WO2004112598A1

WO2004112598A1 - Method of testing and corresponding vision aid

Info

Publication number: WO2004112598A1
Application number: PCT/GB2004/002582
Authority: WO
Inventors: Peter Irons
Original assignee: Tintavision Limited
Priority date: 2003-06-18
Filing date: 2004-06-17
Publication date: 2004-12-29
Also published as: GB0314080D0

Abstract

A method of testing applicable to the provision of a vision aid, such as the selection of a tint for a VDU screen, to assist in alleviation of symptoms in dyslexia and other optical disorders, is based upon a quantitative approach to the identification of the colorimetric parameter within the three dimensions of colour space applicable to the vision aid for optimal patient visual performance. The invention provides a test procedure in which eye trace parameters are associated with a given value of each of the three colorimetric parameters of the vision aid to select the optimum colorimetric values of the vision aid.

Description

METHOD OF TESTING AND CORRESPONDING VISION AID

The present invention relates to a method of testing and corresponding vision aid, particularly a vision aid for use 5 in optical recognition tasks including spacio-temporal serial recognition tasks and reading.

Such a method of testing and corresponding vision aid is disclosed in GB2354169 (Irons) . In this document the method

L0 of testing comprises the steps of carrying out a test in which a vision aid having a value of colorimetric parameters is used by the patient to identify patient response to the test and deriving quantitative data representing the visual benefit to the patient of the

L5 vision aid. The test consists of the patient conducting a task whereby the vision aid is used. The performance of the patient is then quantified by measuring the time needed to perform a specific task. On the basis of this quantitative measurement, a vision aid having different colorimetric

20 parameters is selected and the task is performed again with a different vision aid. The time taken to perform the task is again measured and on the basis of the measurement, a different vision aid is selected. This process is repeated several times until optimum or near optimum colorimetric 5 parameters of the vision aid are established.

The method of testing as described in Irons is an indirect measurement of the visual benefit for a particular patient, as it relies on a measurement of the patient ' s performance 0 of set tasks. The measurement of the patient's benefit is therefore inaccurate and as a result, the selected optimum colorimetric parameters of the vision aid may not necessarily be optimised for the patient as a result of these inaccuracies. 5 Another important problem associated with the method of testing as disclosed in Irons is that the process of selecting the optimal vision aid is slow, as the patient needs to complete the optical tests numerous times to optimise the colorimetric parameters of the vision aid. For most patients, the method of testing takes approximately 1 to 4.5 hours to prescribe a vision aid which provides optimum or near optimum visual benefit to the patient.

The present invention aims to obviate or at least mitigate the above described problems and/or to provide improvements generally.

According to the invention, there are provided an improved method of testing, and an improved test apparatus and vision aid according to any of the accompanying claims.

In an embodiment of the invention, there is provided a method of testing applicable to the provision of a vision aid having colorimetric parameters, the method comprising the steps of providing a vision aid having a chosen value of the colorimetric parameters, assessing the visual benefit provided by the vision aid, and determining whether a different vision aid having a differing selected value of the colorimetric parameters would produce a better result, the step of assessing the visual benefit provided by the vision aid comprising the steps of conducting an optical test in which the vision aid is used optically by the patient to identify patient response to the test, observing the patient's response by means of an eye tracking device, the eye tracking device providing eye tracking data, and deriving quantitative data from the eye tracking data, the quantitative data representing the visual benefit to the particular patient, and analysing the quantitative data whilst the optical test is performed to identify a selected value of the colorimetric parameters of the vision aid which improves or optimises the benefit for the particular patient, and providing a different vision aid whilst the optical test is performed, the vision aid having a different value of the colorimetric parameters corresponding to the selected value to establish a vision aid providing optimal benefit for the particular patient.

The method of testing provides a direct measurement of the visual benefit for a particular patient as the patient response is observed during performance of the task whereby the quantitative data directly represent the visual benefit which is perceived by the patient.

An important aspect of the invention is the use of an eye tracking device which enables objective measurement of the degree or deviation of movement between the eyes and of each individual eye. The eye tracking device comprises spectacles or a pair of infra red goggles and a control box connected to the goggles. The movement of the eye is measured by means of photo detectors in the goggles or spectacles up to a frequency of 1000 Hz. The spectacles or goggles may be remotely connected to the control box so that the patient is not limited in his/her movements. The control box provides eye trace data in the form of eye position and/or motion data.

Alternatively, or additionally, the eye tracking device may comprise an imaging device for recording images of the eye, the eye tracking device further comprising an image processor for processing the images and providing eye trace data in the form of eye position and/or motion data.

The eye tracking device may provide eye trace data with respect to displacements or deviations of the eye in the approximate horizontal direction or x-direction. The eye tracking device may also provide eye trace data with respect to displacements of the eye in the approximate vertical direction or y-direction.

