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Jennifer Birch - One of the best experts on this subject based on the ideXlab platform.
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identification of red green Colour Deficiency sensitivity of the ishihara and american optical company hard rand and rittler pseudo isochromatic plates to identify slight anomalous trichromatism
Ophthalmic and Physiological Optics, 2010Co-Authors: Jennifer BirchAbstract:Screening sensitivity, based on a specific number of errors, of the Ishihara plates and of the American Optical Company (Hardy, Rand and Rittler) plates (HRR plates) was determined by reviewing data obtained for 486 male anomalous trichromats identified and classified with the Nagel anomaloscope. Data were obtained for the 16 screening plates, with Transformation and Vanishing numeral designs, of the 38 plate Ishihara test, and for the four red―green screening plates (with six Vanishing designs) of the HRR test. Sensitivity of the Ishihara plates was found to be 97.7% on 4 errors and 98.4% on 3 errors. Only anomalous trichromats with slight Deficiency, according to the anomaloscope matching range, made 8 errors or fewer. One screening error, a single missed figure, is normally allowed as a pass on the HRR test and 3 errors is often recommended as the fail criterion to eliminate false positive results. Twenty-three subjects made no error on the HRR screening plates and 12 subjects made a single error (35 anomalous trichromats). Screening sensitivity was therefore 92.8% using 2 errors as the fail criterion. Screening sensitivity was reduced to 87% when 3 errors was the fail criterion, and some deuteranomalous trichromats with moderate Deficiency, according to the anomaloscope matching range, were not identified. Individuals who make a maximum of 2 errors on the HRR test, or on the Richmond HRR 4th Edition, should be re-examined with the Ishihara plates to determine their Colour vision status. The present review confirms that the Ishihara test is a very sensitive screening test and identifies people with slight anomalous trichromatism. The HRR test is unsatisfactory for screening and should not be chosen solely for this purpose.
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Pass rates for the Farnsworth D15 Colour vision test.
Ophthalmic and Physiological Optics, 2008Co-Authors: Jennifer BirchAbstract:INTRODUCTION: The Farnsworth D15 test (D15) is used worldwide to select applicants for employment in occupations which require good Colour vision. People with slight Colour Deficiency are intended to pass the D15 and people with significant (moderate/severe) Colour Deficiency to fail. METHODS: Pass rates were determined for 710 adult males with red-green Colour Deficiency using three different pass criteria in general use. RESULTS: Forty-six per cent of subjects were successful when the pass criterion was a circular results diagram (one single transformation of adjacent hues was accepted as a pass), 53% passed when one red-green isochromatic error was allowed and 60% passed when two red-green isochromatic errors were permitted. The pass rate for 200 dichromats was 1.5% on a circular diagram, 3% on one red-green error and 6% on two red-green errors. Protans made fewer errors than deutans and more protans than deutans were successful when either one or two red-green crossings were permitted as a pass. CONCLUSION: A circular results diagram is the preferred pass criterion. This criterion most nearly fulfils the aim of the test to fail all dichromats and people with significant protanomalous and deuteranomalous trichromatism. A circular diagram is also easy to interpret consistently. Re-examination is recommended if there are only one or two red-green isochromatic error lines across the results diagram. This gives individuals with borderline slight/moderate Colour Deficiency an opportunity to pass at the second attempt.
