Method for determining local spatial contrast of an optical lens

Abstract

Method, for example implemented by computer means, for determining a local spatial contrast obtained with an optical lens to be placed in front of at least a portion of an eye, wherein the method comprises: - obtaining an eye model representative of the eye, - obtaining an optical lens model representative of the optical lens to be placed in front of at least a portion of the eye, - determining a point spread function based on the system of the eye model associated with the optical lens model, - convolving a plurality of images with the determined point spread functions so as to obtain a blurred version of the image, - determining the local spatial contrast in the blurred version of the image.

Description

[0001] Method for determining local spatial contrast of an optical lens

[0002] TECHNICAL FIELD

[0003] The disclosure relates to a method, for example implemented by computer means, for determining a local spatial contrast obtained with an optical lens to be placed before at least a portion of an eye. The disclosure also relates to a method for comparing the efficiency of at least two optical lenses as myopia control solutions and a method for optimizing a myopia control optical lens.

[0004] The disclosure further relates to a myopia control optical lens providing a refractive power based on a prescription of the eye of the wearer for correcting an abnormal refraction of the eye of the wearer.

[0005] BACKGROUND OF THE DISCLOSURE

[0006] Myopia of an eye is characterized by the fact that the eye focuses distant objects in front of its retina. Myopia is usually compensated using a concave lens.

[0007] Myopia, also referred as to short-sightedness, has become a major public health problem worldwide. Accordingly, a large effort has been made to develop solutions aiming to slow down myopia progression. The efficacy of these myopia control solutions is usually derived from the comparison of the average myopia progression between a reference group and a control group. Although this is informative at the population level, such type of large-scale trials requires fully developing a myopia control solution and testing it over a long period of time, for example at least 6 months or a year.

[0008] Such type of testing of the efficiency of myopia control solution is very expensive, time consuming and not very compatible with optimizing a myopia control solution. Furthermore, such type of testing does not provide an efficient method for predicting the efficacy of a myopia control solutions.

[0009] Therefore, there is a clear need to have a method that would allow estimating and / or predicting the efficiency of a myopia control solution without the drawbacks of the current trials. SUMMARY OF THE DISCLOSURE

[0010] To this end, the disclosure proposes a method, for example implemented by computer means, for determining a local spatial contrast obtained with an optical lens to be placed before at least a portion of an eye, wherein the method comprises:

[0011] - obtaining an eye model representative of the eye,

[0012] - obtaining an optical lens model representative of the optical lens to be placed before at least a portion of the eye,

[0013] - determining a point spread function based on the system of the eye model associated with the optical lens model,

[0014] - convolving a plurality of images with the determined point spread functions so as to obtain a blurred version of the image,

[0015] - determining the local spatial contrast in the blurred version of the image.

[0016] It has been observed and confirmed that such local spatial contrast obtained with an optical lens provides a good indication of the efficiency of a myopia control solution of such optical lens.

[0017] Advantageously, the method of the disclosure allows to easily determine the local spatial contrast and therefore, obtain easily and quickly a good efficiency indicator of a myopia control solution.

[0018] Determining the local spatial contrast can be done with simulations and does not require producing a large number of the myopia solutions and having a great number of people wear such myopia control solution to be compared with a reference group.

[0019] According to further embodiments which can be considered alone or in combination:

[0020] - the eye model is a standard eye model; and / or

[0021] - the eye model is a -4 diopter myopia eye model based on the Atchison eye model ; and / or

[0022] - the optical lens is placed in front of the eye model in standard wearing conditions; and / or

[0023] - the eye model is customized based on characteristics of the eye; and / or - -

[0024] - the optical lens is a myopia control optical lens configured so as to at least one of slow down, retard or prevent a progress of the myopia of the eye; and / or

[0025] - the local spatial contrast is defined at the scale of a receptive field of a retinal ganglion cell’s of the eye model; and / or

[0026] - the local spatial contrast is defined at the scale of the receptive field of a cell having a characteristic dimension greater than or equal to 30 pm, for example greater than or equal to 50 pm and smaller than or equal to 3500 pm, for example smaller than or equal to 1000 pm, for example smaller than or equal to 750 pm, for example smaller than or equal to 200 pm; and / or

[0027] - the plurality of images comprises at least 10, for example at least 50, for example at least 100, for example at least 500 different images; and / or each image of the plurality of images correspond to natural scenes, for example indoor scenes and / or outdoor scenes; and / or each image of the plurality of images are grayscale images, for example comprising at least 16 different shades of gray, for example comprising at least 256 shades of gray; and / or

[0028] - the method further comprises prior to determining the local spatial contrast, realigning the blurred version of the image on the original image.

