Method for characterizing at least a portion of a lens element

Abstract

A method for characterizing at least a portion of a lens element, for example a myopia control lens element, suitable for a wearer, the lens element providing a first optical function having a refractive power based on a prescription of the wearer and comprising a plurality of optical elements, each of the plurality of optical elements providing one or more optical functions, at least one of the one or more optical functions being different from the first optical function; wherein the method comprises: - obtaining a two-dimensional representation of the local optical power of at least a portion of the lens element using a plenoptic measurement method or a fringe projection profilometry, - determining an optical power distribution over at least a portion of the two-dimensional representation of the lens element, the optical power distribution being in the form of a data representation as a histogram or a stem-and-leaf plot; and - characterizing at least a portion of the lens element within said at least a portion of the two-dimensional representation of the lens element by analyzing the data representation, for example by characterizing the histogram or the stem-and-leaf plot.

Description

Technical Field

[0001] This disclosure relates to a method, for example implemented by a computer device, for characterizing at least a portion of a lens element suitable for a wearer and comprising a plurality of optical elements, each of the plurality of optical elements providing at least one optical power, for example, to mitigate, delay, or prevent at least one of the progression of refractive errors in the wearer's eye.

[0002] This disclosure further relates to a method, for example implemented via a computer device, for inspecting the conformity of a manufactured lens element suitable for a wearer and comprising a plurality of optical elements, each of which provides at least one optical power to mitigate, delay, or prevent at least one of the progression of refractive errors in the wearer's eye.

[0003] This disclosure also relates to a method, for example implemented by a computer device, for controlling a lens element manufacturing process, each lens element being suitable for a wearer and comprising a plurality of optical elements, each of the plurality of optical elements providing at least one optical power to mitigate, delay, or prevent at least one of the progression of refractive errors in the wearer's eye. Background Technology

[0004] Myopia is characterized by the eye focusing distant objects in front of its retina. Myopia is typically corrected with concave lenses, while hyperopia is typically corrected with convex lenses.

[0005] It has been observed that some individuals, particularly children, experience inaccurate focusing when using conventional single-vision lenses for correction, especially when observing objects at near distances (i.e., under near vision conditions). This focusing defect, which is common in myopic children corrected for distance vision, results in images of nearby objects forming behind the retina (even in the fovea region).

[0006] This focusing deficit may affect the progression of myopia in these individuals. It can be observed that, for most of the individuals described, the myopia deficit tends to worsen over time.

[0007] Recent controlled clinical trials have provided evidence that optical elements in the peripheral field of vision, such as microlenses or small lenses, can be beneficial in slowing the progression of myopia. The purpose of these optical elements is to provide an optically blurred image in front of the wearer's retina, thereby triggering a stop signal for eye growth.

[0008] The central area of ​​a lens element with optical elements may not contain optical elements in order to achieve good and clear vision.

[0009] Recent research has also shown that myopia progression can be slowed down using an array of small dots by providing slight diffusion in the peripheral visual field. The basic principle of this solution is to reduce the contrast of the eye's elongated signal in the peripheral visual field.

[0010] In the field of lens elements, which include optical components such as microlenses, small lenses, diffuse points, or defocus concentric rings, an alternation of two main regions can be found: the "refractive region" used to correct the wearer's myopia and the "defocus region" used to control myopia.

[0011] The new optical design features a cluster of small lenses covering the lens elements, without a large “refractive zone” without optical elements: this means that each optical element can produce both myopia Rx correction (or produce blur that is acceptable for the wearer’s good vision) and myopia control defocus signal.

[0012] Different designs of adjacent optical elements have been designed to have refractive designs (single-focal spherical or aspherical, bifocal microlenses) or diffractive designs (Pi-Fresnel microlenses).

[0013] As disclosed in WO 2021 / 069443, characterizing optical elements on lens elements is challenging.

[0014] New designs for optical elements, such as adjacent and smaller diameter elements, or small regions inside the optical element, make characterization more complex.

[0015] Therefore, a new method is needed to characterize at least a portion of a lens element suitable for a wearer and comprising a plurality of optical elements, each of which provides at least one optical power, for example, to mitigate, delay, or prevent at least one of the progression of refractive errors in the wearer's eye. This method should not suffer from the disadvantages of existing methods. Summary of the Invention

[0016] To this end, this disclosure proposes a method, for example implemented via a computer device, for characterizing at least a portion of a lens element suitable for a wearer, such as a myopia control lens element, the lens element providing a first optical function having refractive power based on the wearer's prescription and comprising a plurality of optical elements, each of the plurality of optical elements providing one or more optical functions, at least one of the one or more optical functions being different from the first optical function;

[0017] The method includes:

[0018] - Use deflection measurement or fringe projection profilometry to obtain a two-dimensional representation of the local optical power of at least a portion of the lens element.

[0019] - Determine the power distribution over at least a portion of a two-dimensional representation of a lens element, the power distribution being represented as a histogram or stem-and-leaf plot; and

[0020] The lens element is characterized by analyzing the data representation, for example by characterizing a histogram or stem-and-leaf plot, to represent at least a portion of the two-dimensional representation of the lens element.

[0021] Advantageously, the use of data representation in the form of histograms or stem-and-leaf plots allows for accurate and easy characterization of at least a portion of a lens element, particularly at least a portion of the optical element of the lens element.

[0022] The method disclosed herein allows for the characterization of lens elements using existing deflection measurement devices or fringe projection profile measurement devices. Such measurements can be performed very quickly and easily.

[0023] Alternatively, other deflection measurement methods can be used, such as using a light wave analyzer that projects a beam of light through the lens element and infers the local curvature of the lens element from the measurement of the light deviation.

[0024] The methods disclosed herein are particularly useful for simultaneous multifocal designs because they can be used to characterize even when the lens element generates multiple wavefronts (e.g., for Pi-Fresnel, a 0th-order wavefront and a 1st-order second wavefront).

