RU2186417C2 - Intraocular diffraction lens - Google Patents

Abstract

FIELD: ophthalmologic optics; artificial lenses for eyes. SUBSTANCE: lens is made of biocompatible flexible or hard material, type PMMA. It is, essentially, thin plate one of whose surfaces bears microrelief in the form of annular diffraction grating with luminous profile. Desired optical intensity of intraocular lens is ensured due to phenomena of light diffraction on structural surface. Maximal depth of microrelief profile is equal on entire surface of lens. Its absolute value h_max≫λ_o and amounts to several wavelengths of visible part of spectrum. Diffraction lens has equal optical intensity for at least two wavelengths of visible range of spectrum, that is, it is achromatic or apochromatic. In addition lens is split into even number of sectors having different optical intensities or it is aligned with annular diffraction grating at constant spacing to expand pseudo-accommodation of eye. This expansion makes up 0 to 4 diopters. In order to obtain broken optical axis and to project image onto paramacular part of retina (in case of defective macula) diffraction lens is built integral with linear diffraction grating. Cornea aberration is compensated for. Lens can be implanted through small incision which will essentially reduce post- operation astigmatism of cornea. Intraocular lenses may be manufactured using advanced methods of laser technology. Lens photomatrix is synthesized and replicated by way of stamping. EFFECT: enhanced visual activity of eye with implanted lens; reduced cost of artificial lens. 5 cl, 6 dwg

Description

 The invention relates to ophthalmic optics. It can be used in medicine as an artificial lens (intraocular lens - IOL), implanted in the eye after removal of the natural lens, damaged or affected by cataracts. The lens design can be used as the optical part of all types of IOLs: anterior chamber, posterior chamber, and iris-clip lenses.

 Intraocular refractive lenses are known. Their optical power depends on the refraction of the material, the curvature of the surface and the thickness of the lens. Optimization of lens aberrations is carried out by selecting the radii of curvature or asphering one of the surfaces [1]. A disadvantage of traditional IOLs is: technological difficulties in manufacturing thin and flexible lenses having the necessary optical power for a given refraction of the material; the difficulty of compensating for corneal aberrations, which significantly impair the visual acuity of the eye with an implanted IOL; technological difficulties in manufacturing refractive lenses with aspherical surfaces to compensate for corneal aberrations and intrinsic IOL aberrations.

 Hybrid-type IOLs are also known that implement a method of expanding pseudo-accommodation of the eye by creating a bifocal lens [2], [3]. The hybrid lens device includes refractive and diffractive parts. The diffractive component of the lens is deposited on one of the surfaces of the refractive part. The refractive component forms a clear image on the retina of objects located at far distances from the eye. The combined action of refractive and diffractive elements helps to see objects located nearby. As a result, the refractive-diffractive bifocal IOL allows you to create a clear image of objects located in a certain range of close and long distances on the retina.

 The disadvantages of such a device are difficulties in the production of hybrid IOLs due to the need to combine heterogeneous technologies - the manufacturing technology of traditional lenses and the technology for the synthesis of diffraction structures, as well as the inability to fully compensate for corneal aberrations that worsen visual acuity.

 The closest technical solution for the combination of essential features is a diffraction lens, the zones of which are combined into groups [4]. The lens is bounded by two surfaces, one of which is smooth and the other structured. Optical power is formed only due to diffraction phenomena on the circular zones of the surface microrelief. The microrelief of the lens may be geometric or optical, depending on whether the height or density of the lens material changes accordingly.

The radii of the circular zones of the diffraction lens are determined from the ratio
r $\genfrac{}{}{0ex}{}{\text{2}}{\text{k}}$ = 2fkλ + (kλ) ² , (1)
where f is the focus of the lens;
k is the zone number;
λ is the wavelength of light in the medium.

 Each boundary of the lens zone ends with a step, which introduces a path difference equal to λ into the light beam, which corresponds to a phase jump of 2π. The shape and depth of the surface profile within the zone determine the effectiveness of the lens and the distribution of incident energy over diffraction orders.

