WO2010147477A1

WO2010147477A1 - A method and system for correlation measurements of eye function

Info

Publication number: WO2010147477A1
Application number: PCT/NO2010/000228
Authority: WO
Inventors: Bård DALHØI; Tor Ulleberg; Per Kristian Haug; Nils Morten Wentzel
Original assignee: Heads As
Priority date: 2009-06-15
Filing date: 2010-06-15
Publication date: 2010-12-23
Also published as: EP2442707A1; EP2442707A4

Abstract

The application concerns a method and a system for measuring correlation between different parameters related to visual function and collecting data. A plurality of measuring apparatus and at least one apparatus for visual stimuli are set up around the head of the test person. Trigger signal are connected from a coordinating device to each individual apparatus, and at least one criterion is provided in the coordination device determining when the trigger signal is to be issued to the connected devices. Measured data is stored in a database related to the criterion for issuing the trigger signal.

Description

A method and system for correlation measurements of eye function

The present invention is in the area of a method and a system that may perform these steps of performing correlation measurements of eye function in an test person, and in particular for a method and system for the purpose of measuring parameters that are relevant to classify eye motoric function, neck motoric function, muscle tonus in the neck muscles etc. so that any mutual relevance and the possible correlation between the individual parameters of eye function of the person may be mapped.

The technical development of visual interfaces in general computer technology, mobile telephony and the development of broadband networks, etc., with a number of different entertainment and services enables visual communication through images, movies and symbols that dominate everyday life for many people. This is increasing the degree of visual communication in society, in addition to the traditional situations where vision is a central function such as in traditional schooling, work conditions, etc. The point is that we use our visual feature more and more, and this may result in a number of states which reduces the ability to use vision in everyday life making problems for the individual person. Traditionally one has considered visual problems as a purely optical phenomenon in which any problems may be identified and corrected by optical means. At present, one is becoming more aware of that there is a connection between the eye function and disorders of the neck in patients for example. This relationship is important to identify in order to alleviate a patient from any problems with the vision. It is for example clearly documented in prior art that the eye's close setting when reading and writing are not properly characterized in a person by simply measuring the optical properties of the eye.

Moreover, it is known that the vision is changing and is influenced by the work, increasing age, illness and injury. The new challenges of the eye, as described above, provide also new vision problems, and such visual problems are often experienced by persons as "vague" conditions. In the U.S. there is introduced a new diagnosis called "computer vision syndrome" to classify this type of vision problems. The traditional optical means used to diagnose eye problems cannot detect such conditions with the result that patients remain untreated with coming problems for the patient and society, employers, family and friends.

These problems may be extensive. For example, the Norwegian Research Center for reading and writing in Stavanger estimates that about 400 000 adults in Norway, a country with a population of approx. 4 million inhabitants, have some degree of reading or writing difficulties.

It is assumed that many of these problems are related to disorders of eye functions in persons. It is however important in such studies to separate those individuals who are dyslexic and to exempt them from an "optical treatment". Among youth studies show that approx. 20% of students have some form of writing/reading difficulties. For example, children perform visual testing in schools wherein a nurse is testing reading and writing skills at 6 meters distance. Mapping of the test is showing the letters on the 6 meter distance which indicates the child's ability to have a sharp vision, which has little relevance for the child's ability to read and write on a 12 meter distance. These studies do not reveal any reading or writing problems and not at all the reason for these potential problems.

At present it is also understood that neck injuries may affect eye motoric conditions and thus the eye performance. In Norway, a country with a population of approx. 4 million people, it is estimated that approx. 2 000 to 3000 whiplash injuries happens per year. Examinations have resulted in a recommendation that the diagnosis and objectification of neck injuries should include a visual motoric assessment.

