As mentioned above, diffractive lenses having a continuous and smooth profile without any sharp edges are less susceptible to glare or scattering due to non-uniformities in the path that incident light travels through the lens, and also to produce less halos, while being easier to manufacture according to a calculated profile compared to sawtooth type or binary type gratings or reliefs, for example. A higher diffraction efficiency in any case leads to less stray light. For manufacturing technologies based on diamond turning or similar forms of machining a smooth profile will be more reliable as well as faster and cheaper to fabricate than profiles with sharp edges such as sawtooth or binary profiles.

An important step in the manufacturing of ophthalmic lenses by micro-machining or diamond turning, for example, is mechanical polishing to get rid of cutting traces. It is necessary to get rid of all visible cutting traces to comply with quality requirements and medical regulations for intraocular lenses. Obtaining extremely low levels of cutting traces, however, requires expensive machinery as well as slow cutting. If lenses are polished post-cutting, the machine may be allowed to work faster. Sharp angles, corners or edges in the height profile of diffractive lenses complicate the process of mechanical polishing. If mechanical polishing is not possible in view of the height profile of the lens, one needs to either utilize chemical polishing, which requires hazardous chemicals, or manufacture lenses without the requirement of polishing. The latter leads to much increased manufacturing costs because of one or both of lower yields and more expensive machinery.

Smooth diffractive geometries in accordance with the present disclosure allow for polishing and therefore lead to a significant increase in yield, compared to lenses having sharp transitions in their height profile.

BRIEF DESCRIPTION OF THE FIGURES OF THE PRESENT INVENTION

Accompanying drawings are given solely for the purpose of exemplifying a multifocal aphakic diffractive multifocal lens, whose advantages over prior art were outlined above and will be explained in brief hereinafter.

The drawings are not meant to delimit the scope of protection as identified in the claims nor should they be referred to alone in an effort to interpret the scope identified in said claims without recourse to the technical disclosure in the description of the present invention.

FIG. 1 demonstrates a simplified anatomy of the human eye.

FIGS. 2a and 2b demonstrate a front and side view respectively of a typical ophthalmic multifocal aphakic intraocular lens as known in the art.

FIG. 3 demonstrates a schematic of the optical operation of a known periodic light transmissive circular disk-shaped lens body.

FIGS. 4a and 4b demonstrate a lens with a monofocal central zone with a symmetric multifocal grating as known in the art.

FIGS. 5a and 5b demonstrate a front and side view respectively of an ophthalmic multifocal aphakic intraocular lens according to one embodiment of the disclosed invention.

FIGS. 6a and 6b demonstrate a lens profile with a diffraction grating and a negative power central zone with adjusted power according to one embodiment of the disclosed invention.

FIGS. 7a, 7b and 7c demonstrate a lens profile with a diffraction grating and a central zone with adjusted power according to one embodiment of the disclosed invention.

FIG. 8 demonstrates the respective activation properties of rods and cones in the eye.

FIG. 9 demonstrates the point spread function (SPF) for different eyes and conditions.

FIGS. 10a and 10b demonstrate a lens using a central zone that is substantially concave and promotes far vision very strongly according to one embodiment of the disclosed invention.

FIGS. 10c, 10d, and 10e demonstrate examples of underlying linear grating diffractive unit cells and their respective diffraction efficiencies according to one embodiment of the disclosed invention.

FIGS. 11a and 11b demonstrate a lens according to one embodiment of the disclosed invention.

FIGS. 12a and 12b demonstrate a lens according to one embodiment of the disclosed invention.

FIG. 13a demonstrates a possible design goal for energy distribution for a lens made according to one embodiment of the disclosed invention.

FIG. 13b demonstrates a simulated energy distribution of a lens made according to one embodiment of the disclosed invention.

DETAILED DESCRIPTION OF THE PRESENT INVENTION

- 10 Eye
- 11 Cornea
- 12 Pupil
- 13 Natural crystalline lens
- 14 Retina
- Posterior cavity
- 16 Anterior and posterior chambers
- 17 Far vision
- 18 Intermediate vision
- 19 Near vision
- 20 Optical axis
- 29 Optical axis
- 30 Ophthalmic lens
- 31 Lens body
- 32 Haptic(s)
- 33 Center part
- 34 Front surface
- 35 Rear surface
- 36 Diffraction grating
- 37 Optic diameter
- 38 Outer diameter
- 39 Center thickness
- 40 Lens
- 41 Lens body
- 42 Diffraction grating
- 43 DOE(s)
- 44 Light receiving surface
- 45 Center part
- 46 Primary light beam
- 47 Secondary light beam
- 48 Optical axis
- 50 Multifocal aphakic intraocular lens
- 51 Central lens portion
- 52 Symmetric multifocal grating
- 53 Peripheral lens portion
- 54 Anterior surface
- 55 Posterior surface
- 56 Lens body
- 150 Lens body surface
- 151 Symmetric multifocal diffraction grating
- 152 Monofocal central zone
- 153 Transition point
- 154 Intermediate vision focal point
- 155 Far vision focal point
- 156 Near vision focal point

The vast majority of ophthalmic diffractive trifocal lenses make use of sawtooth profiles. Combining sawtooth profiles of two bifocal diffractive lenses to achieve trifocality is known in the art. This results in diffractive lenses with the usable orders arranged asymmetrically with respect to the 0^thorder, e.g. a trifocal lens might make use of orders 0, +1, and +2 orders or 0, +2, and +3. Such diffraction gratings are henceforth referenced as asymmetric gratings.

One important property of diffractive gratings is the distinction between symmetric and asymmetric diffraction gratings. When ascribing symmetric or asymmetric property to multifocal ophthalmic lenses, what is considered is which orders it makes use of or renders useful. Symmetric diffractive lenses utilize of orders in a way that is symmetric around the 0^thorder. Note that symmetric diffraction gratings are defined by which orders they utilize, not by the intensity of light distribution in these orders. Some symmetric diffractive lenses may be tuned so that there is a significant difference in light intensity between e.g. +1 and −1 orders, i.e. they have an unequal light distribution. A diffraction grating tuned as such would still be considered a symmetric diffraction grating. Most symmetric gratings discussed in this document will use an odd number of contiguous orders and the 0^thorder, e.g. gratings used for trifocal lenses making use of order −1, 0, and +1 or gratings for pentafocal lenses making use of order −2, −1, 0, +1, and +2. However gratings not making use of the 0^thorder can also be considered symmetric. Specifically the symmetric case of a grating making use of the four order −2, −1, +1, and +2 can in some cases be useful for ophthalmic lenses.

The highest possible diffraction efficiency for most useful intensity distribution for diffractive multifocal lenses with an odd number of foci, including trifocal lenses, is provided by smooth sinusoidal surfaces with usable orders symmetrically arranged around the 0^thorder.

When comparing diffractive surfaces, an important factor is the diffractive efficiency. Diffraction efficiency is a measure of how much of the optical power is directed into the desired diffraction orders, or, when talking about diffractive lenses in particular, how much of the optical power is directed into the desired focal points. For bifocal lenses, where the surface of the lens body is optimized to provide an as good vision as possible at two distinct distances, the highest possible diffraction efficiency is reached by using the principles of a phase-matched Fresnel lens, which makes use of a sawtooth or jagged type diffraction pattern. Reference is made to the publication “Refractive and diffractive properties of planar micro-optical elements”, by M. Rossi et al., in Applied Optics Vol. 34, No. 26 (1995) p. 5996-6007, which publication is herein incorporated by reference.