[0029] The disclosure further relates a method for comparing the efficiency of at least two optical lenses as myopia control solutions, wherein the method comprises:

[0030] - determining the local spatial contrast of each optical lens using a method according to the disclosure with the same eye model and image for each optical lens, and

[0031] - comparing the determined local spatial contrasts of each optical lenses.

[0032] According to an embodiment of the disclosure one of the myopia control solutions is a reference myopia control solution.

[0033] The disclosure also relates to a method for optimizing a myopia control optical lens, wherein the method comprises: a) obtaining an initial version of the myopia control optical lens, b) determining the local spatial contrast of the optical lens according to the initial version of the myopia control optical lens using a method according to the disclosure, c) changing the value of at least one parameter of the initial version of the myopia control optical lens, d) determining the local spatial contrast of the modified optical lens according to the modified version of the myopia control optical lens using a method according to the disclosure with the same eye model and image as for the initial version of the myopia control optical lens,

[0034] - repeating steps c) and d)

[0035] - selecting the version of the myopia control optical lens having the smallest local spatial contrast.

[0036] The disclosure also relates to a myopia control optical lens providing a refractive power based on a prescription of the eye of the wearer for correcting an abnormal refraction of the eye of the wearer; wherein

[0037] - the myopia control optical lens comprises at least one optical element having 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 myopia of the eye of the wearer;

[0038] - having a local spatial contrast smaller than or equal to 0.117, for example smaller than or equal to 0.091, for example smaller than or equal to 0.065 at 0 defocus and 0° (central retina), and

[0039] - the modulation transfer function of the myopia control optical lens is greater or equal to 0.07, preferably greater or equal to 0.10, over the range of spatial frequencies comprised from 10 to 25 cycles per degree when measured over a pupil aperture of 5 mm diameter.

[0040] According to an embodiment of the disclosure, the local spatial contrast is determined with a -4 diopter myopia eye model based on the Atchison eye model and adapted to standard wearing conditions relative to the myopia control optical lens, the wearer being a children.

[0041] According to an embodiment of the disclosure, the local spatial contrast is determined as the average value over at least 10 images, for example at least 50 images, for example at least 100 images, for example at least 500 images. According to an embodiment of the disclosure, the local spatial contrast is determined for a downward gaze direction of 20° and a nasal eccentricity of 20° on the retina from the fovea with a defocus of 0D when an image is focused on the retina.

[0042] The optical lens may be a contact lens or a spectacle lens.

[0043] According to a further aspect, the disclosure 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, cause the processor to carry out the steps of any of the methods according to the disclosure.

[0044] The disclosure further relates to a computer readable medium carrying one or more sequences of instructions of the computer program product according to the disclosure.

[0045] Furthermore, the disclosure relates to a program which makes a computer execute the steps of any of the methods of the disclosure.

[0046] The disclosure also relates to a computer-readable storage medium having a program recorded thereon; where the program makes the computer execute the steps of any of the methods of the disclosure.

[0047] The disclosure further relates to a device comprising a processor adapted to store one or more sequences of instructions and to carry out the steps of any of the methods according to the disclosure.

[0048] BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Non-limiting embodiments of the disclosure will now be described with reference to the accompanying drawing wherein: o Figure l is a flowchart of different steps of a method according to the disclosure; o Figure 2 shows local spatial contrast for four images, on the central and peripheral retina as a function of defocus for different values pixel size for an emmetropic eye; o Figure 3 shows local spatial contrast for four images, on the central and peripheral retina as a function of defocus for different values pixel size for a myopic eye; o Figure 4 is a flowchart of different steps of a method according to the disclosure; o Figure 5 illustrates a plan view of a myopia control optical lens according to a first embodiment of the disclosure; and o Figure 6 illustrates a plan view of a myopia control optical lens according to a second embodiment of the disclosure.

[0050] 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.

[0051] DETAILED DESCRIPTION OF EMBODIMENTS OF THE DISCLOSURE

[0052] The disclosure relates to a method, for example implemented by computer means, for determining a local spatial contrast obtained with an optical lens to be placed in front of at least a portion of an eye, for example in front of an eye.

[0053] The inventors have determined a strong correlation between the value of the local spatial contrast in images arriving on the retina of the eye and the efficiency of myopia control solution, for example myopia control lenses.

