Systems and methods for determining refractive characteristics of a first eye and a second eye of a subject

Abstract

The invention relates to a system (100) for determining the refractive characteristics of a first eye and a second eye of a subject. According to the invention, the system (100) comprises a light field display device (60), a positioning system (6) for positioning the position of the first eye and the second eye of the subject (10), a control unit, the light field display device being configured to generate a first light field (71) selectively directed to the first eye (1) and a second light field (72) selectively directed to the second eye (2) respectively, the control unit being adapted to adjust the first light field as a function of at least a first refractive parameter associated with at least a first optical aberration of the first eye, and the control unit being adapted to adjust the second light field as a function of at least a second refractive parameter associated with at least a second optical aberration of the second eye.

Description

Technical Field

[0001] The present invention relates to a system and method for determining the refractive correction of a subject's eye. Background Art

[0002] Many documents describe apparatus and methods for objectively or subjectively determining the refractive characteristics of a subject's eye under monocular or binocular vision conditions.

[0003] Objective refraction is usually obtained using a retinoscope or an autorefractometer. Objective refraction allows the approximate correction for an individual to be determined quickly.

[0004] However, subjective refraction is the method of choice for determining the optimal refractive correction required by a subject. Conventional subjective refraction is obtained using a set of trial lenses and trial frames or using a phoropter with a manual or automated lens changer. These devices typically use lenses whose power changes in steps of 0.25 diopters (D). The Essilor Vision R800 phoropter uses active optical lenses, allowing for continuous power change.

[0005] Document WO 2018 / 104600 (Essilor Int.) discloses a phoropter for measuring the subjective spherical and / or cylindrical refraction of an eye with high resolution. The phoropter comprises a conventional refractive optical system having an optical power that varies in minimum steps, combined with a display device, for example comprising a light field display device, adapted to vary its optical power in steps smaller than a predetermined minimum step size.

[0006] Other documents disclose systems for providing correction of previously identified vision defects based on light field display devices.

[0007] For example, document US 2017 / 0060399 discloses a vision correction system based on a graphical user interface and a graphical display, which displays a corrective image that at least partially compensates for a subject's decreased visual acuity. However, this system does not provide accurate refractive measurement. Document US 2016 / 0042501 A1 also discloses a vision correction display with aberration compensation, which calculates an aberration-compensated image displayed using a light field element based on previously determined optical aberration parameters of the viewer. Document WO 2018 / 091984 A1 discloses a sequential light field projector close to the eye that projects a series of light field components into each eye of the viewer, forming a retinal image that is always focused, so that the viewer perceives monocular depth cues, thereby providing a depth illusion. Documents US 2014 / 0327750 and US 2014 / 0327771 disclose systems and methods for displaying a scene as a light field.

[0008] However, these documents do not disclose methods or apparatus for accurately measuring the refraction of a subject's eye (particularly in binocular vision) or for correcting the refraction of a viewer.

[0009] Having a well-corrected binocular image is indeed important to provide accurate refractive measurements, because monocular refraction may cause accommodation, and binocular refraction without distinguishing between right and left eye refraction cannot handle the very common anisometropia (or binocular disparity between the two eyes).

[0010] Therefore, there is a need for a system and method that can accurately and subjectively determine the refractive correction for each eye under binocular vision conditions to provide him / her with the most comfortable vision correction without the use of additional lenses. Summary of the Invention

[0011] Therefore, an object of the present invention is to provide a system for determining refractive characteristics of a first eye and a second eye of a subject, the system comprising a light field display device having a three-dimensional reference system, a positioning system for positioning the first eye and the second eye of a subject viewing the light field display device relative to the reference system, and a control unit for driving the light field display device, the light field display device being configured to generate a first light field selectively directed toward the first eye of the subject, the first light field being suitable for forming a first image on the first eye of the subject, the control unit being suitable for adjusting the first light field according to at least a first refractive parameter associated with at least a first optical aberration of the first eye, so that the first image is perceived by the first eye. The control unit is adapted to determine the refractive characteristic of the first eye according to the first adjustment value of the first refractive parameter, and the light field display device is configured to generate a second light field selectively directed toward a second eye of the subject, the second light field being adapted to form a second image on the second eye of the subject, the control unit being adapted to adjust the second light field according to at least a second refractive parameter associated with at least a second optical aberration of the second eye, so that the second image is perceived by the second eye as being corrected for the second adjustment value of the second refractive parameter, and the control unit being adapted to determine the refractive characteristic of the second eye according to the second adjustment value of the second refractive parameter.

[0012] The light field display-based system is capable of determining the refractive characteristics of a subject's first and second eyes in monocular or binocular vision without the use of additional lenses and without mechanically moving parts.

[0013] According to some embodiments, the light field display device includes a single screen, and the first light field and the second light field are generated alternately and sequentially by the same area or by two different areas of the light field display device.

[0014] According to another embodiment, the light field display device includes a first screen adapted to generate a first light field selectively directed toward the first eye of the subject and a second screen adapted to generate a second light field selectively directed toward the second eye of the subject.

[0015] According to a particular and advantageous aspect, the system comprises a user interface adapted to record a first response of the subject with respect to a first sharpness of the first image perceived by the first eye and a second response of the subject with respect to a second sharpness of the second image perceived by the second eye, and the control unit is adapted to adjust the first and second light fields, respectively, depending on the recorded first and second responses.

[0016] In a particular embodiment, the user interface is adapted to input values ​​of the first and second refractive parameters, and the control unit is adapted to adjust the first and second light fields, respectively, according to the input values ​​of the first and second refractive parameters.

[0017] According to another particular aspect, the system comprises means for selectively blocking the first light field towards the second eye and / or selectively blocking the second light field towards the first eye.

[0018] According to yet another specific aspect, the light field display device includes a digital display or a multi-layer liquid crystal display device, the digital display including a pixel array and a parallax barrier mask stacked on the pixel array.

[0019] The parallax barrier mask may be selected from a pinhole array, a lenslet array, a microlens array, a lenticular lens array, and a lenticular lens.

[0020] According to another aspect, the light field display device includes a liquid crystal display (LCD) with directional backlighting.

[0021] According to another aspect, the positioning system includes an eye tracker, a 3D scanning device, a camera, a time-of-flight sensor and / or a pupil size measurement device.

