WO2005053521A1

WO2005053521A1 - Method and apparatus for measuring degrees of colour vision deficiencies

Info

Publication number: WO2005053521A1
Application number: PCT/AU2004/001723
Authority: WO
Inventors: Robert Joel Bush
Original assignee: Robert Joel Bush
Priority date: 2003-12-05
Filing date: 2004-12-06
Publication date: 2005-06-16

Abstract

A method and apparatus is disclosed for examining and/or classifying properties of a subject's colour vision. The apparatus consists of a Cathode Ray Tube (CRT) (10) displaying a first colour (20) and a second colour (30), each composed of the same colour components. The subject is required to modify one of the colours within available constraints to match the two colours and parameters are derived from the subject's performance. These parameters are then compared with corresponding parameters which are correlated to a colour vision property. One of the parameters that can be compared relates to an angle of an isochromatic line resulting from the subject's test.

Description

METHOD AND APPARATUS FOR MEASURING DEGREES OF COLOUR VISION DEFICIENCIES

TECHNICAL FIELD This invention relates to the measuring and classification of deficiencies in a subject's colour vision.

BACKGROUND TO THE INVENTION Colour Vision The normal human eye allows the human to "see" what is in the surrounding environment. Light waves from the environment around the human stimulate nerve receptors in the eye which produce signal information which is processed via neural pathways to the visual cortex region of the brain to produce mental picture representations of the surroundings. An important aspect of this light wave information relates to colour. Colour is a property related to the frequency of the light waves.

The normal human eye contains three different types of colour receptors, called cones. Normal human colour vision is consequently trichromatic (tri - three, chromatic - colour (hue)). The colour experience is normally based on a composite impression received through the interplay of the amount of stimulation generated by the three colour cones. The cones are maximally stimulated at different wavelengths of light, roughly equating to red, green and blue. Light of wavelength 558nm will highly stimulate the red cones, of wavelength 531 nm the green cones, and of wavelength 419 nm the blue cones.

Red, green and blue light waves can be combined in different proportions to produce a perception of every colour. For example equal proportions of each produce a grey perception, and a total lack of all produces a black perception. An equal red and green stimulation produces a perception of yellow. Any and all colours may be specified by the relative proportion of the colour components used. As the percentage of red plus the percentage of green plus the percentage of blue will always sum to a value of 1.00, specification of the percentage of two of the colours allows the third to be simply calculated. Accordingly, a comprehensive graphic representation of any and all colours may be made using the percentage of green as the y-axis, and the percentage of red as the x-axis.

If the stimulus from one or more types of these receptors is abnormal, the human will have a different experience in detecting or perceiving light of that colour and accordingly, will also be unable to normally perceive colours resulting from combinations of primary colours detected because of receptors which are abnormal for that or those colours.

De ective colour vision Defective colour vision (commonly referred to as "colour blindness") may be caused by congenital defects (ie genetically linked and existing at birth) or acquired defects such as the effects of aging and accidental/ disease/ substance abuse damage to colour vision receptors or neural pathways. In the general population, around 8% of males and 1% of females have some degree of congenital colour deficiency. Genetic colour vision deficiencies are caused by the inheritance of a lesser number of cones than normal. When there is a complete lack of one type of cone, the colour vision is referred to as dichromatic (di- two, colour) and when there is a partial lack the colour vision remains trichromatic. Deficiencies are referred to in terms relating to the cone type that is lacking, eg red as protan, green as deutan, and blue as tritan.

This lack of cones, and resultant colour perception ability, means that individuals with colour deficient vision perceive a lesser number of colour hues than is colour normal, and will therefore make different colour matches in certain areas. Colour Vision Tests A number of tests exist which are devised to test the presence and form of colour blindness of individuals. One of the more common, (and generally considered best) tests is the Ishihara test which consists of a series of cards containing dots of specific colours, some of which are grouped to form a number. Depending on the type and degree of colour blindness the individual has, the individual may have difficulty perceiving one or more of the digits of the number. This is because the different digits are graded in different colours with respect to each other and the background. In particular, the colours used are chosen from the general isochromatic areas relative to the colour deficiency. The inability to differentiate between certain colours will present itself as an inability to perceive certain digits.

