Method for determining at least one parameter of a person's eye

Abstract

The present invention relates to a method for determining at least one optical parameter of a person's eye, the method comprising: - displaying at least two clear images on the retina of the person's eye, the at least two images including a target and being carried by two light beams substantially focused at at least two different positions in a plane of the pupil of the eye; - adapting a parameter of the target in the image based on the person's feedback related to a change in the parameter of the target in each image; and - determining the at least one optical parameter of the person's eye based on the adaptation of the parameter of the target in each image.

Description

Field of the Invention

[0001] The present invention relates to a method for determining at least one parameter of a person's eye. The present invention further relates to a method for displaying a sharp image on the retina of a person's eye. Background Art

[0002] Optical lenses are typically determined and then manufactured according to the wearer's specifications. For example, in the case of ophthalmic lenses for correcting or improving vision, the ophthalmic lenses are determined according to the prescription of the wearer corresponding to the wearer's vision requirements.

[0003] An ophthalmic prescription may include a spherical power or a cylindrical power prescription and an astigmatism prescription. These prescriptions correspond to corrections that enable the lens wearer to correct their vision defects.

[0004] Today's optometrists use accurate but bulky devices that require rather long and impractical measurements to evaluate the wearer's prescription.

[0005] Especially in developing countries, optometrists may be rare and quite unskilled, and may not be able to afford the expensive prescription measurement requirements.

[0006] An object of the present invention is to provide a cheap, simple and very fast prescription measurement method. Summary of the Invention

[0007] To this end, the present invention proposes a method for determining at least one optical parameter of a person's eye, the method comprising:

[0008] - displaying at least two sharp images on the retina of the person's eye, the at least two images including a target and being carried by two light beams substantially focused at at least two different positions in a plane of the pupil of the eye;

[0009] - adapting a parameter of the target in the image based on the person's feedback related to a change in the parameter of the target in each image; and

[0010] - determining the at least one optical parameter of the person's eye based on the adaptation of the parameter of the target in each image.

[0011] Advantageously, this method allows for the easy determination of the optical parameters of a person's eye using "off-the-shelf" products that were not initially intended for this application. These optical parameters are related to the prescription of the eye, such as diopter, astigmatism, axis and potential higher order aberrations.

[0012] Thus, this method provides a non-invasive, easy-to-use, and inexpensive way to perform subjective digital refraction measurements, especially in developing countries. In the context of the present invention, digital refractometry is refractometry using digital means.

[0013] According to further embodiments that can be considered individually or in combination:

[0014] - adapting the parameters of the target in the image based on the person's feedback related to the parameter changes of the target in each image so as to superimpose the targets of the at least two clear images; and / or

[0015] - displaying at least three clear images on the retina of the person's eye, the at least three images including a target and carried by three light beams substantially focused at at least three different positions in the plane of the pupil of the eye, and determining three optical parameters based on the adaptation of the parameters of the target in each focused content; and / or

[0016] - the adapted parameters of the target are the relative positions of the target in each image;

[0017] - adapting the parameters of the target in each image includes:

[0018] · adapting the horizontal angular position of the target in the image carried by one of the light beams until the person sees that the target of this image and the target of another image carried by another one of the light beams have the same horizontal position in the displayed image on the retina of the eye;

[0019] · adapting the vertical angular position of the target in the image carried by one of the light beams until the person sees that the target of this image and the target of another image carried by another one of the light beams have the same vertical position in the displayed image on the retina of the eye;

[0020] - the adapted parameters of the target are the sizes of the target in each image; and / or

[0021] - adapting the parameters of the target in each image includes:

[0022] · adapting the size of the target in the image carried by one of the light beams in the horizontal direction until the person sees that the target of this image and the target of another image carried by another one of the light beams are in contact with each other in the horizontal direction in the displayed image on the retina of the eye;

[0023] ·Adapt the size of the target of the image carried by one of these light beams in the vertical direction until the person sees that the target of the image and the target of another image carried by another of these light beams are in contact with each other in the vertical direction in the displayed image on the retina of the eye; and / or

[0024] - The determined optical parameters of the person's eye are related to the diopter, astigmatism, and axis position of the person's eye; and / or

[0025] - The feedback of the person is tactile feedback; and / or

[0026] - The feedback of the person is sound feedback; and / or

[0027] - The feedback of the person is provided by answering questions; and / or

[0028] - The method according to the invention is implemented using a head-mounted device adapted to display a plurality of clear images at least on the retina of the person's eye, the plurality of images being carried by a plurality of light beams substantially focused at different positions in the plane of the pupil of the eye.

[0029] According to another aspect, the invention further relates to a device comprising a processor adapted to store one or more sequences of instructions and to perform at least one of the steps of the method according to the invention for determining at least one optical parameter of a person's eye.

[0030] More specifically, the invention relates to a computer program product comprising one or more stored sequences of instructions that are accessible by a processor and that, when executed by the processor, cause the processor to perform at least the following steps of the method according to the invention for determining at least one optical parameter of a person's eye:

[0031] - Display at least two clear images on the retina of the person's eye, the at least two images including a target and being carried by two light beams substantially focused at at least two different positions in the plane of the pupil of the eye;

[0032] - Adapt the parameters of the target in the image based on the person's feedback related to the parameter changes of the target in each image; and

[0033] - Determine the at least one optical parameter of the person's eye based on the adaptation of the parameters of the target in each image.