[0022] The positioning system may be adapted to determine pupil diameter and / or eye gaze direction.

[0023] According to one embodiment, the first light field and the second light field are predetermined such that the first image and the second image comprise at least one common visual stimulus, enabling the subject to fuse the first image and the second image.

[0024] Another object of the present invention is to provide a method for determining the refractive characteristics of both eyes of a subject, the method comprising the steps of:

[0025] a) locating a position of a first eye of the subject relative to a three-dimensional reference system of a light field display device and a position of a second eye relative to the three-dimensional reference system;

[0026] b) generating, using the light field display device, a first light field selectively directed toward a first eye of the subject, the first light field being adapted to form a first image on the first eye of the subject;

[0027] c) adjusting the first light field according to at least a first refractive parameter associated with at least a first optical aberration of the first eye, such that the first image is perceived by the first eye as corrected for a first adjusted value of the first refractive parameter;

[0028] d) determining a refractive characteristic of the first eye according to a first adjustment value of the first refractive parameter;

[0029] e) generating, using the light field display device, a second light field selectively directed toward a second eye of the subject, the second light field being adapted to form a second image on the second eye of the subject;

[0030] f) adjusting the second light field according to at least a second refractive parameter associated with at least a second optical aberration of the second eye, such that the second image is perceived by the second eye as corrected for a second adjusted value of the second refractive parameter;

[0031] g) determining the refractive characteristic of the second eye according to the second adjustment value of the second refractive parameter.

[0032] According to certain aspects, steps b) to c) and steps e) to f) are respectively performed in a time sequence, and during steps b) to c), the second light field is closed or blocked toward the second eye, and during steps e) to f), the first light field is closed or blocked toward the first eye.

[0033] According to another specific aspect, steps b) to c) and steps e) to f) are respectively performed simultaneously.

[0034] In one embodiment, the method comprises an operation according to claim 12 for a first eye in monocular vision and another operation according to claim 12 for a second eye in monocular vision, and an operation according to claim 13 for both the first eye and the second eye in binocular vision.

[0035] According to a particular embodiment, the method further comprises the following steps:

[0036] h) recording a first response of the subject relative to a first sharpness of a first image perceived by the first eye, and

[0037] i) recording a second response of the subject relative to a second sharpness of a second image perceived by the second eye, and

[0038] During step c), the first light field is adjusted according to the first response recorded during step h), and during step f), the second light field is adjusted according to the second response recorded during step i).

[0039] According to certain aspects, the refractive characteristic(s) to be determined include spherical, cylindrical and axial positions, downlight addition values ​​and / or higher order aberrations for the subject's first and second eyes under monocular and / or binocular conditions.

[0040] According to another particular aspect, the first light field and the second light field are predetermined such that the first image and the second image have at least one common feature enabling fusion of the first image and the second image when viewed by the subject.

[0041] According to yet another particular aspect, the first light field is displayed at a first distance from the first eye and the second light field is displayed at a second distance from the second eye, the first distance and the second distance being adjusted according to an interpupillary distance between the first eye and the second eye. BRIEF DESCRIPTION OF THE DRAWINGS

[0042] The following description, with reference to the accompanying drawings, will make clear what the present invention encompasses and how it is accomplished. The present invention is not limited to the embodiments shown in the accompanying drawings. Accordingly, it should be understood that where features in the claims are followed by reference numerals, the inclusion of such reference numerals is solely for the purpose of enhancing the intelligibility of the claims and is in no way intended to limit the scope of the claims.

[0043] Reference is now made to the following brief description, taken in conjunction with the drawings and detailed description, wherein like reference numerals refer to like parts.

[0044] In the attached figure:

[0045] - Figure 1 shows the light characteristics of a conventional 2D image;

[0046] - Figure 2 shows the light properties of a 3D light field;

[0047] - Figure 3 shows the light properties of a 4D light field;

[0048] - Figure 4 shows the light properties of another 4D light field;

[0049] - Figure 5 shows a side view of a first type of light field display device according to the prior art;

[0050] - Figure 6 shows a side view of a second type of light field display device according to the prior art;

[0051] - Figure 7 schematically illustrates a top view of a first embodiment of a system for determining refractive characteristics of an eye of a subject;

[0052] - Figure 8 Schematically illustrating an exemplary system according to a first embodiment;

[0053] - Figure 9 An image of a visual stimulus as viewed by the subject is shown;

[0054] - Figure 10 schematically illustrates a top view of a second embodiment of a system for determining refractive characteristics of an eye of a subject;

[0055] - Figure 11 An exemplary method for searching a sphere according to the present disclosure is presented;

[0056] - Figure 12 shows two images generated in a method for determining the axis of astigmatism according to the present disclosure;

[0057] - Figure 13 Two images generated in a method for determining axis and cylinder of astigmatism according to the present disclosure are shown. DETAILED DESCRIPTION

[0058] In the following description, the drawings are not necessarily drawn to scale, and for the purpose of clarity and brevity or for information purposes, certain features may be shown in generalized or schematic form. In addition, although the manufacture and use of a plurality of different embodiments are discussed in detail below, it should be understood that many inventive concepts that can be implemented in a variety of environments are provided as described herein. The embodiments discussed herein are merely representative and do not limit the scope of the invention. It will also be apparent to those skilled in the art that all technical features defined relative to the method can be transposed to the device alone or in combination, and conversely, all technical features defined relative to the device can be transposed to the method alone or in combination.

[0059] The present disclosure relies on the use of light field display technology to perform subjective refraction of a subject's eye without using an additional set of lenses as in conventional phoroptors.

[0060] definition

[0061] In this document, a light field (LF) is a vector function that describes the amount of light flowing through each point in space in each direction. The amount of light is, for example, luminance (cd / m2 ), which represents the optical power of the surface as a whole over the solid angle.

[0062] Light field displays (LFDs) are a new type of display that is coming to market.

[0063] Conventional display devices generate 2D images where the light characteristics depend on the position (x, y) of each point in the image 3 (see Figure 1 ).