It is often advantageous to first consider linear phase grating since that field has a well-developed theory and can be utilized for diffractive lenses. For the special case of a trifocal linear grating with an equal intensity distribution to each order, it is shown specifically that the optimal solution is a structure without sharp edges in the publication “Analytical derivation of the optimum triplicator”, by F. Gori et al., in Optics Communication 157 (1998), p. 13-16, which publication is herein incorporated by reference.

The publication “Theory of optimal beam splitting by phase gratings. I. One-dimensional gratings”, by L. A. Romero and F. M. Dickey, in Journal of the Optical Society of America Vol. 24, No. 8 (2007) p. 2280-2295, which publication is herein incorporated by reference, discloses this more generally, proving that at the very least that optimal gratings for equal splitting into odd number of orders have continuous profiles. This latter paper provides the mathematical tools to find the optimal linear phase grating for any given set of target orders and any given intensity distribution among those target orders. The optimal grating is defined as the linear diffraction grating with the highest diffraction efficiency for the specified intensity distribution. It is noted that the publications by Gori et al. and Romero et al. discuss linear phase gratings only with the intent of creating beam splitters. By treating the x-axis of the linear grating as the r²space of a diffractive lens, any such linear phase can be turned into a lens. Using the theory from the study by Romero and Dickey it is possible to define the orders of interest and the relative intensity distributions of respective order and find the equation for the optimum (most efficient) grating for those input values. It further shows that at the very least symmetric gratings with a contiguous set of orders have optimum gratings without discontinuities for relatively equal intensity distributions. Some symmetric gratings with non-contiguous order sets also have gratings without discontinuities. In the Romero and Dickey study, only gratings with equal intensity distributions are shown, however using the provided theory gratings with non-equal distributions are also documented. It should be noted that this is one specific way to optimize linear phase gratings. Additionally, there are effects specific for lenses not taken into account by optimization of linear phase gratings, optimizing for these effects can be advantageous when designing lenses according to the present invention.

One important part of the design of a lens according to the present invention is to find a set of symmetric diffractive unit cells without discontinuities that can be used together to provide the desired intensity distribution. There are different ways to calculate and tune symmetric diffractive lenses in the art. One way is to use optimized linear grating transformed into diffractive lenses, as described above and in further detail PCT/EP2019/080758. One early example of a lens based on a symmetric diffractive grating is the 7-focal lens described in the paper by Golub et al., “Computer generated diffractive multi-focal lens” published in Journal of modern optics 39, no. 6 (1992): 1245-1251. As a continuation of this, additional embodiments in the already mentioned Osipov 2015 study as well as the study published in 2012 by Osipov et al. called “Fabrication of three-focal diffractive lenses by two-photon polymerization technique” published in Applied Physics A 107, no. 3 (2012): 525-529. In these papers trifocal, symmetric lenses made by modifications to a sinus grating are disclosed. In these studies by Osipov et al. only one unit cell is used per lens, but with what we now know the diffractive grating for an properly adaptive lens could be constructed from a set of modified sinus gratings made as described. A different approach is also disclosed in U.S. Pat. No. 5,760,871A and IL104316, where a so called asymmetric super Gaussian formula is used to design trifocal gratings with unequal intensity distribution. A set of such diffraction unit cells could be used together, with proper transition zones, to form a proper diffraction grating for an adaptive lens according to the patent. Yet another method is the one described in WO2020053864A1, where the Gerchberg-Saxton iterative algorithm is used to design the surface profile of a pentafocal (having five focal points) lens with a symmetric diffraction grating.

The lens according to the present invention is an ophthalmic lens comprising at least a refractive baseline and at least a first and a second portion, the portions being arranged concentrically around the optical axis, so that a concave shape in the center of the first portion is super positioned onto the refractive baseline and provides an optical power that is between the intended power of far and intermediate vision, and in the second portion a symmetric diffractive grating super positioned on to the refractive baseline, arranged so that, for a design wavelength, the 0^thorder of the symmetric diffractive grating substantially coincides with the power of the refractive baseline as well as an intended intermediate power of the lens.

Proposed multifocal ophthalmic lens addresses problems known in the art as follows: Insofar as symmetrical multifocal diffraction gratings are applied, several problems tend to present themselves such as the combination of a monofocal central zone (providing only far vision) and a multifocal grating with fixed diffraction efficiencies optimized for an aperture of 3 mm, as known in the art, leading to an imbalanced lens, wherein the near vision is particularly overly strong for large apertures. Another one of such technical difficulties to be solved is when a strictly monofocal central zone with optical power exactly coinciding with the diffractive focal point responsible for far vision leads to a decrease in overall efficiency.

Above mentioned difficulties notwithstanding, a strong far vision is the typical criterion to ascertain the success of cataract surgery. This is because a strong far vision is important for all apertures.

As such, disclosed invention specifically concerns the creation of an adaptive multifocal lens comprising a symmetric multifocal diffraction grating. Adaptivity is here defined as a measure of functional light utilization for the human eye. The eye has a much larger depth of field at pupil sizes that are smaller, due to the pinhole effect. Pupil size, not being solely dependent on the pupillary light reflex, is also dependent on the accommodation reflex, which causes the pupil not sufficiently enlarging while focusing on objects of closer proximity. Disclosed invention also addresses this problem so that the power of the central portion of said multifocal lens is adjusted to increase the efficiency and therefore success rate of cataract surgery whilst maintaining the inner 1-mm aperture to essentially provide far vision. This is detailed hereinafter.

According to the study by Kanellopoulos and Asimellis titled “Clear-cornea cataract surgery: pupil size and shape changes, along with anterior chamber volume and depth changes. A Scheimpflug imaging study.” Clinical Ophthalmology (Auckland, NZ) 8 (2014): 2141, cataract surgery on average decreases the photopic pupil with 0.27 mm. Additionally, the pupil sizes reported in medical literature is often the apparent pupil, since it can be measured by optical inspection. However, the more relevant pupil is the anatomical pupil, located closer to the natural lens (in the phakic eye). Following from the Kanellopoulos-Asimellis study, the apparent pupil can be considered as the entrance pupil of the optical system of the eye, while the anatomical pupil is the aperture stop. According to the model in mentioned study, the apparent pupil is 13.1% larger than the anatomical pupil. This will of course vary between individuals as well as between environmental conditions. The apertures referred to in this document are the physical apertures of the eye, specifically of the aphakic and pseudophakic eye. In the medical literature naturally occurring pupil sizes are often given as 2 mm to 8 mm, but for IOLs the relevant aperture size is in most cases up to 5 mm diameter and 6 mm at the most.

In addition to the pupillary light reflex the pupil also responds to the accommodation reflex. The accommodation reflex is a response to focusing on a nearby object and one of its effects is that of constricting the pupil. Because of this latter effect even in scotopic conditions the pupil will not be very large while focusing on nearby objects. Because of this additional near vision provided by an intraocular lens for large pupils is mostly wasted and is ideally not provided.