In prior art a variety of methods and apparatus that may measure head movements of a test person, the movements of an eye pupil etc., and also methods and apparatus for measuring muscle tension, such as in the neck muscles are known. Such individual apparatus may of course be used to measure some aspects of the method suggested above. The challenge is to identify a correlation between such measurable parameters and any condition related to an eye or eyes of a person. The basis for such a survey is different stimulation devices for the eyes, wherein the technical problem is that each individual measurement from such well-known devices and procedures happens within its own individual reference system for the respective unit, and there will be no correlation between the measurements from each respective individual apparatus. Moreover, there will be a geometric defined relationship between different apparatus, the stimulation device, etc., relative to the patient's head position should be repeated at a later date to possibly control measure or identify a potential change or a developing trend over time of a state. It is therefore important that a system for such a survey may set and control equipment used in the study of the person in part to calibrate the equipment in a systematic and consistent manner so that the individual parameters measured may be renormalized and may be measured and compared within a single reference system.

A purpose of the present invention is to provide a method and a system that may perform these steps, and measuring individual parameters related to eye function in a test person in a such way that these parameters are measured in a consistent manner, may be compared with further measurements, previous measurements and also be evaluated individually. Furthermore, there is an intent that a variety of parameters are correlated, or that all parameters are correlated together to identify a possible correlation between parameter values and eye function of the person that is measured.

According to an aspect of the present invention, head movements and gaze fixation may be correlated with a test person during an exercise. For example, the person following a light spot that moves in space in front of the person. An apparatus known from prior art being able to measure head movements while another known device may measure the position of eye pupil of the person. In such a system in accordance with the present invention, for example, a computer could control the movement of the luminous dot in space in front of the person by controlling the light source, turning the light source, control a lens optics, etc., as well as the individual units have a signal correlated with the control of the light spot that initiates a measurement in the devices. Thus the data acquisition is correlated in position comprising a series of measurements where each simultaneous measurement from each individual apparatus is correlated with the position of the light spot. In one embodiment of the present invention the light spot's position may be evenly distributed points on a predefined path, or the location in space of light spots may be detected each time the data is measured and sent to the computer together with the other data from other devices. The measurements can, for example, be sent via a wired connection to the computer which then creates a record wherein each record comprises data like position of the eye pupils, position of light spots, time, etc. Other data that may be recorded or measured is the distance between the head of person and the respective apparatus, the distance between the apparatus, spatial coordinates in relation to a fixation point, and also the distance between such light spots in space that are used as stimuli and the eyes of the person, etc. In this way, the experiment may be repeated at a later stage to investigate a trend in development of the test person, or to compare data from multiple persons. Such data collection provides the basis for establishing a statistics that may provide a basis for estimating the normal range for the individual parameters in a population. The example given above may also comprise electromyography (EMG) needle investigations of muscles electrical activity (introduction of needles) in the neck. Other known methods of measurement of muscle tension is also possible to use, and are within the scope of the present invention. Visual motoric dysfunction may cause increased muscle tonus in the upper neck muscles (suboccipital muscles) because of its intimate proprioceptive/neurological connection with muscles in the eyes.

In the example above, the collected data will be analyzed by comparing the collected data against normative data. Data may also be collected graphically, for example, attempted movements of the person's head are illustrated as an animation as well as other parameters such as the location of pupils of eyes, which may be illustrated with arrows indicating the direction in which the person focuses his eyes. In this way, abnormal development of the experiment will be identified. This may also be automated when parameters such as eye pupil position is compared with normal values, for example for determining if these are within the range of normal values or not. If the values of parameters are outside this range or is different from a normal value this may be signaled by, for example in a report or a physical signal is generated when the experiment is finished. Examples of relevant parameters that are measured and that may be reported or be signaled are different eye movement coordinates, relationships between eye and head movements and muscle tonus, the number of fixation points, the average time for each fixation, reading speed, number of trips/distractions, etc. According to another embodiment of the present invention, data acquisition may be synchronized in time. According to this embodiment, a procedure for example implemented as a computer program in a connected computer, actually measure data on an internal sampling rate for each device used in a measurement system according to the present invention. Then the continuous data stream is started by a common start signal. The data that are collected may then be correlated in time by the data streams from each individual apparatus which is analyzed with respect to this unit's actual internal detected sampling frequency for this specific device.

