Method for characterizing at least part of a lens element

Abstract

Method for characterizing at least part of a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on a prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function, the lens element comprising two surfaces, wherein the method comprises : - obtaining over a measuring pupil positioned on said at least part of the lens element at least a value of the modulation transfer function (MTF) of the lens based on at least one feature of the at least part of the lens element measured over the measuring pupil, - determining a value for an estimator factor over the measuring pupil based on the obtained at least one value of the modulation transfer function (MTF) of the lens over said measuring pupil, - determining for different positions of the measuring pupil on the at least part of the lens element a value of the estimator factor, - characterizing said at least part of the lens element by computing the determined values of the estimator factor at the different positions of the measuring pupil.

Description

[0001] Method for characterizing at least part of a lens element

[0002] TECHNICAL FIELD

[0003] The disclosure relates to a method, for example implemented by computer means, for characterizing at least part of a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on a prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function, the lens element comprising two surfaces.

[0004] The disclosure further relates to a method, for example implemented by computer means, for selecting a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on the prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function.

[0005] The disclosure also relates to a computer program product comprising one or more stored sequences of instructions that are accessible to a processor and which, when executed by the processor, causes the processor to carry out the steps of a method according to the disclosure.

[0006] BACKGROUND OF THE DISCLOSURE

[0007] Myopia of an eye is characterized by the fact that the eye focuses distant objects in front of its retina. Myopia is usually corrected using a concave lens and hypermetropia is usually corrected using a convex lens.

[0008] It has been observed that some individuals when corrected using conventional single vision optical lenses, in particular children, focus inaccurately when they observe an object which is situated at a short distance away, that is to say, in near vision conditions. Because of this focusing defect on the part of a myopic child which is corrected for his far vision, the image of an object close by is also formed behind his retina, even in the foveal area.

[0009] Such focusing defect may have an impact on the progression of myopia of such individuals. One may observe that for most of said individuals the myopia defect tends to increase over time.

[0010] Recent controlled clinical trials provided evidence of the benefit of optical elements, such as microlenses, in the peripheral visual field to slow down myopia progression. The purpose of the optical elements is to provide an optical blurred image, in front of the retina of the wearer, triggering a stop signal to the eyes growth.

[0011] The central area of the lens element having the optical elements may be free of optical elements, to enable a good vision.

[0012] Recent studies also showed that myopia progression could be slowed down by providing a slight diffusion in the periphery visual field, with arrays of small dots. The basic principle of this solution is to decrease the contrast of the eye elongation signal, in the peripheral visual field.

[0013] In the areas of the lens element comprising optical elements (like microlenses, or dots of diffusion, or concentric rings of defocus) we can find altemance of two main areas: the “refractive areas” used to correct the myopia of the wearer, and the “defocus areas” used to control the myopia.

[0014] New optical designs propose arrays of contiguous microlenses covering the lens element, without large “refractive areas” free of optical elements: that means that each optical element creates both functions of myopia Rx correction (or create a blur acceptable for the good vision of the wearer) and myopia control defocus signal.

[0015] Different designs of contiguous optical elements have been designed with refractive designs (unifocal spherical or aspherical, bifocal microlenses) or diffractive designs (Pi-Fresnel microlenses).

[0016] As disclosed in WO2021 / 069443 characterizing optical elements one a lens element is challenging.

[0017] The new design of optical elements, such as contiguous and small diameters, or small areas inside optical elements, make the characterization even more complex.

[0018] The known method does not appear to be very efficient on some of the new designs of optical elements, especially on diffractive designs such as Pi-Fresnel optical elements which have inside each optical elements very small rings and discontinuities. Due to the dimensions of zones inside the optical elements, and due to the diffractive behavior of the optical elements the characterization is made more complex. Modulation transfer function can be used to characterize a lens element.

[0019] Usually, modulation transfer function (MTF) is calculated from the simulated or measured topography of the lens element, through a given aperture for a fixed position on the lens element. A further method may be based on direct PSF measurement thanks to a focalizing optical system.

[0020] The calculation is usually done for a single wavelength, with a unique propagation direction.

[0021] This characterization is, by definition, local and does not account for the large stretch of phenomena produced by the interaction between light and the optical elements.

[0022] Therefore, it appears that there is a need for a new method for characterizing at least part of a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on a prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function. The method should not present the drawbacks of the existing methods and in particular should provide a global characterization of the lens element.

[0023] SUMMARY OF THE DISCLOSURE

[0024] To this end, the disclosure proposes a method, for example implemented by computer means, for characterizing at least part of a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on a prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function, the lens element comprising two surfaces, wherein the method comprises :

[0025] - obtaining over a measuring pupil on said at least part of the lens element at least a value of the modulation transfer function (MTF) of the lens based on at least one feature of the at least part of the lens element measured over the measuring pupil, - determining a value for an estimator factor over the measuring pupil based on the obtained at least one value of the modulation transfer function (MTF) of the lens over said measuring pupil,

[0026] - determining for different positions of the measuring pupil on the at least part of the lens element a value of the estimator factor,

[0027] - characterizing said at least part of the lens element by computing the determined values of the estimator factor at the different positions of the measuring pupil.

[0028] Advantageously, the method of the disclosure allows to derive a global indicator of MTF-based indicators in order to provide a global characterization of a lens element.

[0029] Such characterization, based on measurement can be of great help in both R&D and industrial processes in particular to characterize lens elements.

[0030] Such characterization may provide characterization on the myopia control aspect of the lens element and / or on the acuity aspect of the lens element.

[0031] The method of the disclosure may also be used to introduce tolerances in the lens design, compare two or more lens designs, evaluate drift of the structure of the optical element, for example a microstructure, through its manufacturing process, from insert to coated Rx lens, assess the correspondence between the “wear zone” and MTF mappings, help for perceptual studies (on efficacy and / or visual comfort), help lens designers.

[0032] The versatility of MTF measurements derived from distinct measurement techniques is an essential tool in metrology. Developing such ways to quantitively describe lens elements opens a new field of opportunities to better understand the measurement means, their effect over the measure itself and to produce knowledge on the lens elements effect over vision. Such characterization allows having a common comparison tool to tune metrological capabilities.