For small pupil sizes the pinhole effect is important to consider. A constriction of the pupil increases the depth of focus of the lens, for tiny pupils this effect generally provides a relatively good vision at all distances even with a lens that is providing only a single focus. Many modern multifocal- and enhanced depth-of-focus (EDOF) lenses takes advantage of this effect by allowing the light provided by the lens to be dominated by intermediate or near vision. The argument is that if this is provided in the center of the lens it will work well enough for the user in photopic conditions, because of large depth of field for tiny apertures, while this intensity provided for near and/or intermediate vision can be of use especially for mesopic conditions with slightly larger pupil sizes. A non-diffractive example of higher power in the central region with decreasing power for increasing radius is disclosed in U.S. Pat. No. 10,028,825 with so called continuous power progressive intraocular lenses that introduces a changing power without the use of abrupt steps. While that can be acceptable it is not the ideal solution, as an excellent far vision is seen as the most important parameter of IOLs and the quality of the far vision is indeed what determines clinical success of cataract surgery. Because of this it is important for an IOL to provide a strong far vision for all apertures, with the possible exception for very tiny pupils. Additionally, ophthalmologists often expect the autorefractometer to measure the far in the post-operative eye, and a central power that is too much removed from the far power of the lens can lead to confusion in evaluation of the cataract surgery success. However, a small shift of power towards stronger diopters for very small apertures can be of use to increase the so-called landing zone or sweet spot to increase the chance of clinical success, but in the ideal case this shift should not be as large as to go all the way to an intermediate addition (approximately between 1.5 D to 2.2 D) and certainly not to a near addition (approximately between 3 D and 4.4 D). An ideal shift in the central 1 mm aperture should be below 1.2 D and, in any case, the dominant focus at 1 mm should be below that of the intended intermediate power. It should be noted here that at 1 mm aperture there is usually no developed multifocality. The measured intensity- or MTF-curve will have one dominant peak.

On the other hand, the addition of near and intermediate powers is important for mesopic conditions to enable viable vision for most ranges. Usually, it is desirable to keep the near vision stronger than the intermediate vision to provide a good reading capability without the use of glasses.

It can then be summarized that what is desired is a multifocal lens where the multifocality is provided by a multifocal symmetric grating and for tiny pupils (e.g. 1 mm) the dominating focus should be corresponding to far vision with a slightly stronger optical power than the intended far power, or at the very least weaker than the intended power of the intermediate vision. At 2 a mm aperture a well-developed multifocality (at least three foci) should be present. For pupil sizes of around 3 mm the ideal diffractive multifocal lens should provide strong far vision, strong near vision, and some intermediate vision. For pupils larger than 4.5 mm energy directed to near vision cannot not be used well by the eye. Because of this additional energy directed to near vision should be minimized or small and the energy going to near for 4.5 mm pupil should be less than that for both intermediate and near.

FIG. 1 shows, in a simplified manner, the anatomy of the human eye 10, for the purpose of illustrating the present disclosure. The front part of the eye 10 is formed by the cornea 11, a spherical clear tissue that covers the pupil 12. The pupil 12 is the adaptable light receiving part of the eye 10 that controls the amount of light received in the eye 10. Light rays passing the pupil 12 are received at the natural crystalline lens 13, a small clear and flexible disk inside the eye 10, that focuses light rays onto the retina 14 at the rear part of the eye 10. The retina 14 serves the image forming by the eye 10. The posterior cavity 15, i.e. the space between the retina 14 and the lens 13, is filled with vitreous humour, a clear, jelly-like substance. The anterior and posterior chambers 16, i.e. the space between the lens 13 and the cornea 11, is filled with aqueous humour, a clear, watery liquid. Reference numeral 20 indicates the optical axis of the eye 10.

For a sharp and clear far field view by the eye 10, the lens 13 should be relatively flat, while for a sharp and clear near field view the lens 13 should be relatively curved. The curvature of the lens 13 is controlled by the ciliary muscles (not shown) that are in turn controlled from the human brain. A healthy eye 10 is able to accommodate, i.e. to control the lens 13, in a manner for providing a clear and sharp view of images at any distance in front of the cornea 11, between far field and near field.

Ophthalmic or artificial lenses are applied to correct vision by the eye 10 in combination with the lens 13, in which cases the ophthalmic lens is positioned in front of the cornea 11, or to replace the lens 13. In the latter case also indicated as aphakic ophthalmic lenses.

Multifocal ophthalmic lenses are used to enhance or correct vision by the eye 10 for various distances. In the case of trifocal ophthalmic lenses, for example, the ophthalmic lens is arranged for sharp and clear vision at three more or less discrete distances or focal points, often including far intermediate, and near vision, in FIG. 1 indicated by reference numerals 17, 18 and 19, respectively. Far vision is in optical terms when the incoming light rays are parallel or close to parallel. Light rays emanating from objects arranged at or near these distances or focal points 17, 18 and 19 are correctly focused at the retina 14, i.e. such that clear and sharp images of these objects are projected. The focal points 17, 18 and 19, in practice, may correspond to focal distances ranging from a few meters, to tens of centimeters, to centimeters, respectively. Usually, ophthalmologists choose lenses for the patients so that the far focus allows the patient to focus on parallel light, in the common optical terminology it is that the far is focused on infinity. Ophthalmologists will, when testing patients, commonly measure near vision as 40 cm distance from the eyes and intermediate vision at a distance of 66 cm, but other values can be used.

The amount of correction that an ophthalmic lens provides is called the optical power, OP, and is expressed in Diopter, D. The optical power OP is calculated as the inverse of a focal distance f measured in meters. That is, OP=1/f, wherein f is a respective focal distance from the lens to a respective focal point for far 17, intermediate 18 or near vision 19. The optical power of a cascade of lenses is found by adding the optical powers of the constituting lenses, for example. The optical power of a healthy human lens 13 is about 20 D.

FIG. 2a shows a top view of a typical ophthalmic multifocal aphakic intraocular lens 30, and FIG. 2b shows a side view of the lens 30. The lens 30 comprises a light transmissive circular disk-shaped lens body 31 and a pair of haptics 32, that extend outwardly from the lens body 31, for supporting the lens 30 in the human eye. Note that this is one example of a haptic, and there are many known haptic designs. The lens body 31 has a biconvex shape, comprising a center part 33, a front or anterior surface 34 and a rear or posterior surface 35. The lens body 31 further comprises an optical axis 29 extending transverse to front and rear surfaces 34, 35 and through the center of the center part 33. Those skilled in the art will appreciate that the optical axis 29 is a virtual axis, for the purpose of referring the optical properties of the lens 30. The convex lens body 31, in a practical embodiment, provides a refractive optical power of about 20 D.

In the embodiment shown, at the front surface 34 of the lens body 31 a periodic light transmissive diffraction grating or relief 36 is arranged, comprised of rings or zones extending concentrically with respect to the optical axis 29 through the center part 33 over at least part of the front surface 34 of the lens body 31. The diffraction grating or relief 36 provides a set of diffractive focal points. Although not shown, the diffraction grating or relief 36 may also be arranged at the rear surface 35 of the lens body 31, or at both surfaces 34, 35. In practice, the diffraction grating 36 is not limited to concentric circular or annular ring-shaped zones, but includes concentric elliptic or oval shaped zones, for example, or more in general any type of concentric rotational zone shapes.

In practice the optic diameter 37 of the lens body 31 is about 5-7 mm, while the total outer diameter 38 of the lens 30 including the haptics 31 is about 12-14 mm. The lens 30 may have a center thickness 39 of about 1 mm. In the case of ophthalmic multifocal contact lenses and spectacle or eye glass lenses, the haptics 32 at the lens body 31 are not provided, while the lens body 31 may have a plano-convex, a biconcave or plano-concave shape, or combinations of convex and concave shapes. The lens body may comprise any of Hydrophobic Acrylic, Hydrophilic Acrylic, Silicone materials, or any other suitable light transmissive material for use in the human eye in case of an aphakic ophthalmic lens.