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Performance of Colour‐deficient people on the Holmes–Wright lantern (type A): consistency of occupational Colour vision standards in aviation
Ophthalmic and Physiological Optics, 2008Co-Authors: Jennifer BirchAbstract:INTRODUCTION: The Holmes-Wright lantern type A (H-W A) is an occupational Colour vision test used by the UK Civil Aviation Authority (CAA) and approved by Joint Aviation Requirements (JAR) to select aircrew. Pass, to obtain a CAA Class 1 Aviation medical certificate, can be achieved at three stages of the examination. The Commission Internationale d'Eclairage (CIE) recommends that the Falant pass criteria are used with all approved lanterns. A pass to obtain CIE Colour Vision Standard 2 can be achieved at two stages of the examination. This study examines the consistency of these pass criteria. METHODS: One hundred and twenty-five men with red-green Colour Deficiency were examined. All subjects completed three runs of the nine Colour pairs shown on the H-W A at high brightness, in photopic and scotopic viewing. RESULTS: Ten of 78 deuteranomalous trichromats examined passed to obtain a CAA Class 1 Aviation medical certificate at the first stage of the examination but only two of these subjects were successful at all three stages. Seventeen deuteranomalous trichromats passed to obtain CIE Colour Vision Standard 2 in photopic viewing and 20 subjects (one protanope and 19 deuteranomalous trichromats) passed in scotopic viewing. Only 50% of subjects who passed at the first stage of the examination were also successful at the second stage in either viewing condition. Ten deuteranomalous trichromats passed to obtain CIE Colour Vision Standard 2 in both photopic and scotopic viewing. Forty-three per cent of subjects made red-green errors and 79% made red-white errors at some stage of the examination. CONCLUSIONS: The staged pass criteria used by the CAA and the CIE lack internal consistency when applied to the H-W A. Colour-deficient people who pass to a standard at the first stage of the examination are unlikely to be successful if the examination is continued. The staged pass criteria do not identify individuals with superior Colour discrimination ability and it is difficult to justify selection of personnel for high risk occupations in aviation on this basis.
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Survey of the accuracy of new pseudoisochromatic plates.
Ophthalmic and Physiological Optics, 2007Co-Authors: Jennifer Birch, Lisa M. MckeeverAbstract:The accuracy of three new pseudoisochrometic tests for detecting red–green Colour Deficiency was assessed. These were the Ishihara plates, the Ishihara test for ‘unlettered persons’ and Ohkuma's lest cards. We examined 500 subjects; 471 normal trichromats and 29 Colour-deficient people, Results obtained for the 1989 edition of the Ishiliara places were compared with the 9th edition and the most efficient plates identified. Although normal trichromats may be expected to make several interpretive misreadings, the Ishihara plates were found to be superior to the 9th edition and to the Ohkuma test (1986) for Colour vision screening. The new symbol designs of the Ishihara plates for ‘unlettered persons’ (1990) were found to be very effective for Colour vision screening, and a further study with young children is proposed. The 38 plate I9S9 edition of the Ishihara les; is recommended for use in clinical practice. The designs included in the concise 24 plate edition and the new abbreviated 14 plate edition are not selected from the point of view of accuracy and more reliable results are obtained if the full lest is given or if the practitioner shows only the most efficient designs.
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A redesigned Farnsworth dichotomous B20 test
Color Research and Application, 2000Co-Authors: Jennifer Birch, Paul Chamberlain, Fatma A. SheriffAbstract:The Farnsworth dichotomous B20 test has been reconstructed using a circle of Munsell Hues with value 5: 7 hues have chroma 4, and 13 hues have chroma 2. Results were obtained for 46 normal subjects, 36 subjects with red-green Colour Deficiency, and 1 congenital tritanope. A larger number of deuteranomalous trichromats fail the reconstructed B20 than fail the Farnsworth D15 test. The B20 test gives good protan/deutan classification, when the test is failed, and provides significantly more isochromatic Colour confusions for identifying and classifying tritanopia and tritan Colour Deficiency than the D15 test. © 2000 John Wiley & Sons, Inc. Col Res Appl, 26, S253–S255, 2001
John L. Barbur - One of the best experts on this subject based on the ideXlab platform.
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Occupational Colour vision needs with emphasis on aviation
2020Co-Authors: John L. Barbur, M. Rodriguez-carmonaAbstract:The novel experiments and tests developed for this study yield new data that describe how combinations of luminance contrast and Red / Green (RG) and Yellow / Blue (YB) Colour signals affect task completion times (TCT) and the overall accuracy the operator can achieve. With appropriate design and choice of Colours, it is possible for deutan applicants with thresholds < 4 standard normal CAD units to perform as well as normal trichromats when suprathreshold Colours with RG and YB components are employed in visual displays. As many as 22% of deuteranomalous subjects can be included in this category. In spite of their congenital Colour Deficiency, such applicants can operate safely in the Air Traffic Control (ATC) environment as well as in many other occupations that involve the use of large-field, visual displays.