[0025] According to other embodiments that can be considered individually or in combination:

[0026] - The lens element includes a refractive region configured to provide the wearer with a first optical power based on the wearer's prescription under standard wearing conditions, particularly for foveal visual acuity; and the optical element provides at least a second optical power; and / or

[0027] - The refractive area includes multiple separate island regions; and / or

[0028] - The refractive region is formed as a region excluding the optical element, and each refractive island region is located within an optical element; and / or

[0029] - The refractive region is formed as a region other than the region formed by multiple optical elements; and / or

[0030] - Lens elements include a refractive region configured to provide a first optical power to the wearer under standard wearing conditions, particularly for foveal visual acuity; these optical elements provide at least a second optical power, the first and at least the second optical power being based on the wearer's prescription; and / or

[0031] - Lens elements include a refractive region configured to provide the wearer with a first optical power under standard wearing conditions, particularly for foveal visual acuity; these optical elements provide at least a second optical power, the sum of the first and at least the second optical power being based on the wearer's prescription; and / or

[0032] - Optical elements can provide multiple optical functions simultaneously; and / or

[0033] - A two-dimensional representation of the local optical power of at least a portion of the lens element is obtained on a pupil with a diameter greater than or equal to 3 mm (e.g., greater than or equal to 4 mm) and less than or equal to 9 mm (e.g., less than or equal to 7 mm); and / or

[0034] - A two-dimensional representation of local optical power corresponds to at least 25%, for example, at least 50%, for example, at least 80%, of the surface area of ​​the lens element; and / or

[0035] - A two-dimensional representation of local optical power corresponds to at least a portion of a lens element, which includes at least 10%, for example at least 25%, for example at least 40%, for example at least 80% of the optical element; and / or

[0036] - Images used for deflection measurement methods consist of pixels less than or equal to 0.05 mm × 0.05 mm; and / or

[0037] - Characterizing at least a portion of the lens element includes segmenting the histogram based on identified inflection points; and / or

[0038] - The method further includes, after segmenting the histogram, fitting different portions of the histogram with a Gaussian distribution and determining the skewness and / or kurtosis of the power distribution; and / or

[0039] - The method further includes determining the processed histogram by increasing the bin size of the histogram until the different parts of the histogram are symmetrically distributed and the number of bins of the histogram is greater than or equal to 15 and less than or equal to 36; and / or

[0040] The method further includes fitting the portion of the histogram corresponding to the first optical function with a first Gaussian distribution, and fitting the portion of the histogram corresponding to the optical element with a second Gaussian distribution, and characterizing at least a portion of the lens element includes determining the amplitude ratio at the center power value of both the first and second Gaussian distributions and / or the full width at half maximum (FWHM) ratio of both the first and second Gaussian distributions; and / or

[0041] - The method further includes filtering the histogram with a moving filter (e.g., an averaging filter or a low-pass filter); and / or

[0042] - The lens element has a central region without optical elements, and a two-dimensional representation of the local optical power of at least a portion of the lens element is obtained on the pupil, wherein the distance from the center of the pupil to the optical center of the lens element is greater than or equal to the sum of half the diameter of the central region without optical elements of the lens element and half the diameter of the pupil; and / or

[0043] - This method characterizes at least a portion of the optical element within the at least a portion of the two-dimensional representation of the lens element; and / or

[0044] - At least 50%, for example 90%, for example all optical elements are refractive lenses; and / or

[0045] - At least 50%, for example 90%, for example all optical elements are diffuse microlenses; and / or

[0046] - At least 50%, for example 90%, for example all optical elements are multifocal microlenses; and / or

[0047] - At least 50%, for example 90%, for example all optical elements are diffractive microlenses; and / or

[0048] - A diffractive lens is an adjacent diffractive microlens; and / or

[0049] -The method includes:

[0050] ○ Using a deflection measurement method, obtain at least two two-dimensional representations of the local optical power of at least a portion of the lens element at at least two different wavelengths.

[0051] ○ Determine the power distribution over at least a portion of each of at least two two-dimensional representations of the lens element, and

[0052] ○ Characterize optical elements by comparing at least two determined power distributions; and / or

[0053] - At least one of two different wavelengths corresponds to the nominal wavelength of the diffractive microlens; and / or

[0054] - The lens element includes a refractive region having refractive power based on a prescription for correcting refractive errors in the wearer's eye; and / or

[0055] - At least a portion, for example, all of the front and / or rear surfaces of the lens element are coated; and / or

[0056] - At least a portion, such as all, of the optical elements are located on the front surface of the lens element; and / or

[0057] - At least a portion, such as all, of the optical elements are located on the rear surface of the lens element; and / or

[0058] - At least some, for example all, of the optical elements are located between the front and rear surfaces of the lens element; and / or

[0059] - Characterizing at least a portion of a plurality of optical elements includes identifying the center of at least a portion of the optical elements, for example using the Hough transform algorithm; and / or

[0060] - Characterizing at least a portion of a plurality of optical elements includes at least determining the optical power at the center of at least a portion of the optical elements; and / or

[0061] - Characterizing at least a portion of a plurality of optical elements includes at least determining the global optical power of at least a portion of the optical elements; and / or

[0062] - Characterizing at least a portion of a plurality of optical elements includes determining the optical cylinder value and optical cylinder axis of at least a portion of the optical elements; and / or

[0063] - Characterizing at least a portion of a plurality of optical elements includes at least determining the peripheral optical power of at least a portion of the optical elements; and / or

[0064] Characterizing at least a portion of a plurality of optical elements includes at least determining the asphericity of at least a portion of the optical elements; and / or

[0065] - Characterizing at least a portion of a plurality of optical elements includes at least determining the number of optical elements; and / or

[0066] Characterizing at least a portion of a plurality of optical elements includes at least determining the density of the optical elements; and / or

[0067] Characterizing at least a portion of a plurality of optical elements includes determining the ratio of surfaces of a lens element having an optical power greater than or equal to a first threshold and less than or equal to a second threshold; and / or

[0068] - Characterizing at least a portion of a plurality of optical elements includes at least determining the position of the optical elements; and / or

[0069] Characterizing at least a portion of a plurality of optical elements includes at least determining the size of at least a portion of the optical elements; and / or

[0070] Characterizing at least a portion of a plurality of optical elements includes determining the refractive power around, for example, near, the optical elements, and subtracting said refractive power from a two-dimensional representation of the local refractive power; and / or

[0071] - The optical element has an external shape that can be inscribed within a circle with a diameter greater than or equal to 0.1 mm (e.g., greater than 0.5 mm) and less than or equal to 7.0 mm (e.g., less than or equal to 3.0 mm); and / or

[0072] - Optical components are positioned online; and / or

[0073] - This network is a structured network; and / or

[0074] - Optical elements are positioned along multiple concentric rings; and / or

[0075] - The lens element further includes at least four optical elements, which are organized into at least two adjacent groups of optical elements; and / or