 As the relative aperture of the diffraction lens increases, the distance between the zones decreases, which puts a technological limit on the lens manufacturing methods. To overcome this drawback, the zones in the diffraction lens are divided into several ring groups over the area. The distance between the zones in the center of the lens, measured from the optical axis, corresponds to relation (1). The zones of the subsequent ring structure are combined into "superzones", i.e. their width is equal to the sum of two neighboring zones. The subsequent annular structure of the lens combines the width of three neighboring zones, etc. This is done in order to increase the pitch of the circular diffraction grating and make the lens available for manufacturing by diamond turning. The width of the zone should be greater than the radius of the sharpening tool cutter.

 In order to maintain the same luminous efficiency of each group of zones, the optical depth of the zone profile increases by λ when passing from one group to another, i.e. for the central zones of the first group it is λ, for the first group with "superzones" - 2λ, for the second - 3λ, etc.

 The contrasting solution can be characterized as a lens having diffractive power, in which one group of zones ends with steps with an optical height equal to jλ, and the other group of zones has a profile with optical height mλ, where λ is the design wavelength, aj and m are nonzero and unequal factors.

 The principal unsolved problems are the following: the diffraction lens has a large chromatic aberration, which does not allow it to be used for work in white light; the lens structure is adapted to the production of single samples by diamond turning: the use of mass production technologies is difficult.

 The aim of the present invention is the most complete restoration of visual functions due to the correction of corneal aberrations using diffractive IOL, reducing the weight of the optical part of the lens and reducing postoperative corneal astigmatism.

 The goal is achieved in that the optical power of the intraocular lens is created due to the phenomena of light diffraction on the microrelief of the structured surface of a thin plate. The plate is made of an elastic, biocompatible material (silicone, collagen, hydrogel, etc.) or a rigid material such as PMMA, which absorbs the ultraviolet part of the spectrum. The second surface of the plate is flat and smooth. The microrelief of the first, structured surface is a circular diffraction grating with a kinoform line profile (profile with a “shine”) [5]. The relief-phase profile of the IOL is synthesized in the form of a geometric or optical microstructure. If the optical microstructure is made by changing the density of the lens material (refractive index), then both surfaces of the lens are flat.

The maximum optical depth of the microrelief profile is the same over the entire surface of the lens. Its absolute value h _opt ≫λ _o and amounts to several wavelengths of the visible part of the spectrum. Such a diffraction microrelief is called “deep” [5]. Λ _o denotes the wavelength in vacuum for the region of maximum sensitivity of the eye, called constructive (λ _o = 0.555 μm). The geometric (physical) depth of the microrelief is
h _max = pλ _o / n ₂ -n ₁ = h _opt / Δn, (2)
where p is an integer;
n ₁ and n ₂ are the refractive indices of the eye fluid and the IOL material;
Δn = n ₂ -n ₁ . h _opt / pλ _o - otic depth of the microrelief.

In the proposed invention for patenting, the value of p lies in the range from 3 to 20. The minimum value of h _opt. is equal to the segment in which at least two wavelengths of the visible range of the spectrum fit an integer number of times. These two wavelengths are located in the violet and red parts of the spectrum symmetrically with respect to the structural wavelength λ _o . The diffraction lens has the same optical power, at least for two wavelengths of the visible range of the spectrum, i.e. she is achromatic.

The structured surface of the IOL is made in the form of a circular diffraction grating, the change in the microrelief depth h (r) of which, depending on the radius of the zone r, is calculated from the relation
h (r) = a ₁ -a ₂ r ² + a ₃ r ⁴ . (3)
The coefficient a ₁ in (3) depends on the maximum depth of the step of the diffraction microrelief h (r) and the zone number k.

a ₁ = h _max (k + 1) (4)
Values of h _max are obtained from (2). The radii of the zones r _{k are} determined from (3) by setting h (r) = h _max and substituting into a ₁ k = 1,2,3 ... etc.