We have discovered that the visual benefit for the patient can be derived directly from the eye trace data that are provided by an eye tracking device. This has the important advantage that we can measure visual benefit directly from the eye tracking data whilst the patient performs the optical task. This significantly reduces the overall time necessary to conduct the method of testing. Also, this ensures an objective measurement of the perceived visual benefit or visual perception of the patient or user as no operator actions or patient actions are required to record or interpret the measured data.

In addition, we have discovered that we can control the movement patterns of the eyes by variation of the colorimetric parameters of the vision aid. This enables us to adjust the colorimetric parameters in such a way that optimum visual benefit is achieved for the patient. In addition we can control the synchronisation of the patient's eyes with the vision aid.

Importantly, we have discovered that when visual information is perceived, the activity level of the eyes alternates between one eye more actively perceiving the information and the other eye more actively perceiving the information. This process is referred to as oscillopsia which is a result of alternating suppression of the eyes. We have discovered that the visual benefit is significantly enhanced if oscillopsia is prevented as much as possible which allows both eyes to perceive the information continuously at a more or less equalised level of activity. In this way, the synchronised performance of the eyes is significantly improved.

The method of testing according to an embodiment of the invention thus provides a significant improvement over conventional methods of testing and it enables a more accurate determination of the colorimetric parameters of a vision aid for the patient, thereby optimising the patient's eye response. More importantly, the benefit as received by the patient is objectively and directly quantifiable with great accuracy from the eye tracings. The method has the additional important advantage that it provides an instantaneous analysis of the quantitative data and subsequent determination of the colorimetric parameters which provide optimum visual benefit to the user or patient whilst the patient performs the required optical task.

In another embodiment of the invention, the eye tracking device is adapted to provide eye tracking data of both eyes. This has the important advantage that the visual benefit is quantified in respect of both eyes and the interaction of the patient's eyes in performing the set task or optical test is optimised so as to receive the best possible visual benefit from the selected vision aid.

The reading process when fluent, involves the controlled collection of a series of spatially and temporally coherent data sets, from the visual scene. The spatial coherence is achieved by the calculation of the metrices of the oculomotor response needed to achieve the accurate saccade to the new object of attention in the series. The spatial data for a new saccade is extracted from and dependent upon the quality of the spatial and temporal data being collected in the present fixation. Therefore the quality and quantity of the spatial and temporal data in one fixation controls the spatial and temporal data collected in the subsequent fixation and iteratively in all subsequent fixations. From the eye trace data, the saccade length and saccade frequency are directly derivable. This provides an immediate, quantifiable measure of the visual benefit as the saccade frequency is maximised for optimum visual benefit.

An important advantage of the present invention is that whilst an optical task is performed by the patient, an objective quantitative data analysis of the visual benefit is made. In turn, whilst the task is performed, the vision aid is adapted by appropriate adjustment of the colorimetric parameters. Whilst the task is performed, the perceived visual benefit is quantified directly and further adjustments to the vision and can be made.

In another embodiment of the invention, the quantitative data analysis comprises the step of computing eye trace parameters from the eye tracking data, the eye trace parameters comprising a stamina index, a variance in fix, a variance in speed, a saccade index, a saccade dimension index, mean saccade length, regression index, synchronicity of the left and right eye, visual processing index (VPI), post-saccadic drift index (PSDI) , fixation disparity index (FDI) and/or combinations of the aforesaid parameters.

The stamina index is a measure of the stamina of the patient whilst performing the task. The variance in fix is an indication of the variance of the eye around a fix on an object such as a word. The variance in speed gives an idea of the exhaustion of the patient whilst performing the task.

The post saccade drift index (PSDI) is an index of the proprioceptor feedback to maintain a steady fixation on an object of attention. The index is a measure of the small oscillations of the eye around a certain fix. The index is also an indicator of the use of head movement and body movement to maintain the eyes at a central or a null position as they read across a line of text. In a binocular situation, both eyes are drifting in the same direction. The PSDI tends towards zero as the RGB parameters tend towards the optimum. This is mainly Vestibular-ocular (VOR) reflex mediated, although neck muscle and back muscle reflexes managed by the cerebellum can also be included.

The PSDI is calculated by the differential between the total line saccade length and the sum of the saccades within the line. As the RGB parameters tend towards the optimum, the total line saccade dimension tends towards the sum of the saccades within the eye. When the optimum is achieved, head and body movements during reading are minimal .

The saccade dimension index is a measure of the mean saccade length.

The regression index provides a measure of the patient moving back to a word or visual element whereas the synchronicity is a measure of the alternating suppression or oscillopsia of the eyes .