[0076] - Organize each group of adjacent optical elements into at least two concentric rings with the same center, wherein the concentric rings of each group of adjacent optical elements are defined by the inner diameter of the smallest circle tangent to at least one optical element in the group and the outer diameter of the largest circle tangent to at least one optical element in the group; and / or

[0077] - At least a portion, such as all, of the concentric rings of optical elements are centered on the optical center of the surface of the lens element on which the optical elements are disposed; and / or

[0078] - The concentric rings of the optical element have a diameter between 9.0 mm and 60 mm; and / or

[0079] - The distance between two successive concentric rings of an optical element is greater than or equal to 0.5 mm, defined by the difference between the outer diameter of the first concentric ring and the inner diameter of the second concentric ring, with the second concentric ring closer to the periphery of the lens element; and / or

[0080] - The optical element further includes an optical element radially positioned between two concentric rings; and / or

[0081] - Structured networks are square networks, hexagonal networks, triangular networks, or octagonal networks; and / or

[0082] - The network structure is a random network, such as a Voronoid network; and / or

[0083] - At least some, for example all, of the optical elements have a constant optical power and a discontinuous first derivative between two adjacent optical elements; and / or

[0084] - At least some, for example all, of the optical elements have varying optical power and a continuous first derivative between two adjacent optical elements; and / or

[0085] - At least one, for example all of the optical elements, has the optical function of focusing an image onto a location other than the retina under standard wearing conditions; and / or

[0086] - Under standard wearing conditions and for peripheral vision, at least one optical element has aspherical focusing optical functionality; and / or

[0087] - At least one of the optical elements has cylindrical power; and / or

[0088] - The optical element is configured such that along at least one cross-section of the lens element, or for example, along all cross-sections of the lens element, such as a cross-section passing through the optical center of the lens element, the average spherical power of the optical element increases from a point on said cross-section toward the peripheral portion of said cross-section; and / or

[0089] - The optical element is configured such that, along at least one cross-section of the lens, or for example, along all cross-sections of the lens, the cylindrical power of the optical element increases from a point on the cross-section toward the peripheral portion of the cross-section; and / or

[0090] - The optical element is configured such that along at least one cross-section of the lens, or for example, along all cross-sections of the lens, the average spherical power and / or cylindrical power of the optical element increases from the center of the cross-section toward the peripheral portion of the cross-section; and / or

[0091] - The refractive region includes an optical center, and the optical element is configured such that along at least one, for example at least 50%, for example all, cross sections passing through the optical center of the lens, the average spherical and / or cylindrical power of the optical element increases from the optical center toward the peripheral portion of the lens; and / or

[0092] - The refractive region includes a distance reference point, a near reference point, and a meridian connecting the distance and near reference points. These optical elements are configured such that, under standard wearing conditions, along any horizontal section of the lens, the average spherical and / or cylindrical power of these optical elements increases from the intersection of the horizontal section and the meridian toward the peripheral portion of the lens; and / or

[0093] - The mean spherical and / or cylindrical power increases as a function of the cross section, depending on the position of the cross section along the meridian; and / or

[0094] - The mean spherical and / or cylindrical power increases asymmetrically along the cross section; and / or

[0095] These optical elements are configured such that, under standard wearing conditions, at least one cross-section is a horizontal cross-section; and / or

[0096] - The average spherical and / or cylindrical power of the optical element increases from a first point on the cross-section toward the periphery of the cross-section, and decreases from a second point on the cross-section toward the periphery of the cross-section, the second point being closer to the periphery of the cross-section than the first point; and / or

[0097] - The increasing function of mean spherical and / or cylindrical power along at least one cross section is a Gaussian function; and / or

[0098] - The mean spherical power and / or cylindrical power are quadratic functions increasing along at least one cross section; and / or

[0099] These optical elements are configured such that the average focal distance of the light rays passing through each optical element is the same from the retina; and / or

[0100] - The refractive region is formed as a region other than the region formed as multiple optical elements; and / or

[0101] - For each circular region with a radius greater than or equal to 1 mm (e.g., greater than or equal to 2 mm) and less than or equal to 5 mm (e.g., less than or equal to 4 mm), including a reference frame located at a distance greater than or equal to the radius + 4 mm (e.g., + 5 mm, e.g., + 6 mm) from the pupil of a user looking straight ahead under standard wearing conditions, the ratio between the sum of the areas of the portions of the optical element within the circular region and the area of ​​the circular region is greater than or equal to 20% (e.g., greater than or equal to 30%) and less than or equal to 80% (e.g., less than or equal to 70%, e.g., less than or equal to 60%); and / or

[0102] - At least a portion, such as all, of the optical elements are located on the front surface of the lens element; and / or

[0103] - At least one multifocal refractive lens includes cylindrical power; and / or

[0104] - At least one, for example, all multifocal refractive lenses include an aspherical surface and have or do not have any rotational symmetry; and / or

[0105] -At least one, for example all, optical elements are toric refractive lenses; and / or

[0106] - At least one multifocal refractive lens includes a tortuous surface; and / or

[0107] - At least some, such as all, optical functions include higher-order optical aberrations.

[0108] This disclosure further relates to a method, for example implemented via a computer device, for inspecting the conformity of a manufactured lens element suitable for a wearer and comprising a plurality of optical elements, each of which provides at least one optical power to mitigate, delay, or prevent at least one of the progression of refractive errors in the wearer's eye.

[0109] The method includes:

[0110] - Obtain characterization data relating to at least one optical characteristic of the optical element of the lens element to be manufactured.

[0111] - Optical elements that use the methods described in this disclosure to characterize the manufactured lens elements.

[0112] - The characteristics of the optical elements of the manufactured lens element are compared with this characterization data in order to check the conformity of the manufactured lens element.

[0113] This disclosure also relates to a method, for example implemented via a computer device, for controlling a lens element manufacturing process, wherein each lens element is suitable for a wearer and includes a plurality of optical elements, each of which provides at least one optical power to mitigate, delay, or prevent at least one of the progression of refractive errors in the wearer's eye.

[0114] The method includes the following steps:

[0115] a) Manufacturing lens components according to manufacturing processes.

[0116] b) Determine at least one feature of the lens element manufactured in step a) according to the method of this disclosure.

[0117] c) Record the difference between at least one identified feature and a reference value.

[0118] d) Repeat steps a) through c) periodically and examine how the difference evolves over time.

