0343067B1_D0005.tif" /></maths>

0032The number N of structures included in the pupillary opening diameter D equals:<maths id="math0006"><math display="block"><mrow><mtext>N = D² / 4r₁².</mtext></mrow></math><img file="EP0343067B1_D0006.tif" /></maths>

0033The profile of the structures 110a, 110b, 120a, 120b ... can be continuous as illustrated in FIG. 9B; it can also be sampled, as illustrated in FIG. 9A, for example formed by M levels, phase shifted by 2π / M generating differences in optical delay λ / M.

0034The diffraction efficiency E_not for the order n of such a sampled structure formed of M phase-shifted levels of 2π / M is equal to:<maths id="math0007"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>not</mtext></mrow></msub><mtext> = </mtext><mfrac><mrow><mtext>Energy in order n</mtext></mrow><mrow><mtext>Energy incidence</mtext></mrow></mfrac></mrow></math><img file="EP0343067B1_D0007.tif" /></maths><maths id="math0008"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>not</mtext></mrow></msub><mtext> = </mtext><mfrac><mrow><mtext>(sinπn / M) ²</mtext></mrow><mrow><mtext>(πn / M) ²</mtext></mrow></mfrac><mtext></mtext><mfrac><mrow><mtext>sin²π (1 - n)</mtext></mrow><mrow><mtext>M²sin²π (1 - n) / M</mtext></mrow></mfrac></mrow></math><img file="EP0343067B1_D0008.tif" /></maths>

0035The overall diffraction efficiency E_ng of the lens 100 having two concentric regions 110, 120 of different phase profiles corresponds to the average of the diffraction efficiency E_n110, E_n120 to order n of regions 110, 120, contained in the pupillary opening diameter D, that is:<maths id="math0009"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>ng</mtext></mrow></msub><mtext> = </mtext><mfrac><mrow><msub><mrow><mtext>N₁₀E</mtext></mrow><mrow><mtext>n110</mtext></mrow></msub><msub><mrow><mtext> + N₂₀E</mtext></mrow><mrow><mtext>n120</mtext></mrow></msub></mrow><mrow><mtext>NOT</mtext></mrow></mfrac></mrow></math><img file="EP0343067B1_D0009.tif" /></maths>

0036In the above relation, N₁₀ and N₂₀ denote the number of structures 110a, 110b; 120a, 120b, of each region contained in the pupillary opening diameter D. For example, if the pupillary opening diameter D equals the diameter D₁ of the central region 110, N₁₀ = N₁ and N₂₀ = 0.

0037The diffraction order n = +1 is obtained for relief structures of the sampled kinoform type, as illustrated in FIG. 9A, that is to say structures having a profile composed of M levels with M greater than 2, 2π / M phase shifted.

0038For example, for M = 4 the diffraction efficiency E₁ at the order n = +1 is equal to 0.81, while it is zero for the orders 0 and -1, the remaining energy being distributed in the higher orders.

0039The diffraction orders n = +1 and n = - 1 are obtained simultaneously by a structure of the niche function type generating a phase shift of π, as illustrated in FIG. 10, that is to say an alternation of concentric annular zones generating relative phase shifts of π. The diffraction efficiency of such niche structures generating a phase shift of π is equal to 0.4 for n = +1 and n = -1 while the diffraction efficiency E_not is zero for other orders n.

0040The overall diffraction efficiency of a compound diffractive component, as shown diagrammatically in FIG. 8, of a central region 110 formed of a kinoform sampled in 4 phase-shifted levels of 2π / 4 and of a peripheral region 120 formed of a slot function 0, π as a function of the pupillary opening diameter D is illustrated in FIG. 12.

0041When the diameter D of the pupillary opening is less than or equal to the external diameter D₁ (2R₁) of the central region 110, N = N₁₀ and N₂₀ = 0, the overall diffraction efficiency, E_ng = E_n110 and therefore E_{+ 1g} = 0.81 for n = +1 and E_ng = 0 for n = -1 and n = 0.

0042In conclusion, when the diameter D of the pupillary opening is less than or equal to the external diameter D₁ of the central region 110 the diffractive component has an efficiency of 0.81 for the corrective power + 1 / f (it is recalled that f_not = r₁² / 2nλ).

