Method for the contactless determination of eye and / or eyelid movement

Abstract

Method for the contactless determination of eye and / or eyelid movement, characterized in that between the body surface (1) and at least one reference electrode (2) a potential difference ΔP B and by means of at least one measuring electrode (3) which corresponds to the potential difference ΔP B generated, electric field and the potential change at the measuring electrode (3) generated by an eye and / or eyelid movement is measured relative to the potential of the reference electrode (2) and evaluated as a measure of an eye and / or eyelid movement.

Description

[0001] The invention relates to a method for the contactless determination of eye and / or eyelid movement.

[0002] To determine eye and / or eyelid movement (eyelid movement), it is known to apply electrodes to the skin [1]. If these electrodes are in low-resistance contact with the skin, the voltages measured between the electrodes by means of highly sensitive amplifiers provide a measure of eye movement when no eyelid movement is occurring. EOG (electrooculography) is of crucial importance in medical practice [1], both for the diagnosis and treatment of diseases.

[0003] It is also known to attach piezoelectric motion sensors to the eyelids [1]. Using this method, known as a (mechano-)oculogram (OG), eye movement can also be detected via the piezoelectric sensors, provided the eyelids are not moving.

[0004] A major disadvantage of these methods for determining eye movement, however, is that attaching the electrodes or sensors is very time-consuming and can only be performed by trained personnel. It is also very difficult to attach the electrodes or sensors in such a way that they maintain a consistently good connection to the skin or eyelids for the duration of the examination. In addition, the cabling required for the electrodes or sensors, together with the highly sensitive amplifiers and evaluation unit required for analysis, severely restricts freedom of movement. A further disadvantage of these methods is that automated detection of the signals elicited by eyelid movement is not yet possible.

[0005] Especially for sleep studies, where the patient must spend the entire night with electrodes near their eyes and sensors on their eyelids, this effort means that these types of examinations can only be performed in a specialized sleep laboratory. This has serious consequences for the treatment of patients suffering from trauma, for example. When someone has experienced trauma, it very often leads to nightmares. Falling asleep becomes torture and is postponed as long as possible. This leads to considerable stress and chronic fatigue, which ultimately leads to incapacity to work.

[0006] The usual treatment methods used to date, involving talk therapy and psychotropic drugs, are very lengthy and therefore expensive. However, current research suggests that trauma can be treated very effectively. It has been proven that patients who have learned to lucid dream in a sleep laboratory can end their nightmares by making the resolution, while awake, to dream them to a satisfactory conclusion (see, for example, the work of Dr. Brigitte Holzinger, Institute for Consciousness and Dream Research, Vienna). This, of course, presupposes that you become aware that you are dreaming during the nightmare and then remember that you can modify the nightmare as desired. Practically all patients who have learned to lucid dream were able to end their nightmares within a few dreams, thus becoming free of anxiety and able to return to work quickly.Unfortunately, the number of places in sleep laboratories is very limited, so this therapy option is available to only a very small number of patients. A simple, non-contact, and precise measurement of eye and eyelid movement could therefore help many patients, as it would eliminate the need for a sleep laboratory to learn lucid dreaming quickly and effectively.

[0007] Based on this, the invention is based on the object of developing a method that enables the determination of eye and / or eyelid movement without contact and thus provides an easy-to-use and cost-effective alternative to the classic EOG or OG.

[0008] To solve this problem, the feature combinations specified in method claims 1 to 13 are proposed. Advantageous embodiments and further developments of the invention emerge from the dependent method claims 2 to 13.

[0009] The invention is based on the finding that the body surface constantly exchanges charges with the surrounding air, and the amount of locally exchanged charges depends on the local electrical potential of the body surface. The body surface is therefore constantly surrounded by a cloud of charges (space charges).

[0010] To put it somewhat simply, the body's surface can be viewed as a surface consisting of a multitude of local potential probes [2] that, depending on the local potential, release excess negative or positive charge carriers to the environment. The resulting charge cloud around the body can, however, also partially or completely shield it from external fields.

[0011] Secondly, the invention is based on the realization that the body surface can change both its shape (shape changes) and its physical properties (surface properties). Shape changes affect the geometric properties of the eyes and the skin around the eyes. If the eye is moved, the shape of the body surface inevitably changes, as the eye is not a perfectly spherical shape. The eye is also displaced as a whole in the eye socket by the eye muscles (e.g., pulled slightly backwards or to the side). This also changes the shape of the body surface. Changes in surface properties result, for example, from the degree of stretching of the skin caused by muscle movements, or from the conductivity of the skin and the intensity of perspiration (sweating).