According to another aspect of the present invention, a videotape of a test person may for example be correlated with video frames. A video camera may for example be controlled by providing recording of video frames that are correlated in time with other apparatus used in the system according to the present invention. In this way, a video analysis will be performed. Examples of measurement and analysis that may be executed with such a system is:

- Measurement of motility - examination of eye movements in different directions when the test person follows an object that moves in specific patterns,

- Measurement of accommodation width - how far into the test person's eye it is possible to focus,

- Measurement of close convergence point - how much an eyeball may rotate in close setting.

- Measurement of Fori - measurement of active and passive eye position (hidden strabismus) and refixation.

According to another aspect of the present invention, parameter values that are collected from surveys will be updated in a database wherein different states of an eye function provides a possible search criterion. According to an embodiment of the present invention there is provided a method for measuring the correlation between different parameters related to visual function in a test person, wherein the method includes: setting up a plurality of measuring apparatus around the head of an test person, wherein at least one of the devices includes a stimulation device that may stimulate the eyes of the person when the correlation measurements are performed,

connecting a control input of each respective individual device to a coordinating controlling unit, wherein the control unit may send a readout signal that causes that all devices receiving the signal triggers a sampling of data, and wherein at least one stimulation device in response to a trigger signal stimulates eyes when the measurement is made,

arranging a diaphragm device in a line of sight between a device and the test person's head if this device in the system does not have an appropriate control input that may be connected to the trigger signal from the control unit, and the diaphragm device may be used and is controlled by the trigger signal to open up or close the line of sight,

establishing a common coordinate system in the measurement system so that all parameters may be measured relative to this common coordinate system,

providing at least one criterion in the control unit which the control unit is using to determine when to send out the trigger signal to the connected devices, and all data are to be stored in a data structure reflecting the criterion defined in the control unit.

According to another embodiment of the present invention there is provided a system including apparatuses and a control device that performs step in a procedure according to the present invention.

Such aspects of the present invention as described above and other advantages of the present invention will be more clearly understood after reading the following detailed description with reference to the attached figures. The detailed description is directed to an embodiment of the present invention. The scope of the present invention is defined by the attached claims.

Figure 1 illustrates an example of a lens system that may be used in accordance with the present invention.

Figure 2 shows an example of setting up a system in accordance with the present invention.

Figure 3 shows another embodiment of the present invention.

The starting point for a survey that examines eye function of a test person is that the person is viewing or is presented a visual object that the test person responds to. The expected response is that the person fixates his eyes on the object and/or follows the objects movement in space. This involves moving not only the eyes but also of the head and neck of the test person. A test may for example comprise to follow a light spot which moves across a screen, or the visual object may be text displayed on a screen wherein visual motoric skills that are tested are related to how the person moves eyes and head to find for example a line of text, if the test person is unable to move his gaze to the start of words, etc. and not how the person is actually reading the text, or the test person may follow the motion of a bright light spot in space. Figure 1 shows an example of stimulation device that creates an illusion of a light spot moving in space when the person is positioned in front of the lens system of the device and are looking directly on it. A point- shaped light source is first dispersed in a movable concave lens and then collected by a convex collecting lens that illuminates a bright spot that provides an illusion of being hanging in space in front of the person since the light is collected in the focal points in space. When the concave lens is moved, the corresponding light spot or focal point is moved in space as known to a person skilled in the art. In another embodiment of the present invention, a light source is positioned on the opposite side of the collecting lens side. This provides the same effect as described above. This symmetrical property of the lens system is known to a person skilled in the art. Figure 1 shows the principles for such a facility and a practical implementation may include several optical devices (lenses) as known to a person skilled in the art. The light source and lens arrangement may be placed over the head, or on the side of the head of the test person. Movements or movement of the concave lens may be made with actuators in the spatial x, y and z directions as known in prior art. These movements may be controlled by a program in a computer system providing control signals to the actuators.