[0064] In contrast, a light field display device (or LFD) generates a light field and can control the amount of light not only according to the position (x, y) but also according to at least one direction. Some light field displays generate 3D light fields where the amount of light depends on the position (x, y) and one direction (u) in the image 4 (see Figure 2 ). Generating a 3D light field (x, y, u) is also called 1D integral imaging. Other light field display devices generate a 4D light field, where the amount of light depends on the position (x, y) in the image 5 and the two lateral directions (u, v) (see Figure 3 Generally speaking, the direction of vector u is in the horizontal plane, and the direction of vector v is in the vertical plane. Generating a 4D light field (x, y, u, v) is also called integral imaging. Light field displays typically control the position and direction of each color (e.g., RGB or red-blue-green in a three-color display).

[0065] Ideally, the light field display is like a window and is able to transmit light from each point of the image 5 in an independent direction (see Figure 4 ).

[0066] Different kinds of light field display devices can be used.

[0067] Figure 5 A side view of a known light field display device 60 is shown, comprising a high resolution display panel 20 and a parallax barrier 30. The display panel 20 comprises pixels 21, 22, ... which can be addressed individually. The display panel 20 may comprise a row of pixels, or more generally, a 2D array of pixels. Figure 5 In the example shown, pixels are positioned at a constant spacing (labeled as p) along the X axis in an orthogonal reference system (X, Y, Z). Figure 5 As shown, parallax barrier 30 comprises a plate arranged parallel to the surface of the display panel 20 at a distance designated f from the surface of the display panel 20. The plate includes a plurality of pinholes 31, or micro-apertures, arranged along the X-axis at a pitch designated Δx. Typically, the pixel pitch p is much smaller than the pitch Δx of the pinhole array. Depending on the addressed pixel, the light field passing through the pinholes has a specific vector u relative to the normal of the display panel 20. As a result, LFD 60 generates a 3D light field anywhere in the half-space above the micro-apertures 31. Figure 5 An image plane 50 is shown, which is parallel to the light field display device 60, at a distance l from the parallax barrier 30. The image plane 50 is used for a 4D representation of the light field beams. Each light field beam can be represented by a set of four coordinates (x, y, u, v), where (x, y) represent the coordinates in the plane of the pinholes and (u, v) represent the coordinates in the plane 50 at a distance l. The light field generated depends on the position of the activated pixels. In the plane 50, the distance Δu between two light rays generated by adjacent pixels through the same pinhole depends on the pixel pitch p and the distance f between the display panel and the parallax barrier. Likewise, the maximum aperture of the light field has an angle θ that depends on the pinhole pitch Δx and the distance f. MAX This angle θ MAX Determine using the following formula:

[0068] as well as

[0069] Derived from

[0070] Other types of parallax barriers 30 can be used instead of a pinhole array. For example, the LF can be projected directly into the pupil of the eye by creating virtual pinholes. Each virtual pinhole is associated with a specific source that is turned on separately. For each virtual pinhole, all directions are driven by a spatial light modulator (SLM).

[0071] Figure 6 A side view of another known light field display device 60 is shown, which includes a high-resolution display panel 20 in combination with a lenslet array 40. The lenslet array 40 includes an array of microlenses 41, 42, 43, ..., which are placed near the display panel 20. For example, the lenslet array 40 is arranged on top of the display panel 20. The spacing between the microlenses is marked as Δx, along the X-axis. Depending on the addressed pixel 21, the light field passing through the microlenses 44 has a specific vector u. As a result, the LFD 60 generates a 3D light field in an image plane 50 parallel to the LFD and at a distance l from the lenslet array 40. The generated light field depends on the position of the activated pixel.

[0072] Of course, the above-described light field display device can be operated in a similar manner along direction Y, with a 2D pixel array and a 2D pinhole array, or correspondingly, a 2D grid of reflective surfaces, or a 2D lenslet array, for generating a 4D light field.

[0073] A light field display device is capable of controlling the direction of light rays originating from a point in an image. Therefore, the light field display device can control the position and direction of each light ray forming the light field, without requiring an additional lens with a variable focusing distance. As a result, it is possible to virtually display images at various distances using only the light field display device at a constant distance from the subject's eyes. More precisely, the light field display device 60 is capable of forming images at controlled distances from the light field display device.

[0074] However, a parallax barrier LFD or a lenslet array LFD generally trades off between spatial resolution and angular resolution.

[0075] The properties of the light field can be used to correct for refractive errors in the subject's eye.

[0076] Consider a light field generated using any of the aforementioned types of light field display devices, using parallel light beams. The subject's eye is relaxed. A visual stimulus is displayed at infinity. When the subject's eye is emmetropic, the image (e.g., a point) formed by the emmetropic eye through the cornea, pupil, and lens is focused on the subject's retina. Therefore, the retinal image of the source point is focused on the point on the retina and is perceived clearly. In contrast, when the subject's eye is relaxed but affected by myopia, the image (e.g., a point) formed by the myopic eye (or short-sighted eye) is focused on a point in front of the subject's retina. Therefore, for the myopic eye receiving the light field of parallel light beams, the retinal image of that point is spread out over an area and is perceived vaguely. For example, a light field display device can be used to generate a light field of diverging light beams to compensate for the aberrations of a myopic eye. Then, when the myopic eye is relaxed, the image (e.g., a point) formed by the myopic eye is focused on the subject's retina 19. Therefore, the retinal image of that point is perceived clearly by the myopic subject.

[0077] Similarly, for a subject with a relaxed hyperopic eye, an image of a point formed using a light field with parallel beams is focused behind the subject's retina. Knowing the hyperopic power value, a light field with converging beams can be generated to compensate for the aberrations of the hyperopic eye. Then, when the hyperopic eye is relaxed, the image (e.g., of the point) formed by the LF with converging beams is focused on the subject's retina. Consequently, the retinal image of the point is clearly perceived by the hyperopic subject.

[0078] More generally, knowing the eye's refractive error allows for the generation of a light field that will be focused by the eye. Using a light field display, it is possible to generate light fields corresponding to different ocular aberrations along different directions (e.g., along the X and Y directions). Thus, not only can spherical error be compensated for, but also astigmatism, thereby knowing the eye's axial orientation and the amount of astigmatic error (or cylindrical error).

[0079] This may also include higher-order aberrations (HOAs). Thus, the generated light field is optimized to form a sharp image on the retina (improved deconvolution with more degrees of freedom).