[0119] Specifically, the evolution of at least one parameter of the manufacturing process used to manufacture the lens element is examined over time, and the evolution of this difference over time is related to the evolution of at least one parameter of the manufacturing process over time.

[0120] This disclosure further relates to a computer program product comprising one or more stored instruction sequences that are accessible to a processor and, when executed by the processor, cause the processor to perform the steps of any method of this disclosure.

[0121] This disclosure also relates to a procedure for causing a computer to execute the method disclosed herein.

[0122] This disclosure further relates to a computer-readable storage medium having a program recorded thereon, wherein the program causes a computer to perform the method according to this disclosure.

[0123] This disclosure also relates to an apparatus including a processor adapted to store one or more sequences of instructions and perform the steps of the method according to this disclosure.

[0124] This disclosure also relates to a computer-readable medium that carries one or more sequences of instructions for a computer program product according to this disclosure. Attached Figure Description

[0125] Non-limiting embodiments of the present disclosure will now be described with reference to the accompanying drawings, in which:

[0126] ○ Figure 1 It is a plan view of a lens element that can be characterized by the method according to this disclosure;

[0127] ○ Figure 2 It is a general outline view of a lens element that can be characterized by the method according to this disclosure;

[0128] ○ Figure 3 This is a schematic diagram of the fringe deflection measuring device according to the first configuration;

[0129] ○ Figure 4 This is a schematic diagram of the fringe deflection measuring device according to the second configuration;

[0130] ○ Figure 5 This is an example of a two-dimensional representation of a lens element according to this disclosure;

[0131] ○ Figure 6a and Figure 6b An example representing the radial profile of a diffractive miniature lens;

[0132] ○ Figure 7 The radial profile of the π-Fresnel lens is shown; and

[0133] ○ Figure 8 This represents different steps in the methodology described in this disclosure;

[0134] ○ Figure 9 The effect of reducing the bin size is shown at different average step sizes n between 1 and 64.

[0135] ○ Figure 10 A view of a portion of a lens element that can be characterized by the methods described in this disclosure, and

[0136] ○ Figures 11a to 11c The effect of histogram bin number selection is demonstrated when characterizing a portion of a lens element using the method according to this disclosure.

[0137] The elements in the figures are illustrated for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the figures may be enlarged relative to other elements to aid in understanding the embodiments of this disclosure. Detailed Implementation

[0138] This disclosure relates to a lens element designed to be worn in front of a wearer's eyes.

[0139] In the remainder of this specification, terms such as “upper,” “bottom,” “horizontal,” “vertical,” “above,” “below,” “front,” “back,” or other words indicating relative position may be used. These terms should be understood in the context of wearing the lens element.

[0140] In the context of this disclosure, the term "lens element" can refer to an uncut optical lens or an eyeglass lens or ophthalmic lens that has been edged to fit a particular eyeglass frame, and an optical device suitable for positioning on an ophthalmic lens. In the context of this disclosure, a "lens element" may have a coating, such as a hard coating.

[0141] According to a preferred embodiment of this disclosure, the lens element is a myopia control lens element.

[0142] "Lens element" can also refer to a transparent lens mold used to obtain an optical lens, which has optical elements.

[0143] This disclosure relates to at least one method implemented via a computer device for characterizing at least a portion of a lens element 10.

[0144] like Figure 1 The lens element 10 (e.g., a myopia control lens element) that can be characterized by the methods described herein may include:

[0145] - Refractive zone 12, which provides a first optical function with prescription-based refractive power, such as for correcting refractive errors in the wearer's eye, and

[0146] - A plurality of optical elements 14, each of the plurality of optical elements providing one or more optical functions, at least one of which differs from a first optical function, for example, to mitigate, delay or prevent at least one of the progression of refractive errors in the wearer's eye.

[0147] Typically, the refractive zone provides the primary optical function with refractive power based on the wearer's prescription.

[0148] Each of the plurality of optical elements provides one or more optical functions, at least one of which is different from the first optical function.

[0149] Although not in Figure 1 The text indicates that the refractive region can include multiple separate island-shaped regions, as shown in WO2021198362. The refractive region can be formed as a region other than the optical element, and each refractive island-shaped region is located within an optical element.

[0150] Optical elements can simultaneously provide different optical functions; for example, at least a portion of an optical element can simultaneously provide two optical functions, as disclosed in WO 2019 / 206569 or WO 2021 / 001524. The method according to this disclosure includes using a deflection measurement method to obtain a two-dimensional representation of the local optical power of at least a portion of the lens element. The method of this disclosure can use a fringe deflection measurement method.

[0151] In this disclosure, the method described uses the transmission fringe reflectance measurement method. However, those skilled in the art can readily adapt this disclosure using other deflection measurement methods (such as reflection deflection measurement methods or fringe projection profile measurement methods).

[0152] like Figure 3 As shown, the fringe deflection measurement method involves positioning the lens element 10 to be characterized between an image display device 20 (e.g., a screen) and an image acquisition device 22 (e.g., a camera). Black and white stripes are scrolled on the screen. The scrolling of these stripes is observed via the camera, and its delay or acceleration is related to the light deviation caused locally by the lens element 10.

[0153] According to one embodiment of the method disclosed herein, the distance between the screen and the lens element 10 may be 150 mm, and the distance between the screen and the image acquisition device 22 may be 475 mm.

[0154] The deviation of light is the object of the algorithm, which allows the combination of lens elements and mappings of color levels or gray levels that are proportional to local optical power.

[0155] In order to characterize the lens element, the inventors have proposed to adjust the existing technical images used in conventional fringe deflection measurement methods.

[0156] The inventors have determined that, in order to improve the accuracy of characterization, the image used for deflection measurement can consist of pixels less than or equal to 0.05 mm × 0.05 mm.

[0157] In the context of this disclosure, the feature "image used" corresponds to the transformation result of the image acquired by the image acquisition device 22 using an algorithm. In other words, the calculation is configured to generate a calibrated image such that one pixel covers 0.05 mm × 0.05 mm.

[0158] The method disclosed herein can also be used by using commercially available lens mappers (such as the NIMO proposed by Lambda-X). TM The solution obtains a two-dimensional representation of the local optical power for use.

[0159] This solution has been commercially proposed for mapping contact lenses, and adjustments may be required for larger lenses (such as spectacle lenses).