A constant coefficient a ₂ characterizes the optical power of the IOL in the eye
a ₂ = n ₁ / 2f ₂ Δn, (5)
where f ₂ is the focal length of the lens in the medium. A constant coefficient a ₃ characterizes the change in optical power in the peripheral part of the lens. These changes are necessary to correct corneal aberrations and aberrations caused by the position of the IOL in a converging beam. Coefficient a ₃ introduces a compensating aspherical additive in the wave front that has passed through the IOL:
a ₃ = cn ₁ / 8f $\genfrac{}{}{0ex}{}{\text{3}}{\text{2}}$ Δn (6)
Here, c is the dimensionless coefficient depending on the optical parameters of the IOL, the cornea, and the position of the IOL in the optical system of the eye:
c = f ₁ f ₂ ³ / (n ₁ -1) ² S ₂ ⁴ + 3f ₂ ² / S ₂ ² + 3f ₂ / S ₂ +1 (7)
where f ₁ , f ₂ are the focal lengths of the cornea and lens in the medium, S ₂ is the distance from the lens to the image of the object by the cornea, which is the subject of the lens.

In addition, to increase the depth of focus and increase the volume of pseudo accommodation, a diffraction lens with a kinoform profile is made of two halves (semicircles) or a set of an even number of sectors whose centers lie on the optical axis. Sectors are combined in two groups, each of which covers half the effective area of the lens and has a different optical power. All the light reaching the lens is divided by a lens into two halves of 50% each and is collected in two foci, projecting onto the retina an image of near and distant objects. An increase in the focusing depth is also achieved by introducing a constant-pitch diffraction circular grating into the structure of circular zones. In this case, the radii of the zones r and the height of the relief profile h (r) within each zone are determined from the relation
h (r) = a ₁ -a ₂ □ ra ₂ r ² + a ₃ r ⁴ , (8)
where a ₁ , a ₂ □ _, a ₂ and a ₃ are constants characterizing the depth of the profile, the optical power and its changes, and a ₁ , a ₂ , and ₃ have the same meaning as in (3), and a ₂ ¹ depends on the diffraction angle α on the circular grating with a constant step.

a ₂ □ = n ₁ Sinα / Δn (9)
In addition, the structure of the circular zones is made combined with a linear diffraction grating having a sawtooth line profile and a constant pitch equal to
t = λ / Sinγ, (10)
where γ is the angle of "kink" of the optical axis of the lens.

 An intraocular lens with a fracture of the optical axis projects an image onto the paramacular parts of the retina and is used in cases of damage to the macula.

New features: the maximum microrelief depth of the circular zones of the diffraction lens is a multiple of at least two different wavelengths within the visible range of the spectrum; it is constant over the entire surface of the lens from the center to the periphery; the change in the depth of the profile between the zones h (r) depending on the radius of the zones is made in accordance with the relation (3)
h (r) = a ₁ -a ₂ r + a ₃ r ⁴ ,
where a ₁ , a ₂ and a ₃ are constants, depending on the maximum depth of the relief, the optical power and its changes, necessary to compensate for aberrations of the cornea.

In addition, the diffraction lens is made of an even number of sectors, each half of which draws an angle of 180 ^o and has a different optical power.

In addition, the radii of the circular zones are made in accordance with the relation (8)
h (r) = a ₁ -a ₂ □ ra ₂ r ² + a ₃ r ⁴ ,
where a ₂ □ is a constant characterizing the increased focusing depth.

 In addition, the circular zones of the lens are made combined with a linear diffraction grating having a sawtooth profile and designed to “break” the optical axis and project the image onto the periphery of the retina.

 The proposed solution is illustrated by the following graphic material.

 FIG. 1a, 1b is a general view of the optical part of the diffractive intraocular lens.

 Figure 1, a - the Central section of the lens.

 Figure 1, b is a top view of the location of the circular zones.

 Figure 2 - the course of the rays through the diffractive intraocular lens.

 Figure 3, a, b - profile of the circular zone and spectral sensitivity of the eye.

 Figure 3, a - kinoform profile of the diffraction zone.

 Figure 3, b - spectral sensitivity of the eye (Goldhammer function).