The fixation disparity index is the variation in the disparity of fixation between the two eyes of a patient. It provides a measure of the change in time in the repeat fixation of the eye on a particular object such as a word or cluster of words in a line of text . This measure can influence the rate of the visual processing of the arrayed icons. The fixation disparity index is an important parameter as it provides an indication of the efficiency in the way information is perceived by the patient or user.

The mean of the fixation disparity index and the standard deviation of the fixation disparity index are of particular interest. We have discovered that as optimum visual benefit is perceived, the mean fixation disparity index is minimised and also, the standard deviation of the fixation disparity index is minimised. As the standard deviation of the fixation disparity tends towards zero, the RGB parameters tend towards the optimum for the patient. As the mean fixation disparity tends towards zero, the RGB parameters tend towards the optimum for the person.

Measurement of mean fixation disparity for stated time periods can also be used to calculate the optimal visual conditions. Mean or modal fixation disparity tends towards zero as the RGB parameters and luminosity tend towards the optimum. Standard deviation of fixation disparity tends towards zero as the RGB and luminosity values tend towards the optimum.

The visual processing index (VPI) is the visual processing speed of regularly arrayed icon sets such as the characters or words in a line of text. The visual processing index provides a measure of the rate of reading for lines of text .

The visual processing stamina index (VPSI) is a measure of the changing VPI during a task such as reading.

The saccade length index provides an indication of optimum visual benefit which is perceived by the patient or user. In particular, the total saccade per line of text indicates the length of a line of text. In a preferred embodiment of the invention, the quantitative data analysis is conducted on the basis of a model, the model defining the relationship between the eye trace parameters and colorimetric parameters . The model is based on the physiology of the eye and in particular on the relationship between the saccades and foviations and colorimetric parameters relevant to colour space.

Within the context of the application, by colour space, we mean the 3-dimensional concept of the three colorimetric parameters which any tinted transparent vision aid possesses, namely values with respect to hue (or frequency/wave length) and saturation (or density) and luminosity (or total light energy) .

In relation to hue, the colorimetric parameters may alternatively be identified as "biological/physical colour space" based on values on red/green/blue scales which does provide an alternative definition of colour space. Red/green/blue (or r/g/b) values are of particular relevance in relation to the testing and use of the method of the invention in relation to VDU screens.

The model enables the colorimetric parameters to be calculated such that these have a direct effect on the eye performance. This in turn has a beneficial effect on the visual benefit as received by the patient when using the vision aid. For some parameters such as the stamina index, the model directly links the calculated eye trace parameters to the colorimetric parameters such as contrast, hue and luminescence.

In yet another embodiment of the invention, the eye trace parameters are recorded with respect to all values of the tested vision aid in 3-dimensional perceived colour space, namely hue, saturation and luminosity and/or with respect to all three of the values of the red/green/blue elements of biological/physical colour space.

In an embodiment of the invention, the model may define the relation between improved colorimetric parameters and the fixation disparity index which are readily derivable from the analysis of the eye trace data.

As the optical task is performed by the patient, from the saccade length and the time interval for completing one saccade length, the rate of reading per line is established. This provides an important parameter for determining the colorimetric parameters of the vision aid for which optimum vision benefit including optimum reading is achieved. However, in order to establish the optimum perceived visual benefit, we do not solely rely on minimising the time interval for completing a saccade length but, in addition, the mean disparity fixation index and the standard deviation of the fixation of the disparity index are optimised, together with the saccade line length frequency to establish the colorimetric parameters for which optimum visual benefit is achieved. The model may further define relations between the colorimetric parameters and indices that can be readily derived from the eye trace data . These relations provide an indication of suitable colorimetric parameters of the vision aid to arrive at the optimum visual benefit to the patient.

The model may be based on recorded trends which have been found by conducting previous tests on patients to provide suitable vision aids. One example of such a trend is that, if, following adjustment of the red and green colour parameters no or a negligible improvement in visual perception is found, then the blue colour parameter is adjusted. Once the optimal value for the blue colorimetric parameter is established, the red and green parameters are adjusted. The iterative steps for providing a suitable vision aid on the basis of the model may be recorded to improve subsequent methods of testing. The model may thus be adaptative so as to improve the model which results in an improved vision aid and reduces the overall testing time to provide a suitable vision aid.

In a further embodiment of the invention, the optical test comprises an array task such as a reading test or a spacio- temporal serial recognition task. The optical test may also comprise a non-array task. An example of a non-array task is the searching for and eventual finding of one or more hidden items on a page of data. We have discovered that it is important to separate the types of optical tasks as undertaken by the patient into array tasks and non-array tasks .

The difference between array and non-array tasks includes substantial differences in the use of the muscles of the eye which leads to fundamental differences in the optical problems associated with these two types of tasks. The optical test is adapted to test both the non-array and array task performance of the patient and to provide separate vision aids for both tasks as well as providing a consolidated vision aid which strikes a balance between optimal array tasks and non-array task visual benefit.

