Arrangement for obtaining highly accurate measurements at the eye

Abstract

Arrangement for obtaining highly accurate measurements at the eye (4), comprising an illumination unit (1) for generating a fixation mark (2), a device for transmitting the light of the generated fixation mark (2) into the eye (4), a measuring device (5), and a control unit (6), wherein the illumination unit (1) has a device (7) for selectively changing the direction of incidence of the generated fixation mark (2), and an additional camera (8) for detecting the gaze direction (4', 4'', 4''') of the eye (4) is provided, which, like the illumination unit (1) and the measuring device (5), is connected to the control unit (6), so that the control unit (6) can determine the sufficient agreement between the detected gaze direction (4', 4'', 4''') and the direction of incidence of the presented fixation mark (2', 2'', 2'''), characterized in thatthat the control unit (6) can trigger a measurement process via the measuring device (5) depending on the degree of probability of agreement, and the measurement process is triggered by the control unit (6) via the measuring device (5) when, after a targeted change in the direction of incidence of the generated fixation mark (2), the previously determined average reaction time of the patient has elapsed and the direction of gaze (4', 4'', 4''') thus corresponds with a high probability to the direction of incidence of the presented fixation mark (2', 2'', 2''').

Description

[0001] The present invention relates to a solution for obtaining highly accurate and reproducible measurements in ophthalmological biometry and imaging. This is achieved by increasing the probability of precisely fixing the eye under examination.

[0002] In ophthalmic devices, fixation targets or markers are used for the proper orientation and stabilization of the eye being examined or measured. This is necessary to perform measurements with good signal characteristics and under stable conditions, and / or to minimize distorted diagnostic results due to directional errors.

[0003] An important example is the measurement of the eye's axial length to facilitate the fitting of intraocular lenses (IOLs) for cataract patients, for which, for example, the IOLMaster® from Carl Zeiss Meditec AG can be used. Here, it is crucial that the measurement is performed precisely along the optical axis.

[0004] Another example is repeated OCT measurements of retinal structures, such as nerve fiber layers or edema, to monitor disease progression, for example, glaucoma or age-related macular degeneration. Here, too, sufficiently good fixation is required to perform comparative measurements.

[0005] Although typical measurement times range from fractions of a second to several seconds, usually up to 2 seconds, many patients have difficulty maintaining a stable fixation for the required adjustment and measurement time, which can take up to several minutes in total. Other patients are completely unable to fixate stably. Reasons for this include: • insufficient visual acuity (due to cataracts or similar conditions), • Fatigue, • Accommodation difficulties (due to presbyopia or pupil-dilating medications), • neurological problems (nystagmus, etc.) • uncompensated refractive errors or • Lack of concentration.

[0006] However, incorrect fixation on the provided fixation marks leads to inaccurate measurements. Consequently, a proper diagnosis cannot be made, or, in the case of cataract patients, an optimal IOL cannot be selected.

[0007] Due to the ongoing uncertainty in the state of the art as to whether the patient remains sufficiently stable for measurement after adjustment, automated measurement processes are made more difficult or measurement repetitions are necessary.

[0008] According to the current state of the art, various solutions are known to avoid incorrect fixings.

[0009] For example, German patent DE 10 2005 003 443 A1 describes a technique for guiding the patient's gaze during examination or documentation of the fundus. Here, a fixation mark generated by a surface light modulator is used to align the patient's eye so that the area of ​​the fundus to be observed or documented lies on the optical axis. Verification that the patient's eye is indeed aligned with the fixation mark can only be performed by the operator, who simultaneously observes the fundus.

[0010] A completely different solution for preventing faulty fixation of the eye under examination on presented fixation marks is described in the as-yet-unpublished DE 10 2009 007 732.4. In this solution, the patient is presented with a preferably variable, fatigue-reducing, and attention-promoting fixation mark, without placing high demands on the patient's ability to concentrate. The described arrangement has at least one diffuse optical emission (DOE) for modifying the high-intensity light radiation, whereby the light radiation is modified in such a way that the resulting beam structure can be changed energetically, temporally, spatially, and / or spectrally.