[0012] According to the invention, it is proposed to determine the eye and / or eyelid movement by establishing a potential difference ΔP between the body surface (1) and at least one reference electrode (2). B and by means of at least one measuring electrode (3) which is arranged in such a way that it corresponds to the potential difference ΔP B generated, electrical field, when the eye and / or eyelid move, a potential change occurs at the measuring electrode (3) relative to the potential of the reference electrode (2), and the potential change occurring at the measuring electrode (3) can then be measured and evaluated as a measure of the eye and / or eyelid move.

[0013] A prerequisite for this, however, is that no charge cloud (space charge) can form between the body surface (1) and the reference electrode (2) or the measuring electrode (3), as this can partially or, in extreme cases, completely shield the body surface (1) from the reference electrode (2) and the measuring electrode (3), and then the eye or eyelid movement can no longer be detected. In the following, a space charge-free area is referred to precisely when the density of the space charges in the area under consideration is so small that the influence of the space charges present in this area on the metrological quantity to be determined, here the influence on the electrical potential at the measuring electrode (3) relative to the potential of the reference electrode (2), can be neglected.

[0014] Advantageously, the formation of a charge cloud can be prevented if the potential difference ΔP B both on the distance DSin which the reference electrode (2) is arranged in front of the body surface (1), as well as on the size and area, as well as the arrangement in relation to the measuring electrode (3) and the size and area of the measuring electrode (3). The shape of the measuring electrode (3), whether round, rectangular or triangular, has no fundamental influence on its functionality. The shape of the reference electrode (2) also has no fundamental influence on its functionality. The crucial thing is that the reference electrode (2) surrounds the measuring electrode (3) and thus the currents generated by the space charges can flow almost completely via the reference electrode (2). If the measuring electrode (3) is made very long in one direction and very narrow in the direction at right angles to it, this has a beneficial effect on the detection of a change in viewing direction.Perpendicular to the long extension, the sensitivity for detecting a change in gaze direction is then greatly increased, which makes determining this change in gaze direction much easier. It is assumed that the surface of the measuring electrode (3) is aligned approximately parallel to the body surface.

[0015] About the size of the measuring electrode (3) and the distance D S the measurable area (11) on the body surface (1) is determined. If the area of the measuring electrode (3) and / or the distance D S is increased, the size of the measurable area (11) also increases, and the spatial resolution of the method decreases. The measurable area (11) is defined by the fact that only from this area can charge carriers be exchanged between the body surface (1) and the measuring electrode (3).

[0016] An advantageous embodiment of the invention provides that the measuring electrode (3) and the reference electrode (2) are arranged at a distance D S > 1 mm and D S < 100 mm, preferably at a distance D S > 5 mm and D S < 20 mm, in front of the body surface (1), preferably centrally in front of the eye, and / or a potential difference ΔP B (a voltage) of > 5 V and < 10000 V, preferably a voltage of > 100 V and < 200 V, is generated between the body surface (1) and the reference electrode (2).

[0017] A further embodiment of the invention provides that the potential difference ΔP Bis generated by means of a high-voltage direct current source (9), and for this purpose the positive pole (negative pole) of the high-voltage direct current source (9) is electrically conductively connected (for example by means of a copper wire) to the reference electrode (2), and the negative pole (positive pole) of the high-voltage direct current source (9) is electrically conductively connected to a body electrode (10), and an electrical contact, preferably with a contact resistance of < 2 MΩ, is created with the body surface (1) by means of the body electrode (10). The body electrode (10) can preferably be designed as a gold-coated stainless steel electrode and ensures that a sufficiently low-resistance contact is established between the body surface (1) and the body electrode (10).

[0018] An embodiment of the invention provides that the potential difference ΔP Bis generated by arranging the reference electrode (2) and / or the measuring electrode (3) on or behind a water-repellent and / or electrically polarized surface, preferably the surface of a sleep mask facing the body, and thereby achieving a preferential deposition of positive or negative charge carriers on this surface and thus the potential difference ΔP B between the body surface (1) and the reference electrode (2). For example, the surface of a sleep mask facing the body can be coated with a water-repellent coating (or consist of a water-repellent material) and / or coated with a polarized coating (similar to the material of an electret foil) (or consist of a polarized material), thus promoting the deposition of positive or negative charge carriers due to the surface properties.

