COMPUTER PROGRAM, METHOD, AND APPARATUS FOR DETERMINING A SUBJECT'S VISUAL ACUITY - Patent application

Abstract

The present invention relates to a method for determining at least one functional ocular parameter, namely visual acuity, in particular a computer program for executing a computer-implemented method on a computer-equipped system, the system comprising: an optical system with a display system configured to project visual stimuli independently to a left and right eye of a subject, the visual stimuli comprising a plurality of patches arranged on a background; an eye-tracking system configured to record the gaze directions of the right and left eyes; and a computer configured to control the optical system and to receive recorded data from the eye-tracking system, the method comprising at least the following steps: - performing a trial session for determining visual acuity, the trial session comprising a plurality of the visual stimuli presented to a left eye and / or a right eye of a subject using the optical system; - recording data during said trial session, including information regarding said gaze direction; - determining at least visual acuity from the recorded data of said trial sessions by analyzing the movements of the left and right eyes of the subject in response to the presented visual stimuli of said trial sessions, in particular the correlation of said movements; Including, Here, the patches are characterized by being isoluminant with respect to the background, the patches display a luminance distribution that varies periodically with spatial frequency, and each patch is a bounded set that covers only a portion of the background.

Description

[Technical field]

[0001] The present invention relates to a method for determining the visual acuity of a subject, in particular to a computer program for carrying out the computer-implemented method, and to a system arranged to execute the computer program according to the invention. [Background technology]

[0002] Methods are known in the art for determining functional ocular parameters such as visual acuity, strabismus, relative afferent pupillary defect, and visual field.

[0003] Usually, the evaluation of these parameters requires various equipment and specialized medical personnel to perform the necessary tasks. Therefore, the time required to estimate these parameters increases. Therefore, the more parameters are determined from the subject, the higher the degree of compliance of the subject is required.

[0004] Furthermore, some methods for measuring RAPD, such as the swinging flashlight test, suffer from a high degree of variability in test results between repeated tests.

[0005] Therefore, there is a need for methods that are less complicated in terms of subject compliance and comprehension of the test, and in terms of implementation by practitioners.

[0006] Although virtual reality systems address some of the problems related to the user's vision, see for example US 2017 / 0290504 A1, methods for computer-aided diagnosis of functional eye parameters are still lacking.

[0007] With regard to visual acuity measurement, a problem in the art is the so-called Moiré effect, which places boundaries on displayable items on a screen and can interfere with the proper display of periodic patterns on the display. [Prior art documents] [Patent documents]

[0008] [Patent Document 1] US Patent Publication No. 2017 / 0290504 A1 Summary of the Invention [Problem to be solved by the invention]

[0009] The present invention aims to fill this void. To this end, and in order to overcome the problems associated with methods known in the art, the present invention provides computer programs, computer-implemented methods and systems, in particular neuro-ophthalmoscopy, that aim to solve these problems. [Means for solving the problem]

[0010] Advantageous embodiments are set forth in the dependent claims. [Brief description of the drawings]

[0011] [Figure 1] FIG. 1 illustrates the measurement of pupil diameter according to the present invention to determine RAPD. [Diagram 2] FIG. 2 illustrates diagrammatically one embodiment of the present invention for measuring strabismus. [Diagram 3] FIG. 3 shows a schematic representation of another embodiment of the invention for measuring strabismus. [Figure 4] FIG. 4 shows a schematic diagram of the measurement of a human visual field. [Diagram 5] FIG. 5 shows stimuli and assessments for determining a person's visual acuity. [Figure 6] FIG. 6 shows a schematic diagram of a system according to the invention. [Figure 7] FIG. 7 shows the various patches of stimuli used to determine visual acuity. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0012] According to the present invention, there is provided a computer program, which when executed on a computer, causes a system comprising a computer to execute a method, in particular a computer-implemented method, for determining visual acuity, the system comprising an optical system comprising a display system configured to project visual stimuli independently to the left and right eyes of a subject. The display system may comprise a first and a second display system, such as a first and a second screen. The display system is configured to project visual stimuli independently to the left and right eyes of a subject. The system further comprises an eye-tracking system configured to simultaneously, independently and in a time-resolved manner record the gaze direction and pupil size of the left and right eyes, in particular at a sampling rate, i.e. frame rate, better than 20 Hz, in particular at a sampling rate better than 50 Hz, more in particular at a sampling rate better than 200 Hz. The system further comprises a computer with a processor configured to control the optical system, for example to control the brightness and duration of illumination of the visual stimuli on the display system, and to receive data from the eye-tracking system.

[0013] The method carried out according to the invention comprises at least the following steps: - performing a trial session for determining the visual acuity of the subject, said trial session comprising a plurality of visual stimuli presented by means of an optical system to the left and / or right eye of the subject, in particular presented simultaneously; - recording data during said trial session to determine visual acuity including information regarding gaze direction; - determining at least visual acuity from the recorded data of the trial session by analysing the movements of the subject's left and right eyes in response to the presented visual stimuli of the trial session, in particular the correlation of the movements, in order to determine visual acuity.

[0014] The visual stimulus comprises a plurality of patches arranged on a background, the patches being isoluminant with respect to the background, and the patches being characterized by displaying a luminance distribution that varies periodically with spatial frequency, in particular with only one spatial frequency, where each patch is a bounded set covering only a portion of the background.

[0015] A trial session for determining visual acuity can be configured so that initially there are no eye movements and left and right eye movements are initiated only once the subject recognizes the stimulus.

[0016] The present invention may alternatively or additionally be claimed as a method, in particular a computer-implemented method, which may be configured to interconnect components of a system to perform the steps of the method.

[0017] The present invention allows visual acuity to be measured in one attempt.

[0018] The optical system comprises a display system for displaying visual stimuli to the subject's eyes. To this end, the display system may comprise two display units or two displays configured to present visual stimuli to the left and / or right eye. This presentation may be performed independently for each eye, such that it is possible to present a visual stimulus only to a selected eye, while at the same time presenting no stimulus or a neutral stimulus to the other eye of the subject.

[0019] The display system may comprise two or more different computer screens used for desktop applications, or the display system may comprise only one computer screen optically separated along a vertical line into two display screen sections.

[0020] The system may comprise a chin rest for the subject to reduce head movements relative to the eye tracking system. Alternatively, the display system comprises one or more near-eye displays or similar devices placed directly in front of the eyes, for example at a distance less than 20 cm, at a virtual distance of about 0.2 m to more than 4 m, in particular at a distance of infinity. In particular, a near-eye display in the form of a head-up display or virtual reality goggles (VR goggles) may be worn by the subject during the performance of the method. This allows for a more accurate and controlled testing environment, in particular the chin rest may be omitted in such a system. Furthermore, the use of a near-eye display allows the system to be used in clinical trials requiring the subject to move their head while the gaze positions of both eyes are recorded. Furthermore, such a system can be designed as a portable system, allowing its use in field studies.

[0021] The system further comprises an eye tracking system, which in particular has a time resolution of milliseconds, which corresponds to a frame rate in the range of several hundred Hz, allowing for a time-resolved recording of saccadic eye movements. Typically, eye tracking systems have a frame rate or time resolution of 200 Hz or better.

[0022] However, for determining visual acuity, it is not particularly important to resolve saccadic movements, so it is sufficient for the system to have a low temporal resolution in the range of 30 Hz to 60 Hz.

[0023] The eye tracking system can be located on the display system or can be incorporated into a near-eye display, such as a VR goggle or similar device.

[0024] The eye tracking system is configured to record pupil size and gaze direction data for each eye independently. The recorded data can be evaluated by a computer or the eye tracking system.

[0025] According to another embodiment of the present invention, the trial session comprises multiple trials.

[0026] In general, a trial session includes, among other things, a sequence of at least one trial, where a trial includes at least one visual stimulus, and in particular, a trial includes the presentation of visual stimuli to both eyes, either sequentially or simultaneously.

[0027] According to another embodiment of the present invention, the patches are isochromatic.

[0028] This embodiment is nevertheless capable of providing a colored stimulus that allows for the determination of visual acuity.

[0029] According to another embodiment, at least some of the patches are a different color than the background.

[0030] According to this embodiment, the patches may be isoluminant rather than isochromatic, so that a subject may not be able to distinguish patches of different colors if their color vision is impaired.

[0031] In the latter embodiment, the subject's color vision can be tested simultaneously with or separately from visual acuity.

[0032] According to another embodiment of the invention, the stimulus comprises a plurality of patches, each patch being a bounded set covering a limited area behind the patch, in particular the patches covering a connected area.

[0033] According to another embodiment of the invention, the patches are identical to each other, but are displayed at different positions on the background. The patches according to this embodiment have the same size, shape and luminance distribution.

[0034] According to another embodiment of the present invention, the luminance distribution varies with a single spatial frequency.

[0035] This allows for a unique definition of the subject's visual acuity compared to multiple spatial frequencies, with a single spatial frequency associated with the subject no longer perceiving the patch.

[0036] In particular, when a periodically varying luminance distribution is generated by the assumption of multiple periodic functions, the periodic function with the largest amplitude is considered as the spatial frequency of the luminance distribution. The spatial frequency is considered to generate a luminance distribution with periodically varying luminance. That is, for example, a Gaussian luminance distribution is not considered to be a periodic luminance distribution, even though a Gaussian function may be generated by the superposition of multiple sinusoidal functions that implicitly have spatial frequencies. The spatial frequency of the luminance distribution is considered to be the spatial frequency that gives the luminance distribution periodicity. Preferably, the luminance distribution varies with a single spatial frequency, and therefore exhibits a unique periodicity. In a particular embodiment, the spatial frequency is not smaller than a pixel of the display system.

[0037] According to another embodiment of the invention, the luminance distribution varies periodically along at least one direction with a spatial frequency. The direction may be chosen along a 2D plane of the display system and / or along a direction in an associated Cartesian coordinate system in which these patches may be located. In particular, the periodically varying luminance distribution of each patch varies radially with respect to each patch. That is, the luminance of each patch may vary periodically and radially with respect to the center of the patch.

[0038] According to another embodiment of the invention, the spatial frequency is isotropic, such that during the trials of a trial session, the spatial frequency is the same along all directions of the patch, resulting in a radially symmetric, periodically varying luminance distribution of each patch, such as concentric circles.

[0039] According to another embodiment of the invention, the spatially averaged luminance of the patch is equal to the luminance of the stimulus background against which the patch is displayed to the subject.