[0080] The present disclosure proposes using a light field display device, but rather than correcting or compensating for a subject's eye defects, it instead poses an inversion problem and subjectively determines the refractive error of the subject's eye, particularly under binocular vision conditions, while being able to distinguish the refractive properties of the right eye from the left eye.

[0081] Device

[0082] To this end, we propose a light field display device capable of providing different light fields for the right and left eyes. According to this disclosure, the light field display device displays independent light fields to each eye. This, in turn, enables binocular testing of the eyes while distinguishing the refractive properties of the right and left eyes, without the need for additional lenses.

[0083] Figure 7 A top view of a first embodiment of a system 100 for determining refractive characteristics of a first eye and a second eye of a subject is schematically illustrated.

[0084] Figure 7 The system 100 includes a light field display device 60, a control unit 80, and a positioning system 6 for locating the respective positions of a first eye 1 and a second eye 2 of a subject 10. In the present application, the positioning system 6 also determines the pupil center and pupil diameter of the first eye 1 and the second eye 2, respectively. The positioning system 6 can accurately determine which light rays enter each eye.

[0085] The light field display device 60 may include a high resolution screen in combination with the above-described pinhole array or lenslet array.Other types of light field display devices are contemplated without departing from the scope of this disclosure.

[0086] exist Figure 7 、 Figure 8 、 Figure 10 and Figure 11 , a 3D orthogonal reference system XYZ relative to the light field display device 60 is shown. Generally, the light field display device 60 includes a screen surface located in an XY plane, with the Z axis being orthogonal to the surface of the LFD 60.

[0087] Positioning system 6 may include a camera and a time-of-flight sensor or a 3D sensor. Typically, positioning system 6 is attached to light field display device 60. For example, positioning system 6 detects a first direction 7 and measures a first distance between the center of the pupil of first eye 1 and positioning system 6. Similarly, positioning system 6 detects a second direction 8 and measures a second distance between the center of the pupil of second eye 2 and positioning system 6. Positioning system 6 and / or control unit 80 thereby derive the respective three-dimensional (3D) positions of the subject's first eye 1 and second eye 2 relative to the reference frame (X, Y, Z) of light field display device 60. For example, positioning system 6 transmits the 3D positions of the pupil centers of first eye 1 and second eye 2, respectively, to control unit 80. Advantageously, positioning system 6 also measures the pupil diameters of first eye 1 and second eye 2, respectively, and / or the interpupillary distance between first eye 1 and second eye 2. Positioning system 6 then transmits the measured pupil diameters and / or interpupillary distance to control unit 80. Positioning system 6 and / or control unit 80 may also derive the distances between light field display device 60 and first eye 1 and second eye 2, respectively.

[0088] In short, the control unit 80 receives or derives from the information transmitted by the positioning system 6 the position of the first eye 1 in 3D relative to the reference system (X, Y, Z) of the light field display device 60 and the position of the second eye 2 in 3D relative to the reference system.

[0089] In the first embodiment, Figure 7 and Figure 8 FIG shows a light field display device 60 comprising a first region 61 and a second region 62. The first region 61 and the second region 62 are spatially separated. The first region 61 and the second region 62 are generated by a single display screen, but correspond to different active pixels. Alternatively, the system comprises two separate light field display devices: a first light field display device generates a first light field, and a second light field display device generates a second light field. For example, in FIG. Figure 7In the case of a single display, first region 61 corresponds to the right half of the light field display device in front of first eye 1, and second region 62 corresponds to the left half of the light field display device in front of second eye 2. More specifically, control unit 80 addresses first region 61 of LFD 60 to generate a first light field 71 that is selectively directed toward first eye 1 of subject 10. Control unit 80 addresses second region 62 of LFD 60 to generate a second light field 72 that is selectively directed toward second eye 2 of subject 10. In this way, first eye 1 does not receive second light field 72, and second eye 2 does not receive first light field 71, without requiring an additional blocking device, such as an opaque wall, between the two eyes and the light field display device in the subject's sagittal plane. First light field 71 is shaped to be received only by first eye 1. Independent of first light field 71, second light field 72 is shaped to be received only by second eye 2.

[0090] Under monocular vision conditions, the control unit 80 and the LFD 60 can generate only one of the first light field 71 and the second light field 72. Alternatively, in monocular vision, the first light field 71 and the second light field 72 are generated simultaneously, with one of the first eye 1 and the second eye 2 being occluded. For example, the untested eye is occluded using a person's hand or a card placed in front of the occluded eye. According to another alternative, the first or second light field is directed toward the untested eye (in a monocular examination), and this light field is configured to illuminate the untested eye with a blurred image and relax the untested eye's accommodation.

[0091] Under binocular vision conditions, the first embodiment can simultaneously generate a first light field 71 and a second light field 72 , which are independent of each other.

[0092] exist Figure 7 In the example shown, in binocular vision, both the first eye 1 and the second eye 2 are fixated on a point far behind the LFD 60 screen. Figure 7The first eye gaze direction 11 and the second eye gaze direction 12 are shown, respectively, passing through the pupil centers of the first eye 1 and the second eye 2, and virtual images of these points. For far points, to achieve natural binocular vision, convergence needs to be adjusted based on the distance of the target. Knowing the eye positions and the target distance makes this calculation easy. Based on the desired natural convergence, two light fields 71 ​​and 72 are generated to simulate a virtual target at a given distance. For a point at infinite distance, the first eye gaze direction 11 and the second eye gaze direction 12 are approximately parallel to each other. In far vision, the virtual distance ranges from 4 meters to infinity. Using current approaches, the virtual distance is typically between 4 and 8 meters, for example, 6 meters, with the first eye gaze direction 11 and the second eye gaze direction 12 slightly converging. In near vision, the first eye gaze direction 11 and the second eye gaze direction 12 converge approximately on the same point or image. Furthermore, the light field display device 60 can be configured to generate images of points corresponding to reduced gaze directions in near or intermediate vision, incorporating a predetermined convergence angle between the two eyes. More generally, any distance and direction may be tested using the light field display device 60 .