[0160] In this case, the lens element is located in the horizontal plane of the measuring device and can be displaced in different x and y directions, such as Figure 4 As shown, in the case of the Nimo solution, the optical center of the lens element is not systematically aligned with the collimating measurement beam. Furthermore, in the current version of the Nimo solution, there is no clamp that allows the lens element to be centered; therefore, the inventors propose using the original view of the stripe pattern, which is visible in real-time due to the camera's video mode, and ensuring its centering.

[0161] As explained in WO 2021 / 069443, when such surface measurements are feasible, there is a very strong correlation between the gray levels of the phase derivative image obtained by the deflection measurement method and the optical power values ​​obtained by the surface measurements.

[0162] Therefore, it is clear that the deflection measurement method allows for an accurate two-dimensional representation of the local focal power of at least a portion of the lens element.

[0163] Advantageously, deflection measurement methods, such as stripe deflection measurement methods, are easier, cheaper, and shorter to implement than surface measurements.

[0164] Furthermore, the method disclosed herein allows characterization of at least a portion of a lens element, particularly at least a portion of the optical elements of an optical lens, even if the optical elements are not on one of the front or rear surfaces of the lens element (e.g., between the front and rear surfaces) and / or are diffractive optical elements.

[0165] like Figure 3As shown, the lens element 10 can be positioned on a bracket with its convex surface facing the screen 20. A diffuser to reduce noise in the final result can be placed on the screen, and a wavelength filter can also be placed on the screen, especially when the optical element is a diffractive microlens.

[0166] The image of the stripes displayed on the screen, as seen through the lens element 10, is recorded by the camera 22.

[0167] Figure 5 An example of an optical power map that can be obtained using the fringe deflection measurement method described in this disclosure is shown.

[0168] A two-dimensional representation of local optical power can be obtained using an aperture diameter greater than or equal to 3 mm (e.g., greater than or equal to 4 mm) and less than or equal to 9 mm (e.g., less than or equal to 7 mm).

[0169] A two-dimensional representation of local optical power corresponds to at least 25%, for example at least 50%, or for example at least 80%, of the surface of the lens element.

[0170] The method disclosed herein can be advantageously used to characterize at least a portion of an optical element or a lens element comprising at least a portion of the optical element. Thus, a two-dimensional representation of local optical power can correspond to at least a portion of the lens element comprising at least 10%, for example at least 25%, for example at least 40%, for example at least 80% of the optical element.

[0171] The method according to this disclosure can be used to characterize at least a portion of a lens element having a variety of optical elements with diverse positions and optical functions. Different examples of lens elements with different types of optical elements are described herein. The method of this disclosure can be used, for example, to determine different characteristics of at least a portion of a lens element based on the configuration of the optical elements.

[0172] According to the method disclosed herein, at least a portion of a two-dimensional representation of at least a portion of a lens element obtained by a deflection measurement method, such as all of them used to determine the power distribution on at least a portion of the two-dimensional representation of the lens element.

[0173] The optical power distribution can be obtained over at least a portion of the two-dimensional representation of local focal length based on the number of pixels at each gray level. For storage and computation purposes, the two-dimensional representation typically includes 256 different gray levels.

[0174] Each grayscale level can be converted into a local focal length value. Therefore, it is possible to obtain the focal length distribution over at least a portion of the two-dimensional representation of the lens element.

[0175] Lens elements, such as optical elements of lens elements, are characterized by analyzing the determined power distribution.

[0176] The methods disclosed herein can be used to characterize lens elements with different configurations. The following description illustrates possible configurations for which the methods disclosed herein can be particularly useful.

[0177] The lens element may include a refractive region 12 configured to provide the wearer with a first optical power based on a prescription for the wearer, particularly for foveal vision, under standard wearing conditions, such as for correcting refractive errors in the wearer's eye.

[0178] Wearing conditions should be understood as the position of the lens element relative to the wearer's eye, defined by factors such as the anterior tilt angle, corneal-to-lens distance, pupil-to-corneal distance, center of rotation (CRE)-to-pupil distance, CRE-to-lens distance, and wrap angle.

[0179] The corneal-to-lens distance is the distance between the cornea and the posterior surface of the lens along the visual axis of the eye in the first eye position (which is usually considered to be horizontal); for example, it is equal to 12 mm.

[0180] The pupil-to-corneal distance is the distance between the pupil and the cornea along the visual axis of the eye; it is usually equal to 2 mm.

[0181] The distance from the CRE to the pupil is the distance along the visual axis of the eye between the cornea at its center of rotation (CRE); for example, it is equal to 11.5 mm.

[0182] The distance from the CRE to the lens is the distance along the visual axis of the eye in the first eye position (which is usually considered to be horizontal) between the CRE of that eye and the posterior surface of the lens, for example, equal to 25.5 mm.

[0183] The tilt angle is the angle in a vertical plane between the intersection of the posterior surface of the lens and the visual axis of the eye in the first eye position (which is usually considered to be horizontal), and the normal to the posterior surface of the lens; for example, it is equal to -8°.

[0184] The wrap angle is the angle in the horizontal plane between the normal to the posterior surface of the lens and the visual axis of the eye in the first eye position (which is usually considered to be horizontal), for example, equal to 0°.

[0185] Examples of standard wearer conditions can be defined by an anterior tilt angle of -8°, a corneal-to-lens distance of 12 mm, a pupil-to-corneal 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°.

[0186] The term "prescription" should be understood as a set of optical characteristics, including power, astigmatism, and prism deviation, determined by an ophthalmologist or optometrist to correct visual defects, for example, by means of a lens positioned in front of the wearer's eye. For example, a prescription for myopia includes a power value and an astigmatism value with an axis for distance vision.

[0187] The refractive region can have continuously varying optical power. For example, the optical region can have a gradient multifocal design.

[0188] At least one of the plurality of optical elements 14, for example at least 50%, for example at least 95%, preferably all of the optical elements, has at least one optical function that does not focus the image onto the retina of the wearer’s eye, particularly for peripheral vision and preferably for central and peripheral vision.

[0189] For example, each of the multiple optical elements is transparent across the entire visible spectrum.

[0190] For example, at least one of the plurality of optical elements 14, preferably all of the optical elements, has at least one optical function that focuses an image in front of the retina.

[0191] In the context of this disclosure, “focusing” should be understood as producing a focused spot with a circular cross-section that can be reduced to a single point in the focal plane.

[0192] Advantageously, this optical function of the optical element reduces retinal distortion in the wearer's eye under peripheral vision, thereby allowing for a slowing of the progression of refractive errors in the eye of the wearer of the lens element.