[0040] According to another embodiment of the invention, the visual stimuli are adjusted for different trials with respect to the spatial frequency of the luminance distribution.

[0041] Alternatively, or in addition, the visual stimuli are adjusted for different trials with respect to patch size.

[0042] A combination of both embodiments, or both alone, makes it possible to detect the threshold at which the subject can no longer perceive the patch on the background.

[0043] The previous two embodiments define a trial session, where for each trial the spatial frequency and / or size of the patches are adjusted, in particular where the orientation of the spatial frequency of the luminance distribution is kept constant.

[0044] According to another embodiment of the present invention, the size of the patch and the spatial frequency of the luminance distribution are adjusted for different trials such that the number of periods of the varying luminance distribution within the patch is kept constant. This embodiment essentially discloses that the patch is scaled for different trials.

[0045] According to another embodiment of the invention, the ratio between the size and the number of periods provided in the patch is constant for different trials.

[0046] Size can be the area that the patch covers, the diameter, or the extent along which the spatial frequency of the patch varies.

[0047] According to another embodiment of the present invention, a periodically varying luminance distribution with 0.5 to 100 periods is configured in the patch, in particular independent of the size of the patch. Preferably, each patch comprises a spatially varying luminance distribution with 1 to 5 periods. More particularly, each patch comprises a plurality of periods.

[0048] The above embodiment allows adjusting the size of the patch while maintaining the same appearance of the patch, i.e. making only the patch larger or smaller.

[0049] According to another embodiment of the invention, the patches are arranged randomly and / or non-overlappingly on the background.

[0050] According to another embodiment of the present invention, during a trial session, the patch moves back and forth at least once along a predetermined trajectory, where the gaze tracking system records eye movements and / or eye gaze direction in response to the moving patch. In particular, the trajectory may be a smooth trajectory, i.e., does not constitute abrupt, i.e., not continuous, speed changes in either magnitude or direction.

[0051] The term "smooth" in the context of this specification particularly relates to the property of a trajectory, profile or function that is differentiated in a mathematical sense, i.e. the trajectory, profile or function may not only be continuous but also differentiable.

[0052] In this embodiment, a measurement process for determining visual acuity is defined.

[0053] According to another embodiment of the invention, the patch moves back and forth in one direction, in particular along a horizontal direction, ie a direction extending parallel to an imaginary axis joining the subject's eyes.

[0054] According to another embodiment of the invention, the patch moves back and forth according to a periodic, in particular a sliding, periodic velocity profile for each trial, the velocity profile being the same for all patches, the velocity profile may be circular, elliptical, with respect to position, for example with a constant velocity magnitude.

[0055] According to another embodiment of the invention, the velocity profile may follow a sinusoidal velocity profile along one direction, i.e. the patch moves back and forth along one direction while exhibiting a sinusoidal velocity magnitude.

[0056] According to another embodiment of the invention, during a trial session, a patch is presented to only one eye and then the other eye so that monocular visual acuity can be determined.

[0057] According to another embodiment of the invention, during a trial session the size of the patch is successively reduced or increased after different trials, in particular after the patch has moved at least once along the predefined trajectory.

[0058] This embodiment allows finding the threshold at which a person starts or stops perceiving a moving patch.

[0059] This threshold can be determined in the following embodiment.

[0060] According to another embodiment of the invention, the visual acuity of the subject is determined from the correlation of the recorded eye movement with the patch movement, in particular the visual acuity is determined from the patch size and / or spatial frequency at which the eye movement deviates from the patch movement, in particular the patch trajectory, by a predefined value, in particular this deviation being measured in the form of a least square deviation of the eye movement with respect to the patch movement. Alternatively or additionally, a predefined correlation value, a time difference and / or a spatial difference (lag) between the eye position and the patch position may serve as the predefined value.

[0061] Eye movements may follow the movement of the patch with a time offset, so the predetermined value may be a maximum offset value beyond which a person indicates that they no longer perceive the patch reliably.

[0062] The visual stimulus may comprise a background and a patch disposed on the background, said stimulus may include noise, so the predetermined value may be noise dependent.

[0063] The predetermined value may also be given by a selected number of saccades performed by the subject's eyes during a trial and ending at the location of the patch: if the number of saccades not ending at the location of the patch exceeds the predetermined number, it can be concluded that the subject is no longer perceiving the patch.

[0064] According to another embodiment of the invention, the background is of a uniform color or grey value with uniform brightness.

[0065] According to another embodiment of the invention, the patches maintain a constant distance and a constant relative position with respect to each other, so that the pattern in which the patches are arranged relative to each other on the background does not change when the patches are moved.

[0066] According to another embodiment of the invention, the patches are Gabor patches.

[0067] Gabor patches are particularly well suited for determining visual acuity.

[0068] According to another embodiment of the invention, the intensities of the Gabor patches follow a Gaussian kernel function with variance, in particular an isotropic variance, said Gaussian kernel function being modulated by a sinusoidal plane wave with a given direction and a given period.

[0069] In this embodiment, we further define the appearance of the Gabor patches.

[0070] According to another embodiment of the present invention, the period of the sinusoidal plane wave is within the variance and triple variance of the kernel function.

[0071] According to another embodiment of the invention, the sinusoidal plane wave is centred with its maximum amplitude or zero crossing at the mean value of the location of the Gaussian kernel function.

[0072] According to another embodiment of the invention, the ratio of the variance of the Gaussian kernel of a Gabor patch to the period of the sinusoidal plane wave is constant and in particular does not depend on the size of the Gabor patch.

[0073] According to another embodiment of the invention, the visual stimulus comprises a uniform background, the term "uniform" referring in particular to a monochromatic or grey background having uniform luminance, such that the background does not exhibit any structural features.

[0074] According to another embodiment of the invention, the visual stimulus consists of an area, particularly of uniform color and luminance, on which the patches are irregularly or randomly arranged, which can be considered as the background of the stimulus, which can be kept constant and unaltered throughout the trial session.

[0075] According to another embodiment of the invention, the luminance of the patch, in particular the luminance distribution, is given by a kernel function configured to define the size of the patch, said kernel function being modulated by a periodic function configured to impress a spatial frequency within the patch at which the luminance of the patch varies periodically, in particular this periodic function comprises exactly one spatial frequency.

[0076] This periodic function can be a sine wave function or a square wave function.

[0077] According to another embodiment of the invention, the period of the periodic function, in particular the period of the sinusoidal plane wave, is selected such that the patch comprises between half a period and up to three periods within the size of the patch, in particular the period may range from the variance of the Gaussian kernel to one third of the variance.

[0078] In particular, the periodic function is centered by a maximum or minimum value in the patch.

[0079] For example, if the patch is a Gabor patch, then the sinusoidal plane wave is centered with the maximum amplitude at the mean value of the location of the Gaussian kernel function.

[0080] According to another embodiment of the present invention, the ratio of the variance of the Gaussian kernel of a Gabor patch to the period of the sinusoidal plane wave is constant and in particular does not depend on the size of the Gabor patch. This embodiment is a special case of the previous embodiment, which requires that the ratio between the size of the patch and the number of periods is constant. Therefore, the variance of the Gaussian kernel function can be considered as the size or degree of size of the patch.

[0081] According to another embodiment of the invention, the patch, in particular the Gabor patch, moves along a direction, in particular the horizontal or vertical direction, and the velocity of the patch varies periodically, in particular smoothly periodic, more in particular sinusoidally, such that the patch moves back and forth along said direction in a periodic manner.

[0082] According to another embodiment of the invention, the periodic velocity profile has a frequency between 0.02 Hz and 2 Hz, more particularly between 0.05 Hz and 0.5 Hz.

[0083] According to another embodiment of the invention, the velocity of the patch is varied periodically such that the patch moves back and forth along said direction in a periodic manner, e.g. a zigzag or square wave velocity profile, the latter of which results in an abrupt change in the direction of the patch.

[0084] In particular, the velocity varies periodically with a sliding periodic function.

[0085] Further embodiments are described below that may be combined with the present invention to generically and rapidly determine visual ocular parameters other than visual acuity.

[0086] According to a further embodiment of the invention, the computer program is further configured to execute a method, in particular a computer-implemented method, of determining multiple afferent and efferent functional eye parameters, such as a relative afferent pupillary defect (RAPD), one or more strabismus angles, and / or visual field using the system, wherein the afferent pupillary defect (APD), in particular the relative afferent pupillary defect (RAPD), is determined from a first trial session consisting of a sequence of only a first type of stimuli presented in an automated manner to the left and right eyes of the subject using the display system, and / or the visual field of the subject's left and right eyes is determined from a second trial session consisting of a sequence of only a second type of stimuli presented in an automated manner to the left and right eyes of the subject using the display system, and wherein strabismus is also determined from the first trial session and / or the second trial session. Strabismus may be characterized by one or more strabismus angles, such as horizontal strabismus angle, vertical strabismus angle, and / or torsional strabismus angle. Thus, the method of this embodiment can determine strabismus by determining one, two, or all three of these strabismus angles. In particular, at least the horizontal strabismus angle is determined. In addition, it is also possible to determine the vertical strabismus angle. It should be noted that when determining the strabismus of a subject, any combination of the three strabismus angles can be determined.

[0087] This embodiment solves the problem of providing a shortened and simplified measurement method for various functional eye parameters by a series of one type of visual stimuli, which allows the determination of multiple functional eye parameters using the same system. That is, multiple functional eye parameters are determined in an objective manner during one trial session, here the first trial session or the second trial session. Furthermore, the method allows the measurement of functional eye parameters in an automated manner without the need for the subject to provide verbal or tactile feedback, thereby reducing the complexity of the test and eliminating sources of error. Furthermore, the fully automated execution allows the measurement time for evaluating various functional eye parameters to be reduced, since the subject and the medical personnel do not need to switch between different measurement systems.

[0088] It should be noted that in the context of this specification, the determination of an APD can also include the determination of a RAPD, such that a RAPD can be determined from the same data set when an APD is simultaneously or alternatively determined, and thus in the following only reference is made to APD, rather than both types.

[0089] The afferent and efferent ocular parameters, i.e. functional ocular parameters, may include one or more of the following groups: - APD and / or RAPD; - Strabismus angle; - saccadic peak velocity; - efferent pupillary function; - saccadic accuracy; - smooth pursuit; - Visual field, especially visual field determined by threshold perimetry; - visual acuity; - Fusional amplitude.

