FR3132836A1 - Dilution optic intraocular lens - Google Patents

Abstract

An intraocular lens (12) has an optical center and an optical axis (y). The intraocular lens (12) also has an increasing and continuous radius of curvature from the optical center towards a peripheral edge of the intraocular lens (12) as a function of the distance from the optical axis (y) so that the intraocular lens (12) has an asphericity value substantially equal to the following value: where n is the refractive index of the intraocular lens (12).

Description

Dilution optic intraocular lens

The field of the invention relates to ophthalmology, and more particularly to intraocular lenses.

Cataract is a clouding of the lens of the eye responsible for a progressive decline in vision and increased sensitivity to light. Mainly linked to aging, cataracts can also be caused by trauma, long-term treatment with corticosteroids or certain chronic illnesses such as diabetes.

It has been known for several decades to treat cataracts through a surgical procedure consisting of replacing the clouded lens of the patient's eye with an intraocular lens – or implant. Replacement with an artificial lens is the only solution since it is not possible to restore the transparency of the clouded lens.

Furthermore, an intraocular lens can also be used to treat certain visual deficiencies, including myopia, hyperopia, astigmatism or even presbyopia. Generally, in such a case, the natural lens is preserved, so the intraocular lens constitutes an additive implant. We then speak of phakic implantation. It should be noted that these visual deficiencies can be treated by laser surgery to modify the profile of the cornea but that certain patients have contraindications to such an operation, particularly if they suffer from an autoimmune disease. or corneal pathology.

The Applicant's work led him to propose, in international application WO 2013/110888, an intraocular lens making it possible to both treat cataracts and correct myopia (or hyperopia) and presbyopia.

However, research in the field of intraocular lenses is still very recent and, in the particular case of the joint treatment of cataracts and presbyopia, current solutions do not make it possible to obtain a satisfactory depth of field. In particular, existing intraocular lenses do not provide a sufficiently clear image of an object for near vision.

The present invention improves the situation.

As such, the present invention relates to an intraocular lens, having an optical center and an optical axis, characterized in that it has an increasing and continuous radius of curvature from the optical center towards a peripheral edge of the intraocular lens as a function of the distance to the optical axis so that the intraocular lens has an asphericity value substantially equal to the following value:

where n is the refractive index of the intraocular lens.

In one or more embodiments, the intraocular lens comprises a variable portion on which the radius of curvature is strictly increasing. The variable portion is connected and symmetrical with respect to the optical axis.

The radius of curvature and the distance from the optical axis are for example linked by a polynomial relationship on the variable portion.

In one or more embodiments, the radius of curvature at a given point of the variable portion is determined as follows:

where: - x is the distance from the given point to the optical axis;
- x ₁ is a predetermined distance;
- r(x) is the radius of curvature at the given point;
- R ₀ is the radius of curvature at the optical center; And
- α is a constant depending on the asphericity value.

In one or more embodiments, the constant α is calculated as follows:

Or :
- ρ is the radius of the intraocular lens; And
- l is the length of the variable portion.
In one or more embodiments, the variable portion covers the intraocular lens in its entirety and:

where Q is the asphericity value of the intraocular lens.

In one or more embodiments, the intraocular lens comprises at least one constant portion on which the radius of curvature is substantially constant. Each constant portion is connected and symmetrical with respect to the optical axis.

In one or more embodiments, a constant portion is a central portion extending from the optical center and over which the distance to the optical axis is less than or equal to a first predetermined distance.

The predetermined distance x ₁ is for example equal to the first predetermined distance.

In one or more embodiments, a constant portion is an eccentric portion extending to the peripheral edge and over which the distance from the optical axis is greater than or equal to a second predetermined distance.

In one or more embodiments:

where Q is the asphericity value of the intraocular lens.

In one or more embodiments, the refractive index is between 1.46 and 1.54 and the asphericity has a value between -0.94 and -0.84.

The present invention also relates to a method for determining a radius of curvature profile of an intraocular lens having an optical center and an optical axis, characterized in that it comprises:
- receive ocular biometric measurements from a patient;
- receive parameters of the intraocular lens comprising at least one refractive index value;
- determine a radius of curvature value at the optical center of the intraocular lens as a function of the ocular biometric measurements and one or more of the parameters of the intraocular lens;
- determine, depending on the value of the radius of curvature at the optical center of the lens, an increasing and continuous radius of curvature profile from the optical center of the desired intraocular lens towards a peripheral edge of the intraocular lens as a function of the distance to the optical axis of the intraocular lens so that it has an asphericity value substantially equal to the following value:

where n is the refractive index of the intraocular lens.

The present invention also relates to a computer program comprising instructions for implementing the preceding method, when the instructions are executed by at least one processor.

A non-transitory computer-readable storage medium storing this computer program is also covered.

Finally, the present invention further relates to a method of manufacturing an intraocular lens, characterized in that a radius of curvature profile of the intraocular lens is determined according to the method described above, and in that the intraocular lens is manufactured according to this radius of curvature profile.

