Method and system for measuring of visual functions and / or behavior and / or neurological functions

Abstract

Method for measuring of visual functions and / or behavior and / or neurological functions, the method comprising, during a measuring period: -providing a wearable device (60), for example a headset, including an eye tracker (153) for tracking and registering gaze positions of an eye of a user of the wearable device (60), with respect to the wearable device, the wearable device (60) further including a test area sensor (61) for detecting a test area in front of the wearable device (60); -providing a geometric object (152) in the test area, the object (152) having one or more predetermined geometric characteristics, for example predetermined dimensions and a predetermined shape; - presenting (displaying) a visual stimulus (1) to be followed in a stimulus position in the test area, wherein the stimulus has predetermined positions with respect to the geometric object (152) over time. The invention also provides a system and computer program product.

Description

[0001]P135230PC00 Title: Method and system for measuring of visual functions and / or behavior and / or neurological functions FIELD AND BACKGROUND OF THE INVENTION Measuring the functioning of the visual and nervous systems is a fundamental procedure in medicine. When performed non-invasively, the functional measurements require the patient's interaction with external stimuli and / or the physician’s instruction. Functional tests can include the evaluation of perceptual, motor and cognitive capabilities. Patient compliance and active participation are crucial; therefore, ensuring that the testing is done in the most comfortable way is important. Example 1: in ophthalmology, most functional tests require the patient’s volitional effort and a certain degree of introspection: they need to be able to self-report what they perceive. The clinical “gold standard” for functional testing is perimetry, the measurement of retinal sensitivity in different visual field locations. This test requires the patient to be immobilized with their chin and forehead secured to a medical device. The patient is then instructed to fixate in front of them while different lights appear in their peripheral visual field. After the appearance of each light, they are instructed to promptly press a button on a remote control. Example 2: functional testing is the cornerstone of neurological examination. It is a sequence of physical examinations where the neurologist checks the correct functioning of different neurological aspects: voluntary and reflexive movement, reaction to sensory stimulation, cognitive status, etc. These clinical exams are subjective by nature and heavily rely on the personal experience of the clinician, as well as the patient’s compliance. In the case of neuromotor disorders, the testing becomes more difficult since the patient cannot perform most tests that require sitting still for long periods, which is often required for sensory and cognitive testing. Both examples face at least two issues: requiring the patient to comply with instructions and to be sitting still. A known system and method for patient testing is described in WO2021096361, which provides improved mapping of a visual field. SUMMARY OF THE INVENTION It is an object of the present invention to provide a solution that allows measuring of visual functions and / or behavior and / or neurological functions in a user friendly, comfortable manner. Also, it is an object to achieve a relatively simple and accurate method and system. According to the invention, this object is achieved by the features of the independent claims. According to an aspect there is provided a method for measuring of visual functions and / or behavior and / or neurological functions, the method comprising, during a measuring period: -providing a wearable device, for example a headset, including an eye tracker for tracking and registering gaze positions of an eye of a user of the wearable device, with respect to the wearable device, the wearable device further including a sensor for detecting a test area in front of the wearable device; -providing a geometric object in the test area (preferably in a fixed location), the object having one or more predetermined geometric characteristics, for example predetermined dimensions and a predetermined shape; - presenting (e.g. displaying) a visual stimulus to be followed in a stimulus position in the test area ( in particular in a direction of view relative to the eye), wherein the stimulus has predetermined positions with respect to the geometric object over time; wherein the sensor of the wearable device detects the geometric object, wherein a detection result of the sensor is processed by a data processor (in particular utilizing said one or more predetermined geometric characteristics of the object) for generating spatial information concerning a position of the wearable device with respect to the geometric object, wherein the spatial information is registered over time; -moving the stimulus to be followed in varying directions in the test area and registering the stimulus positions over time; -wherein the eye tracker detects and registers gaze positions of the eye with respect to the wearable device over time; and -determining and registering deviations between the gaze positions and associated ones of the stimulus positions where the stimulus to be followed was presented, utilizing the registered spatial information of the wearable device with respect to the geometric object and the corresponding registered position of the stimulus with respect to the geometric object. In this way, measuring of visual functions and / or behavior and / or neurological functions (i.e. functional testing) can be achieved a non- obtrusive user friendly way, without movement restrictions for the patient. In particular, it allows for free-movement measuring of visual functions and / or behavior and neurological functions, and it has found to be capable of providing accurate measuring results. According to a preferred embodiment, the method further includes: - determining and registering the relative contribution of eye movement and head movement of a user pursuing and / or searching the stimulus. To that aim, for example, the wearable device can include at least one further sensor to measure acceleration and / or reorientation of that device, for example to provide head movement data. Further, an aspect provides a system for measuring of visual functions and / or behavior and / or neurological functions, for example a system configured for carrying out a method according to the invention, the system including: - a wearable device, for example a headset, including at least one eye tracker for tracking and registering gaze positions of an eye of a user of the wearable device over time, the wearable device further including a test area sensor for detecting a test area in front of the wearable device; - a geometric object, to be positioned in the test area, the object having one or more predetermined geometric characteristics, for example predetermined dimensions and a predetermined shape, wherein the test area sensor of the wearable device is configured to detect the geometric object during operation; - a stimulus device for presenting a visual stimulus in a stimulus position in the test area; -a data processor, configured for controlling the stimulus device for presenting visual stimulus to be followed in a stimulus position, and connected to the eye tracker for receiving data representing the gaze positions from the eye tracker , the data processor being programmed for, during a measuring period: -causing the stimulus device to present the stimulus to be followed in the stimulus positions; -receiving data representing the gaze positions from the eye-tracker (153); -causing the stimulus device to move the stimulus to be followed in varying directions and registering the stimulus positions over time; -registering the received gaze positions over time; -receiving and processing detection results of the test area sensor over time to generate spatial information concerning a position of the wearable device (with respect to the geometric object, and registering the spatial information over time; and - determining and registering deviations between the registered gaze positions and associated ones of the registered stimulus positions where the stimulus to be followed was presented (in particular when the gaze position was detected and magnitudes of the deviations), utilizing the registered spatial information of the wearable device with respect to the geometric object and the corresponding registered position of the stimulus with respect to the geometric object. In this way, the above-mentioned advantages can be achieved. The (digital) data processor can e.g. be a computer, configured for executing a respective computer program product (as is described here-below). Also, said stimulus device can be a separate unit or it can e.g. be integrated with the data processor (in which case the data processor is also configured to provide stimulus device functionality). Besides, in another or further embodiment, said stimulus device can be integrated with or in the geometric object. According to a preferred embodiment, the geometric object is a display apparatus, wherein the stimulus device is configured to cooperate with the display apparatus for displaying the stimulus. In this way, a relatively efficient and compact system can be provided, which can achieve ease of use to an operator, the display apparatus (e.g. a display screen) as such providing geometric object functionally as well as stimulus generation to the system, which can avoid having to setup such an object separately from a stimulus generator. The stimulus device can e.g. be a separate unit, capable of connecting to various types of displays (e.g. via a wireless signal link and / or via a suitable wired signal link) for presenting stimuli on each such display. Further, an aspect provides a computer program product stored in a computer readable form, the computer program, when executed on a computer causes the computer to: -causing a stimulus device to present the stimulus to be followed in the stimulus positions; -receiving data