While many of the existing tests to detect colour blindness have been successful, a number of problems exist with many of these tests. Some of the tests require specific lighting conditions to carry out the test. If lighting conditions differ from one test to another, the results can not always be compared with certainty. Other tests require additional skills, and deficiencies in these additional skills can provide results which affect the measurement of the colour blindness. For example, a person who has difficulty in reading numbers or visualising objects or particular shapes may perform more poorly in a test than another person with the same colour vision level, but without the additional deficiencies.

Furthermore, the results of some tests are difficult to interpret and cannot be quantitatively measured. For example, in the Ishihara test, the sum of the cards that are misread in any aspect is the measure of the result. A result of three or more misread cards is usually a good indication that the subject is colour deficient or has Colour Deficient Vision (CDV). However, a CDV diagnosis should only be presumed if a positive CDV response is given to at least one of the appropriate reads. Furthermore, some tests are only able to measure colour defects in certain spectrums and not in others. An international system for colour measurement and specification was established by the Commission Internationale de rEclairage (CIE) in 1931. In this system, colours are represented graphically according to the contributing amount of each of the primary colours red, green and blue. Since the sum of these quantities is always equal to 1, only two quantities need to be specified and accordingly all colours are able to be represented on the CIE chart in a two dimensional manner. The two colours used are red and green. Measurements made with real primary colours can be converted to the CIE system using a simple mathematical formula as would be understood by the person skilled in the art. The CIE diagram is shown in Figure 1.

On the CIE diagram, various useful plots may be made to aid in diagnosing colour deficiencies. For example, if a given subject confuses two colours, these two colours can be plotted on the CIE chart. A line may be drawn joining these two colours. The difference between colours lying on this line cannot be discriminated by the subject. This line is referred to as a confusion line, or an isochromatic line.

The description and characteristics of isochromatic zones has been an important part of colour vision deficiency knowledge for many years. Additive colours are represented by straight lines on the CIE chart representation, and isochromatic zones of average colour deficient individuals having the same type of defect are represented by narrow ellipses whose long axis is on an angle relative to the type of defect present. It is an object of the present invention to provide a method and apparatus for testing, measuring and/ or classifying defects in colour vision, in a manner which is more flexible and produces more accurate and definite results than many of the tests used in the prior art. SUMMARY OF THE INVENTION According to a first aspect of the present invention, there is provided an apparatus for the examination and/ or classification of colour vision properties of a subject, the apparatus comprising: means for presenting to the subject, a first colour, constituted by two or more colour components; means for concurrently presenting to the subject, a second colour, different to the first colour, constituted by the same two or more colour components constituting the first colour; means for allowing the subject to modify the second colour to a colour that the subject perceives to be substantially the same as, or close to, the first colour; and means for deriving one or more parameters of the modified second colour.

According to a second aspect of the present invention, there is provided a method for examining and/ or classifying colour vision properties of a subject, the method comprising: presenting to the subject a first colour, constituted by two or more colour components; concurrently presenting to the subject, a second colour, different to the first colour, constituted by the same two or more colour components constituting the first colour; causing the subject to modify the second colour until the subject perceives the second colour to be substantially the same as, or close to, the first colour; and deriving one or more parameters of the modified second colour.

According to a third aspect of the present invention, there is provided a machine-readable medium containing instructions to cause a machine to perform the method according to the second aspect of the present invention.