The intraocular lens is manufactured for example from a material comprising at least polymethyl methacrylate.

Other characteristics, details and advantages will appear on reading the detailed description below, and on analyzing the attached drawings, in which:

illustrates an optical diagram of an eye;

illustrates an optical diagram of the eye of the in which the natural lens has been replaced by an intraocular lens according to the invention;

illustrates the formation of a circle of confusion with lenses of distinct asphericities;

illustrates a point spread function obtained in far vision for the lenses of the ;

illustrates a point spread function obtained in near vision for the lenses of the ;

illustrates a point spread function obtained in intermediate vision for the lenses of the ;

illustrates a system for determining a radius of curvature profile of an intraocular lens according to the invention;

illustrates a method of manufacturing an intraocular lens according to the invention;

illustrates an embodiment of the radius of curvature profile of the intraocular lens according to the invention; And

illustrates another embodiment of the radius of curvature profile of the intraocular lens according to the invention.

There illustrates an optical diagram of an eye 2. Such a diagram makes it possible to model the eye 2 in the form of a simplified optical system.

As illustrated on the , eye 2 includes a cornea 4, a pupil 6, a lens 8 and a retina 10.

Cornea 4 is the transparent front part of the eyeball and performs the function of transmission and refraction of light. Indeed, the cornea 4, comparable to a converging lens, makes it possible to converge the incident light rays towards the lens 8 which plays a complementary role in the refraction of light.

The profile of the cornea 4 can be characterized by an asphericity value, often denoted Q in the literature. This Q value reflects the nature of the variation in the radius of curvature from the top of the cornea 4 towards its periphery. The vertex corresponds to the intersection of the optical axis y of the cornea 4 with its external surface, that is to say the surface furthest from the pupil 6. On the , the optical axis y of the cornea 4 merges with the optical axis of the lens 8.

Thus, when the value Q is strictly negative (Q<0), the radius of curvature of the cornea 4 increases from the vertex towards the periphery. We then speak of a prolate profile. Conversely, when the Q value is strictly positive (Q>0), the radius of curvature of the cornea 4 decreases from the apex towards the periphery. We then speak of an oblate profile. Finally, when the Q value is zero (Q=0), the radius of curvature of the cornea 4 is constant. The cornea 4 then has a spherical profile.

Generally speaking, a prolate or even hyper-prolate profile is advantageous since it improves visual performance in near vision. The Applicant has also worked on the subject by developing a process, called "advanced isovision" (known by the English name " advanced isovision i on "), consisting of reducing, through laser treatment on the periphery of the cornea 4, the Q value of asphericity. This process also makes it possible to maintain satisfactory performance for distance vision since this essentially requires the central part of the cornea 4, near the vertex.

Laser surgery may, however, be contraindicated for certain patients, particularly those with an autoimmune disease or corneal pathology. For these patients, the only solution is the implantation of an intraocular lens.

Pupil 6 is a circular orifice allowing, through its contraction or dilation, to regulate the quantity of light penetrating into eye 2. Pupil 6 can for example be compared to the diaphragm used in a photographic lens. The diameter of pupil 6 thus varies depending on the ambient light.

In the example illustrated on the , the pupil 6 is represented in a state of maximum contraction, achieved by stimulation of the circular fibers of the iris, in response to high ambient light. In such a case, which corresponds to daytime vision, the diameter of pupil 6 is said to be “photopic”. This photopic diameter is noted here d _p .

When the ambient light is average, for example at dusk, the pupil 6 is in a state of average dilation and its diameter is then described as “mesopic”.

Finally, in the example illustrated on the , the pupil 6 is represented in a state of maximum dilation, achieved by stimulation of the radial fibers of the iris, in response to very low ambient light. In such a case, which corresponds to night vision, the diameter of pupil 6 is called “scotopic”. This scotopic diameter is noted here d _s .

The lens 8 can be compared to a biconvex lens capable of deforming to allow the focusing, in the center of the retina 10, of an object in near vision, in intermediate vision or in far vision. It is the action of the ciliary muscle which makes it possible to modify the curvature of the lens 8 and in particular to increase it significantly to form a clear image of a nearby object on the retina 10. We then speak of accommodation.

Like the cornea 4, the profile of the lens 8 can be characterized by an asphericity value, also denoted Q, which again reflects the nature of the variation in the radius of curvature from the center of the lens 8 towards its periphery. The center can refer here to the intersection of the optical axis y of the lens 8 with its external surface, that is to say the convex surface facing the cornea 4, or with its internal surface, that is to say i.e. the convex surface facing the retina 10.

Lens 8 has a negative asphericity value Q and accommodation consists of further reducing the Q value. However, in presbyopic patients, lens 8 loses its ability to deform and the patient experiences difficulty seeing the nearby objects sufficiently clearly.

Finally, the retina 10 is a neuro-sensory membrane lining the back of the eye 2 and composed of a large number of photoreceptors – called cones and rods – whose role is to convert the light rays received into electrical signals. These electrical signals can then be transmitted to the brain via the optic nerve.