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Colour assessment outcomes – a new approach to grading the severity of color vision loss
2020Co-Authors: M. Rodriguez-carmona, John L. BarburAbstract:INTRODUCTION: Recent studies have shown that a significant percentage of subjects with anomalous, congenital trichromacy can perform the suprathreshold, Colour-related tasks encountered in many occupations with the same accuracy as normal trichromats. In the absence of detailed, occupation-specific studies, an alternative approach is to make use of new findings and the statistical outcomes of past practices that have been considered safe to produce graded, justifiable categories of Colour vision that can be enforced. METHODS: We analyzed traditional color assessment outcomes and measured severity of Colour vision loss using the CAD test in 1363 subjects (336 normals, 705 deutan, 319 protan and 3 tritan). The severity of Colour vision loss was measured in each subject and statistical, pass / fail outcomes established for each of the most commonly used, conventional Colour assessment tests and protocols. RESULTS: The correlation between the number of Ishihara (IH) test plates subjects fail and the severity of RG Colour vision loss was very poor. The 38 plates IH test has high sensitivity when no errors are allowed (i.e., only 0.71% deutans and 0.63% protans pass). Protocols based on zero errors are uncommon since 18.15% of normal trichromats fail. The most common protocols employ either the 24 or the 14 plates editions with two or less errors. These protocols pass almost all normal trichromats, but the deutans and some protans that also pass (when two or less errors are allowed) can be severely deficient. This is simply because the most challenging plates have not been included in the 24 and 14 plates editions. As a result, normals no longer fail, but the deutans and protans that pass have more severe loss of Colour vision since they fail less challenging plates. The severity of Colour vision loss was measured in each subject and statistical, pass / fail outcomes established for each of the most commonly used, conventional Colour assessment tests and protocols. DISCUSSION: Historical evidence and new findings that relate severity of loss to the effective use of Colour signals in a number of tasks provide the basis for a new Colour grading system based on six categories. A single Colour assessment test is needed to establish the applicant’s Colour Vision category which can range from ‘supernormal’ (CV0), for the most stringent, Colour-demanding tasks, to ‘severe Colour Deficiency’, when red / green Colour vision is either absent or extremely weak (CV5).
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Colour vision requirements in visually demanding occupations.
British Medical Bulletin, 2017Co-Authors: John L. Barbur, M. Rodriguez-carmonaAbstract:Normal trichromatic Colour vision (CV) is often required as a condition for employment in visually demanding occupations. If this requirement could be enforced using current, Colour assessment tests, a significant percentage of subjects with anomalous, congenital trichromacy who can perform the suprathreshold, Colour-related tasks encountered in many occupations with the same accuracy as normal trichromats would fail. These applicants would therefore be discriminated against unfairly. One solution to this problem is to produce minimum, justifiable CV requirements that are specific to each occupation. This has been done successfully for commercial aviation (i.e. the flight crew) and for Transport for London train drivers. An alternative approach is to make use of new findings and the statistical outcomes of past practices to produce graded, justifiable CV categories that can be enforced. To achieve this aim, we analysed Colour assessment outcomes and quantified severity of CV loss in 1363 subjects. The severity of CV loss was measured in each subject and statistical, pass/fail outcomes established for each of the most commonly used, conventional Colour assessment tests and protocols. This evidence and new findings that relate severity of loss to the effective use of Colour signals in a number of tasks provide the basis for a new Colour grading system based on six categories. A single Colour assessment test is needed to establish the applicant's CV category which can range from 'supernormal', for the most stringent, Colour-demanding tasks, to 'severe Colour Deficiency', when red/green CV is either absent or extremely weak.