[0090] The term "first" trial session as used herein is not to be understood as an indication that the first trial session must be the first trial session performed in a series of trial sessions, but merely serves the purpose of providing a distinction to different trial sessions, such as a trial session for determining visual acuity (which has no numbering associated with it), a second or third session (which may be performed before or after the first trial session or the trial session for determining visual acuity).

[0091] A visual stimulus is a stimulus that is presented to the subject's eyes. The stimulus may or may not be visible to the subject, for example, when the stimulus is a no-stimulus, a dark stimulus, or a neutral stimulus.

[0092] The visual stimuli of the first type of stimuli may or may not comprise a fixation object, or any object that allows the eye to focus on said object, in particular the first type of stimuli have a predetermined brightness such that upon presentation of the first type of stimuli the pupil size is constricted or dilated.

[0093] In this manner, the first type of stimulus is designed to provide at least a predetermined brightness of the stimulus such that the eye to which the first type of stimulus is presented is exposed to a predetermined, adjustable total brightness. By assessing pupillary constriction or dilation in response to the stimulus, several functional ocular parameters, such as RAPD, can be determined.

[0094] The first type of stimulus that is expected to cause the pupil of the eye to constrict is also referred to in the context of this specification as a light stimulus, and the first type of stimulus that is expected to cause the pupil of the eye to dilate is also referred to in the context of this specification as a dark stimulus.

[0095] In particular, the dark stimulus / no stimulus is represented by the black, specifically unilluminated, display state of the respective display system.

[0096] In particular, the first type of visual stimulus consists of stimulus images.

[0097] In particular, this first type of visual stimulus is different from the stimuli presented during the trial session for determining visual acuity.

[0098] During a central or intermediate portion of the first trial session, a light stimulus can be presented to one eye and a dark stimulus can be presented to the subject's respective other eye at the same time. A dark stimulus can then be presented to one eye at the same time that a light stimulus is presented to the other eye, and this procedure is repeated several times. The first type of stimulus is switched between the subject's left and right eyes during the first trial session.

[0099] In particular, a light stimulus can be presented simultaneously to both eyes and thereafter a dark stimulus can be presented simultaneously to both eyes during an initial and / or final part of the first trial session, in particular at the beginning of the first trial session before the central or middle part is performed and / or at the end of the first trial session after the central or middle part is performed.

[0100] Performance of the initial portion and / or the final portion in the first trial session may serve to establish and / or verify baseline values ​​for constricted and dilated pupil size for both eyes.

[0101] According to another embodiment of the invention, from the initial and / or final part of the first trial session, the efferent pupillary function or efferent pupillary defect is determined. In particular, the efferent pupillary function is determined from the speed at which the pupil dilates after switching from a light stimulus to a dark stimulus. If the dilation speed is below a predefined threshold, the subject may suffer from an efferent pupillary defect or an efferent pupillary dysfunction disorder, for example a disorder due to Horner's disease.

[0102] During the first trial session, pupil size, e.g., pupil diameter or pupil radius, is automatically determined by a computer or eye tracking system from data recorded by the eye tracking system for each trial in a time-resolved manner such that the time course of pupil size, for both eyes, can be determined in relation to the presented stimuli presented at any time in the time course.

[0103] By quantifying the change in pupil size during the first trial session, the ADP, and particularly the RAPD (and efferent pupillary function) can be determined for each eye. Details of how the APD can be determined from the measurement data are detailed in the Examples section.

[0104] Both trial sessions included trials based on similar types of visual stimuli.

[0105] In particular, the first trial session consisted of only the first type of stimuli.

[0106] It should be noted that the display position can be expressed as a pair of angles that describe the position of the display relative to a central gaze direction or primary axis, as is well known to those skilled in the art.

[0107] According to another embodiment of the present invention, the execution of the first trial session comprises the following steps: - recording data by the eye tracking system, said data comprising information about pupil size and gaze direction of the first and second eyes of the subject during the first trial session, in particular a sampling rate of the pupil size and gaze direction having a sampling rate of more than 100 Hz, in particular more than 200 Hz, and in particular the data being recorded for at least 1 second or more; - determining the APD from the recorded data of the first trial session, in particular by computer analysis of the time course of pupil size of the left and right eyes in response to the presented first type of stimuli; - determining at least one strabismus angle or a plurality of strabismus angles from the recorded gaze directions of the first trial session by computer analysis of the magnitude and direction of saccadic eye movements, in particular in response to the presented first type of visual stimuli.

[0108] According to another embodiment of the present invention, the execution of the second trial session comprises the steps of: - recording by the eye tracking system data comprising information regarding the gaze direction of the first eye and the second eye of the subject during a second trial session, in particular wherein a sampling rate for gaze direction detection has a sampling rate of more than 200 Hz and in particular wherein said data is recorded for at least 1 second; - determining the visual field and at least one strabismus angle or a plurality of strabismus angles by computer analysis of the subject's saccadic eye movements from the recorded gaze directions of the second trial session, in particular in response to the presented second type of stimuli.

[0109] In this embodiment, by performing a second trial session having a different type of visual stimulus compared to the first type of stimulus, strabismus can be determined simultaneously with determining the subject's visual field.

[0110] According to another embodiment of the invention, from the data recorded during the first and / or second trial session and from the sequence of the first or second type of stimuli, the following functional ocular parameters are determined: - saccade peak velocity, - Saccade accuracy, is determined from data of the first and / or second trial sessions.

[0111] In this embodiment, the method uses only one or two trial sessions with one or two visual stimuli (separate from the trial session for determining visual acuity), making the method even more versatile since it allows multiple functional ocular parameters to be determined simultaneously using only a single measurement system.

[0112] According to another embodiment of the invention, from the recorded gaze directions of the first trial session, one or more strabismus angles are determined using a computer by analyzing the magnitude and direction of saccadic eye movements or the deviation of the gaze direction of the non-fixating eye from the gaze direction of the fixating eye.

[0113] In particular, the deviation, eg the difference, of the gaze position / direction of the two eyes is determined by a computer and from this deviation the strabismus, in particular the strabismus angle or angles, is determined.

[0114] According to another embodiment of the present invention, the deviation of the gaze position / direction of both eyes, in particular the difference between the gaze directions / positions, is determined by a computer and from this deviation the strabismus, in particular one or more strabismus angles, is determined, where the deviation is determined at least once during a trial session, for example during a first, second (or third or visual acuity determining trial session) trial one eye is exposed to a visual stimulus configured to fixate the eye on the stimulus and the other eye is not exposed to such visual stimulus.

[0115] In the following further advantageous embodiments are disclosed which allow the invention to measure even more functional eye parameters on the same system using the same type of stimuli.

[0116] According to another embodiment of the invention, efferent pupil function of both eyes is determined from data of a sequence of a first type of visual stimuli recorded during a first trial session.

[0117] According to another embodiment of the invention, the gain of smooth pursuit is determined from data recorded during a second trial session of a sequence of a second type of visual stimuli.

[0118] According to another embodiment of the invention, only the first trial session and the trial session for determining visual acuity are performed.

[0119] In this embodiment, two important functional eye parameters, APD and strabismus angle of a subject, can be measured quickly and reliably by simply running a single trial session on the system and a trial session to determine visual acuity.

[0120] According to another embodiment of the present invention, in addition to the trial session for determining visual acuity, exactly two trial sessions, i.e. a first trial session and a second trial session, are performed, in which at least the APD, strabismus angle, and visual field of the subject are determined from data of the sequences of the first type of visual stimuli and the second type of visual stimuli recorded during the first trial session and the second trial session. In particular, the strabismus angle is determined from data recorded either during the first trial session or only during the second trial session.

[0121] According to another embodiment of the present invention, each visual stimulus of the first type of visual stimulus comprises a fixation object displayed on the display system at a display position of the display system, the fixation object being a spatially limited graphical object enabling eye fixation on the fixation object, in particular on a part of the fixation object.

[0122] A spatially bounded graphical object or a discernible portion of a larger object is so small that the direction of gaze when viewing the fixation object indicates the location of the fixation object within 0.1°. In particular, the fixation object is smaller than 1°.

[0123] In particular, a fixation object is an object that can be darker or lighter than the background of the stimulus image.

[0124] For the determination of RAPD, the fixation object is not important, but for the determination of strabismus angle, a fixation object is required. Thus, when determining strabismus angle from the first trial session, the first type of stimuli comprises a fixation object.

[0125] For example, by evaluating the saccade amplitude and in particular the direction of the saccade movement when a first type of stimulus comprising a fixation object is switched from the left eye to the right eye and / or vice versa, the strabismus angle can be determined from the measurement data and diagnosed quantitatively, in particular by computer.

[0126] Computer-generated APD and strabismus measurements can be presented on an interface to trained medical personnel.

[0127] According to another embodiment of the invention, a first type of visual stimulus is displayed alternately to the right and left eye and repeated two or more times, in particular while a non-stimulus or dark stimulus is presented to the respective other eye, and the subject's pupil size and gaze direction are recorded for both eyes by an eye tracking system, in particular at a frame rate of at least 100 Hz.

[0128] This allows the APD and strabismus angle of each eye to be determined.

[0129] According to another embodiment of the present invention, the first trial session comprises a plurality of gaze direction blocks, in which in each gaze direction block, a first type of visual stimulus is repeatedly and alternately presented to the right and left eyes, and for different gaze direction blocks, the fixation object is displayed at different display positions, and in particular, for each gaze direction block, the strabismus angle and the RAPD are determined separately.

[0130] The display location can be selected randomly from a set of display locations, however, it is possible to select the display location of the fixation object depending on the detected corrective saccadic eye movement of the eye when the first type of visual stimulus is switched from one eye to the other.

[0131] In particular, the display positions of the different gaze direction blocks are arranged on the subject's visual field, the display positions are arranged in areas of a 3x3 matrix, in particular, one of the display positions, in particular the central display position, corresponds to the main gaze direction, i.e. straight gaze, and in each gaze direction block, only one such area is addressed by the display position. In this way, the strabismus angle can be measured between each gaze direction block of different areas. The areas may be referred to as combinations of common gaze directions in the vertical and horizontal directions, for example, right down, only upward, only left, upward and left, etc. The main gaze direction can be defined as a gaze direction that is essentially straight with respect to the head.

[0132] During each gaze direction block, data regarding pupil size is recorded to determine the APD.

[0133] As detailed above, during each gaze direction block, a first type of visual stimulus is repeatedly presented to the eye, and this embodiment allows for averaging of detected saccadic movements and pupil size to obtain more accurate results regarding strabismus angle and ADP from the first trial session.