FIG. 3 schematically illustrates, the optical operation of a known periodic light transmissive diffraction grating or relief 42 of a lens 40 comprising a biconvex light transmissive circular disk-shaped lens body 41. This type of lens, combining refractive and diffractive power is also referred to as a hybrid lens. The lens 40 is shown in a cross-sectional view in radial direction of the lens body. The diffraction grating or relief 42 comprises a plurality of repetitive, contiguously arranged, prism shaped transparent diffractive optical elements, DOEs, 43. The DOEs 43 extend in concentric zones around the center part 45 of the lens body 41, in a manner similar to the rings or zones of the grating or relief 36 shown in FIG. 2a. For illustrative purposes, the DOEs 43 of the diffraction grating 42 are shown as well-known jagged or saw-tooth type elements, comprising a continuous, sloping light receiving surface 44, such as a linear or curved sloping light receiving surface 44. Gratings or reliefs in which the DOEs 43 alternate between two heights, spaced apart in radial direction of the lens body 41, are called binary type reliefs (not shown). The repetition period or pitch of the DOEs 43 monotonically decreases in radial direction from the center or optical axis of the lens and varies with the square of the radial distance.

Pitch depends on the refractive index, the design wavelength, and the optical power of the first diffraction order. Pitch is determined so that the optical path difference (OPD) through the lens to the focal point of the first order has a difference of exactly one wavelength per period. To visualise the periodicity of a diffraction grating, one would often plot the diffractive lens profile versus the square of the radius. When plotted as such, the periods (grating pitch) are equidistant, more exactly the period pitch in r²is |2λf|, where λ is the design wavelength and f the inverse of the optical power of the first diffractive order.

In the art, one side of the lens is purely refractive, while the other side has a diffractive grating superpositioned over a refractive base line. The refractive baseline can be e.g., spherical or having some sort of aspherical shape. The diffractive pattern, which is added onto the refractive baseline, may in general be applied to any of the two sides of the lens. Therefore, if a diffractive pattern is to be combined with a refractive surface with some special feature, it generally bears little importance if they are added to the same side or, if one is added to a first side and the other to a second side of the lens. Concurrently, two diffractive patterns may be combined either by super positioning on one side, or by adding them in an overlapping fashion on separate sides. In the disclosures pertaining to the present invention, combining of two lens structures shall always be understood as allowing for both possibilities. The optical power of the lens for a specific diffraction order are calculable by addition of the refractive base power and the optical power of that diffractive order.

An incident or primary light beam 46 that passes the grating 42 and the lens body 41 is, respectively, diffracted and refracted and results in an output or secondary light beam 47. The refracted and diffracted light waves i.e. secondary light beams 47 form a plurality of focal points at the optical axis 48 of the lens 40, due to constructive interference of the light waves 47. Constructive interference occurs when the optical path difference between light waves 47 arriving from the lens body 41, at a particular focal point, is an integer multiple of their wavelength, i.e. the light waves are in-phase, such that their amplitudes add-up in a reinforcing manner. When the difference in optical path length travelled by interfering light waves 47 from the lens body 41 is an odd multiple of half of the wavelength, such that a crest of one wave meets a trough of another wave, the light waves 47 partly or completely extinguish each other, i.e. the light waves are out of phase, not resulting in focal points at the optical axis 48 of the lens body 41.

The points of constructive interference at various distances from the lens body 41 are generally designated diffraction orders. The focal point that corresponds to the focal point that originates due to refractive operation of the curvature of the lens 40 is indicated by order zero, 0. The other focal points are designated by orders +m and −m, wherein m is a positive integer value. That is, m=+1, +2, +3, etc. if the respective focal point occurs at the left-hand side of the zero order when viewed in the plane of the drawing, i.e. at a distance in the direction towards the lens body 41, and designated by orders m=−1, −2, −3, etc. if the respective focal point occurs at the right-hand side of the zero order when viewed in the plane of the drawing, i.e. at a distance in the direction away from the lens body 41. Such as illustrated in FIG. 3.

It is noted that the above allocation of the positive and negative diffraction orders in some publications and handbooks may be reversed with respect to their position relative to the zero order. This, for example, becomes the case when the theory in the publication by Romero et al is applied directly as has been done here. If not otherwise indicated, the present description adheres to the convention as shown in FIG. 3.

The diffraction relief 42 can be designed to provide focal points at different distances from the lens body 41. The periodic spacing or pitch of the DOEs 43 substantially determines where the points of destructive and constructive interference occur at the optical axis 48 of the lens, i.e. the position of the diffractive orders at the optical axis 48. By the shape and height of the DOEs 43 the amount of incident light that is provided at a point of constructive interference, i.e. at or in a particular diffraction order, is controlled.

In case of a diffraction grating or relief 42 providing diffraction orders that are regularly spaced at both sides of the zero order, the grating or relief is called a symmetric wave splitter or diffractive grating, as the incident light beam 46 is diffracted or split into orders that are symmetrically arranged with respect to the zero order. A grating or relief producing a non-regular spacing of diffractive orders, such as +1, +2, −3, −5 is called an asymmetric diffractive grating. The common cases of diffraction gratings producing usable orders at 0th order and +1 or 0^th, +1, and +2 are also asymmetric diffractive gratings.

The light energy in light waves (secondary light beams 47) that are focused or diffracted in focal points or orders that do not contribute to image forming at the retina 14 of the human eye 10 is lost and reduces the overall efficiency of the lens 40, and hence the quality of images perceived by a human being using such lens. In practice, for optimally designing a lens, it is advantageous if the focal points for providing or correcting far, intermediate and near vision to the human eye, such as illustrated in FIG. 1, for example, can be set beforehand, and a diffraction grating 42 is provided that maximizes the overall efficiency of the light energy received from the incident light beam 46 in these pre-set focal points is optimal.

In scientific literature, a diffraction grating optimizing overall efficiency of the light distribution in pre-set or target diffraction orders is found from determining a linear phase-only function or phase profile that generates the target diffraction orders with a maximum overall efficiency n or figure of merit defined as the sum of the normalized light energies of all these target orders. These diffractive gratings can then be shaped into lenses by adjusting the argument so that they have equidistant periods in the r²space.

Those skilled in the art will appreciate that the lens body 41 may comprise a plano-convex, a biconcave or plano-concave shape, and combinations of convex and concave shapes or curvatures (not shown).

FIGS. 4a and 4b illustrate a lens and the functionality of said lens according to PCT/EP2019/080758 by combining a monofocal central zone with a symmetric multifocal grating. FIG. 4a illustrates, by way of example, a height profile or amplitude profile of another embodiment of a trifocal ophthalmic lens in accordance with the present disclosure, along a linear scale as function of the radial distance r, expressed in mm. The amplitude profile or height profile of the embodiment of the ophthalmic lens illustrated in FIG. 15a comprises the surface of the lens body 150, in turn comprising a monofocal central zone, indicated by reference numeral 152 and a diffraction grating 151. The optical axis, running through the center of the lens body, is assumed to be at a radial position r=0, whereas the radial distance r measured in outward direction from the optical axis is expressed in mm along the vertical axis. Reference numeral 160 refers to the outer circumference of the front surface 34 of the lens body 30, as illustrated in FIGS. 2a and 2b. The central zone 152 is monofocal and arranged in this example to have a power coinciding with one for the focal points of the diffraction grating 151.