representing the gaze positions from an eye-tracker; -causing the stimulus device to move the stimulus to be followed in varying directions and registering the stimulus positions over time; -registering the received gaze positions over time; -receiving and processing detection results of a test area sensor of a wearable device over time to generate spatial information concerning a position of the wearable device with respect to the geometric object, and registering the spatial information over time; and - determining and registering deviations between the registered gaze positions and associated ones of the registered stimulus positions where the stimulus to be followed was presented (i.e. when the gaze position was detected and magnitudes of the deviations), utilizing the registered spatial information of the wearable device with respect to the geometric object and the corresponding registered position of the stimulus with respect to the geometric object, and preferably to determine a visual field map of field portions, wherein, for each of said field portions, quality of view is determined in accordance with the quality of view of associated ones of the registered deviations of which the associated stimulus positions are located relative to the gaze position so that the associated stimulus positions are in that field portion, and, for each of said associated ones of the registered deviations, the quality of view is estimated in accordance with the magnitude of that associated one of the registered deviations and with magnitudes of at least preceding or succeeding ones of the registered deviations. Herein, the term computer is to be interpreted broadly, since it can be any device or system capable of providing suitable computer functionality, e.g. it can be a data processor, in particular a digital data processing system or unit, digital electronic hardware, a portable computing device, a cell phone, and / or a similar device, configured for executing respective software (i.e. a respective program, digital code), as will be clear to the skilled person. The computer can e.g. include, be associated and / or coupled to a digital memory for storing the respective program that is to be executed by the computer. Further advantageous embodiments are described in the dependent claims. Further features, effects and details of the invention appear from the detailed description and the drawings. Therein, the same or corresponding features are denoted by the same or corresponding reference signs. BRIEF DESCRIPTION OF THE DRAWINGS Fig.1 is a flow chart of steps for acquisition of data regarding eye movements during a test; Fig.2 is schematic representation of a known system with an example of a visual tracking stimulus being displayed; Fig.3 is a graph showing of horizontal positions of the stimulus over time sh(t); Fig.4 schematically depicts a non-limiting example of a system according to the present invention; Fig.5 schematically depicts a non-limiting further example of a system according to the present invention; Fig.6 schematically depicts an example of a wearable device of the system shown in Fig.4; Figure 7A schematically depicts use of part of the system, when a patient has a first head position; Figure 7B is similar to Figure 7A and shows use the part of the system when the patient has a second head position; and Figure 8 is similar to Figure 4, showing a further example of the invention. DETAILED DESCRIPTION Figures 1-3 show an example, known from WO2021 / 096361 which publication is deemed to be incorporated in the present application by reference in its entirety. The example is configured for testing a patient, in particular for mapping a visual field of view (of an eye of the patient). The known system includes: ^a display screen 52 (see Fig 2), for instance a monitor; and^ a eye-tracker 53 for tracking gaze positions in a direction of viewof an eye on the display, for instance a monitor-integrated eye- tracker: Eyelink 1000 (SR-Research, Ottawa, Canada); and ^a data processor system 54 connected to the display screen 52 forcontrolling the display screen 52 for displaying a visual stimulus 1 in a stimulus position (in this example the center of the stimulus blob) moving over the display screen 52 and connected to the eye tracker 53 for receiving data representing gaze positions from the eye tracker. Data from the eye-tracker 53 are in this known example acquired with a sampling rate of 1000 Hz and down sampled to temporally match the refresh rate of 240 Hz of the display screen 52. It will be appreciated that different sampling rates and different refresh rates can be applied. In the present example, the visual stimulus to be followed is in the form of a Gaussian blob 1 of luminance moving on a uniform gray background 2 (∼ 140 cd / m2) (see Fig.2). The movement has components in an up and down Y-direction and in a horizontal X-direction. The Gaussian blob 1 can be displayed within a range of contrast levels: at maximum contrast (50%) it has a peak luminance of ∼ 385 cd / m2, while when presented at minimum contrast (5%) it has a peak luminance of ∼ 160 cd / m2. The size of the Gaussian blob 1 (full width at half maximum) is 0.83 degrees of visual field, corresponding to size III of Goldman perimeter’s stimulus, a commonly used perimetric device. Persons whose vision is tested are instructed to follow the stimulus 1 with their gaze of the eye being tested. In addition to the stimulus 1 to be followed, other visual stimuli can be displayed as well, which may be moving and / or stationary. In the present example, no other stimuli are displayed. In step 3 (Fig.1) a stimulus trajectory is created, which can consist of a random path with the following constraints: ^The stimulus trajectory 4 must be within the boundaries of thescreen. ^The stimulus trajectory cannot contain periodic autocorrelations.The stimulus trajectory 4 of this example is constructed by generating a velocity vector: where at each time point, velocity values for the horizontal (vx) and vertical (vy) components are drawn from a Gaussian distributions with a mean of 0 and separate standard deviations for horizontal (σh) and vertical (σv) directions. For example, for a standard screen resolution of 1920 × 1080 pixels the horizontal stand deviation can be σh = 64.45 deg / s and the vertical stand deviation can be σv = 32.33 deg / s. Preferably these σ values may be adjusted based on screen dimension and / or specific application, e.g., obtaining a representation of a visual field map under specific conditions (e.g. taking measurements from a person with a known disease or known complaints). The velocity vector can be low pass filtered by convolution with a Gaussian kernel such that a cutoff frequency is achieved, preferably around 10 Hz. Subsequently, via temporal integration, velocities are transformed to positions of the stimulus 1: To induce the person whose vision is tested to perform saccadic movements, quick displacements in random directions can be included in the trajectory of movement, as far as the displayed stimulus to be followed does not fall outside the boundary of the screen. This is achieved by adding such displacements, for instance each time after an interval of a fixed amount of seconds, preferably two, or after random time intervals. In Fig.3 an example of a graph 4' of horizontal component sx of positions over time of a stimulus trajectory is shown. As is shown in Fig.1, this created trajectory 4 is stored in a storage 5. In the present example all data are stored in the same storage 5, but sets of date may also be stored in several data storages. For the data acquisition the person whose vision is tested is positioned in front of the screen, for instance at a viewing distance of 60 cm. In this known method, the head of the tested person is fixed (i.e. must remain stationary) during the test. Figures 5, 6 depict a patient friendly system according to the invention, wherein head fixation is not required anymore. It is noted that instead of a screen other display techniques, such asholography, can be used as well. During operation the stimulus 1 isdisplayed on the screen 52 and moved, movement in x-direction being in accordance with the stimulus trajectory 4 which is read from the storage 5 and movement in y-direction being in accordance with another stimulus trajectory, preferably with the quick displacements in y-direction simultaneous with the quick displacements in x-direction. Figures 4, 5, 6, 7A, 7B depict a system 60, 152, 154, that does not require head fixation. In particular, the system is a system for measuring of visual functions and / or behavior and / or neurological functions, and includes: A wearable device 60, for example a headset, including at least one eye tracker 153 for tracking and registering gaze positions of an eye of a user of the wearable device 60 over time, the wearable device 60 further including a test area sensor 61 for detecting a test area TA in front of the wearable device 60. According to a preferred embodiment, the eye tracker 153 of the wearable device 60 is also configured for tracking and registering pupil size of an eye of a user of the wearable device 60 over time. The wearable device 60 is schematically depicted in Figure 6 (the non- limiting example shows a relatively compact pair of glasses as wearable device, but the device can also e.g. be a headset or head-mounted system). It should be appreciated that the wearable device 60 can be any wearable unit, configured to be worn by (e.g. supported by or on) a head of a (human) patient. Optionally, the wearable device 60 can include a frame 60b defining two eye-facing areas, at least one of which can include a transparent element (e.g. a lens 60a), to be located in front of the user’s eyes during operation (i.e. when worn by the patient). Application of transparent elements 60a in an eye-facing area is not required (e.g. in case a patient does not require a corrective lens in order to be capable of seeing stimuli in the test area). Each op said eye-facing areas can e.g. include a transparent element. Alternatively, an occluder (e.g. a completely opacque “lens”) can be placed in front of one eye of the patient, for monocular testing. The frame 60b of the wearable device is configured to be stably supported on the head of the