System and method for diagnosing eye disorders

Abstract

A system and method are presented for measuring near point of convergence (NPC) and / or convergence recovery point (CRP) of patient's eyes. The system comprises: an eye tracking device configured and operable to provide measured eye-related data of the eyes being indicative of visual axes of the eyes associated with eyes' vergence during a measurement session; a target tracking device, being calibrated with respect to the eye tracking device, and being configured and operable to monitor distances from the eyes to a moving target, onto which the eyes are required to be focused during said measurement session, and to provide measured target-related data indicative of a relative target location relative to the eyes; and a memory and processing circuitry configured and operable to analyze the measured eye-related data and the measured target-related data and determine a relation between a change in the data indicative of the visual axes and data indicative of a change of said distance to the target during movement of said target during the measurement session, and to extract data indicative of said NPC and / or CRP from said relation.

Description

[0001] SYSTEM AND METHOD FOR DIAGNOSING EYE DISORDERS

[0002] TECHNOLOGICAL FIELD AND BACKGROUND

[0003] The present disclosure relates generally to methods of diagnosing eye disorders.

[0004] Near Point of Convergence / Convergence Recovery Point (NPC / CRP) measurements of a patient are very common and today are performed with special ruler, subjective responses of the patient, and practitioners unassisted (without any device) observations of the patient’s eyes behavior.

[0005] GENERAL DESCRIPTION

[0006] Convergence insufficiency (CI) is characterized by a decreased ability to converge the eyes and maintain binocular vision while focusing on a near target. NPC / CRP measurements are a golden standard today for CI detection because of the test’ s simplicity and providing the results in the form of a simple number that may be recorded and compared with the results of future and past measurements. Furthermore, NPC / CRP measurements serve as indicator (i.e. biomarker) to a large set of other pathologic problems, like intermitted exophoria, vertical foria, etc.

[0007] Current procedures of NPC / CRP measurement are performed manually by a specialist (e.g., ophthalmologist or optometrist) using a special ruler with a fixation target installed on it. The patient fixates on the target, and by bringing the target closer to the patient’ s eyes, the distance from the patient’ s eyes at which fixation is lost (i.e., the patient sees double) is measured. This distance / point is called the Near Point of Convergence (NPC) and is denoted as CINPC. The specialist then gradually moves the target away from patient’s eyes and at some stage the patient recovers his vergence and indicates to the specialist that now he sees single. This distance / point is called Convergence Recovery Point (CRP) and is denoted dcRp. Typically, CINPC ^dcpp. There exist conflicting findings for normative values of NPC / CRP measurements, originating, among other reasons, from inaccuracies and insufficient repeatability of the manual measurement technique.

[0008] The aim of the present disclosure is to improve NPC / CRP measurements for diagnostics of CI and some other eye misalignment syndromes, by providing a novel semi-automatic and objective NPC / CRP measurements with the help of an eye tracking system capable of monitoring a change in data indicative of the eyes' visual axes in space and / or a change of a distance between the limbuses of the eyes with high accuracy during a measurement session (during which a distance from the eyes to a target on which the eyes are required to be focused continuously changes). In this connection, it should be understood that the currently used fully manual procedures are based on a mixture of subjective (patient verbal response based) and objective (direct unassisted observation by a specialist) data.

[0009] The present disclosure uses computer vision to measure both the target location and data indicative of the fixation of the patient on the target during an NPC / CRP measurement. The measurement of fixation of the patient's eyes on the target requires measurement of their visual axes' locations in space.

[0010] The present disclosure provides a novel eye tracking technology utilizing determination of data indicative of visual axes of the eyes, associated with eyes' vergence, in a measurement session during which a distance from the eyes to a target, onto which the eyes are required to be focused, is being changed (typically, by moving the target). Such determination of the data indicative of the visual axes may include measurements of the location of the visual axis of each eye in space, enabling to directly deduce the convergence / di vergence of the visual axes. Additionally, or alternatively, the determination of the data indicative of the visual axes includes accurate measurement of a distance between limbus centers of the eyes. Since it is known that such distance decreases as a person focuses on a near target, reduced or delayed convergence of the eyes is indicative of that the eyes do not rotate inward normally during near focusing tasks, resulting in cessation of decrease in limbus-to-limbus distance.

[0011] It should be noted that the term “eyes’ vergence” used in the present disclosure refers to the simultaneous (coordinated) movement of both eyes (eyes' optical / visual axes) in opposite directions. “Eyes’ convergence” refers specifically to the inward turning of the eyes when trying to fixate at near objects, whereas “eyes’ divergence” refers to the outward turning of the eyes when trying to focus on far objects.

[0012] Thus, the technique of the present disclosure enhances current manual procedures with objective data about the patient's lost fixation on the target (NPC data d^pc), and when the patient's eyes regain it back (CRP data d / np.). The technique of the present disclosure not only provides improved results as compared to the known manual procedure, but in addition allows to store the whole eye movements data that may be used for better diagnostics and monitoring of improvement or deterioration of patient’s conditions.

[0013] It should be noted that the present disclosure may utilize any known eye tracking technology able to provide the measured eye-related data indicative of visual axes of the eyes, associated with eyes' vergence. Possible eye tracking technologies include camera / image-based technologies, electro-oculography (EOG), eye-attached tracking, optical tracking, and video-based combination of pupil / comeal reflection. The optical tracking may include photo-oculography (POG) and video-oculography (VOG) methods utilizing reflected light source (typically infrared light) from the eye and sensed by a video camera or some other optical sensor. The video-based combined pupil / comeal reflection method provides two key features, i.e., the corneal reflection (known as the Purkinje reflections) and the pupil center to monitor the regard point. This method can be used with low-priced cameras and is able to compute data indicative of the visual axes in real time.