[0019] A further advantageous embodiment of the invention provides that the potential change at the measuring electrode (3) generated by an eye and / or eyelid movement is converted into a current or voltage change in the output signal of the amplifier (4) by means of an amplifier (4), preferably operated as an impedance converter, and the temporal change in the output signal of the amplifier (4) is measured by means of an analysis unit (5) and evaluated as a measure of an eye and / or eyelid movement. Essentially, only changes in the direction of gaze can be detected, since charges are always flowing away via the input of the amplifier (4). This is essentially due to the fact that the operating point of the input (E) of the amplifier (4) should be approximately in the middle of the possible input voltage range, and the operating point stabilization required for this always requires an input current, even if a low one.The lower limit frequency is then > 0.5 Hz. Due to mains interference (50 Hz and / or 60 Hz), the upper limit frequency is in practice a few Hz (2 to 3 Hz) below the mains frequency. The absolute gaze direction can be determined by adding the changes in gaze direction (eye movements).

[0020] In the following, the invention is explained using an embodiment (see Fig. 1) is explained in more detail.

[0021] The measuring electrode (3) and the amplifier (4) are integrated into a sensor (20). To shield the measuring electrode (3) and the amplifier (4) from ambient interference fields, the amplifier (4) is arranged inside a cup-shaped, electrically conductive shield (21) near the ground, and the measuring electrode (3) is arranged inside the shield (21) near the opening of the cup-shaped shield (21). The cup-shaped shield (21) can be used as a reference electrode (2) or can be electrically connected to it.

[0022] An advantageous embodiment of the invention provides that the amplifier (4) is implemented by means of a JFET transistor (12) (junction field effect transistor), preferably an n-channel JFET transistor, preferably in a common source configuration, and the measuring electrode (3) is electrically connected to the gate (G) of the JFET transistor, and the temporal change in the output signal of the amplifier (4) is measured by means of an analysis unit (5) and evaluated as a measure of eye and / or eyelid movement. For this purpose, the source terminal (S) of the JFET (12) is connected to the negative pole of a DC voltage source (13) and the drain terminal (D) of the JFET (12) is connected by means of the V + -Line (14) is electrically connected to the positive pole of the DC voltage source (13). In the V +A measuring resistor (15) is integrated into the line (14). The drain (D) terminal of the JEFET (12) is connected to the analysis unit (5) by means of a measuring line (16). The output signal (A) of the amplifier (4) is then transmitted to the analysis unit (5) by means of the measuring line (16). There, the output signal (A) is preferably digitized and / or filtered and / or the temporal change in the output signal of the amplifier (4) is measured by means of an analysis unit (5) and evaluated as a measure of eye and / or eyelid movement.

[0023] In order to shield the measuring electrode (3) and the JFET (12) from ambient interference fields, the JFET (12) is placed inside the cup-shaped, electrically conductive shield (21) near the ground, and the measuring electrode (3) is placed inside the shield (21) near the opening of the cup-shaped shield (21). The cup-shaped shield (21) is electrically connected to the terminal (S) of the JFET (12), ensuring that the shield (21) and the terminal (S) are at the same potential. The V + -Line (14) and the measuring line (16) are guided through the wall of the shield (21) in an electrically insulated manner by means of the insulators (17) and (18) respectively.

[0024] An embodiment of the invention provides that in order to generate a defined potential difference ΔP Bbetween the body surface (1) and the sensor (20), the positive pole of the high-voltage direct current source (9) is electrically connected to the terminal (S) of the JFET (12), and the negative pole of the high-voltage direct current source (9) is electrically connected to the body electrode (10) attached to the body surface by means of the charging line (19), and a charging resistor (22) is integrated into the charging line (19) in order to be able to limit the current. Alternatively, the negative pole of the high-voltage direct current source (9) can be connected to the terminal (S) of the JFET (12), and the positive pole of the high-voltage direct current source (9) can be connected to the body electrode (10) attached to the body surface by means of the charging line (19).

[0025] A further advantageous embodiment of the invention provides that the analysis unit (5) evaluates the temporal progression of the output signal (A) of the amplifier (4) to determine the sleep phase, preferably the REM phase (rapid eye movement). The current sleep phase, preferably the REM phase, is then displayed to the sleeper. For this purpose, a signal generator (6), preferably an acoustic and / or optical and / or mechanical signal generator, is proposed. The signal generator (6) is preferably controlled by the analysis unit (5). LEDs that emit light in the visible range can be used as optical signal generators (6), for example. Piezoelectric sound emitters can be used as acoustic signal generators (4), for example. Piezoelectric vibration elements that are applied to the body surface (1) can be used as mechanical signal generators (6).