[0193] According to this disclosure, optical elements can have a specific size. In particular, optical elements can have an external shape that can be inscribed within a circle with a diameter greater than or equal to 0.1 mm and less than or equal to 7.0 mm, preferably greater than or equal to 1.0 mm and less than 3.0 mm, for example less than 2.0 mm.

[0194] Optical components can be positioned on the network.

[0195] The network on which the optical element is located can be a structured network, as shown in WO 2021 / 069443.

[0196] like Figure 2 As shown, the lens element 10 according to this disclosure includes, for example, an object-side surface F1 formed as a convex curved surface facing the object side, and an eye-side surface F2 formed as a concave surface having a curvature different from that of the object-side surface F1.

[0197] At least some, such as all, of the optical elements may be located on the front surface of the lens element.

[0198] At least some, for example all, of the optical elements may be located on the rear surface of the lens element.

[0199] At least some, such as all, of the optical elements may be located between the front and rear surfaces of the lens element. For example, the lens element may include regions with different refractive indices that form the optical elements.

[0200] At least one of the optical elements may have the optical function of focusing an image on a location other than the retina for peripheral vision.

[0201] Preferably, at least 50%, for example at least 80%, for example all optical elements may have the optical function of focusing the image on a location other than the retina for peripheral vision.

[0202] At least for peripheral vision, all optical elements can be configured such that the average focal point of light passing through each optical element is at the same distance from the wearer's retina.

[0203] The optical function, particularly the refractive function, of each optical element can be optimized to provide a focused image at a constant distance from the wearer's retina, especially in peripheral vision. This optimization requires adjusting the refractive function of each optical element based on its position on the lens element.

[0204] Optical elements can be configured such that, at least along one cross section of the lens, the average spherical power of the optical element increases from a point on the cross section toward the periphery of the cross section.

[0205] At least a portion, such as at least 50%, or all of the optical elements, are multifocal microlenses. Advantageously, such multifocal microlenses 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 on a location different from the wearer's retina.

[0206] According to an alternative to this disclosure, at least 50%, for example, all of the optical elements are diffractive microlenses, such as adjacent diffractive microlenses.

[0207] In the context of this disclosure, two optical elements are considered to be adjacent if there exists a path connecting them along which at least one optical power, which differs from the optical power of a prescription based on the wearer, for example, for correcting refractive errors in the wearer's eye, can be measured under standard wearing conditions.

[0208] According to embodiments of this disclosure, at least one, for example all, optical elements have discontinuities, such as discontinuous surfaces (e.g., Fresnel surfaces) and / or discontinuous refractive index distributions.

[0209] Figure 6a An example of the radial profile of a first diffractive lens that can be used in adjacent optical elements of this disclosure.

[0210] Figure 6b An example of the radial profile of a second diffractive lens that can be used in adjacent optical elements of this disclosure.

[0211] A diffractive mini-lens can be a Fresnel mini-lens, whose phase function ψ(r) has a π-phase jump at the nominal wavelength λ0, such as... Figure 7 What we see here. For clarity, these structures can be called "π-Fresnel lenses," unlike single-focus Fresnel lenses where the phase jump is a multiple of 2π. The phase function in Figure 5 The π-Fresnel lens shown primarily diffracts light to two diffraction orders (0th and +1st orders) related to the refractive power P(λ0) = 0 δ and the positive refractive power (e.g., P(λ0) = 3 δ), where λ0 = 550 nm.

[0212] The advantage of this design is that the diffraction grade specifically prescribed for the wearer is not colored, while the diffraction grade used to provide a second optical function to slow the progression of myopia is clearly colored.

[0213] The typical size of the optical element is greater than or equal to 2 mm and less than or equal to 2.5 mm. In fact, the inventors have observed that it is advantageous to keep the size of the optical element smaller than the size of the wearer's pupil.

[0214] For example, the diffraction efficiency of the 0th and +1st orders is about 40% at the nominal wavelength λ0.

[0215] To improve the diffraction order efficiency corresponding to the wearer's prescription, the following can be considered:

[0216] To improve the efficiency of the 0 diffraction order, the value of λ0 can be reduced. Figure 8 a shows the diffraction efficiency at λ0 = 550 nm and Figure 8 b shows the diffraction efficiency at λ0 = 400 nm. It can be noted that in this case, the 0th-order diffraction efficiency is generally high across the entire visible spectrum, while the +1st-order diffraction efficiency is low. In this case, the refractive power of the refractive phase function with a phase jump applied to λ0 = 550 nm should be equal to 1.5. 400 / 550 ≈ 1.1 δ instead of Figure 8 1.5δ in a. This makes it... Figure 7 The ring is widened.

[0217] It can be added or alternatively Figure 7 One of the two configurations shown is set to zero. In this case, the bifocal function is still present due to the remaining Fresnel rings, while the ring set to 0 causes a larger proportion of 0δ diopter.

[0218] Further consideration could be given to using Fresnel structures made of two materials with different refractive indices and different Abbe numbers to obtain... Figure 7 The phase function at λ = λ0 is obtained, and a more uniform efficiency is achieved in the visible spectrum and / or one of the two main diffraction orders is made superior to the other.

[0219] Other combinations with superimposed Fresnel structures could be considered.

[0220] The method disclosed herein is particularly useful for characterizing at least a portion of a lens element comprising a plurality of diffractive microlenses, especially when the plurality of diffractive microlenses are included between the front and rear surfaces of the lens element.

[0221] like Figure 8 The calibration methods shown in this disclosure include at least the following:

[0222] - Two-dimensional representation is obtained in step S1,

[0223] - Step S2 for determining optical power distribution, and

[0224] -Characteristic step S4.

[0225] During step S1, a two-dimensional representation of the local optical power of at least a portion of the lens element is obtained using either a deflection measurement method or a fringe projection profilometry method. The use of a deflection measurement method has been described in detail previously. Those skilled in the art can adapt this description to use the fringe projection profilometry method.

[0226] During step S2, the optical power distribution is determined on at least a portion of a two-dimensional representation of the lens element, the optical power distribution being represented as a histogram or stem-and-leaf plot.

[0227] For example, NIMO TM The device generates a curve showing the pixel count as a function of focal length. Each curve has approximately 2 × 100 values: a focal length vector and a pixel count vector. Averaging can be performed on the different histograms. If this option is selected, it is preferable to interpolate each individual histogram before averaging to ensure a consistent step size across the same common focal length domain.