In a further embodiment of the invention the method comprises the step of observing the patient response by means of a head tracking device for tracking the patient '.s head movements and deriving further quantitative data from the head tracking device representing the visual benefit to the particular patient. Head movement plays an important part in the overall visual perception of a patient. Generally, minimising head movement is an indication that the visual benefit received by the patient is optimal. We have also discovered that the head movement is reduced to a minimum when optimum visual benefit is perceived by the patient .

Often, in response to head movements, the eyes move in the same directions to compensate for any head movement or to achieve a specific effect such as improving the fix depending on the patient's condition. By recording the head movements and including head track data in the model, it is possible to further optimise the visual benefit of the vision aid by adjusting the colorimetric parameters of the vision aid accordingly.

The quantitative data analysis preferably comprises the step of computing head movement parameters from the head tracking data and feeding those head movement parameters into the model to calculate the optimum colorimetric parameters .

Preferably, the colorimetric parameters of the vision aid are set on the basis of an iterative process whereby the vision aid is continually adapted in accordance with the calculated colorimetric parameters to enhance the patient's performance and optimise the visual benefit to the particular patient.

In a particular embodiment of the invention, the steps of assessing the visual benefit and determining whether a different vision aid having a differing selected value of said colorimetric parameters would produce a better result, are first conducted with respect to the luminosity parameter of the vision aid. Once this parameter has been optimised, the red and green parameters of the vision aid are varied iteratively and the visual parameters are calculated from the eye tracings for a number of times to optimise the red and green parameters of the vision aid. The blue parameter or blue colour of the vision aid is then varied iteratively and the visual parameters are calculated from the eye tracings for a number of times to optimise the blue parameter of the vision aid. Finally, the luminosity parameter of the vision aid is varied iteratively and the visual parameters are calculated for a number of times to optimise the luminosity. The order in which the parameters are varied may depend on trends which have been recorded from conducting previous tests or which are recorded or programmed otherwise in the model.

In another embodiment of the invention, there is provided an apparatus adapted to carry out the method as herein before described. In particular, the test apparatus for providing a vision aid having colorimetric parameters may comprise means for providing a vision aid having a chosen value of the colorimetric parameters, means for assessing the visual benefit provided by the vision aid and means for determining whether a different vision aid having a differing selected value of the colorimetric parameters would produce a better result; the assessment means comprising an optical test in which the vision aid is used optically by the patient to identify patient response to the test, the assessment means further comprising an eye tracking device for observing the patient's response, and means for deriving quantitative data from the eye tracking data, the quantitative data representing the visual benefit to that particular patient.

The determination means may comprise means for analysing the quantitative data whilst the optical test is performed' to identify a selected value of the colorimetric parameters of the vision aid which improves or optimises the visual benefit for the particular patient, and the determination means comprises a means for providing a different vision aid whilst the optical test is performed, the vision aid having a different value of the colorimetric parameters corresponding to the selected value to establish a vision aid which provides optimal benefit for the particular patient.

In another embodiment of the invention, the means for analysing the quantitative data comprises computing means for computing eye trace parameters from the eye tracking data. Preferably, the assessment means and determination means are all provided on a computer system whereby the eye tracking data are fed to the computer system and whereby the computer system comprises a VDU on which the optical test is performed. A secondary VDU may be provided to the user or operator to monitor progress of the testing and to further control the process if required. The computing means preferably comprises a model, the model defining the relationship between the eye trace parameters and colorimetric parameters as discussed above. The eye trace parameters are computed with respect to all three values of the tested vision in three dimensional perceived colour space or with respect to all three of the values of the elements of biological/physical colour space.

It is possible to perform the optical tasks or tests iteratively for each of the three elementary colours red, green and blue. However, we have found that it is more effective to start with the luminosity. This is then followed by conducting the tests for red and green, and finally the test is conducted for blue. After this, the test is repeated for the luminosity.

In an alternative embodiment, the model may be sufficiently sophisticated to calculate the desired colour changes and luminosity changes directly from the eye tracings without separate optical tests for each colour and luminosity. In this alternative embodiment, the model defines the relationship between eye trace parameters and the optimum or desired colour changes and luminosity changes .

In a further embodiment, the model is based on trends which are recorded from previous test results by other patients . For example, previous test may indicate that there is a relation between a low fixation disparity index and a low luminosity parameter. In that case, the model includes the trend that for low fixation disparity indices, the luminosity must be increased.

In another embodiment of the invention the apparatus further comprises a head tracking device for tracking the head movements and deriving further quantitative data from the head tracking device which represent the visual benefit to the particular patient .

