Method and device for quantitatively detecting the fusion capacity in conjugate eye movements

Abstract

A method quantitatively determines fusion capacity in conjugate eye movements of a subject. Visual stimuli are provided for stereopsis as a task for the subject, the stimuli being generated at a viewing angle relative to the primary viewing direction of the subject such that the subject must execute a movement of the viewing direction of the eyes away from the primary viewing direction. Each stimulus is presented for a period of time so that the subject perceives the respective stimulus. The subject reacts to the respective stimulus perceived thereby within a reaction time. The reaction time is determined as the duration between presentation of the relevant stimulus and the subject's motor response to the stimulus. The steps are carried out continuously with stimuli for stereopsis at varying cognitive degrees of difficulty. A series of measurements of reaction times is generated at different cognitive degrees of difficulty.

Claims

1. A method for quantitatively detecting the fusion capacity in conjugate eye movements of a subject, comprising the following process steps: (a) providing visual stimuli for stereopsis as a task for the subject, the stimuli being generated at a viewing angle relative to a primary viewing direction of the subject such that the subject must execute a movement of a viewing direction of eyes of the subject away from the primary viewing direction, (b) presenting each stimulus for a given period of time so that the subject can perceive the respective stimulus, (c) the subject reacting to the respective stimulus perceived thereby within a reaction time, triggering a motor reaction to be detected, (d) determining the reaction time as a time between the presentation of the respective stimulus and the detected motor reaction of the subject as a result of the stimulus, wherein steps (a) to (d) are carried out continuously with the stimuli for stereopsis at a varying cognitive degree of difficulty for the subject, wherein a series of measurements in the form of reaction times at different cognitive degrees of difficulties is generated, wherein the stimuli for stereopsis are generated in bent angle positions at a different cognitive degree of difficulty, and a respective reaction time to the stimuli is detected.

2. The method according to claim 1, wherein the bent angle positions have a same bent angle separation from each other.

3. The method according to claim 1, wherein the measured reaction times are compared with target reaction times.

4. The method according to claim 3, wherein the target reaction times are reaction times of healthy persons.

5. The method according to claim 1, wherein the stimuli for stereopsis include at least two images of an object or stochastically generated stereo images which are presented to the subject in optical planes at different distances to the subject.

6. The method according to claim 1, wherein the respective stimuli are an image of a plurality of fixed objects or objects rotating about the axes thereof, one of which having changed in a remote optical plane thereof compared to the optical plane of the other objects as a function of the degree of difficulty.

7. The method according to claim 1, wherein the viewing angle is at least 10°.

8. A method according to claim 1, wherein the viewing angle is a maximum of 45°.

9. The method according to claim 1, wherein an increase in reaction time with increasing degree of difficulty is determined.

10. The method according to claim 1, wherein an assignment of the measurements of the reaction time is done in assignment to the degree of difficulty and to the bent angle.

11. The method according to claim 1, wherein a two-dimensional visual field mapping is generated from the measurements of the response time at the respective degree of difficulty and the respective bend angle.

12. The method according to claim 1, wherein comparison measurements are repeated at a later time for the same subject.

13. The method according to claim 1, wherein the stimuli are generated by a random generator or pseudo-random generator.

14. The method according to claim 1, wherein the visual stimulus for stereopsis is generated virtually, by a virtual reality (VR) headset.

15. A device for quantitatively determining fusion capacity in conjugate eye movements of a subject, comprising: a device for generating and presenting a stimulus for stereopsis as an individual stimulus as a task for the subject, wherein the stimulus is generated in an angle relative to a primary viewing direction of the subject, so that the subject has to perform a movement of a viewing direction of eyes of the subject away from the primary viewing direction, a timer for detecting a respective reaction time to the stimulus at different cognitive degrees of difficulty, an input device for triggering the timer operable by the subject, and processor, which generates a series of measurements of reaction times at different cognitive degrees of difficulty by generating stimuli for stereopsis in bent angle positions at a different cognitive degree of difficulty and detecting the respective reaction time to the stimuli.

16. The device according to claim 15, wherein a virtual reality headset or a head-mounted display is provided for generating and presenting a stimulus for stereopsis.