[0134] In order to determine strabismus in more detail, the following embodiments teach the advantageous performance of a first trial session.

[0135] According to another embodiment of the invention, the fixation object is displayed at the same display position for the same gaze direction block, and the amplitude and direction of the saccadic eye movement are determined from the saccadic eye movements recorded each time the first type of stimulus switches from the left eye to the right eye or from the right eye to the left eye, and in particular the strabismus angle is determined for each gaze direction block such that the strabismus angle is determined in relation to the gaze direction.

[0136] The detected saccadic eye movements can be evaluated in particular by determining a saccade starting point, which is recorded for both eyes when a first type of visual stimulus is switched from one eye to the other eye, and a saccade end point, which is determined for both eyes after the time taken for the eye to which the fixation object is presented after the stimulus switch to focus on the fixation object.

[0137] The direction defined by the vector pointing from the start point to the end point provides information about the direction of the strabismus, and the length of said vector corresponds to the amplitude of the saccadic eye movement and can be related to the magnitude of the strabismus.

[0138] It is also possible to determine torsional strabismus, which is related to the torsion of the eye, which is recorded by an eye-tracking system and can be evaluated by a computer from the data of the eye-tracking system, in particular from the torsion state at the start of the saccadic eye movement and also from the torsion state at the end of the saccadic eye movement, which is derived from the torsion state at the start and end of the saccadic movement.

[0139] The saccadic eye movement in response to the switching of the first type of stimulus is characterized, inter alia, by a direction pointing from the saccade start point to the saccade end point, an amplitude indicating the distance between the saccade start point and the saccade end point, and a twist between the saccade start point and the saccade end point, and a strabismus angle is determined, inter alia, from at least one saccadic eye movement, or from multiple saccadic eye movements.

[0140] The strabismus angle can be expressed as a horizontal angle, a vertical angle, and a torsion angle for each gaze direction.

[0141] It should be noted that the term "same" display position with respect to the first and second display systems refers to corresponding display positions on the first and second display systems that are considered to correspond to the same gaze direction in an ideal eye model (no strabismus).

[0142] According to another embodiment of the present invention, the magnitude and direction of the saccadic eye movement are determined from the recorded saccadic eye movement each time the first type of stimulus switches from the left eye to the right eye or from the right eye to the left eye, and in a subsequent presentation of the first type of visual stimulus to the same eye in the same gaze direction block, the display position of the fixation object is adjusted so as to correct the saccadic eye movement in amplitude and direction as determined from the first type of stimulus presented earlier in the gaze direction block, in particular until the saccadic movement is minimized within the same gaze direction block, and in particular the strabismus angle corresponds to this adjusted display position, and in particular the strabismus angle is determined for each gaze direction, such that the strabismus angle is determined with respect to the gaze direction.

[0143] This embodiment allows for a more robust determination of strabismus angle, as the method is less dependent on accurate values ​​from eye tracking and only needs to demonstrate non-movement of the eyes.

[0144] The terms and definitions of the previous embodiment also apply to this alternative embodiment.

[0145] This embodiment essentially aims to correct corrective saccadic eye movements by presenting a fixation object to the eyes in a shifted and / or rotated manner. In this way, the magnitude, direction and especially the torsion of the strabismus can be determined directly from the position and degree of rotation of the fixation object.

[0146] The strabismus angle is determined, inter alia, by measuring the amplitude and direction between vectors pointing from the start to the end of a saccadic eye movement in response to a switch in the first type of stimulus, and assigning to the strabismus angle its magnitude and opposite direction relative to the adjusted viewing position.

[0147] According to this embodiment, the disparity of the visual stimuli presented to both eyes is used to calculate the strabismus angle. In particular, the disparity is defined as the direction and amplitude of the adjustment applied to the fixation object to correct the corrective saccadic eye movement. The strabismus angle can be expressed as horizontal, vertical and torsion angles for each gaze direction.

[0148] According to another embodiment of the present invention, each visual stimulus of the second type of visual stimuli includes a luminance object displayed on a uniform background at a relative position on a display system, and during a second trial session, the luminance objects of the second type of visual stimuli are displayed sequentially at a plurality of selected relative positions, the second type of visual stimuli are displayed alternately or sequentially to the right eye and the left eye, in particular, a neutral stimulus identical to the second type of stimuli without the luminance object is presented to each other eye, and each time a luminance object is displayed at a selected relative position, it is determined by the computer whether the subject has detected the luminance object at the selected relative position, and if the subject detects the luminance object, the luminance object is displayed at the selected relative position. , and then displayed at a different selected relative position, in particular at a reduced luminance, where the luminance object is displayed again at the selected relative position in a subsequent trial at a reduced luminance (compared to the luminance at which the subject detected the luminance object at this selected relative position), where if the subject does not detect the luminance object at the selected relative position, the luminance object is repeatedly displayed at the selected relative position, with increasing luminance, until the subject detects the luminance object, not necessarily thereafter, thereby determining the luminance detection threshold of each eye of the subject for each selected relative position, and thereby allowing the visual field to be determined in the form of a threshold perimetry.

[0149] The relative positions depend on the subject's current gaze direction. Therefore, the relative positions are provided in a gaze-centered coordinate system. The current gaze direction can be determined by an eye-tracking system.

[0150] The relative positions may be selected from a plurality of relative positions distributed in a quadrant of the field of view, in particular 20, 50 or more relative positions.

[0151] A luminance object is a spatially confined object that is so small that the direction of gaze when viewing the luminance object indicates the location of the luminance object within 0.1°. In particular, a luminance object is larger than 0.1°. For example, a luminance object may have a diameter in the range of 0.1-1.7°, in particular a diameter in the range of 0.3-0.7°, and is placed against a background of uniform luminance.

[0152] The luminance object may be adjusted in terms of its relative position and its luminance and / or size in the second type of stimulus presented to the eye.

[0153] In particular, when the brightness is adjusted, the brightness is decreased or increased by 2 dB to 10 dB, more particularly 2, 4, 6, 8, or 10 dB. The brightness of the object can be controlled by a computer.

[0154] The measurement method with a luminance object arranged relative to the current gaze direction allows different types of evaluations and tests to be performed without the subject having to constantly gaze in a specific direction. Therefore, this test situation requires less adherence from the subject to the test setup and the execution of the method. As described below, the determination of the visual field can be performed in a fully automated manner. Feedback of whether the subject has detected the luminance object can be provided by the subject simply looking at the luminance object, compared to performing additional actions such as pressing a button or speaking out loud. This makes the method more intuitive and less prone to errors.

[0155] The term luminance object specifically relates to the functionality of the object, namely its luminance being able to be changed during the second trial session.

[0156] Thus, the first type of visual stimuli and the second type of visual stimuli differ at least in that the luminance of the first type of visual stimuli is not adjusted during the trial session.

[0157] Luminance objects can be presented as bright objects on a uniform grey or black background with continuous background luminance.

[0158] The second trial session allows for threshold perimetry of the visual field, for which the relative position can be randomly selected from multiple relative positions.

[0159] According to another embodiment of the present invention, the luminance object is deemed to be detected by the subject if a saccadic eye movement towards the displayed luminance object is recorded by the eye tracking system within a first time interval during which the luminance object is displayed, and in particular, the luminance object stimulus is deemed not to be detected by the subject if the first time interval is about 500 milliseconds and no saccadic eye movement towards the luminance object is recorded by the eye tracking system within the first time interval. The duration of the first time interval can be selected to be at least as long as two standard deviations of the mean response time to the visible stimulus, in particular twice as long as the mean response time.

[0160] In particular, the second type of visual stimulus, i.e. the luminance object, is considered to be detected by the subject only if the first saccade of the eye to which the luminance object is presented is greater than 2°, more particularly greater than 3°, towards the relative position of the luminance object's location.

[0161] More specifically, for each second type of stimulus a virtual hit box is defined extending around the location of the luminance object, the size of the hit box being dependent on the location of the luminance object, with the size of the hit box being closer together at locations closer to the central region of the visual field and larger in peripheral regions of the visual field.

[0162] The determination of whether a visual stimulus has been detected, i.e. whether a luminance object has been detected by the subject, is performed automatically and reliably so that accidental saccades can be ruled out by determining whether there is a correlated saccade upon presentation of the luminance object and whether this saccade is in the correct direction, i.e. towards the luminance object, and also whether it is sufficiently along the correct direction towards the luminance object.

[0163] When the eye detects a luminance object (i.e., when the relative position exceeds the eye's perception threshold), the eye makes a saccade toward the luminance object, thereby automatically determining whether the subject detected the luminance object when viewed on the display.

[0164] In this embodiment, automated measurement of the visual field can be performed without the subject having to provide non-visual feedback, such as audio instructions or button presses.

[0165] According to another embodiment of the present invention, the strabismus angle is determined for a relative position selected from saccadic movements, in particular from the amplitude and direction of saccadic eye movements, when the second type of stimulus switches from the left eye to the right eye or from the right eye to the left eye and when the luminance object is deemed to be detected by both eyes.

[0166] According to another embodiment of the present invention, a gaze direction resetting routine is performed, said routine comprising the steps of: - determining, in particular, whether the selected relative display position is located outside the physical tracking limits of the eye tracking system or the physical display limits of the display system, and if "yes": - presenting a suprathreshold object, such as a fixation object or luminance object, having a suprathreshold luminance that exceeds the luminance detection threshold in the current gaze direction of the eye; - moving the above-threshold objects along a trajectory at predetermined horizontal and vertical velocities to new display positions; - in particular hiding objects above a threshold; - performing the steps of the method of the previous embodiment at a selected relative position that is determined to be outside the physical display limits or physical tracking limits of the eye tracking, in particular before the gaze reset routine is executed.

[0167] This gaze direction reset routine may be performed, for example, if the selected relative position at which the attempt is made is outside the display limits of the display system, for example the physical horizontal screen limits.

[0168] Additionally, the gain of smooth pursuit can be determined by evaluating eye movements to above-threshold moving objects from the gaze reset routine.

[0169] Thus, the gaze reset routine may be performed during the first and / or second trial session, or during any other trial session.

[0170] A gaze reset routine may also be necessary and useful, for example, when the visual field needs to be evaluated at a relative position and most or all of the other relative positions for probing the visual field have already been tested. The subject's gaze direction is then reset so that the relative position at which the trial is performed is within the physical limits of the display system or the physical tracking limits of the eye-tracking system.