0043When the diameter D of the pupillary opening is greater than the external diameter D₁ (2R₁) of the central region 110, the efficiency of the diffractive component is determined by the following relationship:<maths id="math0010"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>ng</mtext></mrow></msub><mtext> = </mtext><mfrac><mrow><msub><mrow><mtext>N₁₀E</mtext></mrow><mrow><mtext>n110</mtext></mrow></msub><msub><mrow><mtext> + N₂₀E</mtext></mrow><mrow><mtext>n120</mtext></mrow></msub></mrow><mrow><mtext>NOT</mtext></mrow></mfrac></mrow></math><img file="EP0343067B1_D0010.tif" /></maths> so :<maths id="math0011"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>+ 1g</mtext></mrow></msub><mtext> = 0,4 + 0,41 </mtext><mfrac><mrow><mtext>D₁²</mtext></mrow><mrow><mtext>D²</mtext></mrow></mfrac><mtext> for n = +1</mtext></mrow></math><img file="EP0343067B1_D0011.tif" /></maths><maths id="math0012"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>-1g</mtext></mrow></msub><mtext>= 0,4 - 0,4 </mtext><mfrac><mrow><mtext>D</mtext><msub><mrow><mtext>​</mtext></mrow><mrow><msub><mrow><mtext>1</mtext></mrow><mrow><mtext>2</mtext></mrow></msub></mrow></msub></mrow><mrow><mtext>D²</mtext></mrow></mfrac><mtext> for n = -1</mtext></mrow></math><img file="EP0343067B1_D0012.tif" /></maths><maths id="math0013"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>ng</mtext></mrow></msub><mtext> = 0 for n = 0.</mtext></mrow></math><img file="EP0343067B1_D0013.tif" /></maths>

0044In other words when the diameter D of the pupil opening is greater than the external diameter D₁ of the central region 110, as illustrated in FIG. 12, the overall efficiency of the lens for the correction + 1 / f decreases towards a asymptote at 0.4 while the overall efficiency of the lens for the correction power -1 / f increases towards an asymptote at 0.4.

0045The overall diffraction efficiency E_ng a diffractive component of the type illustrated diagrammatically in FIG. 11 composed of a central region 110 formed of a niche function 0, π and of a peripheral region 120 formed of a kinoform sampled in 4 levels phase shifted by 2π / 4 , as a function of the diameter of the pupillary opening D, is illustrated in FIG. 13.

0046When the diameter D of the pupillary opening is less than or equal to the external diameter D₁ (2R₁) of the central region 110, N = N₁₀ and the overall efficiency E_ng = E_n110, so :<maths id="math0014"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>+ 1g</mtext></mrow></msub><mtext> = 0.4 for n = +1,</mtext></mrow></math><img file="EP0343067B1_D0014.tif" /></maths><maths id="math0015"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>-1g</mtext></mrow></msub><mtext> = 0.4 for n = -1,</mtext></mrow></math><img file="EP0343067B1_D0015.tif" /></maths><maths id="math0016"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>ng</mtext></mrow></msub><mtext> = 0 for n = 0.</mtext></mrow></math><img file="EP0343067B1_D0016.tif" /></maths>

0047In other words, when the diameter D of the pupillary opening is less than or equal to the external diameter D₁ of the central region 110, the lens has an overall efficiency identical and equal to 0.4 for the correction powers + 1 / f and -1 / f.

0048When the diameter D of the pupillary opening is greater than the external diameter D₁ (2R₁) of the central region 110, the overall efficiency of the lens is given by the relation:<maths id="math0017"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>ng</mtext></mrow></msub><mtext> = </mtext><mfrac><mrow><msub><mrow><mtext>N₁₀E</mtext></mrow><mrow><mtext>n110</mtext></mrow></msub><msub><mrow><mtext> + N₂₀E</mtext></mrow><mrow><mtext>n120</mtext></mrow></msub></mrow><mrow><mtext>NOT</mtext></mrow></mfrac></mrow></math><img file="EP0343067B1_D0017.tif" /></maths> so :<maths id="math0018"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>+ 1g</mtext></mrow></msub><mtext> = 0,81 - 0,41 </mtext><mfrac><mrow><mtext>From</mtext><msup><mrow><mtext>​</mtext></mrow><mrow><msup><mrow><mtext>​</mtext></mrow><mrow><mtext>2</mtext></mrow></msup></mrow></msup></mrow><mrow><mtext>D²</mtext></mrow></mfrac><mtext> for n = +1</mtext></mrow></math><img file="EP0343067B1_D0018.tif" /></maths><maths id="math0019"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>-1g</mtext></mrow></msub><mtext> = 0,4</mtext><mfrac><mrow><mtext>D₁²</mtext></mrow><mrow><mtext>D²</mtext></mrow></mfrac><mtext> for n = -1 and</mtext></mrow></math><img file="EP0343067B1_D0019.tif" /></maths><maths id="math0020"><math display="block"><mrow><msub><mrow><mtext>E</mtext></mrow><mrow><mtext>ng</mtext></mrow></msub><mtext> = 0 for n = 0.</mtext></mrow></math><img file="EP0343067B1_D0020.tif" /></maths>

0049In other words, when the diameter D of the pupil opening is greater than the external diameter D₁ of the central region 110, as illustrated in FIG. 13, the overall efficiency of the lens for the correction power + 1 / f increases towards an asymptote at 0.81, while the overall efficiency of the lens for the correction power -1 / f decreases towards 0.