Figure 2 illustrates an embodiment of the present invention where a device 10 is able to follow a person's eye pupil movements. In the bottom of this apparatus there is a light source integrated with a lens system in accordance with the principles demonstrated in Figure 1. The person follows the light spot while the eye tracker 10 reads out positions of pupils of the eyes of the test person. Both eyes of the test person may be detected and followed. Data may be marked as right eye movements, left eye movements etc.

Figure 3 shows another embodiment of the present invention comprising an apparatus to measure and track head movements. The headgear includes LEDs that will give a light signal which optoelectronic position-sensitive detectors placed around the test person may record and distribute, for example x, y, z coordinates relative to an internal reference system for the detector locations. For example, four detectors will be placed on a screen in each corner of the screen, and a person who follows the movements on the screen by moving his head will be registered in the screen's x and y direction coordinates and a distance from the detectors to the movement of the head gear is used as a z coordinate. Such a distance may be measured as the intersection of two lines of sight from the two detectors that have a distance between themselves as known to a person skilled in the art. In this example, a visual stimulus may be displayed on the screen, but it is also possible to have a light spot device as shown in Figure 1. This device may for example be integrated in a frame around the screen.

In other embodiments of the present invention, a light spot may be moved by a frame that may be moved back and forth towards a test person sitting in front of the frame on suitable rails or control tracks arranged in a base plate in the apparatus. A LED diode may for example be mounted in a crosshair in the frame. The wire cross may be made of thin electric wires that provides power for the light diode. These cables may be stretched to the middle points on the respective opposite sides of the frame, wherein the attachment to the frame comprises coils with coiled cord. The coils comprise small electric motors that make it possible to pull the attached cord to/from a coil. In this manner it is possible to move the LED to a certain determined x and y position while movement of the frame on the base plate provides a z coordinate position. A computer program may control the coils and corresponding position as known to a person skilled in the art. In another embodiment of the present invention, a light spot or other object may move in space arranged as a diode or object that is attached to a robot arm like a device which is may be moved in an x, y and z direction as known to a person skilled in the art.

A computer, such as a personal computer, may be equipped with a number of input ports and output ports, such as USB, RS232, parallel port, infrared communications port, such as an IrDA port, Bluetooth etc., as known to a person skilled in the art. As known to a person skilled in the art, it is possible to connect devices with similar interfaces and provide a program that may activate an attached device (trigger signal) and which may also provide read out of data. The time from a trigger signal as been issued until data may be ready for readout may vary according to different factors. The Electronic circuit technology of the device (i.e. CMOS), complexity of the device, type of analog to digital converter that maybe is used are factors that influence the time the measurement needs to be processed in the device. This time may be estimated or may be part of the data sheet for the device. Accordingly it is possible to estimate the correct sampling frequency of a system according to the present invention simply by calculating max delay that is necessary from trigger signal to readout is possible. For example, an eye movement tracker such as Tobii 120 may be used, a head movement tracker of the type Polhenus Liberty may be used, and an EMG system like ME600.

It is further an aspect of the present invention that any external device, aperture mechanism, electronic gadgets, mechanical devices, electro-mechanical device, etc. that may help to start and stop a data-taking of an associated or connected device is within the protective scope of the present invention.

As known to a person skilled in the art, sensors in apparatus as outlined above are usually of analog type. This means that the measurement data must be converted to digital form using a circuit that allows an analog to digital conversion of the signal. As known to a person skilled in the art this comprises providing to a sampling signal a circuit that performs this conversion. In the example given above, the individual apparatus has different sampling frequencies. Tobii has a nominal sampling rate of 120 Hz, Polhemus of 240 Hz and ME6000 at a frequency between 100 and 10 000 Hz. In an embodiment of the present invention where it is desired to make the time-correlation measurements between the various devices two aspects of a system according to the present invention must be clarified. These conditions are the actual sampling frequency of the respective different devices, as well as a common reference point for the start of measurements in different units.