[0171] According to another embodiment of the present invention, during the gaze reset routine, the above-threshold object has a predetermined velocity pattern, particularly in a sequential manner, along the horizontal and vertical directions (as viewed by the subject), and wherein the deviation between the velocity of the detected eye movements following the above-threshold object and the velocity pattern of the above-threshold object is determined for each direction of movement of the above-threshold object, so that smooth tracking can be determined from the gaze reset routine.

[0172] According to this embodiment, for example, in the second trial session, the second type of visual stimulus is selected using a luminance object having a luminance above the subject's detection / perception threshold, where the luminance object is displayed to the subject so as to be presented in the current gaze direction, i.e., "directly in front" of the gaze direction, and the luminance object moves with a predetermined speed pattern. In this case, the above-threshold object corresponds to the luminance object.

[0173] Similarly, the routine may be performed and evaluated during a first trial session with the fixation object, or may be performed and evaluated during a further trial session with a different object.

[0174] Note that an object above the threshold may be a dark object on a light background, or vice versa.

[0175] This embodiment makes it possible to incorporate the determination of smooth pursuit in the first or second trial session, for example by using the same first or second type of visual stimuli.

[0176] According to another embodiment of the invention, the functional ocular parameters determined are: - subject's fusion width; Further comprising: Here, in order to determine the fusion width, the method comprises the steps of: - performing a third trial session, the third trial session comprising a third type of visual stimuli presented simultaneously to the left and right eyes of the subject using the optical system; and - recording data during the third trial session including gaze direction information; - determining at least a fusion width by computer analysis of the vergence between the left and right eyes of the subject in response to the presented third type of visual stimuli of the third trial session from the recorded gaze directions of the third trial session; Further includes:

[0177] According to another embodiment of the present invention, a third type of visual stimulus comprises images having a local spatial structure (each structure having multiple distinct spatial frequencies), and at the start of the third trial session, the images for the left and right eyes are positioned at zero image disparity requiring zero vergence, and thereafter images are presented to the left and right eyes with successively increasing or decreasing disparity, in particular the disparity may be horizontal, vertical or torsion disparity.

[0178] This embodiment allows for the determination of the fusional width by determining the maximum horizontal and / or vertical vergence angle of the eyes at which the subject can still correct the image disparity / disparity of the displayed third type stimulus by vergence eye movements. Any increase in image disparity at this point destroys fusion and vergence decays to a steady state (ideally 0 degrees).

[0179] According to another embodiment of the present invention, the gaze directions of the left and right eyes are recorded by an eye tracking system during any of the trial sessions, and wherein the strabismus angle is determined by subtracting the recorded gaze directions of the left and right eyes, in particular, the gaze directions of the eyes are recorded during the presentation of the first, second, third or fourth type of stimuli.

[0180] It should be noted that any of the trial sessions may be run independently of each other on the system.

[0181] According to a third aspect of the invention, a neuro-ophthalmoscope comprises the features of the system described above and program code stored on a computer for carrying out the method according to the invention.

[0182] Further, the optical system and the eye tracking system are comprised in a near-eye display such as VR goggles, or the optical system comprises a desktop screen and a separate eye tracking system disposed on the computer screen, and when the neuro-ophthalmoscope comprises VR goggles, the goggles further comprise an adjustable lens assembly for each eye such that optical aberrations of each eye of the subject can be corrected by the lens assembly.

[0183] In particular, exemplary embodiments are described below in conjunction with figures, which are appended to the claims and accompanied by texts explaining individual features of the illustrated embodiments and aspects of the invention. Individual features shown in the figures and / or described in said text of the figures may be incorporated (even in separate manner) in the claims relating to the device according to the invention. EXAMPLES

[0184] In the following, an exemplary system according to the invention is disclosed, however, it should be noted that it is also possible to use other systems capable of carrying out the method according to the invention in the same manner.

[0185] The system includes a display system including two displays positioned in front of the subject's eyes, the display system including two displays configured to independently display visual stimuli to the eyes, a first one of the displays positioned to present the visual stimuli to the right eye and a second one of the displays positioned to present the visual stimuli to the left eye.

[0186] Furthermore, the displays are positioned such that visual stimuli can only be presented to one eye, and each eye can only perceive one display. The crosstalk between these displays is 0.2 cd / m 2 must be less than.

[0187] These displays may have an associated coordinate system that describes the display position or location where a visual stimulus or object may be displayed. The coordinate system is essentially the same for both displays, and identical coordinates correspond to the same gaze direction with respect to an eye model with normal functional eye parameters, i.e., with respect to a strabismus angle of 0 degrees.

[0188] Additionally, the system includes an eye tracking system configured to record the eye gaze direction and pupil size, and may be equipped such that eye rotation and other related parameters can also be determined.

[0189] This eye-tracking system has a frame rate of over 200 Hz and is capable of resolving eye saccades into a series of images.

[0190] The eye tracking system may be integrated into the display system or placed in close proximity to the display system, ensuring that the subject's eyes are always visible to the eye tracking system during the trial session.

[0191] The eye tracking system can record data in the form of images of the subject's eyes. The eye tracking system can include modules for determining several eye parameters, such as eye position, pupil position, pupil size, and / or gaze direction.

[0192] The module can transfer the ocular parameters to a computer or include this data in the image data recorded by the eye tracking system.

[0193] The accuracy of determining the pupil size must be better than 0.01 mm, while the accuracy can be better than 0.05 mm.

[0194] Furthermore, in order to determine gaze direction accurately enough, the eye tracking system needs to be configured with an accuracy that is better than 1°.

[0195] The eye-tracking system is connected to the system's computer so that data can be exchanged between the computer and the eye-tracking system.

[0196] The computer is configured to control the eye-tracking system and the display system and thus to carry out the steps of a method according to the invention, in particular a computer-implemented method of the invention. The method can be executed on a computer in the form of a computer program, which causes the computer to control the display system and the eye-tracking system of the system, such that the recording and display of the visual stimuli are coordinated by the computer.

[0197] Further, the computer is configured to analyze the recorded data from the eye-tracking system, and in particular, the computer is capable of time-correlating the recorded data of the eye-tracking system with the presented visual stimuli.

[0198] The display system may include a lens assembly configured to be adjusted to the subject's near vision.

[0199] The display system and eye tracking system may be provided in a single device, i.e., a near-eye display, worn as a headset by a person, for example in the form of virtual reality goggles (VR goggles), which may include a lens assembly.

[0200] The system according to the present invention can then be used to carry out the method to determine a number of functional ocular parameters.

[0201] In accordance with the present invention, a trial session for determining visual acuity may be performed on the system, for example by a computer program, method, or computer-implemented method, the determination of visual acuity being described in the Examples below.

[0202] Determination of APD and RAPD from pupil size and the first trial session Below are provided one or more examples for several functional ocular parameters, detailing how each parameter is determined.

[0203] Traditionally, afferent pupillary defect (APD) is determined by the so-called swinging flashlight test, but this test tends to depend on the expertise of the person performing and evaluating the test, as well as the compliance of the subject.

[0204] The present invention allows tests to be performed repeatedly and reliably in an automated and objective manner.

[0205] Automated performance of the determination of APD requires a system as described in the context of this specification.

[0206] To determine the APD, a first trial session is performed by the subject. The first trial session consists of a number of trials. A trial consists of at least one first type of visual stimulus presented sequentially to at least one eye of the subject. During the trial session, the eye tracking system continuously records the pupil size and gaze direction of both eyes.

[0207] The visual stimuli used in this example for the first trial session are a first type of stimulus that comprises a fixation object, even though a fixation object is not required for the specific purpose of the test regarding the determination of APD.

[0208] The first type of stimuli are those that are bright, or luminous, enough to be expected to cause pupil constriction in healthy individuals, i.e., those not specifically affected by APD. This luminance is around 30 cd / m 2 However, the maximum is 50 cd / m 2 It could be.

[0209] Optionally, at the beginning or end of the first trial session, a dark or non-stimulus may be presented simultaneously to both eyes, capable of dilating the subject's pupils for at least a few seconds or minutes (T0-1, T0-2) (Figure 2, Figure 3). From this measurement, a baseline pupil size can be calculated independently from the recorded time course of the pupil size of each eye. Then, a first type of stimulus is presented simultaneously to both eyes of the subject for a few seconds, such that the minimum pupil size of the binocular pupil constriction is determined independently from the recorded time course of the binocular pupil size.

[0210] After this arbitrary initial alignment, the minimum and maximum pupil size is known for each eye.

[0211] The subject is then presented with a series of trials during which a first type of stimulus, i.e. light stimuli, is presented alternately to the eye and a dark stimulus to the other eye. That is, starting with the left eye, a light stimulus is presented to the left eye for, say, 3 seconds, and a dark stimulus is presented to the right eye for the same duration. Next, a light stimulus is presented to the right eye and a dark stimulus is presented to the left eye for the same duration. The presentation location of the fixation object is only a secondary property for determining the APD.

[0212] This sequence is repeated at least once. To evaluate the recorded data, a frame rate of the eye-tracking system of 60 Hz may be sufficient.

[0213] The first trial session yields a recorded time course of pupil size having hundreds to thousands of data points.

[0214] From the time course, the maximum pupil size before switching of the light stimulus and the minimum pupil size immediately after switching are determined by the processor, in particular the time course of each eye is smoothed against outliers with a smoothing algorithm. Thus, from the time course of both eyes, the processor can calculate the relevant amplitude of the change when exposed to the first type of stimulus. Thus, for each eye, the amplitude between the constricted and dilated pupil is calculated. The difference in the pupil response, i.e. the amplitude between the left and right eyes, indicates the magnitude of the relative afferent pupil defect (RAPD). The absolute amplitude compared to normal data of healthy subjects indicates the afferent pupil defect (APD). The latter is determined for each eye.

[0215] Optionally, average the pupil size of the left and right eye. For this averaged trace, determine the mean pupil size from 0 ms to 80 ms after the onset of the light stimulus. From this value, subtract the smallest pupil size reached after the onset of the light stimulus across all trials. This calculation gives the pupil amplitude. Compare the pupil amplitude of the left and right eyes. The difference indicates the size of the RAPD.

[0216] The second approach consists of subtracting the mean pupil size at the beginning and end of each trial. This value is determined by subtracting the value for the light stimulus for the right eye from the value for the light stimulus for the left eye. The sign and magnitude of the value obtained indicate which eye is affected by the RAPD and to what extent.

