Method for displaying a clear image on the retina of a human eye

Abstract

The present invention relates to a method for displaying a clear image on the retina of a human eye, the person having a prescription for the person's eye, the method comprising: providing at least one optical parameter related to the prescription for the person's eye; providing a plurality of initial sub-images, each initial sub-image corresponding to at least a part of the image to be displayed; providing a plurality of light beams, the plurality of light beams being configured to be substantially focused at 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; 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 displaying on the retina of the human each adapted sub-image carried by the associated light beam.

Description

Technical Field

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

[0002] A head-mounted system (HMD) is an electro-optical device worn on the head by a wearer. Generally, such a system is electronically controlled to switch between different stages or display information to the wearer. A head-mounted system generally resembles a spectacle frame with electronically controlled spectacle lenses.

[0003] The head-mounted system is used according to different usage modes, such as a non-immersive head-mounted system, which allows the wearer to interact with their environment while using the head-mounted system or a cut-off external vision immersive head-mounted system.

[0004] There is a need to provide a head-mounted optical device, such as a head-mounted display system, which is suitable for the wearer, especially in a simple manner and preferably in a later step of manufacturing the optical device, to meet their visual needs, so as to limit the unit production cost.

[0005] In fact, if the wearer needs corrective ophthalmic lenses to correctly view the real world or the displayed information, the head-mounted optical system should be suitable for such requirements.

[0006] Therefore, there is a need to provide an optical device, such as a head-mounted perspective system, which is adapted to the wearer and especially to the prescription of the wearer.

[0007] US 10 451 895 B2 discloses methods and a wearable ophthalmic device, which may include an outward-facing head-mounted light field camera to receive light from the user's surrounding environment and generate digital light field image data.

[0008] EP 3296 797 A1 relates to methods and devices for visually displaying images on a human using a display built into an eye wear. Summary of the Invention

[0009] To this end, the present invention proposes a method for displaying a clear image on the retina of a human eye, the human having a prescription for the human eye, the method comprising:

[0010] - providing at least one optical parameter related to the prescription for the human eye;

[0011] - providing a plurality of initial sub-images, each initial sub-image corresponding to at least a part of the image to be displayed;

[0012] - Providing a plurality of light beams configured to be substantially focused at a plurality of corresponding different positions in a plane of a pupil of the eye, each light beam being configured to carry an associated sub-image;

[0013] - For each sub-image, adapting the sub-image based on the at least one provided optical parameter and a corresponding focusing position of the light beam configured to carry the sub-image to form an adapted sub-image; and

[0014] - Displaying each adapted sub-image carried by an associated light beam on the retina of the person.

[0015] Advantageously, such a method allows customization of a head-mounted display device according to the viewing ability of a user. In fact, such a method allows pre-compensation of an image to be displayed on the retina of the user based on a prescription of the user's eye so as to display a clear image on the retina of the user. Thus, the use of the head-mounted display device and the virtual comfort of the virtual image are optimized for the user.

[0016] 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.

[0017] According to further embodiments that can be considered individually or in combination:

[0018] - Adapting the sub-image includes adapting a relative position of the sub-image in the image to be displayed;

[0019] - Adapting the relative position of the sub-image in the image to be displayed includes:

[0020] · Adapting a horizontal angular position of the sub-image carried by the associated light beam based on the at least one provided optical parameter and the corresponding focusing position of the associated light beam; and

[0021] · Adapting a vertical angular position of the sub-image carried by the associated light beam based on the at least one provided optical parameter and the corresponding focusing position of the associated light beam.

