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Consequences and 'treatment' of colour vision deficiencies.

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This final article on colour vision reviews some of the consequences of colour vision deficiencies. In particular, people with such deficiencies need to be aware of the implications that might he placed on every day tasks such as driving, as well as tasks encountered in educational and occupational settings, and of the requirement for normal colour vision in some professions. This is followed by a discussion of the 'treatment' options available to colour deficient individuals, including colour-tinted lenses that aim to minimise the effects of the deficiency, and gene therapy that eliminates the deficiency.

Consequences of colour vision defects

Steward and Cole (1) carried out a survey to assess the difficulties that are reported by colour deficient observers and concluded that anomalous trichromacy is a nuisance but dichromacy is a serious problem. (1)

At the time when the survey was carried out, most dichromats were aware of their defect and 71% became aware of it because they experienced difficulties with colour-related tasks. Only 27% of anomalous trichromats learned about their defect as a result of their difficulties. The colour vision deficiency therefore had a more noticeable effect on the lives of dichromats than anomalous trichromats. The time at which dichromats and anomalous trichromats learnt about their defect also differed, with 49% of dichromats reporting that they knew of their defect in primary school, but only 8% of anomalous trichromats were aware of it at that stage of their life. Dichromats tended to report more difficulties with everyday tasks than anomalous trichromats. (1)

The selection of colours for clothes, accessories, paints, etc. was the most frequently reported problem by colour deficient patients. (1) Difficulties were also reported with tasks such as the judgment of whether meat is cooked or not, sporting activities, and in the identification of skin burns or rashes. (1) Experimentally, the difficulties that might be experienced by colour deficient observers are evident in a visual search task for a coloured target, in which more time may be needed to locate a coloured target compared to those with normal colour vision. (2) Examples of colours that might be confused by patients with a colour vision deficiency are given in Table 1. Figures 1 and 2 show examples of what the world might look like to a dichromat.

Driving

In total 49% of dichromats and 18% of anomalous trichromats who participated in the Steward and Cole survey (1) reported difficulties with distinguishing the colours of traffic light signals. Some of these observers reported that they use relative brightness or positional cues to distinguish the colour of the lights. Confusing traffic lights with streetlights and difficulties with seeing hazard lights and break lights on other cars, dashboard lights, and some road signals, were also reported by some colour deficient individuals. More protans than deutans tended to report the difficulties.

Individuals with a colour deficiency tend not to make errors in naming the colours of road traffic signals, if the colours chosen are those recommended by the Commission Internationale de l'Eclairage (CIE). (2) However, those with a more severe colour deficiency may sometimes be uncertain and will make some errors. The uncertainty may lead to slower reaction times and a reduction of the distance at which the colour is recognised. (3-5)

The additional problem that might be experienced by protan observers is the failure to see a red light of low intensity, as a result of their reduced sensitivity to long wavelength light. In practical terms, this might result in a problem for seeing car tail/break lights, barrier lights and reflective lights. (2) However, if the red light is too bright, protans will tend to see it as yellow. (2)

The potential problems that colour deficient individuals may face on the road have led to investigations of the incidence of accidents in which colour deficient observers were involved. However, the evidence is equivocal with some studies reporting that drivers with a colour deficiency are involved in a greater number of accidents than those with normal colour vision but others failing to find such an association. (2,5) Currently, there are no colour vision standards for drivers in the UK.

Education

Colour coding is used frequently in the educational setting. In early schooling, colour may be used to code information in books. An extreme example of the use of colour in reading can be found in the 1960s where colour was used to code sounds. (6) In later education, examples of the use of colour can be found in chemistry (eg when titrations are performed), physics (eg colour coding of wires), geography (eg colour coding on maps), geology (eg identification of rocks and minerals by colour) and biology (eg observing microscope slides). Other general examples of the use of colour in school include coloured pens, paints or print on coloured backgrounds, and the use of colour to denote sporting teams.