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Analysis of European Colour vision certification requirements for air traffic control officers
2016Co-Authors: John L. Barbur, M. Rodriguez–carmona, J. Hickey, S. Evans, A. ChorleyAbstract:The advantages of using Colour in large-field, visual displays have been investigated with emphasis on ATC applications. This study examined and quantified the relationship between severity of Colour vision loss in congenital Deficiency and the corresponding changes in visual performance. Analysis of current Colour assessment protocols and the current findings provide the basis for a new system of Colour categories that can be enforced. The report also describes how a Colour category can be selected for a given occupational task by examining the Colour-related requirements and the applicant’s class of Colour Deficiency.
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Variability in normal and defective Colour vision: Consequences for occupational environments
Colour Design, 2014Co-Authors: M. Rodriguez-carmona, John L. BarburAbstract:Abstract New findings in relation to both normal and defective Colour vision provide improved understanding of chromatic mechanisms in human vision and account for much of the variability observed in both normal trichromats and in subjects with congenital Colour Deficiency. The principal methods for assessing Colour vision and the techniques employed to isolate the use of Colour signals are reviewed. Data on the continuous distribution of Colour thresholds within deutan and protan observers and the variability within normal trichromatic Colour vision are presented and the principal factors that contribute to this variability examined. The need to quantify the severity of Colour vision loss and to classify accurately the subject's Colour vision is examined in relation to Colour assessment requirements in occupational environments. A method of establishing pass/fail limits that are functionally safe without disadvantaging subjects with congenital Colour Deficiency is described. Also discussed are the uses of novel Colour tests to reveal acquired loss of chromatic sensitivity as an indication of early-stage diseases of the eye as well as the value such tests may have in early detection and subsequent treatment.
J Birch - One of the best experts on this subject based on the ideXlab platform.
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acquired Colour vision Deficiency in patients receiving digoxin maintenance therapy
British Journal of Ophthalmology, 2002Co-Authors: John G Lawrenson, C Kelly, Annali Lawrenson, J BirchAbstract:Background/aims: Disturbances of Colour vision are a frequently reported sign of digoxin toxicity. The aim of this study was to investigate the incidence of acquired Colour vision Deficiency in elderly hospitalised patients receiving maintenance digoxin therapy. Methods: 30 patients (mean age 81.3 (SD 6.1) years) receiving digoxin were tested using a battery of Colour vision tests (Ishihara, AO Hardy Rand Rittler plates, City tritan test, Lanthony tritan album, and the Farnsworth D15). These were compared to an age matched control group. Serum digoxin concentrations were determined from venous blood samples. Results: Slight to moderate red-green impairment was found in approximately 20–30% of patients taking digitalis, and approximately 20% showed a severe tritan Deficiency. There was no correlation between Colour vision impairment and serum digoxin level. Conclusions: Formal Colour vision testing of elderly patients taking digitalis showed a high incidence of Colour Deficiency, suggesting that impairment of retinal function can occur even at therapeutic drug levels. As a result, Colour vision testing in this population would have limited value for the detection of drug toxicity.
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The clinical use of saturated and desaturated Munsell panel tests
Documenta Ophthalmologica Proceedings Series, 1997Co-Authors: J BirchAbstract:215 people with red–green Colour Deficiency were examined with the Farns-worth D15 test. The 88 subjects who passed completed a desaturated version of the D15, the Adams test. 48 of the 88 subjects passed this test. The 127 subjects who failed the D15 were given a panel test containing more saturated Colours, the Paulson HI6 test. 19 of the 127 subjects passed the HI6. The 4 grades of severity obtained by the combined use of these three tests were compared with Nagel anomaloscope matching ranges and error profiles obtained with the Farnsworth-Munsell 100-hue test. The mean matching ranges and error scores for the 4 categories have a rank order but there is considerable overlap between the individual results in Grades 1 and 2 and Grades 3 and 4. In particular, the H16 is not failed exclusively by dichromats. These data show that the 2-category system of severity based on pass or fail of the Farnsworth D15 is strongly based and is the optimum that can be applied clinically.