[0011] The method proposed in DE 103 59 239 A1 for displaying a fixation mark for ophthalmic treatment devices is also based on a fixation mark designed to promote the patient's attention. The patient aligns the eye to be treated with this fixation mark by foveal focusing. The fixation mark is moved within the patient's field of vision, with the movement being such that the patient can easily follow it. The movement of the fixation mark within the patient's field of vision can be continuous or abrupt, following a predetermined sequence or randomly. This ensures that no unintentional eye movements occur. Depending on the type of movement of the fixation mark, measurement or therapy can be performed differently. For example, if the fixation mark is moved abruptly within the patient's field of vision, diagnosis or therapy is preferably performed only during the short periods of pause in the fixation mark's movement.In contrast, with a constantly moving fixation mark, diagnosis or therapy can also be carried out while the eye follows the movement of the fixation mark.

[0012] The ophthalmic imaging device described in US 2007 / 0291277 A1 integrates a variety of ophthalmic applications and individual devices. In addition to a fundus imaging system, an iris viewer, and an optical coherence tomography (OCT) system, the device also features an optical coherence scanning system. For safe handling and the acquisition of precise measurements and images, the ophthalmic device incorporates various test and fixation targets. The fixation system aligns the eye with the presented fixation target by foveal focusing and maintains it as securely as possible during the examination or imaging process. To achieve this, the fixation system generates fixation targets in the visible wavelength range, preferably between 450 and 600 nm, and projects them onto the eye. The patient must then firmly align their eye with this fixation target.To generate fixation marks, the fixation system in the described solution features a display with approximately 120 × 120 pixels. Besides an LCD display, other screens can also be used to generate the fixation marks. The preferred fixation target is variable in size and presents the eye with rapidly changing visual stimuli.

[0013] Whether the eye being examined is precisely aligned using state-of-the-art solutions can only be determined by the operator visually observing the correct alignment of the target area within the eye, or by the patient confirming the precise alignment with the fixation mark. Even with both methods, the possibility of obtaining erroneous measurements cannot be ruled out.

[0014] Therefore, additional plausibility checks have become standard practice in established solutions. The recorded measurements are checked for plausibility and consistency to eliminate errors caused by incorrect fixation. However, this method only detects gross errors, as these are inherently implausible. Minor deviations in alignment with the fixation mark can produce measurements that, while technically flawed, may still be plausible.

[0015] Current state-of-the-art solutions have the disadvantage that automated measurement acquisition is not possible with these systems. Approaches to preventing incorrect fixations are very time-consuming, unnecessarily prolonging the examination and measurement acquisition, thus further reducing the patient's concentration. Furthermore, the probability of errors during measurement acquisition remains relatively high.

[0016] Current state-of-the-art solutions for ophthalmic laser treatment employ so-called tracking systems that detect unwanted eye movements, i.e., a lack of alignment of the eye with a fixation mark, and follow this eye movement with the laser beam. While this ensures that the laser beam hits the precisely determined spot on the eye, a tracking system is not suitable for targeted alignment, for example, with the optical axis of the eye being examined. Furthermore, such systems are very complex and expensive.

[0017] From DE 10 2006 011 624 A1 a device relating to the alignment of an eye for diagnostic or therapeutic purposes is also known, wherein the direction of gaze does not necessarily have to coincide with the optical axis of the examination or treatment device.The device for aligning an eye consists of a fixation light source for generating a positionable fixation mark and a device for coupling this into a beam path of an ophthalmic device, via whose imaging optics the fixation mark is projected onto the eye to be examined and / or treated, and a control unit with which the image of the fixation mark can be displayed at different distances and angular positions to the optical axis of the ophthalmic device, so that the eye to be examined and / or treated aligns itself to this fixation mark by foveal focusing and assumes a defined position to the optical axis of the ophthalmic device.

[0018] US 6,402,320 B1 discloses an automated method for measuring visual acuity using an electronic visual display, comprising the steps of: presenting a fixation target to draw a subject's attention to the electronic visual display, on which a test screen with at least two separate fields is then displayed, one containing a first test pattern to stimulate the subject and the other a control pattern; then detecting whether an eye movement occurs in response to the test pattern, the presence of the eye movement confirming the subject's ability to recognize the first test pattern; and then repeating the presentation of the fixation target and the display of the test screen with at least one subsequent test pattern, the subsequent test pattern being more difficult to distinguish than the first test pattern.