 Figure 4, a, b is a General view of a two-focus IOL.

 Figure 4, a is a top view of the location of the circular zones.

 Figure 4, b - section of the lens in the directions of AOS.

 FIG. 5. - a simplified optical diagram of the eye with an IOL having an increased depth of focus.

 6, a, b, c, d - diffraction lens with a "fracture" of the optical axis.

 FIG. 6a is a simplified optical diagram of an eye with an IOL projecting an image onto the periphery of the retina.

 FIG. 6b - topology of the arrangement of circular and linear gratings of a diffraction lens.

 6, in - section in the direction of AO.

 6, g - section in the direction of the sun.

 The optical part of the lens proposed for patenting is a thin plate made of an elastic or rigid biocompatible material that absorbs a short ultraviolet part of the visible spectrum. The minimum thickness of the optical part of the IOL is determined by the strength properties of the material and the need to withstand the effects of the lens capsule with its fibrosis. When folded, an elastic lens can be implanted through a small incision in the cornea, which will reduce postoperative astigmatism. The thin IOL is lightweight, which reduces pressure on the surrounding tissues of the eye. The design of the optical part allows you to simulate new optical elements by transferring part of the weight of the lens to the design of the optics.

 Figure 1, a shows the Central section of the diffractive IOL, and figure 1, b is a top view of a fragment of the lens, illustrating the location of the boundaries of the circular zones. The diffractive IOL has a structured surface 1 and a smooth side 2.

The relief depth h is shown in FIG. 1 increased in comparison with the size of the lens. In fact, the thickness of the relief lies in the range of 10–40 μm, and the diameter of the lens corresponds to 5–7 mm. The surface of the IOL between the zones is limited by a smooth curve 3. The shape of the profile within the zone provides the same optical length of the beam from the point of the object to the image point. A lens with this form of structured surface is called kinoform. The boundaries of the zones end with steps 4. The lens is placed in the medium (eye fluid) with a refractive index of n ₁ . The refractive index of the lens itself is indicated as n ₂ . The depth of the structured surface h and the radii of the zones of the diffraction structure are related by relations (3) - (7). Conventionally, the area of the lens can be divided into two parts: the central (paraxial) region 5 (Fig. 1, a) and the ring structure 6 around the periphery. These parts of the lens have different optical powers or different nominal focal lengths. The optical power of the peripheral part is gradually reduced in comparison with the optical power of the center of the lens. Reducing optical power is necessary to compensate for spherical corneal aberration and aberration, depending on the position of the IOL in the structure of the eye.

 In FIG. Figure 2 shows a simplified optical scheme of the eye with an implanted diffractive IOL calculated for distance vision. Here 7 is the cornea, 8 is the diffractive intraocular lens, 9 is the retina. From an object located at infinity, parallel beams enter the eye. After the cornea 7 passes through the cornea 7, the bundles 10 gather in focus for the paraxial rays 11. Due to the spherical aberration of the cornea, the focal plane for the beams 12 entering the peripheral part of the cornea 7 will pass through point 13. The task of the diffractive IOL is to focusing (reducing) these beams on the retina 9. For this purpose, in the proposed invention, the optical power of the IOL is not constant, but varies from the center of the lens to the periphery in accordance with relations (3) - (7).

 Similarly to the natural lens, in which the core has a higher optical power than the periphery, the optical power in the IOL of the proposed invention decreases from the center to the edge of the lens. To do this, the spatial frequency of the circular diffraction grating in the same direction is reduced, which introduces an aspherical additive to the wave front that has passed the IOL, which makes it possible to compensate for corneal aberrations. In fact, the proposed IOL works as an aspherical lens adapted to the individual parameters of the cornea of the patient’s eye. The distance between the zones, calculated in accordance with relation (3), sets the optical power of the lens and the aspherical additive for correcting the front of the light wave transmitted by the IOL.