To get these devices to operate synchronously and produce correlated data, in an embodiment a computer program executes the following steps: 1. connecting all devices in the system to the same computer, and equip the computer with a digital to analog conversion circuit, for example, an I/O card connected to the internal computer bus that enables the program to let the computer send out a square pulse with precise duration where these square pulses are used to synchronize the measurements in the apparatus connected to this signal,

2. connecting the sync pulse directly to Polhemus and ME6000 system and connect the square pulse to an IR - diode mounted in front of the Tobii system, when the pulse goes high, both Polhemus and ME6000 system identify this transition as stop of measurement, while the Tobii system will stop identifying the position of the eye because of the IR LED illumination of the detector, when the pulse goes low again data from the conversion of analog input signals is completed and ready to be sent to the computer as digital values while the system is ready to make a next measurement.

3. starting all data sources, and wait until all equipment is ready to measure, this may involve an extra step for completing for example a calibration of the Tobii eye tracker so that the eyes are followed correctly.

4. first, sending out a plurality of pulses (i.e. low - high - low transitions) with 2-second intervals where the high part of the pulse lasts for example 0.5 seconds, which will provide a basis for measuring the internal sampling frequency of the different instruments, 5. thereafter sending out a single pulse with duration of for example 0.1 seconds to marc a synchronous start of data collection is made for all devices that are connected, which make it possible for an apparatus to carry out measurements, all measurements may be carried out continuously and the data that are collected are organized or indexed by the running clock of the system.

The collected data may then be analyzed as follows: pulse train is analyzed by re- check of all the data collected from the acquired sets of measurement data wherein the synchronization signal (the square pulse described above) goes high. The distance in the number of sample between these positions, combined with knowledge of the time between each pulse is used directly to determine the respective device sampling frequency. If the estimated frequency deviates too much (more than, say, 5%) from the nominal rate specified for each respective device measurements are considered to be incorrect and the results are discarded and the procedure must be done again. Similarly, rejected the results, if not all pulses are recovered in all the data from the respective devices. The first identified pulse is used further to determine the reference point for any recording that all further data collected may be related to or correlated with.

In another embodiment a trigger signal in coordination with a stimulation device is used in an attempt for alignment. For example, a luminous spatial moving bright spot provides the trigger signal every time the bright spot moves in space. Thus, the collected data are correlated with the spatial position of the stimuli device. A program in the computer that controls the movement of the luminous dot as indicated above may also generate a trigger signal for the other instruments in the system. Other examples of generating trigger signals may be that there is text on a screen, and an eye pupil tracker detects that your eyes move from the start of a word to another (between fixing points) or just the end that look hostels, and this detection leads to a trigger signal is generated and supplied to other apparatus in the statement. A program in the computer may continuously read data from the eye pupil tracker and each time movement from one fixation point to another is detected in this sample program a trigger signal for other devices is generated. Detection may be done by an analysis of continuously collected data from the eye pupil tracker, or by a comparator circuit receiving the digital data from the eye pupil tracker. For example, there are two comparator inputs. The first time measurements are performed two registers are loaded with the same data and the register contents are compared in a comparator. The next time data is read out from the eye pupil tracker data is transferred only to one of the registers and thus the new data are compared with the old data. When the comparison is completed the registers are updated so that the next comparison of data from next current read out is compared with data from the current measurement. If there is a difference in the data this will be detected. This means that eye pupils have moved. To make the comparison somewhat immune towards noise it is possible to omit the least significant bites in the digital data that are compared (for example omitting the two least significant bits). The stored data are directly correlated with the motion of eye pupils of a test person. This may also provide statistics for such attempts. In an example of embodiment it is possible to detect how the test person may find a start of a word, end of words, change of line, etc. all detected by the position of the eye pupil compared with the text as it appears on the display.