[0014] Additionally, it should be noted that the present disclosure may utilize any known target tracking technology to provide the measured target-related data. Such technology include camera / image-based technologies, infrared (IR) time-of-flight (ToF) or Lidar, ultrasonic sensors, inertial measurement unit (IMU) on target, and RFID with field strength measurement. For the sake of simplicity, the principles of the present disclosure will be described below using the camera / image-based technology.

[0015] Thus, according to one broad aspect of the present disclosure, it provides a system for measuring near point of convergence (NPC) and / or convergence recovery point (CRP) of patient's eyes, the system comprising: an eye tracking device configured and operable to provide measured eye-related data of the eyes being indicative of visual axes of the eyes associated with eyes' vergence during a measurement session; a target tracking device, being calibrated with respect to the eye tracking device, and being configured and operable to monitor distances from the eyes to a moving target, onto which the eyes are required to be focused during said measurement session, and to provide measured target-related data indicative of a relative target location relative to the eyes; and a memory and processing circuitry configured and operable to analyze the measured eye-related and the measured target-related data and determine a relation between a change in the data indicative of the visual axes and data indicative of a change of said distance to the target during movement of said target during the measurement session, and to extract data indicative of said NPC and / or CRP from said relation.

[0016] The memory and processing utility may be configured and operable to analyze said measured eye-related data of the eyes and determine the change in the data indicative of visual axes of the eyes in space during the measurement session.

[0017] In some embodiments, the data indicative of the visual axes comprises locations of the visual axes in space. In this case, the relation describes a mismatch between a point of intersection of said visual axes and the distance to a control location of the target corresponding to a condition of loss of focus of the eyes on said target.

[0018] In some embodiments, the data indicative of the visual axes associated with the eyes’ vergence comprises a distance between limbus centers of the eyes. The relation describes a change of the distance between the lumbus centers as a function of the change of said distance to the target, enabling to identify a value of the distance between the limbus centers corresponding to a predetermined change in said function, said value corresponding to eyes' vergence condition of loss of focus of the eyes on said target.

[0019] The measurement system or the target tracking device may further comprise a target movement assembly comprising an elongated scale aligned with a rail on which the target is mounted for controlled movement along said rail, thereby enabling to monitor the distances from the subject's eyes to the target during said controlled movement of the target. A movement pattern of the target is calibrated with the eye-related data acquisitions pattern of the eye tracking device thereby enabling to determine said relation between the change in the data indicative of the visual axes associated with the eyes’ vergence and the change of the distance to the target during said movement.

[0020] In some embodiments, the measured eye-related data is image data.

[0021] In some embodiments, the eye tracking device may comprise at least one imaging device, each configured and operable to perform imaging of both eyes of the patient during the measurement session, thereby providing image data of the eyes being the measured eye-related data.

[0022] In some embodiments, the eye tracking device comprises at least two imaging devices, associated with two eyes, respectively, such that at least one of said at least two imaging devices performs imaging of one of the two eyes and at least one other of the at last two imaging devices performs imaging of the other of the two eyes during the measurement session, thereby providing the measured eye-related data of the eyes.

[0023] In some embodiments, the eye tracking device comprises at least two pairs of imaging devices, associated with two eyes, respectively, wherein each pair of the imaging devices performs imaging of the respective eye during the measurement session, thereby providing the measured eye-related data of the eyes.

[0024] In some embodiments, the target tracking device comprises at least one imaging device each associated with the two eyes and configured and operable to perform imaging of the moving target and provide the measured target-related data, each of said at least one imaging device being located at calibrated distance from the one or more imaging devices of the eye tracking device.

[0025] In some embodiments, the target tracking device comprises at least two imaging devices comprising at least one imaging device associated with one of the two eyes and at least one other imaging device associated with the other of the two eyes, said at least two imaging devices being configured and operable to perform imaging of the moving target and provide said measured target-related data, said at least two imaging devices being located at calibrated distances from the one or more imaging devices of the eye tracking device.

[0026] According to another broad aspect of the present disclosure, it provides a method for measuring near point of convergence (NPC) and / or convergence recovery point (CRP) of patient's eyes, the method comprising: providing measured eye-related data of the patient's eyes, indicative of visual axes of the eyes associated with eyes' vergence during a measurement session, and providing measured target-related data collected during the measurement session during which a target, onto which the eyes are required to be focused, is controllably moved with respect to the eyes, said measured target-related data being indicative of a relative target location relative to the eyes; processing said measured eye-related data and said measured target-related data and determining a relation between a change in the data indicative of visual axes of the eyes and data indicative of a change of said distance to the target during movement of said target, and extracting data indicative of said NPC and / or CRP from said relation.

[0027] Said processing may comprise: analyzing the measured eye-related data and determining the change in said data indicative of the visual axes in space during the measurement session.

[0028] In some embodiments, said data indicative of the visual axes comprises locations of the visual axes in space, said relation describing a mismatch between a point of intersection of said visual axes and the distance to a control location of the target corresponding to a condition of loss of focus of the eyes on said target.