[0034] The invention further relates to a computer-readable medium carrying one or more sequences of instructions of the computer program product according to the invention.

[0035] Another object of the present invention relates to a method for displaying a clear image on the retina of a human eye of a person having a prescription for the person's eye, the method comprising:

[0036] - determining at least one optical parameter related to the prescription for the person's eye according to the present invention;

[0037] - providing a plurality of initial sub-images, each initial sub-image corresponding to at least a part of the image to be displayed;

[0038] - providing a plurality of light beams configured to be substantially focused on a plurality of corresponding different positions in the plane of the pupil of the eye, each light beam being configured to carry an associated sub-image;

[0039] - for each sub-image, adapting the sub-image based on the at least one provided optical parameter and the corresponding focusing position of the light beam configured to carry the sub-image to form an adapted sub-image; and

[0040] - displaying on the retina of the person each adapted sub-image carried by the associated light beam.

[0041] Advantageously, such a method allows a head-mounted display device to be customized according to the viewing ability of the user. In fact, such a method allows pre-compensation of the image to be displayed on the retina of the user based on the prescription of the user's eye in order to display a clear image on the retina of the user.

[0042] Thus, different people with different prescriptions can use a single head-mounted device, and the images to be displayed on the retina of each person are corrected based on the prescription of the person's eye determined by the same head-mounted device.

[0043] According to another aspect, the present invention further relates to a device comprising a processor adapted to store one or more sequences of instructions and to execute at least one of the steps of the method according to the present invention for displaying a clear image on the retina of an eye.

[0044] More specifically, the present invention relates to a computer program product comprising one or more stored sequences of instructions that are accessible by a processor and that, when executed by the processor, cause the processor to perform at least the following steps of the method according to the present invention for displaying a clear image on the retina of a human eye.

[0045] The present invention further relates to a computer-readable medium carrying one or more sequences of instructions of the computer program product according to the present invention.

[0046] Unless otherwise specifically stated, it will be apparent from the following discussion that throughout the specification, discussions using terms such as "computing", "operation", etc. refer to actions and / or processes of a computer or a computing system or similar electronic computing device, which manipulate data represented as physical (such as electronic) quantities in the registers and / or memories of the computing system and / or convert it into other data similarly represented as physical quantities in the memories, registers or other such information storage, transmission or display devices of the computing system.

[0047] Embodiments of the present invention may include a device for performing the operations herein. This device may be specially constructed for the desired purpose, or it may include a general-purpose computer or a digital signal processor ("DSP") selectively activated or reconfigured by a computer program stored in the computer. Such a computer program may be stored in a computer-readable storage medium, such as but not limited to any type of disk, including floppy disks, optical disks, CD-ROMs, magneto-optical disks, read-only memories (ROMs), random access memories (RAMs), electronically programmable read-only memories (EPROMs), electrically erasable programmable read-only memories (EEPROMs), magnetic or optical cards, or any other type of medium suitable for storing electronic instructions and capable of being coupled to a computer system bus.

[0048] The processes and displays presented herein are not inherently related to any particular computer or other device. A variety of general-purpose systems may be used with programs in accordance with the teachings herein, or it may prove convenient to construct a more specialized device to perform the desired method. The desired structure of various such systems will become apparent from the following description. In addition, embodiments of the present invention are not described with reference to any specific programming language. It will be appreciated that various programming languages may be used to implement the teachings of the present invention described herein. BRIEF DESCRIPTION OF THE DRAWINGS

[0049] Embodiments of the present invention will now be described, by way of example only and with reference to the following drawings, in which:

[0050] - Figure 1 is a view of the lens / eye optical system seen from the side;

[0051] - Figure 2 and Figure 3 is a perspective view of the lens / eye system;

[0052] - Figure 4 is an illustration of a flowchart of a method for determining the optical parameters of a person's eye according to the present invention;

[0053] - Figure 5Shows the resulting images seen by people with different visual defects;

[0054] - Figure 6 and Figure 7 Show image formation using a micro-projector with and without an offset between the eye pupil and the optical axis of the micro-projector for emmetropic eyes, respectively;

[0055] - Figure 8 and Figure 9 Show image formation using a micro-projector with and without an offset between the eye pupil and the optical axis of the micro-projector for myopic eyes, respectively;

[0056] - Figure 10 Is a diagram of a schematic eye model;

[0057] - Figure 11 Is a diagram of a flowchart of a method for determining an optical parameter of a person's eye according to another embodiment of the present invention; and

[0058] - Figure 12 Is a diagram of a flowchart of a method for displaying a clear image on the retina of a person's eye according to the present invention;

[0059] - Figure 13 Shows image formation using two micro-projectors respectively according to a method for displaying a clear image on the retina of the eye of a person with refractive error, such as a person with myopia.

[0060] The elements in the drawings are illustrated only for simplicity and clarity and are not necessarily drawn to scale. For example, the dimensions of some elements in the drawings may be enlarged relative to other elements to help increase the understanding of the embodiments of the present invention. Detailed Description

[0061] The present invention relates to a method for determining an optical parameter of a person's eye. The optical parameter to be determined is related to the diopter, astigmatism and axis position of a person's eye.