[0033] According to further embodiments which can be considered alone or in combination:

[0034] the measuring pupil has a spatial characteristic dimension greater than or equal to 2 mm, for example greater than or equal to 4mm, and smaller than or equal to 8 mm, for example smaller than or equal to 6 mm; and / or at least one surface of the lens element comprises optical elements and the at least one feature of the lens element measured over the measuring pupil is based on topographic measurements of said at least one surface of the lens element on said measuring pupil; and / or

[0035] - the at least one feature of the lens element measured over the measuring pupil is based on interferometric measurements of light transmitted or reflected by said at least one surface of the lens element; and / or

[0036] - the at least one feature of the lens element measured over the measuring pupil is based on photometric measurements of light transmitted or reflected by said at least one surface of the lens element; and / or

[0037] - the at least one feature of the lens element measured over the measuring pupil is based on deflectometry or reflectometry measurements over said at least one surface of the lens element; and / or

[0038] - the at least one feature of the lens element measured over the measuring pupil is based on wavefront measurements of light transmitted or reflected by said at least one surface of the lens element; and / or

[0039] - the local lens estimator factor relates to the loss of visual contrast provided by the at least part of the lens element; and / or

[0040] obtaining at least a value of the modulation transfer function (MTF) over a measuring pupil comprises determining different MTF values at at least two different spatial frequencies values, for example at least three different spatial frequencies values, for example at least four different spatial frequencies values; and / or

[0041] for each position of the measuring pupil the method further comprises determining a curve of MTF values over a given range of spatial frequencies and the estimator factor relates to the integrated value of said curve over a given range of spatial frequencies, for example from 0 to 5 cycl / deg, for example the estimator factor relates the integrated value of said curve from 5 to 30 cycl / deg; and / or

[0042] - the lens element comprises optical center as defined in ISO 13666:2019(E), section 3.2.15, and the at least part of the lens element including said measuring pupil when located at at least two different positions comprise the optical center of the lens element; and / or

[0043] - the at least part of the lens element including said measuring pupil when located at said at least two selected positions has a spatial characteristic dimension greater than or equal to 10 mm and smaller than or equal to 50 mm; and / or

[0044] - the at least part of the lens element comprises at least 40%, for example at least 60%, for example at least 80% of the surface of the lens element; and / or

[0045] - the at least part of the lens element comprises at least 25%, for example at least 40%, for example at least 60%, for example at least 80% of the optical elements of the lens element; and / or

[0046] at least 50%, for example 90%, for example all, of the optical elements are multifocal lenslets; and / or

[0047] at least 50%, for example 90%, for example all, of the optical elements are diffractive lenslets; and / or

[0048] - the diffractive lenses are contiguous diffractive lenslets; and / or

[0049] at least 50%, for example at least 90%, for example all, of the optical elements are refractive lenslets; and / or

[0050] at least 50%, for example at least 90%, for example all, of the optical elements are diffusive lenslets; and / or

[0051] - the lens element comprises a refraction area having a refractive power based on the prescription for correcting an abnormal refraction of an eye of the person; and / or

[0052] at least part, for example all, of the front and / or the back surface of the lens element is covered with a coating; and / or

[0053] at least part, for example all, of the optical elements are located on the front surface of the lens element; and / or

[0054] at least part, for example all, of the optical elements are located on the back surface of the lens element; and / or

[0055] at least part, for example all, of the optical elements are located between the front and the back surfaces of the lens element; and / or characterizing at least part of the plurality of optical elements comprises at least identifying the center of at least part of the optical elements, for example using a Hough transform algorithm; and / or

[0056] characterizing at least part of the plurality of optical elements comprises at least determining the optical power at the center of at least part of the optical elements; and / or characterizing at least part of the plurality of optical elements comprises at least determining the global optical power of at least part of the optical elements; and / or

[0057] characterizing at least part of the plurality of optical elements comprises at least determining the optical cylinder value and the optical cylinder axis of at least part of the optical elements; and / or

[0058] characterizing at least part of the plurality of optical elements comprises at least determining the peripheral optical power of at least part of the optical elements; and / or

[0059] characterizing at least part of the plurality of optical elements comprises at least determining the asphericity of at least part of the optical elements; and / or

[0060] characterizing at least part of the plurality of optical elements comprises at least determining the number of optical elements; and / or characterizing at least part of the plurality of optical elements comprises at least determining the density of optical elements; and / or characterizing at least part of the plurality of optical elements comprises determining the ratio of the surface of the lens element having an optical power greater than or equal to a first threshold value and smaller than or equal to a second threshold value; and / or

[0061] characterizing at least part of the plurality of optical elements comprises at least determining the positions of the optical elements; and / or characterizing at least part of the plurality of optical elements comprises at least determining the size of at least part of the optical elements; and / or characterizing at least part of the plurality of optical elements comprises determining the optical power of the holder around the lens element and subtracting said optical power to the two-dimension representation of the local optical power; and / or

[0062] - the optical elements have a contour shape being inscribable in a circle having a diameter greater than or equal to 0.05 mm, for example greater than or equal to 0.1 mm, for example greater than or equal to 0.5 mm, for example greater than or equal to 0.8 mm and smaller than or equal to 7.0 mm, for example smaller than or equal to 3.0 mm, for example smaller than or equal to 1.5 mm, for example smaller than or equal to 1.2 mm; and / or - the optical elements are positioned on a mesh; and / or - the mesh is a structured mesh; and / or

[0063] - the optical elements are positioned along a plurality of concentric rings;

[0064] and / or

[0065] - the lens element further comprises at least four optical elements organized in at least two groups of contiguous optical elements; and / or

[0066] each group of contiguous optical element is organized in at least two concentric rings having the same center, the concentric ring of each group of contiguous optical element being defined by an inner diameter corresponding to the smallest circle that is tangent to at least one optical element of said group and an outer diameter corresponding to the largest circle that is tangent to at least one optical elements of said group; and / or at least part of, for example all the concentric rings of optical elements are centered on the optical center of the surface of the lens element on which said optical elements are disposed; and / or

[0067] - the concentric rings of optical elements have a diameter comprised between 9.0 mm and 60 mm; and / or