[0029] In some embodiments, said data indicative of the visual axes associated with the eyes’ vergence comprises a distance between limbus centers of the eyes, said relation describing a change of said distance between the lumbus centers as a function of the change of said distance to the target, enabling to identify a value of the distance between the limbus centers corresponding to a predetermined change in said function, said value corresponding to eyes' vergence condition of loss of focus of the eyes on said target.

[0030] In some embodiments, said measured eye-related data is image data.

[0031] In some embodiments, said providing of the measured eye-related data comprises performing image acquisitions by at least one imaging device, each associated with two eyes, and providing said measured eye-related data.

[0032] In some embodiments, said providing of the measured eye-related data comprises performing image acquisitions by at least two imaging devices associated with two eyes, respectively, and providing said measured eye-related data. In some embodiments, said providing of the measured target-related data comprises imaging the target while said target is moved along a rail aligned with an elongated scale, and monitoring the distances from the subject's eyes to the target during the movement of the target, a movement pattern of the target being calibrated with the measured eye-related data acquisitions pattern.

[0033] In some embodiments, said providing of the measured target-related data comprises imaging of the moving target by at least one imaging device, each associated with the two eyes, each of said at least one imaging device being located at calibrated distance from one or more imaging devices of the eye tracking device.

[0034] In some embodiments, said providing of the measured target-related data comprises imaging of the moving target by at least two imaging devices associated with the two eyes, respectively, said two imaging devices being located at calibrated distances from the respective two pairs of the imaging devices of the eye tracking device.

[0035] BRIEF DESCRIPTION OF THE DRAWINGS

[0036] In order to better understand the subject matter that is disclosed herein and to exemplify how it may be carried out in practice, embodiments will now be described, by way of non-limiting examples only, with reference to the accompanying drawings, in which:

[0037] Fig- 1 is a schematic illustration of the configuration and operation of the NPC / CRP measurement system of the present disclosure;

[0038] Fig- 2 shows an exemplary configuration of a NPC / CRP measurement system of the present disclosure including a total of 6 cameras, 3 cameras for each eye;

[0039] Fig. 3 exemplifies a method of the present disclosure for NPC / CRP measurements;

[0040] Figs. 4A-4C show a few specific examples of NPC / CRP measurement techniques of the present disclosure, utilizing visual axis-based approach for NPC / CRP measurement and limbus distance based approach for NPC / CRP measurement, wherein Fig. 4A shows the measurement of NPC while the target is moved towards the eyes, Fig. 4B shows the measurement of CRP while the target is moved away from the eyes, and Fig. 4C shows the change in the distance between the centers of limbuses;

[0041] Fig. 5A exemplifies the measurement procedure using the measurement system configured according to the present disclosure; and

[0042] Figs. 6A-6B exemplify measurement results of the technique of the present disclosure, showing a condition of the abnormal change in the convergence / divergence of the visual axes of the patient's eyes determined via a change of the distance between the centers of the limbuses of the eyes.

[0043] DETAILED DESCRIPTION OF EMBODIMENTS

[0044] Fig. 1 shows schematically the NPC / CRP measurement system 100 according to the principles of the present disclosure. The system 100 includes an eye tracking device 120, a target tracking device 130. The location and orientation of target tracking device 130 is calibrated with respect to the location and orientation of eye tracker device 120.

[0045] As will be described below, with such calibration when eye tracking device finds orientation and location of eyes (visual axis, optical axis, limbus center), it is possible to calculate relative location of the eyes with respect to a target onto which the eyes are required to be focused during the target movement, and consequently it is possible to calculate the distance of eye features being tracked, such as limbus, from the target. Additionally, the calibration allows to calculate if visual axes are pointing towards the target and other relations between the target TR and the eyes.

[0046] The system 100 is associated (i.e., includes or used with) a target assembly 110 which is configured to allow controllable change of a distance between the target (on which patient's eyes are focused) and the patient's eyes during a measurement session. Typically, this can be implemented by movement of the target. Also, the system 100 is associated with (i.e., includes or is connectable to) a memory and processing circuitry 150

[0047] The NPC is the last location (the smallest measured distance) of the target during the target's movement towards the eyes, at which both visual axes coincide with the location of the target, and CRP is the first location (the closest to the eyes) of the target during the target's movement away from the eyes, at which target location is again coinciding with the convergence point of both visual axes.

[0048] The target assembly 110 may generally be of any known suitable configuration and typically may include a moving target TR and a ruler. In some embodiments, the target assembly 110 may utilize, for example, a modified Accommodation Convergence Rule (Bernell) ruler (not shown) and a target TR. The target may be equipped with a special marker MR. The target TR is used to fixate the patient's eyes on.

[0049] The eye tracker device 120 is configured and operable to provide measured eye- related data of the eyes being indicative of visual axes of the eyes in space during the measurement session. The eye tracker device 120 may generally be of any known suitable configuration. The eye tracker device 120 includes at least one camera associated with each eye of the patient and is configured and operable to measure the position and orientation of the optical axis of each eye of the patient. For example, the eye tracker device 120 may include an adjustable head-mounted apparatus with camera(s) in front of the participant’s eyes.

[0050] In some embodiments, the eye tracker device 120 may be configured and operable to measure the position and orientation of the optical axis of each eye of the patient with no required calibration. Such eye tracker device 120 may be configured as described in U.S. Patent Nos. 12,056,274 and 12,066,624, the entire disclosure of which, except for any definitions, disclaimers, and inconsistencies, is incorporated herein by reference.