[0062] Such a parameter allows the determination of the ophthalmic prescription of a person's eye. In fact, the ophthalmic prescription can include a positive or negative power prescription and an astigmatism prescription. These prescriptions correspond to the corrections that enable the wearer of the lens to correct his / her visual defect.

[0063] Traditionally, optical quantities (i.e., power and astigmatism) are defined for a given lens under its wearing conditions. Figure 1 Shows a side view of a lens / eye optical system and shows the definitions based on an example of a progressive multifocal ophthalmic lens with a front complex surface used in the remainder of the specification.

[0064] The center of rotation of the eye is designated as Q'. The axis Q'F', shown by a dotted line in the figure, is a horizontal axis passing through the center of rotation Q' of the eye and extending in front of the wearer; in other words, the axis Q'F' corresponds to the subjective viewing direction. The point at which this axis intersects the front surface of the lens is called the fitting cross CM. The fitting cross is marked on the lens to allow the optician to position the lens. The fitting cross is generally located 4 mm above the geometric center of the front surface of the lens.

[0065] The vertex sphere, also known as the apical sphere, having its center at Q' and radius q', is defined as the sphere tangent to the rear surface of the lens at the point O, which corresponds to the intersection of the rear surface of the lens with the axis Q'F'.

[0066] As an example, a radius q' value of 25.5 mm corresponds to a standard value and provides satisfactory results when wearing the lens.

[0067] Figure 1 The given viewing direction shown by the solid line in corresponds to the position of the eye rotated about Q' and the point J on the vertex sphere.

[0068] In the so-called Fick system, the viewing direction can also be identified in spherical coordinates by two angles α and β.

[0069] The angle α is the angle between the axis Q'F' and the projection of the line Q'J onto the vertical plane containing the axis Q'F', and this angle appears in the Figure 1 figure of.

[0070] The angle β is the angle between the axis Q'F' and the projection of the line Q'J onto the horizontal plane containing the axis Q'F'. Thus, a given viewing direction corresponds to the point J on the vertex sphere or the coordinate pair (α, β).

[0071] At a given viewing direction, the image of a point M in object space located at a given object distance is formed between two points S and T corresponding to a minimum distance JS and a maximum distance JT (this minimum distance and maximum distance will be the sagittal focal length and the tangential focal length in the case of a toric surface and a point M at infinity).

[0072] In Figure 1 the example of, the image of a point at infinity in object space is formed at the point F' on the axis Q'F'. The points S and T coincide, which is equivalent to stating that the lens is locally spherical in the subjective viewing direction. The distance D is the back vertex power of the lens.

[0073] Figure 2 and Figure 3 show a perspective view of the lens / eye system.

[0074] Figure 2Shows the position of the eye and the reference system associated with the eye. In the subjective viewing direction, α = β = 0, which is called the subjective viewing direction. Points J and O coincide.

[0075] Figure 3 Shows the position of the eye and the reference system associated with it in the direction (α, β).

[0076] Figure 2 and Figure 3 Shows the fixed reference system {x, y, z} and the reference system {xm, ym, zm} associated with the eye in order to clearly show the rotation of the eye. The reference system {x, y, z} has point Q' as the origin, and the x-axis is the Q'F' axis (point F' is not shown in Figure 2 and Figure 3 and passes through point O. This axis points from the lens towards the eye and is in line with the measurement direction of the astigmatic axis. The {y, z} plane is the vertical plane. The y-axis is vertical and points upwards. The z-axis is horizontal, and the reference system is a direct orthogonal coordinate system. The reference system {xm, ym, zm} associated with the eye is centered at point Q'. The xm-axis is defined by the viewing direction JQ' and coincides with the {x, y, z} reference system in the case of the subjective viewing direction. Listing's law gives the relationship between the {x, y, z} coordinate system and the {xm, ym, zm} coordinate system for each viewing direction (see "Optique Physiologique" by Le Grand, Volume 1, published by Revue d'Optique in Paris in 1965).

[0077] The cross-section of the lens can be drawn in the (O, x, y) plane defined in reference Figure 2 . The tangent to this curve at point O is inclined at an angle called the front tilt angle with respect to the (O, y) axis.

[0078] The cross-section of the lens can also be drawn in the (O, x, z) plane. The tangent to this curve at point O is inclined at an angle called the wrap angle with respect to the (O, z) axis.

[0079] Using these elements, the diopter and astigmatism of the wearer under normal wearing conditions can be defined for each viewing direction.

[0080] Consider the object point M at the object distance given by the Eikonal function for the fixation direction (α, β).

[0081] The Eikonal function is a function that associates the usual distance of an object point with each direction of gaze. Typically, in distance vision following the main direction of gaze, the object point is at infinity. In near vision following a direction of gaze that is basically corresponding to an angle α of approximately 36.6° in the nasal direction and an angle β of approximately 6°, the object distance is approximately 30 cm to 50 cm. To learn more details about the possible definition of the Eikonal function, reference can be made to US Patent US-A-6,318,859. The document describes the Eikonal function, its definition, and its modeling method. For the method of the present invention, the point can be at infinity or not at infinity. The Eikonal function can be a function of the refractive error of the wearer.

[0082] In object space, for a point M on the corresponding ray, the object proximity ProxO is defined as the reciprocal of the distance MJ between the point M and the point J of the apex sphere:

[0083]

[0084] This enables the calculation of the object proximity within the thin lens approximation for all points of the apex sphere, which is used to determine the Eikonal function. For a real lens, the object proximity can be considered as the reciprocal of the distance between the object point and the front surface of the lens on the corresponding ray.