[0068] - the distance between two successive concentric rings of optical elements is greater than or equal to 0.5 mm, the distance between two successive concentric rings being defined by the difference between the outer diameter of a first concentric ring and the inner diameter of a second concentric ring, the second concentric ring being closer to the periphery of the lens element; and / or

[0069] - the optical element further comprises optical elements positioned radially between two concentric rings; and / or

[0070] - the structured mesh is a squared mesh or a hexagonal mesh or a triangle mesh or an octagonal mesh; and / or

[0071] - the mesh structure is a random mesh, for example a Voronoid mesh; and / or at least part, for example all, of the optical elements have a constant optical power and a discontinuous first derivative between two contiguous optical elements; and / or

[0072] at least part, for example all, of the optical elements have a varying optical power and a continuous first derivative between two contiguous optical elements; and / or at least one, for example all, of the optical element has an optical function of focusing an image on a position other than the retina in standard wearing conditions; and / or

[0073] at least one optical element has a non-spherical focused optical function in standard wearing conditions and for peripheral vision; and / or

[0074] at least one of the optical elements has a cylindrical power; and / or - the optical elements are configured so that along at least one, section of the lens element, for example a section passing by the optical center of the lens element, the mean sphere of optical elements increases from a point of said section towards the peripheral part of said section; and / or

[0075] - the optical elements are configured so that along at least one section of the lens the cylinder of optical elements increases from a point of said section towards the peripheral part of said section; and / or

[0076] - the optical elements are configured so that along the at least one section of the lens the mean sphere and / or the cylinder of optical elements increases from the center of said section towards the peripheral part of said section; and / or

[0077] - the refraction area comprises an optical center and the optical elements are configured so that along at least one, for example at least 50%, for example any, section passing through the optical center of the lens the mean sphere and / or the cylinder of the optical elements increases from the optical center towards the peripheral part of the lens; and / or

[0078] - the refraction area comprises a far vision reference point, a near vision reference, and a meridian joining the far and near vision reference points, the optical elements are configured so that in standard wearing conditions along any horizontal section of the lens the mean sphere and / or the cylinder of the optical elements increases from the intersection of said horizontal section with the meridian towards the peripheral part of the lens; and / or - the mean sphere and / or the cylinder increase functions along the sections are different depending on the position of said section along the meridian; and / or

[0079] - the mean sphere and / or the cylinder increase functions along the sections are unsymmetrical; and / or

[0080] - the optical elements are configured so that in standard wearing conditions the at least one section is a horizontal section; and / or - the mean sphere and / or the cylinder of optical elements increases from a first point of said section towards the peripheral part of said section and decreases from a second point of said section towards the peripheral part of said section, the second point being closer to the peripheral part of said section than the first point; and / or

[0081] - the mean sphere and / or the cylinder increase function along the at least one section is a Gaussian function; and / or

[0082] - the mean sphere and / or the cylinder increase function along the at least one section is a Quadratic function; and / or

[0083] - the optical elements are configured so that the mean focus of the light rays passing through each optical element is at a same distance to the retina; and / or

[0084] - the refractive area is formed as the area other than the areas formed as the plurality of optical elements; and / or

[0085] for every circular zone having a radius comprised between 2 and 4 mm comprising a geometrical center located at a distance of the framing reference that faces the pupil of the user gazing straight ahead in standard wearing conditions greater or equal to said radius + 5mm, the ratio between the sum of areas of the parts of optical elements located inside said circular zone and the area of said circular zone is comprised between 20% and 70%; and / or

[0086] for every circular zone having a radius comprised between 2 and 4 mm comprising a geometrical center located at a distance of the framing reference that faces the pupil of the user gazing straight ahead in standard wearing conditions greater or equal to said radius + 5mm and smaller than or equal to +10 mm, the ratio between the sum of areas of the parts of optical elements located inside said circular zone and the area of said circular zone is comprised between 20% and 70%; and / or

[0087] at least part, for example all, of the optical elements are located on the front surface of the lens element; and / or

[0088] - the at least one multifocal refraction lenslet comprises a cylindrical power;

[0089] and / or

[0090] - the at least one, for example all, multifocal refractive lenslet comprises an aspherical surface, with or without any rotational symmetry; and / or at least one, for example all, of the optical elements is a toric refractive lenslet; and / or

[0091] at least one multifocal refractive lenslet comprises a toric surface; and / or at least part, for example all, optical functions comprise high order optical aberrations; and / or

[0092] - the lens element comprises at least one continuous scattering area having a characteristic dimension d greater than or equal to 2 mm, wherein any subarea of characteristic dimension dsub comprised in the at least one continuous scattering area, with dsub greater than or equal to 0.05 mm, verifies:

[0093] |%Iscat_area - %Iscat_subarea | < 0.2 * %Iscat_area

[0094] with

[0095] %Iscat_area the average intensity ratio of light scattered by the continuous scattering area, and

[0096] %Iscat_subarea the average intensity ratio of light scattered by the subarea; and / or

[0097] - the lens element further comprises a scattering region comprising the at least one scattering area and having variable light scattering property between the geometrical center of the lens element and the periphery of the lens element; and / or

[0098] - the scattering property increases radially from the geometrical center of the lens element to the periphery of the lens element and / or

[0099] a central region of the lens element, consisting of the region at a distance smaller than or equal to 10 mm from a reference point, has a haze smaller than or equal to 0.5%; and / or

[0100] a peripheral region of the lens element, consisting of the region at a distance greater than or equal to 15 mm, from a reference point, has a haze greater than or equal to 1%; and / or

[0101] - the lens element further comprises a transition region disposed between the central region and the peripheral region of the lens element, and the variation of haze between the central region and the transition region and / or the variation of haze between the transition region and the peripheral region is continuous; and / or

[0102] - the lens element further comprises a plurality of continuous scattering areas positioned on a structured mesh; and / or - the lens element further comprises a plurality of continuous scattering areas arranged as a plurality of concentric scattering rings with a haze greater than or equal to 1% alternating with clear areas with a haze smaller than or equal to 0.3%; and / or

[0103] the lens element is an ophthalmic lens intended to be worn on or in front of an eye of a wearer having at least one prescribed refractive power Px and wherein the at least one continuous scattering area provides an optical function of not focusing an image on the retina of the eye of the wearer so as to slow down the progression of the abnormal refraction of the eye.