[0019] Furthermore, US 2005 / 0286019 A1 discloses a device and a method for treating and / or diagnosing a patient's eye. A light source generates a fixation light and a procedure light (for treatment and / or diagnosis). A scanning device deflects the fixation light to generate a fixation pattern on the eye and deflects the procedure light to generate a procedure pattern on the eye. A controller controls the scanning device such that the fixation and procedure patterns move relative to each other and / or the fixation pattern changes dynamically.

[0020] The present invention aims to develop a solution for obtaining highly accurate and reproducible measurements of the eye. The ophthalmological device should have a simple basic design and allow for easy, preferably automated, operation.

[0021] According to the invention, the problem is solved by the features of the independent claims. Preferred embodiments and configurations are the subject of the dependent claims.

[0022] This task is solved by the arrangement for obtaining highly accurate, reproducible measurements at the eye, consisting of an illumination unit for generating a fixation mark, a device for transmitting the light of the generated fixation mark to the eye, a measuring device, and a control unit, in that the illumination unit has a device for selectively changing the direction of incidence of the generated fixation mark, and an additional camera for detecting the eye's gaze direction is provided, which, like the illumination unit and the measuring device, is connected to the control unit, so that the control unit can determine the sufficient correspondence between the detected gaze direction and the presented direction of incidence of the generated fixation mark and, depending on the correspondence, a measurement process can be triggered.

[0023] The control unit triggers the measurement process via the measuring device when, after a targeted change in the direction of incidence of the generated fixation mark, the previously determined average reaction time of the patient has elapsed and the direction of gaze thus corresponds with a high probability to the direction of incidence of the presented fixation mark, and / or when, after a targeted change in the direction of incidence of the generated fixation mark, a pupillary constriction is detected by the camera, and / or the measurement process is triggered via the measuring device in a time range of 0.1 to 0.5s after a blink, whereby blink closures are detected by means of the camera and the control unit.

[0024] The proposed technical arrangement provides a solution for obtaining highly accurate measurements of the eye. Since the specific areas of the eye where measurements are taken are irrelevant, the arrangement according to the invention can be used with any ophthalmological diagnostic device equipped with a camera and a measuring system. The measuring arrangement is not limited to an optical measuring system; for example, it could also be an ultrasound measuring system for biometry or imaging.

[0025] The invention is described in more detail below with reference to exemplary embodiments. The schematic diagrams of the arrangement according to the invention are shown in: Fig. 1: a correspondence between the detected gaze direction and the direction of incidence of the generated fixation mark and in Fig. 2: a discrepancy between the detected viewing direction and the direction of incidence of the generated fixation mark.

[0026] The arrangement according to the invention for obtaining highly accurate, reproducible measurements at the eye consists of an illumination unit for generating a fixation mark, a device for transmitting the light from the generated fixation mark to the eye, a measuring device, and a control unit. The illumination unit has a device for selectively changing the direction of incidence of the generated fixation mark. An additional camera is provided for detecting the eye's gaze direction; this camera, like the illumination unit and the measuring device, is connected to the control unit. The control unit determines the sufficient correlation between the detected gaze direction and the presented direction of incidence of the generated fixation mark and triggers a measurement process depending on the degree of probability of correlation.

[0027] In a first advantageous embodiment, the illumination unit for generating a fixation mark is based on visible light, preferably in the green to red range, with a single or area light source being used as the illumination unit. Preferably, fixation marks can be displayed with the illumination unit that are variable in intensity, shape, color, and size. The existing device for selectively changing the direction of incidence of the generated fixation mark is designed such that the direction of incidence can be changed abruptly or continuously. Imaging optics are preferably used to transmit the light from the generated fixation mark to the eye.

[0028] The camera detects the eye's gaze direction by measuring the position of the iris, scleral structures (such as blood vessels), or pupil, or defined reflection points or patterns. For this purpose, the camera is preferably designed to record individual images and video sequences and transmit them to the control unit. In addition to the camera for detecting the eye's gaze direction, ambient lighting is provided, for example, using an infrared LED, preferably in the 700 to 950 nm range. This ambient lighting can be switched off during the measurement process, for example, to avoid interfering with the measurement. Furthermore, the camera may include image processing for determining the direction of movement and transmitting directional information to the control unit.

