Confessions of a colour blind physician

Colour vision restrictions for driving: an evidence-based perspective on regulations in ASEAN countries compared to other countries

Colour vision deficiency is an impairment in discriminating colours. Beyond occupational opportunities, colour vision-based restrictions may limit driving, which is a daily task for many people. This review aims to compare existing colour vision requirements for obtaining a driving license in southeast Asian countries to the rest of the world. Subsequently, to review existing published literature and provide evidence-based recommendations for future guidelines for colour-deficient drivers. Color vision requirements for obtaining a driving license vary widely amongst countries. While colour-deficient drivers may face mild challenges in driving, increased awareness and developing effective compensatory strategies could enable them to drive safely. The current evidence does not support a strict exclusion of all colour-deficient individuals from driving. Instead, emphasis is needed on screening to increase awareness and insight into their disability. Future studies should consider compensatory adaptive strategies that are specific for high-risk situations such as challenging driving conditions.

Color vision restrictions for medical school admission: a discussion on regulations in ASEAN countries compared to countries across the world

Color vision deficiency impairs one's ability to perceive and discriminate colors. Color-deficient individuals may face discrimination in various occupations, particularly in medical school admissions. This discussion seeks to compare the existing color vision requirements for entry to medical school in Southeast Asian countries as compared to countries across the world. Following this, we explore the published evidence in this field, to provide recommendations for future guidelines that will maximize the occupational opportunities for color-deficient individuals.

Color Vision Deficiency Among Doctors: Can We Make Useful Adaptations to the Color Codes Used in the Clinical Environment?

ABSTRACT

Color vision deficiency (formerly known as color blindness) is common as a congenital and as an acquired condition. Some professions, most famously commercial aviation, require their members to demonstrate normal color vision. In the United States and United Kingdom, no restriction is placed on the ability of the color-deficient doctor to practice medicine, although there is evidence that certain clinical discriminations are harder for such doctors. Generally ignored has been the difficulty and the potential for error that arises from the use of color codes in clinical equipment. In this review, we introduce the basic concepts of color deficiency, summarize evidence for the challenges it poses to the doctor, examine global variation in policy, show the potential for confusion among clinical color codes, and suggest how the current situation could be improved to enhance both patient safety and the well-being of the color-deficient doctor.

The handicap of abnormal colour vision

All people with abnormal colour vision, except for a few mildly affected deuteranomals, report that they experience problems with colour in everyday life and at work. Contemporary society presents them with increasing problems because colour is now so widely used in printed materials and in computer displays. Equal opportunity law gives them protection against unfair discrimination in employment, so a decision to exclude a person from employment on the grounds of abnormal colour vision must now be well supported by good evidence and sound argument. This paper reviews the investigations that have contributed to understanding the nature and consequences of the problems they have. All those with abnormal colour vision are at a disadvantage with comparative colour tasks that involve precise matching of colours or discrimination of fine colour differences either because of their loss of colour discrimination or anomalous perception of metamers. The majority have problems when colour is used to code information, in man-made colour codes and in naturally occurring colour codes that signal ripeness of fruit, freshness of meat or illness. They can be denied the benefit of colour to mark out objects and organise complex visual displays. They may be unreliable when a colour name is used as an identifier. They are slower and less successful in search when colour is an attribute of the target object or is used to organise the visual display. Because those with the more severe forms of abnormal colour vision perceive a very limited gamut of colours, they are at a disadvantage in the pursuit and appreciation of those forms of art that use colour.

Search for coloured objects in natural surroundings by people with abnormal colour vision

BACKGROUND

People with abnormal colour vision often report difficulty seeing coloured berries and flowers in foliage, which suggests they will have a diminished capacity for visual search when target objects are marked out by colour. There is very little experimental evidence of the effect of abnormal colour vision on visual search and none relating to search for objects in natural foliage.

METHOD

We showed 79 subjects with abnormal colour vision (seven protanopes, 10 deuteranopes, 16 protanomals and 46 deuteranomals) and 20 subjects with normal colour vision photographs of natural scenes and asked them to locate clumps of red berries, to trace the length of a red string on grass and to name the season depicted in a photograph taken in the Autumn and the same scene photographed in the Summer. Colour vision was assessed using the Ishihara, the Medmont C100, the Farnsworth D15, the Richmond HRR and the Nagel anomaloscope.

RESULTS

All the subjects with abnormal colour vision located fewer clumps of red berries than those with normal colour vision. The subjects who failed the Farnsworth D15 performed significantly worse than those who passed but the distribution of scores in the two groups overlaps. The majority of subjects with abnormal colour vision could not trace the full length of the string: only 38 per cent of anomalous trichromats who passed the Farnsworth D15 test and three per cent of those who failed it were able to trace the full length of the string. Fifty-five per cent of those classed as having a mild deficiency by the HRR test could trace the whole string. Most dichromats were unable to identify the Autumn season and those who did may have been assisted by guessing. Most (94 per cent) of those who passed the Farnsworth D15 test and all those classified as having a 'mild' deficiency by the HRR test could identify the season.