As explained previously, lens 8 can, often due to aging, undergo progressive opacification responsible for a decline in vision and increased sensitivity to light. This well-known condition – cataract – is treated by replacing lens 8 with an intraocular lens.

There thus illustrates an optical diagram of the eye 2 in which the natural lens 8 has been replaced by an intraocular lens 12.

By comparison with the lens 8 shown on the , it should be noted that the intraocular lens 12 comes practically into contact with the pupil 6. The pupil diameter makes it possible to identify, in a given state of dilation or contraction of the pupil 6, the part of the intraocular lens 12 requested and crossed by light rays.

In the case illustrated on the , the intraocular lens 12 replaces the lens 8. However, the intraocular lens 12 can also be a phakic (or phakic) intraocular lens, in which case the lens 8 is preserved. A phakic intraocular lens can be placed in front of or behind the pupil 6 and can correct certain visual deficiencies, notably presbyopia. In the context of the invention, the intraocular lens 12 can designate both an intraocular lens replacing the lens 8 and a phakic intraocular lens.

The remainder of the description presents the characteristics of the intraocular lens 12 according to the invention which makes it possible to treat both cataracts and presbyopia. This intraocular lens 12 is able to replace the natural lens 8 and to offer a satisfactory depth of field, in particular by improving the resolution for objects in close vision.

First of all, it should be remembered that asphericity, whether for the cornea 4, the lens 8 or the intraocular lens 12, is associated with spherical aberrations. For a lens, we speak of spherical aberration – or aberration of sphericity – when para-axial light rays, therefore parallel to the optical axis of the lens, refracted respectively by a peripheral zone and a central zone of the lens do not do not converge on the same plane.

This phenomenon is the consequence of the imperfection of the lens at the exit from which the wavefront is not completely flat. We can then define a phase shift in relation to a theoretical perfect lens and approximate it by a combination of Zernike polynomials. In particular, the following Zernike polynomial – qualified as a radial polynomial – corresponds to the spherical aberration:

Furthermore, for a given lens having a refractive index n, the coefficient of the preceding Zernike polynomial, in the linear combination of the phase shift of the wavefront, is zero if the asphericity value Q of the lens is the following:

Indeed, the following form of the coefficient of the Zernike polynomial corresponding to the spherical aberration can be deduced, among others, from the work of Guang-ming Dai, notably in the article “Theoretical analysis for spherical aberration induction with low-order correction in refractive surgery” (Applied Optics, vol. 51, No. 18, p. 3966-3976, June 20, 2012):

Or :
- n is the refractive index of the lens;
- p is the pupil radius; And
- R ₀ is the radius of curvature at the optical center of the lens.

Therefore, when the asphericity value Q of a lens is equal to the remarkable value -1/n ² , the para-axial light rays converge in the same plane.

When the asphericity value Q of the lens is strictly greater than the remarkable value -1/n ² , the para-axial light rays refracted by the peripheral zone of the lens converge on a plane closer to the lens than the para-axial rays. -axial refracted by the central zone of the lens. In other words, the peripheral para-axial rays converge in front of the central para-axial rays. We then speak of positive spherical aberrations.

Conversely, when the asphericity value Q of the lens is strictly less than the remarkable value -1/n ² , the para-axial light rays refracted by the peripheral zone of the lens converge on a plane further away from the lens as the para-axial rays refracted by the central zone of the lens. In other words, the peripheral para-axial rays converge behind the central para-axial rays. We then speak of negative spherical aberrations.

The Applicant's work led him to become interested in lenses having an asphericity value Q different from the remarkable value -1/n ² . The Applicant has thus studied the optical performance of lenses presenting an asphericity value Q multiple of the remarkable value -1/n ² , therefore asphericity values Q of the type -k/n ² , where k is a relative integer.

The Applicant then discovered that a lens having an asphericity value Q equal to -2/n ² has remarkable properties and makes it possible to improve the depth of field and obtain a much sharper image of a nearby object. . These different results are illustrated on the , there , there and the , and explained below.

There illustrates the formation of a circle of confusion with lenses of distinct asphericities. The first converging lens L ₁ has an asphericity value Q equal to -1/n ² while the second converging lens L ₂ has an asphericity value Q equal to -2/n ² . For each of these lenses, a light source S was positioned on the optical axis y of the lens at a distance D corresponding to near vision. Consequently, the light rays coming from the light source S and passing through the peripheral edge of the lens are divergent rays.

As illustrated on the , the para-axial rays coming from the light source S converge at the object focal point F of the lens which corresponds to the intersection of the optical axis y and the object focal plane PF of the lens. This principle is the same for the first converging lens L ₁ and the second converging lens L ₂ .

The divergent rays coming from the light source S converge at a focal point distinct from the object focal point F – denoted F ₁ for the first converging lens L ₁ and F ₂ for the second converging lens L ₂ – which corresponds to the intersection of the optical axis y and the focal plane PF ₁ for the first converging lens L ₁ or PF ₂ for the second converging lens L ₂ . We see that the focal point F ₂ is much further away from the object focal point F than the focal point F ₁ .