[0085] For the same direction of gaze (α, β), the image of a point M with a given object proximity is formed between two points S and T corresponding respectively to the minimum focal length and the maximum focal length (which will be the sagittal focal length and the tangential focal length). The quantity Prox I is called the image proximity of the point M:

[0086]

[0087] By analogy with the case of a thin lens, thus for a given direction of gaze and a given object proximity, that is, for a point in object space on the corresponding ray, the refractive power Pui can be defined as the sum of the image proximity and the object proximity.

[0088] Pui = ProXO + ProxI (3)

[0089] Using the same notation, for each direction of gaze and a given object proximity, the astigmatism Ast is defined as:

[0090]

[0091] This definition corresponds to the astigmatism of the light beam produced by the lens.

[0092] Under normal wearing conditions, the possible definitions of the optical power and astigmatism of the lens can thus be calculated as explained in the paper by B. Bourdoncle et al., entitled "Ray tracing through progressive ophthalmic lenses" (Proceedings of the 1990 International Lens Design Conference, edited by D.T. Moore, Society of Photo-Optical Instrumentation Engineers, UK).

[0093] In addition to the power prescription, a prescription in the ophthalmic field can include an astigmatism prescription. Such a prescription consists of an axis value (in degrees) and a modulus value (in diopters). The modulus value represents the difference between the maximum and minimum optical powers in a given direction, which difference allows the correction of the wearer's visual default. According to this convention, the axis represents the orientation of one of the two optical powers relative to a reference axis and along a given direction of rotation. The TABO convention can be used. In this convention, the reference axis is horizontal and the direction of rotation is counterclockwise when looking at the wearer. The 45° axis corresponds to the axis that connects the upper right quadrant and the lower left quadrant in an inclined orientation when looking at the wearer. Such an astigmatism prescription is measured for the wearer at distance vision. The term "astigmatism" is used to refer to a pair (modulus, axis). That term is sometimes used to specify only the modulus. It is easy for a person skilled in the art to understand what is meant depending on the context. A person skilled in the art also realizes that the wearer's power / astigmatism prescription is usually described in terms of spherical, cylindrical, and axis.

[0094] Reference Figure 4 , the method at least comprises the following steps:

[0095] - A display step S2,

[0096] - An adaptation step S4, and

[0097] - A determination step S6.

[0098] During the display step S2, three clear images carried by three light beams are displayed on the retina of a human eye. In other words, each clear image is carried by an associated light beam that is substantially focused in the plane of the pupil of the eye.

[0099] In the sense of the present invention, a light beam being substantially focused in a plane means that the light beam is focused at a maximum distance of 10 mm from the plane of the pupil, thus ensuring a clear display of the image on the retina.

[0100] These three light beams are substantially focused at three different positions in the plane of the pupil of the eye, also called "focal points".

[0101] Thus, each focus point of the pupil acts as a micro-projector, emitting light towards the retina. The focusing of multiple light beams at different positions in the plane of the eye's pupil allows for an increase in the size of the eye movement box (EMB) and is the basis for pupil dilation.

[0102] This display step S2 can be implemented using a head-mounted display device as disclosed in US 2016 / 033771 A1. In fact, the working principle of the head-mounted display device of US 2016 / 033771 A1 is based on a micro-projector, and the light emitted by it is reflected towards the eye by a holographic mirror. More precisely, this light is substantially focused in the plane of the wearer's pupil (see Figure 2 A and Figure 2 B) of US 2016 / 033771 A1). This results in a very small eye movement box. To increase the size of the eye movement box, the holographic mirror focuses the light from the micro-projector at N different positions (see Figure 3 A and Figure 3 B of US 2016 / 033771 A1, where N = 2), each position corresponding to a specific wavelength. These wavelengths are very close to each other such that the wearer cannot perceive the difference.

[0103] Alternatively, this display step S2 can also be implemented using a head-mounted display device based on a light field display (LFD) as disclosed in WO 2018 / 091984 A1.

[0104] Each of the three images displayed during the display step S2 includes a target. The target is, for example, a dot or a cross-like symbol.

[0105] Figure 5 Shows the resulting images seen by people with different visual defects in the case where the three displayed clear images are the same and each includes a cross located at the same position in each image.

[0106] For simplicity, let's consider that the distances of the three focus points from the pupil center are equal and the distances from each other are equal.

[0107] If the person is emmetropic, the person sees a single cross in his / her central vision, as shown Figure 5 on the left (Case A). However, if the person has myopia or hyperopia, the person sees three different crosses, as shown Figure 5 at the center of (Case B), and their relative distances are a function of their spherical lens prescription. Finally, if the person has astigmatism, the person also sees three different crosses, as shown Figure 5 on the left (Case C), and their relative horizontal and vertical distances are associated with their cylindrical lens prescription.

[0108] These differences can be with respect toFigures 6 to 9 To explain, these figures show a micro - projector 10 emitting two light rays 12, 14 (only two for simplicity) through an optical system 16 represented by black brackets, towards an eye 20 including a pupil 22 and a retina 24. Figure 6 and Figure 7 relates to an emmetropic eye, while Figure 8 and Figure 9 relates to ametropic eyes, such as myopic eyes.

