Activities of daily living
Nearly 90% of dichromats and up to two-thirds of anomalous trichromats reported difficulties with everyday tasks that involve colour [
4]. Tables
2 and
3 show the difficulties reported by persons with CVD, and the difficulties sub-analysed within each subtype of CVD [
4],[
22].
Table 2
Difficulties in everyday life reported by 151 CVD subjects and 302 NCV subjects
Clothing colours | 23.8 | 1.0 | <0.0001 |
Workplace/hobbies colours eg. pie charts | 13.2 | 1.0 | <0.0001 |
Natural colours | 40.4 | 1.0 | <0.0001 |
Colours relating to cooking s eg. Identification of cooked versus raw meat | 31.7 | 8.6 | <0.0001 |
Sports colours eg. shirts of players | 21.2 | 1.3 | <0.0001 |
Skin colours | 3.3 | 1.7 | 0.0007 |
Television colours setting | 6.0 | 0.7 | 0.0002 |
Table 3
Percentage of subjects with different types of CVD reporting difficulty in everyday tasks
Clothing/goods colours | 86 | 66 | 78 | 71 | 0 |
Workplace/hobbies colours | 68 | 23 | 50 | 33 | 0 |
Plant/flower identification | 57 | 18 | 44 | 26 | 0 |
Ripeness of fruits and vegetables | 41 | 22 | 31 | 27 | 0 |
Cooked versus raw meat | 35 | 17 | 33 | 20 | 0 |
Sports colours | 32 | 18 | 19 | 23 | 0 |
Adjust television colour settings | 27 | 18 | 28 | 18 | 2 |
Skin colours eg. sunburn, rashes | 27 | 11 | 17 | 17 | 0 |
Previously taken wrong medication due to colour difficulties | 0 | 3 | 3 | 1 | 0 |
Even amongst NCV individuals during the early part of life, they can develop CVD as they age. Acquired CVD or ACVI can occur due to age-related crystalline changes in lens, age-related maculopathy and conditions such as diabetes, glaucoma and optic neuritis. They can also be caused by medications such as digoxin, sildenafil, chloroquine and ethambutol. ACVI are often tritan (blue-yellow) in nature. Tritan defects cannot be detected using the Ishihara chart. Instead, the Hardy, Rand and Rittler plates may be more useful as tritan plates are also included and the severity of the defects can be graded [
6]. Alternatively, the Farnsworth D15 test may be used [
6].
Driving and accidents
Safe driving requires the driver to recognise colour-coded traffic lights and road signage. A case control study showed that both CVD and NCV subjects who were qualified to drive were in similar proportions (83.4% and 83.8% respectively) [
22]. However, regular use of a car was significantly less common among CVD subjects than NCV subjects [
22].
Reading road traffic signals tend to be less difficult for CVD observers compared to maritime, aviation and rail signals because the former is viewed from much shorter distances. Furthermore, they are assisted by cues such as position of traffic lights, relative brightness and movement of other traffic [
3],[
4],[
36]. Nevertheless, experimental studies have shown that people with CVD make more errors recognizing the colours of road traffic signals than those with normal vision [
37],[
38]. Deuteranopes have significantly reduced ability to notice red, orange and green colour-coded traffic control devices compared to NCV subjects [
39]. Protans are known to have reduced visual range for red signals compared to NCV observers [
36],[
40]. About 18-20% of anomalous trichromats and 50-60% of dichromats admitted to difficulty recognizing road traffic signals while 10-15% of protans admitted to difficulty seeing red signal lights [
4],[
23],[
41].
Atchison DA et al. showed that response times and error rates for recognising red and yellow lights were increased in CVD subjects compared to NCV subjects [
38]. On the contrary, Tagarelli et al. showed there were no differences between the two groups in identifying the colours of traffic light signals. However, when the relative positions of the traffic lights were changed, more CVD subjects had difficulty identifying the colours than NCV subjects but the difference was not statistically significant [
22].