The first converging lens L ₁ and the second converging lens L ₂ both have a negative asphericity value Q, which means that the radius of curvature varies increasingly from the optical center towards the peripheral edge. The curvature, which is inversely proportional to the radius of curvature, therefore varies in a decreasing manner from the optical center towards the peripheral edge. Therefore, when the asphericity value Q is negative, the ability of the converging lens to focus light rays decreases as they move away from the optical center of the lens. The lower the asphericity value Q, the greater the gap between the ability of the lens to converge the central light rays and the ability of the lens to converge the peripheral light rays.

The circle of confusion is illustrated on the for each of the converging lenses L ₁ and L ₂ . The circle of confusion of the first converging lens L ₁ is denoted CC ₁ while the circle of confusion of the second converging lens L ₂ is denoted CC ₂ . In reality, this is a purely schematic illustration since the circle of confusion is in fact included in the object focal plane PF orthogonal to the optical axis y. The circle of confusion, which in fact designates a luminous disk, corresponds to the projection into the object focal plane PF of the light rays coming from the light source S.

It appears that the circle of confusion CC ₂ is wider than the circle of confusion CC ₁ and therefore has lower luminous illuminance. This difference in light illumination between the two circles of confusion results in a difference in sharpness for the image of the light source S in the object focal plane PF. In other words, since the circle of confusion CC ₂ is wider than the circle of confusion CC ₁ , the light intensity of the rays coming from the light source S is distributed over a larger area and the image of the light source S in the focal plane object PF is therefore more easily distinguished. The image of the source S in the object focal plane PF appears much sharper with the second converging lens L ₂ than with the first converging lens L ₁ .

This reduction in light illuminance represents a “dilution” of brightness. The Applicant thus calls "dilution optics" the use of an asphericity value Q equal to -2/n ² acting as a bandwidth to filter divergent rays. Near this asphericity value Q, the divergent rays are no longer perceived by the retina 10 because they are too weak and only the para-axial light rays form a particularly well focused point spreading function, therefore a clear image in the focal plane object PF.

In near vision, it is therefore more advantageous for the intraocular lens 12 to have an asphericity value Q equal to -2/n ² rather than -1/n ² to reduce the luminous illumination of the circle of confusion and thus improving the sharpness of the image.

The Applicant has thus developed an approach that goes against the grain of what is usually sought for the correction of presbyopia. Until now, the challenge in the field of intraocular lenses was to succeed in making the divergent rays converge as close as possible to the object focal point of the intraocular lens 12, located in the center of the retina 10, to obtain a clear vision of a close object. The Applicant here proposes a completely different paradigm in which the intraocular lens 12 presents an asphericity and a radius of curvature profile making it possible to make the divergent rays “diverge” even further or, to be more precise, to make them converge at a focal point. – F ₂ on the – further from the object focal point – F on the – where the para-axial rays converge. The circle of confusion obtained – CC ₂ on the – thus presents lower illumination and the image of an object in the object focal plane is consequently sharper.

Furthermore, even if a very large part of the light rays coming from a nearby object are divergent and are therefore distant from the object focal point of the para-axial rays, at least part of the light rays coming from an object, even close, are para-axial and sufficient to obtain an image in the object focal plane.

The Applicant carried out a comparative simulation of the performances of the converging lens L ₁ , presenting an asphericity value Q equal to -1/n ² , and of the converging lens L ₂ , presenting an asphericity value Q equal to - 2/n ² . For each of these converging lenses, the light source S was positioned first at a distance D corresponding to far vision, here D=10m, then to near vision, here D=0.2m, and finally to an intermediate vision, here D=0.5m. For each converging lens and for each distance, light rays were emitted by the light source S intended for the converging lens tested. The result of the simulation consisted of recording all the impacts of light rays incident in the object focal plane PF, measuring the distance of each impact to the object focal point F and displaying, in the form of a histogram, the distribution of the impacts . The result obtained corresponds to a point spreading function.

As explained previously, the intraocular lens 12 is intended to replace the crystalline lens 8 to allow the focusing, in the center of the retina 10, of an object in near vision, in intermediate vision or in far vision. In the simulation presented here, the converging lens L ₂ corresponds to the intraocular lens 12, the light source S corresponds to any object and the object focal point F therefore corresponds to the center of the retina 10.

There illustrates the point spread function obtained in distance vision for L lenses₁and L₂.

As shown in this figure, the converging lens L ₁ has a peak of less than 20% around the object focal point F, while the converging lens L ₂ has a peak close to 40%, which means that the converging lens L ₂ has a greater capacity than the converging lens L ₁ to converge the incident light rays in far vision at the object focal point F. We also observe that the spreading function of the converging lens L ₁ is more extensive than that of the lens convergent L ₂ , which means that the impacts of incident light rays furthest from the object focal point F are closer to it for the converging lens L ₂ than for the converging lens L ₁ .

There illustrates the point spread function obtained in near vision for L lenses₁and L₂.