[0104] The disclosure further relates to a method, for example implemented by computer means, for selecting a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on the prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function, the method comprising:

[0105] - providing a lens element,

[0106] - characterizing at least part of the lens element according to a method of the disclosure,

[0107] - selecting the lens element based on the characterization of said at least part of the lens element.

[0108] The method for selecting a lens element according to the disclosure may further comprise providing a threshold value for the values of the estimator factor and selecting the lens element by comparing the computed values of the estimator factor with the threshold value.

[0109] In some embodiments, the estimator factor is normalized against a reference modulation transfer function value obtained on a microstructure-free zone of the lens element, preferably located in a clear optical region, either central or peripheral.

[0110] Advantageously, through such normalization, the effect of the microstructures on the modulation transfer function mapping can be isolated and quantified independently from the baseline optical quality of the lens. This normalization allows a direct comparison between different positions of the measuring pupil and between different lens elements, thereby providing an improved characterization of the lens element.

[0111] The disclosure further relates to a computer program product comprising one or more stored sequences of instructions that are accessible to a processor and which, when executed by the processor, causes the processor to carry out the steps of the any method of the disclosure.

[0112] The disclosure also relates to a program which makes a computer execute the method of the disclosure.

[0113] The disclosure further relates to a computer-readable storage medium having a program recorded thereon, wherein the program makes the computer execute a method according to the disclosure.

[0114] The disclosure also relates to a device comprising a processor adapted to store one or more sequence of instructions and to carry out the steps of the method according to the disclosure.

[0115] The disclosure also relates to a computer readable medium carrying one or more sequences of instructions of the computer program product according to the disclosure.

[0116] BRIEF DESCRIPTION OF THE DRAWINGS

[0117] Non-limiting embodiments of the disclosure will now be described with reference to the accompanying drawing wherein:

[0118] o figure 1 is a plan view of a lens element that may be characterized by a method according to the disclosure;

[0119] o figure 2 is a general profile view of a lens element that may be characterized by a method according to the disclosure;

[0120] o figures 3a and 3b represent examples of a diffractive lenslets radial profile;

[0121] o figure 4 illustrates a 7t-Fresnel lens radial profile;

[0122] o figure 5a and 5b illustrates diffraction efficiencies of a 7t-Fresnel lens profile as a function of the wavelength;

[0123] o figure 6 is a flowchart illustrating a characterization method according to the disclosure,

[0124] o figure 7a illustrate MTF mapping criteria based on myopia control, o figure 7b illustrates MTF mapping criteria based on visual acuity, and o figure 8 is a flowchart illustrating a selecting method according to the disclosure.

[0125] Elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figure may be exaggerated relative to other elements to help to improve the understanding of the embodiments of the present disclosure.

[0126] DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

[0127] The disclosure relates to a method for characterizing at least part of a lens element, for example a myopia control lens element, adapted for a wearer, for example intended to be worn in front of an eye of a wearer, for example an optical mold such as a transparent optical mold or an optical film or a transparent optical film or an optical wafer such as a transparent optical wafer.

[0128] In the description, terms like « up », « bottom », « horizontal », « vertical », « above », « below », « front », « rear » or other words indicating relative position may be used. These terms are to be understood in the wearing conditions of the lens element.

[0129] In the context of the present disclosure, the term "lens element" can refer to a semi-finished optical lens, an uncut optical lens or a spectacle optical lens edged to fit a specific spectacle frame or an ophthalmic lens and an optical device adapted to be positioned on the ophthalmic lens. The “lens element” in the context of the present disclosure may have a coating such as a hardcoat.

[0130] The “lens element” may also refer to a transparent lens mold used to obtain an optical lens, the transparent lens mold having optical elements.

[0131] The disclosure relates at least to a method, implemented by computer means for characterizing at least part of the lens element 10.

[0132] As represented on figure 1, a lens element 10 that may be characterized by the method of the disclosure may provide a first optical function having an optical power based on the prescription of the wearer.

[0133] The optical power of the first optical function may be a spherical power and a cylindrical power.

[0134] In the example represented on figure 1, the lens element comprises a holder comprising a refraction area 12 providing the first optical function by having a refractive power based on the prescription for correcting an abnormal refraction of an eye of the wearer.

[0135] The lens element 10 to be characterized by the method of the disclosure may further comprise a plurality of optical elements 14, for example at least twenty. Each optical element 14 of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function.

[0136] Typically, at least one of the optical functions provided by the optical elements is such as to slow down, retard or prevent a progress of the abnormal refraction of the eye of the person, for example myopia of the eye.

[0137] The method of the disclosure may be used to characterize at least part of lens elements having different configurations. The following description illustrates the possible configuration for which the method of the disclosure may be particularly useful.

[0138] The lens element may comprise a refraction area 12 configured to provide to the wearer in standard wearing conditions, in particular for foveal vision, a first optical power based on the prescription of the wearer for correcting an abnormal refraction of said eye of the wearer.

[0139] The wearing conditions are to be understood as the position of the lens element with relation to the eye of a wearer, for example defined by a pantoscopic angle, a Cornea to lens distance, a Pupil-cornea distance, a center of rotation of the eye (CRE) to pupil distance, a CRE to lens distance and a wrap angle.

[0140] The Cornea to lens distance is the distance along the visual axis of the eye in the primary position (usually taken to be the horizontal) between the cornea and the back surface of the lens; for example equal to 12mm.

[0141] The Pupil-cornea distance is the distance along the visual axis of the eye between its pupil and cornea; usually equal to 2mm.

[0142] The CRE to pupil distance is the distance along the visual axis of the eye between its center of rotation (CRE) and cornea; for example equal to 11.5mm.

[0143] The CRE to lens distance is the distance along the visual axis of the eye in the primary position (usually taken to be the horizontal) between the CRE of the eye and the back surface of the lens, for example equal to 25.5mm.