[0022] - The method further includes determining a focusing position in the plane of the pupil of the eye for each of the plurality of light beams;

[0023] - The focusing positions of the plurality of light beams are regularly spaced apart from each other in the plane of the pupil of the eye;

[0024] - The adapted sub-images are displayed on the retina of the person sequentially;

[0025] - The adapted sub-images are displayed on the retina of the person simultaneously;

[0026] - 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;

[0027] - The wavelengths of the plurality of light beams are included in a narrow wavelength band that is 50 nm wide;

[0028] - Provide at least three optical parameters related to the prescription for the person's eye;

[0029] - The at least one provided optical parameter of the person's eye is related to the diopter, astigmatism, and axis position of the person's eye;

[0030] - Providing at least one optical parameter related to the prescription for the person's eye includes:

[0031] · Display at least two clear images on the retina of the person's eye, the at least two images including a target and carried by two light beams that are substantially focused at 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 target is a point;

[0035] - The target is a one-dimensional image;

[0036] - The target is a two-dimensional image.

[0037] According to another aspect, the present invention further relates to a display device adapted to provide a plurality of light beams configured to be substantially focused at 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 and adapted to at least perform the steps of the method of the present invention.

[0038] According to another aspect, the present invention further relates to a device including a processor adapted to store one or more instruction sequences and perform at least one of the steps of the method according to the present invention for displaying clear images on the retina of an eye.

[0039] More specifically, the present invention relates to a computer program product comprising one or more sequences of stored 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 a method for determining at least one optical parameter of a person's eye according to the present invention using a display device according to the present invention:

[0040] - Provide at least one optical parameter related to a prescription for the person's eye;

[0041] - Provide a plurality of initial sub-images, each initial sub-image corresponding to at least a part of an image to be displayed;

[0042] - Provide a plurality of light beams that are 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;

[0043] - For each sub-image, adapt 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

[0044] - Display each adapted sub-image carried by an associated light beam on the retina of the person.

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

[0046] Unless otherwise specifically stated, it will be appreciated that throughout the specification, discussions using terms such as "computing", "operating", etc. refer to actions and / or processes of a computer or computing system or similar electronic computing device that manipulate and / or transform data represented as physical (such as electronic) quantities within the registers and / or memories of the computing system into other data similarly represented as physical quantities within 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 memory (ROM), random access memory (RAM), electrically programmable read-only memory (EPROM), electrically erasable programmable read-only memory (EEPROM), 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. Various general-purpose systems may be used with the programs according to the teachings herein, or it may prove convenient to construct more specialized devices 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 have not been 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 are perspective views of the lens / eye system;

[0052] - Figure 4 is a diagrammatic illustration of a flowchart of a method for displaying a clear image on the retina of a human eye according to the present invention;

[0053] - Figure 5 shows 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 9Shows image formation using a micro-projector with and without an offset between the eye pupil and the optical axis of the micro-projector for myopia;

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

[0057] - Figure 11 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; and

[0058] - Figure 12 and Figure 13 Is a diagram of a flowchart of a method for determining the optical parameters of a person's eye according to two embodiments of the present invention.

[0059] 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

[0060] 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 the person's eye.

[0061] As is well known, 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 wearer of the lens to correct his / her visual defect.

[0062] Traditionally, optical quantities (i.e., power and astigmatism) are defined for a given lens in its wearing conditions. Figure 1 Shows a view of the lens / eye optical system seen from the side and shows the definitions based on an example of a progressive multifocal ophthalmic lens having a front complex surface used in the remainder of the specification.

[0063] The center of rotation of the eye is called Q'. The axis Q'F' shown by the dotted line in the figure is the horizontal axis passing through the center of rotation of the eye Q' and extending in front of the wearer; in other words, the axis Q'F' corresponds to the main 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.

[0064] The vertex sphere, also called the vertex ball, with its center at Q' and radius q', is defined as the spherical surface that is tangent to the back surface of the lens at point O, which corresponds to the intersection of the back surface of the lens and the axis Q'F'.

[0065] As an example, a radius q' value of 25.5 mm corresponds to the standard value and provides satisfactory results when wearing the lens.

[0066] Figure 1 The given viewing direction shown by the solid line in [reference] corresponds to the position of the eye rotating around Q' and the point J on the apex sphere.

[0067] In the so-called Fick system, the viewing direction can also be identified in spherical coordinates by two angles α and β.