Traditional diffraction lenses operating in the + 1st diffraction order are characterized by high chromatic aberration. For every 3 diopters of the optical power of the lens, one diopter accounts for longitudinal chromatic aberration. In the patented IOL, this drawback is eliminated by switching to diffraction lenses with a "deep" phase profile or the so-called multi-order or harmonic lenses [6], [7]. The lens synthesized in accordance with relation (3) has a microprofile depth h _max ≫λ. The delay of the optical path at h _max leads to the fact that the IOL has the same focal lengths for a number of wavelengths in the visible range of the spectrum, i.e. the lens will be achromatized. The degree of achromatization will depend on the depth of the microrelief of the lens. In the patented IOL, the degree of achromatization and the depth of the microrelief of the lens are established taking into account the spectral sensitivity of the eye, specified by the Goldhammer function [8].

Figure 3, a presents the profile shape of the circular zone of the diffraction lens, and figure 3, b - curve of the spectral sensitivity of the eye, the maximum of which corresponds to the constructive wavelength (λ _o = 0.555 μm). The diffraction profile is limited by a smooth curve 3 connecting the minimum and maximum elevation of the relief. For all circular zones, the minimum h _min and maximum heights h _max lie on planes parallel to smooth surface 2. The profile shape between the zones is made in a parabola, for peripheral zones with a small distance between the zones it is approximated by a straight line. With this form of the profile, the principle of tautochronism is observed, i.e. the differences in the path of the beams from the point of the object to the point of the image for all the rays passing through the zone are equal to each other.

In the invention proposed for patenting, the maximum optical height of the relief h _{opt is a} multiple of the structural wavelength λ _o . Then, in accordance with (2)
h _opt = h _max Δn = pλ _o
For example, at p = 10 (i.e. when ten wavelengths λ _o fit in h _opt ), the geometric profile height is
h _max = pλ _o / Δn = 10 □ 0.555 / 0.1549 = 35.83 μm
It is taken into account that n ₂ = 1.492 for IOL from PMMA, and the refractive index for ophthalmic fluid is n ₁ = 1.337, then Δn = 0.1549.

The calculated height of the microrelief (h _max = 35.83 μm) is a multiple of a number of wavelengths of the visible spectrum. For all these spectral lines, called resonance lines [7], focal distances coincide with the focus for the constructive wavelength λ _o . Resonant wavelengths can be determined from the relation
λ = pλ _o / (p ± 1), (11)
where p = 1,2,3 .... In this case, for the visible part of the spectrum, the resonant wavelengths are 0.691, 0.611, 0.555, 0.500, 0.463 μm. In figure 3, b they are marked by straight lines. With this choice of the depth of the microrelief, the greatest impact on the retina will have 3 wavelengths: λ _f = 0.500, λ _o = 0.555 and λ _k = 0.611 μm. The luminous efficiency for other resonant wavelengths will not exceed 5% (Fig. 3, b).

 The diffractive IOL works as an apochromatic lens, since the focal distances for the 3 wavelengths of the visible spectrum are equal to each other. Light from the visible wavelengths located between the resonance lines is focused along the optical axis, creating a rainbow color around the main point of the image. The presence of a rainbow color (secondary spectrum) will lead to a partial decrease in the contrast sensitivity of the eye for individual (non-resonant) wavelengths. Visual acuity as a whole will be reduced slightly.

Other options for performing the microrelief of the IOL are possible. To eliminate the chromaticity of the position and the synthesis of the achromatic structure, it is sufficient that at least two resonance wavelengths fit in the region of the visible spectrum bounded by the spectral sensitivity curve of the eye (Fig. 3, b). In this case, with λ _k = 0.610 μm and λ _f = 0.520 μm, more than 50% of the light energy (taking into account the light sensitivity of the eye) will be concentrated in the main focus of the IOL. Other resonance lines of the spectrum will contribute to the image (Fig. 3, b) ~ 5-6% of light. In this case, the depth of the microrelief will be h _max = 24.4 μm and the IOL will be achromatized.