Description

DESCRIPTION OF THE INVENTION WITH REFERENCE TO EXEMPLARY EMBODIMENTS

(1) Advantageous embodiments of the present invention will be explained in more detail with reference to the drawing figures. Recurring features are identified only once with a reference numeral for the sake of clarity. Shown are:

(2) FIG. 1 a greatly simplified schematic representation of a device for carrying out the method according to the invention;

(3) FIG. 2 a greatly simplified schematic representation of the primary viewing direction;

(4) FIG. 3 a greatly simplified schematic representation of a stimulus for disparity in a viewing angle α relative to the primary viewing direction according to a further example of the method according to the invention;

(5) FIG. 4 a greatly simplified schematic representation of a stimulus for disparity at different arc angle β dimensions of the field of vision range in accordance with a further example of the method according to the invention;

(6) FIG. 5 mean values of the reaction times of all viewing directions with stimuli at 330, 660 and 990 arcsec of disparity difference for healthy subjects as well as subjects with mild or moderate concussion;

(7) FIG. 6 an illustration of the plot of the mean values of the reaction times of all viewing directions over several weeks at stimuli of 330, 660 and 990 arcsec of disparity difference for healthy subjects as well as subjects with mild or moderate concussion;

(8) FIG. 7 a representation of the positions of viewing directions determined by the method according to the invention where there is no ability to fuse as a function of different bent angle positions in the visual field of subjects with mild concussion immediately after admission to the clinic, one week after the accident and two months after the accident;

(9) FIG. 8 a representation of the positions of deficits in the ability to merge, determined by the method according to the invention, as a function of viewing directions with no fusion capacity relative to subjects with moderate concussion immediately after hospital admission, one week after the accident and two months after the accident;

(10) FIG. 9a-9b graphical representations (viewing direction mapping) of the reaction times in msec of healthy subjects (called controls here) as a function of different bent angle positions in the visual field at different levels of difficulty S (FIG. 9a) and a graphical representation (visual field mapping) of the increase in response time in milliseconds with increasing difficulty of the stereoscopic stimulus (“gain”) in healthy subjects (“gain controls”) from the measurements of FIG. 9a; and

(11) FIG. 10a-10f representations of the development of a concussion over a period of 70 days from a subject with mild TBI, using graphical representations (visual field mapping) of the reaction times as a function of different bent angle positions in the visual field at different levels of difficulty S, and the respective associated graphical representation of the increase in reaction time in msec with increasing degree of difficulty (gain) at 10 days after concussion (FIGS. 10a and 10b), at 30 days after concussion (FIGS. 10c and 10d) and at 70 days after concussion (FIG. 10e and FIG. 10f).

(12) FIG. 1 shows an example of a device for the quantitative acquisition of measurements in connection with fusion capacity in conjugate eye movements of a subject P. The device 1 comprises an imaging module 2, which serves to generate a disparity difference stimulus 9 at a viewing angle α which lies outside the primary viewing direction 21. The stimulus 9 is shown in FIG. 1 viewed from the side. In the present case, for example, a stimulus 9 acting three-dimensionally on the subject P is generated in a monitor 7 or display 6 in the form of four objects 19 in the form of balls lying in the optical plane 10. In this case, one ball is shown with a certain disparity difference from the other 3 balls, that is to say with respect to the position of its optical plane relative to the optical plane of the three other balls. The stimulus 9 is used to determine the fusion capacity, in conjugate eye movements, of for example stereoscopic images which are outside the primary viewing direction, i.e. in a visual field in which the muscles which control eye movement are stressed or tense.

(13) The stimulus is set at different degrees of difficulty S, i.e. at a different disparity difference relative to the main virtual plane. For this purpose, one object 19′ of the four objects 19 is represented with a certain disparity difference, that is to say it is shown in a different optical plane 10′ relative to the optical plane 10 of the other three objects 19. The degree of disparity difference, i.e. the distance between optical plane 10′ and optical plane 10 in FIG. 1 represents the degree of difficulty of the disparity difference of the stimulus. The farther the distance between the main virtual plane and the plane of the different object, the lower the degree of difficulty (the easier it is to detect the difference in disparity of the subject); the closer the optical plane 10′ comes to the optical plane 10 the higher the level of difficulty (the more difficult it is to detect the difference in disparity for the subject). The difficulty level is set in the units of arcsec in the system.

(14) The subject P can be equipped for this purpose with a VR (VR=Virtual Reality) headset 8 in which two images which are different for the right and left eyes, respectively, are generated by a computer program such that in binocular viewing by the subject P′s brain the images are seen as the only stereoscopic image in the display 6 of the VR headset 8. According to FIG. 3, the stimulus 9 using the four objects 19, wherein one object has a difference in disparity, is presented to the subject P successively with different differences in disparity and thus in different virtual optical planes 10′. When the subject P recognizes one ball of the four balls that has a difference in disparity, it triggers a corresponding reaction, from which the reaction time is measured from the time the stimulus 9 is given to the time the reaction is triggered. For example, the subject presses the button of a four-button manual input 11 (e.g. a touchpad) which represents the ball in question.