[0144] The pantoscopic angle is the angle in the vertical plane, at the intersection between the back surface of the lens and the visual axis of the eye in the primary position (usually taken to be the horizontal), between the normal to the back surface of the lens and the visual axis of the eye in the primary position; for example, equal to -8°.

[0145] The wrap angle is the angle in the horizontal plane, at the intersection between the back surface of the lens and the visual axis of the eye in the primary position (usually taken to be the horizontal), between the normal to the back surface of the lens and the visual axis of the eye in the primary position for example equal to 0°.

[0146] An example of standard wearer condition may be defined by a pantoscopic angle of -8°, a Cornea to lens distance of 12 mm, a Pupil-cornea distance of 2 mm, a CRE to pupil distance of 11.5 mm, a CRE to lens distance of 25.5 mm and a wrap angle of 0°.

[0147] The term “prescription” is to be understood to mean a set of optical characteristics of optical power, of astigmatism, of prismatic deviation, determined by an ophthalmologist or optometrist in order to correct the vision defects of the eye, for example by means of a lens positioned in front of his eye. For example, the prescription for a myopic eye comprises the values of optical power and of astigmatism with an axis for the distance vision.

[0148] The refractive area may have a continuous variation of optical power. For example, the optical area may have a progressive addition design.

[0149] At least one, preferably all of the, optical element of the plurality of optical elements 14, has an optical function of not focusing an image on the retina of the eye of the wearer, in particular for peripheral vision and preferably for central and peripheral vision.

[0150] For example, each optical element of the plurality of optical elements is transparent over the whole visible spectrum.

[0151] For example, at least one, preferably at least 50%, for example at least 80%, for example at least 95%, for example all of the, optical element of the plurality of optical elements 14, has an optical function of focusing an image in front of the retina.

[0152] In the sense of the disclosure “focusing” is to be understood as producing a focusing spot with a circular section that can be reduced to a point in the focal plane.

[0153] For example, at least one, preferably at least 50%, for example at least 80%, for example at least 95%, for example all of the, optical element of the plurality of optical elements 14, has an optical function of providing a blurred image on the retina.

[0154] Advantageously, such optical functions of the optical element reduces the deformation of the retina of the eye of the wearer in peripheral vision, allowing to slow down the progression of the abnormal refraction of the eye of the person wearing the lens element.

[0155] According to the disclosure, the optical elements may have specific sizes. In particular, the optical elements may have a contour shape being inscribable in a circle having a diameter greater than or equal to 0.05 mm, for example greater than or equal to 0.1 mm, for example greater than or equal to 0.5 mm, for example greater than or equal to 0.8 mm, for example greater than or equal to 1 mm and smaller than or equal to 7.0 mm, preferably smaller than or equal to 5.0 mm, for example smaller than or equal to 3.0 mm, for example smaller than or equal to 2.0 mm.

[0156] The optical elements may be positioned on a mesh.

[0157] The mesh on which the optical elements are positioned may be a structured mesh as illustrated in WO2021 / 069443.

[0158] As illustrated on figure 2, a lens element 10 according to the disclosure comprises an object side surface Fl, for example formed as a convex curved surface toward an object side, and an eye side surface F2 for example formed as a concave surface having a different curvature than the curvature of the object side surface Fl.

[0159] At least part, preferably at least 50%, for example at least 80%, for example at least 95%, for example all, of the optical elements may be located on the front surface of the lens element.

[0160] At least part, preferably at least 50%, for example at least 80%, for example at least 95%, for example all, of the optical elements may be located on the back surface of the lens element.

[0161] At least part, preferably at least 50%, for example at least 80%, for example at least 95%, for example all, of the optical elements may be located between the front and back surfaces of the lens element. For example, the lens element may comprise zones of different refractive indexes forming the optical elements.

[0162] At least one of the optical elements, preferably at least 50%, for example at least 80%, for example at least 95%, for example all may have an optical function of focusing an image for peripheral vision on a position other than the retina.

[0163] Preferably, at least 50%, for example at least 80%, for example all, of the optical elements may have an optical function of focusing an image for peripheral vision on a position other than the retina.

[0164] All of the optical elements may be configured so that the mean focus of the light rays passing through each optical element is at a same distance to the retina of the wearer, at least for peripheral vision. The optical function, in particular the dioptric function, of each optical element may be optimized so as to provide a focus image, in particular in peripheral vision, at a constant distance of the retina of the eye of the wearer. Such optimization requires adapting the dioptric function of each of the optical element depending on their position on the lens element.

[0165] The optical elements may be configured so that at least along one section of the lens the mean sphere of the optical elements increases from a point of said section towards the periphery of said section.

[0166] At least part of the optical elements, preferably at least 50%, for example at least 80%, for example at least 95%, for example all of the optical elements are mutifocal lenslets. Advantageously, such multifocal lenslet may have a first optical power corresponding to the prescription and a second optical power different from the first optical power so as to focus light other than on the retina of the wearer.

[0167] According to an alternative of the disclosure, preferably at least 50%, for example at least 80%, for example at least 95%, for example all of the optical elements are diffractive lenslets, for example contiguous diffractive lenslets.

[0168] In the context of the present disclosure, two optical elements are to be considered contiguous if there is a path linking the two optical elements all along which one may measure in standard wearing conditions at least one optical power different from the optical power based on the prescription of the wearer for correcting an abnormal refraction of the eye of the wearer.

[0169] According to an embodiment of the disclosure, at least one, preferably at least 50%, for example at least 80%, for example at least 95%, for example all of the optical elements, has discontinuities, such as a discontinuous surface, for example Fresnel surfaces and / or having a refractive index profile with discontinuities.

[0170] Figure 3a represents an example of a first diffractive lens radial profile of a contiguous optical element that may be used for the disclosure.

[0171] Figure 3b represents an example of a second diffractive lens radial profile of a contiguous optical element that may be used for the disclosure.

[0172] The diffractive lenslet may be a Fresnel lenslet whose phase function \| / (r) has Ti phase jumps at the nominal wavelength Xo, as seen in Figure 4. One may give these structures the name “7t-Fresnel lenses” for clarity’s sake, as opposition to unifocal Fresnel lenses whose phase jumps are multiple values of 2K. The 7t-Fresnel lens whose phase function is displayed in Figure 5 diffracts light mainly in two diffraction orders (order 0 and +1) associated to dioptric powers P(Xo) = 0 5 and a positive one, for example P(Xo) = 3 5, with Xo = 550 nm.