 The ability of an intraocular lens to restore normal vision is significantly limited by the fact that the traditional single-focus refractive IOL, in contrast to the natural lens, has a fixed (constant) focal length. The implanted IOL does not allow the process of accommodation of the eye, i.e. focus on the retina image of objects located at different distances. The maximum range of distances at which objects are visible with sufficient clarity is determined by the depth of field of view. The latter depends on the diameter of the pupil of the eye and even with a minimal pupil is insufficient for a clear vision. Single-focus IOLs have a limited range of pseudo-accommodation, so after surgery, an additional improvement in vision with glasses is required.

 The patented diffractive IOL can be converted into a lens having two or more focal lengths. The presence of two foci leads (with far and near vision) to observation along with a focused image, defocused as a background. As clinical trials show, a defocused image is suppressed in the corresponding parts of the brain.

 In FIG. 4 shows the design of a bifocal diffraction lens. To create a bifocal IOL, the lens aperture is divided into an even number of sectors. As an example, figure 4 shows a lens consisting of 4 sectors. One part of sectors 14 and 15, covering half the effective area of the lens, has a diffraction structure synthesized in accordance with relation (3). The other, 16 and 17, has a similar diffraction pattern, made in accordance with (3), but having a focal length different from the first. The center of each quarter of the circle (figure 4) lies on the optical axis. All incident light is equally divided between sectors and enters two focal points. With a change in the diameter of the pupil of the eye, the ratio of light energies arriving at each focal point remains constant. Thus, the bifocal diffractive IOL proposed for patenting, unlike refractive bifocal and multifocal analogs, does not lead to distance vision loss caused by accidental retinal flare, for example, from headlights of oncoming cars and other similar effects [3].

характеризуют оптическую силу сферической и конической (тороидальной волны). Величина
a₂□ = n₁Sinα/Δn,
где α - угол дифракции света на круговой решетке с постоянным шагом.In addition, an increase in the volume of pseudo-accommodation of the eye can be achieved without dividing the lens aperture into sectors having different optical powers. The technical solution proposed for patenting is based on the creation of a diffractive lens with an increased depth of focus. If the structure of the microprofile of the diffraction lens is combined with a circular diffraction grating with a constant step, this will lead to a “compression” of the lens caustic in the transverse direction and its “stretching” along the optical axis. The depth of focus, determined by diffraction at the lens aperture, increases several times in comparison with the traditional, refractive analog. A diffraction element combining a zone plate and a circular grating works like a tandem of a refractive lens and an axicon, forming a bright “light cord” along the optical axis [9], [10]. The length of the "cord" along the optical axis can be selected so that the volume of pseudo accommodation is 0 - 4 diopters. To achieve this goal, relation (3) has the form (8)
h (r) = a ₁ -a ₂ □ ra ₂ r ² + a ₃ r ⁴ ,
where are the constants

characterize the optical power of a spherical and conical (toroidal wave). Value
a ₂ □ = n ₁ Sinα / Δn,
where α is the angle of diffraction of light on a circular lattice with a constant step.

 In FIG. 5 shows a simplified optical scheme with a diffractive intraocular lens having an increased depth of focus. Beams of light after the cornea 7 enter the combined diffraction lens 18/19. It consists of a lens 18, the zones of which are made in accordance with relation (3) and an additional circular diffraction grating (axicon) 19, which has a constant step and kinoform profile of the structured surface. In fact, both circular lattices 18 and 19 are combined into one element, the zones of which are synthesized in accordance with relation (8). The other surface of the IOL facing the retina is smooth.

 After passing through the combined lens 18/19, the light is divided into two beams 20 and 21, which, after repositioning, form a “compressed” caustic 22 in the region of the retina 9, elongated along the optical axis [10]. The image of the point at infinity is transformed by the 18/19 lens into a “line” elongated along the optical axis.

In clinical practice, if the central part of the retina (macula) is damaged, it is necessary to design the image on a photosensitive surface located outside the macula. In this case, a refractive wedge is added to the implanted IOL to “break” the optical axis. In the thin diffraction lens proposed for patenting, this task was accomplished by adding to the circular structure synthesized in accordance with relation (3) a linear diffraction grating with a step
t = λ / Sinγ,
where λ _o = 0.555 μm, and γ is the required angle of "fracture" of the optical axis. A doublet of circular and linear diffraction gratings will project an image of objects on the surface of the retina outside its central part.