patient, and can e.g. include one or more frame sections that are configured to be supported on a nose, ears and / or other sections of a user’s head. In case one or more corrective lenses are to be applied, it is preferred that such an element 60a is an optical elements that is interchangeable (for changing refractive correction, depending on the respective eye of the patient). The headset preferably includes two eye trackers 153 (known per se, and schematically indicated in Fig.6), for tracking gaze positions (in a non- contact manner) of both eyes of the user over time (and optionally for detecting pupil size of each eye over time). Eye tracking as such can be achieved in various ways as will be appreciated by the skilled person, for example optically wherein each eye tracker 153 includes an eye detector arranged to optically detect the respective eye (i.e. image the eye), in which case respective optical detecting results (e.g. images) can be processed to provide eye gaze positions (an optionally pupil size). For example it is common knowledge that light, typically infrared, is reflected from the eye and can be sensed by a the eye tracker 153 (e.g. a video camera or optical sensor). Various eye tracking methods are known, e.g. video-based eye tracking using corneal reflection (the first Purkinje image) and the center of the pupil as features to track over time, or the so-called dual-Purkinje eye tracker, using reflections from the front of the cornea (first Purkinje image) and the back of the lens (fourth Purkinje image) as features to track, or tracking by imaging features from inside the eye (such as the retinal blood vessels), and following these features as the eye rotates. See https: / / en.wikipedia.org / wiki / Eye_tracking. The eye tracker 153 can e.g. process respective detection results and generate an eye tracking signal (e.g. a digital detection result) providing preferably instantaneous eye gaze position information (and optionally instantaneous pupil size information) concerning the eye that it is tracking (during operation). In an embodiment, the eye tracker 153 can e.g. include a data processor that is separate from a respective eye sensor, the sensor and data processor being interconnected e.g. via a wireless or wired communication link for communication sensor detection results to the data processor to be processed thereby (as will be clear to the skilled person). Anon-limiting example of such a headset is known from Pupil LabsGmbH and commercialized under the name Neontm. The wearable device 60 further includes a test area sensor 61 (schematically shown in Figure 6) for detecting a test area in front of the wearable device 60, during operation. The test area sensor 61 can be mounted to or integrated with the frame 60b of the wearable device 60, and can e.g. include a camera configured for imaging the test area TA during operation (respective light emanating from the test area TA being indicated with arrows TL in Fig.6). In particular, the test area sensor 61 is configured to receive incoming light TL, i.e. light that is generally directed from an environment towards the wearable device 60. A field of view FOV (shown with dashed lines in Fig.6) of the test area sensor 61 preferably has a virtual center line F that extends in parallel with a posterior direction PD associated with the wearable device 60 (the posterior direction PD in particular being a substantially normal direction with respect to the eye facing areas or elements 60a of the wearable device 60, and e.g. being a posterior direction of a head of a user when wearing the device 60). A respective angle φ of the field of view of the test area sensor 61 can e.g. be at least 45 degrees and is preferably at least 90 degrees or more, so that a relatively large test area TA can be detected by the sensor 61. The system has a geometric object 152, to be positioned in the test area TA, the object having one or more predetermined geometric characteristics, for example predetermined dimensions and a predetermined shape. In the example, the geometric object 152 has a generally rectangular shape, in particular a rectangular contour, when seen in front view. It will be appreciated that they can also have different shapes, e.g. curved or rounded contours or contour sections when see in front view, or a combination of straight and curved shapes. As an example, the geometric object 152 can have a first predetermined dimension Q1 (see Fig.4, 7A), for example a horizontal width of the object or a distance between a first pair of sections (e.g. external edges) of the object 152. Similarly, the object 152 can have a second predetermined dimension Q2, for example a vertical height of the object or a distance between another pair of sections (e.g. external edges) of the object 152. It is preferred that the geometric object 152 has a fixed shape and fixed dimensions, during operation (i.e. during a test of a patient). The test area sensor 61 of the wearable device 60 is configured to detect the geometric object 152 during operation, i.e. when the wearable device 60 is worn by a patient and the patient is located at a certain distance TD from the test area TA (see Fig.7A, showing the wearable device 60 located in a user position, as well as the spaced-apart geometric object 152 located in the test area TA). It is preferred that each said predetermined dimension of the geometric object 152 concerns a part or section of the object that can be optically detected by the test area sensor 61 with a relatively high contrast, providing efficient subsequent image processing, as will be appreciated by the skilled person. It follows that the predetermined dimension of the geometric object 61 can concern a part or section of a contour of the object (e.g. an edge or external corner section). Alternatively or in addition, the geometric object 61 can be provided with one or more optical tracking markers MK (see Fig.8) for defining respective points or sections (and providing respective predetermined object dimensions) that are to be detected by the test area sensor 61 of the wearable device 60. For example, the markers MK can be provided on respective fixed positions of the geometric object 61. According to a preferred embodiment, the wearable 60 device includes one or more further sensors 65 (one being schematically indicated in Figure 6) to measure acceleration and / or (re-)orientation of that device. For example, the wearable 60 can include one or more of an accelerometer, gyroscope and inertial measuring unit ( IMU) to that aim, as will be clear to the skilled person. The system includes a stimulus device 154c for presenting a visual stimulus 1 in a stimulus position in the test area TA. Moreover, according to a preferred convenient embodiment, the geometric object is a display apparatus 152. In that case, the stimulus device 154c is configured to cooperate with the display apparatus 152 for displaying the stimulus 1 (see Fig.4). As an example, the display apparatus 152 and stimulus device 154c are interconnected via a signal link 158 (e.g. a data transfer cable, for example a video cable, e.g. a hdmi-cable), such that the stimulus device 154c can transmit a signal (e.g. a video signal) to the display apparatus 152 for displaying the stimulus 1 (on / by the display apparatus 152). For example, the display apparatus 152 can correspond to (and function substantially the same as) the display apparatus 52 described above concerning Figures 1-3. The stimulus 1 can also correspond to the (type of ) stimulus used in the example concerning Figures 1-3, but that is not required. Besides, the stimulus device 154c can correspond to (and function substantially the same as) the stimulus device 54 described above concerning Figures 1-3. As is described above regarding Figure 2, during operation (as provided by the stimulus device 154c and display apparatus 152), the stimulus 1 can have movement components in an up and down Y- direction and in a horizontal X-direction (see figure 4). The system includes a data processor 154, configured for controllingthe stimulus device 154c for presenting visual stimulus 1 to be followed in a stimulus position, and connected to the eye tracker 153 for receiving data representing the gaze positions from the eye tracker 153. According to a preferred embodiment (see Figure 5), the stimulus device 154c is integrated with the data processor 154 (i.e. the data processor is configured to provide stimulus device functionality). The data processor 154 can be communicatively connected to the wearable device 60 during operation, e.g. via a suitable signal link 159 (see Fig.4), in particular for receiving measurement data from the wearable device 60, more particularly detection results of the respective eye tracker(s) 153, detection results from the respective test area sensor 61, and detection results (if any) from optional further respective sensor(s) 65 such as sensor for measuring movement, acceleration, (re-)orientation and / or position (e.g. accelerometer, gyroscope, and / or IMU) of the wearable device 60. In the example of Figure 4, the data processor 154 is schematically depicted as a single unit, having an integrated stimulus device 154c, the data processor 154 being connected to both the wearable device 60 and the display device 152 via suitable signal transmission links (e.g. data transmission cables 158, 159). Alternatively (see e.g. Figure 5), the data processor can be a data processing system 154 composed of a separate data processing section 154a and a separate stimulus device section 154c, the sections being e.g. interlinked via one or more suitable signal links 156, 157 and an intermediate hub 154b. In particular, the data processor 154 can include a separate data processing unit 154a, e.g. a portable computer or a cell phone, and an optional separate connector hub unit 154b that is configured to provide communication ports for connecting various components 154a, 154c of the data processor 154, i.e. for allowing data- communication between those components 154a, 154c via suitable signal links 156, 157 (e.g. data transfer cables, for example computer-network cables and / or usb-cables or the-like). The connector hub unit 154b can also be configured for connecting the wearable device 60 to the components of the data processor, via