[0228] like Figure 8 In addition to step S2, which determines the optical power distribution, the method may also include a filtering step S3.

[0229] During filtering step S3, the histogram or stem-and-leaf plot is filtered using a moving filter (e.g., an averaging filter or a low-pass filter).

[0230] In reality, the data obtained from determining the optical power distribution in step S2 may still be noisy. To smooth the results, using a moving average filter may be advantageous. The filtered curve is then used to segment the complete histogram.

[0231] During the characterization step S4, at least a portion of the lens element in the two-dimensional representation of the lens element is characterized by analyzing the data representation, for example by characterizing a histogram or stem-and-leaf plot.

[0232] Characterizing at least a portion of the lens element may include a segmentation step S41. During segmentation step S41, the histogram or stem-and-leaf plot obtained in step S2 is segmented based on the identified inflection points. The core principle is to separate the histogram or stem-and-leaf plot according to the inflection points between the refractive region peak and the optical element peak. To achieve this, the inventors propose using a filter that detects local minima in the smoothed histogram or stem-and-leaf plot.

[0233] like Figure 8 The method shown, according to this disclosure, may further include a fitting step S412 following the segmentation step S41. During the fitting step S412, different portions of the histogram or stem-and-leaf plot are fitted with a Gaussian distribution to determine the skewness and / or kurtosis of the photoluminescence distribution.

[0234] The method disclosed herein may include a processed histogram determination step S414 following the segmentation step S41. During the processed histogram determination step S414, the processed histogram is determined by increasing the bin size of the histogram until the different portions of the histogram are symmetrically distributed and the number of bins in the histogram is greater than or equal to 15 and less than or equal to 36.

[0235] like Figures 11a to 11c As shown, adjusting the bin size and / or number of bins in the histogram helps to characterize a portion of the lens element.

[0236] Figure 10 It is a two-dimensional representation of the local optical power of at least a portion of a lens element. Figure 10 The representation is obtained by using a lens mapper for myopia control lenses and performing detailed lens mapping and analysis using a 40 mm field of view.

[0237] like Figure 10As shown, around most of the optical elements 14 (small lenses in this example), there is a localized negative power region 13, which corresponds to the boundary between the lens element 14 and the refractive region 12.

[0238] The negative optical power value region 13 is due to the curvature change between the optical element 14 and the refractive region 12.

[0239] Figure 11a Is Figure 10 The histogram obtained on the pupil is represented in the figure, where there are 160 bins and the width is 0.1 D.

[0240] like Figure 11a As shown, at this resolution in the histogram representation of local optical power, three optical power peaks appear. The highest peak P1 corresponds to the optical power value of refractive region 12, the second peak P2 corresponds to the optical power of optical element 14, and the third peak P3 corresponds to the optical power of negative optical power value region 13.

[0241] The presence of the third peak, P3, reduces the accuracy of the measurement results and complicates the automation of characterization. Therefore, it is necessary to adjust the two-dimensional representation of local optical power to improve its accuracy and facilitate the automation of lens element characterization.

[0242] Adjusting the bin size and / or number of bins in the histogram allows for the removal of the third peak while maintaining sufficiently high resolution to accurately determine the values ​​of the first peak P1 and the second peak P2.

[0243] Figure 11b Is Figure 10 The histogram obtained on the pupil is shown in the figure, where there are 15 bins and the width is 1.07 D.

[0244] Figure 11c Is Figure 10 The histogram obtained on the pupil is represented in the figure, where there are 36 bins and the width is 0.45D.

[0245] The inventors have observed that having 15 to 36 bins is an optimized range to allow for accurate characterization of the lens elements while removing the presence of the third peak corresponding to the negative power value region 13.

[0246] Even if the lens element does not have a microlens, this optimization of the box number can still be used, because it is worthwhile to provide a method that can characterize a wide variety of lens elements with different types of optical elements.

[0247] Raw data measured by instruments is not always accessible, especially raw data measured with commercially available instruments. Therefore, it is not always easy to recalculate the bins used for histograms. The inventors propose overcoming this limitation by taking local averages of these values. The curves can be re-expressed according to different fixed averaging step sizes, thus recreating processed histograms that describe pixel count variations with focal length. By doing so, instead of precise pixel summation, an average number of pixels is calculated. This bin reduction effectively reduces the focal length resolution of the initial histogram. Figure 9 This demonstrates the reduction.

[0248] In addition to the processed histogram determination step S414, the method according to this disclosure may also include a second fitting step S416.

[0249] During the second fitting step S416, the portion of the histogram corresponding to the first optical function is fitted using a first Gaussian distribution, and the portion of the histogram corresponding to the optical element is fitted using a second Gaussian distribution.

[0250] To fit the combined peak at the refractive region and the junction, the inventors proposed using a least-squares fitting adjustment, for example in Matlab, to fit a Gaussian curve to the combined peak. This yields the amplitude, central focal length, and standard deviation. Alternatively, the data can be fitted using two Gaussian distributions instead of one, obtaining the central value of each peak. However, the difference in means can be quite small (below 0.06 D), and given the number of available points, using a single Gaussian fit is statistically more robust.

[0251] For optical element peaks, a simple fit can be derived from the optical element peaks to produce the same three parameters as described previously: mean, amplitude, and standard deviation.

[0252] Characterizing at least a portion of the lens element may include determining the amplitude ratio at the center power value of both the first Gaussian distribution and the second Gaussian distribution and / or the full width at half maximum (FWHM) ratio of both the first Gaussian distribution and the second Gaussian distribution.

[0253] Such parameters are good indicators for the design of lens elements and allow for easy comparison between lens elements.

[0254] The methods disclosed herein are of particular interest for rapidly evaluating overall design aspects and for quickly comparing different batches of lens components (e.g., optical lenses).

[0255] The method disclosed herein can be implemented to characterize lens elements including adjacent aspherical microlenses.

[0256] The optical power distribution of at least a portion of the lens elements, including adjacent aspherical microlenses, comprises only a single peak around the global power of the microlenses, and thus depends on the curvature of these aspherical microlenses. This peak is far less "symmetrical" than the peak of the optical power distribution obtained with adjacent spherical microlenses, but rather diffuses more to the left of the peak, due to the aspherical profile causing the power to decrease with the eccentricity of the microlenses.