[0173] An advantage of this design is that the diffraction order dedicated to the prescription of the wearer is not chromatic whereas the one used to provide the second optical function to slow down myopia progression is very chromatic.

[0174] A typical size for the optical element is greater than or equal to 2mm and smaller than or equal to 2.5mm. Indeed, the inventors have observed that maintaining an optical element size smaller than the wearer eye pupil size is advantageous.

[0175] For example, the diffraction efficiency of the 0 and +1 orders is of about 40% at the nominal wavelength Xo.

[0176] To increase the efficiency of the diffraction order corresponding to the wearer prescription one may consider the following:

[0177] To increase the efficiency of the diffraction order 0 one may decrease the value of Xo. Figure 5a shows the diffraction efficiencies with X« = 550nm and figure 5b shows the diffraction efficiencies if o = 400nm. One can notice that in this case, the diffraction efficiency of order 0 is generally higher, whereas the efficiency of order +1 is lower, on the whole visible spectrum. In this case the dioptric power of the refractive phase function to which we apply the phase jumps should be equal to 1.5*400 / 550 ~ 1.1 5 for Xo = 550 nm instead of 1.5 5 in Figure 5a. This results in a widening of the rings of Figure 4.

[0178] One may in addition or alternatively set to zero one ring out of two of the configurations illustrated on Figure 4. In this case, the simultaneously bifocal function still exists due to the remaining Fresnel rings, while the rings set to 0 induce a more important proportion of 05 dioptric power.

[0179] One may further consider applying Fresnel structures made of two materials with two different refraction indices and different Abbe numbers to obtain the phase function of Figure 4 at X = Xo and to get more homogeneous efficiencies on the visible spectrum and / or to privilege one of the two main diffraction orders in relation to the other.

[0180] Other combinations with superimposed Fresnel structures could be considered. Other type of optical elements could be considered such as diffractive optical elements or diffusive optical elements.

[0181] The organization of the optical elements may also be according to concentric rings, for example 10 to 12 concentric rings of contiguous optical lenslets. The optical element may comprise an optical center as defined in ISO 13666:2019 (E), section 3.2.15. The concentric rings of optical lenslets may be centered on the optical center of the optical element.

[0182] The optical elements may also be arranged according to a hexagonal arrangement.

[0183] As stated earlier, sole curvature and optical power characterizations of optical elements, in particular of optical element for slowing down myopia progression, are not sufficient to thoroughly characterize the optical element, in particular the myopia progression slowdown optical elements.

[0184] To trust that the designs elaborated through optical simulations are faithfully crafted on the lens element, there is a need for a new characterization method. The estimator factor determined with the method according to the disclosure may come as an addition to existing surface metrology.

[0185] Lens elements are more and more complex elements with specific optical functions. It is important to characterize these. Mechanical measurements may no longer be sufficient while PSF / MTF quantities could be a tool to describe intrinsic lens element characteristics. PSF and MTF are usually computed or measured on a local probe area, typically based on a human eye pupil’s dimension.

[0186] The disclosure relates to a method to map MTF based criteria over at least part of a lens element, for example over the full lens element. Although the disclosure is described in detail with MTF based criteria, the disclosure may be implemented with PSF based criteria such a map of "acuity" even if not exactly calculated as a MTF.

[0187] According to the disclosure, the MTF measurement / calculation map may be transformed to what it should be in the referential of the wearing conditions. Alternatively, the target criteria wished in the wearing conditions may be transformed in the referential of the measuring device.

[0188] Typically, the lens element comprises optical center as defined in ISO 13666:2019(E), section 3.2.15, and the at least part of the lens element comprise the optical center of the lens element. Indeed, the region comprising the optical center is of most optical interest since is most used by the wearer.

[0189] Preferably, the measurements are done in a measuring referential based on the lens element referential according to the optical center as defined in ISO 13666:2019(E), section 3.2.15. According to an embodiment of the disclosure, the at least part of the lens element has a spatial characteristic dimension greater than or equal to 10 mm and smaller than or equal to 50 mm. Advantageously, this allows covering a large region of the optical element, therefore providing an accurate characterization of the lens element.

[0190] According to an embodiment, the at least part of the lens element comprises at least 40%, for example at least 60%, for example at least 80% of the surface of the lens element.

[0191] According to an embodiment, the at least part of the lens element comprises at least 25%, for example at least 40%, for example at least 60%, for example at least 80% of the optical elements of the lens element, advantageously, this allows characterizing regions of the lens element that provide a myopia control optical function.

[0192] As illustrated on figure 6, the method of the disclosure comprises:

[0193] a MTF value obtaining step S10,

[0194] an estimator value determining step S20,

[0195] a scanning step S30, and

[0196] a characterization step S40.

[0197] During the MTF value obtaining step S10, at least a value of the modulation transfer function (MTF) is obtaining over a measuring pupil positioned on said at least part of the lens element of the lens. The value of the MTF is obtain based on at least one feature of the at least part of the lens element measured over the measuring pupil.

[0198] The measuring pupil may have a spatial characteristic dimension greater than or equal to 2 mm, for example greater than or equal to 4mm, and smaller than or equal to 8 mm, for example smaller than or equal to 6 mm. Typically, the dimension of the measuring pupil is based on a human eye pupil’s dimension.

[0199] The MTF value obtaining step S10 may be carried out in a plane colinear to the optical axis of the lens element. Alternatively, the MTF value obtaining step S10 may be carried out using an eye model so as to include wearing conditions in the measurements.

[0200] During the MTF value obtaining step S10, the at least one value of the modulation transfer function (MTF) over the measuring pupil may be obtain by determining different MTF values for at least two different spatial frequencies values, for example at least three different spatial frequencies values, for example at least four different spatial frequencies values.

[0201] For example, for each position of the measuring pupil the method further comprises determining a curve of MTF values over a given range of spatial frequencies for example between 0 and 30 cycl / deg.