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Acquired tritanopia in diabetic maculopathy
Documenta Ophthalmologica Proceedings Series, 1997Co-Authors: J BirchAbstract:Ten patients with diabetic maculopathy and VA of 6/12 or better (20 eyes) were examined with a battery of Colour vision tests consisting of pseudoischromatic plates, the Farnsworth D15, the Farnsworth-Munsell 100-hue test (FM 100-hue) and a modified TNO test. Severe tritan defects were diagnosed by the Birch tritan plates in all 20 eyes and by the D15 test in 18 eyes. Acquired type 3 dichromatism (tritanopia) was confirmed by the TNO test in 17 eyes. Six patients (12 eyes) failed to interpret red-green screening plates in the Ishihara test. FM 100-hue error scores were generally very high and a tritan axis of confusion could be discerned in only 5 plots by inspection. Further analysis in terms of Colour difference vectors, angle and S index, failed to identify significant polarity. It is concluded that red-green deficits occur in type 3 dichromatism, which results in poor overall hue discrimination. Other clinical tests are therefore recommended to diagnose the type of acquired Colour Deficiency when FM 100-hue error scores are very large.
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Colour Vision Requirements of Firefighters
Occupational Medicine, 1996Co-Authors: Thomas Hengist Margrain, J Birch, Christopher G. OwenAbstract:To perform their job safely firefighters must be able to identify Colours on industrial gas cylinders, portable fire extinguishers, road traffic signals and several pieces of firefighting equipment. Although good Colour vision is necessary we believe that the existing Colour vision standard, which bars entry to the fire service to applicants who fail more than two plates of the Ishihara test, is unnecessarily stringent. We have identified and quantified the Colour coded information encountered by firefighters. Colours were plotted on the CIE chromaticity diagram (1931) and isochromatic zones, which document the Colour confusions of Colour deficient observers, superimposed. This novel technique established possible Colour confusions in different types of Colour Deficiency. Analysis of the results showed that red/green dichromats (protanopes and deuteranopes), severe deuteranomalous trichromats who fail the Farnsworth D15 test, and protanomalous trichromats are unsuitable for firefighting work. However, people with slight deuteranomalous trichromatism who pass the D15 test, are not disadvantaged and can be employed safely as firefighters. A new Colour vision standard and a new testing procedure is recommended.
John D. Mollon - One of the best experts on this subject based on the ideXlab platform.
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Sons and mothers: classification of Colour-deficient and heterozygous subjects by counterphase modulation photometry
Documenta Ophthalmologica Proceedings Series, 1997Co-Authors: G. Jordan, John D. MollonAbstract:In the OSCAR test of Estavez et al (1983) red and green lights are modulated in counterphase and the subject is asked to adjust their relative depths of modulation so as to minimize flicker. In a population consisting of normal mothers and carriers of Colour Deficiency (classified by their sons’ performance on the Nagel anomaloscope), the OSCAR settings of the mothers were strongly correlated with those of their sons. Protan and deutan carriers formed discrete populations; and many individual carriers of protan deficiencies could be distinguished from normals with confidence. Protan and deutan sons were distinguished from each other with complete reliability, but some deutan sons, and most deutan carriers, fell within the distribution of normal settings.