[0093] Figure 8 An example of a system 100 for determining refractive characteristics of both eyes of a subject according to a first embodiment is shown. Figure 8 System 100 is based on a light field display device 60 comprising a high-resolution display screen 20 incorporating a microlens array 40. By selectively activating some pixels 23 in first and second regions 61, 62 while keeping other pixels 24 off, light field display device 60 generates two spatially separate light fields: a first light field 71 and a second light field 72 that provide different refractive characteristics for each eye. In the example shown, first eye 1 is myopic, and first light field 71 provides -1D spherical refractive correction, while second eye 2 is emmetropic, and second light field 72 provides no refractive correction. Here, some pixels 23 are on while others 24 are off, with different spacing between on and off pixels and / or different patterns of on and off pixels in first and second regions 61, 62. This enables the simultaneous generation of, for example, a first light field 71 of a diverging beam directed toward first eye 1 and a second light field 72 of a parallel beam directed toward second eye 2. Visual stimulation at a selected distance is generated simultaneously by first and second light fields 71, 72. The visual stimuli here are essentially dots for the first eye 1 and the second eye 2, in order to perform fusion under binocular vision conditions.

[0094] exist Figure 8The first eye movement frame 13 and the second eye movement frame 14 are shown above. The eye movement frames 13 and 14 correspond to the areas where the first eye 1 and the second eye 2 can see the stimulus, respectively. The eye movement frames 13 and 14 are spatially restricted so that the first eye 1 only sees the first stimulus generated by the first area 61, and the second eye 2 only sees the second stimulus generated by the second area 62. Figure 8 , three microlenses 41 in the first area 61 provide a first light field that enters the pupil of the first eye 1 , and four other microlenses 42 in the second area 62 provide a second light field that enters the pupil of the second eye 2 .

[0095] Figure 9 Shown in Figure 8 An exemplary visual stimulus as viewed by a subject under binocular vision conditions is shown. The two retinal images are fused, allowing subject 10 to clearly see the image of point 91 in the subject's visual field 90, with each eye receiving different and appropriate refractive correction. The stimulus image is formed by the superposition or fusion of the first stimulus and the second stimulus. For example, the stimulus image appears as a glowing point on a black background.

[0096] Figure 10 A schematic top view of a second embodiment of a system 100 for determining refractive characteristics of a first eye 1 and a second eye 2 of a subject 10 is shown. Instead of using two separate regions 61 and 62 of a light field display 60, a single light field region 63 is used to generate a first light field 71 and a second light field 72. In the second embodiment, the first light field 71 and the second light field 72 are generated in a temporally alternating manner, or in other words, sequentially. In a variation of the second embodiment, the first light field 71 and the second light field 72 can be generated using partially overlapping regions of the light field display.

[0097] Similar to the first embodiment, the positioning system 6 determines the positions of the first eye 1 and the second eye 2, which enables the control unit 80 and the light field display device 60 to selectively direct the first light field 71 to the first eye 1 of the subject 10 and the second light field 72 to the second eye 2 of the subject.

[0098] Under monocular vision conditions, for the second embodiment, only one of the first and second light fields is generated at a time. Therefore, only one eye receives the light field selectively directed to this eye without any blocking device.

[0099] In binocular vision, for the second embodiment, the first light field 71 and the second light field 72 are generated alternately, but the alternation is rapid. In other words, the first light field 71 and the second light field 72 are generated at an alternating frequency above a threshold between 20 Hz and 120 Hz to enable fusion of the images seen by the two eyes. For example, the stimulus may be an optotype.

[0100] method

[0101] We will now describe how an eye examination can be performed using system 100 for determining refractive characteristics of a subject's first and second eyes. Optometry is only part of a more comprehensive eye examination, and we will focus here on the refractive portion of distance vision and optionally near vision.

[0102] Using the system 100 for determining the refractive characteristics of a subject's first and second eyes according to any of the above-described embodiments to generate independent light fields selectively directed toward each eye, the disclosed method is capable of independently determining the appropriate refractive correction for each eye, whether under monocular or binocular vision conditions, and without the need for additional lenses.

[0103] The light field display device 60 is positioned in front of the subject's eyes. The working distance, or in other words, the distance between the subject's eyes and the surface of the light field display device 60, can vary greatly depending on the type of light field display device. Some light field displays are designed for very short working distances, such as 5mm to 50mm for AR / VR applications. Other light field displays are designed for short to medium working distances, such as 300mm to 600mm for smartphones or tablets. Still other light field displays can be designed for long working distances, such as in TV-like applications (2-5m).

[0104] For distance refraction measurements, it is important to display a virtual image close to infinity to reduce accommodation, regardless of the physical location of the light field display. This virtual image of the stimulus is also formed by the light field display.

[0105] According to the present disclosure, in order to selectively generate an appropriate light field directed toward each eye, it is necessary to accurately know the pupil diameter and position of each eye in the reference frame of the light field display device. The pupil diameter and position are used to estimate which light rays generated by the light field display device can be used to reach the eye pupil and which rays are not. This can be accomplished using the camera and time-of-flight sensor of positioning system 6 or using a 3D sensor, as described above.

[0106] If combined Figure 7 、 Figure 8 and Figure 10 The described system 100 for determining refractive characteristics of a first eye and a second eye of a subject is adapted to generate at least two independent light fields, i.e., one light field for each eye simultaneously or in a time-multiplexed manner. This setup is capable of processing two separate images (one for each eye) and two different corrections, i.e., a refractive correction specific to each eye.

[0107] Each light field 71, 72 is generated for a specific correction, such as sphere (Sph), cylinder and axis (Cyl and Axis), and ultimately higher-order aberrations (HOA). Each light field 71, 72 is generated based on the considered pupil diameter, the distance between the light field display device and the eye, the distance between the target virtual image and the eye, the characteristics of the screen, and the target image on the retina. For example, different models based on ray tracing can be used to simulate the light field. For the desired image on the retina, the ray tracing model is used to propagate all rays that form the image of a given defect in the eye back to the LFD, and the corresponding generated rays are selected.

[0108] As an illustration, we describe in detail herein the method for determining refraction in distance vision.

[0109] The method generally consists of several stages, labeled A, B, and C, which are described in detail below. For stages A and B (respectively), testing is performed on the left or right eye under monocular vision conditions, and then stages A+B are performed on the other eye. For stage C, testing is performed under binocular vision conditions.