[0054] Therefore, the method of the disclosure may be used to evaluate or even predict the efficiency of a myopia control solution.

[0055] The myopia control solution that may be evaluated by the method of the disclosure may be any kind of solution or combination of solutions that is to slow down progression of myopia, in particular for young kids.

[0056] For example, the myopia control solution or its combination is selected among a list consisting of: myopia control ophthalmic lenses, myopia control contact lenses, myopia control optical lenses and optical system having optical transformation.

[0057] The myopia control solution may be myopia control optical lenses comprising, in addition to a refractive zone, optical elements configured not to focus light on the retina of the wearer. The method of the disclosure is not limited to any specific myopia control solution and may be used to evaluate the efficiency of any myopia control solution for a person.

[0058] As illustrated on figure 1, a method according to the disclosure comprises at least:

[0059] - obtaining an eye model representative of the eye SI,

[0060] - obtaining an optical lens model representative of the optical lens to be placed in front of at least a portion of the eye S2,

[0061] - determining a point spread function based on the system of the eye model associated with the optical lens model S3,

[0062] - convolving a plurality of images with the determined point spread functions so as to obtain a blurred version of the image S4, and

[0063] - determining the local spatial contrast in the blurred version of the image S6.

[0064] The method of the disclosure is particularly adapted to determining local spatial contrast for a contact lens or an optical lens intended to be a spectacle lens.

[0065] Preferably, the optical lens is myopia control optical lens configured so as to at least one of slow down, retard or prevent a progress of the myopia of the eye.

[0066] During step SI, an eye model representative of an eye is provided, for example is provided or download from a data base.

[0067] The eye model obtained during step SI, may be a standard eye model.

[0068] Numerous schematic eye models exist in the literature, for example the Atchison model detailed in David A. Atchison “Optical models for human myopic eyes” Vision Research, Volume 46, Issue 14, July 2006, Pages 2236-2250. This parametric eye model adapts to myopic spherical prescriptions and is based on population averages of eye data measurements (e.g., wavefront aberrations, axial lengths, MRI scans of the retina).

[0069] For lens assessment and optimization purposes, one should try to use an eye model that is as close to the target population or subject as possible. Therefore, it may be advantageous to adapt a base model to population or user data. In other words, the eye model is customized based on characteristics of the eye.

[0070] The base eye model could be either from the literature as mentioned above, or a best guess that is specific to the population or user.

[0071] The parameter specific to a population or user data could be for instance: wavefront aberrations, central and / or peripheral refraction, keratometry, axial lengths, retinal shape measurement.

[0072] In some examples, the inventors have used an Atchison model and have customized the retina shape in order to fit peripheral defocus values of myopic Asian children, which were aggregated from the following articles:

[0073] - X. Chen, "Characteristics of peripheral refractive errors of myopic and non- myopic Chinese eyes," Vision Research, 2010,

[0074] - P. Kang, "Peripheral Refraction in Different Ethnicities," Investigative Opthalmology & Visual Science, 2010, and

[0075] - C. Sng, "Peripheral Refraction and Refractive Error in Singapore Chinese Children," Investigative Ophthalmology & Visual Science, 2011.

[0076] Moreover, the cornea shape was also changed to fit the average spherical aberration in average children, data from Relationship between higher-order wavefront aberrations and natural progression of myopia in school children (Hiraoka, 2017).

[0077] During step S2, an optical lens model representative of the optical lens to be placed in front of at least a portion of the eye is obtain, for example is provided or download from a data base.

[0078] Myopia control lenses can be modelled or measured, for example using measuring devices provided by Zygo™. In addition to the lens, the following parameters related to the eye model and its associated object environment can be varied:: wearer pupil diameter, defocus, light source eccentricity, focus proximity and gaze lowering.

[0079] During step S3, a point spread function is determined, for example calculated, based on the system of the eye model associated with the optical lens model. The point spread function is preferably determined, for example calculated, on the retina of the eye model.

[0080] According to an embodiment of the disclosure, polychromatic point spread functions can be determined by summing monochromatic point spread function determined at different wavelengths, for example following the spectral sensitivity of human photoreceptors (for the S, M and the L cones). Preferably, the point spread functions comprise pixels being approximately rectangular, for example square. Preferably, all the pixels of the point spread functions have the same shape and dimensions. The dimension of the pixels of the point spread function may be greater than or equal to 0.5 pm and greater than or equal to 2 pm, for example the pixels of the point spread functions are square and have a dimension of 1 pm.