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A Study of Women Heterozygous for Colour
1993Co-Authors: Deficiencies Jordan, John D. MollonAbstract:We have examined the Colour vision of 43 female subjects in the age range 30-59 yr of whom 31 were obligate carriers of various forms of Colour Deficiency and the rest were women who had no known Colour-deficient relatives. In the case of all the carriers we established the phenotypes of their Colourdeficient sons. As a group, carriers made significantly more errors on the Ishihara plates and showed enlarged matching ranges on the Nagel anomaloscope, but we could not replicate earlier reports of increased error scores on the Farnswo~Mu~ll 100-Hue test or of systematic shifts in Rayleigh match mid-points. We did find that the Colour matches of carriers of deuteranomaly were significantly displaced from those of normals in a ratio-matching task in which a mixture of 546 and 600 nm was matched with a mixture of 570 and 690 nm. Owing to X-chromosome inactivation, women who are heterozygous for anomalous trichromacy ought to have at least four types of cone in their retinae and we ask whether thii affords them an extra dime~ion of Colour vision, by analogy to New World monkeys where ~te~zygous females gain triehromacy in a basically dichromatic species. Many carriers of anomalous trichromacy exhibited no evidence for tetrachromacy, in that they accepted large-field Rayleigh matches following a rod bleach and they were unable to set unique matches in our ratio-matching task. However, eight carriers of anomalous trichromacy-and no other subject-refused large-field Rayleigh matches; and we found one carrier of deuteranomaly who was apparently able to make unique matches in the ratio-matching task.
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A study of women heterozygous for Colour deficiencies
Vision Research, 1993Co-Authors: G. Jordan, John D. MollonAbstract:Abstract We have examined the Colour vision of 43 female subjects in the age range 30–59 yr of whom 31 were obligate carriers of various forms of Colour Deficiency and the rest were women who had no known Colour-deficient relatives. In the case of all the carriers we established the phenotypes of their Colour-deficient sons. As a group, carriers made significantly more errors on the Ishihara plates and showed enlarged matching ranges on the Nagel anomaloscope, but we could not replicate earlier reports of increased error scores on the Farnsworth-Munsell 100-Hue test or of systematic shifts in Rayleigh match mid-points. We did find that the Colour matches of carriers of deuteranomaly were significantly displaced from those of normals in a ratio-matching task in which a mixture of 546 and 600 nm was matched with a mixture of 570 and 690 nm. Owing to X-chromosome inactivation, women who are heterozygous for anomalous trichromacy ought to have at least four types of cone in their retinae and we ask whether this affords them an extra dimension of Colour vision, by analogy to New World monkeys where heterozygous females gain trichromacy in a basically dichromatic species. Many carriers of anomalous trichromacy exhibited no evidence for tetrachromacy, in that they accepted large-field Rayleigh matches following a rod bleach and they were unable to set unique matches in our ratio-matching task. However, eight carriers of anomalous trichromacy—and no other subject—refused large-field Rayleigh matches; and we found one carrier of deuteranomaly who was apparently able to make unique matches in the ratio-matching task.
M. Rodriguez-carmona - One of the best experts on this subject based on the ideXlab platform.
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Occupational Colour vision needs with emphasis on aviation
2020Co-Authors: John L. Barbur, M. Rodriguez-carmonaAbstract:The novel experiments and tests developed for this study yield new data that describe how combinations of luminance contrast and Red / Green (RG) and Yellow / Blue (YB) Colour signals affect task completion times (TCT) and the overall accuracy the operator can achieve. With appropriate design and choice of Colours, it is possible for deutan applicants with thresholds < 4 standard normal CAD units to perform as well as normal trichromats when suprathreshold Colours with RG and YB components are employed in visual displays. As many as 22% of deuteranomalous subjects can be included in this category. In spite of their congenital Colour Deficiency, such applicants can operate safely in the Air Traffic Control (ATC) environment as well as in many other occupations that involve the use of large-field, visual displays.