a signal link 159 (e.g. a data transfer cable). Advantageously, the data processor 154 is programmed for, during a measuring period: -causing the stimulus device 154c to present the stimulus to be followed (via the display apparatus 152) in the stimulus positions (e.g. on a screen of the display apparatus 152, see Figures 4, 5); -receiving data representing the gaze positions (and pupil size, if available) from the eye-tracker 153 (of the wearable device 60); -causing the stimulus device 154c to move the stimulus 1 to be followed in varying directions (on the screen of the display apparatus 152) and registering the stimulus positions over time; -registering the received gaze positions (i.e. received from the from the eye-tracker 153) over time, and optionally registering received pupil size -if available- over time; -receiving and processing detection results of the test area sensor 61 over time to generate spatial information concerning a position of the wearable device 60 with respect to the geometric object (in this case the display apparatus) 152, and registering the spatial information over time; and - determining and registering deviations between the registered gaze positions and associated ones of the registered stimulus positions where the stimulus 1 to be followed was presented when the gaze position was detected and magnitudes of the deviations, utilizing the registered spatial information of the wearable device 60 with respect to the geometric object 152 and the corresponding registered position of the stimulus 1 with respect to the geometric object 152. In a preferred embodiment, the data processor is configured to process detection results of the test area sensor 61 over time to generate spatial information concerning a position of the geometric object 152, using a computer vision (e.g. image recognition) algorithm that is configured to detect the presence of the object 152 in test area sensor images presented / fed to the algorithm. It is preferred that the computer vision algorithm can detect (and e.g. measure or estimate) one or more geometric characteristics of the geometric object that correspond to the one or more predetermined geometric characteristics of that object 152. Also, the data processor 154 can be configured to use one or more predetermined geometric characteristics, for example one or more predetermined dimensions Q1, Q2 of the object 152, for determining a real- time spatial position, e.g. a distance TD between the object 152 and the wearable device 60 (see Figure 7A) and / or a viewing angle or rotational orientation of the wearable device 60 with respect to the object 152, based on a recognized object in test area sensor data. To that aim, the one or more predetermined geometric characteristics Q1, Q12 of the geometric object 152 can e.g. be stored in the data processor 154, for example in a digital memory of the data processor 154. For example, the data processor 154 can be configured to match one or more predetermined dimensions Q1, Q2 of the object 152 to corresponding detected (e.g. measured or estimated) dimensions of the object as detected in the output of the computer vision algorithm, to find the spatial position, e.g. the distance TD between the object 152 and the wearable device 60 and / or a rotational orientation therebetween. It will be appreciated that optionally, the data processor 154 can be configured to make use of predetermined calibration data (e.g. stored in a memory of the data processor) concerning test area sensor data on an initial calibration run, using e.g. a test object located in the test area TA at a certain predetermined distance from the wearable device 60, in the processing of test area sensor data concerning the geometric object 152. In the latter case, the test object may be the same as the actual geometric object 152, but that is not required. It will also be appreciated that the computer vision algorithm can be implemented in various ways. For example, the algorithm can be configured to implement, for instance, an edge detector configured to detect four edges of a rectangular object 152, e.g. based on the contrast difference between the object and a surrounding environment. Alternatively or additionally, the computer vision algorithm can include or be based on a neural network trained for object recognition. Alternatively or additionally, the computer vision algorithm can be configured to detect one or more of the afore- mentioned optical tracking markers MK provided on the object (if any). Moreover, it is preferred that the data processor 154 is configured to process detection results from the one or more optional further respective sensor(s) 65 such (e.g. from an accelerometer, gyroscope, and / or IMU) of the wearable device 60, in the determining of the spatial information of the wearable device with respect to the geometric object 152. For example, these one or more further sensors 65 can provide head movement data concerning head movement or reorientation (e.g. rotation) with respect to three orthogonal axes, which head movement data can be combined (by the data processor 154) with computer vision algorithm detection results to improve the spatial information result. In particular, during operation, resulting head movement data can be used (by the data processor 154) in a step of determining and registering the relative contribution of eye movement and the head movement of the user pursuing (following) the stimulus 1. Further, it is preferred that various components of the system are (actively) synchronized during operation, in particular time-synchronized, to improve precision. According to an embodiment, the system (e.g. data processor 154) is configured to synchronize detection results of one or more sensors 61, 65, 153 of the wearable device with the visual stimulus 1 (generated by stimulus device 154c). For example, respective sensor data can be time-stamped (e.g. by the respective sensors) and / or respective system components 61, 65, 153, 154c can be interconnected via a synchronization signal line (e.g. a network communication signal line) to allow synchronized operation, as will be clear to the skilled person. Also, for example, the data processor 154 can be configured to use predetermined time delays (if any), e.g. time delay calibration data, concerning received input data that is to be processed. According to a non-limiting example, time-stamping can include the following information or data A, B, C (as input items / data): A. Detection results, e.g. video data, coming from testing area sensor 61, coupled with a timestamp for each data sample of those detection results; B. Gaze position data provided by the eye tracker 153, including e.g. at least x- and y-coordinates for each eye, coupled with a timestamp for each data sample of the gaze position data; and C. Position data of stimulus 1 coupled with a timestamp for each position data sample. To the skilled person it will be clear that the system can include one or more timestamp providers, configured to provide said timestamps, in various ways. In an embodiment of the invention, timestamps for above- mentioned input items A and B can originate from a data processing section 154a of the processor 154 (e.g. an internal clock), while those for input item C can originate from e.g. an internal clock of the stimulus device 154c . In that case it is preferred that a predetermined time offset (if any) is available between timestamps (e.g. internal clocks) provided by these different (remote) system components 154a, 154c. For example, the system can be configured to send one or more round- trip messages from the stimulus device 154c to the data processing section 154a of the processor 154, for determining or calculating the timestamp offset. Preferably, multiple of these timestamp offset measurements are conducted before each visual test, after which preferably the measurement with a shortest round-trip time is selected and utilized as the timestamp (clock) offset. According to an embodiment, concerning stimulus 1 timestamps (input item C), a delay can exist between when a stimulus timestamp is initially recorded (e.g. by the processor 154) and when the stimulus 1 is physically displayed on the geometric object 152. This delay can arise e.g. due to inherent hardware characteristics of the geometric object 152 (i.e. if the object 152 is a computer monitor, it can require time to convert an instruction for initiating the stimulus display and a physical display of the stimulus). The system is preferably configured to account for this delay, in particular using respective (predetermined) calibration data. To that aim, preferably, the system can be calibrated, for example using a device for TTL triggering (Transistor-Transistor Logic triggering), providing the respective delay calibration data. An example of this device is the “mBlack Box ToolKit v2” (known per se, see https: / / www.blackboxtoolkit.com / ). It is equipped with a USB TTL module that captures when timestamps of input item C are saved and with photodiodes to detect when stimuli (e.g. stimulus 1) are actually presented on the geometrical object 152 in the testing area. This measurement is preferably repeated multiple times across different regions of object 152, for instance at the center, and the centers of each quadrant, yielding an average delay value that can be accounted for into the original timestamps of input item C (concerning position data of the stimulus 1). It will be appreciated that the data processor 154 can be configured in various ways for determining (and e.g. storing) spatial information concerning e.g. the wearable device 60 and a position of an eye of a user (and optionally pupil size of the eye of the user) carrying the wearable device 60. It has been found that good results can be achieved in case the data processor 154 is programmed for: -generating a first triplet of orthogonal x-y-z coordinates representing the position of geometric object 152 with respect to the wearable device 60, and using those coordinates in determining and registering deviations between the eye gaze positions and associated ones of the stimulus positions where the stimulus 1 to be followed was presented. Also, according to a preferred embodiment, the data processor 154 can be programmed for: - generating