No definite conclusion has been reached as to the effect of colour vision deficiency on an individual's education. In some studies, the presence of a colour vision defect has been associated with lower grades and poorer school performance. (7,8) However, Cumberland et al. (9) found that colour vision deficiency was not significantly associated with the performance of seven-year-olds in mathematics, reading, a 'copy a design' task and 'draw a man' task. The performance of 16-year-olds in mathematics and reading was significantly poorer for individuals with colour vision deficiency than with normal colour vision, but these differences were deemed functionally unimportant. There was also no difference in the highest qualification level achieved by the two groups. These findings were in agreement with some earlier studies (10,11) and led Cumberland et al. (9) to question the value of colour vision screening at school.

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Although there are no clear conclusions on the effects of colour vision deficiency on educational achievements, a child who is experiencing learning problems for other reasons may be further handicapped by a colour vision deficiency (12) and may feel anxious and different. (13) The importance of an early awareness of the presence of a colour vision deficiency was advocated by Cole, (14) as only this will enable the child and the teachers to adopt appropriate strategies to minimise the effects of the defect and ensure that appropriate career advice is offered.

Occupational requirements

The presence of a colour vision defect has an effect on an individual's career choice. In the Steward and Cole survey,' 43% of dichromats and 29% of anomalous trichromats reported that having a colour vision defect affected their choice of career and almost 25% of the respondents said that the defect precluded them from an occupation.

Individuals with a colour vision deficiency also reported difficulties with colour tasks at work. (1) The presence of new technology can be seen as an advantage to overcome such difficulties; for example the colours on a visual display unit (VDU) can be manipulated to allow easier discrimination, or instruments can be used when fine discrimination or precise colour matching is required. However, new technology also means that colour is now used extensively, eg in complex computerised displays.

When assessing a patient's colour vision for occupational purposes with plate tests (eg the Ishihara test), the order of presentation should be randomised. The practitioner should also ensure that the patient is not wearing tinted contact lenses that have been designed to improve colour discrimination (see later), as this is usually not allowed for occupational testing; if such an aid was used then the result must be appropriately annotated.

Police force

Good colour vision is seen as an important aspect for effective policing and is needed for accurate colour naming (eg when describing the colour of a vehicle involved in a crime), visual search for coloured objects (eg at a crime scene), and identification of colour codes (eg to indicate whether a firearm is ready to use). (15) Concerns have been expressed over the recent changes to the colour vision standards for the police force. (15) These changes mean that now only monochromats are not allowed to enter the profession. (16) The standards specify that dichromats and severe anomalous trichromats are acceptable but 'should be instructed in coping strategies'. The Farnsworth D15 has been recommended to assess the colour vision of the applicant, but this test will not provide sufficient information about the severity of the defect. Although it is recognised that individuals with a colour vision deficiency may be excluded from some specific tasks, these recruits may learn about this only once they have entered the force, which is also of obvious concern. (15)

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Aviation

Colour coding is used extensively in aviation. Coloured lights are used on the ground (eg to demarcate runways), on aircrafts (eg navigation lights), and to mark out tall structures around airports, as well as being used in a coloured signal gun by the control tower, in case of radio communication failure. (2) Individuals with a colour vision deficiency make errors in laboratory simulations of aviations signals (17) and many cannot distinguish the colours of the signal gun used by the control tower. (18) It has been argued that although coloured signals are important in aviation, there is a lot of redundancy and individuals with a colour deficiency therefore have other cues available to them. (2) However, it is this redundancy that increases the safety level in the aviation industry and removing one of the cues, ie. colour, for the colour deficient individual could compromise safety. (2)

The UK Civil Aviation Authority requires a medical certificate before a pilot's licence can be issued. A Class 1 certificate is needed for a professional flying licence and a Class 2 certificate is required for a private flying licence. In both instances, colour vision is initially assessed using the Ishihara pseudoisochromatic plates. A pass on this test indicates normal colour vision and satisfies the requirements of both standards. Until recently, a failure on the Ishihara plates would have indicated the need for a Holmes Wright Lantern test to assess whether the applicant can recognise the colours used in aviation. However, following the recommendations of a report on the minimum colour vision standards for professional flight crew, (19) and as of September 1 2009, (20) the Colour Assessment and Diagnosis (CAD) Test (a computerised colour vision test) is used to assess the colour vision of those who fail the Ishihara plates.