[0109] The optical system 16 is configured to substantially focus the light rays emitted by the micro - projector in the plane of the pupil 22.

[0110] At Figure 6 when the optical axis Z1 of the micro - projector 10 coincides with the optical axis Z2 of the eye 20, both light rays 12, 14 are focused at the center of the eye pupil and then form two points A' and B' on the retina 24.

[0111] As Figure 7 shown above, when the optical axis Z2 of the eye 20 is offset relative to the optical axis Z1 of the micro - projector 10, the positions of points A' and B' on the retina 24 do not change because the eye is emmetropic.

[0112] However, for a myopic eye as Figure 8 and Figure 9 shown, light from infinity is focused in the dashed - line plane 26 instead of on the retina. This dashed - line plane 26 is located in front of the retina 24 of the eye.

[0113] Therefore, referring to Figure 8 , again considering a single micro - projector 10 focused at the center of the eye pupil 22, a clear image is still shown on the retina 34.

[0114] However, when the optical axis Z2 of the eye is offset relative to the optical axis Z1 of the micro - projector 10, for a myopic eye, the positions of points A' and B' on the retina 24 are offset, as Figure 9 shown above.

[0115] As a result, if a person is myopic, light from two micro - projectors showing the same content will reach the retina at different positions and the image will no longer be clear on the retina. Instead, the two images are offset and superimposed. Moreover, there are as many images as there are focal points on the eye pupil.

[0116] Of course, the same observation applies to wearers with hyperopia and wearers with astigmatism.

[0117] Then, during step S4, the parameters of the target in each image are adapted based on the feedback related to the parameter changes of the target in the person's view.

[0118] In fact, referring to Figure 10 the schematic eye model shown above, the wave vector k of the plane (Oxy) that comes from the half-space in front of the eye and strikes the pupil 22 at point M in The light ray guided by is refracted by the phase function of the eye into the wave vector k when passing through the pupil of the eye and striking the retina 24 at point P out .

[0119] Point M corresponds to the "focus point", and the sum of the k in vectors corresponds to the image content, represented by the box 30 in Figure 10 . The sum of all points P corresponding to all vectors k in depicts the image generated on the retina.

[0120] The coordinates (X, Y) of point P can be determined as follows:

[0121]

[0122] where:

[0123] · d is the distance between the plane (Oxy) of the pupil and the retina, which is considered as the plane (ΩXY) for simplicity,

[0124] · (x, y) are the coordinates of point M in the plane of the pupil,

[0125] · (ka, kb, kc) are the coordinates of the wave vector k in , where k = 2π / λ, λ is the wavelength, and

[0126] · S eq = S + C / 2, where S is the maximum diopter, C ≤ 0 is the astigmatism, and 0 ≤ θ ≤ 180° is the axis position.

[0127] Therefore, in the paraxial approximation where d / c ≈ d, the position difference between two points P1 and P2 on the retina corresponding to two points M1 and M2 on the pupil illuminated by the corresponding wave vectors k in,1 and k in,2 is expressed as:

[0128]

[0129] Therefore, when two focal points M1 and M2 of the pupil are illuminated by two different light rays, the position difference between the corresponding points P1 and P2 on the retina depends on the difference in the inclination angles of these light rays and the position difference of the focal points M1 and M2 on the pupil, rather than on the absolute positions of M1 and M2 on the pupil. Therefore, the simultaneous shift of the focal points M1 and M2 with the same incident light direction only results in the offset of P1 and P2 on the retina.

[0130] To this end, in each iteration, the target location parameters in each image are modified, and the person provides his / her feedback related to this change.

[0131] The person's feedback is preferably acoustic feedback, provided for example by answering questions such as asking whether the targets projected onto his / her retina from one iteration to the next are closer to or farther from each other, or asking other similar questions.

[0132] In addition, the person's feedback can be haptic feedback.

[0133] Advantageously, the adapted parameters of the target are preferably the relative positions of the target in each image. In this case, the step S4 of adapting the parameters of the target in each image at least includes a step S42 of adapting the horizontal position of the target of the image and a step S44 of adapting the vertical position of the target of the image.

[0134] During step S42, the horizontal angular position of the target of the image carried by one of the light beams is adapted until the person sees that the target of this image and the target of another image carried by another light beam have the same horizontal position in the display image on the eye retina.

[0135] In the same way, during step S44, the vertical angular position of the target of the image carried by one of the light beams is adapted until the person sees that the target of this image and the target of another image carried by another light beam have the same vertical position in the display image on the eye retina.

[0136] Therefore, during the implementation of steps S42 and S44, when the person is asked whether two points of the targets projected onto his / her retina from one iteration to the next are closer to or farther from each other, the horizontal and vertical angular position values of the targets in the image change with each iteration according to the person's response until the person sees the two targets superimposed, i.e., having the same vertical position and the same horizontal position in the display image on the eye retina. For visibility, these points can correspond to, for example, the centers of symbols similar to crosses.

[0137] For example, the cross can be offset pixel by pixel in the horizontal and / or vertical direction at each iteration.

[0138] Advantageously, this method does not require the eyes to be completely stationary relative to the focal point. The only requirement is that the focal point is contained within the pupil of the eye.