The eye tracking device may comprise an infra red, video or other suitable eye tracking device which is adapted to objectively gather information on, and to objectively measure, the degree of displacement of movement between the eyes or each eye to optimise movement patterns during saccades and foviations for edge detection in iterative array tasks for the purpose of calculating indices of movement or degrees of displacement of movement for use in determining interventions for improving the efficiency of the visual system in the performance of edge detection in the perception of iterative arrays. The use of eye movement tracking equipment provides data from which parameters of eye movement behaviour or eye tracking parameters during the array tasks are calculated such that these parameters can be modified and optimised by objective changes in the output indices in response to changes in the visual characteristics of the target. The eye tracking parameters are controlled by varying the font or icon size, luminosity of background or foreground, saturation or hue of background or foreground and the RGB ratios of background or foreground of a VDU screen.

In another embodiment of the invention, the apparatus comprises a computer programme for the analysis of the eye tracking parameters and the use of these parameters in the determination of changes in the visual characteristics of the target material allowing the optimisation of these indices for the individual patient's visual benefit.

In a further embodiment of the invention, there is provided a computer comprising a computer programme for the analysis of the eye tracking parameters.

Optimisation within the context of the application is achieved by optimising various parameters which are calculated from the eye tracings. Optimisation includes optimisation of fixation stability and intra-fixational eye movements (fixed variance index) at the conclusion of each saccade, optimisation of eye teaming or synchronisation during reading, optimisation of post-saccadic drift, optimisation of fixation disparity and optimisation of saccades dimension. Other visual parameters as disclosed above may also be optimised.

The de-suppression of the use of visual data from an eye maximises the reading speed and maximises the oral reading fluency. Also, it improves the binocularity or synchronicity of the patient's eyes.

In another embodiment of the invention, the vision aid may comprise a visual interface such as an information panel, display, or desktop such as the desktop or screen which is commonly found on personal computers.

One object of the invention is to apply a method and apparatus for testing of a vision aid to create visual ergonomic indices of visual stress which can be used to identify optimal RGB parameters for the viewing of text.

Another object of the invention is to create visual ergonomic indices of visual stress allowing objective comparison of the effects of software/desktop design on the visual stress of individuals or populations. A further object of the invention is to create visual ergonomic indices enabling identification of members of populations who are limited in their access to text. These objectives and other objectives are achieved with the method and apparatus as defined in the accompanying claims.

In another embodiment of the invention there is provided a method of testing which is applicable to the provision of a vision aid having colorimetric parameters, the method comprising steps of providing a vision aid having a chosen value of the colorimetric parameters; assessing the visual benefit provided by the vision aid by carrying out an optical test in which the vision aid is used optically by the patient or user to identify patient response to the test; observing the patient response by means of an eye tracking device, the eye tracking device providing eye tracking data and deriving quantitative data from the eye tracking data, the quantitative data representing the visual benefit to the particular patient; and analysing the quantitative data whilst the optical test is performed to identify a selected value of the colorimetric parameters of the vision aid which improves or optimises the benefit for the particular patient.

In this way, the analysis of quantitative data whilst the optical test is performed provides instantaneous information on the performance of the particular vision aid and allows the operator or therapist to assess the visual benefit. This particular aspect of the invention is advantageous in comparing visual benefits or in assessing the user's perception of a visual interface or visual aid so as to establish the performance, ergonomics or therapeutic effect of these vision aids or visual interfaces.

For example, in software applications it is important that information is readily distinguishable by the user and that the information is clearly presented. To date, no means have been available to assess the visual performance of the software applications. Alternative applications may comprise instrument panels in manufacturing facilities such as chemical plants and energy plants. These applications may also comprise instrument displays or instrument panels such as those used in manufacturing facilities and vehicles. The above method provides an effective way of establishing the ergonomic characteristics of the visual interfaces .

In another embodiment of the invention, there is provided an apparatus for testing visual interfaces having colorimetric parameters, the apparatus comprising means for providing a visual interface having a chosen value of colorimetric parameters, providing means for assessing the visual benefit provided by the visual interface, the assessment means comprising an optical test in which the visual interface is used optically by the patient or user to identify the user's response to the test, the assessment means further comprising an eye tracking device for observing the patient response, and means for deriving quantitative data from the eye tracking data, the quantitative data representing the visual benefit to the particular patient, and means for analysing the quantitative data whilst the optical test is performed to identify a selected value of the colorimetric parameters of the vision aid which improves or optimises the benefit to the particular patient.

The invention will now be described by way of example only and with reference to the accompanying drawings in which:

Figure 1 shows a flow diagram representing the steps of a method of testing according to an embodiment of the invention;

Figure 2 presents an eye tracing of a person taking an optical test without a vision aid;

Figure 3 shows an eye tracing of a patient subjected to an optical test using a vision aid;

Figure 4 shows another flow diagram representing the steps of a method of testing of Figure 1 in more detail; and

Figure 5 shows binocular eye tracings of the post-saccadic drift of a patient.