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In order to obtain a Class a certificate, the candidate must pass the CAD test. (21) A Class 2 certificate can be issued to someone who fails the Ishihara test but with the limitation of daytime flying only; this limitation however can be removed if the candidate passes the CAD testy. (22) A national private pilot licence can be used for recreational flying and the standards are based on those set by the DVLA for driving. Therefore, there are no requirements for a colour vision assessment. (20)

Maritime industry

Maritime navigation relies heavily on the recognition of coloured signals. The great distances and adverse weather conditions that might be involved can make the recognition of these even more difficult. The majority of individuals with a colour vision defect make errors on a lantern test that simulates the red, green and white of maritime signals. (23) The errors made by daltonians were also evident in a field study, (24) which also found that protan observers failed to see distant red signals more frequently than observers with normal colour vision, and in a laboratory simulation. (25)

The Merchant Shipping Regulations specify the medical and eyesight standards for seafarers. (26) Colour vision is initially assessed using the Ishihara pseudoisochromatic plates. A candidate who wishes to work on the deck but fails the Ishihara test can have their colour vision reassessed with Holmes Wright B Lantern. A failure on the lantern will then mean that a certificate with a restriction will be issued, which prevents the individual from performing navigational and lookout duties. For engineers and radio officers, colour vision should be re-tested using the D15 or the City University Test, and restrictions on working with coloured cables and equipment applied if these tests are failed.

Railway industry

Small coloured signals have to be identified by train drivers and other railway personnel, sometimes from a considerable distance. Most individuals with a colour vision deficiency will make errors when identifying the red, green and yellow lights when tested with the Holmes Wright Lantern Type A. (27) Train drivers in the UK are therefore required to have normal colour vision as assessed by the Ishihara plates. (28)

Medical and allied health professions

There are no requirements for normal colour vision in the medical and allied health professions. However, a change in colour can be a sign of illness or abnormality. Doctors with a colour vision deficiency have reported problems with recognising skin colour changes, the use of coloured charts, prints, slides and codes, the use of test-strips for blood and urine tests, and recognising signs during ophthalmoscopy and otoscopy. (29,30)

When doctors with a red-green colour deficiency were asked to assess clinical photographs to determine whether an abnormality was present, in some instances they failed to spot the signs of an illness (31,32) or to correctly outline the area of abnormality. (33) When outlining the area of abnormality, practitioners with a colour deficiency were relying on cues other than colour, eg lightness or reflections. (33) Doctors with a colour vision deficiency were also not as confident as those with normal colour vision when giving their responses about the clinical photographs. (31,32)

Abnormal colour vision can also become a problem for histopathologists and laboratory personnel who prepare slides. Those with colour vision deficiencies made more errors on a slide identification task than those with normal colour vision, but the slides were chosen to include colours that are likely to be confused by individuals with a colour vision deficiency. (34) The errors were not confined to the use of a particular stain, indicating that it might be difficult to overcome the errors by simply using a specific stain. However, it has been argued that this is only a minor inconvenience that can be overcome with the help of colleagues. It was also suggested that it should not be used to stop colour vision deficient individuals from entering the profession. (35)

Some medical students also report difficulties as a result of a colour vision deficiency and those that relate to medical practice are similar to the difficulties reported by medical practitioners. However, medical students also referred to problems related to the teaching methods used during their studies. (29)