The histograms obtained in this figure are consistent with the and the previous considerations on the circle of confusion. We observe in particular, for the converging lens L ₂ , that the peaks at around 5% are located at the ends of the spreading function, which is not the case for the peaks at around 12% for the converging lens L ₁ . Furthermore, the spreading function obtained for the converging lens L ₂ is much more extensive than that obtained for the converging lens L ₁ , which confirms that the converging lens L ₂ makes it possible to further “diverge” the divergent incident light rays. or more precisely to make them converge at a greater distance from the object focal point F.

Finally, the illustrates the point spread function obtained in intermediate vision for L lenses₁and L₂.

The histogram obtained for intermediate vision presents both characteristics that are observed for distance vision and characteristics that are observed for near vision. Thus, for the converging lens L ₂ , we find a high peak at the object focal point F and peaks at the ends of the spreading function.

It is therefore particularly advantageous for the intraocular lens 12 to have an asphericity value Q equal to -2/n ² . Such an intraocular lens 12 not only makes it possible to obtain a clearer image of an object in near vision, which is necessary for the correction of presbyopia, but also to obtain better performance in distance vision and vision. intermediate. This results in a better depth of field for the patient.

There illustrates a system 14 for determining a radius of curvature profile of the intraocular lens 12.

The system 14 may be made available to a practitioner or healthcare professional, for example an ophthalmic surgeon, when a patient suffering from cataract, presbyopia or both is to undergo surgery for replacement. of the lens 8 of an eye 2 by the intraocular lens 12. Of course, such an operation can also consist of replacing the lens 8 of both eyes of the patient.

The system 14 is configured to determine a radius of curvature profile of the intraocular lens 12 suitable for both cataract and presbyopia correction. The resulting radius of curvature profile can then be used to select an intraocular lens 12 already existing and ready to be used for the operation. Alternatively, the radius of curvature profile can also be used to fabricate a custom intraocular lens 12.

The system 14 thus makes it possible to implement at least in part the method of manufacturing the intraocular lens 12 illustrated in the .

As illustrated on the , the system 14 includes an interface 16, a processing unit 18 and a database 20.

The interface 16 is configured to allow the practitioner or healthcare professional to interact with the system 14 to generate a radius of curvature profile adapted to the patient. The interface 16 is for example a man-machine interface allowing a user to enter the data necessary for generating the radius of curvature profile.

The interface 16 may be provided with display means, for example a touch screen or not, and include printing means for printing information relating to the determined radius of curvature profile.

In reference to the , the interface 16 receives, during an operation 800, ocular biometric measurements from a patient.

Ocular biometry is a preoperative examination making it possible to calculate the desired power of the intraocular lens 12. This examination results in the measurement of several characteristics of the patient's eye 2, the subsequent use of which is to calculate the power of the intraocular lens. 12, depends on the mathematical model used.

Typically, ocular biometric measurements include at least axial length and keratometry.

Axial length corresponds to the distance between the anterior surface of cornea 4 and the fovea at the level of the retinal pigment epithelium 10. The anterior surface of cornea 4 designates the surface furthest from pupil 6. On average , the axial length is 23 millimeters (mm). Of course, the axial length can be different from one patient to another, particularly in myopic or hyperopic patients. We thus observe that the axial length is higher in myopic patients than in emmetropic patients and that, conversely, the axial length is lower in hyperopic patients than in emmetropic patients. The axial length is often noted L.

Keratometry, often denoted K, makes it possible to quantify the refractive power of the cornea 4. Keratometry can be calculated by measuring the radii of curvature of the anterior face of the cornea 4 along the two main meridians thereof.

More generally, the measurements carried out in the context of ocular biometrics can concern corneal topography, for example the toricity, symmetry and asphericity of the cornea 4.

As part of ocular biometrics, it is also possible to measure the depth of the anterior chamber. Anterior chamber depth is the distance between the corneal epithelium 4 and the anterior lens capsule 8. Anterior chamber depth averages 3.11 millimeters (mm) and varies depending on the ametropia or the age of the patient.

The ocular biometric measurements are for example entered, via interface 16, by the practitioner or healthcare professional taking part in the operation.

Those skilled in the art understand that ocular biometrics are well known in themselves and are not, strictly speaking, the subject of the present invention. Therefore, the preceding considerations are not exhaustive and ocular biometric measurements may include other measurements than those cited here.

During an operation 810, the interface 16 receives parameters from the intraocular lens 12 comprising at least one refractive index value n.

The refractive index n is in fact necessary since, as explained previously, the intraocular lens 12 must have a radius of curvature profile so that it has an asphericity value Q equal to -2/n ² .

Typically, the material used to manufacture the intraocular lens 12 comprises at least polymethyl methacrylate. This material can be hydrophilic, in which case the refractive index is approximately 1.46, which corresponds to an asphericity value Q approximately equal to -0.938. Alternatively, this material can be hydrophobic, in which case the refractive index is approximately 1.54, which corresponds to an asphericity value Q approximately equal to -0.842. Generally speaking, the refractive index is between 1.46 and 1.54, in which case the target asphericity value Q is ideally between -0.94 and -0.84.