[0051] It is known that the optical axis, being the symmetrical axis of the eye, is displaced from the visual axis which connects the target with the fovea. For the purposes of measuring NPC / CRP, data indicative of "behavior" of the visual axis is required. In some embodiments, the NPC / CRP is extracted from measurements of abnormal change in the convergence / di vergence of the visual axes of the patient's eyes.

[0052] Normally, according to the given tasks, both visual axes of the patient's eyes are pointing to the target, i.e. when target moves closer, the eyes gradually converge so that their visual axes continue pointing at the target. When target moves further away, the eyes gradually diverge. When target is too close, at least one of the eyes becomes incapable of pointing to the target. This may be accompanied by a number of abnormal eye movements, like quickly switching between a state in which one of the eyes points to the target and the other eye does not, or one of the eyes starts slowly drifting away from the target.

[0053] To measure visual axes’ locations in space and to determine whether the visual axis points towards the target TR, a one-time calibration step may be performed to determine the constant (per patient) displacement of the visual axis from the optical axis. Thus, the continuous tracking of the optical axes of the eyes provided by the eye tracker device 120 may be easily transformed into respective tracking of the visual axis, enabling measurement of the visual axes' locations in space.

[0054] In some embodiments (which may be alternative or additional embodiments), the visual axes behavior (data indicative of the visual axes of the eyes) can be determined from a measured distance between limbus centers of the eyes (i.e., points of intersection of the optical axes with the limbus plane) provided by the eye tracker device 120. The distance between limbus centers of the eyes changes as a function of the change of the measured distance to the target. When the target is moving towards the eyes in order to determine NPC, the distance between limbus centers gradually decreases, as the eyes continuously verge towards the target, i.e. while visual axis of each eye points towards the target. In this embodiment, the time when the distance between the centers of the limbuses stops decreasing, corresponds to the time when the patient fails to converge towards the target, and the distance from the target to the eyes at that moment is defined as NPC. When the target is moving away from the eyes, the distance between limbus centers gradually increases, while visual axis of each eye points towards the target. In order to determine CRP, the target initially is brought to the distance smaller than NPC and is gradually moved away from the eyes. At some distance, usually larger than NPC, the patient succeeds in pointing both of their visual axes towards the target. Starting from this point the angle between visual axes starts decreasing gradually and the distance between the centers of the limbuses starts gradually to increase. This point is defined as CRP. In these embodiments, the calibration of displacement of the visual axis from the optical axis may not be required.

[0055] The target TR position during the measurement session is tracked by the target tracker 130 which may include at least one imager (camera) 140. Such a camera may, for example, be a forward-facing camera mounted on the head-mounted apparatus of the eye tracker device 120. As noted above, the target may be equipped with the marker MR which may be attached to the target TR in such a way that it does not block the target TR itself and that forward-facing camera will always have MR in its field of view, even when the target is very close to the eyes. During the measurement session, the distance between the patient's eyes and the target is being continuously changed while the patient's eyes follow the target with their gaze. The distance relation between the target TR and the MR is fixed, therefore the distance between the target TR and the eyes can be determined even if the camera of the target tracking device cannot properly image the target, which is typically smaller than the marker and is brought closer to the eyes, since the marker always can be imaged.

[0056] The target TR may be a small object, like a dot or a small letter. The eye tracking 120 is configured and operable to measure the relative eyes’ location in 3D and is not exposed to the target and thus the measured eye-related data provided by the eye tracker 120 is not indicative of the relative target TR location.

[0057] The measured eye-related data of the eyes (which is indicative of the visual axes of the eyes) continuously provided by the eye tracker device 120 during a measurement session, and the measured target-related data indicative of the relative target location provided by the target tracking device 130 during said measurement session, enable to determine a relation between a change in said data indicative of the visual axes and a change of the distance to the target during movement of said target. This relation is indicative of the NPC and / or CRP

[0058] The memory and processing circuitry 150 is configured and operable to determine the relative location of the eye tracking device 120 and the target tracking device 130, as will be described below.

[0059] According to the present disclosure, the memory and processing circuitry 150 is capable of automatically and objectively analyzing and processing the measured eye- related data (provided by the eye tracking device) and measured target-related data (provided by the target tracking device) and determining at what distance the patient's eyes fail to verge (NPC) and when their ability to verge is restored (CRP). More specifically, the memory and processing circuitry 150 receives said measured eye-related data of the eyes from the eye tracking device 120 and receives said measured target- related data from the target tracking device 130. The received data is analyzed by memory and processing circuitry 150 to determine, from the measured eye-related data, the data indicative of visual axes of the eyes in space associated with eyes' vergence during a measurement session, and to utilize the visual axis related data together with the measured target-related data indicative of the relative target location relative to the eyes during the measurement session to determine the relation between the change in visual axes relating data and the change of said distance to the target during the measurement session. Then the memory and processing circuitry 150 extracts data indicative of said NPC and / or CRP from said relation.

[0060] In some embodiments, the measurement session and data analysis include a continuous measurement of the position and orientation of the visual axis of each eye (by the eye tracker 120) and a continuous measurement of the relative target location (by the target tracker 130). As noted above, the NPC is the last location (the smallest measured distance) of the target during the target's movement towards the eyes, at which both visual axes coincide with the location of the target, and CRP is the first location (the closest to the eyes) of the target during the target's movement away from the eyes, at which target location is again coinciding with the convergence point of both visual axes. The automatic and objective measurements with the eye tracking device and the target tracking device according to the present disclosure make the tests much more accurate and repeatable, as compared to the currently practiced manual tests. It should be understood that irrespective of whether the target movement is automatic or not) the measurement technique is automatic as compared to the conventional technique being manual in the meaning that such automatic technique does not rely / is independent of patient's response about his / her arrival to double-seeing the target as utilized in the manual technique.

