WO2012028755A1

WO2012028755A1 - Multifocal ophthalmic lens and method for obtaining same

Info

Publication number: WO2012028755A1
Application number: PCT/ES2011/070559
Authority: WO
Inventors: Walter Daniel Furlan; Genaro Saavedra Tortosa; Amparo PONS MARTÍ; Juan Antonio Monsoriu Serra; Arnau Calatayud Calatayud; Laura REMÓN MARTÍN; Fernando GIMÉNEZ PALOMARES; Juan Luis Rojas Salegui; Eva Larra Mateos; Pedro José SALAZAR SALEGUI
Original assignee: Universitat De Valencia; Universidad Politecnica De Valencia; Ajl Opthalmic, S.A.; ANDRÉS BOU, Pedro
Priority date: 2010-09-02
Filing date: 2011-07-28
Publication date: 2012-03-08
Also published as: ES2379164B2; ES2379164A1

Abstract

The invention relates to a hybrid diffractive/refractive multifocal ophthalmic lens which can be used as an intraocular lens or contact lens and which is produced on the basis of a refractive lens in which the thickness of one of the faces is increased using a function constructed from an aperiodic but ordered step function by means of an iterative method. Consequently, chromatic aberration is reduced and the depth of field of the lens is increased and, since no notched surfaces are required, the lens can be used as a contact lens.

Description

MULTI FOCAL OPHTHALMIC LENS AND PROCEDURE FOR OBTAINING

D E S C R I P C I Ó N

FIELD OF THE INVENTION

The present invention applies to multifocal lenses that can be used as an intraocular lens or contact lens. In particular, the invention relates to a lens with less chromatic aberration and greater depth of field than prior art lenses.

BACKGROUND OF THE INVENTION

Multifocal ophthalmic lenses may be in the form of contact lenses, intraocular lenses or glasses. The principle on which intraocular and contact multifocal lenses are based is the brain's natural ability to adapt to far or near vision by choosing between the images produced by the lens. When the visual system simultaneously receives two images on the retina, it selects the sharpest of the two, and deletes the other. In cataract surgery, multifocal intraocular lens implants are becoming more frequent, with which optimal distance and near vision vision are sought at the same time. It is thus possible to avoid blurring in close distances that occurs with monofocal lenses. In addition, multifocal designs try to avoid the presence of halos associated with chromatic aberration.

There are different designs of intraocular multifocal lenses on the market. These designs can be classified, in general, into refractive designs and diffractive designs. However, for contact lenses there are only refractive models. In refractive designs the lens is subdivided into different annular zones in which 2 different radii of curvature alternate providing 2 associated powers each of them for "far" and "near" vision, respectively. An example of this type of lens is the ReZoom © intraocular lens from AMO.

In other words, refractive multifocal intraocular lenses use a multizonal method, that is, two powers are defined that are incorporated within rings or circular refractive zones with different radii of curvature. These types of lenses are pupil-dependent since the size of the pupil limits the number of useful areas of the lens and consequently its response within the visual system.

Diffractive multifocal lenses use the optical principles of diffraction combined with those of refraction to generate two independent foci. The bifocal effect is achieved by inducing the simultaneous formation of a distant focus (refractive effect) and a close one obtained by carving on one of its faces a Fresnel zonal plate diffractive lens "blazé" or "kinoform". Such an element is shown in Fig. 1, where it can be seen that it is a structure formed by circular rings with a pitch that increases proportionally to the radius r, such that it is periodic in A ² . Therefore, when incorporating the "blazé" zone plate, the resulting diffractive multifocal lens has a characteristic "sawtooth" profile on one of its faces that follows the distribution of the zones (Fig. 1) of the zone plate of Fresnel With monochromatic illumination, a "blazé" zonal plate has a single focus, that is, it has a diffraction efficiency of 100% when working with the wavelength for which it has been designed. The saw teeth of these lenses are difficult to produce using conventional turning techniques and applied to contact lenses would be uncomfortable for the user, which is why this application does not exist in the market. An example of a lens that attempts to alleviate these problems can be found in US Patent 6536899 B1. This patent describes a multifocal hybrid lens (diffractive-refractive) that is constituted by a set of annular zones of the same area, each divided into at least two sub-zones, so that the profile varies continuously as it passes from any Subzone to the adjacent. This periodic structure in the square radial coordinate has at least two foci, whose number and intensity depends on the subdivision made, but on which only one of them is free of chromatic aberrations.