Significantly higher proportion of CVD subjects preferred daytime driving over night-time driving compared to NCV subjects [
22]. This could be due to difficulty identifying the reflectors on the road and identifying the lights of the car ahead at night [
22]. Confusion of traffic lights and street lights was also noted in one-third of CVD drivers [
4]. The detection of dashboard warning lights (which are often red) was significantly more difficult for protans than deutans (17% versus 3% respectively) [
4].
In terms of accident rates, studies reported that CVD drivers did not have more road traffic accidents than NCV drivers [
21],[
22],[
36],[
42]. However, protans showed significantly more rear end collisions and accidents by overlooking red rear, stop and warning lights than colour normal [
36]. Rear end collisions seemed more prevalent amongst protans because the red lights of the rear end appeared dimmer to them, resulting in delayed perception in poorly illuminated areas. Deutans caused more accidents than NCV drivers at traffic light controlled intersections, although this was not statistically significant [
36]. A case control study also showed that there was no increased risk of unintentional workplace injuries amongst CVD subjects [
21].
Restriction of career options and workplace discrimination
Individuals with CVD appeared to have restricted career options. A 1971 study found that only 214 out of 569 CVD subjects made suitable choices of career [
43]. Table
4 shows careers and occupations known to be affected by CVD [
23],[
24]. The Commission Internationale de L'Éclairage recommends that normal colour vision be a prerequisite for pilots of scheduled passenger aircraft, especially large aircraft, and is mandatory for other commercial pilots to pass a lantern test and should not have a protan (red-deficient) colour vision deficiency [
44].
Table 4
Career and occupations known to apply a colour vision standard
NORMAL COLOUR VISION | Commercial airline pilots, air traffic controllers, technical and maintenance staff at airports, aircraft pilots and engineers in the armed services, naval officers, submarine personnel, masters and watchkeepers on merchant marine vessels, customs and excise officers, train drivers, railway engineers and maintenance staff; workers in industrial colour quality assurance and colour matching, workers in fine art reproduction and photography, some electrical and electronic engineers |
COLOUR VISION STANDARD APPLIED BUT ACCEPTS SOME WITH SLIGHT CVD | Fire fighters, police officers, some electrical and electronic engineers, some ranks in the armed services, hospital laboratory technicians, merchant seamen |
OCCUPATIONS WHERE CVD IS A DISADVANTAGE AND COLOUR VISION STANDARD MAY APPLY | Art teaching, bacteriology, botany, chemistry, interior design, histopathology, horticulture, geology, diamond grading, metallurgy |
According to Birch, coloured signals may be preferred to short wavelength radio for communication in the armed forces because radio signals can be intercepted [
23]. Hence, vocations such as signals personnel and again aircraft pilots will be unsuitable for individuals with CVD.
In the railway industry, train drivers and other rail workers must be able to recognize red, yellow and green signals at distances up to 1 km, sometimes under conditions of poor visibility due to fog or rain. Hovis JK and Oliphant D reported that 97% of individuals with CVD failed a lantern test (CNLAN) that was found to provide a reasonable functional assessment of colour discrimination for the rail industry [
45]. Vingrys AJ and Cole BL, in their literature review to determine whether colour vision standards were justified for the transport industry, found that CVD observers made more errors and had significantly slower reaction times in recognising coloured signal lights [
46]. It concluded that there was sufficient evidence to warrant retention of colour vision standards in transport industries where the highest standards of safety are expected.
Severe CVD is generally unacceptable in the police force. Conflict of evidence regarding identification of clothing or vehicles or items using colours at the scene of crime may interfere with jurisdiction in criminal or forensic cases [
23].
CVD applicants can be recruited as fire fighters if they pass the Ishihara's test. Should they fail this colour vision test, they would have to undertake the Farnsworth-Munsell Standard D15 test (FMD-15) [
47]–[
49]. Protans are not accepted in the fire brigade because of their reduced visibility of red signs and traffic signals. In addition, oxygen (black) and acetylene (maroon) gas cylinders are similar in shape and might be confused due to this CVD [
49]. Other critical tasks which require colour discrimination among the firefighters include interpretation of computer displays in communications units, assessment of gas level in gas detectors, use of indicator papers, identification of zone of fire on building evacuation and fault indicator panels, deduction of the burning substance based on the colour of the smoke and flames and distinction of hydraulic and pressure hoses, fire extinguishers, gas cylinders, pipes, ducts, and triage labels [
47].