[0257] Therefore, the location, shape, and width of the peak are good indicators for small lens design.

[0258] The method disclosed herein provides a way to easily distinguish between spherical and aspherical microlens designs: spherical lenses have symmetrical peaks, while aspherical lenses have asymmetrical peaks.

[0259] The method disclosed herein can be used to characterize lens elements having aspherical microlenses positioned on concentric circles, such as Figure 1 As shown and disclosed in more detail in WO 2019 / 166659.

[0260] More generally, the location, shape, and width of different peaks are good indicators for the design of microlenses and Rx regions. The method disclosed herein is also a good solution for easily comparing a batch of different lens elements in production, allowing for a limitation on the number of lens elements to be measured in very detail.

[0261] The method disclosed herein can be used to check the conformity of manufactured lens elements. In fact, the conformity of manufactured lens elements can be easily checked by comparing the characteristics of the optical elements of the manufactured lens element with the characterization data of a reference optical lens.

[0262] The methods disclosed herein can also be used to control lens manufacturing processes, particularly by examining the evolution of certain features identified on manufactured lenses using the methods disclosed herein over time.

[0263] The evolution of certain identified characteristics over time can be correlated with at least one parameter of the manufacturing process. Advantageously, this method is simple, inexpensive, and non-destructive, allowing for easy implementation of process control.

[0264] The present disclosure has been described above with the aid of embodiments, but is not intended to limit the general inventive concept. Many further modifications and variations will be apparent to those skilled in the art upon reference to the foregoing illustrative embodiments. These embodiments are given by way of example only and are not intended to limit the scope of the disclosure, which is defined solely by the appended claims.

[0265] In the claims, the word "comprising" does not exclude other elements or steps, and the indefinite articles "a" or "an" ("a" or "an") do not exclude a plural. The mere fact that different features are described in mutually different dependent claims does not imply that combinations of these features cannot be used advantageously. Any reference numerals in the claims should not be construed as limiting the scope of this disclosure.

Claims

1. A method for characterizing at least a portion of a lens element suitable for a wearer, such as a myopia control lens element, the lens element providing a first optical function having a refractive power based on the wearer's prescription and comprising a plurality of optical elements, each of the plurality of optical elements providing one or more optical functions, at least one of the one or more optical functions being different from the first optical function; in, The method includes: - A two-dimensional representation of the local optical power of at least a portion of the lens element is obtained using a deflection measurement method or a fringe projection profilometry method. - Determine the power distribution over at least a portion of the two-dimensional representation of the lens element, the power distribution being represented as a histogram or stem-and-leaf plot; and - The lens element is characterized by analyzing the data representation, for example by characterizing the histogram or stem-and-leaf plot, to represent at least a portion of the at least portion of the two-dimensional representation of the lens element.

2. The method according to claim 1, wherein, The two-dimensional representation of the local optical power corresponds to at least 25% of the surface of the lens element.

3. The method according to any one of the preceding claims, wherein, The two-dimensional representation of the local optical power corresponds to at least a portion of the lens element, the portion comprising at least 10% of the optical element.

4. The method according to any one of the preceding claims, wherein, Images used for deflection measurement methods consist of pixels less than or equal to 0.05 mm × 0.05 mm.

5. The method according to any one of the preceding claims, wherein, Characterizing at least a portion of the lens element includes segmenting the histogram based on identified inflection points.

6. The method as described in the preceding claim, wherein, The method further includes, after segmenting the histogram, fitting different portions of the histogram with a Gaussian distribution and determining the skewness and / or kurtosis of the optical power distribution.

7. The method according to claim 5, wherein, The method further includes determining the processed histogram by increasing the bin size of the histogram until different portions of the histogram are symmetrically distributed and the number of bins in the histogram is greater than or equal to 15 and less than or equal to 36.

8. The method according to claim 7, wherein, The method further includes fitting the portion of the histogram corresponding to the first optical function with a first Gaussian distribution, and fitting the portion of the histogram corresponding to the optical element with a second Gaussian distribution, and characterizing at least a portion of the lens element includes determining the amplitude ratio at the central focal power value of both the first Gaussian distribution and the second Gaussian distribution and / or the full width at half maximum (FWHM) ratio of both the first Gaussian distribution and the second Gaussian distribution.

9. The method according to any one of the preceding claims, wherein, The method further includes filtering the histogram using a moving filter.

10. The method according to any one of the preceding claims, wherein, At least 50% of the optical elements are refractive microlenses.

11. The method according to any one of the preceding claims, wherein, At least 50% of the optical elements are diffuse microlenses or diffractive microlenses.

12. The method according to any one of the preceding claims, wherein, A two-dimensional representation of the local optical power of at least a portion of the lens element is obtained on a pupil with a diameter greater than or equal to 3 mm and less than or equal to 9 mm.

13. The method according to the preceding claim, wherein, The lens element has a central region without optical elements, and a two-dimensional representation of the local optical power of at least a portion of the lens element is obtained on the pupil, wherein the distance from the center of the pupil to the optical center of the lens element is greater than or equal to the sum of half the diameter of the central region of the lens element without optical elements and half the diameter of the pupil.

14. A method for inspecting the conformity of a manufactured lens element, the manufactured lens element being suitable for a wearer and comprising a plurality of optical elements, each of the plurality of optical elements providing at least one optical power to mitigate, delay, or prevent at least one of the following: the progression of refractive error in the wearer's eye. in, The method includes: - Obtain characterization data relating to at least one optical characteristic of the optical element of the lens element to be manufactured. - An optical element characterized by the method described in any one of claims 1 to 13, - The characteristics of the optical elements of the manufactured lens element are compared with the characterization data in order to check the conformity of the manufactured lens element.

15. A method for controlling a lens element manufacturing process, each lens element being suitable for a wearer and comprising a plurality of optical elements, each of the plurality of optical elements providing at least one optical power to mitigate, delay, or prevent at least one of the progression of refractive errors in the wearer's eye, wherein... The method includes the following steps: a) Manufacturing lens components according to manufacturing processes. b) Determine at least one feature of the lens element manufactured in step a) by the method of any one of claims 1 to 13. c) Record the difference between at least one identified feature and a reference value. d) Repeat steps a) through c) periodically and examine how the differences evolve over time. Specifically, the evolution of at least one parameter of the manufacturing process used to manufacture the lens element is examined over time, and the evolution of the difference over time is related to the evolution of at least one parameter of the manufacturing process over time.

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