[0061] Additionally, the measurement technique of the present disclosure provides recording of the dynamics of eyes' vergence loss / recovery, thus allowing to store important dynamic data, beyond the single number for NPC / NPR distance of a particular procedure.

[0062] In some embodiments, said data indicative of the visual axes comprises locations of the visual axes in space. The relation between the change in visual axes relating data and the change of said distance to the target during the measurement session describes a mismatch between a point of intersection of said visual axes and the distance to a control location of the target corresponding to a condition of loss of focus of the eyes on said target.

[0063] In some embodiments, the memory and processing circuitry 150 determines the data indicative of the visual axes by extracting, from the measured eye-related data provided by the eye tracker, a distance between limbus centers of the eyes. In this case, the relation between the change in the visual axes related data and a change of the distance to target related data describes a rate of change of the distance between the lumbus centers as a function of the change of the distance to the target. This enables to identify a value of the distance between the limbus centers corresponding to a predetermined change in said function, said value corresponding to eyes' vergence condition of loss of focus of the eyes on said target.

[0064] Turning back to Fig. 1, the memory and processing circuitry 150 is typically a computerized / electronic utility having data input and output 152, 154. The memory and processing circuitry is connectable (via wires or wireless communication of any known suitable type) to the eye tracking device 120 and the target tracking device 130. The memory and processing circuitry 150 receives the measured target-related data provided by the target tracking device 130 being indicative of relative locations of the target during the movement, and the measured eye-related data provided by the eye tracking device 120 being indicative of the relative locations of the eyes' optical / visual axes.

[0065] As noted above, the memory and processing circuitry analyses the measured eye- related data to determine the behavior of the eyes' visual axes in space by directly determining a change of the distance between limbus centers of the eyes from the images being acquired, and / or directly determining a change of the position and orientation of the optical axes of the eyes and transforming this into those of the visual axes of the eyes. The memory and processing circuitry 150 utilizes a pre-stored relative location (calibration data) of the eye tracker 120 and the target tracker 130 to determine the location of the eyes and the target at any given moment of time when receiving data from both the target tracker 130 and the eye tracker 120.

[0066] As noted above, the relative location of the eye tracker 120 and the target tracker 130 may be factory pre-calibrated. Specifically, in the embodiments where the eye tracking and the target tracking devices utilize cameras, this calibration may be performed by showing the eye tracker and target tracker cameras special markers with known relative location, thus enabling the calculation of the relative location of the eye tracker’s and the target tracker’s cameras by performing any known type of stereo cameras calibration procedure. Thus, the first and second measured target-related data can be processed by the memory and processing circuitry 150 to determine the NPC and / or CRP.

[0067] It should be noted that the measured eye-related data may be indicative of the erroneous behavior of patients' eyes, which can be properly identified by the memory and processing circuitry to disregard the respective measured eye-related data. To this end, the neural network can be used, which is properly learned and trained to identify such erroneous data.

[0068] Reference is made to Fig. 2 exemplifying a configuration of a NPC / CRP measurement system 100 of the present disclosure including cameras / sensors of the eye tracking device 120 and target tracking de4vice 130 and in data communication with the memory and processing circuitry 150 described above. Generally, the eye tracking device 120 may include a single camera imaging both eyes of the patient; or may include one or more cameras for imaging each of the patient's eyes.

[0069] In the present non-limiting example of Fig. 2, the system 100 includes 6 cameras, including 3 cameras for each eye. In this example, the eye tracking device 120 includes at least two pairs of imaging devices (Al, A2) and (B1,B2), associated with two eyes, respectively, i.e., each pair of the imaging devices performs imaging of the respective eye during the measurement session, both pairs thereby providing the measured eye-related data of the eyes indicative of the visual axes of the eyes. The target tracking device 130 includes two imaging devices, A3 and B3, associated with the two eyes, respectively, and configured and operable to perform imaging of the moving target and provide measured target-related data about relative target location relative to the eyes during the measurement session. The two imaging devices, A3 and B3, of the target tracking device 130 are located at calibrated distances from the respective two pairs of the imaging devices, (Al, A2) and (B1,B2), of the eye tracking device. The measured eye-related data from the eye tracking device and the distance related measured target-related data from the target tracking device are used to determine the relation between a change in the data indicative of the visual axes and a change of the distance to the target during movement of the target being indicative of the NPC and / or CRP. In some embodiments, the system 100 (or target tracking device 130) includes a target movement assembly (170 in Fig. 5) including an elongated scale aligned with a rail (172 in Fig. 5) on which the target TR is mounted for controlled movement along the rail, thereby enabling to monitor the distances from the patient's eyes to the target during the controlled movement of the target. A movement pattern of the target TR may be calibrated with the measured eye-related data acquisitions pattern of the eye tracking device 120 thereby enabling to determine the relation between the change in the data about the visual axes and the change of the distance to the target during the movement. Generally, either using automatic movement of the target or not, the distance measurements by the target tracking device are correlated with the eye-related data acquisition by the eye tracking device.

[0070] Reference is made to Fig. 3 showing a flow diagram 200 exemplifying a method of measuring near point of convergence (NPC) and / or convergence recovery point (CRP) of patient's eyes according to the principles of the present disclosure. In this non-limiting example, the eye tracking and the target tracking are performed using camera-based technology.