 A simplified optical diagram of the eye, working in conjunction with a doublet of a diffraction lens and a linear diffraction grating with a constant step, is presented in figa. Beams of light after passing through the cornea 7 enter the combined lens 23/24. It consists of a circular diffraction lens 23 made in accordance with relation (3) and a linear lattice 24 having a constant pitch and a sawtooth profile of a structured surface. The grating 24 serves as a traditional refractive wedge. The light that has passed 23 after the “diffraction wedge” 24 diffracts at an angle to the optical axis, projecting the image onto the paramacular part of the retina. The combination lens 23/24 can be manufactured by laser phototechnology in the form of a single element with a structured and smooth surface. The topology of the diffraction pattern is shown in FIG. 6, b, 6, c and 6, d.

 The main advantages of the proposed technical solution are as follows. Compared with the known intraocular lenses, the proposed IOL compensates for corneal aberrations, improves the quality of the optical image and visual acuity.

 It can work like an achromatic or apochromatic system, reducing position chromatism and decreasing the secondary spectrum. The wavelengths for which chromatism is completely eliminated are selected taking into account the spectral sensitivity of the eye.

 Structurally proposed for patenting, the IOL can be made in the form of a thin elastic plate with a microrelief on one of the surfaces. This will allow you to implant the lens through a small incision in the cornea, which will significantly reduce postoperative corneal astigmatism.

 To expand the volume of accommodation of the eye with an implanted intraocular lens, a bifocal diffractive IOL and a lens with an increased focusing depth are proposed for patenting as variants of the main technical solution. The expected expansion of the volume of accommodation will be 0-4 diopters, which is comparable with the volume of accommodation of the eye with a natural lens for "near".

 A variant of a diffraction lens with a “fracture” of the optical axis will find application for treating eyes with a damaged central part of the retina. Projecting the image onto the paramacular part of the retina will restore the patient’s vision.

 A significant advantage of the patented diffractive IOL is the ability to manufacture lenses using laser phototechnologies, followed by replication by stamping from a pre-fabricated matrix.

 The proposed diffractive IOL provides a fundamentally new application possibilities that are absent in the known analogues. It will allow to restore visual functions to the fullest by correcting corneal aberrations, reducing IOL intrinsic chromatism, reducing the influence of the secondary spectrum, reducing lens weight and eliminating postoperative astigmatism.

Sources of information
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 2. G.J. Swanson, Diffractive / refractive Lens Implant, United States Patent, N 5,089,023, Feb. 18. (1992).

 3. V.P. Koronkevich, G.A. Lenkova, I.A. Iskakov et al. Bifocal diffraction-refractive intraocular lens // Avtometriya, N6, p. 26, (1997).

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 6. D. Faklis, G.M. Morris Spectral properties of multiorder diffractive lenses // Appl.Opt. V.34, N 14/10 May, P.2462-2468 (1995).

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Claims (4)