[0029] The control unit determines the correlation between the detected gaze direction and the presented beam direction of the generated fixation mark and triggers a measurement process if the detected gaze direction is highly likely to correspond to the presented beam direction of the generated fixation mark. In a further embodiment, the control unit triggers a measurement process if the detected gaze direction is highly likely to correspond to the presented beam direction of the generated fixation mark. The probability is already increased if the direction of the change in eye position is consistent with the change in beam direction resulting from the altered position of the fixation mark (right / left, up / down). The probability is even higher if the change in eye position is predominantly proportional to the change in the position of the fixation mark.

[0030] This shows the Fig. Figure 1 shows a schematic representation of a first embodiment of the arrangement according to the invention, in which there is always a correspondence between the detected gaze direction and the direction of incidence of the generated fixation mark. The arrangement for obtaining highly accurate measurements at the eye consists of an illumination unit 1 for generating a fixation mark 2, an imaging optic 3 for transmitting the light from the generated fixation mark 2 to the eye 4, a measuring device 5, and a control unit 6. The illumination unit 1 has a device 7 for selectively changing the direction of incidence of the generated fixation mark 2. An additional camera 8 is provided for detecting the gaze direction of the eye 4; this camera, like the illumination unit 1 and the measuring device 5, is connected to the control unit 6.The control unit 6 determines the correspondence between the detected gaze direction and the presented beam direction of the generated fixation mark 2 and triggers a measurement process depending on the degree of probability of correspondence. For the sake of simplicity, the ambient lighting is not shown separately here. This could, for example, also be integrated into the camera. The imaging optics 3 can be designed such that a focused image of the fixation mark on the retina of the patient's eye can be achieved even in the case of refractive errors in the patient's eye. For this purpose, suitable adjustments of the focal length of the imaging optics 3 can be used, for example, by shifting lenses, changing the refractive power of variable lenses, or curvatures of mirrors.Alternatively, such adjustments to the divergence of the fixation mark light can also be made in the lighting device 1 or in the device 7 for targeted changes to the direction of incidence of the generated fixation mark 2.

[0031] While the patient's head is usually fixed on the chin and / or forehead rest of the ophthalmic examination device, the patient's eye to be examined is aligned with the optical axis of the ophthalmic examination device. The control unit 6 activates both the illumination unit 1 and the device 7 for selectively changing the direction of the beam of light to generate the fixation mark 2, in order to create a sequence of fixation marks 2 that are focused into the eye 4 via the imaging optics 3.

[0032] For example, a variable diffractive optical element (DOE) can be used as a device 7 for targeted modification of the direction of incidence of the generated fixation mark 2, with which the fixation mark can be shaped and deflected accordingly.

[0033] Instead of a lighting unit 1 with a device 7 for targeted change of the beam direction of the fixing mark 2, several spatially separated light sources or a surface light source in the form of an electro-optical display, e.g. a TFT-LCD display, can be used.

[0034] Simultaneously, the control unit 6 activates the camera 8 to detect the gaze direction of eye 4. This can be done, for example, by measuring the position of the iris (structures) or pupil (center and / or periphery) of eye 4. Due to the fixed head position, the position of the pupil represents a measure of the gaze angle of the eye 4 being examined, since a change in gaze direction can therefore only be achieved by rotating eye 4.

[0035] The following simple sequence could be sufficient for correlating the direction of incidence of the fixation mark 2 to be presented to the eye 4: -> Fixing mark 2' left, -> Fixing mark 2'' right and -> Fixing mark 2''' central.

[0036] The changes in the direction of the incoming light beam would preferably be between ±2° and ±10° in the visual field, in order to provoke a sufficient response while avoiding unnecessary strain on the patient. In principle, larger or smaller changes in direction can also be used, but this increases the effort and uncertainty of detecting the change in gaze direction.

[0037] The camera 8 detects the corresponding viewing direction (4', 4'' and 4''') of eye 4, whereby individual images and video sequences can be recorded.

[0038] The speed of the sequence for changing the direction of the generated fixation mark 2 should be fast enough for the patient to easily follow, while also not unnecessarily prolonging the overall measurement time. Although there are no strict limits for this, speeds of 0.5 to 5 Hz seem suitable.