In a survey by Spalding, (29) almost 50% of doctors reported that they had difficulties with ophthalmoscopy, either in medical practice or as students. A number also reported difficulties with conducting the Ishihara test. Some of the clinical photographs used in the studies by Campbell and colleagues (31) included ocular structures, eg a pale conjunctiva and retinal haemorrhages. In general, these abnormalities were recognised by the colour deficient practitioners, although an optometrist with a colour vision defect reported problems with differentiating pigment from blood, and with spectacle frame selection. (36)

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A colour vision defect can also become a problem for dentists and dental personnel, when shades of teeth have to be matched. (37) Dental personnel with a colour vision defect can make more errors than those with normal colour vision in this task. (38)

Practitioners who have a colour vision defect should adopt a safe working practice. In reality, a diagnosis is rarely based on just one sign, as the patient's history is usually available in addition to the symptoms and other signs. When asked about overcoming their difficulties, doctors with a colour vision deficiency reported that they use closer observation, ask others for help, or pay more attention to the history. (29,30) The use of filters for microscopy (39) and ophthalmoscopy (36) has also been advocated. However, the medical practitioner with a colour deficiency will be able to adopt those strategies only if they know about their defect. Some researchers who investigated the topic proposed the need for colour vision screening at the beginning of medical studies, especially since some doctors only learn about their defect after they qualify. (30)

Other professions

Individuals with a colour vision deficiency may also be prohibited from working as fire fighters, (40) electricians, (41) or performing certain duties in the Armed Forces. (42,43) In other professions, formal colour vision testing might not take place, but normal colour vision may be needed to perform the job successfully, eg jobs in which precise colour matching is required. Although normal colour vision is certainly not a requirement for artists and sports professionals, they can also experience some difficulties as a result of their altered colour vision. (1) However, the colour vision defect should not be seen as a barrier to succeeding in those professions. (44-48)

Treatment of colour deficiency

Attempts have been made to cure colour vision deficiencies or to minimise their effects since the 19th Century. (49) Some of the methods that have been tried include eye exercises, staring at flashing red and green lights, vitamins, colour education and coloured filters. (50)

Coloured filters

The use of coloured filters to improve daltonians' colour discrimination was first proposed by Seebeck in the 19th Century. (51) Spectacles, hand-held devices, loupes, monocles and contact lenses have all been used as the means of introducing the filters into the visual system. (50) A coloured filter will alter the luminance and chromaticity of an object viewed through it. When coloured filters are recommended for colour vision deficiency, these are often used monocularly or two differently coloured filters are worn. This results in a chromatic and luminance discrepancy between the two eyes (Figure 3 and Figure 4).

The filter would improve a daltonian's discrimination of two colours if it increased the chromatic difference between those colours. It has been shown that certain coloured filters change the chromaticity of the hues used in the Farnsworth D15 test in such a way that the set spans a greater number of isochromatic lines, thus improving the discrimination of those hues. (52,53) Subjects who performed the test monocularly through the filters do use this chromatic cue. (52) However, just as a coloured filter can increase the chromatic difference between two colours, it can also make the discrimination of some colours more difficult or impossible. (54)

To benefit from the disparate chromatic information available from the two eyes when a filter is worn monocularly, the daltonian could make voluntary comparisons of the two images. Although chromatic discrimination is not independent in the two eyes, (55) suggestions have been made that useful information could also be obtained from the disparate monocular inputs in binocular viewing. (56-58)

In addition to altering the chromaticity of an object, a coloured filter will also alter its luminance. The filter's effect on the object's luminance depends on the transmission spectrum of the filter and the spectral power distribution of the object, eg a red filter will make green objects appear dim but it will only have a small effect on red objects. A daltonian could therefore learn that objects that have their luminance significantly reduced by a red filter are green. This was the principle behind the first filters that were used as an aid for the daltonians in the 19th Century; a patient was given a pair of glasses that had one red and one green lens that would allow "discrimination of red from green by their different effect on the eye". (59) This principle has been also utilised in a number of other aids. (51) Red, green, or both filters have usually been employed, (51) but an aqua filter that works by introducing luminance cues has been reported to have a 62% success rate. (60)

