Errors reading the Ishihara pseudoisochromatic plates made by observers with normal colour vision

Background: Ishihara pseudoisochromatic plates are one of the best screening tools for red‐green colour vision deficiencies. Although a majority of persons with normal colour vision read all plates correctly, a significant proportion makes mistakes. The purpose of this study was to obtain results for normal trichromats reading the Ishihara plates and analyse the misreading responses to seek clinical implications. Methods: A sample of 249 (161 female) was tested with the Ishihara pseudoisochromatic plates. The number and nature of errors were recorded and typical errors, those that observers with abnormal colour vision were expected to make, were distinguished from other kinds of error. Results: Out of 249 normal trichromats, 111 individuals (45 per cent) misread at least one plate. Females made up to six total errors and males up to five total errors. When only typical errors were counted, all the normal trichromats made two or fewer errors. There was no significant gender difference for either total or typical errors. Conclusion: It is suggested that clinicians count only typical errors when administering the Ishihara test. Using a criterion of no more than two typical errors for a diagnosis of normal colour vision could improve the specificity and sensitivity of the test.     

Normality of colour vision in a compound heterozygous female carrying protan and deutan defects

Background: Inherited red‐green colour vision defects are quite common, affecting one in 12 males, but are less common in women, affecting about one in 250. Because red‐green defects are X‐linked, nearly 15 per cent of females are heterozygous carriers of red‐green colour deficiency. In addition, about one in 150 females are ‘double carriers’, where both of their X chromosomes have L/M gene arrays encoding a red‐green defect. If a woman carries the same type of colour vision defect on each X‐chromosome, she will be red‐green colour deficient, whereas if she carries opposing defects (protan versus deutan) on each X chromosome, she will have normal colour vision, owing to the process of X‐inactivation. These women are referred to as compound heterozygotes, though very few have been reported. Questions remain about whether the colour vision capacity of these women is comparable to that of ‘normal’ trichromats. Methods: We examined a compound heterozygote carrier of both protanopia and deuteranomaly. We also examined male members of her family representing both forms of red‐green defect carried by the female proband. Complete colour vision testing was done, including Rayleigh matches, pseudoisochromatic plates, unique hue measurements and 100‐Hue tests. Flicker‐photometric ERG estimates of L : M cone ratio were obtained, as were Medmont C100 settings. Results: Genetic analyses provided direct confirmation of compound heterozygosity. The compound heterozygote showed Schmidt's sign, consistent with an extreme skew in her L : M cone ratio and usually associated with protan carrier status. Conclusion: Apart from Schmidt's sign, we found the colour vision of the compound heterozygote to be indistinguishable from that of a normal trichromat.     

Survey of the accuracy of new pseudoisochromatic plates

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.     

Detection of functional vision loss using the Ishihara plates

Many techniques have been described for the detection of functional visual loss. We report four cases in which Ishihara pseudo-isochromatic colour plates gave objective evidence of functional vision loss. In all cases the patients were able to read the first test pattern (No. 12), but could not distinguish any of the following pseudo-isochromatic numbers (plates 2–17). However, they experienced no difficulty in tracing the winding lines (plates 18–24), demonstrating that they in fact had normal colour vision.     

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

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.     

Use of the Farnsworth—Munsell 100-Hue test in the examination of congenital colour vision defects

Results for the Farnsworth-Munsell 100-Hue test are reported for 238 male subjects with congenital colour vision defects (47 protanopes, 17 protanomalous trichromats, 57 deuteranopes and 117 deuteranomalous trichromats). The results are analysed in terms of the error score and the presence of an axis of confusion. A wide range of results is obtained in each diagnostic group and the error score cannot be used to distinguish between dichromats and anomalous trichromats. Approximately 50% of subjects with anomalous trichromatism obtain error scores less than 100 without an axis of confusion. These subjects could be mistakenly identified as having normal colour vision if pseudoisochromatic and colour matching tests are not employed. The prime use of the F-M 100 Hue test is in vocational guidance.     