[0081] During step D4, a plurality of images is convolved with the determined point spread functions so as to obtain a blurred version of the different images.

[0082] According to the disclosure, the plurality of images comprises at least 10, for example at least 50, for example at least 100, for example at least 500 images. The images correspond to natural scenes for example indoor scenes and / or outdoor scenes.

[0083] Geisler, W. S. (2008). Visual perception and the statistical properties of natural scenes. Annu. Rev. Psychol., 59, 167-192, provides a very large overview of the statistics of natural scenes.

[0084] Images of natural scenes are very different from visual acuity charts. In particular natural scenes have spectrum which follows a power law in l / f“; for example a = 1. The exponent varies depending on the content of the natural scenes, depending on the amount of man-made elements in the scene.

[0085] Images of the natural world have been found to display a remarkably consistent spatial frequency spectrum, such that the spectral amplitude (amount of contrast at a given spatial frequency) decreases with increasing spatial frequency (f), following a relationship where amplitude is proportional l / f“.

[0086] As indicated in J. Jason Me Anany, Kenneth R. Alexander (2008). Spatial frequencies used in Landolt C orientation judgments: Relation to inferred magnocellular and parvocellular pathways. Vision Research 48 (2008) 2615-2624, the function relating center object frequency to Landolt C angular subtense is nonlinear on log-log coordinates whereas natural scene image have a substantially linear function on log-log coordinates.

[0087] The images are selected to provide a greater number of spatial frequencies. The images may be black and white images for simplicity.

[0088] Typically, the images are selected from an images data base such as the Van Hateren image set referred to in Van Hateren, J. H., & van der Schaaf, A. (1998). Independent component filters of natural images compared with simple cells in primary visual cortex. Proceedings of the Royal Society of London. Series B: Biological Sciences, 265(1394), 359-366.

[0089] To obtain the image as projected on the retina, the images are convolved with the determined point spread functions corresponding to the different optical parameters.

[0090] Alternatively, a database of hyperspectral images may be used for the LSC calculation. In this case, the image at each wavelength within the hyperspectral image would be convolved with the corresponding monochromatic PSF. The final image would be the weighted sum of each convolved monochromatic image, The weights would account for both the wavelength intensity embedded within the hyperspectral image and the spectral sensitivity of the human photoreceptors. An example of relevant database is for instance http: / / vision.seas.harvard.edu / hyperspec / (Chakrabarty & Zickler, 2011).

[0091] The images may be re-scaled in order for the image pixels to have the same size as the determined point spread functions pixel size, for example square pixel of 1 pm side. For the convolution of each image with the determined point spread function, one may use the fftconvolve function from the Scipy package (Python), using the “same” mode that conserves the size of the original image.

[0092] The method according to the disclosure may further comprise prior to determining the local spatial contrast, a re-aligning step S5 during which the blurred version of the image on the original image.

[0093] The convolution of an image with a determined point spread function has the effect of slightly shifting images relative to the original ones. As it is best to have the same patch of image to be within the cell’s receptive field, the method may further comprise a step of re-aligning the convolved images on the original one. For that the inventors have developed a custom method based on maximum correlation between the original and the convolved image. The method is wrapped up in a Python function (CalcXYshift).

[0094] During step S6, the local spatial contrast in the blurred version of the image is determined, for example calculated.

[0095] The local spatial contrast is defined at the scale of a retinal ganglion cell’s receptive field, and may be calculated as follows. The inventors have used the blurred images and defined a generic receptive field as a circular 2D gaussian. One may then define the receptive field diameter as twice the standard deviation parameter c of the 2D gaussian. The diameter of the receptive fields was chosen based on measurements in human retina. The receptive field of human parasol cells ranges roughly from 100 to 200 pm, with a median at 144 pm for ON cells and 123 pm for OFF cells. Human midget cells have a receptive field diameter ranging from roughly 30 to 100 pm, and the median for ON cells is 64 pm and 46 pm for OFF cells. The inventors have used 120 pm as standard diameter for the generic receptive field. A weight w_i corresponding to the value of the 2D gaussian is attributed to each pixel within the receptive field.

[0096] Each pixel has an intensity I_i and l image is the mean intensity over the entire image. The pixel’s intensity is then converted into a Weber contrast, defined as:

[0097] „ > h limage

[0098] 1~ T1image

[0099] The mean intensity in the receptive field may then defined as: and the local spatial contrast as:

[0100] One may then get the pixels comprised within that contour as a Numpy array of coordinates and compute the local spatial contrast with the above formula, for each image in the plurality of blurred images. For most images, the method is robust to a variation of the size of the receptive field, within the range of the measured diameters.