at least one pair of orthogonal x-y coordinates representing the position of an eye with respect to the test area TA. Also, preferably, the data processor 154 can be programmed for: -generating a second triplet of orthogonal x-y-z coordinates representing the position of a head or its movement along these axes, of a user of the wearable device 60. Moreover, according to a preferred embodiment, the data processor 154 is programmed for: -determining and registering deviations between the gaze positions and associated ones of the stimulus positions where the stimulus 1 to be followed was presented when the gaze position was detected andmagnitudes of the registered deviations, anddetermining a visual field map of field portions, such that for each of said field portions, quality of view is determined in accordance with quality of view estimates of associated ones of the registered deviations of which the associated stimulus positions are located relative to the gaze position so that the associated stimulus positions are in that field portion, and, for each of said associated ones of the registered deviations, the quality of view is estimated in accordance with the magnitude of that associated one of the registered deviations and with magnitudes of at least preceding or succeeding ones of the registered deviations. During operation, the system can carry out a method for measuring of visual functions and / or behavior and / or neurological functions, the method comprising, during a measuring period: providing the wearable device 60 (wherein the device is worn by a user), wherein the eye tracker 153 tracks and registers gaze positions of an eye of a user of the wearable device 60, with respect to the wearable device 60. During the measuring period, the test area sensor 61 of the wearable detects the test area TA in front of the wearable device 60. Also, during the measuring period, the geometric object 152 (in this case the display apparatus) is located in the test area TA (preferably in a fixed location), the object 152 having said one or more predetermined geometric characteristics Q1, Q2. As is shown in Figure 7A, during operation, the wearable device 60 may have e.g. a first position / orientation with respect to the geometric object 152, at a first point of time of the respective measuring period. Moreover, during the measuring period, the visual stimulus 1 is being displayed (in this case by the geometric object 152) to be followed and / or searched in a stimulus position in the test area TA in a direction of view relative to the eye. The stimulus has predetermined positions with respect to the geometric object 152 over time. In the example, this means that the display apparatus, providing the stimulus 1, displays the stimulus 1 in predetermined positions over time (under control of the stimulus device 154c). The sensor 61 of the wearable device 60 detects the geometric object 152 (during the measuring period), wherein a detection result of the sensor 61 is processed by the data processor 154 (utilizing said one or more predetermined geometric characteristics of the object) for generating spatial information concerning a position of the wearable device 60 with respect to the geometric object (as is described above), wherein the spatial information is registered over time. The stimulus 1 to be followed and / or searched is moved in varying directions in the test area and the stimulus positions are registered over time. Besides, a user may move his head over time, as is e.g. being shown in Figure 7B which shows a reorientation of the wearable device 60 (associated with user movement), which can lead to e.g. a change in a distance TD’ between the wearable device 60 and the geometric object 152 (in this case being the display apparatus itself), and / or a change in viewing angle (i.e. rotational position of the wearable device 60 with respect to the geometric object 152). The eye tracker 153 detects and registers gaze positions of the eye with respect to the wearable device 60 over time (and optionally also its pupil size). Also, deviations between the gaze positions and associated ones of the stimulus positions where the stimulus 1 to be followed was presented, are determined and registered (by the data processor 154), utilizing the registered spatial information of the wearable device 60 with respect to the geometric object 152 and the corresponding registered position of the stimulus 1 with respect to the geometric object 152. This can be achieved via an afore-mentioned computer vision algorithm (as described above), optionally in combination with data received from one or more further sensors 65 such as an accelerometer, gyroscope and / or IMU. For example, during operation, the data processor 154 executes a computer vision algorithm that detects (and e.g. measures or estimates) the geometric object 152 in the data (images) received from the test area sensor 60. In particular, the data processor 154 can use one or more predetermined geometric characteristics of the object 152 (e.g. stored in a respective memory), for example one or more predetermined dimensions Q1, Q2 of the object 152, to determine a real-time spatial position, e.g. a distance TD, TD’ between the object 152 and the wearable device 60 (see Figure 7A, 7B) and / or a viewing angle or rotational orientation of the wearable device 60 with respect to the object 152, based on the recognized object 152 in the data. The data processor 154 can be configured to match one or more predetermined dimensions Q1, Q2 of the object 152 to corresponding detected (e.g. measured or estimated) dimensions of the object as detected in the output of the computer vision algorithm, to find the spatial position, preferably including both distance and orientation , between the object 152 and the wearable device 60. Further, time-synchronization is preferably applied during operation, as is described above, in particular for synchronizing operation of the one or more sensors 61, 65, 153 of the wearable device 60 with operation of the stimulus device 154c. According to an example, once the time-synchronization has been applied (by the processor 154), the processor 154 can process the resulting data to detect the geometrical object 152. During use, preferably, the geometrical object 152 is identified (by the processor 154) in the video data coming from the test area sensor 61, e.g. using a contour algorithm to identify boundaries of the object 152 and a pose computation to estimate a distance between the test area sensor 61 and the geometric object 152. More in detail, this can be achieved by following a standard contour detection procedure for each frame of the testing area video, such as e.g.: - converting each video frame to grayscale frame; - thresholding the resulting grayscaled frames; - finding contours in the images, using e.g. an algorithm described in “Topological Structural Analysis of Digitized Binary Images by Border Following”, Satoshi Suziki and Keiichi Abe, Computer Vision, Graphics, and Image Processing 30,32-46 (1985), wherein algorithm is configured to iteratively scan the frames looking for an ensemble of pixels that forms contours in the images; - finding convex hulls of resulting contours regarding the geometric object 152; and - approximate the convex hulls to a (simpler) polygon so that a final output includes the vertices of the detected geometric object 152. An alternative embodiment can e.g. include the detection of the geometric object 152 using ARUCO markers MK (known per se) displayed on screen (at fixed positions), e.g. along its edges. This is a well known approach in computer vision, see here for more information: https: / / docs.opencv.org / 4.x / d5 / dae / tutorial_aruco_detection.html. It follows that according to an embodiment, the system can be configured to display one or more markers MK on the screen 152 (e.g. four markers MK, at or near the edges of the screen, see Figure 8), wherein the processor 154 can be configured to identify the one or more markers MK (from the video data coming from the test area sensor 61), e.g. to estimate a distance between the test area sensor 61 and the geometric object 152. According to a non-limiting example, the data processor 154 can be programmed to generate a first triplet of orthogonal (x-y-z) coordinates representing the position of geometric object 152 with respect to the wearable device 60 based on the detected markers MK. More particularly (see Figure 8), for example, the data processor 154 can execute a computer vision algorithm that detects (and e.g. measures or estimates) the geometric object 152 in the data (images) received from the test area sensor 60, wherein the data processor 154 can use one or more predetermined dimensions Q1’, Q2’ relating to the markers MK of the object 152 (e.g. distances Q1’, Q2’ between those markers MK) to determine a real-time spatial position between the object 152 and the wearable device 60 and / or a viewing angle or rotational orientation of the wearable device 60 with respect to the object 152. The data processor 154 can e.g. be configured to match one or more predetermined marker- related dimensions Q1’, Q2’ of the object 152 to corresponding detected (e.g. measured or estimated) marker-related dimensions of the object as detected in the output of the computer vision algorithm, to find the spatial position, preferably including both distance and orientation, between the object 152 and the wearable device 60. Instead of ARUCO markers MK, different types of fiducials can be applied, e.g. ARToolKit markers, ARTag markers or AprilTag makers (all known per se). For example, a distance from the geometric object 152 to the testing area sensor 61 can be computed by solving a classic Perspective-n-Point (PnP) pose computation (see e.g. the publication “Pose Estimation for Augmented Reality: A Hands-On Survey”, Eric Marchand, Hideaki Uchiyama, Fabien Spindler” IEEE Transactions on Visualization and Computer Graphics, 2016, 22 (12), pp.2633 – 2651; https: / / inria.hal.science / hal-01246370 / document) to estimate an object pose of the geometric object 152 given a set of object points (for example, vertices), as well as an intrinsic matrix and distortion coefficients of the testing area sensor 61; for example, when the geometrical object 152 has