0050We will now describe 4 examples of lenses according to the present invention.

EXAMPLE 1

0051We want to make a lens with a correction power in near vision P_P = -2.5 diopters, favored in high luminance and maintained at a minimum low luminance threshold and a correction power in far vision P_L = -4 diopters favored in low luminance.

0052The lens meeting these criteria includes:<ul id="ul0002" list-style="dash"><li>a refractive lens of constant power 1 / f ′ = -3.25 diopters, and</li><li>a diffractive component with a power 1 / f = 0.75 diopters, of the type illustrated in appended FIG. 8 composed of a central region 110 formed of a kinoform sampled in M ​​levels (4 levels for example) and a peripheral region 120 formed by a niche function in 0, π.</li></ul>

0053The central region 110 of the diffractive component works in the +1 order. It provides a focal length + f with an E diffraction efficiency_1g = 0.81. The correction power of the central region 110 of the lens, the only active at high luminance is therefore: 1 / f + 1 / f ′ = 0.75 - 3.25 = -2.50 diopters with constant efficiency.

0054The peripheral region 120 of the active diffractive component with low luminance works both in the orders n = +1 and n = -1 with the efficiency E_{+ 1g} = 0.4 and E_-1g = 0.4. It provides the two focal lengths + f and -f with a diffraction efficiency of 0.4.

0055The peripheral region therefore provides two powers of correction: 1 / f + 1 / f ′ = 0.75 - 3.25 = -2.5 diopters and -1 / f + 1 / f ′ = -0.75 - 3.25 = -4 diopters.

0056The effectiveness of these two corrections is constant and equal to 0.4 for the peripheral region 120 alone. Considering the lens 100 the efficiencies of these two corrections (-2.5 and -4 diopters) decrease and increase respectively with the pupillary opening diameter D, from D greater than D₁.

0057The effectiveness of the near vision correction and the far vision correction thus obtained is illustrated in FIG. 14 appended. FIG. 14 shows that the lens conforming to this first example does indeed favor near vision with high luminance while maintaining a correction threshold in near vision with low luminance, on the one hand, and allows far vision with low luminance on the other hand.

EXAMPLE 2

0058We want to make a lens with a correction power in near vision P_P = -2.5 diopters favored in high luminance, a correction power in intermediate vision P_I = -3.25 diopters favored in low luminance and a correction power in far vision P_L = -4 diopters favored in low luminance.

0059The lens meeting these criteria includes:<ul id="ul0003" list-style="dash"><li>a refractive component comprising a central power region 1 / f ′ = -2.875 diopters and a peripheral power region 1 / f˝ = -3.625 diopters, and</li><li>a diffractive component with a power 1 / f = 0.375 diopters of the type illustrated in FIG. 8 comprising a central region 110 formed of a kinoform sampled of 4 levels and a peripheral region 120 formed of a niche function 0, π.</li></ul>

0060The central and peripheral regions of the refractive component and of the diffractive component are placed respectively opposite, that is to say that they have identical external radii.

0061The central region 110 of the diffractive component works in the +1 order. It provides a focal length + f with an E diffraction efficiency_1g = 0.81. The correction power of the central region 110 of the lens is therefore: 1 / f + 1 / f ′ = 0.375 - 2.875 = -2.50 diopters with constant efficiency.

0062The peripheral region of the diffractive component works in both n = +1 and n = -1 orders with efficiency E_{+ 1g} = 0.4 and E_-1g = 0.4. It provides the two focal lengths + f and -f with a diffraction efficiency of 0.4.

0063The peripheral region 120 therefore provides two correction powers: 1 / f + 1 / f˝ = 0.375 - 3.625 = -3.25 diopters and -1 / f + 1 / f˝ = -0.375 - 3.625 = - 4 diopters.

0064The effectiveness of these two corrections is constant and equal to 0.4 for the peripheral region 120 alone. Considering the overall lens, the effectiveness of these two corrections -3.25 diopters and -4 diopters which correspond respectively to the correction required for intermediate vision and far vision increases with the pupillary opening diameter D from D greater than D₁.

0065The effectiveness of the lens for near vision, intermediate vision and far vision, as a function of the diameter of the pupillary opening D, is illustrated diagrammatically in FIG. 15. This shows that the lens corresponds to the conditions required, namely a near vision favored in high luminance and an intermediate vision and a far vision favored in low luminance.