[0068] The angle α is the angle between the Q'F' axis and the projection of the straight line Q'J on the vertical plane containing the Q'F' axis, and this angle appears in the figure of [reference]. Figure 1 of [reference].

[0069] The angle β is the angle between the Q'F' axis and the projection of the straight line Q'J on the horizontal plane containing the Q'F' axis. Therefore, the given viewing direction corresponds to the point J on the apex sphere or the coordinate pair (α, β).

[0070] In a given viewing direction, the image of a point M in the object space located at a given object distance is formed between two points S and T corresponding to the minimum distance JS and the maximum distance JT (the minimum distance and the maximum distance will be the sagittal focal length and the tangential focal length in the case of the toric surface and the point M at infinity).

[0071] In Figure 1 the example of [reference], the image of a point at infinity in the object space is formed at the point F' on the Q'F' axis. The points S and T coincide, which is equivalent to stating that the lens is locally spherical in the principal viewing direction. The distance D is the posterior crown of the lens.

[0072] Figure 2 and Figure 3 show a stereogram of the lens / eye system.

[0073] Figure 2 show the position of the eye and the reference system associated with the eye. In the principal viewing direction, α = β = 0, which is called the principal viewing direction. The points J and O coincide.

[0074] Figure 3 show the position of the eye and the reference system associated with it in the direction (α, β).

[0075] Figure 2 and Figure 3 show 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 the point Q' as the origin, and the x-axis is the Q'F' axis (the point F' is not shown in Figure 2 andFigure 3 shown in Figure 3 and passes through point O. This axis points from the lens towards the eye and is in line with the direction of measurement 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 main 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).

[0076] It is possible to plot the section of the lens 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.

[0077] It is also possible to plot the profile of the lens 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.

[0078] Using these elements, it is possible to define the dioptric power and astigmatism of the wearer under normal wearing conditions for each viewing direction.

[0079] Consider the object point M at the object distance given by the Eikonal function for the viewing direction (α,β).

[0080] The Eikonal function is a function that associates the usual distance of the object point with each viewing direction. Typically, in distance vision following the main viewing direction, the object point is at infinity. In near vision following a viewing direction corresponding essentially to an angle α of approximately 36.6° in absolute value towards the nose side and an angle β of approximately 6°, the object distance is approximately 30 cm to 50 cm. To know more details about the possible definition of the Eikonal function, reference can be made to US Patent US-A-6,318,859. This 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.

[0081] In the object space, the object proximity ProxO for a point M on the corresponding ray is defined as the reciprocal of the distance MJ between the point M and the point J of the apex sphere:

[0082]

[0083] This enables the calculation of object proximity within the thin lens approximation for all points for head-up viewing, 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.

[0084] For the same viewing direction (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:

[0085]

[0086] By analogy with the thin lens case, thus for a given viewing direction and a given object proximity, i.e., for a point in object space on the corresponding ray, the optical power Pui can be defined as the sum of the image proximity and the object proximity.

[0087] Pui = ProxO + ProxI

[0088] Using the same notation, the astigmatism Ast is defined for each viewing direction and a given object proximity as:

[0089]

[0090] This definition corresponds to the astigmatism of the light beam produced by the lens.

[0091] Under normal wearing conditions, the possible definitions of the optical power and the 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" (1990 International Lens Design Conference, edited by D.T. Moore, Proceedings of the Society of Photo-Optical Instrumentation Engineers (SPIE), UK).

[0092] In addition to the diopter prescription, a prescription in the ophthalmic field may 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 diopters in a given direction, which difference allows for the correction of the wearer's visual default. According to this convention, the axis represents the orientation of one of the two diopters relative to a reference axis and along a given direction of rotation. The TABO convention may 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, when looking at the wearer, connects the upper right quadrant and the lower left quadrant in an inclined orientation. 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 diopter / astigmatism prescription of a wearer is typically described in terms of spherical, cylindrical, and axis.