coplanar vertices, the PnP pose computation can be achieved using an algorithm as described in the document “Infinitesimal Plane-based Pose Estimation”, Toby Collins and Adrien Bartoli, https: / / encov.ip.uca.fr / publications / pubfiles / 2014_Collins_etal_IJCV_plane.p df. According to an embodiment, subsequently, the time series of the geometric object 152 vertices can be upsampled to align with a sampling rate of the gaze data provided by the eye-tracker 153; this can be achieved by selecting a nearest timestamp point from the respective gaze data series. Simultaneously, a timestamp associated with the stimulus 1 positions can also be upsampled to match the gaze data's sampling rate. Finally, according to an embodiment, the stimulus 1 series of positions can undergo a transformation from coordinates within the geometric object 152 to coordinates within the video data provided by the testing area sensor 61; this transformation can be accomplished using the detected vertices of object 152 and a homography transformation technique. In this way, gaze position data can be obtained from eye-tracker sensors 153 and stimulus 1 position data in the same coordinate system of reference (given by the test area sensor 61) with time-synchronized timestamps. As follows from the above, the method can include generating a first triplet of orthogonal x-y-z coordinates representing the (3-dimensional) position of geometric object 152 with respect to the wearable device 60, and using those coordinates in determining and registering deviations between the eye gaze positions and associated ones of the stimulus positions where the stimulus 1 to be followed was presented. Further, the method preferably includes generating at least one pair of orthogonal x-y coordinates representing the position of an eye with respect to the test area TA. Also, the method preferably includes generating a second triplet of orthogonal x- y-z coordinates representing the position of a head or its movement along these axes, of a user of the wearable device 60. In this way, straightforward processing of the data can be achieved. It will be appreciated that the data processor 154 can be configured to carry out data processing based on various coordinate systems, such as a common 3 dimensional Carthusian orthogonal x-y-z-system or differently (e.g. by using a spherical coordinate system). Moreover, the method preferably includes, for measuring a quality of view over a visual field of view of an eye: determining and registering deviations between the gaze positions and associated ones of the stimulus positions where the stimulus 1 to be followed / searched was presented when the gaze position was detected andmagnitudes of the registered deviations, anddetermining a visual field map of field portions, wherein, for each of said field portions, quality of view is determined in accordance with quality of view estimates of associated ones of the registered deviations of which the associated stimulus positions are located relative to the gaze position so that the associated stimulus positions are in that field portion, and, for each of said associated ones of the registered deviations, the quality of view is estimated in accordance with the magnitude of that associated one of the registered deviations and with magnitudes of at least preceding or succeeding ones of the registered deviations. As will be appreciated, the present invention can be embodiment in a computer program product stored in a computer readable form, the computer program, when executed on a computer causes the computer to provide above-described method steps., in particular: -causing a stimulus device 154c to present the stimulus 1 to be followed (searched) in the stimulus positions; -receiving data representing the gaze positions (and optionally the pupil size) from an eye-tracker 153; -causing the stimulus device 154c to move the stimulus 1 to be followed and / or searched in varying directions and registering the stimulus positions over time; -registering the received gaze positions (and optionally the pupil size) over time; -receiving and processing detection results of a test area sensor 61 of a wearable device 60 over time to generate spatial information concerning a position of the wearable device 60 with respect to the geometric object 152, and registering the spatial information over time; and - determining and registering deviations between the registered gaze positions and associated ones of the registered stimulus positions where the stimulus 1 to be followed was presented when the gaze position was detected and magnitudes of the deviations, utilizing the registered spatial information of the wearable device 60 with respect to the geometric object 152 and the corresponding registered position of the stimulus 1 with respect to the geometric object 152, and preferably to determine a visual field map of field portions, wherein, for each of said field portions, quality of view is determined in accordance with the quality of view of associated ones of the registered deviations of which the associated stimulus positions are located relative to the gaze position so that the associated stimulus positions are in that field portion, and, for each of said associated ones of the registered deviations, the quality of view is estimated in accordance with the magnitude of that associated one of the registered deviations and with magnitudes of at least preceding or succeeding ones of the registered deviations. Preferably, the method also includes determining and registering the relative contribution of eye movement and / or head movement. It follows that the invention can provide a system for free- movement measuring of visual functions and / or behavior and neurological functions. According to an example, the system can include a wearable eye- tracking device with at least two sensors (e.g. cameras 153 facing the eyes of the patient, and a test area sensor (e.g. camera) 61 facing the environment, as well as one or more optional sensors 65 to measure movement and / or position (e.g. accelerometer, gyroscope, IMU). According to a particular variant, the frontal test area sensor 61 of the eye-tracking device 60 is used to record (image) an environment in front of the patient while they perform a test by looking at visual stimuli 1 displayed on the display apparatus 152. Respective images (i.e. video data) from the sensor 61 is analyzed using e.g. a computer vision algorithm that detects the presence of the display apparatus 152 in the environment. As is mentioned before, the algorithm can implement, for instance, an edge detector to locate the (four) edges of the display apparatus 152 based on the contrast difference between light of the display apparatus 152 and the surrounding environment. Alternatively, a neural network trained for object recognition can be applied. It is preferred that detection of the display apparatus 152 is carried out for every frame (image) of the sensor data (video data). As follows from the above, knowing the real physical size Q1, Q2 of the display apparatus 152, it is possible to extrapolate the distance TD between the patient wearing the eye-tracking glasses and the screen. For each image provided by the test area sensor 61 (e.g, frame of the video), the following information is known: • the triplet of x-y-z coordinates representing the position of the display apparatus 152 with respect to the patient wearing the wearable device 60, including viewing distance; • two pairs of x-y coordinate representing each eye's position with respect to the environment recorded by the wearable device 60 and, indirectly, with respect to the display apparatus 152 detected in the environment; • the triplet of x-y-z coordinates representing the position of the head of the patient or its movement along these axes; and • a numerical description of the status of the visual stimulus 1 displayed on the screen. For instance, in the case of a pursuit task, the numerical description of the visual stimulus would be the x and y coordinates representing its position on the display apparatus 152. With this information, it is possible to correct for an eventual movement of the patient (voluntary or not), at least as long as the display apparatus 152 is within the range of the test area sensor of the wearable device 60. Herein, the invention is described with reference to specific examples of embodiments of the invention. It will, however, be evident that various modifications and changes may be made therein, without departing from the essence of the invention. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, alternative embodiments having combinations of all or some of the features described in these separate embodiments are also envisaged. However, other modifications, variations, and alternatives are also possible. The specifications, drawings and examples are, accordingly, to be regarded in an illustrative sense rather than in a restrictive sense. For the purpose of clarity and a concise description features are described herein as part of the same or separate embodiments, however, it will be appreciated that the scope of the invention may include embodiments having combinations of all or some of the features described. In the claims, any reference signs placed between parentheses shall not be construed as limiting the claim. The word ‘comprising’ does not exclude the presence of other features or steps than those listed in a claim. Furthermore, the words ‘a’ and ‘an’ shall not be construed as limited to ‘only one’, but instead are used to mean ‘at least one’, and do not exclude a plurality. The mere fact that certain measures are recited in mutually different claims does not indicate that a combination of these measures cannot be used to an advantage. For example, as will be clear to the skilled person, the stimulus has predetermined positions with respect to the geometric object over time, in which case the predetermined positions can be achieved in various ways. For example, the stimulus positions can be computed, e.g. in real time based on a gaze of the observer (i.e. a user). Also, the stimulus positions can be randomly generated. The stimulus positions (with respect to the geometric object) can e.g. be stored both for use in (quasi) real-time and for further processing.