CONCLUSIONS

All people with abnormal colour vision, even those with a very mild deficiency, have some degree of impairment of their ability to see coloured objects in natural surroundings. A pass at the Farnsworth D15 test or a 'mild' classification with the Richmond HRR test identifies those likely to have the least problems with visual search and identification tasks. The results have practical implications for the selection of personnel in occupations that involve visual search in natural terrain.

Blind to the risk: an analysis into the guidance offered to doctors and medical students with colour vision deficiency

BACKGROUND/OBJECTIVES

Doctors and medical students with colour vision deficiency (CVD) are less capable and less confident at identifying colour in a wide range of clinical scenarios, some of which could be potentially life-threatening. There have been numerous calls for screening and counselling over the last 25 years.

SUBJECTS/METHODS

Surveys were sent to all 33 UK medical schools and 154 acute trusts, to ascertain what screening and support exists for doctors with CVD. The response rate was 95%.

RESULTS

1.4% of acute trusts and 16.7% of medical schools screen for CVD. 3.4% of trusts and 10.0% of medical schools had CVD-specific advice which they give to medical professionals. Guidance and advice given varied widely between different schools and trusts.

DISCUSSIONS

Despite research showing a clear problem and lack of support for doctors with CVD, there has been a failure to respond by the medical profession. Screening, national guidance, counselling, and further research is needed to provide full support for practitioners with CVD and ensure patient safety.

The colors of natural scenes benefit dichromats

Dichromacy impairs color vision and impoverishes the discrimination of surface colors in natural scenes. Computational estimates based on hyperspectral imaging data from natural scenes suggest that dichromats can discriminate only about 10% of the colors discriminated by normal trichromats. These estimates, however, assume that the colors are equally frequent. Yet, pairs of colors confused by dichromats may be rare and thus have small impact on overall perceived chromatic diversity. This study estimated, empirically, how much dichromats are disadvantaged in discriminating surface colors drawn from natural scenes. The stimulus for the experiment was a scene made of real three-dimensional objects painted with matte white paint and illuminated by a spectrally tunable light source. In each trial the observers saw the scene illuminated by two spectra in two successive time intervals and had to indicate whether the colors perceived in the objects in the two intervals were the same or different. The spectra were drawn randomly from hyperspectral data of natural scenes and therefore represented natural spectral statistics. Four normal trichromats and four dichromats carried out the experiment. It was found that the number of pairs that could be discriminated by dichromats was almost 70% of those discriminated by normal trichromats, a proportion much higher than anticipated from estimates of discernible colors. Moreover, data from model simulations show that normal trichromats and dichromats use lightness differences for discrimination in about 40% and 50% of the discriminable pairs, respectively. Together these results suggest that the color distributions of natural scenes benefit the color vision of dichromats.

Spatial visual function in anomalous trichromats: Is less more?

Color deficiency is a common inherited disorder affecting 8% of Caucasian males with anomalous trichromacy (AT); it is the most common type of inherited color vision deficiency. Anomalous trichromacy is caused by alteration of one of the three cone-opsins’ spectral sensitivity; it is usually considered to impose marked limitations for daily life as well as for choice of occupation. Nevertheless, we show here that anomalous trichromat subjects have superior basic visual functions such as visual acuity (VA), contrast sensitivity (CS), and stereo acuity, compared with participants with normal color vision. Both contrast sensitivity and stereo acuity performance were correlated with the severity of color deficiency. We further show that subjects with anomalous trichromacy exhibit a better ability to detect objects camouflaged in natural gray scale figures. The advantages of color-deficient subjects in spatial vision performance could explain the relatively high prevalence of color-vision polymorphism in humans.

Development and validation of a questionnaire assessing the quality of life impact of Colour Blindness (CBQoL)

Background

Congenital colour vision deficiency (CVD), commonly called ‘colour blindness’, affects around 8% of men and 0.4% of women. Although many aspects of health (e.g. change in colour of urine) and healthcare (e.g. coloured medication, colour-coded diagnostic tests), and modern life depend upon colour coding (e.g. graphs, maps, signals), the impact of colour blindness on everyday life is not generally considered a topic of importance. This study is the first to create and validate a questionnaire measuring the quality of life (QoL) impact of being colour blind.

Methods

This study consisted of two phases. Firstly, the questionnaire design and development phase was led by an expert panel and piloted on a focus group. Secondly, an online sample of 128 men and 291 women filled in the questionnaire, and the psychometric properties of the questionnaire were analysed using principal components analysis (PCA). The scores of colour blind (CB) participants and normal-sighted controls, controlling for age and sex, were compared using matched t-tests.