[0139] According to a preferred embodiment, the display step S2 and the adaptation step S4 can be performed sequentially, i.e., for two of the three light beams, and then repeated when adding the third light beam. In fact, during the display step S2, two clear images carried by two light beams are first displayed on the retina of a person's eye. For these two images, during the step S4, the parameters of the target in the image are adapted based on the person's feedback related to the parameter changes of the target in each image, preferably until the person sees that the targets of the two images have the same position in the displayed images on the eye retina. Then, a third clear image carried by the third light beam is also displayed on the retina, and during the step S4, the parameters of the target in the image are adapted based on the person's feedback related to the parameter changes of the target in the third image, preferably until the person sees that the target of the third image and the target of the first image have the same position in the displayed images on the eye retina.

[0140] During the determination step S6, the optical parameters of the person's eye are determined based on the adaptation of the parameters of the target in each image.

[0141] In fact, based on the changes in the horizontal angular position and vertical angular position of the target in the image required for the person to see only one cross, the optical parameters of the person's eye can be determined.

[0142] In other words, based on the differences in the horizontal and vertical directions between the initial angular position and the final angular position of the target in the image and knowing the position of the focal point and the function that relates the angular deviation perceived by the person to the true angular deviation of the target in the image, the optical parameters of the person's eye can be determined. The initial position of the target in the image corresponds to the setting of the display device for a emmetropic eye. The final position of the target in the image corresponds to the setting of the display device when adapted to a non-emmetropic person, i.e., when the person sees two targets superimposed.

[0143] In fact, once (a1, b1) and (a2, b2) are known, the expression (6) yields two equations for solving three variables S, C, and θ. Thus, by introducing a third point M3, at least two additional equations can be expressed from the expression (6), allowing the determination of the three optical parameters S, C, and θ.

[0144] The position of the focal point can be predetermined during the calibration step.

[0145] For example, let us consider that the person has myopia and astigmatism, where the spherical error is S, the cylindrical power is C, and the axis is 0°. Thus, the horizontal power error is Sh = S, and the vertical power error is Sv = S + C, and the horizontal and vertical powers are the extreme powers, expressed in diopters (δ).

[0146] Using a model that allows relating the prism deviation (in prism diopters (Δ)) to the spherical error, such as Prentice's law, the angular deviation perceived by a person between the crosses 'i' and 'j' in the horizontal and vertical directions can be expressed as:

[0147]

[0148] Where:

[0149] -d h (i,j) is the horizontal distance (in mm) between the focal point of the cross 'i' and the focal point of the cross 'j';

[0150] -d v (i,j) is the vertical distance (in mm) between the focal point of the cross 'i' and the focal point of the cross 'j'.

[0151] Therefore, if an offset of n h (i,j) pixels of the cross 'j' is necessary for superimposing the crosses 'i' and 'j' in the horizontal direction, and an offset of n v (i,j) pixels of the cross 'j' is necessary for superimposing the crosses 'i' and 'j' in both the horizontal and vertical directions, and knowing the angular size dP Δ (which is a construction parameter), the angular deviation perceived by a person between the crosses 'i' and 'j' in the horizontal and vertical directions can also be expressed as:

[0152]

[0153] Based on equations (7) and (8), the spherical error S and the cylindrical power C for a person's eye are determined.

[0154] Of course, this determination can be generalized to prescriptions with non-zero cylindrical axis positions.

[0155] Similarly, models other than Prentice's law can also be used to determine the optical parameters of a person's eye.

[0156] Although in this embodiment for determining the optical parameters related to the refractive power and astigmatic prescription of a person's eye, three clear images are displayed on the retina of the person's eye, and these clear images are carried by three light beams focused on three different points in the plane of the eye's pupil, it can be noted that multiple clear images can be displayed on the retina, and these multiple clear images are carried by multiple associated light beams focused on multiple different points in the plane of the eye's pupil, thereby allowing for a more accurate determination of the optical parameters related to its prescription.

[0157] In addition, if the cylindrical lens is empty, it is only necessary to determine the spherical lens to require that two clear images be displayed on the retina of the eye, and the two clear images are carried by two light beams focused on two different points in the plane of the pupil of the eye.

[0158] Of course, although in this embodiment, the distances of the focal points from the center of the pupil are equal and the distances from each other are equal, the method can be extended to other display devices configured to display multiple clear images on the retina of the eye and the distances of the focal points from the center of the pupil of the eye are not equal and / or the distances from each other are not equal, and the multiple clear images are carried by multiple associated light beams focused on multiple different points in the plane of the pupil of the eye. In this case, the positions of the focal points should be determined in advance during the calibration step.

[0159] Reference Figure 11 , another embodiment of the method is different from the previous embodiment in that the adapted parameter of the target is the size of the target in each image, rather than the relative position of the target in each image. In this embodiment, the position and size of the target in each initially displayed image are the same.

[0160] In this case, step S4 for adapting the parameters of the target in each image includes step S46 for adapting in the horizontal direction and step S48 for adapting in the vertical direction.

[0161] During step S46 for adapting in the horizontal direction, the size of the target of the image carried by one of the light beams is adapted in the horizontal direction until the person sees the target of this image in contact with the target of another image carried by another light beam in the horizontal direction in the displayed image on the retina of the eye.

[0162] In the same way, during step S48 for adapting in the vertical direction, the size of the target of the image carried by one of the light beams is adapted in the vertical direction until the person sees the target of this image in contact with the target of another image carried by another light beam in the vertical direction in the displayed image on the retina of the eye.