According to a fourth aspect of the present invention, there is provided a method for the examination and/ or classification of colour vision properties of a subject, the method comprising: correlating an angle of an isochromatic line resulting from a colour vision test of the subject with a colour vision property. According to a fifth aspect of the present invention, there is provided a machine-readable medium containing instructions to cause a machine to perform the method according to the fourth aspect of the present invention. BRIEF DESCRIPTION OF THE DRAWINGS A preferred embodiment of the invention will now be described with ref erence to the following drawings in which: Figure 1 - shows the International CIE colour diagram; Figure 2 - shows a CIE plot showing isochromatic lines for protans; Figure 3 - shows a CIE plot showing isochromatic lines for deutans; Figure 4 - shows a screen of one arrangement of a test according to the present invention; Figure 5 - shows a plot of the movement of the Test Square colour and the isochromatic line of the Surround Box colour in RGB colour space; Figure 6 - shows various Surround Box positions in RGB colour space; Figure 7 - shows arc colour movements about a Surround Box in RGB colour space; and Figure 8 - shows a colour movement plot of a Test Box through respective isochromatic lines for deutans and protans of the Surround Box in RGB colour space.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT Vision displays such as televisions and monitors are made up of many dots. Red, green or blue phosphor, grouped in a way such that one of each dot forms a pixel. A particular pixel colour is produced by exciting the red, green and blue dots in a certain intensity ratio. All three dots excited equally will produce a white pixel, while exciting none of the dots will produce a black pixel. Variations between these extremes can produce a wide variety and range of colours in common systems. For example, yellow may be produced by exciting the red and green dots with no blue while orange may be produced by exciting red at full intensity and green at half intensity with no blue. Orange may be turned to brown by reducing the intensity of the red and green and adding a small amount of blue. In the case of a Cathode Ray Tube (CRT) display, the pixels are excited by a beam of electrons, causing the phosphor to luminesce. The beam of electrons is produced by an electron gun, one for each of the red, green and blue dots. The intensity of the excitation is dependent on the intensity of the electron beam, which in turn is dependant on the level of control signals input to each gun. In common systems, the intensity level of each gun can be varied between 0 and 255, giving the large number of possible colour combinations (in excess of 16 million). Other forms of displays use plasma cells, light emitting diodes or even organic structures whose photo properties can be controlled.

Because the colour spectrum or "colour space" of the display is provided by a combination of Red, Green and Blue components, this colour space will herein be referred to as RGB colour space.

An aspect of the present invention has been made possible by the realisation that the RGB colour space as generated by a standard cathode rate tube may be equated to the colour space displayed by the CIE diagram. In particular, confusion or isochromatic lines run through all parts of the colour space represented by the RGB colour space of a CRT and can be plotted on an RGB representation with results that are similar to the CIE representation.

The measurement of a subject's colour vision is most preferably carried out on a computer with a cathode ray tube (CRT) monitor. Control of the computer may be made through any convenient input device such as a keyboard or mouse.

Figure 4 shows the screen display that is presented to the subject in performing the tests. Figure 4 shows screen 10 of a cathode ray tube monitor (not shown) which depicts an inner square (test square) 20 surrounded by an outer square (surround box) 30. Slide bar 21 allows the user to adjust the intensity of red, green and blue colour components of the inner square 20. There may also be provided meter windows (not shown) to provide a numerical representation of the level of each of the components. This numerical representation is between 0 and 255, indicating from 0, that there is no component of that colour in the colour displayed in inner box 20 while a measure of 255 indicates maximum intensity of that colour component in inner box 20. Each colour component of red, green and blue has its own meter.

In use, the subject will be presented with the screen as shown in Figure 4 in which box 30 will be a preset colour and box 20 will be another preset colour and the subject will be required to adjust slide bar 21 to vary the colour of inner box 20 until the subject considers that the colour in box 20 matches (or comes close to) that of box 30.

The movement of the slide bar results in a change of the two or more colour components (for example red and green). The degree of change may be preprogrammed as required, and may be pre-set for a given test.

Conceivably, a test could be presented which requires individual adjustment of the two or more colour components, each one with its own slide bar.

The movement of slide bar 21 may be effected by a mouse, keyboard arrow keys or by way of a touch screen. Of course any other suitable input means may be used as will be understood by the person skilled in the art. The final selection of colour as perceived by the subject is then easily quantitatively measured with the precise number value of each of the colour components of the red, green and blue as selected by the subject.