Furthermore, the practitioner or health professional can enter other parameters via interface 16, in particular the constant A well known in the field of ocular biometrics. The constant A was introduced during the development of the SRK regression formula – named after its inventors Sanders, Retzlaff and Kraff – and its value, evaluated statistically, is approximately equal to 118. This value can be adjusted by the practitioner or healthcare professional using the system 14 via the interface 16. The SRK regression formula makes it possible to evaluate the power of the intraocular lens 12 as follows:

where P is the power of the intraocular lens 12.

Here again, those skilled in the art understand that other parameters relating to the desired intraocular lens 12 can be entered via interface 16.

The processing unit 18 is configured, in general, to determine characteristics of the desired intraocular lens 12 and, in particular, the radius of curvature profile thereof.

As illustrated on the , the processing unit 18 comprises a memory 22 and a processor 24.

The memory 22 is configured to store instructions whose implementation, by the processor 24, results in the operation of the processing unit 18. The memory 22 is for example a non-transitory storage medium readable by a computer storing instructions in the form of a computer program

Referring again to the , the processing unit 18 determines, during an operation 820, a radius of curvature value R ₀ at the optical center of the desired intraocular lens 12 as a function of the ocular biometric measurements and one or more of the parameters of the intraocular lens 12.

Several mathematical models are likely to be used by the processing unit 18 to determine the value of the radius of curvature R ₀ at the optical center of the intraocular lens 12. Thus, in addition to the first generation SRK regression formula mentioned more above, other formulas – called theoretical – can be used to calculate the power of the desired intraocular lens 12 and deduce the value of the radius of curvature R ₀ . The two formulas are in fact linked by the following relationship:

Among these theoretical formulas, we can notably cite the second generation SRK II formula, the third generation SRK T, Holladay and Hoffer Q formulas, the fourth generation Holladay 2 and Haigis formulas or even the fifth generation Barrett II formula. It should be noted that several of these formulas also take into account the relative position of the intraocular lens 12 in relation to the cornea 4 of the patient's eye 2.

During an operation 830, the processing unit 18 determines, as a function of the radius of curvature value R ₀ at the optical center of the lens, an increasing and continuous radius of curvature profile from the optical center of the intraocular lens 12 desired towards a peripheral edge of the intraocular lens 12 as a function of the distance from the optical axis y of the intraocular lens 12 so that the latter has an asphericity value Q substantially equal to -2/n ² .

The radius of curvature profile will be discussed below with reference to the and to the .

By “substantially equal”, it is understood here that, ideally, the asphericity value Q of the intraocular lens 12 is equal to -2/n ² to obtain the performances presented previously with reference to the , there , there and the .

However, in practice, it is difficult to exactly achieve the asphericity value Q desired for the intraocular lens 12, in particular due to the inaccuracies inherent in the means and equipment used, whether at the level of the system 14 for determining the profile of radius of curvature or during the subsequent manufacture of the intraocular lens 12. Advantageously, the asphericity value Q actually achieved by the manufactured intraocular lens 12 deviates by 5% from the ideal value -2/n ² . Preferably, this error percentage is 1%.

Finally, during an operation 840, the intraocular lens 12 is manufactured according to the radius of curvature profile determined by the processing unit 18. Here again, the manufacture of an intraocular lens from a radius profile of curvature is widely known in the field of ophthalmology. The operations of such manufacturing are therefore not detailed here, as are the technical means necessary for the manufacture of the intraocular lens 12.

As explained above, the intraocular lens 12 is for example manufactured from a material comprising at least polymethyl methacrylate.

The database 20 is configured to store information collected or calculated by the processing unit 18. For example, the database 20 can store all or part of a patient's ocular biometric measurements as well as all or part of the parameters of the intraocular lens 12 and the radius of curvature profile of the intraocular lens 12. Such information may in particular be useful if the same patient is subsequently required to undergo a new surgical procedure.

In the example illustrated on the , the database 20 is located at the level of the system 14. However, the database 20 can also be deported from the system 14 and be located, for example, at the level of a remote server, for example accessible via an extended network .

The radius of curvature profile, which is in particular the subject of operation 830, is commented below with reference to the and to the which illustrate the variation of the radius of curvature of the intraocular lens 12 from the optical center towards a peripheral edge of the intraocular lens 12 as a function of the distance x from the optical axis y. The radius of curvature profile is here symmetrical with respect to the optical axis y.

The radius of curvature at the optical center of the intraocular lens 12 is denoted R ₀ , while the radius of curvature at the peripheral edge of the intraocular lens 12 is denoted R _p . The r(x) value of the radius of curvature and the distance x to the optical y axis are in millimeters (mm).

It can be noted that the distance x to the optical axis y of a given point of the intraocular lens 12 can also correspond to a pupillary radius since, as illustrated in the , the intraocular lens 12 almost comes into contact with the pupil 6 and the axis of symmetry of the latter coincides with the optical axis y of the intraocular lens 12.