[0202] The MTF calculation is based on at least one feature of the at least part of the lens element measured over the measuring pupil.

[0203] According to an embodiment of the disclosure, at least one surface of the lens element comprises optical elements and the at least one feature of the lens element measured over the measuring pupil is based on topographic measurements of said at least one surface of the lens element on said measuring pupil. For example, the topographic measurements are done using contact measurements.

[0204] According to an embodiment of the disclosure, the at least one feature of the lens element measured over the measuring pupil is based on interferometric measurements of light transmitted or reflected by said at least one surface of the lens element.

[0205] For example, the measurements are done using Zygo Interferometer or any other device available to measure the global altitude of microstructured lens.

[0206] In such configuration it is required to compute the measured optical phase map before the MTF calculation itself.

[0207] According to an embodiment of the disclosure, the at least one feature of the lens element measured over the measuring pupil is based on photometric measurements of light transmitted or reflected by said at least one surface of the lens element.

[0208] According to an embodiment of the disclosure, the at least one feature of the lens element measured over the measuring pupil is based on deflectometry or reflectometry measurements over said at least one surface of the lens element.

[0209] According to an embodiment of the disclosure, the at least one feature of the lens element measured over the measuring pupil is based on wavefront measurements of light transmitted or reflected by said at least one surface of the lens element.

[0210] In the embodiments where the MTF calculation is based on deflectometry or wavefront measurement, an optical phase map is obtained that is straightly injected into the calculations.

[0211] The phase map may be obtained using characterization device and method disclosed in WO2023186763 and in WO2021069443. A further option is to measure local PSF by scanning the probe beam over the whole and calculate a local Fourier Transform to get a MTF in each point.

[0212] During the estimator value determining step S20, a value for an estimator factor is determined over the measuring pupil based on the obtained at least one value of the modulation transfer function (MTF) of the lens over said measuring pupil, According to a preferred embodiment, the local lens estimator factor relates to the loss of visual contrast provided by the at least part of the lens element.

[0213] Typically, when for each position of the measuring pupil the method comprises determining a curve of MTF values over a given range of spatial frequencies and the estimator factor relates to the integrated value of said curve over a given range of spatial frequencies, for example from 0 to 5 cycl / deg, for example the estimator factor relates the integrated value of said curve from 5 to 30 cycl / deg.

[0214] Advantageously, the estimator factor determined based on the integrated value of said MTF curve over the given range of spatial frequencies from 0 to 5 cycl / deg provides a good characterization of the myopia control function of the optical element.

[0215] Figure 7a illustrates a MTF mapping dedicated to myopia control based on the integration over a spatial frequencies domain between 0 and 5 cycl / deg. Such mapping is obtained for a Stellest™ myopia lens.

[0216] Advantageously, the estimator factor determined based on the integrated value of said MTF curve over the given range of spatial frequencies from 5 to 30 cycl / deg provides a good characterization of the visual acuity function of the lens element.

[0217] Figure 7b illustrates a MTF mapping dedicated to visual acyuity based on the integration over a spatial frequencies domain between 5 and 30 cycl / deg. Such mapping is obtained for a Stellest™ myopia lens.

[0218] In some embodiments, the modulation transfer function is computed or measured under a broadband illumination corresponding to the visible spectral range, instead of a single monochromatic wavelength. Such a configuration provides estimator factors that are closer to the actual visual perception of the wearer and allows the method to capture chromatic influences on the optical performance of the lens element.

[0219] During the scanning step S30, a value of the estimator factor is determined for different positions of the measuring pupil on the at least part of the lens element. Typically at least part of the lens element surface is scan by moving the measuring pupil along a predetermined path over the surface of the lens element so as to cover the at least part of the lens element to be characterized.

[0220] In some embodiments, the measuring pupil is displaced over the lens element according to a scanning protocol defined in polar, spherical or cylindrical coordinates, for example with respect to the optical center or geometric center of the lens element. Such coordinate systems may be selected in order to mimic the natural visual exploration of the wearer or to reduce computation time. For example, for a lens element exhibiting a rotational symmetry, a radial scanning protocol may be sufficient to reconstruct the global mapping of the estimator factor. The choice of appropriate coordinate system and corresponding aperture size may help us to reduce calculation time. We may for instance use a polar system to describe a lens that exhibits a revolution symmetry or pseudo-symmetry. As such, a scan of a single surface along the radius of the lens with a selected aperture would allow to estimate the behavior of the full object.

[0221] During the characterization step S40, said at least part of the lens element is characterized by computing the determined values of the estimator factor at the different positions of the measuring pupil.

[0222] Typically, the method of the disclosure allows obtaining final maps of estimator factors, that can be used as relative indicator of quality of a lens element based on different criteria (comparison with respect to an insert or a golden unit over selected spatial frequencies domain).

[0223] Advantageously, the computation process is rather fast and allows for a global appraisal of the lens element with entry data such as altitude maps obtained from the Zygo Interferometer or phase maps obtain using the method and device disclosed in WO2023186763 and in WO2021069443.

[0224] As such the method of the disclosure could be implemented as an industrial control means to check lens production quality.

[0225] In some embodiments, the method is implemented within an industrial metrology workflow using interferometric or wavefront-based devices, for example Zygo™ interferometers, or reflection-based deflectometry equipment. The computation of the estimator factor mapping from such measurement data is sufficiently fast to allow real-time or near real-time assessment of lens elements during or after production. This integration into quality control processes ensures that the manufactured lens elements conform to the intended design. Once the estimator factor maps are determined, either through a numeric file, either a 2D graphic, here are examples of what can be done:

[0226] - maps can be represented in color or gray shade, or with level lines

[0227] - a visual inspection and subjective appreciation may be made with the maps - the scale may be adapted locally for better visibility.

[0228] - representation may be made in 3D

[0229] The map may be analyzed with various criteria, locally or fully. The goal is for example to identify local checking parameters, far vision, near vision, center with corresponding specifications. Doing so one may valid conformity of the design or not.

[0230] For instance, from these estimator factor maps, we can derive data specific to each criteria for each lens.

[0231] The disclosure may include considering two points / zone of interest, and / or the of path between both points / zones of interest such as the gradient, roughness, peak-to-valley, for example the method may include a 2D profiles representation.