It is also important to calibrate the individual apparatus. The units provide spatial coordinates in a three-dimensional coordinate system. These coordinate systems are basically rooted in each individual unit and must be coordinated so that measurement data may be compared. It is also within the scope of the present invention to provide calculations of parameter values between uncorrelated coordinate systems (translation equations as known to a person skilled in the art). It is for example possible to establish a set of common points in space of the system which is known in each respective coordinate system. For example, the following steps in a procedure may be:

1. identifying a surface, such as a permanent plan in a screen that displays text, the bright spots in a coordinate system for this screen

2. establishing two surfaces that are in the head tracker's coordinate system 3. establishing a cube in the eye pupil tracker coordinate system (3 axes/areas)

4. selecting common points in all coordinate systems where the surfaces/lines in the respective coordinate systems intersect or overlap. Examples of calibration procedures in accordance with the present invention may be divided into two calibration procedures. The calibration routine needs be done once for each new installation (or after the system has been moved or changed), and there is also a calibration which may be done for each individual test person. In an example of embodiment of the present invention, the coordinate system of the stimuli device is used as a reference coordinate system for the whole system. This means that it is sufficient to transform data from the head tracker and the eye pupil tracker coordinate systems to coordinates in the coordinate system of the stimuli device.

Some examples of calibration procedures:

Calibration at initial setup: Alignment of stimuli device coordinates with head follower's coordinate system which is needed only to be done when initially setting up the system. Then one may assume that these coordinate systems will always be in the same position relative to each other. In an example where a display is used as part of the stimulation device head tracker detectors may be located in corners of this display. The position of the display's corners may be measured manually in advance. Thus, position data from the detector will then provide coordinates in the overall system's coordinate system when the display surface is used as the main reference for the system, as described above.

Calibration for each person: The eye pupil tracker system defines a cube in space relative to the position in space of the eye pupil tracker system. This position may be made known to the system, for example, by measuring the position of this device relative to the surface of the display that is used in the example above for the stimuli device. Thus, all the position data from the eye pupil tracker may be transformed to the coordinate system that is anchored to the surface of the display. Examples of data that may be measured in systems in accordance with the present invention are related to the type of apparatus used in a system assembly. Therefore, a system in accordance with the present invention comprises a library of computer software routines which may for example be executed in a computer in the system providing calibration of specific apparatus, transformation of data from one coordinate system to another, and run time routines for data acquisition. Individual calibration of respective instruments may also be done. For example will the following data be calibrated and used for the examples of instruments used in the examples of systems in accordance with the present invention:

Polhemus Liberty: o Distance (x, y, z) and angle (azimuth, elevation, roll) in relation to the apparatus.

Tobii X120: o Direction of gaze relative to the location of an object displayed on a screen (x, y coordinates) o Direction of gaze from the eye (x, y, z coordinates) o Position of eye in spatial coordinates (mm) (x, y, z) o Position of the eye relative to the Tobii X120 device (x, y, z) o Size of the pupil of each respective eye o Validation code for each eye (right eye, left eye, etc.)

In another embodiment of the present invention, a synchronization signal is generated manually by a person who leads an investigation or the subject itself. A synchronization signal may be started when the test person's head is in a certain position, for example, or is viewing a particular object on a display. In other examples of embodiment a synchronization signal is used as a trigger signal triggering start of data acquisition.

The correlation may also be established when the head to the test person moves to extreme positions of the head. A trigger signal or synchronization signal as described above may be given to a system in accordance with the present invention by a person pressing a button, wherein the button is interfaced to a computer in the system. A program in the computer may detect the pressing of the button and then start a measurement/calibration etc. as described above.

In an example of embodiment of the present invention accommodation is measured. An object and not a light spot as described above will continually be moved towards the nose of the test person. When the test person experiences that the object is visually unclear, the test person presses a button as described above. The distance between the object and the nose tip may be measured in different ways. For example, a forehead band, as shown in Figure 3 may include a distance measuring device of a type for example used in compact digital cameras. In an example of embodiment a program is recognizing the face in a picture of the test person and then the position of the nose in the picture. The Autofocus function of the camera may then be used to identify the distance. In another example of embodiment, a forehead tie may be equipped with a simple radio transmitter, ultrasonic transmitter or other similar transmitter and the distance may be identified by triangulation as known to a person skilled in the art.