The values obtained from this process are then compared with a database which consists of statistical data derived from numerous previous tests to provide an indication of the form of deficiency of the subject's colour vision, if any. This statistical data may consist of raw RGB values, distance measurements (see below), angle measurements (see below) or any other data relating to desirable parameters from the test results. Figure 5 shows a representation of confusion lines as plotted in an RGB colour space.

This figure shows conceptually the aspects of the colour movement flow relevant to the colour vision deficiency being examined. The fixed colour red and green coordinates are shown as the surround box coordinates, these do not change. The adjustable colour in the example follows the line noted as test square movement. The coordinates are initially set at the far left and move horizontally from around red 11 green 40, to red 20 green 40. The movement is then linear to a point red 25 green 48, moving through the isochromatic zone for the subject at around red 23 green 46. The colour at that point will be perceived as the same as the fixed colour red 33 green 33, and will in effect disappear for the subject. The colour movement then moves linearly to a point near the fixed colour, red 35 green 34, which will appear to be the closest colour match available to a colour normal, and then travels to a termination point at around red 48 green 31.

Colour matching A graphic representation of the colours used in a matching exercise may be . done by noting the point of the fixed colour figure coordinates, and by using a line to connect the coordinates of the colours which are presented in a variable colour figure.

A closest perceived colour match exists when the colour of a variable figure appears to be the closest to the colour of a set figure using the colours available. When the colours appear to match they appear to be of the same colour, or are isochromatic (one colour). As the eye is generally unable to discriminate between very small colour increments, colours with minor coordinate differences appear to be the same, and areas bounded by the coordinates are referred to as isochromatic zones (one colour zones).

The isochromatic zones of colour normal individuals may be described as small ellipses surrounding the fixed colour coordinates. Closest colour matches are chosen at the closest graphic coordinate points of the variable figure colour to the set figure colour.

The isochromatic zones of colour deficient individuals are much larger. They may be treated as lines over a wide range of coordinate values. Colours representing the coordinates along the lines appear to be the same. Closest colour matches are chosen at variable figure coordinate points that are close to the isochromatic line coordinates relating to the set figure colour coordinates. These choices are quite different than colour normal choices. Figures 2 and 3 show isochromatic lines on a CIE chart for protans and deutans respectively.

The isochromatic lines of any and all colour deficient individuals relative to the set colours coordinates may be specifically and accurately referred to by lines' acute angle to the x-axis on a 2-D graph representing red/ green colour space. A particular condition is indicated by the different angles, and are indicative of severity.

The actual angle of the isochromatic line to the x-axis is indicative of the type of colour blindness.

These exercises were done by proven protans and proven deutans. These tests involved moving the adjustable colour box (or Test Square) colour through a 90 degree arc north west and south east of the surround box (or fixed colour box) coordinates, the colour deficient individual's task was to find a specific point within that arc where they felt the adjustable box colour was the exact colour as the surround box. In general, there was only one specific match. Each of the subjects was examined in six different arc distances from each surround box. There were five surround boxes spread 15/30, 30/15, 33/33, 40/40 and 50/30. This scenario is illustrated in Figures 6 and 7. Figure 6 in particular, shows a graphical representation of the range of colours possible on a computer display, and a sample of the colour coordinate points examined for which isochromatic lines for colour deficient individuals have been identified.

The actual colour settings used for example at the "40/40" point would be red 40%, green 40%, and blue 20%. If the total colour setting was to be 300, for example, they would be specified as red 120, green 120, and blue 60. For a total setting of 500, it would be red 200, green 200, and blue 100. Both settings would be represented by the same coordinate point. In practice, this allows the same exercise to be done but with a different appearance. The match point coordinates of each of these different subjects for a specific surround box were determined to be a line, eg all of the seven points were within a very small standard deviation of a straight line.

Within a group of individuals for each surround box, each individual has a different angle of intersect with the "X" axis. The different degrees of separation are closely bunched and there exists a clear separation between protan and duetan areas.