At a transition point 153, at a radial position of the lens body at a distance of about 0.5 mm from the optical axis, the continuous amplitude profile h(r) 152 of the monofocal central zone ends and continuous in the symmetric multifocal diffraction grating profile H(r) 151 of the diffraction grating. In the embodiment shown, the transition point 153 is at the surface 150 of the lens body.

In this example, the design wavelength λ of the lens is assumed at 550 nm, the index of refraction n of the lens body is set to 1.492, and the index of refraction n_m of the medium surrounding the lens body is assumed 1.336.

FIG. 4b shows the intensity simulation of the lens in FIG. 4a for four different aperture sizes, 1 mm, 2 mm, 3 mm, and 4.5 mm. The aperture, or the pupil, is assumed to correspond to double radius of the lens. The energy is depicted along the vertical axis, in a relative scale, where for each aperture the maximum number is set to 1. The computer simulated light intensity distributions assume a biconvex lens body of an ophthalmic lens of the type shown in FIGS. 2a, 2b, designed for targeting a zero-order focal point at 20 diopter, D, and focal points for near and far vision at 21.675 D and 18.325 D, respectively, symmetrically positioned with respect to the zero order. Reference numeral 154 refers to diffraction order 0, providing a focal point for intermediate vision, reference numeral 155 refers to the focal point for far vision at 18.325 D and reference numeral 156 refers to the near vision focal point at 21.675 D. It can be seen in the graph the exact positions of these peaks vary slightly with aperture, as discussed elsewhere this effect can be purposely used in lens design.

A lens constructed in this manner provides a good Far even for very small pupils. There are two main drawbacks with a design like this. Firstly, Inserting the monofocal central zone to the diffraction grating reduces diffraction efficiency. Secondly, when using this architecture to provide full vision (including Far vision, intermediate vision and near vision) it is necessary to balance the intensity distribution to provide a desired intensity distribution for photopic conditions, e.g., an aperture diameter of 3 mm. For a trifocal lens this usually involves providing a stronger far vision compared to other distances, however with relatively strong near and some intermediate vision. Because of the skew towards near vision needed in the diffraction grating to make up for the strong far vision in the center such a design leads to a too strong relative near energy at larger apertures.

FIG. 5a shows a top view of an ophthalmic multifocal aphakic intraocular lens 50, working in accordance with the present invention, and FIG. 5b shows a side view of the lens 50. The difference over the prior art, exemplified in FIG. 2 are in the optics of the lens. The lens body 56 has a biconvex shape, comprising a front or anterior surface 54 and a rear or posterior surface 55. The skilled person would know that for some embodiments one or both of the anterior surface 54 and the posterior surface 55 might be concave or planar, depending on the refractive baseline needed for a specific application. In this application of the invention the lens body, in accordance with the present disclosure, comprises a peripheral lens portion 53 and a central lens portion 51 that is combined with a symmetric multifocal diffraction grating 52. The lens is constructed such that, for a design wavelength, one of the diffractive orders of the symmetric multifocal diffraction grating 52 contributes to the far vision of the lens, the 0^thorder of the symmetric multifocal diffractive grating contributes to the intermediate vision of the lens, and yet another diffraction order contributes to near vision. In some embodiments the symmetric multifocal grating has three focal points, in other embodiments the number of focal points is a higher, odd, number, such as 5, 7, or 9. The central lens portion 51 has a dominant main optical power that is somewhere in between the powers of the intermediate and the far vision. FIGS. 5a and 5b shows a lens where one side of the lens is purely refractive, while the other side has a diffractive grating superpositioned over a refractive base line. As explained above in relation to FIG. 3, this is only one possible configuration. It is possible, for example, to distribute the diffractive grating over both sides, or superposition the diffractive grating to either side of a plano-convex or plano-concave lens. When a diffractive pattern is said to be combined with a refractive surface it can have either of these meanings.

The shape or height profile of the refractive baseline for any of the portions of the lens may be selected among a plurality of continuous refraction profiles known from monofocal lenses, such as spherical, or based on monofocal diffractive surface, or aspherical surfaces, which are among the most general known shapes of monofocal lenses known in the art. Monofocal diffractive surfaces refers to the phase-matched Fresnel lenses discussed earlier. By adjusting the phase matching number an arbitrarily wide unbroken monofocal zone can be created through diffractive optics. It is possible combine different types of refractive surfaces in one lens, so that the central portion and the peripheral portion consist of different types of refractive surfaces. The manufacturing of refractive of diffractive surfaces can be carried out by any of laser micro machining, diamond turning, 3D printing, or any other machining or lithographic surface processing technique, for example.

The present invention describes a way to create lens that maintains the advantages of the prior art lens in FIG. 4a and that increases diffraction efficiency and significantly increases the amount of light usable for the human eye.

This involves changes to two parts of the lens, the central portion of the lens, approximately within the 1 mm aperture, and the symmetric multifocal diffraction grating. By changing these two structures in concert we can arrive at the desired traits. FIG. 6 describes one such possible change to the central portion of the lens profile.

One very important property of a multifocal lens turns out to be the exact placement of the dominant optical power for very tiny apertures, e.g. as measured at 1 mm aperture. While FIG. 4a shows a lens profile where the optical power of the central zone perfectly aligns with one of the non-zero orders of symmetric multifocal diffractive grating, the central zone in FIG. 6a shows the profile of lens with a monofocal central zone that is slightly adjusted towards the 0^thorder, used for intermediate vision. Exactly as in FIG. 4a as well as in PCT/EP2019/080758 a so-called transition point, as marked by the dashed vertical lines in the figure, around the peak closest to the optical axis (the optical axis passes in this image vertically through the center of the plotted lens profile).

A monofocal central zone adds a local negative optical power to the center of the lens, relative to a refractive baseline. In the prior art it was proscribed that this power should be identical to the absolute power of the diffractive order responsible for far vision. However, a slight shift of power in a monofocal central zone can be used to achieve a more favorable light distribution. It has been found that a small decrease of the power of the central zone can have several positive effects. (1) It increases, when chosen correctly, the overall diffraction efficiency and over all the portion of the light usable for the eye, (2) it decreases the intensity of the unusable light that has lower power than the intended far vision, (3) by broadening the peak of vision it broadens the landing zone, and is a way to choose the power at e.g. a 1 mm aperture. In some configuration it can produce an asymmetric peak for the focal point providing far vision. Especially the broadening of the landing zone (sweet spot) by slight shift of power towards stronger diopters for very small apertures can be important to increase the chance of clinical success.

In terms of the specific example present here, FIG. 6b shows the simulated relative intensity peaks for four different apertures. The power shift decreases the undesired peak, here present around 17 D, and redirects some of that light to the 0^thorder (intermediate vision). The peak responsible for far vision can be found around 18.35 D. These features can be compared with FIG. 4b, where the most impactful change is the weakening of the undesired peak around 17 D in FIG. 6, meaning that more light is rendered useful for the eye.