Claims

Claims 1. Method for measuring of visual functions and / or behavior and / or neurological functions, the method comprising, during a measuring period: -providing a wearable device (60), for example a headset, including an eye tracker (153) for tracking and registering gaze positions of an eye of a user of the wearable device (60), with respect to the wearable device, the wearable device (60) further including a test area sensor (61) for detecting a test area in front of the wearable device (60); -providing a geometric object (152) in the test area, the object (152) having one or more predetermined geometric characteristics, for example predetermined dimensions and a predetermined shape; - presenting a visual stimulus (1) to be followed in a stimulus position in the test area, wherein the stimulus has predetermined positions with respect to the geometric object (152) over time; wherein the test area sensor (61) of the wearable device (60) detects the geometric object (152), wherein a detection result of the sensor (61) is processed by a data processor (154) for generating spatial information concerning a position of the wearable device (60) with respect to the geometric object, wherein the spatial information is registered over time; -moving the stimulus (1) to be followed in varying directions in the test area and registering the stimulus positions over time; -wherein the eye tracker (153) detects and registers gaze positions of the eye with respect to the wearable device (60) over time; and -determining and registering deviations between the gaze positions and associated ones of the stimulus positions where the stimulus (1) to be followed was presented, utilizing the registered spatial information of the wearable device with respect to the geometric object and the corresponding registered position of the stimulus (1) with respect to the geometric object.