[0163] As indicated above, the method is preferably implemented using a head-mounted device adapted to display multiple clear images at least on the retina of a person's eye, and the multiple images are carried by multiple light beams substantially focused at different positions in the plane of the pupil of the eye. For example, the head-mounted display devices disclosed in US 2016 / 033771 A1 or WO 2018 / 091984 A1 can be used to implement the method according to the present invention.

[0164] To this end, a computer program product may be stored in the memory of a head-mounted display device, the computer program product including one or more sequences of stored instructions that are accessible by a processor of the head-mounted display device and that, when executed by the processor, cause the processor to perform the steps of the method according to the present invention.

[0165] Another object of the present invention relates to a method for displaying a clear image on the retina of a person's eye, the person having a prescription for this eye.

[0166] As in the foregoing method, this display method is preferably implemented using a head-mounted device adapted to display a plurality of clear images at least on the retina of a person's eye, the plurality of images being carried by a plurality of light beams substantially focused at different positions in a plane of the pupil of the eye.

[0167] In the same way, a computer program product may be stored in the memory of a head-mounted display device, the computer program product including one or more sequences of stored instructions that are accessible by a processor of the head-mounted display device and that, when executed by the processor, cause the processor to perform the steps of the method according to the present invention and as described hereinafter.

[0168] Reference Figure 12 , the display method at least includes the following steps:

[0169] - A parameter determination step S50,

[0170] - A sub-image providing step S52,

[0171] - A display device providing step S54,

[0172] - An adaptation step S56, and

[0173] - A display step S58.

[0174] During the parameter determination step S50, at least one optical parameter related to the prescription for a person's eye is advantageously determined according to the previous method and using an adapted head-mounted display device as disclosed in US 2016 / 033771 A1 or WO2018 / 091984 A1.

[0175] During the sub-image providing step S52, a plurality of initial sub-images are provided. Each initial sub-image corresponds to at least a part of the image to be displayed.

[0176] In S54, multiple light beams are provided. These light beams are configured to be substantially focused on multiple corresponding different positions in the plane of the pupil of the eye. In the sense of the present invention, the light beams being substantially focused in the plane means that the light beams are focused at a maximum distance of 10 mm from the plane of the pupil, thereby ensuring a clear image display on the retina.

[0177] In addition, each light beam is configured to carry an associated sub - image.

[0178] Then, during the adaptation step S56, for each sub - image, the sub - image is adapted based on at least one provided optical parameter and the corresponding focusing position of the light beam configured to carry the sub - image to form an adapted sub - image.

[0179] Therefore, each sub - image is calculated according to the needs of the wearer, that is, according to the prescription of the eye.

[0180] Preferably, adapting the sub - image includes adapting the relative position of the sub - image in the image to be displayed. Adapting the relative position of the sub - image in the image to be displayed includes:

[0181] - a horizontal adaptation step S62, and

[0182] - a vertical adaptation step S64.

[0183] During this horizontal adaptation step S62, the horizontal angular position of the sub - image carried by the associated light beam is adapted based on at least one provided optical parameter and the corresponding focusing position of the associated light beam.

[0184] Similarly, during the vertical adaptation step S64, the vertical angular position of the sub - image carried by the associated light beam is adapted based on the provided optical parameters and the corresponding focusing position of the associated light beam.

[0185] The focusing position in the plane of the pupil of the eye can be determined for each light beam during the calibration step.

[0186] During the display step S58, each adapted sub - image carried by the associated light beam is displayed on the retina of the person.

[0187] The offset of all pixels of each sub - image based on the optical parameters of the person's eye allows the sub - images from the multiple focal points to be properly superimposed. The sub - images from the multiple focal points are thus perceived by the person as a single clear image.

[0188] Figure 13 A method for displaying a clear image on the retina of the eye of a person with refractive error, such as a person with myopia, is shown. In this example, let's consider the content of the image to be displayed (by Figure 10The square 30 in (represented) includes two vertically aligned disks, one black and one white.

[0189] In addition, for simplicity, only two light beams 42, 44 from two micro - projectors are shown, which are substantially focused on two corresponding focal points M1 and M2 in the plane Oxy of the pupil. In the example, these two focal points are aligned on the Oy axis. The first light beam 42 carries the associated sub - image represented by the square 46, and the second light beam carries the associated sub - image represented by the square 48.

[0190] Each sub - image is calculated and adapted according to the prescription of the human eye and the corresponding focal position of the light beam. Thus, the contents of the first and second sub - images are vertically offset from each other in their frames, allowing the first and second sub - images from the focal points M1 and M2 to be properly superimposed on the retina.

[0191] The adapted sub - images can be displayed sequentially or simultaneously on the human retina.

[0192] According to a preferred embodiment, the focal positions of the plurality of light beams are regularly spaced apart from each other in the plane of the pupil of the eye.

[0193] According to another embodiment compatible with the foregoing embodiment, the wavelength of at least one of the plurality of light beams is different from the wavelength of at least one other of the plurality of light beams. Preferably, these wavelengths are very close to each other such that a person cannot perceive the difference in image color.

[0194] Advantageously, this method allows the head - mounted display device to be customized according to the viewing ability of the user. In fact, this method allows pre - compensation of the images to be displayed on the user's retina based on the prescription of the user's eyes in order to display clear images on the user's retina.