[0039] Additionally, the patient's attention can be increased by using fixation marks whose intensity, shape, color and size can be changed.

[0040] Since eye examinations are usually carried out in darkened rooms, it is advisable to illuminate the eye 4 to be examined by an ambient light so that the pupil can be reliably detected by the camera 8.

[0041] For ambient lighting, an LED, preferably with an infrared spectrum, can be used. This has the advantage that the patient is not dazzled and is not distracted from aligning with the fixation mark.

[0042] The control unit 6 compares the directions of incidence of the fixation mark 2 generated by the device 7 with the gaze directions of the eye 4 detected by the camera 8. If the control unit 6 determines that the detected gaze direction of the eye 4 corresponds with a high probability to the presented direction of incidence of the generated fixation mark 2, a measurement process, for example an ocular length measurement, is triggered via the measuring device 5.

[0043] While the direction of the beam of the generated fixation mark 2 changes in a controlled sequence, the patient's reaction is determined by detecting the gaze direction of their eye 4. The measurement process is only triggered by the control unit 6 via the measuring device 5 when proper alignment of the eye 6 with the fixation mark is particularly likely.

[0044] To illustrate, the Fig. 2. Herein is a schematic representation of the arrangement according to the invention in which there is a discrepancy between the detected viewing direction and the direction of incidence of the generated fixation mark.

[0045] While the beam direction of the fixation mark 2' presented to eye 4 is from the left, the camera 8 also detects a central gaze direction (4''') of eye 4. In this case, the control unit 6 determines that the detected gaze direction of eye 4 does not correspond to the presented beam direction of the generated fixation mark 2. Therefore, a measurement process is not triggered.

[0046] In a second embodiment, the average reaction time of the patient, i.e. the time that elapses until the patient has aligned his eye with the presented fixation mark, is analyzed in a first phase.

[0047] The arrangement used here also corresponds to the one in Fig. The device shown in Figure 1 consists of an illumination unit 1 for generating a fixation mark 2, an imaging optic 3 for focusing the generated fixation mark 2 onto the eye 4, a measuring device 5, and a control unit 6. The illumination unit 1 has a device 7 for selectively changing the direction of incidence of the generated fixation mark 2. An additional camera 8 is provided for detecting the gaze direction of the eye 4. This camera, like the illumination unit 1 and the measuring device 5, is connected to the control unit 6. The camera 8 detects the corresponding gaze direction (4', 4'', and 4''') of the eye 4, preferably recording video sequences.

[0048] Here too, the patient's head is usually fixed to the chin and / or forehead rest of the ophthalmic examination device, and the patient's eye to be examined is aligned with its optical axis. The control unit 6 activates both the illumination unit 1 and the device 7 for precisely changing the direction of the beam of light for the fixation mark 2 to be generated, in order to produce a sequence of fixation marks 2 that are focused into the eye 4 via the imaging optics 3.

[0049] The change in the direction of the incoming beam of the fixation mark 2 to be presented to the eye 4 can be carried out either according to a predetermined sequence or randomly.

[0050] In contrast to the first embodiment, the control unit 6 analyzes the patient's average reaction time, i.e., the time until a match is achieved between the detected gaze direction and the presented beam direction of the generated fixation mark 2. For this purpose, the video sequences transmitted by the camera 8 are used, which are recorded, for example, at frequencies of 1 to 200 Hz.

[0051] The determined average reaction time of the patient can be stored by control unit 6, for example, as a weighted average.

[0052] In the second phase, the determined average reaction time of the patient is used by the control unit 6 to trigger a measurement process via the measuring device 5 after a targeted change in the direction of the beam of the generated fixation mark 2.

[0053] This second embodiment has the advantage that, after analyzing the patient's average reaction time, the measurement processes can proceed continuously, quickly and without additional interruptions.

[0054] In an advantageous embodiment of this second embodiment, the camera 8 can also be used during the measurement processes to additionally detect the direction of gaze of the eye 4 (for control purposes).

[0055] In a further advantageous embodiment, the solution described in the second embodiment is used to enable length measurements at the eye outside the optical axis by selectively controlling the direction of the incident beam of the generated fixation mark 2 and thus the gaze direction of the eye 4. A large number of such measurements makes it possible to determine the peripheral shape of the eye.