[0217] The time course through the first trial session and the associated recorded temporal pupil size are shown in Figure 1. In this example, a RAPD in the right eye is detected because the amplitude of the change in light stimulus from the right eye to the left eye is greater than the amplitude of the change in pupil size from the left eye to the right eye.

[0218] One advantage of the present method is that strabismus angle can also be determined within one trial session using the same type of visual stimuli.

[0219] Determination of efferent pupillary function The initial and final portions of the first trial session may be conducted as detailed above to establish baselines of constricted and dilated pupil size at the beginning or end of the first trial session. To this end, a light stimulus may be presented simultaneously to both eyes followed by a dark stimulus presented simultaneously to both eyes, or vice versa.

[0220] From the initial and / or final portion of the first trial session, the efferent pupillary function or efferent pupillary defect is determined. In particular, the efferent pupillary function is determined by the processor from the recorded time course of the size of the pupil of the eye. The efferent pupillary function is determined from the speed or time interval of the pupil dilation after switching from a light stimulus to a dark stimulus. If the speed of dilation is below a predetermined threshold speed or if the time interval is longer than a predetermined time interval, the subject may suffer from an efferent pupillary defect or an efferent pupillary dysfunction disorder (e.g., a disorder due to Horner's disease).

[0221] The rate of dilation can be determined from the slope of the time course or by determining the time interval required for the pupil to dilate after the stimulus switches from light to dark.

[0222] Determination of strabismus angle from the first trial session 2 and 3, to determine the strabismus angle from the first trial session in addition to the RAPD, the first type of stimulus comprises a fixation object. The fixation object can be a spatially limited object that allows the subject to fixate the gaze on the fixation object. For example, the object can be a bright dot with a diameter on the order of 1° or an object displayed in a landscape.

[0223] In the first trial session, in different trials T1, T2, T3, and T4, the first type of stimulus is repeatedly presented alternately to the left and right eyes as described in the previous section.

[0224] Eye and pupil recordings from the eye tracking system are filtered to remove blink events from the data set. Data with eye movement velocities faster than 600° / s are removed from the data set.

[0225] In a first embodiment of the determination of the strabismus angle, the following steps are performed:

[0226] The first trial session is subdivided into gaze direction blocks, where during each gaze direction block, during trials T1, T2, T3, T4, the fixation object is displayed at the same display location, and during different gaze direction blocks, the fixation object is displayed at different selected display locations. In general, nine display locations are selected from a 3 × 3 matrix centered on the primary gaze direction (i.e., directly in front of the center, 0,0). Each selected display location is a combination of one of three horizontal gaze directions selected from the tuple [-α,0°,+α] with α in the range of 10° to 25° and one of three vertical gaze directions selected from the tuple [-β,0°,+β] with β in the range of 10° to 25°.

[0227] Thus, during the first trial session, nine gaze direction blocks were performed, during which the first type of stimuli alternated between the right and left eyes as described for the determination of the APD, while for each gaze direction block a fixation object was presented at one of the selected display locations.

[0228] The recorded gaze direction 100 and pupil size data are evaluated for APD as described above and for strabismus angle. For the strabismus angle, a corrective saccade 101 of the eye is recorded each time the first type of stimulus 11 switches from the left eye to the right eye and vice versa. If the subject does not suffer from strabismus, there may be no corrective saccade. If the subject suffers from strabismus, a corrective saccade will be prominent. The direction and amplitude of the corrective saccade allow the strabismus angle to be quantified. Furthermore, the strabismus angle may be determined in relation to its vertical, horizontal or torsional magnitude by the choice of the display position of the fixation object. Thus, the horizontal, vertical and / or torsional strabismus angle may be determined for the first trial session.

[0229] In particular, the left eye's horizontal gaze position / direction is subtracted from the right eye's horizontal gaze position / direction when the gaze is directed at one of the nine viewing positions, resulting in one value for the horizontal relative deviation, i.e. horizontal strabismus angle, with respect to the viewing position, i.e. gaze direction, for each of the nine viewing positions.

[0230] In a similar manner, the vertical and twisted squint angles can be calculated for each of the nine display positions.

[0231] Thus, the direction, amplitude, and torsion of this modified saccadic eye movement indicate the horizontal, vertical, and torsional strabismus angles of each eye.

[0232] In this embodiment, APD and strabismus angle can be determined using one trial session with one type of visual stimulus, effectively integrating two different tests into one test series, thereby reducing the time required to establish two functional eye parameters.

[0233] In another embodiment, the strabismus angle is determined by the following steps:

[0234] The first trial session according to this alternative embodiment is subdivided into gaze direction blocks, with the fixation object being displayed at different selected display locations in different gaze direction blocks.

[0235] In the first gaze direction block, as described in the previous section, a first type of object is repeatedly displayed alternately to the left and right eyes. The stimulus has a fixation object at the display position.

[0236] However, the corrective saccade is evaluated after the first visual stimulus is switched from one eye (e.g., the left eye) to the other eye (e.g., the right eye). Now, according to the evaluated corrective saccade, the display position of the fixation object is adjusted so that the display position compensates for the expected corrective saccade in the next trial in which the visual stimulus is switched again from one eye, e.g., the left eye, to the other eye, e.g., the right eye. During the first gaze direction block, the goal is to adjust the display positions of the fixation objects of the left and right eyes so that the corrective saccade is corrected in either switch direction. This adjustment of the display position of the fixation object is repeated in the same manner in the subsequent gaze direction blocks.

[0237] Typically, nine display positions are selected from a 3x3 matrix centered on the main gaze direction (i.e. directly in front of the center, 0,0). Each selected display position is a combination of one of three horizontal gaze directions selected from the tuple [-α,0°,+α] with α in the range of 10°-25° and one of three vertical gaze directions selected from the tuple [-β,0°,+β] with β in the range of 10°-25°. According to another embodiment, as described above, depending on the evaluated corrective saccade, the display position of the fixation object displayed to the right eye is adjusted, while the display position of the fixation object displayed to the left eye is not changed. Once the correction of the corrective saccade of the right eye is achieved, the display position of the left eye is adjusted, while the display position of the fixation object displayed to the right side remains fixed.

[0238] The direction and amplitude (i.e., disparity) of the adjusted viewing position relative to the unadjusted viewing position allows for the quantification of the strabismus angle. Furthermore, the strabismus angle can be determined in relation to the magnitude of its vertical, horizontal, or torsion, depending on the choice of the adjusted viewing position of the fixation object.

[0239] In this embodiment, (R)APD and strabismus angle can be determined using one trial session with one type of visual stimulus, thus integrating two different tests into one test series, thereby reducing the time required to establish two functional eye parameters.

[0240] Both embodiments for determining the strabismus angle have in common that they determine the total angle of phoria (i.e. the strabismus angle) for each viewing position, i.e. gaze direction. For each of the nine viewing positions, the strabismus angles, in particular the horizontal strabismus angle and the vertical strabismus angle, are calculated, where for the situation where the right eye fixates the fixation object, the strabismus angle is determined for the left eye and vice versa, i.e. for the situation where the left eye fixates the fixation object, the strabismus angle is determined for the left eye.

[0241] Thus, during the first trial session, nine gaze direction blocks are carried out, during which the first type of stimuli are alternated between the right and left eyes as described for the determination of the APD, while in each gaze direction block the fixation object is displayed in one of the display positions selected and specifically adjusted so that the strabismus angle is determined.

[0242] Determining the field of view With reference to FIG. 4, in accordance with the present invention, the method allows for determining the subject's visual field 400 (see FIG. 4A) simultaneously with determining the strabismus angle.

[0243] For this purpose, in a second trial session, the subject is presented with a second type of visual stimulus. It should be noted that the second trial session may be performed before or after the first trial session, or instead of the first trial session.

[0244] The second type of stimuli comprises luminance objects, which are compact, ie spatially limited and localized objects that can be displayed on a display system.

[0245] The second type of stimulus consists of a uniform background upon which luminance objects are displayed.

[0246] The second type of stimulus is adjustable in terms of the luminance object and its luminance on the display system. Furthermore, the relative position of the luminance object (also called relative display position in the context of this specification) can be adjusted so that the luminance object is displayed at a selected position in the subject's field of view. The position at which the luminance object is displayed on the display system is therefore dependent on the subject's gaze direction. Said relative position is a position given relative to the current gaze direction of the eyes. Therefore, the relative display position is also called gaze-centered display because the current gaze direction 403 determines the origin of the display position.

[0247] Thus, to display a luminance at a particular relative position, two criteria must be met for that relative position to be perceptible to the subject: a) The display position of the relative position of the luminance object must be within the limitations of the display system, otherwise the luminance object cannot be displayed. b) The display position of the relative position of the luminance object must be within the range of the eye tracking system, otherwise eye position or pupil size cannot be determined.

[0248] To assess the subject's visual field 400, a map of the subject's visual field is generated, which contains spatially resolved information on the threshold (see FIG. 4A in the form of grey values ​​indicating the perception threshold in the visual field map; the darker the lower the perception threshold), below which the subject does not perceive a luminance object if its luminance is below said threshold at the relative position where the test is performed. This approach is also called threshold perimetry. Thus, the subject's visual field is determined using the threshold perimetry method, and a visual field map 401 is obtained.

[0249] To generate said map 401, a threshold is determined for a number of different relative positions 402 distributed over the field of view (see Figures 4A and 4B).

[0250] A trial to determine the visual field begins with the onset of a second type of stimulus 403 having a luminance object displayed at a selected one of the multiple relative locations and ends approximately 500 milliseconds after an eye movement is made in the direction of the luminance object. Such a trial is classified as "seen" or deemed to be detected by the subject. If no eye movement is made in the direction of the stimulus within approximately 1000 milliseconds, the trial is classified as "not seen" or deemed not detected by the subject. In each trial, one of the multiple relative locations is tested.

[0251] For example, the luminance is 10 cd / m 2 The second type of visual stimulus consisted of a bright dot approximately 0.5° in diameter presented on a uniform background of 100 ms. The second type of visual stimulus was presented for a duration of 200 ms.

[0252] The luminance of the luminance object varies depending on the relative position of the luminance object and on whether or not a stimulus was deemed to be detected at that particular position in a preceding trial of the second trial session. Initially, the initial luminance of the luminance object is selected to be 2 dB higher than the age-corrected normal value for that relative position. If the stimulus is deemed to be detected after a trial, the luminance of the luminance object is subsequently reduced by 2 dB, but not in particular in subsequent trials. After a detected stimulus, the relative position of the luminance object is changed in the next trial. If the stimulus is not recognized, i.e. deemed not to be detected, the luminance of the luminance object is adaptively increased, for example by 2 dB to 10 dB, in particular by 2, 4, 6, 8, or 10 dB. This procedure is repeated until the threshold is exceeded once. Alternatively, the luminance of the luminance object can be adaptively increased or decreased, rather than by a fixed amount.