(15) If the subject actuates the manual input 11, for example a push-button or a touchpad, the reaction time from the presentation of the stimulus 9 to the actuation of the manual input device 11 is measured by a time-recording device 3 and fed to a control and evaluation module 4 and is assigned to the respective level of difficulty in arcsec. Thereafter, the test is continued with a stimulus 9 in the form of four objects 19, wherein the same or another of the four objects 19 is shown at a different disparity difference, i.e. at a different degree of difficulty S, and thus in a different optical plane 10′. The control and evaluation module 4 can have an output 5 (e.g. to a printer) as well as a monitor 7 for displaying the measurements. Furthermore, the control and evaluation module 4 expediently comprises a storage device 17. The visual stimuli 9 of different degrees of difficulty are shown in dashed lines in FIG. 1.

(16) The illustration according to FIG. 2 shows the primary viewing direction 21 of a person. The primary viewing direction 21 corresponds to the center C of the visual field. In the primary viewing direction 21, the muscles controlling the eye movement need not be stressed or strained. The primary direction of vision 21 has no significance regarding the evaluation of a concussion. For this reason, a stimulus 9 for disparity is given in a viewing area outside the primary viewing direction 21, i.e. in a viewing area in which the muscles controlling the eye movement actually have to be stressed. Such a viewing direction is indicated in FIG. 3 by the reference numeral 22 and lies in an angle α relative to the primary viewing direction 21. The stimulus 9 is generated in this viewing direction 22 according to the method according to the invention.

(17) The graph of FIG. 5 shows disparity measurements of varying degrees of difficulty (330 arcsec, 660 arcsec and 990 arcsec) of three different subject groups, healthy subjects, mild TBI subjects and moderate TBI subjects. For this purpose, the disparity investigations were carried out in different viewing directions α relative to the primary viewing direction and averaged over all measured primary viewing directions. FIG. 5 shows that the mean response times are significantly prolonged in patients with mild and moderate concussion. The method according to the invention thus makes it possible to detect a slight concussion (mild TBI) compared to a healthy person without concussion.

(18) Furthermore, it is also possible by means of the method according to the invention to test a subject as to whether the subject has suffered a mild concussion (mild TBI) or a moderate concussion (moderate TBI). As a result, appropriate measures can be initiated. For example, when a moderate concussion (moderate TBI) is determined, an athlete may be excluded from exercise for a prolonged period of time.

(19) FIG. 6 shows a monitoring of the development of a concussion using the method according to the invention. For this purpose, the fusion capacity of the conjugate eye movements of all subjects with moderate or mild concussion (moderate and mild TBI) at various times were plotted versus time at T1 (detection immediately after admission), T2 (detection one week after the accident) and T3 (detection two months after the accident). FIG. 6 shows that the mean reaction times in patients with mild and moderate concussion normalize over time, but even after 70 days do not reach the values of healthy control persons.

(20) According to a further embodiment of the method according to the invention, in a viewing direction 22, the visual field range 18 can be divided into specific, fixed bent angle positions β. For example, in the example shown in FIG. 4, a total of eight bent angle positions β1-β8 are set. These are the bent angle positions 0°, 45°, 90°, 135°, 180°, 225°, 270° and 315°. At each of these fixed bent angle positions, a disparity stimulus 9 of varying difficulty S is issued. In FIG. 4, for the sake of illustration, a stimulus 9 has been drawn in at a bent angle of β6 (225°). The respective bent angle positions β1-β8 are preset in the control and evaluation module 4, presented accordingly to the subject by the VR headset 8 and assigned to the reaction time measurements and levels of difficulty.

(21) The control and evaluation module 4 expediently comprises a random-number generator or pseudo-random generator 13, which ensures that the individual stimuli 9 of different degrees of difficulty S and the respective bent angle positions β are randomly presented to the subject P. This prevents cognitive learning effects from falsifying the measurement result.

(22) An evaluation of the fusion capacity in conjugate eye movements as a function of the respective bent angle position β is shown in FIG. 7 for patients with mild concussion and in FIG. 8 for patients with moderate concussion, on the one hand immediately after their admission, one week after the accident as well as two months after the accident. As is clear from FIG. 7, in persons with mild concussion there is no further impairment of the visual field with respect to the fusion capacity in conjugate eye movements after one week.