[0056] In a third embodiment, highly accurate measurements at the eye are achieved by generating fixation marks and focusing them into the eye via an imaging optic, to which the patient can align his eye regardless of his refractive error.

[0057] The order according to the Fig.The assembly 1 also consists of an illumination unit 1 for generating a fixation mark 2, with a device 7 for selectively changing its beam direction, an imaging optic 3 for focusing the generated fixation mark 2 onto the eye 4, a measuring device 5, and a control unit 6. An additional camera 8 is provided for detecting the eye 4's gaze direction; this camera, like the illumination unit 1 and the measuring device 5, is connected to the control unit 6. The control unit 6 determines the correspondence between the detected gaze direction and the presented beam direction of the generated fixation mark 2 and triggers a measurement process depending on the probability of correspondence.

[0058] In addition, the imaging optics 3 has an optical, multifocal element with which the generated fixation mark 2 is simultaneously focused into different planes of the eye 4 to be examined.

[0059] As an optical, multifocal element, in addition to a diffractive optical element (DOE), a Fresnel lens can also be used, which realizes multiple foci.

[0060] The optical, multifocal element can generate both discrete fixation marks for different refractive errors of e.g. -10, -50 and -100 diopters as well as an entire range, for example from +3 to -15 diopters.

[0061] The creation of multifocal fixation marks should increase the probability that precise alignment with the presented fixation mark can be achieved even in patients with refractive errors.

[0062] Generating a multifocal fixation mark is possible because the fixation mark serves only to achieve precise alignment of the eye under examination, enabling highly accurate measurements. The requirements for the necessary resolution are therefore relatively low.

[0063] Regardless of the specific design of the arrangement according to the invention for obtaining highly accurate measurements at the eye, it is advantageous if the speed of the sequence for changing the direction of the incoming beam of the generated fixation mark can be varied. This makes it possible to better address the individual characteristics of each patient (children, adults, seniors, etc.) and to further optimize the measurements.

[0064] In a final embodiment of the arrangement according to the invention, the camera can additionally detect pupil constriction and use it as an indicator that the eye is precisely aligned with the presented fixation mark. This is also independent of the specific embodiment of the arrangement according to the invention.

[0065] The arrangement according to the invention provides a solution with which highly accurate measurements of the eye can be obtained in a simple manner. The ophthalmological device, with its simple basic structure, allows for easy, preferably automated, operation.

[0066] Highly accurate measurements are achieved by triggering the measurement process only when the eye being measured is correctly aligned, i.e., when there is a match between the detected gaze direction and the presented beam direction of the generated fixation mark. The proposed solution thus forms the fundamental prerequisite for the development and introduction of semi- and fully automatic measuring devices in ophthalmology.

[0067] By additionally using an optical, multifocal element as part of the imaging optics, it can be ensured that the proposed solution is applicable regardless of the refractive error of the eye being measured and delivers highly accurate measurements.

[0068] By additionally considering the time of the last eyelid closure, the measurement can be advantageously triggered in such a way that a measurement is highly likely to occur without the occurrence of a disruptive eyelid closure or tear film disruption. Preferably, eyelid closure is detected via the camera and the control unit, and the measurement is triggered 0.1 to 0.5 seconds after the last eyelid closure.