[0071] In the embodiments where the measured eye-related data is analyzed to extract locations of the visual axes in space, the method 200 is preceded by step 202 in which a calibration of the visual axis of the patient is performed. The specialist / operator inputs or accesses patient's ID and other patient-related data such as interpupillary distance (IPD), age, sex, special notes. Then, the head mounted device of the eye tracker 120 is put on the patient's head and the alignment procedure is performed. During the alignment procedure, the specialist / operator adjusts the position of the eye tracking camera(s) to the patient's IPD and head, so that the camera(s) is / are located in the correct position before the patient's eyes. The patient is guided to help fine-tune alignment to the eye tracking channels. In this step, the patient receives corresponding instructions, and the calibration is performed.

[0072] The calibration procedure may be performed as follows: The right eye’s vision is blocked by a certain instrument. For 20-30 seconds, the patient's left eye is presented with a calibration target on a computer monitor. The patient follows the calibration target with their left eye. The eye tracking system 120 records these eye movements and calculates the optical axis location for each position of the calibration target, as well as the visual to optical axis angle for the left eye. In addition, it validates the visual axis tracking error as a sanity test to validate that the “Neural Network” works with the required accuracy on this specific patient. On top of it, this data may be used to improve eye tracking performance for the specific patient by annotating and adding the data to the training set. The same procedure is then repeated for the right eye.

[0073] In step 204 the measurement session is performed during which the target TR is moved (automatically or manually) towards (to determine NPC) or away from (to determine CRP) the patient’s nose while the eye tracking device and target tracking device operate to provide and record (i) measured eye-related data of the eyes being indicative of visual axes of the eyes, and (ii) measured target-related data indicative of a relative target location.

[0074] Then, either step 206 or step 208, or both of them, is / are performed.

[0075] In step 206, the measured eye-related data and the distance measured target- related data are processed to determine locations of the visual axes in space as a function of the distance to the target (constituting the relation between a change in the visual axes related data and a change of distance to the target). This is followed by step 210 in which a mismatch between a point of intersection of the visual axes and the distance to a control location of the target is identified.

[0076] In step 208, the measured eye-related data and the distance measured target- related data are processed to determine a change in distance between limbus centers of the eyes (constituting the data indicative of the visual axes associated with the eyes’ vergence) as a function of the change in the distance to the target. The rate of change of the distance between the centers of the limbuses corresponds to the rate of target movement towards or away from the eyes. This is followed by identification of the abnormal change in the rate of change of the distance between the limbus centers as a function of the change of the distance to the target (constituting the relation between a change in the visual axes related data and a change of distance to the target) - step 212. More specifically, a value of the distance between the limbus centers corresponding to a predetermined change in said function is identified, where this value corresponds to eyes' vergence condition of loss of focus of the eyes on said target. The point where an abnormal change in the distance between the centers of the limbuses is identified corresponds to NPC, when the target is moving towards the eyes. The point where the change between the centers of limbuses starts to correspond to the rate of the target movement away from the eyes is identified as CRP.

[0077] The operation of the system 100 may be properly verified. To this end, manual measurements by the specialist / operator are performed simultaneously with the measurements obtained by the eye tracking system 120. The target TR is located directly in front of the patient's eyes to be focused on and is moved slowly towards the patient’s nose at a slow rate until the patient sees double (diplopia) (NPC). At this NPC break point, the patient tells the specialist / operator that he / she sees double and also presses a button on the keyboard at the same time. The target is then backed away from the patient’s nose at the same rate until the patient's eyes see a single, indicating the CRP. The patient then tells the specialist / operator that the eyes see single again while simultaneously pressing the same button. This step is repeated (the “NPC / CRP test”) several times (at least 3 times) for each patient. During this step, the eye tracking system 120 also records the video of the eyes and of the target.

[0078] Reference is made to Figs. 4A-4C exemplifying NPC / CRP measurement techniques of the present disclosure, utilizing visual axis-based approach for NPC / CRP measurement and limbus distance-based approach for NPC / CRP measurement.

[0079] Fig. 4 A shows NPC measurement. The target TR starts at the far distance D and is gradually moved towards the eyes, while the patient is instructed to focus his gaze on the target all the time. The visual axis of left eye LVA, the visual axis of the right eye RVA, the distance between centers of limbuses of both eyes (Inter-Limbi distance - ILD), the distance D of the target TR to the eyes, as well as location of the target TR in space are measured. While the target moves closer, and the patient maintains the gaze of both of his eyes on the target, the angle between LVA and RVA increases and ILB decreases (Fig. 4C). The Near Point of Convergence, NPC, is defined as a minimal distance from the target TR to the eyes at which vergence breaks, i.e. the patient cannot verge both of his eyes towards the target. At this point the patient starts seeing double or suppresses images from one of the eyes. Objectively, this is characterized by the fact that at least one of the visual axes stops pointing to the target. Also, it is characterized by the fact that the angle between LVA and RVA stops increasing and the distance ILB stops decreasing. The distance ILB can even start slightly increasing, when the patient suppresses an image from one of his eyes, and the suppressed eye goes to the more natural position (e.g., directed straight).