(23) In contrast, the fusion capability in persons with moderate concussion as shown in FIG. 8 is noticeably disturbed even after a week, especially with regard to viewing to the right and left. In addition, it can be seen from FIG. 8 that the impairment of the fusion capacity immediately after the accident is particularly high with regard to viewing to the left and to the right.

(24) FIGS. 7 and 8 clearly show that the method according to the invention can enable a quantitative assessment of the fusion capacity in conjugate eye movements of a subject to be made, the results of which can be used for the assessment of the degree of severity of the concussion. The method according to the invention thus makes it possible to carry out a relevant differentiation with comparatively simple means.

(25) Tab. 1 shows corresponding measurements of the reaction times in msec of a healthy person. For this purpose, conjugate eye movement measurements were made on a select group of healthy persons at different bent angle positions β (0° “down,” 45° “down and right,” 90° “to the right,” 135° “up and right,” 180° “up,” 225° “up and left,” 270° “to the left,” 315° “down and left” at stimuli 9 with different difficulty levels S (330, 660 and 990 arcsec). “Gain Controls” refers to the increase in response time with increasing difficulty S in healthy individuals. The gain was calculated for every angle.

(26) TABLE-US-00001 TABLE 1 Gain RT RT RT Controls Viewing Controls Controls Controls [msec/ direction β 330 arcsec 660 arcsec 990 arcsec 330 arcsec] Up 180 692 603 569 106 Up and right 135 703 603 581 111 To the right 90 670 625 603 56 Down and right 45 715 615 592.5 111.25 Down 0 690 602 580 99 Down and left 315 715 625 603 101 To the left 270 680.5 603 603 77.5 Up and left 225 692 603 574.5 103.25

(27) FIG. 9a shows a corresponding two-dimensional visual field mapping of healthy persons based on the measurements. With a corresponding visual field mapping, an effective means is provided which allows the examining doctor to recognize at a glance the state of the fusion capacity in the conjugate eye movements of a subject.

(28) FIG. 9b is a graphical representation of the increase in response time in msec as the degree of difficulty of the stereoscopic stimulus (gain) increases in healthy subjects (“gain controls”) for the measurements of FIG. 9a. There is an increase in response time in a range of 60-100 msec as the degree of difficulty increases from 990 arcsec of disparity difference to 660 arcsec of disparity difference and from 660 arcsec to 330 arcsec of disparity difference, respectively.

(29) Tab. 2 shows corresponding measurements of the reaction times in msec of a person 10 days after having suffered a concussion (TBI 10 days after). “x” means that the subject did not achieve fusion of the images of both eyes at this viewing angle and did not detect a disparity difference.

(30) “#VALUE!” in the table means that there was no fusion in these measured viewing directions and therefore no gain value could be given.

(31) TABLE-US-00002 TABLE 2 Reac- Reac- Reac- Viewing Viewing tion tion tion GAIN direction in direction time time time [msec/ the diagram β 330 660 990 330 arcsec] Up 180 x x 1800 #VALUE! Up and right 135 x 1100 x #VALUE! To the right 90 x x x #VALUE! Down and right 45 x 2800 x #VALUE! Down 0 2200 x x #VALUE! Down and left 315 1500 2300 1500 1200 To the left 270 1800 3200 2200 1900 Up and left 225 x 2100 2200 #VALUE!

(32) FIG. 10a shows a corresponding two-dimensional visual field mapping based on the above measurements. The illustration shows that 10 days after the concussion, conjugate eye movement in the viewing directions to the right, up and right, up and down, and thus a fusion of the image impressions of the right and left eyes is difficult or impossible.

(33) FIG. 10b shows the increase in reaction time in msec only in viewing directions with existing fusion as the degree of difficulty of the stereoscopic stimulus increases (gain). 10 days after the concussion, the reaction time increase was ca. 1000 msec with an increase of the degree of difficulty from 990 arcsec of disparity difference to 660 arcsec of disparity difference and from 660 arcsec to 330 arcsec of disparity difference and thus a factor of 10 higher than in healthy persons.

(34) Thus, in this subject, the plot of reaction times and gain at 10 days post-concussion reveals a complete lack of fusion in conjugate eye movement to the right, markedly longer reaction times to the left and significantly increased reaction times (gain) for increasingly difficult stereoscopic stimuli.