[0101] The measure of the local spatial contrast is also robust to a change of the ratio between the pixel size of the determined point spread function and the pixel size of the image. The pixel size of the determined point spread function may be fixed at 1 pm, but the pixel size of the images is more difficult to control and know precisely. The pixel size may be fixed in the eye model.

[0102] The size of human’s photoreceptors is known. The inventors have therefore varied the size of the pixels in the image, i.e. the relative size of the image compared to the determined point spread function, to assess its effect on the variation of local spatial contrast with defocus.

[0103] If the pixel size is smaller, the image has a size which is closer to the one of the determined point spread function, and one may expect the image to be much more blurred after the convolution.

[0104] On the contrary, if the pixel size is large, the image has a size which is much larger than the determined point spread function and the spatial details will remain resolved.

[0105] The inventors have explored pixel sizes that are close to the diameter of human photoreceptors. In the periphery of the retina, the rods are 2pm in diameter and the cones 6pm. In the fovea, the cones are 1.5pm in diameter.

[0106] Figure 2 represents local spatial contrast for an emmetropic human with pupil diameter 5mm and focus proximity 0D (far vision), for different sizes of the images pixels. It is equivalent to changing the ratio between the size of the point spread function and the size of the image.

[0107] First, one may observe that, in an emmetropic eye, local spatial contrast is indeed smaller when the pixel size is smaller, which means when the image size is closer to that of the determined point spread function.

[0108] Second, one may observe that with smaller pixel size (i.e. smaller image compared to the determined point spread function), the position of the maximum gets closer to 0 pm in some but not all images.

[0109] Figure 3 represents local spatial contrast for a myopic human with pupil diameter 5mm and focus proximity 0D (far vision), for different sizes of the images pixels. In a myopic eye with single vision lenses, the inventors have obtained similar results as in the emmetropic eye, as illustrated on figure 3. Similar variations of local spatial contrast are observed with different pixel sizes.

[0110] The change of local spatial contrast with defocus is robust against a change in the relative size of the image, in a physiological range. In general, the inventors have determined that at the scale of the photoreceptors in the peripheral retina, the observed effect is robust.

[0111] The method of the disclosure is particularly advantageous as it allows determining the local spatial contrast at a local scale, namely the scale of the retinal ganglion cell’s receptive fields.

[0112] In a non-limitive manner, the local spatial contrast might also be obtained by different methods. For example, by fitting a contrast model (defined by the above equation with l image as a free parameter) on experimental data. This additional method is detailed in Goldin, M.A., Lefebvre, B., Virgili, S. et al. Context-dependent selectivity to natural images in the retina. Nat Commun 13, 5556 (2022). https: / / doi.org / 10.1038 / s41467-022-33242-8 (https: / / doi.org / 10.1038 / s41467-022-

[0113] 33242-8)

[0114] The method according to the disclosure is based on experimental results on mice. The inventors have recorded the retinal ganglion cell’s response to the change in local spatial contrast associated with different optical conditions. It therefore includes retinal physiology.

[0115] A second advantage is that considering retinal specificities (the receptive fields) allows to aim for contrast reduction in only the spatial frequency domains that trigger the largest response, in both values and directions. This would yield a myopia control effect while preserving good contrast transfer in the rest of the frequency spectrum, thus leading to better visual acuity compared to lenses which lower contrast indiscriminately across object frequencies.

[0116] The inventors have determined that the lower the local spatial contrast the more efficient an optical lens is at slowing down myopia progression.

[0117] Therefore, the method of the disclosure can be used to evaluate, for example predict, the myopia control efficacy of lenses using the local spatial contrast in images arriving on the retina. This prediction can be then used to optimize and personalize myopia control lenses.

[0118] The disclosure further relates to a method for comparing the efficiency of at least two optical lenses as myopia control solutions.

[0119] As illustrated on figure 4, the method may comprise: - determining the local spatial contrast of each optical lens S10, using a method according to the disclosure with the same eye model and image for each optical lens, and

[0120] - comparing the determined local spatial contrasts of each optical lenses S20.

[0121] The method of the disclosure is particularly efficient to compare optical lenses configured to slow down myopia progression.

[0122] The method of the disclosure may be used to estimate the efficiency of a given myopia control solution, for example of an optical lens configure to slow down myopia progression. For example, the method of the disclosure may be implemented with one of the myopia control solutions being a reference myopia control solution.