[0080] Fig. 4B shows CRP measurement. The target TR starts at the close distance D to the eyes, closer than NPC, and gradually moves father away from the eyes to the distance much larger then NPC. As with NPC, the visual axis of left eye (LVA), the visual axis of the right eye (RVA), the distance between centers of limbuses of both eyes ILD, the distance D of the target TR to the eyes, as well as location of the target TR in space are measured. While target TR moves further away, the patient attempts to verge both of his eyes on the target. Usually, he fails to do it on the distances that are smaller than NPC (Fig. 4A). Convergence Recovery Point, CRP, is defined as a minimal distance at which the patient successfully converges at the target. At this point, subjectively, the patient starts seeing the target TR as single again (if he saw it as double before). Objectively, both of his visual axes (LVA and RVA) start pointing to the target. Starting from this point, while target TR continues to move further away, distance D between the centers of the limbuses starts gradually increasing (Fig. 4C) and the angle between the visual axes starts gradually decreasing, corresponding to the distance D from the target TR to the eyes.

[0081] Fig. 5 exemplifies the measurement procedure performed using the measurement system configured according to the present disclosure. As shown, the system includes the eye tracking device 120 and the target tracking device 130 and further includes / utilizes the target movement assembly 170. The latter includes an elongated scale (not shown) aligned with the rail 172 on which the target TR is mounted for controlled movement along said rail (movement path), and also includes a marker MR where a change in the location of the marker with respect to the target during the measurement session is known. In this specific example the target is in the form of a small letter |”E” and the marker is in the form of a duck. In this specific condition of the measurement session the target is much closer to the patient’s eyes than the target. In this non-limiting example, the target tracking device 130 includes two forward-facing cameras A3 and B3 associated with the two eyes of the patient, i.e., each configured for monitoring a change of the distance between the respective eye and the target TR. It should be noted that the controlled movement of the target may be manual or automatic or semi-automatic. The eye tracking device 120 includes a pair of cameras associated with / imaging each eye - one pair of such cameras Bl and B2 being seen in the figure. As shown the forward-facing cameras of the target tracking device are mounted on the head-mounted apparatus of the eye tracking device 120. Also shown in the figure is a calibration setup which may be used once for determining a calibrated angular orientation between the optical and visual axes for each eye. Also shown are the two visual axes, VAI and VA2, of the two eyes. The visual axes are drawn on the figure after calculation (by the memory and processing circuitry 150), to demonstrate the convergence of both visual axes of the patient on the target TR.

[0082] Reference is made to Figs. 6A and 6B exemplify measurement results of the technique of the present disclosure, showing a condition of the abnormal change in the convergence / di vergence of the visual axes of the patient's eyes determined via a change of the distance between the centers of the limbuses of the eyes.

[0083] Figs. 6A-6B exemplify the following test. Practitioner moves the target TR bringing it gradually closer towards the patient’s eyes till the target TR reaches some distance that is smaller than NPC (as exemplified in Fig. 5). At this point, the practitioner stops moving the target and gradually starts moving it in the opposite direction further away from the eyes and stops on some distance from the eyes that is larger than RCP. Then, the practitioner repeats this sequence 2 more times. During this test the patient tries to maintain the binocular fixation on the target TR all the time. When the distance is smaller than NPC, the patient fails to maintain the binocular fixation on the target TR, and when the distance is larger than RCP the patient regains binocular fixation.

[0084] In this specific example, the forward facing cameras of the target tracking device are tracking the marker MR that is physically connected to the target TR via a (aluminum) ruler. The relative location of the target TR and marker MR is factory calibrated, i.e., when the system (the memory and processing circuitry) calculates location of the target TR relative to the eyes, it can accurately calculate the location of the marker MR, based on this factory calibration information. At the same time, in this example, the cameras of the eye tracking device are tracking the visual axis of each eye, as well as the center of the limbus of each eye (tracked limbuses are depicted in Fig. 6B).

[0085] Dark blue graph G1 in Fig. 6A represents the distance between the centers of limbuses (Y axis) as a function of time (X axis). White graph G2 on the Fig. 6A represents the distance from the target TR to the mid point between two limbuses (Y axis) as a function of time (X axis). On the bottom graph in Fig. 6A, it is clearly seen that there are 3 times when the target is moved to the closest distance to the eyes and then moved further away. The top graph in Fig. 6A represents a subgraph of the bottom graph, emphasizing one of such moments. At some stage before the target distance graph G2 reaches its minimum, the distance between the centers of the limbuses (graph Gl) stops decreasing and even starts growing. This is exactly the moment when the vergence breaks and patient fails to maintain binocular fixation on the target TR. The distance of the target TR to the eyes (or to the mid-point between the centers of the limbuses) is NPC. The vertical white line L in the top graph of Fig. 6A shows exactly this point.

Claims

CLAIMS:

1. A system for measuring near point of convergence (NPC) and / or convergence recovery point (CRP) of patient's eyes, the system comprising: an eye tracking device configured and operable to provide measured eye-related data of the eyes being indicative of visual axes of the eyes associated with eyes' vergence during a measurement session; a target tracking device, being calibrated with respect to the eye tracking device, and being configured and operable to monitor distances from the eyes to a moving target, onto which the eyes are required to be focused during said measurement session, and to provide measured target-related data indicative of a relative target location relative to the eyes; and a memory and processing circuitry configured and operable to analyze the measured eye-related data and the measured target-related data and determine a relation between a change in the data indicative of the visual axes and data indicative of a change of said distance to the target during movement of said target during the measurement session, and to extract data indicative of said NPC and / or CRP from said relation.

2. The system according to claim 1, wherein the memory and processing utility is configured and operable to analyze said measured eye-related data of the eyes and determine the change in the data indicative of visual axes of the eyes in space during the measurement session.