[0195] Thus, different people with different prescriptions can use a single head - mounted device, and the images to be displayed on each person's retina are corrected based on the prescription of the person's eyes determined by the same head - mounted device.

[0196] The present invention has been described above by way of examples without limiting the general inventive concept.

[0197] Many further improvements and variations can also be proposed for those skilled in the art who refer to the foregoing illustrative embodiments. These embodiments are given by way of example only and are not intended to limit the scope of the present invention, which is determined only by the appended claims.

[0198] In a claim, 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 mean that a combination of these features cannot be used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the invention.

Claims

1. A method for determining at least one optical parameter of a person's eye, the method comprising: - displaying at least two clear images on the retina of the person's eye, the at least two clear images including a target and carried by two light beams substantially focused at at least two different positions in a plane of the pupil of the eye; - adapting a parameter of the target in the images based on feedback of the person related to a parameter change of the target in each image so as to superimpose the targets of the at least two clear images; and - determining the at least one optical parameter of the person's eye based on the adaptation of the parameter of the target in each image, wherein the adapted parameter of the target is a relative position of the target in each image, and adapting the parameter of the target in each image includes: - adapting a horizontal angular position of the target of the image carried by one of the light beams until the person sees that the target of the image and the target of another image carried by the other light beam have the same horizontal position in a displayed image on the retina of the eye; - adapting a vertical angular position of the target of the image carried by one of the light beams until the person sees that the target of the image and the target of another image carried by the other light beam have the same vertical position in a displayed image on the retina of the eye, or the adapted parameter of the target is a size of the target in each image, and adapting the parameter of the target in each image includes: - adapting a size of the target of the image carried by one of the light beams in a horizontal direction until the person sees that the target of the image and the target of another image carried by the other light beam are in contact with each other in the horizontal direction in a displayed image on the retina of the eye; - adapting a size of the target of the image carried by one of the light beams in a vertical direction until the person sees that the target of the image and the target of another image carried by the other light beam are in contact with each other in the vertical direction in a displayed image on the retina of the eye.

2. The method according to claim 1, wherein, Displaying at least three clear images on the retina of the person's eye, the at least three clear images including a target and carried by three light beams substantially focused at at least three different positions in a plane of the pupil of the eye, and determining three optical parameters based on the adaptation of the parameter of the target in each focused content.

3. The method according to claim 1, wherein The determined optical parameter of the person's eye is related to the diopter, astigmatism and axis position of the person's eye.

4. The method according to claim 1, wherein The feedback of the person is tactile feedback.

5. The method according to claim 1, wherein The feedback of the person is sound feedback.

6. The method according to claim 5 above, wherein, The feedback of the person is provided by answering a question.

7. The method according to any one of claims 1 to 6 is implemented using a head-mounted device adapted to display a plurality of clear images at least on the retina of the person's eye, the plurality of images being carried by a plurality of light beams substantially focused at different positions in a plane of the pupil of the eye.

8. A computer program product comprising one or more sequences of stored instructions that are accessible by a processor and, when executed by the processor, perform at least the following steps: - Display at least two clear images on the retina of the person's eye, the at least two clear images including a target and carried by two light beams that are substantially focused at two different positions in a plane of the pupil of the eye; - Adapt parameters of the target in the images based on feedback of the person related to parameter changes of the target in each image so as to superimpose the targets of the at least two clear images; And - Determine the at least one optical parameter of the person's eye based on the adaptation of the parameters of the target in each image, wherein the adapted parameters of the target are the relative positions of the target in each image, and adapting the parameters of the target in each image includes: - Adapt the horizontal angular position of the target of the image carried by one of the light beams until the person sees that the target of the image and the target of another image carried by the other light beam have the same horizontal position in the displayed image on the retina of the eye; - Adapt the vertical angular position of the target of the image carried by one of the light beams until the person sees that the target of the image and the target of another image carried by the other light beam have the same vertical position in the displayed image on the retina of the eye, or the adapted parameters of the target are the sizes of the target in each image, and adapting the parameters of the target in each image includes: - Adapt the size of the target of the image carried by one of the light beams in the horizontal direction until the person sees that the target of the image and the target of another image carried by the other light beam are in contact with each other in the horizontal direction in the displayed image on the retina of the eye; - Adapt the size of the target of the image carried by one of the light beams in the vertical direction until the person sees that the target of the image and the target of another image carried by the other light beam are in contact with each other in the vertical direction in the displayed image on the retina of the eye.

9. A computer-readable medium carrying one or more sequences of instructions of the computer program product as claimed in claim 8.

10. A method for displaying clear images on the retina of a person's eye, the person having a prescription for the person's eye, the method comprising: - Determine at least one optical parameter related to the prescription for the person's eye according to any one of claims 1 to 7; - Provide a plurality of initial sub-images, each initial sub-image corresponding to at least a part of an image to be displayed; - Provide a plurality of light beams configured to be substantially focused at a plurality of corresponding different positions in a plane of the pupil of the eye, each light beam being configured to carry an associated sub-image; - For each sub-image, adapt the sub-image based on the at least one provided optical parameter and the corresponding focal position of the light beam configured to carry the sub-image to form an adapted sub-image; and - Display each adapted sub-image carried by the associated light beam on the retina of the person.

Images