[0110] During monocular examination, the untested eye may need to be occluded. During phases A and B, a light field may be made to illuminate both eyes and one eye (the eye not undergoing refraction measurement Rx) may be occluded, for example using a person's hand or a card in front of the occluded eye.

[0111] Alternatively, the light field can be made to illuminate only the eye being measured, while the other eye does not perceive the light field but only a dark background.

[0112] Alternatively again, another light field may illuminate the untested eye, which generates a blurred retinal image on the untested eye to relax accommodation.

[0113] According to yet another alternative, a first light field is displayed to the first eye as a first image, while a second light field is displayed to the second eye as a second image. More precisely, the first light field generates a first retinal image for the first eye, while the second light field generates a second retinal image for the second eye. The first and second light fields contain a portion of the first and second images that is commonly seen by both eyes, typically a peripheral portion. To test the first eye, only a specific portion of the first light field, typically at its center, includes an image of, for example, an optotype, while the center of the second light field is empty or lacks the specific portion or has significantly reduced contrast. The central portion is switched between the first and second light fields for testing the second eye, while the common peripheral portion remains unchanged. The combination of the first and second light fields enables the simulation of a common 3D object in the common portion of the images. This combination provides accommodation of the first and second eyes at a specific virtual distance corresponding to the common portion of the first and second images. Furthermore, because only one of the first or second light fields contains the other (typically central) portion of the first or second image, this specific portion is only seen by the eye being tested. Thus, the refraction of a single eye can be tested while both eyes are trying to accommodate at a predetermined accommodation distance.

[0114] Stage A. Spherical search (monocular)

[0115] It is recommended to apply and adopt the fog method. This well-known method consists in adding a refractive power (for example +1.50D) to the initial refractive value in order to form an image in front of the retina. This makes it possible to relax the accommodation. The initial refractive value is generally comprised between -20D and +20D. The initial refractive value is generated by the light field display device without the need for additional lenses. The additional fog value (for example +1.5D) is also generated by the light field display device without the need for additional lenses. The image is seen blurry and the visual acuity is low. The method then uses only the light field display device to gradually reduce this additional spherical lens in steps of, for example, 0.25D and finds the optimal acuity and stops when the acuity no longer improves. The spherical lens value is the highest value that gives the maximum acuity.

[0116] The fog method is simulated on one eye using a light field display device. The initial refraction, labeled (S0, C0, A0), can be determined from a previous refractive examination or obtained by another objective method, where S0 represents the initial refractive value, C0 is the initial cylindrical value, and A0 is the initial axial value. The light field display device generates a light field corresponding to a refraction of (S0+ΔS, C0, A0), where ΔS represents the variable refraction. ΔS is initially set to +1.50 diopters so as to generate a blurred image of the retina and relax the accommodation. The light field is then modified to gradually reduce ΔS and improve acuity until an optimal spherical value is determined. The optimal spherical value generally corresponds to a first image being clearly seen by the subject. Using a light field display device, the step size does not have to be 0.25D. The step size of ΔS can be lower than 0.25D. For example, in a light field display device including a display screen in combination with a parallax barrier or a lenslet array (such as Figure 5 and 6 In the case of (as shown), the minimum step size of ΔS depends on the pixel pitch p and the pinhole pitch or microlens pitch Δx of the display screen 20. If the refraction is purely spherical, this stage A is equivalent to changing the distance of the virtual image generated by the light field display device.

[0117] If there is no initial value, the full sphere is searched

[0118] In this case, the light field display is used to simulate a Badal optometer. In other words, the light field display is used to generate a virtual image closer to the eye and stops when the image is clearly visible, giving a first estimate of the spherical equivalent (SE = S + C / 2). For example, the image can be an optotype or a pattern image with fine detail.

[0119] Figure 11 An example is shown with a light field display 60 at a distance of 500 mm from the subject's eye 1. The light field display is configured to generate a light field corresponding to a +10D spherical diopter, or in other words, 100 mm behind the eye 1, so that the virtual image 51 is 600 mm in front of the light field display 60. This distance is gradually increased to infinity (position 52), whereupon the virtual image is located behind the screen (position 53) until it is again located in front of the LFD (position 54) between 0 and 400 mm. The method stops at a very clear first position, corresponding to a distance d that allows the determination of the optimal spherical value S using the simple relationship S = -1 / d.

[0120] Based on the principles of Badal's ophthalmometer, this method is able to relax accommodation even if the subject's refraction is unknown, while maintaining the same visible size of the image at different virtual distances.

[0121] Stage B. Cylindrical search (monocular)

[0122] A light field display device is used to determine the axial position value using a method equivalent to a cross-cylindrical lens.

[0123] Consider a light field display device 60 generating a light field 71 directed toward the eye 1 of a subject 10. In this case, light field 71 corresponds to diverging or converging light rays simulating spherical refraction S0 and cylindrical refraction C0 relative to an axial position A0. The resulting image can correspond to an optotype or a cloud of black dots. Typically, spherical refraction S0 is determined at the optimal SE found in stage A, as disclosed in stage A for far vision.

[0124] Phase B of this test involves changing the original axis position of the cylinder from its initial value (S0, C0, A0) and presenting to the same eye 1 an image of the same source with two different axis position values: A0+ΔA and A0-ΔA (ΔA depends on A0 and the selected cross-cylinder value of 0.25D or 0.50D). If A0 is the optimal value, the subject perceives the two images as having the same degree of blur. If not, A0 is changed to A in the preferred direction. The two images are presented to the same eye, one with A+ΔA and the other with A-ΔA, until the subject perceives both images as having the same degree of blur.

[0125] According to an exemplary embodiment, a light field display device alternately presents two different axial position values ​​(one image corresponding to A+ΔA and the other image corresponding to A-ΔA) to the same eye, with the alternation frequency being low enough so that the subject can perceive the changes in the displayed light field and compare their corresponding blur levels.

[0126] According to another exemplary embodiment, two different regions of a light field display device are used to simultaneously generate two images corresponding to two different axial position values ​​directed toward the same eye.

[0127] Figure 12 An example of two images 93 and 94 generated side by side in the field of view 90 of the subject 10 in monocular vision is shown. For example, image 93 corresponds to a region with a correction of (S0, C0, A0+ΔA), while image 94 corresponds to a region with a correction of (S0, C0, A0-ΔA). This allows the subject to compare and determine whether the two images 93 and 94 have the same degree of blur.