Figure 1 illustrates a method 10 of testing applicable to the provision of a vision aid having typically three colorimetric parameters in colour space. The vision aid may for example be a transparent tinted plastic overlay for use in assisting the reading of array or non-array matter.

Likewise, the vision aid may be provided in the form of the selection of the colorimetric parameters as the background colour or tint for a visual display screen. In such a case, the vision aid is not in the form having an actual physical presence, but consists of the provision in the screen of the identified colorimetric parameters, whether in relation to hue, luminosity and colour density or in relation to red/green/blue (RGB) values including or excluding luminosity, which are obtainable from a video display unit (VDU) by means of the appropriate control instructions of a VDU colour control system. Other vision aids include tinted spectacles and tinted screen cover devices for visual display units not having a colour control system.

Preferably, the method 10 of testing is implemented on a computer system utilising dedicated software which conducts the optical test and the processing of the eye trace parameters including assessing the visual benefit as provided by the vision aid.

In accordance with the method of the invention, the first step 12 comprises the steps of providing stored values for the eye trace parameters and providing a vision aid having a chosen value of each of colorimetric parameters. The vision aid is preferably implemented by adjusting the foreground and background colour parameters of the computer screen.

The start values of both the eye trace parameters and the colorimetric parameters may be based on intuition or experience by the tester and may be set as default values in the software which are suitable for iteratively arriving at the optimal colorimetric parameters for the vision aid by testing. It is possible that these default values are manually set by means of a preliminary simple test which may comprise a cursory rate of reading test.

The next step 14 in the method comprises starting the optical test by providing a task to the patient. Such a task may comprise an array task such as reading a text or a non-array task such as identifying specific objects from multiple objects. Initially the vision aid has set values of the colorimetric parameters which correspond to the default colorimetric parameters 16.

During performance of the test by the patient, eye tracings are recorded 18. Also, whilst the test is still being performed, eye trace parameters are calculated and stored 20. By default, the calculation and storage of the eye trace parameters may for example occur after an initial batch of data has been recorded and stored. The calculated trace parameters are then compared to the previous trace parameters 22 and if the parameters indicate an improvement, then new colorimetric parameters of the vision are calculated 24 on the basis of the model 26 and the vision aid is adjusted in accordance with the improved colorimetric parameters. The recording of the eye traces 8, calculation of the parameters 20 and comparison 22 then takes place again to iteratively arrive at the optimum colorimetric parameters for the vision aid by repetition of these steps 16, 18, 20, 22 until there is no or a negligible improvement in the visual benefit as measured from the eye trace parameters and calculated therefrom.

The accompanying Figures 2 and 3 present typical eye tracings of a left eye and a right eye (Series 1 and Series 2 respectively) for displacements of the eye in an approximate horizontal or x-direction of a patient who reads text in black on a white background (Figure 2) and the same patient reading the same text with the aid of a vision aid (Figure 3) whereby the text is presented with such colorimetric parameters that the vision aid provides optimal visual benefit to the patient.

In Figures 2 and 3 each "sawtooth" or "ramp" 100,200 represents a saccade. In this case, the saccade is associated with the perception of a part of the text that is presented to the patient. The superimposed smaller "steps" 102,202 represent a word or a group of words of the perceived part of the text. As the tracings are recorded over time, from the saccade length, the rate of reading or saccade frequency can be calculated. The rate of reading is an important parameter to assess the visual performance of the patient. Generally (near) optimum visual benefit is achieved when the saccade frequency is maximised.

As is clearly visible from the eye tracings, the saccades 200 are greater than the saccades 100 when the vision aid is used. The patient is thus able to perceive a larger part of the text per saccade. Also, the horizontal eye displacements are greater when the vision aid is used. This reduces the effort needed to read and increases the perceived visual benefit to the patient.

Without the vision aid, as is shown in Figure 2, the activity of the eyes over the saccades 100 alternates between the left and the right eye. This is a result of alternating suppression of the eyes and this is considered undesirable to enhance the visual perception of the patient. From the eye tracings of the patient using the vision aid it is evident that the discrepancy between the activity levels of the eyes (oscillopsia) is suppressed and consequently the activity levels of both eyes are approximately similar during the testing activity. This indicates that both eyes are active in the perception of the text which is beneficial.

Figure 4 presents the test procedure 400 of the test routine of Figure 1 in further detail. As the test is started and the optical task is performed 410, 412, the colorimetric parameters of the vision aid are set to an initial value 414. The eye tracings are recorded 416 and the eye trace parameters are calculated and stored 418. In this particular embodiment of the invention the eye trace parameters are limited to the saccade frequency or the rate of reading of an individual line during an array task, the mean fixation disparity index and the standard deviation of the fixation disparity index.