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Colour assessment outcomes – a new approach to grading the severity of color vision loss
2020Co-Authors: M. Rodriguez-carmona, John L. BarburAbstract:INTRODUCTION: Recent studies have shown that a significant percentage of subjects with anomalous, congenital trichromacy can perform the suprathreshold, Colour-related tasks encountered in many occupations with the same accuracy as normal trichromats. In the absence of detailed, occupation-specific studies, an alternative approach is to make use of new findings and the statistical outcomes of past practices that have been considered safe to produce graded, justifiable categories of Colour vision that can be enforced. METHODS: We analyzed traditional color assessment outcomes and measured severity of Colour vision loss using the CAD test in 1363 subjects (336 normals, 705 deutan, 319 protan and 3 tritan). The severity of Colour vision loss was measured in each subject and statistical, pass / fail outcomes established for each of the most commonly used, conventional Colour assessment tests and protocols. RESULTS: The correlation between the number of Ishihara (IH) test plates subjects fail and the severity of RG Colour vision loss was very poor. The 38 plates IH test has high sensitivity when no errors are allowed (i.e., only 0.71% deutans and 0.63% protans pass). Protocols based on zero errors are uncommon since 18.15% of normal trichromats fail. The most common protocols employ either the 24 or the 14 plates editions with two or less errors. These protocols pass almost all normal trichromats, but the deutans and some protans that also pass (when two or less errors are allowed) can be severely deficient. This is simply because the most challenging plates have not been included in the 24 and 14 plates editions. As a result, normals no longer fail, but the deutans and protans that pass have more severe loss of Colour vision since they fail less challenging plates. The severity of Colour vision loss was measured in each subject and statistical, pass / fail outcomes established for each of the most commonly used, conventional Colour assessment tests and protocols. DISCUSSION: Historical evidence and new findings that relate severity of loss to the effective use of Colour signals in a number of tasks provide the basis for a new Colour grading system based on six categories. A single Colour assessment test is needed to establish the applicant’s Colour Vision category which can range from ‘supernormal’ (CV0), for the most stringent, Colour-demanding tasks, to ‘severe Colour Deficiency’, when red / green Colour vision is either absent or extremely weak (CV5).
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Colour vision requirements in visually demanding occupations.
British Medical Bulletin, 2017Co-Authors: John L. Barbur, M. Rodriguez-carmonaAbstract:Normal trichromatic Colour vision (CV) is often required as a condition for employment in visually demanding occupations. If this requirement could be enforced using current, Colour assessment tests, a significant percentage of subjects with anomalous, congenital trichromacy who can perform the suprathreshold, Colour-related tasks encountered in many occupations with the same accuracy as normal trichromats would fail. These applicants would therefore be discriminated against unfairly. One solution to this problem is to produce minimum, justifiable CV requirements that are specific to each occupation. This has been done successfully for commercial aviation (i.e. the flight crew) and for Transport for London train drivers. An alternative approach is to make use of new findings and the statistical outcomes of past practices to produce graded, justifiable CV categories that can be enforced. To achieve this aim, we analysed Colour assessment outcomes and quantified severity of CV loss in 1363 subjects. The severity of CV loss was measured in each subject and statistical, pass/fail outcomes established for each of the most commonly used, conventional Colour assessment tests and protocols. This evidence and new findings that relate severity of loss to the effective use of Colour signals in a number of tasks provide the basis for a new Colour grading system based on six categories. A single Colour assessment test is needed to establish the applicant's CV category which can range from 'supernormal', for the most stringent, Colour-demanding tasks, to 'severe Colour Deficiency', when red/green CV is either absent or extremely weak.
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Variability in normal and defective Colour vision: Consequences for occupational environments
Colour Design, 2014Co-Authors: M. Rodriguez-carmona, John L. BarburAbstract:Abstract New findings in relation to both normal and defective Colour vision provide improved understanding of chromatic mechanisms in human vision and account for much of the variability observed in both normal trichromats and in subjects with congenital Colour Deficiency. The principal methods for assessing Colour vision and the techniques employed to isolate the use of Colour signals are reviewed. Data on the continuous distribution of Colour thresholds within deutan and protan observers and the variability within normal trichromatic Colour vision are presented and the principal factors that contribute to this variability examined. The need to quantify the severity of Colour vision loss and to classify accurately the subject's Colour vision is examined in relation to Colour assessment requirements in occupational environments. A method of establishing pass/fail limits that are functionally safe without disadvantaging subjects with congenital Colour Deficiency is described. Also discussed are the uses of novel Colour tests to reveal acquired loss of chromatic sensitivity as an indication of early-stage diseases of the eye as well as the value such tests may have in early detection and subsequent treatment.