[0128] The light field display device is then used to determine the lenticular value using a method equivalent to a cross lenticular method.

[0129] This step of the test involves changing the original cylinder values ​​from the initial values ​​(S0, C0, A0) and presenting two different values: C0 + ΔC and C0 - ΔC. If C0 is the optimal value, the subject perceives both images as having the same degree of blur. If not, C0 is changed to C in the preferred direction. The two images are presented to the same eye, one with C + ΔC and the other with C - ΔC, until the subject perceives both images as having the same degree of blur.

[0130] According to an exemplary embodiment, a light field display device alternately presents two different cylindrical values ​​to the same eye (one image corresponding to C+ΔC and the other image corresponding to C-ΔC).

[0131] According to another exemplary embodiment, two different regions of a light field display device are used to simultaneously generate two images corresponding to two different cylindrical values ​​directed to the same eye.

[0132] Figure 13 An example of two images 95 and 96 generated side by side in subject 10's field of view 90 during monocular vision is shown. For example, image 95 corresponds to a region with a correction of (S0 - ΔC / 2, C0 + ΔC, A0), while image 96 corresponds to a region with a correction of (S0 - ΔC / 2, C0 - ΔC, A0). The spherical value is changed to S0 - ΔC / 2 to operate at a constant SE. This allows the subject to compare and determine whether the two images 95 and 96 have the same degree of blur.

[0133] Alternatively, a light field display device is used to simultaneously determine the axial position value and the cylindrical value.

[0134] The light field display device is configured to display N different corrections simultaneously. For example, the light field display device simultaneously generates multiple images corresponding to different corrections with varying axial values ​​and cylindrical values.

[0135] The initial value is defined here in the J0 / J45 reference system: [C0*cos(2*A); C0*sin(2*A)]=[X0; Y0].

[0136] The light field display device generates four images corresponding to four different choices: [X0+δ; Y0], [X0-δ; Y0], [X0; Y0-δ] and [X0; Y0-δ] where δ is a small step size (in diopters).

[0137] For each value of δ, subjects identified the preferred direction, or in other words, the image that was the less blurry of the four options.

[0138] Alternatively, the four different choices may correspond to the following: [X0+δ / √2; Y0+δ / √2], [X0-δ / √2; Y0-δ / √2], [X0-δ / √2; Y0+δ / √2], [X0+δ / √2; Y0-δ / √2].

[0139] In another example, a light field display device generates six images corresponding to six different selections:

[0140] [X0+δ*cos(0); Y0+δ*sin(0)], [X0+δ*cos(60°); Y0+δ*sin(60°)],

[0141] [X0+δ*cos(120°); Y0+δ*sin(120°)], [X0+δ*cos(180°); Y0+δ*sin(180°)],

[0142] [X0+δ*cos(240°); Y0+δ*sin(240°)] / [X0+δ*cos(300°); Y0+δ*sin(300°)].

[0143] For each δ value, subjects identified the preferred direction, or in other words, the image with the least blurriness among the six choices.

[0144] Alternatively, in the case of multiple choices, the subject's response may be collected automatically based on the detected gaze direction, for example using an eye tracker or camera of the positioning system 6. Typically, the level of the spherical lens S is adjusted by +0.25D for every -0.50D added to the cylinder value.

[0145] Other methods can be used to determine the axis position and cylinder values. In particular, if the initial values ​​are unknown, a complete search can be performed. For example, a light field display device generates a light field with a continuously varying cylinder (0.5D to 1.0D) along a variable axis position from 0 to 180 degrees, and the method is stopped when the subject determines the optimal focus position. Alternatively, a fixed cylinder value (0.5D) can be tested in the four main directions, such as in the four-quadrant method.

[0146] The sphericity can also be checked using a light field display device. For example, by displaying two images sequentially or simultaneously, one adding +0.25D and the other adding -0.25D to the found sphericity value, it can be checked whether the found sphericity is the maximum value that provides the best acuity.

[0147] Stage C. Binocular Optimization and Inspection

[0148] First, a light field display device generates separate views of the same test for each eye under binocular vision conditions. For example, a common portion of both images is used to fuse the images, while letters are presented only to the left eye and the same letters are placed in a different position for the right eye. The subject compares the clarity. If the clarity of the two views differs, the balance of the two spheres can be determined. This test is performed in distance vision, initially with a monocular refraction for each eye.

[0149] Here, the light field display device generates two light fields with the same image, with the two refractive errors previously found in the monocular vision of the right eye (SR, CR, αR) and the left eye (SL, CL, αL). This step enables the comparison of the clarity of the image seen by the two eyes in the same accommodation state. The light field display device then generates a light field with an additional spherical lens (for example, +0.5D) for both eyes. The subject is asked to compare the degree of blur of the two images. If the degree of blur is the same, no balance is required. If the degree of blur is different, +0.25D or +0.50D needs to be added to the eye that sees the less blurred image in order to balance the two eyes. The spherical lens values ​​of the two eyes are then reduced in steps of -0.25D to achieve maximum acuity.

[0150] Then, use the light field display device to conduct binocular or stereo testing.

[0151] Conventional binocular vision testing is typically performed by separating the images directed to the right and left eyes, for example using prisms, color filters, and / or polarization testing.

[0152] The ability of the light field display device to display two separate light fields for the left and right eye, respectively, is used here to examine stereoscopic performance with refraction.

[0153] More precisely, for an image at infinity, the last test and adjustment was + / - 0.25 D. A +0.25 D spherical addition for both light fields should blur the binocular vision, while a -0.25 D spherical addition value should not change the binocular vision at all.

[0154] Lightfield displays can also be used to determine refraction in near vision. For example, one approach is based on assessing a subject's accommodative range. The lightfield display is configured to display images at different distances with the refractive correction found in distance vision. The shortest distance at which visual acuity is maintained corresponds to the accommodative range. Generally speaking, the required downlight for near vision is approximately two-thirds of the accommodative range (in diopters).

[0155] Thus, the same light field display device is able to determine refraction in near vision.