Next, the improvement in the visual parameters is assessed 420. If one or more of the visual parameters have improved, new colorimetric parameters are calculated on the basis of the model whereby the model defines the relationship between colour space and the visual parameters that are calculated.

The test is then performed again using the calculated visual parameters for the vision aid until optimum visual benefit achieved. Optimum visual benefit is achieved when the standard deviation of the fixation disparity index is minimised, the saccade frequency maximised and the mean fixation disparity index is minimised.

Another basic model for calculating the visual benefit received on the basis of eye tracings of both eyes is presented with reference to Figure 5. The graph 500 shows the post saccadic drift index (PSDI) which is the apparent drift of the centre of fixation, forwards or backwards from the landing point of the saccade. This index tends towards zero as the RGB parameters tend towards the optimum. This is mainly Vestibular-ocular (VOR) reflex mediated, although neck muscle and back muscle reflexes managed by the cerebellum can be included.

The index is calculated from the differential between the total line saccade length 502 and the sum of the saccades within the line (internal saccade lengths 504) . As the RGB parameters tend towards the optimum, the total line saccade dimension tends towards the sum of the saccades within the eye. For these RGB parameters, the head/ body movement are minimised during perception of the visual information.

In the graph 500, the total line length is 586 units and the internal saccade length is 1480 units. The PSDI is calculated as the actual line length/total internal line saccades. From the graph 500, for the test person the PSDI is 0.39.

In general, the PSDI tends to 1 as the RGB parameters tend towards the optimum for a person, so by adjusting the RGB parameters, recording the eye tracings and calculating the PSDI whilst a test person is simultaneously performing a task, the optimum RGB parameters are selected when the PSDI is 1 or is within the closest possible range of 1.

The embodiments of the invention enable the determination of colorimetric parameters to optimise visual performance or edge detection in terms of various eye trace parameters as herein discussed. The precisely determined colorimetric parameters have been found to have improved vision effects on patients in terms of effecting beneficially edge detection, and boundary conditions capabilities. This is believed to be due to a beneficial effect on the neurological system resulting from enhanced edge detection on the visual/auditory/logic areas of the brain.

Not only do patients suffering from dyslexic and other visual disorders benefit from this apparatus, but we have discovered that people who ordinarily do not have any visual impairments, benefit from a vision aid as herein before described and can increase their level of perception by using a vision aid which has colorimetric parameters as defined by a method of testing and/or an apparatus of testing as herein before described.

In many embodiments of the invention, the patient uses the RGB values determined by the method of the invention to preset their visual display unit for optimal results for themselves in terms of visual interpretation of graphic and other data. The optimisation of this process has been found to produce enhanced reading/interpretation ability in relation also to white paper pages without the need for an overlay. It has also been found that repeated testing at chosen time intervals produces further beneficial results due to the facts that individual's colour requirements change over time.

Claims

1. A method of testing applicable to the provision of a vision aid having colorimetric parameters, the method comprising the steps of : a) providing a vision aid having a chosen value of said colorimetric parameters; b) assessing the visual benefit provided by said vision aid; and c) determining whether a different vision aid having a differing selected value of said colorimetric parameters would produce a better result; d) said step of assessing the visual benefit provided by said vision aid comprising carrying out an optical test in which said vision aid is used optically by said patient to identify patient response to said test; e) observing said patient's response by means of an eye tracking device, the eye tracking device providing eye tracking data, and deriving quantitative data from the eye tracking data, the quantitative data representing said visual benefit to that particular patient; characterised by f) analysing said quantitative data whilst said optical test is performed to identify a selected value of said colorimetric parameters of said vision aid which improves or optimises said benefit for said particular patient, and; g) providing a different vision aid whilst said optical test is performed, said vision aid having a different value of said colorimetric parameters corresponding to the selected value to establish a vision aid providing optimal benefit for said particular patient.

2. A method according to claim 1, characterised by the eye tracking device being adapted to provide eye tracking data of both eyes.

3. A method according to claim 2, characterised by the quantitative data analysis being conducted to optimise the benefit for the patient in respect of both eyes.

4. A method according to any of the preceding claims, characterised by the derivation of quantitative data comprising the step of computing eye trace parameters from the eye tracking data, the eye trace parameters comprising a stamina index, variance in fix, post saccadic drift index, saccade dimension index, mean saccade length, regression index, synchronicity, saccade frequency, visual processing index and/or combinations of the aforesaid parameters .

5. A method according to any of the preceding claims, characterised by the quantitative data analysis being conducted on the basis of a model, the model defining the relationship between the eye trace parameters and the colorimetric parameters.

6. A method according to claim 4 or 5, characterised by the eye trace parameters being recorded with respect to all values of the tested vision aid in three-dimensional perceived colour space, namely hue and saturation and luminosity, or with respect to all three of the values of the red/green/blue elements of biological/physical colour space including hue and/or saturation and/or luminosity.