It might be possible that useful information can also be obtained from the discrepancy between monocular luminances under binocular viewing conditions. It has been suggested that the discrepant monocular luminances can lead to the perception of lustre that could be used by colour-deficient individuals to improve their colour discrimination. (51,61,62) However, this cue might be of only limited use to the daltonian. (62,63)

The development of an optimal filter

An optimal coloured filter would change a daltonian's spectral sensitivities to ones that resemble those of normal trichromats. In the case of the dichromat, the filter would have to change the sensitivity of the present cone to that of the missing one. (64) This filter would have to be worn monocularly and with the assumption that the signals about the cone catches from the two eyes are kept separate. The situation is more complex for the anomalous trichromat, as two cone sensitivities need to be considered and a filter that alters the sensitivity of one cone will most certainly alter the sensitivity of the other. Theoretically, a binocularly worn filter that increases the separation of the peak cone spectral sensitivities should improve the colour discrimination of an anomalous trichromat. (64) However, the design of an optimal filter is further complicated by the presence of the short wavelength sensitive cone (S-cone), whose sensitivity curve shows some overlap with those of the long wavelength sensitive cone (L-cone) and medium wavelength sensitive cone (M-cone). Therefore, any filter that changes the spectral sensitivities of the L- and M-cones might also affect the sensitivity of the S-cone, and this could result in an undesirable reduction of discrimination of some colours.

Filters that change a daltonian's performance on a particular test or task, from that typical without a filter to that of a normal trichromat, have been determined theoretically and some have been tested. (51,65,66) These theoretical analyses aim to change the chromatic information only for specific tasks, and often only for a given observer, in such a way that allows that daltonian to solve the task. These analyses assume that the filters are worn binocularly, or if worn monocularly that the information from the eye wearing the filter does not interact with that from the eye without the filter.

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Commercially available filters

The X-Chrom lens and the ChromaGen lens system are two commercially available coloured filters that have been prescribed to improve the colour vision of daltonians.

The X-Chrom lens

The X-Chrom lens is a red-coloured contact lens that is worn over the nondominant eye. (67) It has generally been agreed that this lens is not a cure for colour vision deficiencies, but opinions vary on its ability to improve the colour discrimination of daltonians. (67-69) The studies that have looked at the effectiveness of this lens agree that it improves performance of colour deficient subjects on pseudoisochromatic plate tests. (70-74) However, this does not necessarily indicate improved chromatic discrimination as the lens could simply be introducing a luminance edge between the figure and the background that allows the patient to identify the figure.

The reported effects of the X-Chrom lens on arrangement colour vision tests, such as the Farnsworth Munsell 100 Hue test and the D15 test, are inconsistent. Some patients improve their score when wearing the lens whereas others show no improvement or even poorer discrimination with the lens than without it. (72-75) The X-Chrom filter also does not affect the daltonian's performance on the Farnsworth Lantern test. (71,75) The lens does provide both chromatic and luminance cues on the D15 test and some patients do use the chromatic ones when performing the test. (52) Unfortunately, in the study that reported this finding, the test was performed monocularly and the result therefore cannot be related to real life, where viewing is binocular. However, Taylor (72) did find that the monocularly worn X-Chrom lens improved binocular discrimination.

It has been suggested that a learning process may take place when a colour-deficient patient is equipped with a monocular filter. (67,72,76) However, not all studies report an improvement in the test results with increased wear time. (73,74,77)

The ChromaGen lens system

The ChromaGen lens system consists of coloured filters that are available in a range of hues and densities (Figure 5). These can be prescribed in the form of spectacle or soft contact lenses. The lens is usually fitted monocularly to the non-dominant eye, although success has also been reported when two different hues are used in the two eyes. (77,79)

To select the optimal filter, the patient is asked to view a multicoloured display on a computer screen or a printed sheet, (78) or the plates of the Ishihara test. (80) The patient then observes the same image through the various filters in spectacle form and reports any changes in terms of the number and brightness of colours seen, presence of fluorescence, or a 3D effect. The patient is fitted with a trial lens of the chosen hue and invited to observe the natural world. The density of the tint can also be adjusted at this stage.