[0093] Reference Figure 4 , the display method at least includes the following steps:

[0094] - A parameter providing step S10,

[0095] - A sub-image providing step S12,

[0096] - A display device providing step S14,

[0097] - An adaptation step S16, and

[0098] - A display step S18.

[0099] During the parameter providing step S10, at least one optical parameter related to the prescription for a person's eye is provided.

[0100] As mentioned above, the optical parameter may be related to the diopter, astigmatism, and axis of a person's eye (such as the spherical, cylindrical, and axis of a person's eye).

[0101] Preferably, at least three optical parameters are provided: the spherical, cylindrical, and axis of a person's eye.

[0102] The optical parameter related to the prescription for a person's eye may advantageously be pre-measured by an eye care practitioner (such as an optometrist) and then provided. The optical parameter related to the prescription of the eye may be stored in a memory.

[0103] During the sub-image providing step S12, a plurality of initial sub-images are provided. Each initial sub-image corresponds to at least a part of the image to be displayed on the retina of the eye.

[0104] In S14, multiple light beams are provided. The light beams are configured to be substantially focused at multiple corresponding different positions in the plane of the pupil of the eye, also referred to as "focus points". In the context 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, thus ensuring a clear display of the image on the retina.

[0105] Furthermore, each light beam is configured to carry an associated sub-image. In other words, each sub-image is carried by an associated light beam that is substantially focused in the plane of the pupil of the eye.

[0106] Thus, each focus point of the pupil acts as a micro-projector, emitting light towards the retina. The focusing of the multiple light beams at different positions in the plane of the pupil of the eye allows for an increase in the size of the eye movement box (EMB) and is the basis for pupil expansion.

[0107] An adapted head-mounted display device can be used to provide the light beams. In the context of the present invention, an adapted head-mounted display device is a head-mounted display device configured for displaying images, including at least providing multiple light beams, each carrying a sub-image, and the light beams being adapted to be substantially focused at multiple corresponding different positions in the plane of the pupil of the eye. For example, both US 2016 / 033771 A1 and WO 2018 / 091984 A1 disclose such adapted head-mounted devices.

[0108] In fact, the principle of operation of the head-mounted display device of US2016 / 033771 A1 is based on a micro-projector, the light emitted by which 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 Figure 2 and Figure 3 B of US2016 / 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 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.

[0109]

[0110] According to an embodiment, the present invention relates to a display device adapted to provide multiple light beams configured to be substantially focused at multiple corresponding different positions in the plane of the pupil of the eye, each light beam being configured to carry an associated sub-image and adapted to at least perform the following steps:

[0111] - Parameter providing step S10,

[0112] - Sub - image providing step S12,

[0113] - Display device providing step S14,

[0114] - Adaptation step S16, and

[0115] - Display step S18.

[0116] Thus, during the adaptation step S16, for each sub - image, the initial sub - image is adapted based on at least one of the provided optical parameters and the corresponding focal position of the beam configured to carry the sub - image to form an adapted sub - image.

[0117] Therefore, each sub - image is calculated according to the needs of the wearer, i.e., according to the eye prescription.

[0118] In fact, for the same image to be displayed on the retinas of different people's eyes, due to their different visual defects, these people will not perceive this image in the same way in the end.

[0119] For simplicity, let's consider that the image to be displayed includes a cross. Figure 5 Shows the resulting images seen by people with different visual defects in the case of displaying three clear sub - images and these sub - images being the same (i.e., crosses located at the same positions in each image). For simplicity, let's consider that the distances of three corresponding focal points from the pupil center are equal and the distances from each other are equal.

[0120] If a person is emmetropic, the person sees a single cross in his / her central vision, as Figure 5 shown on the left (Case A). However, if a person has myopia or hyperopia, the person sees three different crosses, as Figure 5 shown at the center of (Case B), and their relative distances are a function of their spherical lens prescription. Finally, if a person has astigmatism, the person also sees three different crosses, as Figure 5 shown on the left (Case C), and their relative horizontal and vertical distances are associated with their cylindrical lens prescription.