[0123] The efficiency of the reference myopia control solution may have been determined using clinical trials. The reference myopia control solution may be a single vision lens.

[0124] Advantageous, the method of the disclosure allows a quiet and efficient comparison of myopia control solutions.

[0125] The method of the disclosure may also be used to optimize or customize a myopia control solution.

[0126] For example, the disclosure may relate to a method for optimizing a myopia control optical lens, for example a contact lens or an optical lens intended to be a spectacle lens configured to slow down myopia progression.

[0127] The method may comprise: a) obtaining an initial version of the myopia control optical lens, b) determining the local spatial contrast of the optical lens according to the initial version of the myopia control optical lens using a method according to the disclosure, c) changing the value of at least one parameter of the initial version of the myopia control optical lens, d) determining the local spatial contrast of the modified optical lens according to the modified version of the myopia control optical lens using a method according to the disclosure with the same eye model and image as for the initial version of the myopia control optical lens,

[0128] - repeating steps c) and d) - selecting the version of the myopia control optical lens having the smallest local spatial contrast.

[0129] The eye model may be customized for a group of wearers, for example Asian children or European children or even customized for a given wearer, for example based on measurements done on the eye of the wearer. Therefore, the myopia control optical lens can be customized or optimized specifically for a group of wearers or for a given wearer.

[0130] The disclosure also relates to a myopia control optical lens providing a refractive power based on a prescription of the eye of the wearer for correcting an abnormal refraction of the eye of the wearer.

[0131] - the myopia control optical lens comprises at least one optical element having an optical function, for example a transparent 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 myopia of the eye of the wearer;

[0132] - having a local spatial contrast smaller than or equal to 0.117, for example smaller than or equal to 0.091, for example smaller than or equal to 0.065 at 0 defocus and 0° (central retina), and

[0133] - the modulation transfer function of the myopia control optical lens is greater or equal to 0.07, preferably greater or equal to 0.10, over the range of spatial frequencies comprised from 10 to 25 cycles per degree when measured over a pupil aperture of 5 mm diameter.

[0134] According to the disclosure, a transparent optical function is to be understood as having no effect on the spectral components of light.

[0135] The disclosure relates to a myopia control optical lens intended to be worn by a wearer and to provide a refractive power based on a prescription of the wearer for correcting an abnormal refraction of the eye of the wearer.

[0136] According to some embodiments, the myopia control optical lens is a spectacle lens element intended to be worn in front of an eye of a wearer. In the sense of the disclosure, a spectacle lens may be an uncut (not edged) spectacle lens or a spectacle lens edged to fit in a spectacle frame. According to some embodiments, the myopia control optical lens is a contact lens element intended to be worn on an eye of a wearer.

[0137] The myopia control optical lens comprises at least one optical element, for example a plurality of optical element, for example at least 3 optical elements, for example at least 50 optical elements, each having an optical function of not focusing an image on the retina of the eye of the wearer so as to slow down progression of myopia of the eye of the wearer.

[0138] In the sense of the disclosure "focusing" is to be understood based on geometrical optics as producing a focusing beam that can be reduced to a minimum spot in the focal plane, for example in standard wearing conditions with no accommodation of the eye of the wearer and for an object point at a distance greater than or equal to 1.5 m for example greater than or equal to 4 m.

[0139] Advantageously, such optical functions of the optical elements reduce the elongation of the eye of the wearer in peripheral vision, allowing to slow down the progression of the myopia of the eye of the person wearing the myopia control optical lens.

[0140] According to some embodiments, the lens elements comprise optical elements, such as lenslets, having an optical function of focusing an image other than (rather than) on the retina of the eye of the wearer, for example in standard wearing conditions with no accommodation of the eye of the wearer and for an object point located at a distance of the eye greater than or equal to 1.5 m for example greater than or equal to 4 m, so as to slow down progression of the abnormal refraction, for example myopia, of the eye of the wearer.

[0141] A first myopia control optical lens (referred to as LI) is depicted in figure 5. LI comprises optical elements 1 having a concentric ring configuration with lenslets having a non-spherical optical function, i.e. a transparent optic al function not having a single focus point, for example having an aspherical surface. The geometry of the aspheric lenslets, for example having a 1.12 mm diameter, has been calculated so as to generate a volume of non-focus light, also referred to as depth of focus, ranging from 1.1 to 1.9 mm in front of the retina at any eccentricity, serving as myopia control. LI further comprises a refraction area comprising a clear central area 2 and a peripheral area 3.