[0156] Although representative methods and articles have been described in detail herein, those skilled in the art will appreciate that various substitutions and modifications can be made without departing from the scope of the disclosure as described and defined by the following claims.

Claims

1. A system (100) for determining refractive characteristics of a first eye and a second eye of a subject (10), the system comprising: - a light field display device (60) having a three-dimensional reference system; - a positioning system (6) for locating the three-dimensional position of a first eye and a second eye of a subject (10) viewing the light field display device (60) relative to the reference system; - a control unit (80) for driving the light field display device (60); - the control unit (80) and the light field display device (60) are configured to use the three-dimensional position of the first eye (1) relative to the reference system to generate a first light field (71) selectively directed towards the first eye (1) of the subject (10), the first light field (71) being adapted to form a first image on the first eye (1) of the subject (10), the control unit (80) being adapted to adjust the first light field (71) according to at least a first refractive parameter associated with at least a first optical aberration of the first eye, such that the first image is perceived by the first eye as corrected for a first adjusted value of the first refractive parameter, the control unit (80) being adapted to determine a refractive characteristic of the first eye according to the first adjusted value of the first refractive parameter, and The control unit (80) and the light field display device (60) are configured to use the three-dimensional position of the second eye relative to the reference system to generate a second light field (72) selectively directed to the second eye (2) of the subject (10), the second light field (72) being suitable for forming a second image on the second eye (2) of the subject (10), the control unit (80) being suitable for adjusting the second light field (72) according to at least a second refractive parameter associated with at least a second optical aberration of the second eye, so that the second image is perceived by the second eye as being corrected for a second adjusted value of the second refractive parameter, and the control unit (80) being suitable for determining the refractive characteristics of the second eye according to the second adjusted value of the second refractive parameter.

2. The system (100) according to claim 1, wherein The light field display device (60) comprises a single screen, and wherein the first light field (71) and the second light field (72) are generated by the same area or by two different areas of the light field display device (60).

3. The system (100) according to claim 1, wherein The light field display device (60) includes a first screen and a second screen, wherein the first screen is adapted to generate a first light field (71) selectively directed toward the first eye (1) of the subject (10), and the second screen is adapted to generate a second light field (72) selectively directed toward the second eye (2) of the subject (10).

4. The system (100) according to claim 1 or 2, comprising a user interface adapted to record a first response of the subject (10) relative to a first sharpness of the first image perceived by the first eye and a second response of the subject (10) relative to a second sharpness of the second image perceived by the second eye, and wherein, The control unit (80) is adapted to adjust the first light field (71) and the second light field (72) according to the recorded first response and the second response, respectively.

5. The system (100) according to claim 4, wherein The user interface is adapted to input values ​​of the first refractive parameter and the second refractive parameter, and wherein the control unit (80) is adapted to adjust the first light field (71) and the second light field (72) according to the input values ​​of the first refractive parameter and the second refractive parameter, respectively.

6. The system (100) according to claim 1 or 2, comprising means for selectively blocking the first light field (71) towards the first eye (1) and / or selectively blocking the second light field (72) towards the second eye (2).

7. The system (100) according to claim 1 or 2, wherein: The light field display device (60) comprises a digital display or a multi-layer liquid crystal display device, wherein the digital display comprises a pixel array and a parallax barrier mask stacked on the pixel array.

8. The system (100) according to claim 1 or 2, wherein: The positioning system (6) includes an eye tracker, a 3D scanning device, a camera, a time-of-flight sensor and / or a pupil size measurement device.

9. The system (100) according to claim 1 or 2, wherein: The positioning system (6) is suitable for determining the direction of eye gaze.

10. The system (100) according to claim 1 or 2, wherein The first light field (71) and the second light field (72) are predetermined such that the first image and the second image include at least one common visual stimulus, enabling the subject (10) to fuse the first image and the second image.

11. A method for determining refractive characteristics of both eyes of a subject (10), the method comprising the steps of: a) locating the three-dimensional position of the first eye (1) of the subject (10) relative to a three-dimensional reference system of a light field display device (60) and the three-dimensional position of the second eye (2) relative to the three-dimensional reference system; b) using a control unit (80) and the light field display device (60), generating a first light field (71) selectively directed toward the first eye (1) of the subject (10) using the three-dimensional position of the located first eye (1) relative to the three-dimensional reference system, the first light field (71) being suitable for forming a first image on the first eye (1) of the subject (10); c) adjusting the first light field (71) according to at least a first refractive parameter associated with at least a first optical aberration of the first eye, such that the first image is perceived by the first eye as corrected for a first adjusted value of the first refractive parameter; d) determining a refractive characteristic of the first eye according to a first adjustment value of the first refractive parameter; e) using the control unit (80) and the light field display device (60), generating a second light field selectively directed toward the second eye (2) of the subject (10) using the three-dimensional position of the located second eye (2) relative to the three-dimensional reference system, the second light field (72) being suitable for forming a second image on the second eye (2) of the subject (10); f) adjusting the second light field (72) according to at least a second refractive parameter associated with at least a second optical aberration of the second eye, such that the second image is perceived by the second eye as corrected for a second adjusted value of the second refractive parameter; g) determining a refractive characteristic of the second eye according to a second adjustment value of the second refractive parameter.

12. The method according to claim 11, wherein Steps b) to c) and steps e) to f) are respectively performed in time sequence, and wherein, during steps b) to c), the second light field (72) is closed or blocked toward the second eye (2), and wherein, during steps e) to f), the first light field (71) is closed or blocked toward the first eye (1).

13. The method according to claim 11, wherein Steps b) to c) and steps e) to f) are respectively performed simultaneously.

14. The method according to claim 11, comprising an operation according to claim 12 for the first eye (1) in monocular vision and another operation according to claim 12 for the second eye (2) in monocular vision, and an operation according to claim 13 for the first eye (1) and the second eye (2) simultaneously in binocular vision.

15. The method according to claim 11, further comprising the steps of: h) recording a first response of the subject relative to a first sharpness of the first image perceived by the first eye, and i) recording a second response of the subject relative to a second sharpness of the second image perceived by the second eye, and wherein, during step c), the first light field (71) is adjusted according to the first response recorded during step h), and wherein, during step f), the second light field (72) is adjusted according to the second response recorded during step i).

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