[0121] Therefore, each sub - image should be calculated according to the prescription of a person's eyes so that a person with a visual defect sees a single cross on his / her retina in the same way as an emmetropic person.

[0122] These differences can be regarding Figures 6 to 9To 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 relate to emmetropic eyes, while Figure 8 and Figure 9 relate to ametropic eyes, such as myopic eyes.

[0123] The optical system 16 is configured to substantially focus the light rays emitted by the micro-projector in the plane of the pupil 22.

[0124] 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 two points A' and B' are formed on the retina 24.

[0125] As Figure 7 shown above, when the optical axis Z2 of the eye 20 is offset with respect 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.

[0126] However, for a myopic eye as Figure 8 and Figure 9 shown, light from infinity is focused in the dashed plane 26 instead of on the retina. This dashed plane 26 is located in front of the retina 24 of the eye.

[0127] 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.

[0128] But when the optical axis Z2 of the eye is offset with respect 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.

[0129] 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 is no longer 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.

[0130] Of course, the same observation applies to people with hyperopia and astigmatism. Preferably, during the adaptation step S16, pre-compensation is performed on the relative positions of each sub-image in the image to be displayed. Adapting the relative position of the sub-image in the image to be displayed includes:

[0131] - Horizontal adaptation step S22, and

[0132] - Vertical adaptation step S24.

[0133] During the horizontal adaptation step S22, 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.

[0134] Similarly, during the vertical adaptation step S24, the vertical angular position of the sub-image carried by the associated light beam is adapted based on the provided optical parameter and the corresponding focusing position of the associated light beam.

[0135] In fact, referring to Figure 10 the schematic eye model shown above, the light ray guided by the wave vector k in in the half-space in front of the eye and impinging on the pupil 22 at point M in the plane (Oxy) is refracted by the phase function of the eye into the wave vector k out .

[0136] 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.

[0137] The coordinates (X, Y) of point P can be determined as follows:

[0138]

[0139] Where:

[0140] · d is the distance between the plane (Oxy) of the pupil and the retina, which is considered as the plane (ΩXY) for simplicity,

[0141] · (x, y) are the coordinates of point M in the plane of the pupil,

[0142] · (ka, kb, kc) are the coordinates of the wave vector k in , where k = 2π / λ, λ is the wavelength, and

[0143] · S eq = S + C / 2 where S is the maximum refractive power, C ≤ 0 is the astigmatism, and 0 ≤ θ ≤ 180° is the axis position.

[0144] Thus, in the paraxial approximation where d / c ≈ d, corresponding to the wave vectors k in,1 and k in,2The positional difference between two points P1 and P2 on the retina corresponding to two illuminated points M1 and M2 is expressed as:

[0145]

[0146] Thus, when two focal points M1 and M2 of the pupil are illuminated by two different light rays, the positional 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 positional difference between the focal points M1 and M2 on the pupil, rather than on the absolute positions of M1 and M2 on the pupil. Therefore, a simultaneous shift of the focal points M1 and M2 with the same incident light ray direction only results in an offset of P1 and P2 on the retina.

[0147] The focal position in the plane of the pupil of the eye can be determined for each light beam during a preliminary calibration step.

[0148] Furthermore, according to a preferred embodiment, the focal positions of the plurality of light beams are advantageously regularly spaced apart from each other in the plane of the pupil of the eye.

[0149] During the display step S18, each adapted sub - image carried by the associated light beam is displayed on the retina of the person.

[0150] The offset of all the pixels of each sub - image based on the optical parameters of the person's eye allows the sub - images from the plurality of focal points to be superimposed. The sub - images from the plurality of focal points are thus perceived by the person as a single clear image.

[0151] Figure 11 A method for displaying a clear image on the retina of the eye of a person with refractive error, such as a myopic person, is shown. In this example, let us consider that the image content to be displayed (represented by the Figure 10 box 30 in) includes two vertically aligned disks, one black and one white.