The current invention exploits this in the following way:

CV Classification A surround box is displayed, together with a Test Square (see Figure 4) for two different fixed colour coordinate settings. The CDV individual sets a perceived match. The type of deficiency, and a measure of severity is determined from the angle of that match, along with those of matches made at increasing coordinate distances from the same fixed colour coordinates and/ or by a comparison of angles derived from matches made at a different fixed colour coordinate positions. These tests have been conducted across a broad range of computer screens and the separation of colour normals from CDV has been 100%. The classification of the type of CDV by reference to the angle is reliable in most cases. Because some slight overlap may be caused by different characteristics of the displays, an additional exercise using a calibrated display may be necessary for accurate diagnosis.

CDV Screening A useful application of this invention is as a screening exercise to separate colour "normals" and colour vision deficient individuals. Such tests use a colour movement range of coordinates for the Test Square which include positions close to the surround box and which also utilize isochromatic line coordinates. Colour "normals" perceive colour matches at close coordinate positions with the actual Surround Box coordinates, while colour vision deficient individuals colour matches are all closely related to their respective isochromatic line coordinates. Such a situation is illustrated in Figure 8.

These tests have been conducted under scientific parallel testing conditions with Ishihara 2002 plates with over 200 males, 12 - 14 years of age, using an inexpensive CRT screen and accurate results were obtained. 95% consistency with +3 plate errors for indication of CDV was achieved, with 5% false negatives and no false positives. 95% accuracy of type of deficiency (protan or deutan) using comparison of two fixed colour box angles was achieved. 70% consistency with +2 plate colour normal misreads, which were considered slight colour discrimination subjects, but not colour deficient, was achieved when sort criteria were supplemented with relative red%, green% information. The 30% false positives included 60% CDVs (including the false negative for the +3 plate errors). CDV Education An additional application of this invention is in the demonstration and education of CDV characteristics. In one example of this application, the Surround Box (SB) is a wide vertical bar, with three appended Test Squares so that it appears as an E. The middle of the E is set at the same colour as the SB. The CDV matching choice for the NW are at eg 7% distance is set in the top E segment, and that of the SE are in the bottom. The figure is then fleshed out from top to bottom by the colours representing the coordinates on the Isochromatic line from each of the CDV matching choices and a filled box appears. To the CDV this box appears to be of one solid colour, while to a Colour Normal (CN) the display is a dramatic presentation of a CDV condition.

The invention may also be used to provide a self-testing system, which takes a subject through a series of tests as described above. The results of the test may then be compared with pre-stored "angle records" and correlated with a type and degree of colour blindness. The subject may then choose to seek further medical advice.

Because psi plates are designed around average isochromatic zone estimates for different types using a computer display as a medium means, accurate and consistent presentations need to be assured. Inherent problems encountered by this approach and why the present invention overcomes them are referred to below:

Problem: Colour control and luminance calibration needs to be managed to a standard range,

Solution: Colour matching is not a static application and as long as the phosphor illumination wave separation is adequate; comparable and consistent data are produced by a range of both colour and luminance environments.

Problem: Care in the figure designs needs to eliminate the affect of any edging caused by pixel matrixes, and management of the viewing platform need to be in place to reduce the effect of viewing angle to the screen face, Solution: The colour figure being used needs to be clear, and is the same figure is seen by CN and CDV edging is expected, and an advantage.

Problem: Screen refreshes may be affected by colour afterimages and colour contrasts of the previous screen,

Solution: The exercises are interactive, and there are several on each screen refresh so that there is appropriate time and involvement in the task to eliminate this problem.

Problem: Fully saturated spectral wavelengths cannot be produced on computer screens so that dichromatics cannot be separated from trichromatics,

Solution: Dichromatics are relatively rare, and this is not seen as a major problem for a screening application.

The diagnostic style of use moves the Adjustable box colour movement across the isochromatic zone of the deficiency type. One difference of dichromatics, and trichromatics is in the extent of lack of the relevant colour cones, and a consequent variation in the angle of the coordinate match to fixed colour coordinate would exist. Screen calibration to known verified CDVs is one valid solution.