Furthermore, the desired power P at the optical center of the intraocular lens 12 is here equal to 23 m ^-1 – we also use the diopter (δ) as the equivalent vergence unit. The refractive index n is here approximately equal to 1.49. We can approximately deduce the value of the asphericity Q and the radius of curvature R ₀ at the optical center of the intraocular lens 12:

The intraocular lens 12 comprises a variable portion on which the radius of curvature is strictly increasing. The variable portion is connected and symmetrical with respect to the optical axis y.

In the radius of curvature profile shown on the , the variable portion covers the intraocular lens 12 in its entirety. In other words, the intraocular lens 12 has a strictly increasing and continuous radius of curvature from the optical center towards the peripheral edge of the intraocular lens 12 as a function of the distance x from the optical axis y.

The intraocular lens 12 may also comprise at least one constant portion on which the radius of curvature is substantially constant. Each constant portion is connected and symmetrical with respect to the optical axis y.

By “substantially constant”, it is understood here that, ideally, the radius of curvature is the same at every point of the constant portion. However, in practice, it is difficult to obtain perfect stability, in particular due to the inaccuracies inherent in the means and equipment used, whether at the level of the system 14 for determining the radius of curvature profile or during subsequent manufacturing. of the intraocular lens 12. Advantageously, on a constant portion of the intraocular lens 12 manufactured, the radius of curvature value deviates by 5% from the targeted value. Preferably, this error percentage is 1%.

In the radius of curvature profile shown on the , the intraocular lens 12 comprises a constant portion corresponding to a zone Z ₁ , a variable portion corresponds to a zone Z ₂ and another constant portion corresponds to a zone Z ₃ . On the contrary, the radius of curvature profile illustrated on the does not include a constant portion.

The constant portion Z ₁ is a central portion extending from the optical center and over which the distance x from the optical axis y is less than or equal to a first predetermined distance. The first predetermined distance here is approximately equal to 0.75 mm.

The constant portion Z ₃ is an eccentric portion extending to the peripheral edge and over which the distance x from the optical axis y is greater than or equal to a second predetermined distance. The second predetermined distance here is approximately equal to 4.5 mm.

The variable portion Z ₂ is a portion over which the distance x from the optical axis y is between the first predetermined distance and the second predetermined distance.

On the variable portion, the radius of curvature and the distance x from the optical axis y are for example linked by a polynomial relationship. This polynomial relationship is typically of degree 2.

The radius of curvature at a given point of the variable portion can be determined as follows as a function of the distance x from the optical axis y:

Or :
- x is the distance from the given point to the optical axis y;
- x ₁ is a predetermined distance;
- r(x) is the radius of curvature at the given point;
- R ₀ is the radius of curvature at the optical center; And
- α is a constant depending on the asphericity value Q.

When the intraocular lens 12 comprises a variable portion and a constant portion corresponding to a central portion, and the radius of curvature satisfies the previous equation, the predetermined distance x ₁ is equal to the first predetermined distance.

The constant α allows the intraocular lens 12 to reach the target asphericity value Q by appropriate growth of the radius of curvature on the variable portion. The constant α is less than or equal to the target asphericity value Q and is therefore strictly negative. The constant α is all the lower in absolute value as the variable portion occupies a large surface area of the intraocular lens 12. In other words, the presence of one or more constant portions results in a higher constant α in absolute value only in the absence of any constant portion.

The radius of curvature profile shown on the does not include any constant portion – therefore no constant portion corresponding to a central portion – and is therefore obtained with the following parameters:

The equation verified by the radius of curvature of the intraocular lens 12 is then the following:

Conversely, in the embodiment illustrated on the , the intraocular lens 12 comprises the constant portion Z ₁ and the constant portion Z ₃ . The radius of curvature profile on the variable portion Z ₂ is obtained with the following parameters:

The constant α is strictly less than the asphericity value Q to compensate for the interruption or delay in progression of the radius of curvature caused by each constant portion. Thus, the constant α of the equation for the radius of curvature of the is less than that of the equation for the radius of curvature of the , so as to achieve, at the peripheral edge of the intraocular lens 12, the same value of radius of curvature R _p starting from the same radius of curvature R ₀ at the optical center of the intraocular lens 12.

The constant α depends on the length of the variable portion, or more precisely on the difference in distance x from the optical axis y between the interior edge of the variable portion, that is to say the edge closest to the center optical of the intraocular lens 12, and the outer edge of the variable portion, that is to say the edge furthest from the optical center of the intraocular lens 12.

The constant α is for example calculated as a function of the ratio between the length of the variable portion and the radius of the intraocular lens 12. The radius of the intraocular lens 12 designates here the distance x to the optical axis y of the peripheral edge of the intraocular lens 12. On the and the , the radius of the intraocular lens 12 is equal to 5 mm.

The constant α can thus be calculated as follows:

Or :
- ρ is the radius of the intraocular lens 12; And
- l is the length of the variable portion.