The lens profile in FIG. 6a makes use of a diffraction grating that is identical to that of the lens in FIG. 4a, but in FIG. 6a the central zone has a negative power that is 0.275 D smaller in absolute terms. The symmetric diffraction grating is constructed to provide an order separation of 1.675 D. while the monofocal central zone has a curvature arranged to add a negative power to the refractive baseline of the lens that is 1.4 D. As simulated in FIG. 6b the dominant peak for a small 1 mm aperture is 1.2 D below the intended intermediate peak, rather than the 1.675 D of the nominal power of the diffraction order coinciding with far vision. This increases overall efficiency and broadens slightly peak for far vision. It is a tool that is very important and that is very useful when used in the right way.

A purely monofocal shape has been chosen for the central portion of these lenses because it is advantageous to have a very dominant far vision for small apertures and far vision that is at least stronger than the other for all larger apertures. However, it is not necessary to use a purely monofocal zone to achieve this. FIGS. 7a, 7b, and 7c exemplify a different choice of central zone. It is advantageous to use a transition zone between the central portion and the diffraction grating that is located close to the peak of the first peak of the diffraction grating. FIG. 7a shows such a lens profile. The vertical dashed lines in FIG. 7a points out the transition point, corresponding to the center of the transition zone. To avoid a sudden change in the profile there is a smooth transition between the central portion, that is very geared towards the far vision, and the first ridges of the symmetric diffraction grating, which are fully trifocal and arranged to slightly favor near vision. This specific example is made in such a way that the smooth transition between the two zones is carried out in parameter space, rather than just adding a transition between two heights.

Such central portion, that is not purely monofocal, could be constructed as a aspheric lens segment, as a modified spherical segment or as several spherical segments stitched together. Additionally, it can be calculated through the same means used to calculate diffractive unit cells for the multifocal symmetric diffractive grating. Several different ways to create such unit cells are discussed earlier in this document. If the latter method is used it is often advantageous to create a unit cell that strongly promotes the diffractive focal point responsible for far vision and then use only a portion of that unit cell. The more it is skewed towards far vision, the more it can be made to resemble a purely monofocal lens portion. Near the correct position of the crest closest to the center of the lens it is then transitioned to a diffraction grating with a substantially different light distribution. It can be noted that for a lens like this with a nominal order separation of 1.675 D, as in the present example, the first grating period, counted from the lens center, would end at and aperture of 1.62 mm (0.81 mm distance from the center). This is a large portion of the lens and illustrates the fact that it needs to be constructed carefully and that it needs more than one feature to achieve the desired light distribution. In the present case the transition point is at an aperture of 1.25 mm and a unit cell like the one shown in FIG. 7c was used for the central zone. This shape is very strongly geared towards far vision (here arranged to coincide with the +1 order of the unit cell), as can be seen in the plot of the efficiency distribution of the unit cell in question. However, the portion between the two vertical dashed lines was not used. Instead, the optical axis of the lens roughly coincides with dashed line to the right in the image of the unit cell. The central portion of the lens then consists of roughly the portion of the unit cell shown not between the two dashed vertical lines. Around the vertical line to the left (close to the left shoulder of the unit cell) the lens data is created by transition in parameter space. It is of course also possible to make an abrupt transition between the central zone and the multifocal diffraction grating. A central zone such as the one exemplified in FIG. 7a is essentially monofocal, but with shape that is more similar to the diffractive grating, which increases total efficiency of the lens. This provides further opportunity to tune total efficiency and exact power of the peak at 1 mm aperture.

FIG. 7b shows the simulated relative intensity peaks for four different apertures. The symmetric diffraction grating is constructed to provide an order separation of 1.675 D. As simulated in FIG. 7b the dominant peak for a small 1 mm aperture is, however, only 0.65 D below the intended intermediate peak. The undesired peak at 17 D is here visibly smaller than corresponding peaks in FIGS. 4b and 6b, indicating higher efficiency for the lens in FIG. 7a. This higher efficiency is also clearly born out in simulation as well as measurements from actual lenses. However, this graph also very clearly states the main drawback of the lens of FIG. 7a: the high energy directed towards near vision for large apertures. At a 4.5 mm aperture the near energy is here much higher than that of intermediate vision and even similar in strength to that of far vision. Much of this near light from large apertures cannot be used by the eye. So even if the diffraction efficiency is high, the physiological light efficiency for large apertures is much lower than what is ideal. To solve this problem, what's needed is a fully adaptive lens.

FIG. 8 illustrates the respective activation of rods and cones in the eye. Because of luminance levels and the pupil diameters, cones are dominant in photopic conditions, whereas rods are dominant in mesopic and scotopic conditions.

Based on the specific response of cones and rods in the eye's retina, the main three modes of eye function under different illuminance levels (cd/m²), photopic (bright light), scotopic (low light conditions) and mesopic (intermediary) are observed. The brightness level of the object observed, the background and surroundings determine the activity of rods and cones by retinal illuminance level (light intensity). Therefore, eye spectral response is directly related, and influenced by illuminance levels to which it is exposed, as depicted in FIG. 8. Pupil size is a linear function of the log of equivalent luminance (log cd/m²) calculated for large fields for adapting luminances from photopic to mesopic conditions (for further information, one may refer to: W. Adrian, “Spectral sensitivity of the pupillary system,” Clin. Exp. Optom., vol. 86, no. 4, pp. 235-238, 2003).

Pupil size plays an important role in achieving functional vision levels in the pseudophakic eye, since the eye is not able to produce a refractive change in response to object proximity. Pupil diameter is the main predictor for increased pseudoaccommodation and near visual acuity, as well as reading performance by determining the retinal blur area and the depth-of-field (refer to: E. Fonseca, P. Fiadeiro, R. Gomes, A. S. Trancon, A. Baptista, and P. Serra, “Pupil function in pseudophakia: Proximal miosis behavior and optical influence,” Photonics, vol. 6, no. 4, 2019).

Diffraction is the dominant limiting factor in small pupil diameters, while at large sizes, aberrations contribute more to retinal blur (referring to: A. Roorda and D. R. Williams, “The arrangement of the three cone classes in the living human eye,” Nature, vol. 397, no. 6719, pp. 520-522, 1999). FIG. 9 shows the typical point spread function (PSF) of the eye as a function of pupil size. Studies have shown that the balance between diffraction (which blurs the image for small pupils) and aberrations (affecting the lateral resolution) is somewhere between 2 mm and 4 mm pupils, depending on the individual (See A. Roorda et al., “What can adaptive optics do for a scanning laser ophthalmoscope?”, Bull. Soc. Belge Ophtalmol., no. 302, pp. 231-244, 2006). Larger aberrations for large pupils are yet another reason why light directed to near vision cannot be physiologically utilized.

FIG. 9 illustrates the point spread function (SPF) for different eyes and conditions. The top row shows the point spread function of an eye with no aberrations. As the pupil size increases the PSF decreases in size, offering the potential for higher resolution. The lower row shows the point spread functions for an eye with typical aberrations. In this case aberrations, particularly for the larger pupil sizes, blur the PSF.

Additionally, pupil size is a function of accommodation stimulus position for different ages (J. F. Zapata-Díaz, H. Radhakrishnan, W. N. Charman, and N. López-Gil, “Accommodation and age-dependent eye model based on in vivo measurements,” J. Optom., vol. 12, no. 1, pp. 3-13, 2019). A correlation between maximum pupil size and age, represents a −0.23 mm reduction in distance pupil diameter per decade of life, so that individuals in their 50s show an average pupil of 5.0 mm and individuals in their 80s present a 4.1 mm average pupil (E. Fonseca, P. Fiadeiro, R. Gomes, A. S. Trancon, A. Baptista, and P. Serra, “Pupil function in pseudophakia: Proximal miosis behavior and optical influence,” Photonics, vol. 6, no. 4, 2019).