[0142] A second the myopia control optical lens (referred to as L2) is depicted in figure 6. L2 comprises optical elements 1 having a honeycomb configuration of spherical lenslets having a spherical optical function, i.e. each providing a single focus point of an far distance point. The lenslets, for example having a 1.03 mm in diameter, introduce myopic defocus at a plane in front of the retina by a relative positive power (+3.50 D).

[0143] For both LI and L2, the surface without lenslets provides distance correction and the two configurations of lenslets provided a similar density of lenslets that is about 40% of the total surface area of the lens element.

[0144] The myopia control optical lens according to the disclosure has a local spatial contrast smaller than or equal to 0.117, for example smaller than or equal to 0.091, for example smaller than or equal to 0.065 at 0 defocus and 0° (central retina).

[0145] In the sense of the disclosure, the local spatial contrast of the myopia control optical lens is to be understood with a -4 diopters myopia eye model based on the Atchison eye model. The myopia control optical lens is placed in standard wearer conditions relative to the eye model.

[0146] The local spatial contrast is determined for a lowering gaze direction of 20° and an eccentricity corresponding to peripheral vision / retina, for example of 20° with a defocus of 0D at the level of the retina.

[0147] More generally, the lowering gaze direction is linked with a signal obtained when the light passes through the lenslets, a lowering gaze direction of 20° is to be understood as an example.

[0148] The local spatial contrast corresponds to the average value of the local spatial contrast determined for at least 10 different images, for example at least 50 different images, for example at least 100 different images, for example at least 500 different images.

[0149] The images may be selected from the Van Hateren image set.

[0150] The standard 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, an eye rotation center (ERC) to pupil distance, an ERC to lens distance and a wrap angle.

[0151] The Cornea to lens distance, also referred to a vertex 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. The Pupil-cornea distance, also referred to as the anterior chamber depth, is the distance along the visual axis of the eye between its pupil and cornea; usually equal to 2mm.

[0152] The ERC to pupil distance is the distance along the visual axis of the eye between its center of rotation (ERC) and pupil; for example equal to 11.5mm.

[0153] The ERC 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 ECR of the eye and the back surface of the lens, for example equal to 25.5mm.

[0154] 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°.

[0155] 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°.

[0156] An example of standard wearer conditions may be defined by Cornea to lens distance of 12mm, a Pupil to cornea distance of 2mm, an ERC to pupil distance of 11.5mm, an ERC to lens distance of 25.5mm, a pantoscopic angle of 8°, a and a wrap angle of 0°.

[0157] The myopia control optical lens according to the disclosure has a modulation transfer function of the myopia control optical lens is greater or equal to 0.07, preferably greater or equal to 0.10, over the range of spatial frequencies comprised from 10 to 25 cycles per degree when measured over a pupil aperture of 5 mm diameter.

[0158] Advantageously, the range of values of the modulation transfer function, for example for foveal vision, ensures that the visual performance of the myopia control optical lens are preserved, in particular during reading activities.

[0159] The modulation transfer function, for example for foveal vision, is greater or equal to 0.15, preferably greater or equal to 0.25 over the range of spatial frequencies comprised from 10 to 15 cycles per degree, when measured through the optical elements for a pupil aperture of 4mm centered at 6.6 mm from the optical center of the myopia control optical lens. The modulation transfer function, for example for foveal vision, is greater or equal to 0.07, preferably greater or equal to 0.10, over the range of spatial frequencies comprised from 20 to 25 cycles per degree, when measured through the optical elements for a pupil aperture of 4mm centered at 6.6 mm from the optical center of the myopia control optical lens.

[0160] The modulation transfer function, for example for foveal vision, is greater or equal to 0.70, preferably greater or equal to 0.85, over the range of spatial frequencies comprised from 0.5 to 3 cycles per degree, when measured through the optical elements for a pupil aperture of 4mm centered at 6.6 mm from the optical center of the myopia control optical lens.

[0161] The modulation transfer function, for example for foveal vision, is a horizontal modulation transfer function or a vertical modulation transfer function, preferably a horizontal modulation transfer function.

[0162] As it is well known to the skilled artisan, the modulation transfer function is notably used to quantify the optical quality of lens elements.