1. A diffractive intraocular lens with relief-phase circular zones made of biocompatible material, characterized in that the radius of the zones - r and the profile height h (r) within each zone are related by the ratio
h (r) = a ₁ -a ₂ r ² + a ₃ r ⁴ ,
where a ₁ , a ₂ and a ₃ are constants characterizing the depth of the profile, optical power and changes in the optical power of the lens, and
and ₁ = h _opt (k + 1) / Δn;
a ₂ = n ₁ / 2f ₂ Δn;
a ₃ = cn ₁ / 8f ₂ ³ Δn,
where h _opt = pλ _o is the optical depth of the relief;
λ _o - constructive wavelength in vacuum;
p = 1, 2, 3.. . integer;
k is the number of the circular zone;
Δn = n ₂ -n ₁ is the difference between the refractive indices of the lens material (n ₂ ) and ophthalmic fluid (n ₁ );
f ₂ is the focal length of the lens in the medium;
c is a dimensionless coefficient depending on the optical parameters of the lens, cornea and the position of the lens relative to the cornea and retina. 2. A diffractive intraocular lens with relief-phase circular zones made of biocompatible material, characterized in that it is made in the form of a set of an even number of equal sectors, half of which together form an angle of 180 ^o , and the neighboring sectors of each pair have different optical power , zone boundaries — r and profile height h (r) within each zone for all sectors are related by
h (r) = a ₁ -a ₂ r ² + a ₃ r ⁴ ,
where a ₁ , a ₂ and a ₃ are constants characterizing the depth of the profile, optical power and changes in the optical power of the lens, and
and ₁ = h _opt (k + 1) / Δn,
and ₂ = n ₁ / 2f _1,2 Δn,
a ₃ = cn ₁ / 8f ³ _1,2 Δn,
where h _opt = pλ _o is the optical depth of the relief;
λ _o - constructive wavelength in vacuum;
p = 1, 2, 3.. . integer;
k is the number of the circular zone;
Δn = n ₂ -n ₁ is the difference between the refractive indices of the lens material (n ₂ ) and ophthalmic fluid (n ₁ );
f ₁ - the focal length of the lens in the medium of the first group of sectors forming an angle of 180 ^o ;
f ₂ is the focal length of the second group of sectors, c is a dimensionless coefficient depending on the optical parameters of the lens, cornea and the position of the lens relative to the cornea and retina. 3. A diffractive intraocular lens with relief-phase circular zones made of biocompatible material, characterized in that a circular diffraction grating with a constant step is added to the structure of the microprofile of the lens, and the radius of the zones r and the profile height h (r) within each zone are related by the ratio
h (r) = a ₁ -a ₂ 'ra ₂ r ² + a ₃ r ⁴ ,
where a ₁ , a ₂ , a ' ₂ and a ₃ are constants characterizing the depth of the profile, the optical power of toroidal and spherical waves, respectively, and changes in the optical power of the lens, and
and ₁ = h _opt (k + 1) / Δn,

a ₂ = n ₁ / 2f ₂ Δn,
a ₃ = cn ₁ / 8f ₂ ³ Δn,
where h _opt = p _o λ is the optical depth of the relief;
λ _o - constructive wavelength in vacuum;
p = 1, 2, 3.. . integer;
k is the number of the circular zone;
Δn = n ₂ -n ₁ is the difference in the refractive indices of the lens (n ₂ ) and ophthalmic fluid (n ₁ );
α is the diffraction angle on a circular grating with a constant step;
f ₂ is the focal length of the lens in the medium;
c is a dimensionless coefficient depending on the optical parameters of the lens, cornea and the position of the lens relative to the cornea and retina. 4. A diffractive intraocular lens with relief-phase circular zones made of biocompatible material, characterized in that the microprofile structure is combined with a linear diffraction grating having a sawtooth-shaped stroke profile and a constant pitch equal to
t = λ / Sinγ,
where γ is the angle of "kink" of the optical axis of the lens, and the profile height h (r) within each circular zone and the radius of the zones - r are related by
h (r) = a ₁ -a ₂ r ² + a ₃ r ⁴ ,
where a ₁ , a ₂ and a ₃ are constants characterizing the depth of the profile, optical power and changes in the optical power of the lens, and
and ₁ = h _opt (k + 1) / Δn,
and ₂ = n ₁ / 2f ₂ Δn,
a ₃ = cn ₁ / 8f ₂ ³ Δn,
where h _opt = pλ _o is the optical depth of the relief;
λ _o - constructive wavelength in vacuum;
p = 1, 2, 3.. . integer;
k is the number of the circular zone;
Δn = n ₂ -n ₁ is the difference between the refractive indices of the lens material (n ₂ ) and ophthalmic fluid (n ₁ );
f ₂ is the focal length of the lens in the medium;
c is a dimensionless coefficient depending on the optical parameters of the lens, cornea and the position of the lens relative to the cornea and retina.

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