Alternatively, diagnosis of the distance at which a disappearing match is possible is a solution.

The above has been described with reference to a particular embodiment however, it will be understood by the person skilled in the art that many variations and modifications may be made within the scope of the present invention. For example, while the invention has been described using a CRT display, it will be understood that any three-primary colour light system may be used.

Claims

CLAIMS:

1. An apparatus for the examination and/ or classification of colour vision properties of a subject, the apparatus comprising: means for presenting to the subject, a first colour, constituted by two or more colour components; means for concurrently presenting to the subject, a second colour, different to the first colour, constituted by the same two or more colour components constituting the first colour; means for allowing the subject to modify the second colour to a colour that the subject perceives to be substantially the same as, or close to, the first colour; and means for deriving one or more parameters of the modified second colour.

2. An apparatus according to claim 1 wherein the one or more parameters is an angle of a line with respect to a given reference, the line being defined by coordinates of the modified second colour and coordinates of the first colour on a coordinate chart.

3. An apparatus according to claim 3 wherein the given reference is a horizontal axis on a coordinate chart.

4. An apparatus according to claim 1 wherein the one or more parameters of the second colour are the coordinates of the modified second colour on a coordinate chart.

5. An apparatus according to claim 1 wherein the one or more parameters is a distance between coordinates of the modified second colour and coordinates of the first colour on a coordinate chart.

An apparatus according to any one of claims 1 to 5 further comprising correlating means for correlating the one or more parameters with a colour vision property.

7. An apparatus according to claim 1 wherein the first and second colours can be set for different tests.

8. An apparatus according to claim 1 wherein the means for displaying the first and second colours to the subject is a cathode ray tube.

9. An apparatus according to any one of claims 2 to 5 wherein the coordinates of the first and second colours relate to intensity values of the two or more colour components constituting the first and second colours.

10. An apparatus according to claim 1 wherein the means for allowing the subject to modify the second colour is in the form of a slide bar displayed on the presenting means.

11. An apparatus according to claim 10 wherein upon actuation of the slide bar, at least one of the at least two components of the second colour are modified, thereby modifying the second colour.

12. An apparatus according to any of the preceding claims wherein the first colour is presented as a first block and the second colour is presented as a smaller second block within the first block.

13. An apparatus according to any of the preceding claims, wherein the two or more colour components are red and green.

14. A method for examining and/ or classifying colour vision properties of a subject, the method comprising: presenting to the subject a first colour, constituted by two or more colour components; concurrently presenting to the subject, a second colour, different to the first colour, constituted by the same two or more colour components constituting the first colour; causing the subject to modify the second colour until the subject perceives the second colour to be substantially the same as, or close to, the first colour; and deriving one or more parameters of the modified second colour.

15. A method according to claim 14 wherein the one or more parameters is an angle of a line with respect to a given reference, the line being defined by coordinates of the modified second colour and coordinates of the first colour on a coordinate chart.

16. A method according to claim 15 wherein the given reference is a horizontal axis on a coordinate chart.

17. A method according to claim 14 wherein the one or more parameters of the second colour are the coordinates of the modified second colour on a coordinate chart.

18. A method according to claim 14 wherein the one or more parameters is a distance between coordinates of the modified second colour and coordinates of the first colour.

19. A method according to any one of claims 14 to 18 further comprising the step of correlating the one or more parameters with a colour vision property.

20. A method according to any one of claims 14 to 19 wherein the first and second colours are set for a given test.

21. A method according to claim 14 wherein the first and second colours are presented on a cathode ray tube (CRT).

22. A method according to claim 21 wherein the first colour is presented as a first block and the second colour is presented as a smaller, second block within the first block.

23. A machine-readable medium containing instructions to cause a machine to perform the method according to any one of claims 14 to 22.

24. A method for the examination and/ or classification of colour vision properties of a subject, the method comprising: correlating an angle of an isochromatic line resulting from a colour vision test of the subject with a colour vision property.

25. A machine-readable medium containing instructions to cause a machine to perform the method of claim 24.