[0026] An advantageous embodiment of the invention provides that the analysis unit (5) transmits the temporal progression of the output signal (A) of the amplifier (4) by means of a wireless bidirectional data transmission (7), preferably by means of Bluetooth, to an evaluation unit (8), preferably a PC or a smartphone, and that the evaluation unit (8) evaluates the signal to determine the sleep phase, preferably the REM phase. The determined information about the current sleep phase is transmitted from the evaluation unit (8) to the analysis unit (5) via the wireless bidirectional data transmission (7), and the current sleep phase, preferably the REM phase, is displayed to the sleeper by means of a signal transmitter (6), preferably by means of an acoustic and / or optical and / or mechanical signal transmitter. The evaluation unit (8) then also makes it possible to record the progression of the sleep phases and evaluate them at a later time.

[0027] A further advantageous embodiment of the invention provides that the output signal A of the amplifier (4) transmitted via the measuring line (16) to the analysis unit (5) is sampled by the analysis unit (5) with a sampling frequency of F ABT = 2 · N · F NETZ (with N = 1, or 2, or 3, or 4, ....), preferably with N = 4, is digitized and interference from the mains frequency F NETZ , preferably at a frequency of F NETZ = 50 Hz and / or F NETZ = 60 Hz, by forming a moving average (simple moving average (SMA) 2-N-th order) over 2·N sampling points (arithmetic mean over 2·N sampling values) over the last 2·N sampling values from the digitized output signal (A) of the amplifier (4).

[0028] Further embodiments of the invention are described with reference to Fig. 2 explained. Fig. Figure 2 shows an example of three sensors (20) per eye integrated into a sleep mask (30) or glasses (30). Multiple sensors (20) are required if the gaze direction of the eyes is to be determined. Multiple sensors (20) also facilitate a reliable distinction between an eyelid movement and an eye movement. An advantageous arrangement of the sensors (20) is shown. Fig. 2. Two sensors (20) are placed near the nose, slightly above and below the eye, respectively. The third sensor (20) is placed at eye level on the edge of the eye on the side of the eye opposite the nose. The body electrode (10) is placed above the nose on the forehead. The signal transmitter (6) is placed below the body electrode (10) on the nose. The bidirectional wireless data transmission (7) is advantageously placed on the nose, slightly below the signal transmitter (6).

[0029] In principle, the method proposed here is also suitable as a replacement for conventional EEG and ECG, as well as for the location and therapeutic evaluation of acupuncture points. A further application of the proposed method is seen in a therapeutic aid for epileptics and / or narcoleptics and / or as a technical aid for monitoring / preventing fatigue in safety-relevant activities (e.g., truck drivers). For these applications, it is advantageous to be able to determine and evaluate eyelid movement without contact, preferably using sensors integrated into commercially available glasses. Eyelid movement can be used to reliably determine how often and how long epileptic seizures occur and last. If this data is stored and evaluated at a later time, it becomes possible for the first time to create a reliable medication plan based on objective facts.The eyelid movement can also be used to determine the level of vigilance (based on a slowing down of the speed with which the eyelid is closed and / or opened and / or the frequency with which the eyelid is closed and opened) and thus prevent accidents or injuries caused by fatigue or an impending seizure (epilepsy, narcolepsy) (the user receives a warning signal from the sensor, e.g. a vibration alarm, and can then stop his truck or lie down in time). Literature: [1]: Clinical Electroencephalography; Stephan Zschocke; Springer Verlag (1995); ISBN 3-540-54766-5. [2] : dtv-Encyclopedia of physics; German paperback publisher (1971); ISBN 3-423-03048-8.