[0253] To determine the field of view, for example, 54 relative positions in the central field of the eye can be selectively examined. Luminance objects are displayed at relative positions, resulting in over-representation of display positions near the nasal step, along the vertical meridian, and in the central field. The relative positions cover a field of view with a diameter of 120°.

[0254] If a luminance object cannot be displayed at the selected relative position, e.g. due to limitations of the display system or the eye-tracking system, another of the eight relative positions is selected. If only relative positions already tested remain, a gaze reset procedure may be performed, during which a suprathreshold stimulus appears and the subject must follow it.

[0255] For this purpose, a suprathreshold stimulus appears in the current gaze direction / position. This stimulus can be in the form of a luminance object with suprathreshold luminance, for example, which may first be moved horizontally at 8° per second to a new horizontal position, followed by a vertical movement at 8° per second to a new vertical position.

[0256] Then, a luminance object (which may have a lower luminance) is displayed at the relative position that was previously out of range.

[0257] For each relative position, a perceptual threshold, also called threshold, is determined. Perceptual sensitivity is calculated for each relative position using the average of the least bright stimulus deemed detected and the most bright stimulus deemed not detected.

[0258] Determining smooth pursuit from gaze resetting procedures: Smooth pursuit can also be determined by evaluating eye movements in response to moving suprathreshold objects from the gaze reset procedure. For this purpose, recorded eye saccades are excluded from the smooth pursuit analysis. Right, left and vertical eye movements are separated. The average difference between the velocity of the eye movement and the velocity of the suprathreshold object movement, expressed as a percentage, can be defined as gain. A gain of 100% means that the eye movement perfectly tracks the suprathreshold object velocity.

[0259] fixation, gaze holding, square wave jerk, nystagmus Fixations can be determined during any trial session. In this analysis, smooth pursuit eye movements during gaze resetting and all saccades with amplitudes exceeding 3° are excluded. In particular, saccadic responses following newly presented stimuli are excluded.

[0260] Such fixation events are analyzed separately for five different relative positions in the eye-centered visual field: right gaze, left gaze, up gaze, down gaze, and main gaze.

[0261] Fixation stability corresponds to the number of changes in eye fixation while a suprathreshold object is continuously present on the screen, the numbers indicate the time spent within 3° of the suprathreshold stimulus and the number of fixation losses per minute (% of target).

[0262] Additionally or alternatively, the frequency of square wave eye movements may be determined during the first and / or second trial sessions. Square wave eye movements are defined as two horizontal saccades (outward and inward) of equal amplitude less than 5°±1°, separated by a time interval of 200 ms to 400 ms. The number of such events per minute is counted regardless of fixation, luminance, or the presence of suprathreshold objects.

[0263] Presence or absence of other (non-square-wave) saccadic intrusions: Any event involving consecutive saccades, i.e., two saccades with no intervening fixation event, is classified as a saccadic intrusion. As well as square-wave eye movements, double saccadic pulses, horizontal nystagmus, macrosaccadic oscillations, microsaccadic oscillations, and opsoclonus are identified.

[0264] Presence or absence of nystagmus: Nystagmus is defined as a drift in eye position of more than 1° per second in a constant direction for more than 5 seconds. The average velocity of the slow phase is used as the magnitude of the nystagmus. This is determined in each of the five patient-centered gaze positions / directions, i.e., relative positions.

[0265] Gaze holding function: Only data for right gaze, left gaze, up gaze, and down gaze are included. Similar to nystagmus detection, it determines whether or not there is an eye movement drift in the opposite direction to the gaze position / direction (e.g., pupil drift downward during up gaze, right drift during left gaze, etc.). If drift is present, the gaze holding is deemed abnormal. Drift is quantified using the same algorithm as nystagmus.

[0266] It is noted that all these parameters can be assessed during a single trial session, dramatically reducing measurement times.

[0267] Determining saccade accuracy Additionally, saccade accuracy can be determined from the sequence of second type stimuli simultaneously for each strabismus angle and visual field of the subject from any session. Only subsequent second type stimuli that are deemed detected and displayed at different relative positions are selected for analysis by the computer to determine saccade accuracy. This selection can also be performed automatically by the computer.

[0268] The first saccade that exceeds 3° in the direction of the relative position of the luminance object (±20°) is used for analysis. The difference (percentage) between the distance between the relative position of the subsequent second stimulus and the magnitude of the first saccade is calculated. This difference corresponds to the saccade accuracy.

[0269] Saccade accuracy is determined separately for rightward, leftward, and vertical saccades.

[0270] For each of the three types of saccades, the median error (as a percentage of the target amplitude) can be calculated, and the number (percentage) of measured oversaccades can be calculated, the latter being defined as saccades with an amplitude exceeding 10% of the target amplitude.

[0271] Because large saccades are physiologically underscaled in the variance of saccade accuracy determination, the above numbers are corrected for target amplitude: an amplitude-dependent average age-correlated underscale is subtracted from each trial.

[0272] Peak velocity determination To determine peak velocity, saccadic eye movements are analyzed, particularly from data recorded during the second trial session, and the peak velocity of eye movement during the saccade is determined. Even if the saccade is shorter than 1 second, the peak velocity can be expressed in degrees / second. In further or alternative embodiments, saccades recorded during the first, third, or fourth trial sessions are analyzed for peak velocity in the same manner.

[0273] Determination of fusion width To determine the fusional width, a third trial session needs to be run on the system, where the third trial session comprises a third type of visual stimuli presented simultaneously to the subject's left and right eyes by the optical system.

[0274] Therefore, in addition to the first and second trials, a third type of stimulus needs to be presented to the subject.

[0275] Fusion width is determined from the binocular gaze directions recorded during the third trial session.

[0276] A third type of stimulus comprises an image or structure object and can be focused.

[0277] This image is then displayed to the subject with increasing disparity, in particular with continuously increasing disparity, while an eye-tracking system records the gaze direction of both eyes. To be able to correct the image disparity, the eyes are expected to perform vergence movements.

[0278] The disparity of the images increases until the subject can no longer perform a convergence movement of the eyes and the gaze direction of the eyes switches back to an essentially straight or natural gaze direction.

[0279] The fusional width corresponds to the maximum disparity of the image presented to the subject for which the subject is still able to adjust the gaze direction of the eyes with the necessary vergence to compensate for the disparity.

[0280] The fusional width can be determined along the horizontal, vertical, and / or other directions. The fusional width can be given as the maximum convergence angle between the eyes.

[0281] Determining visual acuity To determine visual acuity, an exemplary embodiment may perform a trial session as illustrated below.

[0282] Visual acuity can be determined independently of the first, second and / or third trial sessions. The numbering of the trial sessions is provided solely as a means to distinguish between various trial sessions that may be performed in accordance with the present invention and does not in any way imply an order in which these trial sessions should be performed.

[0283] Thus, the trial session for determining visual acuity may be carried out before or after any of the first, second, or third trial sessions.

[0284] The trial session for determining visual acuity comprises a number of visual stimuli that are presented during different trials to the subject's left and right eyes using the optical system. Preferably, the patches 501, in particular the Gabor patches, are presented in a side-to-side sequential manner such that the visual acuity for each eye is determined separately for each eye.

[0285] The patches may be Gabor patches. In general, the patches should be isoluminant, have the form of a bounded set, cover a connected region, and have a periodic spatial intensity distribution that can be related to the spatial frequency imprinted on the patch. Thus, the intensity distribution is completely comprised by the patch.

[0286] Each stimulus comprises a number of patches 501, which are displayed to the subject on a uniform background, preferably in an irregular pattern on a display system. The patches are preferably arranged so that they do not overlap. On average, the patches should cover about 0.01% to 20% of the background, while the minimum distance should be twice the size or diameter of the patch.

[0287] These patches can be displayed on a uniform, especially grey, background with uniform luminance, and these patches 501 are displayed by lighter and darker areas on said background, provided that they are essentially isoluminant to the background.

[0288] The term "isoluminant" specifically refers to a property of a patch such that when the luminance of the patch is spatially averaged over the patch, the averaged luminance is equal to the background.

[0289] The term "chromatic uniformity" specifically refers to the property of a patch such that when its color is spatially averaged over the patch, the averaged color is equal to the color of the background.

[0290] Multiple patches are presented simultaneously in each stimulus. In each trial, the patches 501 have identical properties except for their location on the display system. "Position" and "location" in the context of these patches refer to the same property.

[0291] The patches can be characterized by their size, shape, and intensity distribution. In particular, these Gabor patches are defined by a Gaussian kernel function with variance, in particular isotropic variance, such that the Gabor patch appears as a circular object, said Gaussian kernel function being modulated by a sinusoidal plane wave with a given direction and a given period / spatial frequency. Thus, the size of the Gabor patch can be the variance of the Gaussian kernel, and when the variance is isotropic, the shape is circular, and the periodicity of the intensity distribution is provided by a periodic function, i.e., a sinusoidal plane wave function.

[0292] The period of a periodic function can be thought of as the wavelength of the periodic function.

[0293] For example, the frequency of such a Gabor sinusoidal plane wave lies in the range of single and triple variance. However, other frequencies can also be selected. Advantageously, the spatial frequency and variance can be selected such that one period is constituted by the Gabor patch, i.e. the variance and period are for example identical but at least proportional to each other. The sinusoidal plane wave may be centered by its maximum amplitude at the mean value of the Gaussian kernel function, or alternatively by a zero crossing. The ratio of the variance of the Gaussian kernel to the period of the sinusoidal plane wave of the Gabor patch may be constant. This allows Gabor patches of different sizes to be displayed during different trials, while the appearance of the Gabor patch remains essentially the same, allowing it to be scaled up or down.

[0294] Alternatively, instead of Gabor patches, patches with concentric rings of light and dark forming a ring pattern can be used (see FIG. 7A), where the outer ring of each patch defines the size of the patch (by the diameter of the outer ring) and the number of light and dark rings can define the spatial frequency of the patch, or more precisely, its periodic function. The kernel function can be a circular step function. The rings are isoluminant.