7. A method according to any of the preceding claims, characterised by the optical test comprising an array task such as a reading test or a non-array task.

8. A method according to any of the preceding claims, characterised by the method comprising the step of observing the patient's response by means of a head tracking device for tracking the patient's head movements and deriving further quantitative data from the head tracking device representing said visual benefit to that particular patient.

9. A method according to claim 8, characterised by the quantitative data analysis comprising the step of computing head movement parameters from the head tracking data.

10. A method according to any of the preceding claims, characterised by steps a) to g) being conducted with respect to the luminosity parameter of the vision aid, the steps a) to g) being conducted with respect to the red/green parameters of the vision aid, and steps a) to g) being conducted with respect to the blue parameter of the vision aid.

11. Apparatus adapted to carry out a method accordingly to any one of claims 1 to 10.

12. A vision aid having a value of colorimetric parameters which represents visual benefit selected or made or adapted to be set by a method comprising the step of using the results of a method of testing according to any one of claims 1 to 10.

13. A test apparatus for providing a vision aid having colorimetric parameters, comprising: means for providing a vision aid having a chosen value of said colorimetric parameters, and; means for assessing the visual benefit provided by said vision aid, and; means for determining whether a different vision aid having a differing selected value of said colorimetric parameters would produce a better result; the assessment means comprising an optical test in which said vision aid is used optically by said patient to identify patient response to said test; the assessment means further comprising an eye tracking device for observing said patient's response, and means for deriving quantitative data from the eye tracking data, the quantitative data representing said visual benefit to that particular patient, characterised by the determination means comprising means for analysing said quantitative data whilst said optical test is performed to identify a selected value of said colorimetric parameters of said vision aid which improves or optimises said benefit for said particular patient, and; the determination means comprising means for providing a different vision aid whilst said optical test is performed, said vision aid having a different value of said colorimetric parameters corresponding to the selected value to establish a vision aid providing optimal benefit for said particular patient.

14. An apparatus according to claim 13, characterised by the means for analysing the quantitative data comprises computing means for computing eye trace parameters from the eye tracking data, the eye trace parameters comprising a stamina index, variance in fix, variance in speed, post saccadic drift index, saccade dimension index, mean saccade length, regression index, synchronicity, visual processing index, and/or combinations of the aforesaid parameters.

15. An apparatus according to claim 14, wherein the computing means comprises a model, the model defining the relationship between the eye trace parameters and the colorimetric parameters . -so¬

le. An apparatus according to claim 14 or 15, characterised by the eye trace parameters being recorded with respect to all three values of the tested vision aid in three-dimensional perceived colour space, namely hue and saturation and luminosity, or with respect to all three of the values of the red/green/blue elements of biological/physical colour space.

17. An apparatus according to any of claims 11, 13 to 16, characterised by the vision aid being provided by the colours of a computer screen, the optical test being performed on the screen, the eye trace data being recorded in the computer, the computer further providing the determination means.

18. An apparatus according to any of claim 13 to 17, characterised by the method comprising the step of observing the patient's response by means of a head tracking device for tracking the patient's head movements and deriving further quantitative data from the head tracking device representing said visual benefit to that particular patient.

19. A method according to any of claims 1 to 10 or an apparatus according to any of claims 13 to 18, characterised by the vision aid and comprising a visual interface such as an instrument panel, desk top or computer screen.

20. A method of testing applicable to the provision of a vision aid having colorimetric parameters, the method comprising the steps of: a) providing a vision aid having a chosen value of said colorimetric parameters; b) assessing the visual benefit provided by the vision aid; c) the assessment step comprising carrying out an optical test in which the vision aid is used optically by the patient to identify patient response to the test; d) observing the patient response by means of an eye tracking device, the eye tracking device providing eye tracking data, and deriving quantitative data from the eye tracking data, the quantitative data representing the quantitative visual benefit to that particular patient; characterised by e) analysing the quantitative data whilst the optical test is performed to identify a selected value of the colorimetric parameters of the vision aid which improves or optimises the benefit for the particular patient.

21. An apparatus of testing applicable to the provision of a vision aid having colorimetric parameters, comprising: a) means for assessing the visual benefit provided by the vision aid, the assessment means comprising means for carrying out optical test in which the vision aid is used optically by the patient to identify patient's response to the test; b) means for observing the patient's response by means of an eye tracking device, the eye tracking device providing eye tracking data, and means for deriving quantitative data from the eye tracking data, the quantitative data representing the visual benefit to the particular patient; characterised by the apparatus comprising means for analysing the quantitative data whilst the optical test is performed to identify a selected value of the colorimetric parameters of the vision aid which improves or optimises the benefit for the particular patient. 22 A method of providing a vision aid and an apparatus for testing a vision as herein described and as shown in any of the accompanying drawings.