Claims

[1] Method for the contactless determination of eye and / or eyelid movement, characterized by that between the body surface (1) and at least one reference electrode (2) a potential difference ΔP B and by means of at least one measuring electrode (3) which corresponds to the potential difference ΔP B generated, electric field and the potential change at the measuring electrode (3) generated by an eye and / or eyelid movement is measured relative to the potential of the reference electrode (2) and evaluated as a measure of an eye and / or eyelid movement. [2] Method according to claim 1, characterized bythat the potential change at the measuring electrode (3) generated by an eye and / or eyelid movement is converted into a current or voltage change in the output signal of the amplifier (4) by means of an amplifier (4), preferably operated as an impedance converter, and the temporal change in the output signal (A) of the amplifier (4) is measured by means of an analysis unit (5) and evaluated as a measure of an eye and / or eyelid movement. [3] Method according to claim 2, characterized by that the amplifier (4) is implemented by means of a JFET transistor, preferably in a source circuit, and the measuring electrode (3) is electrically connected to the gate of the JFET transistor and the temporal change of the output signal (A) of the amplifier (4) is measured by means of an analysis unit (5) and evaluated as a measure of an eye and / or eyelid movement. [4] Method according to one of claims 2 to 3, characterized bythat the analysis unit (5) evaluates the time course of the output signal of the amplifier (4) to determine the sleep phase, preferably the REM phase, and the current sleep phase, preferably the REM phase, is displayed to the sleeper by means of a signal generator (6), preferably by means of an acoustic and / or optical and / or mechanical signal generator, and the signal generator (6) is controlled by the analysis unit (5). [5] Method according to one of claims 2 to 3, characterized bythat the time profile of the output signal of the amplifier (4) is transmitted from the analysis unit (5) by means of a wireless bidirectional data transmission (7), preferably by means of Bluetooth, to an evaluation unit (8), preferably a PC or a smartphone, and is evaluated by the evaluation unit (8) to determine the sleep phase, preferably the REM phase, and the determined information about the current sleep phase is transmitted from the evaluation unit (8) to the analysis unit (5) via the wireless bidirectional data transmission (7) and the current sleep phase, preferably the REM phase, is displayed to the sleeper by means of a signal transmitter (6), preferably by means of an acoustic and / or optical and / or mechanical signal transmitter. [6] Method according to one of claims 2 to 3, characterized bythat the analysis unit (5) evaluates the time course of the output signal of the amplifier (4) to determine the vigilance and / or to determine an epileptic seizure and, in the event of detected fatigue and / or a detected epileptic seizure, the detected fatigue and / or the detected epileptic seizure, preferably the start of the epileptic seizure, is displayed by means of a signal generator (6), preferably by means of an acoustic and / or optical and / or mechanical signal generator, and the signal generator (6) is controlled by the analysis unit (5). [7] Method according to one of claims 1 to 6, characterized by that the potential difference ΔP Bbetween the body surface (1) and the reference electrode (2) by means of a high-voltage direct voltage source (9) and for this purpose the positive pole (negative pole) of the high-voltage direct voltage source (9) is electrically conductively connected to the reference electrode (2) and the negative pole (positive pole) of the high-voltage direct voltage source (9) is electrically conductively connected to a body electrode (10) and by means of the body electrode (10) an electrical contact, preferably with a contact resistance < 2 MΩ, is created with the body surface (1). [8] Method according to claim 7, characterized by that a preferably adjustable voltage of > 5 V and < 10000 V, preferably a voltage of > 100 V and < 200 V, is generated by means of the high-voltage direct voltage source (9). [9] Method according to one of claims 1 to 8, characterized bythat the reference electrode (2) is arranged on or behind a water-repellent and / or an electrically polarized surface, preferably the surface of a sleep mask facing the body, and thereby a preferential deposition of positive or negative charge carriers on this surface and thus the potential difference ΔP B between the body surface (1) and the reference electrode (2). [10] Method according to one of claims 1 to 9, characterized by that the measuring electrode (3) and the reference electrode (2) are at a distance D S > 1 mm and D S < 100 mm, preferably at a distance D S > 5 mm and D S < 20 mm, in front of the body surface (1), preferably centrally in front of the eye. [11] Method according to one of claims 1 to 10, characterized by that the potential difference ΔP B so to the distance D Sand / or the arrangement and / or size of the measuring electrode (3) and / or arrangement and / or size of the reference electrode (2) is adjusted so that a space charge-free area is created between the metrologically detectable area (11) on the body surface (1) and the measuring electrode (3). [12] Method according to one of claims 1 to 11, characterized by that the direction of gaze of the eyes is determined by means of several measuring electrodes (3) and reference electrodes (2), preferably three per eye. [13] Method according to one of claims 2 to 12, characterized by that the output signal of the amplifier (4), preferably by means of the analysis unit (5), with a sampling frequency of F ABT = 2 · N · F NETZ is digitized and interference from the mains frequency F NETZ , preferably at a frequency of F NETZ = 50 Hz and / or F NETZ= 60 Hz, by forming a moving average over 2·N sampling points over the last 2·N samples from the digitized output signal of the amplifier (4), preferably by means of the analysis unit (5), filtered out.

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