The pupillary system ability to dilate can be reduced because of traumatic situations of the eye, such as cataract surgery. Therefore, a psuedophakic eye is less diluted than normal under scotopic, mesopic and photopic static illuminance conditions (referring to: H. K. Bhatia, S. Sharma, and P. Laxminarayana, “Ophthalmology and Clinical Research Report Clin Med International Library,” pp. 2-5, 2015, and A. J. Kanellopoulos, G. Asimellis, and S. Georgiadou, “Digital pupillometry and centroid shift changes after cataract surgery,” J. Cataract Refract. Surg., vol. 41, no. 2, pp. 408-414, 2015). Postoperative pupil diameter is reduced by approximately −0.3 mm compared to preoperative measurements (A. J. Kanellopoulos and G. Asimellis, “Clear-cornea cataract surgery: Pupil size and shape changes, Along with anterior chamber volume and depth changes. A Scheimpflug imaging study,” Clin. Ophthalmol., vol. 8, pp. 2141-2151, 2014.)

Additionally, measurement conditions can affect the level of retinal illuminance. Most scientific research is based on monocular pupillometry, where in reality an IOL performance should be evaluated for binocular vision. The binocular dynamic pupillometer is necessary to accurately determine pupil size under binocular conditions. It is known that light stimuli bring about more contraction to the pupil rather than monocular vision, since the indirect reflection of the pupillary system in binocular conditions is added to the direct reflection for single eye stimulation.

Surgeons can predict the postoperative pupil size, affecting the refractive outcomes and subsequent patient satisfaction after cataract surgery, if they can accurately and reproducibly determine the preoperative pupil size. This is the basics of pupil-customized cataract surgery (PCCS) which means predicting and maximizing the postoperative visual performance and subsequent patient satisfaction by the preoperative assessment of pupil size in cataract patients (for further information see Cataract surgery: Maximizing outcomes through research by H. Bissen-Miyajima, M. P. Weikert, and D. D. Koch, published in 2014).

As has already been discussed hitherto, the visual system is more sensitive to light coming in through the center of the eye pupil than to light entering from the periphery of the pupil due to the SCE. The SCE can significantly improve defocused image quality and defocused vision, particularly for tasks that require veridical phase perception.

These findings may be used clinically in assessing visual performance after cataract surgery and may have significance in terms of IOL design. Diffractive multifocal intraocular lenses provide vision for far, Intermediate, and near vision. The ideal energy distribution between them differs for different pupil sizes. For small pupils the dominating focus should be at far vision with a slightly stronger optical power than Far. For pupil sizes of around 3 mm the ideal diffractive multifocal lens should provide strong far vision, strong fear vision, and some intermediate vision. For pupils larger than 4.5 mm energy directed to near vision cannot not be used well by the eye. Because of this, as little additional energy as possible should be directed to near and the energy going to near for 4.5 mm pupil should be less than for both intermediate and near.

Therefore, multifocal intraocular lenses should ideally distribute the light energy between the foci in a way that in mesopic illuminance levels, nearly 80% of the light energy is directed to the far and near vision, while in scotopic illuminance levels, this nearly 80% of the light energy should ideally be distributed to the far and intermediate vision.

FIG. 10a shows an example of a lens according to the present invention. To obtain a fully adaptive lens the intensity distribution of the diffractive grating should change as a function of the distance from the optical center. FIG. 10a shows a lens profile, less the refractive baseline, that uses a central zone that is substantially concave and promotes far vision very strongly but is tuned to harmonize better with the multifocal grating of the lens. A transition point at an aperture of 1.25 mm, around the first peak leads into a symmetric multifocal grating consisting of a set of differently tuned diffractive unit cells. The first periods outside of the central portion constitute a relatively balanced diffractive grating that promotes near vision more than intermediate and far, this is then with increasing distance from the optical center transitioned over several steps to a diffractive grating that promotes far strongly, and especially disfavors near vision with regards to both far and intermediate vision. It is of course the case, that even if near vision is slightly favored in the region of the lens in between the central portion and approximately the 3 mm apertures, far vision has for all pupil size in this range the dominant intensity share, because of the far promoting central portion.

It is of course possible and often useful, to create an adaptive lens that has a fully monofocal central zone, such as in FIG. 6a. In such a configuration you have an adaptive lens with a strictly defined focal point for all diameters smaller than that of the transition point. Adaptive lenses using strictly monofocal central zones have slightly lower overall light efficiency compared to the type of lens described in FIG. 10, however, lens designs with the strictly monofocal central zone have practically been shown to be more robust in response to manufacturing and material perturbations. Material perturbations can be slight difference in refractive index between material batches. Monofocal central zones can also have some advantages for postoperative autorefractometer measurements. Because of these reasons the choice of central zone will have to be done on a case-by-case basis.

FIG. 10b shows the simulated relative intensity peaks for four different apertures. The symmetric diffraction grating is nominally constructed to provide an order separation of 1.675 D. As shown in the simulation data the dominant peak for a small 1 mm aperture is, however, only 0.6 D below the intended intermediate peak. To summarize the data in FIG. 10b, we see here that (1) the dominant focus at the 1 mm aperture is placed in between far and intermediate powers (18.32 D and 20 D, respectively), (2) the portion of energy directed to near vision (at about 21.7 D) is higher at 3 mm than at any of the other shown apertures, the intermediate energy is (3) at the 2 mm aperture weaker than both far and near, while (4) at 4.5 mm the near intensity is weaker than far as well as intermediate. At all apertures from 2 mm and above far is the strongest type of vision.

To create an adaptive diffractive lens according to the present invention it is necessary to use diffraction efficiencies that changes as a function of aperture. FIGS. 10c, 10d, and 10e show examples of underlying linear grating diffractive unit cells and their respective diffraction efficiencies. The efficiencies are calculated with standard methods from linear grating profile data. This diffraction efficiency calculation can of course be carried out on any arbitrarily unit cell of any shape. In this specific lens and with used conventions it is arranged so that the −1 order corresponds to light arranged for Near vision, 0^thorder corresponds to light arranged for intermediate vision, and +1 order corresponds to light arrange for far vision. The total diffraction efficiency given for each of these three figures is the sum of the diffraction efficiencies of the three desired diffraction orders. FIG. 10c shows the diffractive efficiencies of the profile shape used in the lens portion marked as G1 in FIG. 10a. Near vision is promoted in favor of other depths, while those of far and intermediate are kept similar. FIG. 10d shows the diffractive efficiencies of the profile shape used in the lens portion marked as G2 in FIG. 10a. Far vision is here promoted in favor of other depths, but especially light distributed to near vision is kept very low. FIG. 10e shows the diffractive efficiencies of the profile shape used in the lens portion marked as G3 in FIG. 10a. Here energy distributed to far and intermediate vision are kept relatively similar, while additional near light is kept very low. For large apertures, essentially apertures above 4.5 mm there is very small to no benefit of intensity provided to near vision. The limit on the gratings and/or refractive shapes used here comes down to undesired effects. As is discussed further below it is possible to construct an adaptive lens according to the present invention with e.g., a peripheral, bifocal sawtooth grating or peripheral portion with a refractive power corresponding to far vision. These are two examples of ways to reduce additional intensity to near vision to essentially zero. Of course, they can confer negative optical properties, such as glare and halo effects.