OBJECT OF THE INVENTION

The object of the invention is to improve the depth of field and decrease the chromatic aberration of a multifocal ophthalmic lens in all foci. For it, proposes a diffractive-refractive hybrid lens obtained from a refractive base lens, in which its surface is modified by a predetermined function. This function G _s (u) is an aperiodic step function, ordered by an iterative procedure, which is expressed as:

/

if p _SJ ≤u≤q _SJ

G _s (u) =

where S represents the number of iterations (greater than 2) used to generate the aperiodic sequence, Λ / is the number of segments (steps) of the aperiodic function, where these segments are separated by N- 1 regions limited by (p _s , i, qs _, ¡) with / = 1, 2, ..., / V-1 and which will depend on the sequence chosen; yu = 1 -rW with values 0 <u <1, where A ² = x ² + ² is the radial coordinate and b is the maximum radius of the diffractive zone.

G can be any of the functions of the group Cantor, Thue-Morse, Paper Folding, Period-Doubling, Silver Mean, Bronze Mean, Copper Mean, Nickel Mean and Rudin-Shapiro. The base refractive lens can be monofocal, toric and / or aspherical.

BRIEF DESCRIPTION OF THE FIGURES

In order to help a better understanding of the features of the invention in accordance with a preferred example of practical realization thereof, the following description of a set of drawings is attached, where the following has been represented by way of illustration:

Figure 1 .- is a representation of a blazé diffractive lens with Fresnel zones according to the state of the art.

Figure 2.- is a representation of the Cantor function used as an example of an aperiodic function to generate the surface of the lens of the invention.

Figure 3.- is a graph that represents the profile of the lens of the invention according to the Cantor function.

Figure 4 shows a comparison between the foci in a refractive monofocal lens and the foci of the lens object of the invention based on the Cantor function. Figure 5.- is a representation of the Thue-Morse function used as an example of an aperiodic function to generate the surface of the lens of the invention. Figure 6 shows a comparison between the foci in a refractive monofocal lens and the foci of the lens object of the invention based on the Thue-Morse function.

DETAILED DESCRIPTION OF THE INVENTION

The lens object of the invention is designed for use as an intraocular lens or as a contact lens since its surface is not serrated. It is a multifocal lens and therefore adapted for simultaneous correction of both the refractive defect associated with the eye in which it is placed (implanted), as well as its presbyopia. The lens is generated on the basis of a refractive lens in which the thickness of one of the lens faces is increased using a function constructed from an aperiodic sequence but ordered by an iterative procedure. The function that defines the thickness of the lens is defined as:

e (x, y) = F (x, y) + M- G _s (u),

where u = 1 -rV¿> ² , r is the radial coordinate defined as r ² = x ² + ² and b is the maximum radius of the diffractive zone. In this way the thickness of the starting lens F (x, y) is modified with the standard aperiodic step function G _s (u), multiplied by a weight factor M that provides the difference in powers between the different regions of the lens and that it can be positive or negative as will be seen later. This function is constructed in a staggered way by means of the following mathematical expression:

/

if p _SJ <u≤q _sl

N

G _s (u) =

1 u -q _SJ

if q _s , ≤u≤p _s where S represents the number of iterations (greater than 2) used to generate the aperiodic sequence, Λ / is the number of segments (steps) of the aperiodic function, where these segments are separated by N-1 regions limited between (p _s , i, qs _, ¡) with / = 1, 2, ..., / V-1 and which will depend on the sequence chosen; yu = 1 -rW with values 0 <u <1, where r ^? = x ² + ² being radial coordinate and b the maximum radius of the diffractive zone. In this way, the function G _s {ü) is monotonously increasing in the N segments arranged aperiodic and constant between these segments.

The lens thus generated behaves like a diffractive-refractive hybrid lens in which annular zones alternate with two different radii of curvature that give rise to the main foci of the lens. The diffraction produced by the different aperiodic distributed rings provides the internal structure of each of these foci and depends on the aperiodic function chosen. In a preferential example, it starts with the Cantor function as shown in Fig. 2. This function is generated from the aperiodic sequence ordered by the Cantor fractal that can be constructed by the iterative procedure. Starting from two elements A and B, the sequence {ABA} is constructed first and then S times A is replaced by ABA and B by BBB, so the following sequences would be {ABABBBABA},

{ABABBBABABBBBBBBBBABABBBABA}, ... and so on. In this case, the number of segments 'A' (black bars in Fig. 2) arranged aperiodic up to a generation level S is N = 2 ^S. From this aperiodic sequence, the Cantor function G _s (u) is linearly increasing in the N = 2 ^S steps (segments 'Α') and constant between said steps (segments 'B').