Even among healthcare professionals, CVD can be disadvantageous to doctors and dentists. Difficulties faced by CVD doctors and medical students are summarised in Table
5[
5],[
17].
Table 5
Difficulties faced by CVD doctors and medical students
1 | Body colour changes: pallor, cyanosis, jaundice |
2 | Skin rashes, erythema and lymphangitis |
3 | Blood and urine test strips |
4 | Ophthalmology: disc pallor, diabetic changes, haemorrhage versus pigmentation, glaucoma, haemorrhage in anterior chamber, Kayser Fleischer rings |
5 | Body products: blood versus bile in urine, faeces, sputum, vomit |
6 | Otoscopy: inflamed drum, wax versus blood |
7 | Microscopy |
8 | Mouth and throat conditions |
9 | Ishihara test giving |
10 | Chemistry end-points |
11 | Tissue identification in surgery |
12 | Gangrene and sores |
CVD doctors tend to avoid the following specialties where normal colour vision is important: histopathology, microbiology, haematology, dermatology, ophthalmology, surgery, anaesthesia (uses differently coloured gas tanks) [
17]. A 1990 case control study showed that CVD dentists made significantly more errors in the hue and chroma aspects of shade selection, hence affecting their ability to select prosthetic teeth to match natural teeth [
50]. Hue is the quality that distinguishes one family of colours from another based on their different wavelengths in the visible spectrum. Chroma is the saturation, intensity, or strength of the hue.
Nearly one-quarter of CVD subjects reported having colour difficulties in previous jobs, as well as being precluded from an occupation because of their CVD [
4]. Steward and Cole showed that 43% of dichromats and 29% of anomalous trichromats reported their CVD had affected their choice of career [
4]. 46% of dichromats and 15% of anomalous trichomats also reported colour difficulties with everyday work, and this was statistically significant when compared with NCV subjects [
4].
However, a 2004 questionnaire survey revealed that CVD people had little difficulty in maintaining permanent employment [
22]. Nonetheless, they were more likely to hold subordinate jobs, for example, as agents, clerks or servants, whereas NCV subjects preferred autonomous activities, such as commercial and trade work [
22]. A subsequent study in 2005 also revealed that there was no significant difference between proportion of CVD and NCV people in the major occupational groups except for transport operations, aircraft and ship officers, electrical and electronic engineering, as well as fibre and textile processing [
51].
The effect of colour on appetite is important because poor growth and malnutrition due to poor oral intake, can affect the young and old respectively. Colour perception of food can adversely affect the appetite and taste perception of CVD people. A food study in 1978 demonstrated that addition of red dye to fruit flavoured beverages increased the perceived sweetness by 5-10%, while an addition of blue dye to cherry or strawberry flavoured beverages decreased sourness and fruit flavour by 20% [
52].
Colours are often used to differentiate the different types of oral medications. Steward and Cole reported that some CVD subjects in their study had previously taken the wrong medications due to difficulties with colour [
4]. Depending on what medication was taken, the adverse outcomes could range from insignificant to fatal. Patients who habitually mix their medications without the external packaging in the same pill storage compartment would be more prone to such hazards.
CVD may also affect the interpretation of coloured dipstick results used in healthcare [
5],[
17],[
53]. A case–control study involving patients who had ACVI due to diabetic retinopathy showed that diabetics made significantly more errors in interpreting urinary glucose dipstick results than non-diabetic controls [
53]. This would make monitoring of glycemic control more difficult, although monitoring is more commonly done via serum glucose today.
With increasing age and concurrent rising incidence of malignancies, detecting and awareness of colour-related signs and symptoms become important for susceptible individuals. Nonetheless, Spalding (1995) and Spalding (2004) mentioned difficulties in detecting hemoptysis, hematemesis, hematuria and bloody stools reported by these affected individuals [
5],[
17]. Detecting these presenting symptoms early would allow earlier diagnosis and treatment of any underlying sinister conditions, such as lung cancer, upper gastrointestinal bleeds, bladder cancer and colorectal cancer.