It is important to understand that these unit cells are specific examples. In the lens shown in FIG. 10a several more different unit cells are present. It is often advantageous to slowly progress the relative intensity distributions as a function of aperture. It is possible to use unit cells with very different diffractions efficiencies and resulting energy distributions than those shown in this example.

FIG. 11a shows another lens diffractive profile according to the disclosed invention and demonstrates one additional way to change the dominant power of the central portion of the lens. In FIG. 6a a lens profile is demonstrated where the dominant power at small apertures was tuned by changing the curvature of the central zone. The placement of the dominant optical power at small apertures, such as 1 mm, can also be tuned very carefully by horizontal shifting of the central profile (that is, in a direction normal to the optical axis) of the central portion. The lens profile in FIG. 11a is, except for this horizontal shift, identical to the profile shown in FIG. 10a up to an aperture of approximately 2.4 mm. FIG. 11b shows the simulated relative intensity peaks for four different apertures. It is meaningful to compare this model data with the data in the FIG. 10b. Because of this relatively small change in the profile of FIG. 11a the dominant peak at 1 mm is moved approximately 0.8 D closer to the power intended for far vision. This arrangement lowers overall efficiency slightly, as calculated over the full range of vision, but it provides a stronger far vision. It further provides for very tiny apertures a dominant power that is close to that of the intended far power, which can be advantageous in some circumstances, for examples for some methods to measure eye power post operatively.

One additional change between the lens profiles in FIGS. 10a and 11a, respectively, is that the latter exhibits a higher diffractive lens profile outside of approximately apertures of 2.4 mm. This portion of the lens is here geared towards increasing intensity directed towards far vision more strongly for very large apertures. One possible design choice if even stronger weakening of near light for large apertures would be desired is to make use of a bifocal sawtooth grating for example for apertures larger than 4.5 mm. Such a bifocal sawtooth grating could be arranged to provide additional light only for far and intermediate vision. Yet another option would be to use a monofocal sawtooth structure for large apertures. Such a structure would then need to be much higher than the multifocal gratings.

It should be further noted that the central portion, up to around the crest closest to the lens center, and the diffraction grating are separable and that a small horizontal shift of the central portion doesn't have to be joined by an equal shift of the diffractive grating. Likewise, a shift of the diffraction grating does not have to joined by an equal shift of the central zone. On the contrary, it can often be advantageous to shift the central portion and the diffraction grating relative to each other. Specifically, it can often be advantageous to perform a shift so that the ridge closest to the lens center is thinner than typically expected by the formula for a well-formed lens. A different way to phrase this is to say that it is often found to be advantageous to move the central zone and the first trough of the diffractive grating closer to each other than expected from the standard formula for Fresnel zone plates. Such a configuration can increase overall light efficiency and is a viable way to construct a lens according to the present invention.

FIG. 12a shows yet another lens profile for an adaptive multifocal lens according to the present invention. It is important to understand that the profile in shown here is less the refractive base line, understood to be the same over the whole optic. One important feature of this lens profile is that it contains a purely refractive portion that is arranged to provide light for far vision only. In this example this refractive portion covers roughly all apertures outside of the 5 mm aperture. Such refractive portions should not be considered when peak-to-peak height of the diffractive profile is calculated. Having a refractive portion at the periphery of a multifocal lens can be a good way to create a strongly adaptive lens. In the present case all light will be directed towards far vision for apertures larger than 5 mm. It could increase the risk of halo effects.

A second important feature of the diffractive lens profile in FIG. 12a is a purely monofocal center. In this example the central zone is formed to have a negative power that is 0.125 D lower than the nominal absolute difference between the orders responsible for far and intermediate power. The transition point between the central zone and the symmetric multifocal diffraction grating is marked by the vertical, dashed line at an aperture of 1.14 mm. The symmetric diffraction grating is constructed in a fashion that is relatively similar to the one depicted in FIG. 10a. The diffraction grating is geared towards near vision until an aperture of about 2.8 mm, then it is with increasing aperture tune more and more strongly for far, and to some extent intermediate vision.

FIG. 12b shows the simulated relative intensity peaks for four different apertures. The symmetric diffraction grating is nominally constructed to provide an order separation of 1.675 D. As shown in the simulation data the dominant peak for a small 1 mm aperture is 1.4 D below the intended intermediate peak. To summarize the data in FIG. 12b, we see here that (1) the dominant focus at the 1 mm aperture is placed in between intended far and intermediate powers (18.32 D and 20 D, respectively), (2) intensity of near, relative to that of far intensity, is stronger at 3 mm than at any of the other shown apertures, the intermediate intensity (3) is at the 2 mm aperture weaker than both far and near, while (4) at 4.5 mm the near intensity is weaker than far as well as intermediate. At all apertures from 2 mm and above far is the strongest type of vision. The undesired peak around 17 D is larger than e.g. the peak shown in FIG. 10b, this is due to the choice of central zone.

FIG. 13a is an illustration of what is a possible goal energy distribution for lens designs according to the patent. This ideal distribution for an adaptive diffractive multifocal lens is based on the arguments of workings of the human eye earlier in this document. The illustration indicates for each of near, intermediate, and far vision the desired energy distribution at apertures up to 6 mm. It can be assumed that values within ±5 percentage points are within the ideal region. Often a lens made according to the present invention will not fall into the ideal region for all types of vision nor for all apertures. Further, it should be noted that this demonstrates an ideal outcome, only taking the energy distribution into consideration. Especially the very dramatic exchange of near energy with intermediate energy when going from a mesopic pupil to a scotopic pupil is difficult realize fully. When making a design of a lens according to the present invention it is often necessary to take into consideration if the main prioritization for the peripheral part of that specific design should be correct energy distribution or if minimization of aberrations and undesired photic phenomena should be prioritized. Very efficient ways to change the energy distribution for large apertures include bifocal sawtooth gratings and purely monofocal zones. For example, the bifocal sawtooth grating could be arranged to provide only light for far and intermediate vision for large apertures. A peripheral monofocal zone, as illustrated in FIG. 12a, can be arranged to provide light for far vision only. However, both these structures can increase the risk of unwanted photic phenomena, especially halo effects.

FIG. 13b shows, as a function of aperture, the simulated energy distribution between far, intermediate, and near vision for the hybrid lens in FIG. 10a. The aperture is here seen as simply double the lens radius. In this simulation far vision is dominant at all apertures, at an aperture of 2 mm energies for near and intermediate vision are relatively similar. Near energy has a maximum plateau for apertures 2.5 mm to 3 mm, while intermediate energy has a minimum plateau for approximately the same aperture range. For apertures larger than 3.1 mm near energy is decreasing with increasing apertures, while intermediate energy is increasing with increasing aperture. The cross-over point is estimated to be close to the 4.5 mm aperture. The data in the graph is composed by first calculating the spectrum at 8 apertures per period of the diffractive grating, all in all at 105 different apertures. For each aperture the intensity of each vision is approximated with the local maximum peak in the in the position of respective type of vision. The graph is then plotted using the sliding mean values for each type of vision, using for each point in the graph data for a whole period. A less undulating line would be arrived at if calculations were made at e.g., only troughs or crests.