[0163] The modulation transfer function may be determined by: measuring the 3D surface of the lens element, determining a 2D representation of optical path differences of a light beam arriving normal to the lens element at a certain wavelength for example 550nm , determining the point spread function over a pupil aperture of 4mm centered at 6.6 mm from the optical center of the lens element, and determining the modulation transfer function over said pupil by a Fourier transform operation.

[0164] 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.

[0165] 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. In the context of the present disclosure, the term "lens element" can refer to an uncut optical lens or a spectacle optical lens edged to fit a specific spectacle frame or an ophthalmic lens.

[0166] 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

CLAIMS1. Method, for example implemented by computer means, for determining a local spatial contrast obtained with an optical lens to be placed in front of at least a portion of an eye, wherein the method comprises:- obtaining an eye model representative of the eye,- obtaining an optical lens model representative of the optical lens to be placed in front of at least a portion of the eye,- determining a point spread function based on the system of the eye model associated with the optical lens model,- convolving a plurality of images with the determined point spread functions so as to obtain a blurred version of the image,- determining the local spatial contrast in the blurred version of the image.

2. The method according to claim 1, wherein the local spatial contrast is defined at the scale of a receptive field of a retinal ganglion cell’s of the eye model.

3. The method according to claim 1 or 2, wherein the local spatial contrast is defined at the scale of the receptive field of a cell having a characteristic dimension greater than or equal to 30 pm and smaller than or equal to 3500 pm.

4. the method according to any of claims 1 to 3, wherein the plurality of images comprises at least 10 different images.

5. the method according to any of claims 1 to 4, wherein each image of the plurality of images correspond to natural scenes, for example indoor scenes and / or outdoor scenes.

6. The method according to any of claims 1 to 5, wherein each image of the plurality of images are grayscale images, for example comprising at least 16 different shades of gray, for example comprising at least 256 shades of gray.

7. The method according to any of claims 1 to 6, wherein the eye model is a standard eye model.

8. The method according to any of claims 1 to 7, wherein the eye model is customized based on characteristics of the eye.

9. The method according to any of the preceding claims, wherein the optical lens is myopia control optical lens configured so as to at least one of slow down, retard or prevent a progress of the myopia of the eye.

10. The method according to any of the preceding claims, wherein the method further comprises prior to determining the local spatial contrast, re-aligning the blurred version of the image on the original image.

11. Method for comparing the efficiency of at least two optical lenses as myopia control solutions, wherein the method comprises:- determining the local spatial contrast of each optical lens using a method according to any of claims 1 to 10 with the same eye model and image for each optical lens,- comparing the determined local spatial contrasts of each optical lenses.

12. Method according to claim 11, wherein one of the myopia control solutions is a reference myopia control solution.

13. Method for optimizing a myopia control optical lens, wherein the method comprises: a) obtaining an initial version of the myopia control optical lens, b) determining the local spatial contrast of the optical lens according to the initial version of the myopia control optical lens using a method according to any of claims 1 to 10, c) changing the value of at least one parameter of the initial version of the myopia control optical lens, d) determining the local spatial contrast of the modified optical lens according to the modified version of the myopia control optical lens using a method according to anyof claims 1 to 10 with the same eye model and image as for the initial version of the myopia control optical lens,- repeating steps c) and d)- selecting the version of the myopia control optical lens having the smallest local spatial contrast.

14. Myopia control optical lens providing a refractive power based on a prescription of the eye of the wearer for correcting an abnormal refraction of the eye of the wearer; wherein- the myopia control optical lens comprises at least one optical element having 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 myopia of the eye of the wearer;- having a local spatial contrast smaller 0.117, and- the modulation transfer function of the myopia control optical lens is greater or equal to 0.07, preferably greater or equal to 0.10, over the range of spatial frequencies comprised from 10 to 25 cycles per degree when measured over a pupil aperture of 5 mm diameter.

15. The myopia control optical lens according to claim 14, wherein the local spatial contrast is determined with a -4 diopter myopia eye model based on the Atchison eye model in standard wearer conditions relative to the myopia control optical lens.

16. The myopia control optical lens according to claim 14 or 15, wherein the local spatial contrast is determined for a lowering gaze direction of 20° and an eccentricity of 20° with a defocus of 0D.

17. The myopia control optical lens according to any of claims 14 to 15, wherein the local spatial contrast is determined as the average value over at least 10 images.

18. The myopia control optical lens according to any of claims 14 to 17, wherein the optical lens is a contact lens or a spectacle lens.

19. 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 methods according to claims 1 to 13.

20. A computer readable medium carrying one or more sequences of instructions of the computer program product according to claim 19.

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