[0152] Furthermore, 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 box 46, and the second light beam carries the associated sub - image represented by the box 48.

[0153] Each sub - image is calculated and adapted according to the prescription of the person's eye and the corresponding focal position of the light beam. Thus, the content of the first and second images and the second sub - image 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.

[0154] The adapted sub-images can be displayed sequentially or simultaneously on the retina of a person.

[0155] According to another embodiment compatible with the foregoing embodiments, the wavelength of at least one of the plurality of light beams is different from the wavelength of at least another of the plurality of light beams. Preferably, the wavelengths are very close to each other such that a person cannot perceive a difference in the image color.

[0156] 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 image to be displayed on the retina of the user based on the prescription of the user's eyes in order to display a clear image on the retina of the user.

[0157] 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 eyes determined by the same head-mounted device.

[0158] As indicated above, this 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 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.

[0159] To this end, a computer program product can be stored in the memory of the 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.

[0160] Although in the previous embodiments of the display method, the optical parameters related to the prescription of a person's eyes can be advantageously pre-measured and provided by an eye care practitioner during the parameter providing step S10 or stored on the memory of the head-mounted device, the optical parameters related to the prescription of a person's eyes can be advantageously provided by determining them using the same adapted head-mounted device. In fact, referring to Figure 12 , this method for determining the optical parameters of a person's eyes at least includes the following steps:

[0161] - A display step S32,

[0162] - An adaptation step S34, and

[0163] - A determination step S36.

[0164] During the display step S32, three clear images carried by three light beams are displayed on the retina of a person's eye. In other words, each clear image is carried by an associated light beam that is substantially focused in a plane of the pupil of the eye.

[0165] These three light beams are substantially focused at different positions in the plane of the pupil of the eye, also referred to as "focal points".

[0166] Thus, each focal 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 pupil of the eye allows for an increase in the size of the eye movement box (EMB) and is the basis for pupil expansion.

[0167] This display step S32 can be implemented using a head-mounted display device as disclosed in US 2016 / 033771 A1 or WO 2018 / 091984 A1.

[0168] Each of the three images displayed during the display step S2 includes a target. The target is a point or a one-dimensional image or a two-dimensional image. The target is, for example, a symbol or a symbol similar to a cross, as Figure 5 shown above.

[0169] Then, during step S34, the parameters of the target in each image are adapted based on the person's feedback related to the parameter changes of the target in each image.

[0170] Referring to equation (6) and as previously disclosed, 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 between the focal points M1 and M2 on the pupil, and does not depend 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 ray direction only results in the offset of P1 and P2 on the retina.

[0171] To this end, in each iteration, the parameters of the target in each image are modified, and the person provides his / her feedback related to this change.

[0172] The person's feedback is preferably acoustic feedback, for example, provided by answering a question, such as asking whether the targets projected on his / her retina from one iteration to the next are closer to or farther from each other, or asking other similar questions.

[0173] In addition, the person's feedback can be tactile feedback.

[0174] Advantageously, the adapted parameter of the target is preferably the relative position of the target in each image. In this case, the step S34 of adapting the parameter 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.

[0175] 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 the other light beam have the same horizontal position in the display image on the eye retina.

[0176] 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 the other light beam have the same vertical position in the display image on the eye retina.

[0177] Thus, during the implementation of steps S42 and S44, when the person is asked whether the two points of the target projected on his retina from one iteration to the next are closer or farther from each other, the horizontal and vertical angular position values of the target in the image change according to the person's response at each iteration until the person sees the two targets superimposed, that is, 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 center of a cross-like symbol.

[0178] For example, the cross can be offset pixel by pixel in the horizontal and / or vertical direction at each iteration.

[0179] Advantageously, this method does not require the eye 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.