For an intraocular lens 12 possibly comprising a constant portion corresponding to a central portion and/or a constant portion corresponding to an eccentric portion, the constant α can then be calculated as follows:

Or :
- x ₁ is the first predetermined distance, which is equal to the predetermined distance of the equation of the radius of curvature on the variable portion; And
- x ₂ is the second predetermined distance.

We note in particular that, when the intraocular lens 12 does not include any constant portion, as illustrated in the , the first predetermined distance is zero and the second predetermined distance is equal to the radius of the intraocular lens 12, so that we find α = Q.

The present invention makes it possible to highlight the ophthalmic performances of an intraocular lens having an asphericity value Q substantially equal to -2/n ² . However, the preceding considerations and results may have applications in fields of optics other than ophthalmology, in particular optical systems involving one or more converging lenses. For example, the teaching of the present invention can be used in the design of a telescope, an optical microscope, an astronomical telescope or even a photographic lens to improve the depth of field. It is then advantageous for each converging lens of such an optical system (or only part of the converging lenses) to have an asphericity value Q substantially equal to -2/n ² . In particular, the series association of several coaxial converging lenses having such characteristics allows filtering of divergent light rays. Concerning again the field of ophthalmology, an asphericity value Q substantially equal to -2/n ² can also be advantageous for a contact lens, also called a corneal lens.

Claims (15)

Intraocular lens (12), having an optical center and an optical axis (y), characterized in that it has an increasing and continuous radius of curvature from the optical center towards a peripheral edge of the intraocular lens (12) as a function of the distance (x) to the optical axis (y) so that the intraocular lens (12) has an asphericity value (Q) substantially equal to the following value:

where n is the refractive index of the intraocular lens (12). Intraocular lens (12) according to claim 1, characterized in that it comprises a variable portion (Z ₂ ) on which the radius of curvature is strictly increasing, said variable portion being connected and symmetrical with respect to the optical axis (y ). Intraocular lens (12) according to claim 2, characterized in that the radius of curvature and the distance (x) to the optical axis (y) are linked by a polynomial relationship on the variable portion. Intraocular lens (12) according to claim 2 or 3, characterized in that the radius of curvature at a given point of the variable portion is determined as follows:

Or :
- x is the distance from the given point to the optical axis (y);
- x ₁ is a predetermined distance;
- r(x) is the radius of curvature at the given point;
- R ₀ is the radius of curvature at the optical center; And
- α is a constant depending on the asphericity value (Q). Intraocular lens (12) according to claim 4, characterized in that the constant α is calculated as follows:

Or :
- ρ is the radius of the intraocular lens (12); And
- l is the length of the variable portion. Intraocular lens (12) according to claim 4 or 5, characterized in that the variable portion covers the intraocular lens (12) entirely and in that:


where Q is the asphericity value of the intraocular lens (12). Intraocular lens (12) according to one of claims 2 to 5, characterized in that it comprises at least one constant portion on which the radius of curvature is substantially constant, each constant portion being connected and symmetrical with respect to the axis optical (y). Intraocular lens (12) according to claim 7, characterized in that a constant portion is a central portion (Z ₁ ) extending from the optical center and over which the distance (x) to the optical axis (y) is less than or equal to a first predetermined distance. Intraocular lens (12) according to claim 8 taken in combination with claim 4 or 5, characterized in that the predetermined distance x ₁ is equal to the first predetermined distance. Intraocular lens (12) according to one of claims 7 to 9, characterized in that a constant portion is an eccentric portion (Z ₃ ) extending to the peripheral edge and over which the distance (x) to the optical axis (y) is greater than or equal to a second predetermined distance. Intraocular lens (12) according to one of claims 7 to 10 taken in combination with claim 4 or 5, characterized in that:

where Q is the asphericity value of the intraocular lens (12). Intraocular lens (12) according to one of the preceding claims, characterized in that the refractive index (n) is between 1.46 and 1.54 and in that the asphericity has a value (Q) between -0.94 and -0.84. Method for determining a radius of curvature profile of an intraocular lens (12) having an optical center and an optical axis (y), characterized in that it comprises:
- receive (800) ocular biometric measurements from a patient;
- receive (810) parameters of the intraocular lens (12) comprising at least one refractive index value (n);
- determine (820) a radius of curvature value (R ₀ ) at the optical center of the intraocular lens (12) as a function of the ocular biometric measurements and one or more of the parameters of the intraocular lens (12);
- determine (830), as a function of the radius of curvature value at the optical center of the lens, an increasing and continuous radius of curvature profile from the optical center of the desired intraocular lens (12) towards a peripheral edge of said intraocular lens (12) as a function of the distance (x) to the optical axis (y) of said intraocular lens (12) so that the latter has an asphericity value (Q) substantially equal to the following value:

where n is the refractive index of the intraocular lens (12). Computer program comprising instructions for implementing the method according to claim 13, when said instructions are executed by at least one processor (24). Method of manufacturing an intraocular lens (12), characterized in that a radius of curvature profile of said intraocular lens (12) is determined according to the method of claim 13, and in that the intraocular lens (12) is manufactured (840) according to this radius of curvature profile.