Results

The PCA resulted in a questionnaire with three domains (or subscales): QoL for Health & Lifestyle, QoL for Work, and QoL for Emotions. Controlling for age, there was a significantly greater negative impact on QoL for CB people than normal-sighted controls in regards to confusion over colour in various aspects of their health (p = 5 × 10⁻⁷), work (p = 1.3 × 10⁻⁷), and emotional life (p = 6 × 10⁻⁵).

Conclusion

Colour blindness can significantly impact quality of life for health, emotions, and especially careers. The tool developed here could be useful in future clinical studies to measure changes in CBQoL in response to therapy in conditions where colour vision is affected. We also discuss ways in which everyday problems related to colour vision might be reduced, for example, workplaces could avoid colour coding where a non-colour alternative is possible.

Frequency of color blindness in pre-employment screening in a tertiary health care center in Pakistan

Objective:

To describe the frequency of color vision deficiency among Pakistani adults presenting for pre-employment health screening in a tertiary care hospital.

Methods:

The cross-sectional study was carried out at the Aga Khan University Hospital, Karachi, and the data was collected for color vision deficiency, age, gender, and job applied for from pre-employment examination during 2013-2014. IBM SPSS 20 was used for statistical analysis.

Results:

Three thousand four hundred and thirty seven persons underwent pre-employment screening during 2013 and 2014; 1837 (53.44%) were males and 1600 (46.65%) females. The mean age was 29.01 (±6.53) years. A total of 0.9% (32/3437) persons had color vision deficiency with male being 1.4% and female 0.4%.

Conclusion:

Color vision deficiency was observed in 0.9% of candidates screened for pre-employment health check up in a tertiary care hospital. The color vision deficiency was predominantly present in male individuals.

New Colors for Histology: Optimized Bivariate Color Maps Increase Perceptual Contrast in Histological Images

BACKGROUND

Accurate evaluation of immunostained histological images is required for reproducible research in many different areas and forms the basis of many clinical decisions. The quality and efficiency of histopathological evaluation is limited by the information content of a histological image, which is primarily encoded as perceivable contrast differences between objects in the image. However, the colors of chromogen and counterstain used for histological samples are not always optimally distinguishable, even under optimal conditions.

METHODS AND RESULTS

In this study, we present a method to extract the bivariate color map inherent in a given histological image and to retrospectively optimize this color map. We use a novel, unsupervised approach based on color deconvolution and principal component analysis to show that the commonly used blue and brown color hues in Hematoxylin-3,3'-Diaminobenzidine (DAB) images are poorly suited for human observers. We then demonstrate that it is possible to construct improved color maps according to objective criteria and that these color maps can be used to digitally re-stain histological images.

VALIDATION

To validate whether this procedure improves distinguishability of objects and background in histological images, we re-stain phantom images and N = 596 large histological images of immunostained samples of human solid tumors. We show that perceptual contrast is improved by a factor of 2.56 in phantom images and up to a factor of 2.17 in sets of histological tumor images.

CONTEXT

Thus, we provide an objective and reliable approach to measure object distinguishability in a given histological image and to maximize visual information available to a human observer. This method could easily be incorporated in digital pathology image viewing systems to improve accuracy and efficiency in research and diagnostics.

Colour Vision Deficiency: Is it a Handicap? A Narrative Review of its Impact on Medical & Dental Education and Practice

Colour vision is required in medical and dental practices. This article seeks to present the impact of colour vision deficiency (CVD) on medical, dental education and practices using narrative review of literature. Relevant English publications, comprising of experimental and observational studies, topic and systemic reviews, meta-analyses and randomised controlled trials, were searched and identified from PubMed, National University of Singapore (NUS) database, Cochrane electronic databases and Proceedings of the thirteenth Symposium of the International Research Group on CVD. “Google” and “Google Scholar” were used to search for paramedical literature. Seventy articles were retrieved, of which 38 were included in this review. It shows that CVD affects broad spectrum of medical, dental education and practices, and varies in its impact. Detecting colour cues in clinical practice constitutes one of the many complex processes in establishing the clinical diagnoses, thus the deficiency alone may not handicap the clinicians. Nonetheless, early colour vision screening for medical and dental students, and practitioners would result in early recognition of their limitations and allow time for devising coping strategies.