[0180] According to a preferred embodiment, the display step S32 and the adaptation step S34 can be performed sequentially, that is, for two of the three light beams, and then repeated when adding the third light beam. In fact, during the display step S32, first two clear images carried by two light beams are displayed on the retina of the person's eye. For these two images, during step S34, based on the person's feedback related to the parameter change of the target in each image, the parameter of the target in this image is adapted, preferably until the person sees that the targets of the two images have the same position in the display image on the eye retina. Then, a third clear image carried by the third light beam is also displayed on the retina, and during step S34, based on the person's feedback related to the parameter change of the target in the third image, the parameter of the target in this image is adapted, 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 display image on the eye retina.

[0181] During the determination step S36, the optical parameters of the human eye are determined based on the adaptation of the parameters of the target in each image.

[0182] In fact, based on the changes in the horizontal and vertical angular positions of the target in the image required for the person to see only one cross, the optical parameters of the human eye can be determined.

[0183] In other words, based on the differences in the horizontal and vertical directions between the initial and final angular positions 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 human 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.

[0184] In fact, once (a 1 , b 1 ) and (a 2 , b 2 ) 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.

[0185] The position of the focal point can be predetermined during the calibration step.

[0186] For example, let's consider a person suffering from 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).

[0187] Using a model that allows relating the prism deviation (in prism diopters (Δ)) and the spherical error, such as Prentice's law, the angular deviation perceived by the person between the crosses 'i' and 'j' in the horizontal and vertical directions can be expressed as:

[0188]

[0189] where:

[0190] - d h (i,j) is the horizontal distance (in mm) between the focal point of the displayed cross 'i' and the focal point of the displayed cross 'j';

[0191] - d v(i,j) is the vertical distance (expressed in mm) between the focus point displaying cross 'i' and the focus point displaying cross 'j'.

[0192] Thus, if an offset of n h (i,j) pixels of cross 'j' is necessary for superimposing cross 'i' and 'j' in the horizontal direction, and an offset of n v (i,j) pixels of cross 'j' is necessary for superimposing cross 'i' and 'j' in both the horizontal and vertical directions, and knowing the angular size of pixel dP Δ (which is a construction parameter), the angular deviation between cross 'i' and 'j' perceived by a person in both the horizontal and vertical directions can also be expressed as:

[0193]

[0194] According to equations (7) and (8), the spherical error S and cylindrical error C for a person's eye are determined.

[0195] Of course, this determination can be extended to prescriptions with non-zero cylindrical axis positions.

[0196] Similarly, models other than Prentice's law can also be used to determine the optical parameters of a person's eye.

[0197] Although in this embodiment for determining the optical parameters related to the diopter and astigmatism 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 pupil of the eye, 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 pupil of the eye, thereby allowing for a more accurate determination of the optical parameters related to its prescription.

[0198] Furthermore, if the cylinder is empty, determining only the sphere requires displaying two clear images on the retina of the eye, and these two clear images are carried by two light beams focused on two different points in the plane of the pupil of the eye.

[0199] Of course, although in this embodiment, the distances of the focus points from the center of the pupil are equal and the distances from each other are equal, this method can be extended to other display devices configured to display multiple clear images on the retina of the eye and where the distances of the focus points from the center of the pupil of the eye are not equal and / or the distances from each other are not equal, and these 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 focus points should be determined in advance during the calibration step.

[0200] ReferenceFigure 13 , another embodiment of the determination method differs 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.

[0201] In this case, step S34 for adapting the parameter of the target in each image includes step S46 for adapting in the horizontal direction and step S48 for adapting in the vertical direction.

[0202] 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 target of this image seen by a person contacts the target of another image carried by another light beam horizontally in the display image on the retina of the eye.

[0203] 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 target of this image seen by a person contacts the target of another image carried by another light beam vertically in the display image on the retina of the eye.

[0204] Similar to the aforementioned method, this determination method is preferably implemented using a head-mounted device suitable for displaying a plurality of clear images at least on the retina of a person's eye, and the plurality of images are carried by a plurality of light beams substantially focused at different positions in the plane of the pupil of the eye.