(35) Tab. 3 shows corresponding measurements of the reaction times in msec of a person 30 days after the concussion is suffered (TBI 30 days after). “x” means that the subject did not fuse the images of both eyes at this viewing angle and did not detect a disparity difference.

(36) “#VALUE!” in the table means that there was no fusion in these measured viewing directions and therefore no gain value could be given.

(37) TABLE-US-00003 TABLE 3 Reac- Reac- Reac- Viewing Viewing tion tion tion GAIN direction in direction time time time [msec/ the diagram β 330 660 990 330 arcsec] Up 180 x x 3100 1900  Up and right 135 x 4000 x #VALUE! To the right 90 x x x #VALUE! Down and right 45 x x x #VALUE! Down 0 2400 x x 400 Down and left 315 2600 2500 2400 150 To the left 270 1900 1800 1700 150 Up and left 225 x 1600 1600 900

(38) FIG. 10c shows a corresponding two-dimensional visual field mapping based on the above measurements. The illustration shows that 30 days after the concussion, conjugated eye movements to the right, up and right, up and down are still difficult or impossible.

(39) FIG. 10d shows the increase in reaction time in msec only in viewing directions with existing fusion and increasing degree of difficulty of the stereoscopic stimulus (gain). At 30 days post-concussion, the reaction time increase was still significantly increased from 150 to 1900 msec/330 arcsec as the degree of difficulty increased from 990 arcsec of disparity difference to 660 arcsec of disparity difference, and from 660 arcsec to 330 arcsec of disparity difference.

(40) Tab. 4 shows corresponding measurements of the reaction times in msec of a person 70 days after suffering a concussion (TBI 70 days after).

(41) TABLE-US-00004 TABLE 4 Reac- Reac- Reac- Viewing Viewing tion tion tion GAIN direction in direction time time time [msec/ the diagram β 330 660 990 330 arcsec] Up 180 900 850 1300 275 Up and right 135 1000 1250 980 385 To the right 90 1750 1250 1050 600 Down and right 45 1300 1050 850 350 Down 0 1150 950 990 220 Down and left 315 1500 1000 950 525 To the left 270 1000 1000 1100 50 Up and left 225 1000 1200 900 350

(42) FIG. 10e shows a corresponding two-dimensional visual field mapping based on the above measurements. The illustration shows that 70 days after the concussion, there is now proper fusion in the direction of view to the right, but the reaction times are still longer.

(43) FIG. 10f shows the increase in reaction time in msec now in all directions with existing fusion and increasing degree of difficulty of the stereoscopic stimulus (gain). At 70 days post-concussion, the reaction time increase was still prolonged from 275 to 600 msec/330 arcsec as the degree of difficulty increased from 990 arcsec of disparity difference to 660 arcsec of disparity difference and from 660 arcsec to 330 arcsec of disparity difference, respectively.

(44) After 70 days, there was thus a marked improvement in stereoscopic vision, but not yet a complete normalization, as the comparison with the healthy subjects (FIG. 9) shows.

(45) In summary, it should therefore be stated that with the method according to the invention or the device according to the invention, the severity of a concussion can be determined in the context of a rapid test and measures can be taken effectively in view of avoiding long-term damage in the case of a concussion. This is of particular importance for those at risk, such as athletes or military personnel. The device for carrying out the method according to the invention can also be used as a portable test device on site, e.g. at sports fields, in the field and the like.

(46) Alternatively or additionally, the measurement results or derived data can also be output via a data output 12, for example an interface, to other users who are connected by means of a cable connection 20/wireless connection 20, e.g. to a modem 14. If necessary, the data can be supplied via the modem 14, a network or the Internet 15 and stored centrally from there, for example in a computer cloud 16.

(47) The setting of the viewing angle α is preferably in a range of at least 10° to a maximum of 45°, preferably a maximum of 40°. This range is sufficient for carrying out the measurements against the background of stress on the nerves controlling the eye muscles and is also technically possible in connection with the use of a VR headset.

LIST OF REFERENCE SIGNS

(48) 1 Device 2 Imaging module 3 Time recording device 4 Control and evaluation module 5 Output 6 Display 7 Monitor 8 VR headset 9 Stimulus 10 Optical plane 11 Manual input 12 Data output 13 Random generator 14 Modem 15 Internet 16 Computer cloud 17 Memory 18 Visual field range 19 Object 20 Cable connection/wireless connection 21 Primary viewing direction 22 Viewing direction P Subject S Degree of difficulty T Reaction time