Studies that have evaluated the ChromaGen lens system by considering the patients' reports and feedback regarding their perceived change in colour perception report high success rates. Harris (79) reported that at the time of lens trial, 97% of patients rated their perceived improvement in colour vision as significant or better, although this number was lower after a period of at least three months of lens wear. Hodd (81) found that the success rate was 100% for deuteranomalous trichromats and 36% for deuteranopes; protons were not well represented in the study.

In a clinical evaluation of the ChromaGen lens system, it was reported that like the X-Chrom lens, it does a fairly good job with helping patients to pass the Ishihara test, but its effects on the Farnsworth D15 and the Farnsworth Lantern vary greatly among patients, with most still failing these tests. (77) The investigators concluded that the lens cannot be used as a method of curing patients with colour vision deficiencies, and it should definitely not be used to allow patients to gain entry into occupations where normal colour vision is required. In a subjective questionnaire all subjects indicated that their colour perception with the lens was better than what they had been used to. Difficulties in dim light and some problems with motion and distance perception were reported. There was no evidence for the existence of a learning process throughout the study.

Other aids and strategies

Individuals with a colour vision deficiency report that they cope with their difficulties by asking colleagues, using instruments, separating coloured objects and avoidance of tasks in which colour is involved. (1) With the improving technology and advancing research, it is now possible to simulate what the world looks like to a dichromatic observer. (82,83) Such tools allow designers and manufacturers to check what their product would look like to a dichromatic observer and therefore, if possible, to make adjustments to the colours they use, for example on a webpage.

A true cure of congenital colour vision deficiency can only be offered with gene therapy. In fact, just this year, a group of researchers reported that they were able to cure adult monkeys of red-green colour deficiency with gene therapy. (84,85) The monkeys were given subretinal injections of a viral vector that carried the therapeutic transgene in order to replace the missing visual pigment. The researchers believed that the new photopigment did not have to establish new neural connections, but an extra dimension of colour vision developed from the splitting of the existing chromatic pathway. More research is required however before such therapy might become available to humans.

Advice for individuals with a colour vision deficiency

If a patient is diagnosed with a colour deficiency, the optometrist should be able to offer advice on the nature of the deficiency, which might include advice on the genetic nature of the defect, and give examples of situations in which the problem might become evident. If dealing with a child, examples of how the colour vision deficiency might become apparent in educational settings should be given, and the parents and the child should be informed that certain professions have a requirement for normal colour vision. When giving such advice, it is important to remember that not all patients will be accepting of the diagnosis and some may initially respond with disbelief and denial. (1)

Conclusion

Most daltonians report that their altered colour vision brings about difficulties in everyday tasks where colour is involved. It is quite clear that knowing that the defect exists is paramount to minimising its deleterious effects. Even though coloured filters have been developed to improve the daltonian's colour discrimination, these filters do not restore normal colour vision. The only true treatment for congenital colour vision deficiency will be available with gene therapy, a technique that still requires further investigation.

Module questions

Course code: C-12407)

Please note, there is only one correct answer. Enter online or by the form provided

An answer return form is included in this issue. It should be completed and returned to CET initiatives (c-12407) OT, Ten Alps, One New Oxford Street, High Holborn, London, WC1A 1NU by December 18 2009

1. In Steward and Cole's survey, the most frequently reported difficulty by individuals with a colour vision deficiency was:

a) The selection of colours of clothing and paints

b) Tuning of colours on the television sot

c) Identification of skin colour changes

d) Identification of colours of traffic lights

2. Individuals with a protanopic defect:

a) Will improve their identification of a red light with an increase of luminance

b) Are always certain when naming the colours of traffic lights

c) Will improve their ability to see red light, but not identify it as red, with an increase of luminance

d) Cannot hold a drivers licence in the UK

3. The new colour vision standards for the police force recommend that:

a) Only monochromats are excluded

b) Monochromats and dichromats are excluded

c) All individuals with a colour vision deficiency are excluded

d) Individuals with a moderate/severe colour vision deficiency are excluded

4. According to the most recent advice, which tests are recommended for colour vision testing of applicants for a professional pilot's licence?