3. The system according to claim 1 or 2, wherein said data indicative of the visual axes comprises locations of the visual axes in space, said relation describing a mismatch between a point of intersection of said visual axes and the distance to a control location of the target corresponding to a condition of loss of focus of the eyes on said target.

4. The system according to claim 1 or 2, wherein said data indicative of the visual axes associated with the eyes’ vergence comprises a distance between limbus centers of the eyes, said relation describing a change of said distance between the lumbus centers as a function of the change of said distance to the target, enabling to identify a value of the distance between the limbus centers corresponding to a predetermined change in saidfunction, said value corresponding to eyes' vergence condition of loss of focus of the eyes on said target.

5. The system according to any one of the preceding claims, further comprising a target movement assembly comprising an elongated scale aligned with a rail on which the target is mounted for controlled movement along said rail, thereby enabling to monitor the distances from the subject's eyes to the target during said controlled movement of the target, a movement pattern of the target being calibrated with the eye-related data acquisitions pattern of the eye tracking device thereby enabling to determine said relation between the change in the data indicative of the visual axes associated with the eyes’ vergence and the change of the distance to the target during said movement.

6. The system according to any one of the preceding claims, wherein said measured eye-related data is image data.

7. The system according to claim 6, wherein the eye tracking device comprises at least one imaging device, each configured and operable to perform imaging of both eyes of the patient during the measurement session, thereby providing image data of the eyes being the measured eye-related data.

8. The system according to claim 6 , wherein the eye tracking device comprises at least two imaging devices, associated with two eyes, respectively, such that at least one of said at least two imaging devices performs imaging of one of the two eyes and at least one other of the at last two imaging devices performs imaging of the other of the two eyes during the measurement session, thereby providing the measured eye-related data of the eyes.

9. The system according to claim 6, wherein the eye tracking device comprises at least two pairs of imaging devices, associated with two eyes, respectively, wherein each pair of the imaging devices performs imaging of the respective eye during the measurement session, thereby providing the measured eye-related data of the eyes.

10. The system according to any one of claims 7 to 9, wherein the target tracking device comprises at least one imaging device each associated with the two eyes and configured and operable to perform imaging of the moving target and provide the measured target-related data, each of said at least one imaging device being located at calibrated distance from the one or more imaging devices of the eye tracking device.

11. The system according to any one of claims 7 to 9, wherein the target tracking device comprises at least two imaging devices comprising at least one imaging device associated with one of the two eyes and at least one other imaging device associated with the other of the two eyes, said at least two imaging devices being configured and operable to perform imaging of the moving target and provide said measured target-related data, said at least two imaging devices being located at calibrated distances from the one or more imaging devices of the eye tracking device.

12. A method for measuring near point of convergence (NPC) and / or convergence recovery point (CRP) of patient's eyes, the method comprising: providing measured eye-related data of the patient's eyes, indicative of visual axes of the eyes associated with eyes' vergence during a measurement session, and providing measured target-related data collected during the measurement session during which a target, onto which the eyes are required to be focused, is controllably moved with respect to the eyes, said measured target-related data being indicative of a relative target location relative to the eyes; processing said measured eye-related data and said measured target-related data and determining a relation between a change in the data indicative of visual axes of the eyes and data indicative of a change of said distance to the target during movement of said target, and extracting data indicative of said NPC and / or CRP from said relation.

13. The method according to claim 12, wherein said processing comprises: analyzing the measured eye-related data and determining the change in said data indicative of the visual axes in space during the measurement session.

14. The method according to claim 12 or 13, wherein said data indicative of the visual axes comprises locations of the visual axes in space, said relation describing a mismatchbetween a point of intersection of said visual axes and the distance to a control location of the target corresponding to a condition of loss of focus of the eyes on said target.

15. The method according to claim 12 or 13, wherein said data indicative of the visual axes associated with the eyes’ vergence comprises a distance between limbus centers of the eyes, said relation describing a change of said distance between the lumbus centers as a function of the change of said distance to the target, enabling to identify a value of the distance between the limbus centers corresponding to a predetermined change in said function, said value corresponding to eyes' vergence condition of loss of focus of the eyes on said target.

16. The method according to any one of claims 12 to 15, wherein said measured eye- related data is image data.

17. The method according to claim 16, wherein said providing of the measured eye- related data comprises performing image acquisitions by at least one imaging device, each associated with two eyes, and providing said measured eye-related data.

18. The method according to claim 16, wherein said providing of the measured eye- related data comprises performing image acquisitions by at least two imaging devices associated with two eyes, respectively, and providing said measured eye-related data.

19. The method of any one of claims 12 to 18, wherein said providing of the measured target-related data comprises imaging the target while said target is moved along a rail aligned with an elongated scale, and monitoring the distances from the subject's eyes to the target during the movement of the target, a movement pattern of the target being calibrated with the measured eye-related data acquisitions pattern.

20. The method according to any one of claims 16 to 19, wherein said providing of the measured target-related data comprises imaging of the moving target by at least one imaging device, each associated with the two eyes, each of said at least one imaging device being located at calibrated distance from one or more imaging devices of the eye tracking device.

21. The method according to any one of claims 16 to 19, wherein said providing of the measured target-related data comprises imaging of the moving target by at least two imaging devices associated with the two eyes, respectively, said two imaging devices being located at calibrated distances from the respective two pairs of the imaging devices of the eye tracking device.

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