The profile of the lens face that gives rise to the multifocality is shown in Fig. 3 as the upper curve. The stepped curve shows the difference (increased by a factor of 10) between the designed surface (upper curve) and the base refractive surface (lower curve) or lens starting surface, in this case monofocal, that is, it directly represents G _s (or). In the areas where the aperiodic function takes a constant value the two surfaces share the same radii of curvature and therefore the same power, which would correspond to the power from afar. In the growing areas of the Cantor function, the designed surface has a smaller radius of curvature so that the lens will have greater power (near power).

The lenses generated with a function based on an aperiodic sequence but ordered by an iterative procedure are multifocal and have several main foci surrounded by multiple secondary foci. These secondary foci appear as a result of the interferences between the different areas of the lens and being axially distributed in the vicinity of each main focus together provide a composite focus with a greater depth of field. This result, for an aperiodic Cantor function with S = 2 for monochromatic illumination (wavelength, = 550 nm), is shown in Fig. 4b. The radius of the monofocal spherical starting lens is 1 1, 4 mm and / W = 18 m. For comparison, Fig. 4a shows the result that is obtained for the monofocal lens refractive starting in air. The refractive index of the lens is 1,493.

Thanks to the presence of these secondary foci, a lens with lower chromatic aberrations is obtained. Indeed, when using polychromatic illumination, the chromatic dispersion causes that the images provided by a conventional lens do not coincide in the same plane for the different wavelengths, causing the typical halos associated with the chromatic aberration. On the other hand, each main focus of the lens object of the invention exhibits a greater axial extension thanks to the presence of the secondary foci, resulting in a partial overlap between them for the different wavelengths. That is, the focus for the red and the focus for the blue overlap in certain axial positions next to the foci of the intermediate wavelengths providing a quasi "white" focus and consequently with a smaller chromatic aberration.

In another particular example, the Thue-Morse function is taken as a G function. The thio-Morse aperiodic sequence is generated by the iterative method H _s = {H _S -iHs-i} for S> 1 and / - / _{1 =} {A}. H _s is obtained from H _{s by} exchanging 'A' and 'Β', whereby H ₂ = {AB}, H ₂ = {BA}, H ₃ = {ABBA}, ¾ = {BAAB}, .. The number of segments' A 'or' B 'at a generation level S is N = 2 ^S' Based on this sequence, the aperiodic function of Thue-Morse is defined as a monotonously increasing function in segments' A 'while takes a constant value in segments 'B'. The resulting Thue-Morse function for S = 5 is shown in Fig. 5. Following a procedure similar to that performed with the preferential example based on the Cantor function, Fig. 6 compares Monochromatic normalized axial irradiance for a refractive monofocal type lens of refractive index 1, 493 on index 1, 336 (spherical base lens) and a multifocal lens based on the Thue-Morse aperiodic sequence constructed on it base lens with S = 4 and M = 56 m. Again, several main foci surrounded by multiple secondary foci are observed as a result of the interferences between the different areas of the lens that also provide an extension of the depth of field and a lower chromatic aberration in each main focus.

Like the functions of Cantor and Thue-Morse, to achieve a greater depth of field and a lower chromatic aberration, one of the aperiodic functions selected from the group comprising: Period-Doubling, Silver Mean, Bronze Mean, Copper Mean can be used , Nickel Mean, Rudin-Shapiro and Paper Folding.

The profile that gives rise to the multifocality of the lens of the invention may be distributed over the entire diameter of the lens, or be located in the central area thereof. The alternation between far and near zones can also be reversed if a negative value is assigned to the weight factor M.

Designs are also allowed to compensate for astigmatisms and aberrations of the eye, which are based on a base refractive lens that is toric and / or aspherical.

The designs in which the base refractive lens is toric are intended to compensate for the astigmatism of the cornea. The designs in which the base refractive lens is aspherical are intended to compensate for the positive spherical aberration of the cornea. Toricity and asphericity can be implemented on any of the lens faces. The function F (x, y) that provides the thickness of the base lens is represented in this case as follows:

F (x, y) = EC - A (x, y) - B (r)

Where EC is the center thickness of the lens, A (x, y) is the sagite of the toric surface at a point (x, y) of the surface y B (r) + a ₄ r ⁴ + a ₆ r ⁶ + a _g r ⁸

it is the sagite of the aspherical surface at a coordinate point r (radial distance measured from the optical axis of the lens). In the previous equation c is the curvature of the surface at the vertex of the same and k is the asphericity constant (k = 0 implies a spherical surface, k = - \ a parabolic surface, -1 </ <0 prolata ellipsoid, k <- \ hyperboloid yk> 0 Oblate ellipsoid), being ₄ , ₆ and ₈ the fourth, sixth and eighth order aspherical coefficients respectively