In another embodiment of the present invention convergence of the test person is measured. In an example a bright light spot, such as an LED is used and is moved towards the nose of the test person. Simultaneously correlated measurements of eye pupil tracker data are recorded.

According to other aspects of the present invention, it is possible to identify the reactions in the neck muscles correlated with visual tests of various kinds. Such reactions may be measured under short or long time intervals where the eye is stimulated in the test. A test may for example only last a few seconds while in other cases, a reading test, for example, last for several minutes.

It is also known that there is a neurological link between the jaw joint/jaw muscles and muscles of the eye. Measurement of the respective muscles and muscle groups may be correlated with eye pupil measurements as described above. It is within the protective scope of the present invention that any measurement that may be controlled using a trigger signal as described above may be used to make correlation measurements in accordance with the present invention. It is also within the scope of the present invention that each cross- correlation between the parameters measured may be carried out and are covered by the principles in accordance with the present invention. Generally, it is important to understand that the present invention comprises a trigger signal that may be generated on the basis of any condition set up in the system. For example, it may be required that the device 1 (for example head tracker) and device 2 (for example eye tracker) of the system both have signal values above a specified threshold (logical AND function), or that at least one of the devices have such data (Logical OR function). Any such combination/solution is within the scope of the present invention.

According to another aspect of the present invention, a system in accordance with the present invention is used to collect data from many test persons. Such data may be organized in a database. Records in the database may be made searchable via diagnosis codes, parameter values, etc. Such measurements provide statistically normal values for parameters that are measured. Moreover, it establishes parameter ranges that represent a variation range for each parameter that are measured. This allows health professionals to make a correct diagnosis of a patient examined with the present system solution.

Claims

Claims:

1. A method for measuring correlation between different parameters related to visual function in a test person, wherein the method comprises the steps of:

setting up a plurality of measuring apparatus around the head of the test person, wherein at least one of the apparatus comprises a visual stimuli device that may stimulate the eyes of the test person during the measurements,

connecting a trigger signal to each respective individual apparatus from a coordinating device,

arranging if necessary a diaphragm device in a line of sight between a device and the test person's head and connect the diaphragm device to the trigger signal,

establishing a common coordinate system among the plurality of measuring apparatus so that all parameters may be measured relative to this common coordinate system,

providing at least one criterion in the coordinating device determining when the trigger signal is to be issued to the connected devices,

reading out the data when a specific measurement is finished and store these data in a data structure related to the criterion for issuing the trigger signal.

2. The method according to claim 1, wherein the at least one criterion for issuing the trigger signal is a common start signal.

3. The method according to claim 1, wherein the at least one criterion for issuing the trigger signal is a continuously running clock, and where the criterion is a specified increment of the clock rate.

4. The method according to claim 1, wherein the at least one criterion for issuing a trigger signal is a detection of a state of at least one apparatus in the system, or a state of data read out from at least one apparatus in the system.

5. The method according to claim 4, wherein the at least one criterion comprises a logical function between the states detected from the read out signals from the at least one apparatus.

6. The method according to claim 1, wherein the at least one criterion for issuing the trigger signal is an activation of a button connected to the controlling device.

7. The method according to claim 1, wherein the method comprises calibrating the apparatus used in the system.

8. The method according to claim 1, wherein data collected from a plurality of test persons are stored in a data structure comprising a relational database, wherein it then is possible to search data related to a certain condition for correlating the measurements.

9. The method according to claim 8, wherein the data collected is used to establish normative values for vision-related data collected in accordance with the method.

10. The method according to claims 1 and 9, wherein the at least one criterion for issuing the trigger signal comprises comparing collected data with normative data.

11. A system for measuring correlation between different parameters related to visual function of a test person, wherein the system performs a method according to claim 1 to 10.