Claims

[1] Arrangement for obtaining highly accurate measurements at the eye (4), comprising an illumination unit (1) for generating a fixation mark (2), a device for transmitting the light of the generated fixation mark (2) into the eye (4), a measuring device (5), and a control unit (6), wherein the illumination unit (1) has a device (7) for selectively changing the direction of incidence of the generated fixation mark (2), and an additional camera (8) for detecting the gaze direction (4', 4'', 4''') of the eye (4) is provided, which, like the illumination unit (1) and the measuring device (5), is connected to the control unit (6), so that the control unit (6) can determine the sufficient agreement between the detected gaze direction (4', 4'', 4''') and the direction of incidence of the presented fixation mark (2', 2'', 2'''). characterized by, that the control unit (6) can trigger a measurement process via the measuring device (5) depending on the degree of probability of agreement, and the measurement process is triggered by the control unit (6) via the measuring device (5) when, after a targeted change in the direction of incidence of the generated fixation mark (2), the previously determined average reaction time of the patient has elapsed and the direction of gaze (4', 4'', 4''') thus corresponds with a high probability to the direction of incidence of the presented fixation mark (2', 2'', 2'''). [2] Arrangement according to claim 1, characterized by , that as a lighting unit (1) for generating a fixing mark (2) one or more individual light sources or also a surface light source is used which emit visible light, preferably in the green to red spectral range. [3] Arrangement according to one of claims 1 and 2, characterized by, that the illumination unit (1) for generating a fixation mark (2) is designed such that fixation marks (2) that can be varied in intensity, shape, color, divergence and size can be represented. [4] Arrangement according to one of the aforementioned claims, characterized by , that the device for transmitting the light of the generated fixation mark into the eye is an imaging optic (3) which has an optical, multifocal element. [5] Arrangement according to one of the aforementioned claims, characterized by , that the device (7) for targeted change of the direction of incidence of the generated fixation mark (2) is designed such that the direction of incidence can be changed abruptly or continuously. [6] Arrangement according to one of the aforementioned claims, characterized by , that the camera (8) detects the gaze direction (4', 4'', 4''') of the eye (4) by measuring the position of the pupil or the iris or scleral structures. [7] Arrangement according to one of the aforementioned claims, characterized by , that the camera (8) for detecting the direction of gaze (4', 4'', 4''') of the eye (4) is designed in such a way that individual images and video sequences can be recorded. [8] Arrangement according to one of the aforementioned claims, characterized by , that the camera (8) is designed in such a way that changes in the directions of movement are detected and this directional information is transmitted to the control unit (6). [9] Arrangement according to one of the aforementioned claims, characterized by , that in addition to the camera (8) for detecting the direction of gaze (4', 4'', 4''') of the eye (4) there is ambient lighting. [10] Arrangement according to claim 9, characterized by , that for ambient lighting, for example, an LED is used which emits infrared light, preferably in the spectral range of 700 to 950 nm. [11] Arrangement according to claim 9, characterized by, that the ambient lighting remains switched off during the measurement process. [12] Arrangement according to one of the aforementioned claims, characterized by , that the measuring process is triggered by the control unit (6) via the measuring device (5) when the detected viewing direction (4', 4'', 4''') corresponds with a high probability to the direction of incidence of the presented fixation mark (2', 2'', 2'''). [13] Arrangement for obtaining highly accurate measurements at the eye (4), comprising an illumination unit (1) for generating a fixation mark (2), a device for transmitting the light of the generated fixation mark (2) into the eye (4), a measuring device (5), and a control unit (6), wherein the illumination unit (1) has a device (7) for selectively changing the direction of incidence of the generated fixation mark (2), and an additional camera (8) for detecting the gaze direction (4', 4'', 4''') of the eye (4) is provided, which, like the illumination unit (1) and the measuring device (5), is connected to the control unit (6), so that the control unit (6) can determine the sufficient agreement between the detected gaze direction (4', 4'', 4''') and the direction of incidence of the presented fixation mark (2', 2'', 2'''). characterized by, that the control unit (6) can trigger a measurement process via the measuring device (5) depending on the degree of probability of agreement, and the measurement process is triggered by the control unit (6) via the measuring device (5) when a pupillary constriction is detected by the camera (8) after a targeted change in the direction of incidence of the generated fixation mark (2). [14] Arrangement for obtaining highly accurate measurements at the eye (4), comprising an illumination unit (1) for generating a fixation mark (2), a device for transmitting the light of the generated fixation mark (2) into the eye (4), a measuring device (5), and a control unit (6), wherein the illumination unit (1) has a device (7) for selectively changing the direction of incidence of the generated fixation mark (2), and an additional camera (8) for detecting the gaze direction (4', 4'', 4''') of the eye (4) is provided, which, like the illumination unit (1) and the measuring device (5), is connected to the control unit (6), so that the control unit (6) can determine the sufficient agreement between the detected gaze direction (4', 4'', 4''') and the direction of incidence of the presented fixation mark (2', 2'', 2'''). characterized by, that depending on the degree of probability of agreement, a measurement process can be triggered by the control unit (6) via the measuring device (5), and eyelid closures are detected by means of the camera (8) and the control unit (6), and the measurement process is triggered via the measuring device (5) in a time range of 0.1 to 0.5s after an eyelid closure.

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