[0232] The disclosure may include plotting distribution curves that may be derived from maps to bring metrics for the appreciation of the designs.

[0233] The disclosure may include determining and analyzing histograms which are of interest to analyze maps locally. Other statistics can be set for example the ratio of the surface (or the size of the zone) with a certain "acuity criteria" above a certain level.

[0234] According to the disclosure, new maps may be obtained from computation of previous criteria for example it can be an error map between nominal and measured values.

[0235] In some embodiments, the values of the estimator factor computed over the lens element are further processed through annular integrations around the optical center, for example by computing average values over concentric rings of equal radial width. Such annular integration allows the extraction of global quality descriptors of the lens element, in particular for distinguishing regions dedicated to far vision, near vision, or structured zones. In further embodiments, additional statistical analyses of the mapping are carried out, for example by computing error maps between nominal and measured values, by extracting histograms of local values, or by deriving gradient or peak-to-valley metrics along selected directions.

[0236] The method of the disclosure is particularly useful to characterize at least part of a lens element comprising a plurality of diffractive lenslet, in particular when comprised between the front and back surfaces of the lens element. As illustrated on figure 8, the disclosure further relates to a method for selecting a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on the prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function, the method comprising:

[0237] - a lens element providing step S50, during which a lens element is provided, - a characterization step S60 during which at least part of the lens element is characterized according to a method of the disclosure, and

[0238] - a selecting step S70 during which the lens elements are selected based on the characterization of said at least part of the lens element.

[0239] The selecting method of the disclosure may further comprise providing a threshold value for the values of the estimator factor and selecting the lens element by comparing the computed values of the estimator factor with the threshold value.

[0240] The disclosure has been described above with the aid of embodiments without limitation of the general inventive concept. Many further modifications and variations will be apparent to those skilled in the art upon making reference to the foregoing illustrative embodiments, which are given by way of example only and which are not intended to limit the scope of the disclosure, that being determined solely by the appended claims.

[0241] In the claims, the word “comprising” does not exclude other elements or steps, and the indefinite article “a” or “an” does not exclude a plurality. The mere fact that different features are recited in mutually different dependent claims does not indicate that a combination of these features cannot be advantageously used. Any reference signs in the claims should not be construed as limiting the scope of the disclosure.

Claims

1. -27- CLAIMS1. Method for characterizing at least part of a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on a prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function, the lens element comprising two surfaces, wherein the method comprises :3.- obtaining over a measuring pupil positioned on said at least part of the lens element at least a value of the modulation transfer function (MTF) of the lens based on at least one feature of the at least part of the lens element measured over the measuring pupil,4.- determining a value for an estimator factor over the measuring pupil based on the obtained at least one value of the modulation transfer function (MTF) of the lens over said measuring pupil,5.- determining for different positions of the measuring pupil on the at least part of the lens element a value of the estimator factor,6.- characterizing said at least part of the lens element by computing the determined values of the estimator factor at the different positions of the measuring pupil.

2. The method according to claim 1, wherein the measuring pupil has a spatial characteristic dimension greater than or equal to 2 mm, for example greater than or equal to 4mm, and smaller than or equal to 8 mm, for example smaller than or equal to 6 mm.

3. The method according claim 1 or 2, wherein at least one surface of the lens element comprises optical elements and the at least one feature of the lens element measured over the measuring pupil is based on topographic measurements of said at least one surface of the lens element on said measuring pupil.

4. The method according to any of the preceding claims, wherein the at least one feature of the lens element measured over the measuring pupil is based oninterferometric measurements of light transmitted or reflected by said at least one surface of the lens element.

5. The method according to any of the preceding claims, wherein the at least one feature of the lens element measured over the measuring pupil is based on photometric measurements of light transmitted or reflected by said at least one surface of the lens element.

6. The method according to any of the preceding claims, wherein the at least one feature of the lens element measured over the measuring pupil is based on deflectometry or reflectometry measurements over said at least one surface of the lens element.

7. The method according to any of the preceding claims, wherein the at least one feature of the lens element measured over the measuring pupil is based on wavefront measurements of light transmitted or reflected by said at least one surface of the lens element.

8. The method according to any of the preceding claims, wherein the local lens estimator factor relates to the loss of visual contrast provided by the at least part of the lens element.

9. The method according to any of the preceding claims, wherein obtaining at least a value of the modulation transfer function (MTF) over a measuring pupil comprises determining different MTF values at at least two different spatial frequencies values, for example at least three different spatial frequencies values, for example at least four different spatial frequencies values.

10. The method according to claim 9, wherein for each position of the measuring pupil the method further comprises determining a curve of MTF values over a given range of spatial frequencies and the estimator factor relates to the integrated value of said curve over a given range of spatial frequencies, for example from 0 to 5 cycl / deg, for example the estimator factor relates the integrated value of said curve from 5 to 30 cycl / deg.

11. The method according to any of the preceding claims, wherein the lens element comprises optical center as defined in ISO 13666:2019(E), section 3.2.15, and the at least part of the lens element including said measuring pupil when located at at least two different positions comprise the optical center of the lens element.

12. The method according to the preceding claim, wherein the at least part of the lens element including said measuring pupil when located at said at least two selected positions has a spatial characteristic dimension greater than or equal to 10 mm and smaller than or equal to 50 mm.

13. The method according to any of the preceding claims, wherein the at least part of the lens element comprises at least 40%, for example at least 60%, for example at least 80% of the surface of the lens element.

14. A method for selecting a lens element, for example a myopia control lens element, adapted for a wearer, said lens element providing a first optical function having a power based on the prescription of the wearer, and comprising a plurality of optical elements, for example at least twenty optical elements, each optical element of the plurality of optical elements providing one or more optical functions, at least one of which is different from the first optical function, the method comprising:19.- providing a lens element,20.- characterizing at least part of the lens element according to a method of any of claims 1 to 13,21.- selecting the lens element based on the characterization of said at least part of the lens element.

15. The method according to claim 14, further comprising providing a threshold value for the values of the estimator factor and selecting the lens element by comparing the computed values of the estimator factor with the threshold value.

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