Recognition of simulated cyanosis by color-vision-normal and color-vision-deficient subjects

There are anecdotal reports that the recognition of cyanosis is difficult for some color-deficient observers. The chromaticity changes of blood with oxygenation in vitro lie close to the dichromatic confusion lines. The chromaticity changes of lips and nail beds measured in vivo are also generally aligned in the same way. Experiments involving visual assessment of cyanosis in vivo are fraught with technical and ethical difficulties A single lower face image of a healthy individual was digitally altered to produce levels of simulated cyanosis. The color change is essentially one of saturation. Some images with other color changes were also included to ensure that there was no propensity to identify those as cyanosed. The images were assessed for reality by a panel of four instructors from the NSW Ambulance Service training section. The images were displayed singly and the observer was required to identify if the person was cyanosed or not. Color normal subjects comprised 32 experienced ambulance officers and 27 new recruits. Twenty-seven color deficient subjects (non-NSW Ambulance Service) were examined. The recruits were less accurate and slower at identifying the cyanosed images and the color vision deficient were less accurate and slower still. The identification of cyanosis is a skill that improves with training and is adversely affected in color deficient observers.

Colour change in cyanosis and the confusions of congenital colour vision deficient observers

Visual recognition of cyanosis is an important clinical activity. While pulse oximetry is almost universal in the hospital environment, there are circumstances where it is not available or may be unreliable. Cyanosis recognition is affected by lighting colour. In addition, there is, mainly anecdotal, evidence that people with greater colour vision deficiencies (CVDs) have particular difficulty and there is no effective lighting strategy to assist in the observation. The change of blood colour with oxygenation has been shown to lie close to the direction of colour confusions made by congenital red-green dichromats. The important sites of observation are lips, nail beds and palm creases. 10 subjects who were known to be chronically hypoxaemic were recruited from the chronic respiratory program. Their blood oxygen saturation (SpO(2)) varied from 84% to 96% pre-exercise, and 61-84% post-exercise. Ten normal subjects were recruited whose SpO(2) was 99% or 100%. The spectral radiances of lips, nail beds and palm creases were measured using a telespectroradiometer and compared with the spectral radiances of a white tile of known spectral reflectances measured in the same location. This is a non-contact method of measurement, avoiding the blanching caused by pressure of contact methods. The spectral reflectances were calculated, and the chromaticities calculated for a Planckian radiator T = 4000K. Measurements on lips yielded the most consistent results. The colour changes pre- and post-exercise and compared with normal colour lie generally along a deutan confusion line. These results show the direction of the colour change and confirm the, previously anecdotal, difficulties in detecting cyanosis by observers with CVDs.

Harnessing color vision for visual oximetry in central cyanosis

Central cyanosis refers to a bluish discoloration of the skin, lips, tongue, nails, and mucous membranes, and is due to poor arterial oxygenation. Although skin color is one of its characteristic properties, it has long been realized that by the time skin color signs become visible, oxygen saturation is dangerously low. Here we investigate the visibility of cyanosis in light of recent discoveries on what color vision evolved for in primates. We elucidate why low arterial oxygenation is visible at all, why it is perceived as blue, and why it can be so difficult to perceive. With a better understanding of the relationship between color vision and blood physiology, we suggest two simple techniques for greatly enhancing the clinician's ability to detect cyanosis and other clinical color changes. The first is called "skin-tone adaptation", wherein sheets, gowns, walls and other materials near a patient have a color close to that of the patient's skin, thereby optimizing a color-normal viewer's ability to sense skin color modulations. The second technique is called "biosensor color tabs", wherein adhesive tabs with a color matching the patient's skin tone are placed in several spots on the skin, and subsequent skin color changes have the effect of making the initially-invisible tabs change color, their hue and saturation indicating the direction and magnitude of the skin color shift.

Assessment of inherited colour vision defects in clinical practice

BACKGROUND

Colour vision deficiency (CVD) has a high prevalence and is often a handicap in everyday life. Those who have CVD will be better able to adapt and make more informed career choices, if they know about their deficiency. The fact that from 20 to 30 per cent of adults with abnormal colour vision do not know they have CVD suggests that colour vision is not tested as often as it should be. This may be because of practitioner uncertainty about which tests to use, how to interpret them and the advice that should be given to patients on the basis of the results. The purpose of this paper is to recommend tests for primary care assessment of colour vision and provide guidance on the advice that can be given to patients with CVD.

METHODS

The literature on colour vision tests and the relationship between the results of the tests and performance at practical colour tasks was reviewed.

RESULTS

The colour vision tests that are most suitable for primary care clinical practice are the Ishihara test, the Richmond HRR 4th edition 2002 test, the Medmont C-100 test and the Farnsworth D15 test. These tests are quick to administer, give clear results and are easy to interpret. Tables are provided summarising how these tests should be interpreted, the advice that can be given to CVD patients on basis of the test results, and the occupations in which CVD is a handicap.

CONCLUSION

Optometrists should test the colour vision of all new patients with the Ishihara and Richmond HRR (2002) tests. Those shown to have CVD should be assessed with the Medmont C-100 test and the Farnsworth D15 test and given appropriate advice based on the test results.