a) Ishihara test and CAD test

b) Ishihara test and Lantern

c) Ishihara test and anomaloscope

d) The Lantern and anomaloscope

5. If a candidate for a private pilot's licence fails the Ishihara test, they will:

a) Be given a class 2 certificate with a restriction of daytime flying only, and this restriction cannot be lifted

b) Not be given a class 2 certificate but can still obtain the licence

c) Be given a class 2 certificate with a restriction of daytime flying only, but this restriction might be lifted after further testing

d) Not be given a class 2 certificate and cannot obtain the licence

6. Which of the following about the colour vision requirements for a national private pilot licence is correct?

a) The applicant's colour vision does not need to be assessed

b) The applicant must have normal colour vision as assessed by the Ishihara test

c) The applicant can be an anomalous trichromat but not a dichromat

d) The applicant must have normal colour vision as assessed by the anomaloscope

7. Seafarers who want to work on the deck but fail the Ishihara test are advised that:

a) They will not be able perform their chosen occupation

b) They should have their colour vision retested with the Lantern Test

c) They should have their colour vision retested with the D15 test

d) They should have their colour vision retested with the anomaloscope

8. The improvement of performance on pseudoisochromatic plates with a monocular coloured filter:

a) Indicates definite improvement of colour discrimination

b) Indicates a possible introduction of a luminance cue between the figure and the background

c) Does not occur with the X-Chrom lens

d) Does not occur with a ChromaGen lens

9. If a colour deficient person wears a red coloured filter/lens, the luminance of a red object:

a) Will be altered by more than that of a green object

b) Will be altered by less than that OF a green object

c) Will be altered by the same amount as a green object

d) Will be unaltered

10. The ChromaGen lens system:

a) Restores normal colour vision in individuals with colour vision deficiency

b) Should be used to allow colour deficient patients to pass occupational tests

c) Improves performance on pseudoisochromatic plates

d) Does not affect the luminance of objects viewed through the lens

11. Doctors with a colour vision deficiency:

a) Do not make errors when identifying signs from clinical photographs

b) Do not make errors when identifying signs from histophathology slides

c) Make some errors when identifying signs from clinical photographs but are just as confident as those with normal colour vision

d) Make some errors when identifying signs from clinical photographs and are less confident than those with normal colour vision

12. A research report published in 2009 indicated that:

a) Tritan colour deficiency could be cured with gene therapy

b) Red-green colour deficiency can be cured with a new set of coloured filters

c) Red-green colour deficiency can be cured with gene therapy in men

d) Red-green colour deficiency can be cured with gene therapy in monkeys

Monika Formankiewicz BOptom MCOptom PhD

References

See www.optometry.co.uk/references

Monika Formankiewicz is a senior lecturer in the Department of Optometry and Ophthalmic Dispensing at Anglia Ruskin University. Her PhD work concentrated on colour and spatial vision. Dr Formankiewicz is a member of the Anglia Vision Research group.
Table 1

Examples of colours that might be confused by colour
deficient observers

Colour deficiency Examples of colours that might be confused

Protanope Blue--green/white/red
 Pale blue/purple/magenta
 Red/orange/yellow/green

Deuteranope Purple/Grey/greenish blue-green
 Red/orange/yellow/green
 Red/brown, green/brown

Tritanope Yellow/white
 Violet/yellow-green
 Red/red-purple
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Title Annotation:COLOUR VISION PART 4: COURSE CODE: C-12407
Author:Formankiewicz, Monika
Publication:Optometry Today
Geographic Code:4EUUK
Date:Nov 20, 2009
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