2. Method according to claim 1, wherein the wearable device further including a sensor for measuring the head movement of a user, the method including: - determining and registering a relative contribution of eye movement and a measured head movement of the user.

3. Method according to claim 1 or 2, wherein the geometric object is a display apparatus (152), wherein the stimulus (1) is displayed by the display apparatus (152).

4. Method according to any of the preceding claims, including: generating a first triplet of orthogonal (x-y-z) coordinates representing the position of geometric object (152) with respect to the wearable device (60), and using those coordinates in determining and registering deviations between the eye gaze positions and associated ones of the stimulus positions where the stimulus (1) to be followed is presented.

5. Method according to any of the preceding claims, including: generating at least one pair of orthogonal (x-y) coordinates representing the position of an eye with respect to the test area.

6. Method according to any of the preceding claims, including: generating a second triplet of orthogonal (x-y-z) coordinates representing the position of a head or its movement along these axes, of a user of the wearable device (60).

7. Method according to any of the preceding claims, including, for measuring a quality of view over a visual field of view of an eye: determining and registering deviations between the gaze positions and associated ones of the stimulus positions where the stimulus (1) to be followed is presented when the gaze position was detected and magnitudes of the registered deviations, and determining a visual field map of field portions, wherein, for each of said field portions, quality of view is determined in accordance with quality of view estimates of associated ones of the registered deviations of which theassociated stimulus positions are located relative to the gaze position so that the associated stimulus positions are in that field portion, and, for each of said associated ones of the registered deviations, the quality of view is estimated in accordance with the magnitude of that associated one of the registered deviations and with magnitudes of at least preceding or succeeding ones of the registered deviations.

8. System for measuring of visual functions and / or behavior and / or neurological functions, for example a system configured for carrying out a method according to any of the preceding claims, the system including: - a wearable device (60), for example a headset, including at least one eye tracker (153) for tracking and registering gaze positions of an eye of a user of the wearable device (60) over time, the wearable device (60) further including a test area sensor (61) for detecting a test area in front of the wearable device (60); - a geometric object (152), to be positioned in the test area, the object having one or more predetermined geometric characteristics, for example predetermined dimensions and a predetermined shape, wherein the test area sensor (61) of the wearable device (60) is configured to detect the geometric object (152) during operation; - a stimulus device (154c) for presenting a visual stimulus in a stimulus position in the test area; -a data processor (154), configured for controlling the stimulus device (154c) for presenting visual stimulus (1) to be followed in a stimulus position, and connected to the eye tracker (153) for receiving data representing the gaze positions from the eye tracker (153), the data processor (154) being programmed for, during a measuring period: -causing the stimulus device (154c) to present the stimulus to be followed in the stimulus positions;-receiving data representing the gaze positions from the eye-tracker (153); -causing the stimulus device (154c) to move the stimulus (1) to be followed in varying directions and registering the stimulus positions over time; -registering the received gaze positions over time; -receiving and processing detection results of the test area sensor (61) over time to generate spatial information concerning a position of the wearable device (60) with respect to the geometric object (152), and registering the spatial information over time; and - determining and registering deviations between the registered gaze positions and associated ones of the registered stimulus positions where the stimulus (1) to be followed was presented, utilizing the registered spatial information of the wearable device (60) with respect to the geometric object (152) and the corresponding registered position of the stimulus (1) with respect to the geometric object (152).

9. The system according to claim 8, wherein the geometric object is a display apparatus (152), wherein the stimulus device (154c) is configured to cooperate with the display apparatus (152) for displaying the stimulus (1).

10. The system according to claim 8 or 9, wherein the stimulus device (154c) is integrated with the data processor (154).

11. The system according claim 9 or 10, wherein the system is configured to display one or more markers (MK) on the display apparatus (152).

12. The system according to any of the claims 8-11, wherein the data processor (154) is further programmed for: -generating a first triplet of orthogonal (x-y-z) coordinates representing the position of geometric object (152) with respect to the wearable device (60), and using those coordinates in determining and registering deviationsbetween the eye gaze positions and associated ones of the stimulus positions where the stimulus (1) to be followed was presented.

13. The system according to any of the claims 8-12, wherein the data processor (154) is programmed for: - generating at least one pair of orthogonal (x-y) coordinates representing the position of an eye with respect to the test area.

14. The system according to any of the claims 8-13, wherein the data processor (154) is programmed for: -generating a second triplet of orthogonal (x-y-z) coordinates representing the position of a head or its movement along these axes, of a user of the wearable device (60).

15. The system according to any of the claims 8-14, wherein the data processor (154) is programmed for: -determining and registering deviations between the gaze positions and associated ones of the stimulus positions where the stimulus to be followed was presented when the gaze position was detected andmagnitudes of the registered deviations, anddetermining a visual field map of field portions, such that for each of said field portions, quality of view is determined in accordance with quality of view estimates of associated ones of the registered deviations of which the associated stimulus positions are located relative to the gaze position so that the associated stimulus positions are in that field portion, and, for each of said associated ones of the registered deviations, the quality of view is estimated in accordance with the magnitude of that associated one of the registered deviations and with magnitudes of at least preceding or succeeding ones of the registered deviations.

16. The system according to any of claims 8-15, wherein the wearable device (60) is also configured for tracking pupil size of an eye of a user of the wearable device (60).

17. The system according to any of claims 8-16, wherein the wearable (60) device includes one or more further sensors (65) to measure acceleration and / or reorientation of that device, for example to provide head movement data.

18. A computer program product stored in a computer readable form, the computer program, when executed on a computer causes the computer to: -causing a stimulus device (154c) to present the stimulus to be followed in the stimulus positions; -receiving data representing the gaze positions from an eye-tracker (153); -causing the stimulus device (154c) to move the stimulus (1) to be followed in varying directions and registering the stimulus positions over time; -registering the received gaze positions over time; -receiving and processing detection results of a test area sensor (61) of a wearable device (60) over time to generate spatial information concerning a position of the wearable device (60) with respect to the geometric object (152), and registering the spatial information over time; and - determining and registering deviations between the registered gaze positions and associated ones of the registered stimulus positions where the stimulus (1) to be followed was presented, utilizing the registered spatial information of the wearable device (60) with respect to the geometric object (152) and the corresponding registered position of the stimulus (1) with respect to the geometric object (152), and preferably to determine a visual field map of field portions, wherein, for each of said field portions, quality of view is determined in accordance with the quality of view of associated ones of the registered deviations of which the associated stimulus positions are located relative to the gaze position so that the associated stimulus positions are in that field portion, and, for eachof said associated ones of the registered deviations, the quality of view is estimated in accordance with the magnitude of that associated one of the registered deviations and with magnitudes of at least preceding or succeeding ones of the registered deviations.

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