[0205] In the same way, a computer program product can be stored in the memory of a head-mounted display device, and the computer program product includes one or more stored instruction sequences that can be accessed by the processor of the head-mounted display device and, when executed by the processor, cause the processor to execute the steps of the method according to the present invention and as described above.

[0206] The method according to the present invention advantageously allows customizing the head-mounted display device according to the viewing ability of the user. In fact, this method allows pre-compensating the images to be displayed on the retina of the user based on the prescription of the user's eyes in order to display clear images on the retina of the user, thereby ensuring the use of a head-mounted display device optimized for the user.

[0207] Therefore, 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 eyes determined by the same head-mounted device.

[0208] The present invention has been described above by means of embodiments without limiting the general inventive concept.

[0209] Many further improvements and variations can be proposed by those skilled in the art who have referred 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.

[0210] 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 used to advantage. Any reference signs in the claims should not be construed as limiting the scope of the present invention.

Claims

1. A method for displaying a clear image on the retina of a human eye, the human having a prescription for the human eye, the method being adapted to a see-through head-mounted device and comprising: - providing at least one optical parameter related to the prescription for the human eye; - providing a plurality of initial sub-images, each initial sub-image corresponding to at least a part of an image to be displayed; - providing a plurality of light beams, the plurality of light beams being 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, adapting the sub-image based on the provided at least one optical parameter and a corresponding focusing position of the light beam configured to carry the sub-image to form an adapted sub-image, wherein adapting the sub-image includes adapting a relative position of the sub-image in the image to be displayed; and - displaying each adapted sub-image carried by an associated light beam on the retina of the human, wherein providing at least one optical parameter related to the prescription for the human eye includes: - displaying at least two clear images on the retina of the human eye, the at least two clear images being two-dimensional symbols and carried by two light beams substantially focused at at least two different positions in a plane of the pupil of the eye; - adapting parameters of the two-dimensional symbols in the images based on feedback of the human related to parameter changes of the two-dimensional symbols in each image; and - determining the at least one optical parameter of the human eye based on the adaptation of the parameters of the two-dimensional symbols in each image.

2. The method according to claim 1, wherein adapting the relative position of the sub-image in the image to be displayed includes: - adapting a horizontal angular position of the sub-image carried by an associated light beam based on the at least one provided optical parameter and a corresponding focusing position of the associated light beam; and - adapting a vertical angular position of the sub-image carried by an associated light beam based on the at least one provided optical parameter and a corresponding focusing position of the associated light beam.

3. The method according to any one of the preceding claims 1 to 2, wherein the method further includes determining a focusing position in a plane of the pupil of the eye for each of the plurality of light beams.

4. The method according to claim 3, wherein the focusing positions of the plurality of light beams are regularly spaced apart from each other in a plane of the pupil of the eye.

5. The method according to claim 3, wherein the adapted sub-images are sequentially displayed on the retina of the human.

6. The method according to claim 3, wherein the adapted sub-images are simultaneously displayed on the retina of the human.

7. The method according to claim 3, wherein a wavelength of at least one of the plurality of light beams is different from a wavelength of at least one other of the plurality of light beams.

8. The method according to claim 7, wherein the wavelengths of the plurality of light beams include a narrow wavelength band of 50 nm wide.

9. The method according to claim 3, wherein, at least three optical parameters related to the prescription for the person's eye are provided.

10. The method according to claim 3, wherein, the at least one provided optical parameter of the person's eye is related to the diopter, astigmatism and axis position of the person's eye.

11. A perspective head-mounted device, the device being adapted to provide a plurality of light beams, the plurality of light beams being configured to be substantially focused on 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 and being adapted to at least perform the steps of the method according to claim 1.

12. A computer program product, the computer program product comprising one or more stored sequences of instructions, the one or more sequences of instructions being accessible by a processor and, when executed by the processor, causing the processor to use the device according to claim 11 to at least perform the steps according to claim 1.

13. A computer-readable medium, the computer-readable medium carrying one or more sequences of instructions of the computer program product according to claim 12.

Images