EXAMPLE 3

0066We want to make a lens with a correction power in near vision P_P = - 2.5 diopters maintained at a minimum threshold in high luminance and favored in low luminance and a correction power in far vision P_L = - 4 diopters favored in high luminance.

0067The lens meeting these criteria includes:<ul id="ul0004" list-style="dash"><li>a refractive lens of constant power 1 / f ′ = - 3.25 diopters, and</li><li>a diffractive component with a power 1 / f = 0.75 diopters of the type illustrated in appended FIG. 11 composed of a central region 110 formed of a niche function 0, π and of a peripheral region 120 formed of a sampled kinoform of M levels (4 levels for example).</li></ul>

0068The central region of the diffractive component works in orders n = +1 and n = -1 with efficiency E_{+ 1g} = 0.4 and E_-1g = 0.4. It provides the two focal lengths + f and -f with a diffraction efficiency of 0.4.

0069The central region 110 therefore provides two correction powers: 1 / f + 1 / f ′ = 0.75 - 3.25 = -2.50 diopters and -1 / f + 1 / f ′ = -0.75 - 3.25 = -4 diopters.

0070The effectiveness of these two corrections - 2.50 diopters and -4 diopters is constant and equal to 0.4 for the central region 110.

0071The peripheral region 120 of the diffractive component works in the +1 order. It provides a focal length + f with an E diffraction efficiency_{+ 1g} = 0.81. The correction power of the peripheral region 120 of the lens is therefore: 1 / f + 1 / f ′ = 0.75 -3.25 = -2.50 diopters with a constant efficiency of 0.81.

0072Considering the global lens, this correction of -2.50 diopters therefore increases with the pupillary opening diameter D from D greater than D₁.

0073FIG. 16 which schematically illustrates the effectiveness of the lens for the powers of correction in near vision and in far vision shows that the lens conforming to the aforementioned third example meets the expected criteria, namely a near vision maintained at a threshold in high luminance and favored in low luminance and a far vision favored in high luminance.

EXAMPLE 4

0074We want to make a lens with a correction power in near vision P_P = -2.50 diopters favored in low luminance, a correction power in intermediate vision P_I = -3.25 diopters favored in high luminance and a correction power in far vision P_L = -4 diopters favored in high luminance.

0075The lens meeting these criteria includes:<ul id="ul0005" list-style="dash"><li>a refractive component comprising a central power region 1 / f ′ = -3.625 diopters and a peripheral power region 1 / f˝ = -2.875 diopters, and</li><li>a diffractive component with a power 1 / f = 0.375 diopters of the type illustrated in FIG. 11 appended, comprising a central region 110 formed of a sampled kinoform of 4 levels and a peripheral region 120 formed of a niche function 0, π.</li></ul>

0076The central region and the peripheral region of the refractive component and of the diffractive component are placed respectively opposite, that is to say that they have identical external radii.

0077The central region 110 of the diffractive component works in the orders n = +1 and n = -1 with the efficiency E_{+ 1g} = 0, 4 and E_-1g = 0.4. It provides two focal points + f and -f with a diffraction efficiency of 0.4. The central region 110 of the lens therefore provides two correction powers: 1 / f + 1 / f ′ = 0.375 - 3.625 = -3.25 diopters and -1 / f + 1 / f ′ = -0.375 - 3.625 = -4 diopters.

0078The efficiency of these two corrections -3.25 diopters and -4 diopters is constant and equal to 0.4 for the central region 110.

0079The peripheral region 120 of the diffractive component works in the +1 order. It provides a focal length + f with an E diffraction efficiency_{+ 1g} = 0.81. The correction power of the peripheral region of the lens is therefore: 1 / f + 1 / f˝ = 0.375 - 2.875 = -2.5 diopters.

0080The effectiveness of this correction of -2.5 diopters is constant and equal to 0.81 for the peripheral region 120 alone. Considering the global lens, the effectiveness of this correction of -2.5 diopters increases to 0.81 with the pupillary opening diameter D from D greater than D₁.

0081The attached FIG. 17 which schematically represents the effectiveness of the correction of the lens in near vision, in intermediate vision and in far vision shows that the lens according to the fourth example meets the aforementioned criteria, namely: a near vision favored in low luminance as well as an intermediate vision and a far vision favored in high luminance.

0082The hologram necessary for the production of the diffractive component having two different phase profiles in accordance with the present invention can be generated using any means known per se to those skilled in the art, in particular by etching, molding or recording. .

0083Of course the present invention is not limited to the embodiments which have just been described but extends to all variants in accordance with its spirit.