[0295] In different trials, the diameter and "width" of the rings, and therefore the frequency of the ring pattern, can be adjusted so that neither the number nor the brightness of the rings changes.

[0296] Again with regard to the characteristics of a general patch, the patch comprises a periodic pattern or shape given by a periodic function, said periodic function being modulated with a kernel function configured to provide not only a size but also an outer contour and an unmodulated brightness or luminance distribution.

[0297] The periodic function may be a sine wave function, but may also be selected as a square wave function or a triangular wave function. It should be noted that a periodic function can only be associated with one spatial frequency. That is, even a square wave function can be mathematically represented by a superposition of sine wave functions, and the square wave function exhibits a unique period, which is referred to when referring to the period of a spatial frequency.

[0298] To determine visual acuity, a patch of initial size, in particular a Gabor patch, is moved back and forth on the display system along a predefined trajectory 502, and an eye tracking system records the eye movements 503 of the eye on which the patch is displayed. This trajectory may constitute a back and forth movement along one axis or direction. The velocity profile of said movement may be sinusoidal or any other periodic but continuous or smooth velocity profile.

[0299] For example, the size of the patch can be chosen to be small so that the subject does not initially detect the patch and therefore no eye movements are recorded. Any saccades that occur can be evaluated for their end position, where if a saccade ends at a position where the patch is displayed, the patch can be counted as having been detected or recognized by the subject.

[0300] If the subject fails to detect the moving patch, the frequency can be conversely decreased while the patch size is increased such that the ratio between patch size and number of cycles per patch remains constant.

[0301] Alternatively, or in addition, a trial session may begin with a patch size large enough for the subject to detect and follow the patch movement, and in subsequent trials the patches become successively smaller and higher in spatial frequency until the eyes fail to follow the patch movement or the lag or correlation between the patch movement and the eye movement exceeds a predetermined value.

[0302] The predefined trajectory may be linear, i.e., movement along one direction, with a sinusoidal velocity profile 502 that is the same for all displayed patches. For example, the trajectory may include 2-3 periods of periodic movement until a new trial is performed, e.g., with a smaller or larger patch. The maximum velocity during the sinusoidal movement shall not exceed 20° / s, and in particular shall not exceed 10° / s.

[0303] The gaze is expected to follow this trajectory for as long as, or as soon as, patch 501 is perceived by the subject.

[0304] In the evaluation step, the eye movement can be filtered for any saccadic eye movement, and only non-saccadic eye movement (503) is analyzed for visual acuity. The filtered eye movement and the patch movement are compared in terms of correlation and delay. If the subject perceives the patch, both movements should be approximately the same, but if the subject does not perceive the patch, for example because the patch size is too small, the eye movement will not be sufficiently correlated or will be significantly delayed with respect to the patch movement. In FIG. 5B, the subject can follow the patch, as can be seen by comparing the Gabor patch movement 502 to the eye movement 503.

[0305] However, as disclosed in the previous paragraph, the saccade movement can alternatively or additionally be analyzed with respect to its end point and / or start point, and if the end point and / or start point coincide with the location of a patch, the patch can be considered as being perceived by the subject.

[0306] Usually, visual acuity is estimated by a visual acuity chart (e.g. "Landolt C"), but in this embodiment, visual acuity can alternatively be determined by a moving patch. As the patches are essentially small patches of stripes, they are also subject to Moire effects or interference. However, as Gabor patches in particular are relatively small, they also have a small effect on the display due to interference. In contrast, if a stripe pattern is selected that covers the entire screen, the displayed stripe pattern may appear much larger than intended, since the intended stripe pattern displayed by individual pixels of the screen may cause such effects. This will not happen with the patches according to the present invention, particularly Gabor patches.

[0307] 6 shows a schematic diagram of an exemplary embodiment of a system 1 according to the present invention. System 1 includes an external computer 2 connected to a display system 4, an eye tracking system 5, an optical system 3 comprising a lens assembly 6, and a fixation mechanism 7 for mounting the optical system 3 to a subject's head 8. In another embodiment, the optical system may be included in a device arranged and configured to be placed in front of the subject's eyes, such that a fixation mechanism is required.

[0308] Furthermore, the optical system comprises a transmitting device 8 for wirelessly transmitting the recorded data to an external computer. The transmitting device 8 is also configured to receive instructions from the external computer 2 so that the external computer 2 can control the optical system 3. The optical system 3 may comprise a non-transitory memory storage (not shown) for storing computer program instructions and the recorded data. Furthermore, the optical system 3 may further comprise a processor (not shown) configured to execute the computer program stored in the memory storage. The processor is further configured to be controlled by the external computer 2, i.e. to receive instructions from the external computer 2, send confirmations and control the display system 4 as well as the eye-tracking system 5 of the optical system 3. This allows any trial session of the method according to the invention to be fully automated.

[0309] Optical system: The optical system 3 comprises a housing capable of forming a light-tight enclosed volume between the subject's eye and the display system 4 and containing the components of the optical system 3 .

[0310] Furthermore, the optical system 3 comprises a lens assembly 6 for adjusting the refractive power and correcting the optical aberrations of the subject. The lens assembly 6 is adjustable in terms of its refractive power and virtual distance correction of the displayed stimuli or images. For this purpose, the lens assembly 6 may comprise a spherical lens and a cylindrical lens. The eye tracking system 5 may consist of two cameras, each constructed and arranged to record one eye of the subject. These cameras are for example infrared cameras. The display system 4 comprises two displays or display parts, one for each eye.

[0311] The data recorded by the eye tracking system 5 is stored in a memory of the optical system 3 so that it can be correlated in time with the stimuli presented to the human eye.

[0312] External computer: The external computer 2 may be a conventional computer configured to receive user input and display data on a display of the computer 2. The computer 2 also includes a transmitting device for transmitting and receiving information in a wireless manner. The external computer 2 may be connected to the optical system 3 via the transmitting device.

[0313] Figures 7A)-C) show various exemplary embodiments of patches: Figure 7A) shows a circular patch with three concentric high intensity rings, equidistantly spaced from each other such that a radial spatial frequency is imprinted on the patch.

[0314] Figure 7B) shows a Gabor patch, where the periodic function is a sinusoidal plane wave along a single direction of the patch, and three extrema from the plane wave are visible within the Gaussian kernel. The maximum intensity of the plane wave is at the center of the Gaussian kernel.

[0315] The patch disappears into the background, which is solid grey and has no "hard" boundaries.

[0316] Figure 7C) is a rectangular patch with a sinusoidal plane wave along one direction of the square such that the intensity of the patch is modulated along that direction. The patch has a clearly discernible border.

Claims

A computer program for causing a computer system including a computer to execute a method implemented on the computer for determining at least one functional eye parameter, namely visual acuity, the method comprising: implementing program code executable on at least one hardware processor on a non-transitory computer-readable storage medium, the system being an optical system comprising a display system configured to project visual stimuli independently onto a subject's left and right eyes, wherein the visual stimuli comprise a plurality of patches arranged on a background, the optical system, a visual target tracking system configured to record the fixation directions of the right and left eyes, and the computer configured to control the optical system and receive data recorded from the visual target tracking system, the method comprising at least the following steps: - Executing a trial session for determining the visual acuity, the trial session comprising presenting a plurality of the visual stimuli to the subject's left and / or right eye using the optical system; - Recording data during the trial session including information regarding the fixation direction; - Determining at least the visual acuity by analyzing the movements of the subject's left and right eyes in response to the presented visual stimuli in the recorded data of the trial session; including the patch being characterized in that the patch has the same luminance as the background, the patch displays a luminance distribution that varies periodically with spatial frequency, and each patch is a bounded set covering only a part of the background; the visual acuity of the subject is determined from the correlation between the recorded eye movement and the movement of the patch and / or from the correlation between the recorded eye position and the position of the patch; the computer program. **Claim 2** The computer program according to claim 1, wherein the patches are identical to each other and are displayed at different positions on the background. **Claim 3** The computer program according to claim 1 or 2, wherein the patches have the same size, shape, and luminance distribution. **Claim 4** The computer program according to any one of claims 1 to 3, wherein the spatial frequency is isotropic such that the spatial frequency is the same along all directions of the patch during the trials of the trial session.

5. The computer program according to any one of claims 1 to 4, wherein the spatially averaged luminance of the patch is equal to the luminance of the background.

6. The computer program according to any one of claims 1 to 5, wherein the visual stimulus is adjusted for different trials, at least with respect to the spatial frequency of the luminance distribution of the patch.

7. The computer program according to any one of claims 1 to 6, wherein the visual stimulus is adjusted for different trials, at least with respect to the size of the patch.

8. The computer program according to claim 6 or 7, wherein the size of the patch and the spatial frequency of the luminance distribution are adjusted for different trials such that the number of periods of the changing luminance distribution within the patch is kept constant.

9. The computer program according to any one of claims 6 and 7 or 8, wherein the ratio of the size of the patch to the period of the spatial frequency is constant.

10. The computer program according to any one of claims 1 to 9, wherein the patch is arranged to irregularly overlap and / or not overlap on the background.

11. The computer program according to any one of claims 1 to 10, wherein during the trial session, the patch reciprocates at least once along a predetermined trajectory, and the visual target tracking system records eye movements and / or the fixation direction of the eye in response to the moving patch.

12. The computer program according to claim 11, wherein the patch reciprocates according to a periodic velocity profile for each trial.

13. The visual acuity is determined from the size of the patch or the spatial frequency of the patch such that the eye movement deviates from the movement or position of the patch by a predetermined value. The computer program according to any one of claims 1 to 12.

14. The computer program according to any one of claims 1 to 13, wherein the patches maintain a constant distance and a constant relative position with respect to each other so that when the patches are moving, the pattern in which the patches are arranged relative to each other on the background does not change.

15. A system, in particular a neuro-ophthalmoscope (1), comprising an optical system (2) comprising a display system (4) configured to project visual stimuli independently onto the left and right eyes of a subject, a fixation tracking system (5) configured to record the fixation direction and pupil size of the left and right eyes, a computer (2) configured to control the optical system (2) and receive data recorded by the fixation tracking system (5), and a program code stored in the computer (2) for executing the computer program according to any one of claims 1 to 14, wherein the optical system (2) and the fixation tracking system (5) are provided in a near-eye display such as a VR goggle, and the near-eye display further comprises an adjustable lens assembly (6) for each eye such that the optical aberration of each eye of the subject can be corrected by the lens assembly (6). The system, in particular the neuro-ophthalmoscope (1).

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