As a particular example, the design from a monofocal spherical intraocular lens of power 19.5 D and refractive index n ₂ = 1, 4930, with radii of curvature has been considered for obtaining the function B (r). , 5 mm and 22.89 mm for the anterior and posterior face respectively, which once implemented in the eye is submerged in aqueous humor (n _{1 =} 1, 336) It has been considered a model eye with a cornea of power 43 D and asphericity constant -0.26. A ray tracing program (OSLO, Lambda Research Corporation) has been used to obtain the aspherical profile (B (r)) of the front face of the lens that minimizes spherical aberration of the eye. Thus, for this specific example, the following values have been obtained for the design parameters of the intraocular lens k = -2.8085, at ₄ = -0.000194 mm ^"3 , at ₆ = 3.2880e-6 mm ^{" 5} and ₈ = 1 .4718e -8 mm ^"7 .

Another design-free parameter is the total number of zones, which is set by the number of iterations S used to generate the function ordinarily ordered. The minimum number of zones is given by S = 2. In general, the greater the number of areas, the higher resolution or image quality, although its construction is more complicated.

Like any diffractive lens, the lens of the invention can become apodized, making the relative height of the zones not the same in all of them.

Thanks to the invention, a great depth of field is obtained for both intraocular lenses and contact lenses. In the context of contact lenses, this means less dependence on pupil size and therefore less effort is necessary in the adaptation process. An additional advantage is that the areas thus produced do not have edges as in the case of Fresnel lenses, which makes it possible to use them as contact lenses and not only as intraocular lenses.

On the other hand, being designs with smooth variations of the profile between zones, the proposed lenses can be constructed with the same technology that is currently used for the manufacture of monofocal lenses, that is, with micrometric precision lathes.

Claims

one . Diffractive-refractive hybrid multifocal ophthalmic lens characterized in that its thickness is given by the function e (x, y) = F (x, y) + / WG _s (u), with u = ~ \ -? / B ² , where b the maximum radius of the diffractive zone, F (x, y) the thickness of a base refractive lens based on the Cartesian coordinates (x, y) and G _s (u) an aperiodic and ordered step function by an iterative process, where S is the number of iterations, and that is expressed as

/

if p _SJ ≤u≤q _s

G _s (u) =

.

S ¹ <ls, i ^≤u≤ Ps, i ÷ i

where 0 <u <1, and where N is the number of steps of the aperiodic function, where these steps are separated by N-1 regions limited between (p _s , i, qs _, ¡) with / = 1, 2 ,. .., / V-1 and whose number will depend on the sequence chosen; yu = ~ \ -? / b ² with values 0 <u <1, where r is the radial coordinate and b is the maximum radius of the diffractive zone.

2. Ophthalmic lens according to claim 1 characterized in that G _s is the Cantor function, where N = 2 ^S

3. Ophthalmic lens according to claim 1 characterized in that G _s is the Thue-Morse function, where A / = 2 ^{S 1}

4. Ophthalmic lens according to claim 1 characterized in that G _s is a function selected from the group consisting of: Period-Doubling, Silver Mean, Bronze Mean, Copper Mean, Nickel Mean, Rudin-Shapiro and Paper Folding.

5. Ophthalmic lens according to any of the preceding claims, characterized in that the base refractive lens is monofocal, toric and / or aspherical.

6. Ophthalmic lens according to claim 5 characterized in that the base refractive lens is aspherical and / or toric, and at least one of its faces has a thickness F defined by the function

F (x, y) = EC - A (x, y) - B (r)

where EC is the center thickness of the lens, A (x, y) is the sagite of the toric surface at a point (x, y) of the surface y

, 4, 6, 8

B {r) = - + a _A r + a ₆ r + a _s r

2 2

l + [l - (l + *) cr is the sagite of the aspherical surface at a point of coordinate r, c is the curvature of the surface at the apex of it and k is the asphericity constant, being ₄ , a ₆ and ₈ the fourth, sixth and eighth order asphericity coefficients respectively

7. Procedure for obtaining a diffractive-refractive hybrid multifocal ophthalmic lens, where starting from a refractive lens the surface of said lens is modified by a function, characterized in that the function is an aperiodic stepped function ordered by an iterative procedure, which is expressed how

G _s (u) =

where 0 <u <1, and where N is the number of steps of the aperiodic function, where these steps are separated by N-1 regions bounded between (p qs _, ¡) with / = 1, 2, ..., / V-1 and whose number will depend on the sequence chosen; yu = ~ \ -? / b ² with values 0 <u <1, where r ^≥ = x ² + and ² where r is the radial coordinate and b is the maximum radius of the diffractive zone.