The new Richmond HRR pseudoisochromatic test for colour vision is better than the Ishihara test

Aim: The Hardy‐Rand‐Rittler (HRR) pseudoisochromatic test for colour vision is highly regarded but has long been out of print. Richmond Products produced a new edition in 2002 that has been re‐engineered to rectify shortcomings of the original test. This study is a validation trial of the new test using a larger sample and different criteria of evaluation from those of the previously reported validation study. Methods: The Richmond HRR test was given to 100 consecutively presenting patients with abnormal colour vision and 50 patients with normal colour vision. Colour vision was diagnosed using the Ishihara test, the Farnsworth D15 test, the Medmont C‐100 test and the Type 1 Nagel anomaloscope. Results: The Richmond HRR test has a sensitivity of 1.00 and a specificity of 0.975 when the criterion for failing is two or more errors with the screening plates. Sensitivity and specificity become 0.98 and 1.0, respectively, when the fail criterion is three or more errors. Those with red‐green colour vision deficiency were correctly classified as protan or deutan on 86 per cent of occasions, with 11 per cent unclassified and three per cent incorrectly classified. All those graded as having a ‘mild’ defect by the Richmond HRR test passed the Farnsworth D15 test and had an anomaloscope range of 30 or less. Not all dichromats were classified as ‘strong’, which was one of the goals of the re‐engineering and those graded as ‘medium’ and ‘strong’ included dichromats and those who have a mild colour vision deficiency based on the results of the Farnsworth D15 test and the anomaloscope range. Conclusions: The test is as good as the Ishihara test for detection of the red‐green colour vision deficiencies but unlike the Ishihara, also has plates for the detection of the tritan defects. Its classification of protans and deutans is useful but the Medmont C‐100 test is better. Those graded as ‘mild’ by the Richmond HRR test can be regarded as having a mild colour vision defect but a ‘medium’ or ‘strong’ grading needs to be interpreted in conjunction with other tests such as the Farnsworth D15 and the anomaloscope. The Richmond HRR test could be the test of choice for clinicians who wish to use a single test for colour vision.     

Comparison of Ishihara and Hardy-Rand-Rittler Pseudoisochromatic Plates in Non-Arteritic Anterior Ischaemic Optic Neuropathy

Pseudoisochromatic plates, such as Ishihara and Hardy-Rand-Rittler (HRR) tests, are designed as screening tools to test colour vision defects. The tests are often designed to detect congenital red-green colour blindness and their measurement properties for acquired optic neuropathies are not known. The aim of this study is to determine the sensitivity and specificity of Ishihara and HRR pseudoisochromatic plates in detecting dyschromatopsia in patients with unilateral non-arteritic anterior ischaemic optic neuropathy. Nineteen such patients were tested using Ishihara and the HRR plates in the affected and the unaffected (control) eye. The results were correlated to that on an anomaloscope (Oculus HMC Anomaloskop MR^®). Mild deuteranomaly was the dyschromatopsia detected by an anomaloscope in the affected eye of the patients. The sensitivity and specificity of the Ishihara test in the affected eyes are 75% and 40%, respectively. The sensitivity and specificity of the HRR test in eyes affected with non-arteritic anterior ischaemic optic neuropathy are 100% and 20%, respectively. It is concluded that the anomaloscope that was considered the “gold standard” has several limitations and may not detect all acquired dyschromatopia. On the other hand, whilst it is correct that pseudoisochromatic plates are screening tests and the results must be correlated with other optic nerve functions, the HRR test has a higher sensitivity and specificity than Ishihara colour plates in detecting dyschromatopsia in non-arteritic anterior ischaemic optic neuropathy eyes.     

Is screening for congenital colour vision deficiency in school students worthwhile? A review a

This review analyses the literature on screening for congenital colour vision deficiency in school students, which predominantly uses the Ishihara test. The review was framed with respect to the established Wilson and Jungner criteria for screening programs. These criteria relate to the characteristics of the condition concerned, the performance of the screening test, the existence of treatment options and the performance of screening programs. The literature reviewed suggests that congenital colour vision deficiency has not been shown to increase risk of road traffic crashes and is not a preclusion to driver licensing in most developed countries. The occurrence of congenital colour vision deficiency has been used to limit entry into certain occupations; however, the value of screening school students with regard to occupational preclusion is questionable. Stronger evidence exists indicating no association between congenital colour vision deficiency and level of educational achievement. Studies showing any association between congenital colour vision deficiency and other health and lifestyle impacts were rare. The most commonly used screening test (using Ishihara pseudoisochromatic plates) performs well with respect to detecting red‐green colour vision deficiencies. Finally, the only interventions we identified for congenital colour vision deficiency were management ones around the availability of specific tinted lenses and computer programs to aid colour perception in certain tasks. Given this picture, the weight of evidence appears to be in favour of not adopting (or discontinuing) routine colour vision screening programs for school students; however, it may be worthwhile for a career advisor to refer school students to an optometrist or ophthalmologist for colour vision screening, upon expression of interest in an occupation where normal colour vision is either particularly desirable or is a regulatory requirement.     

Binocular function after surgical treatment of infantile esotropia

The Eye Handbook (EHB) is the most frequently downloaded smartphone application with diagnostic tools for eye-care providers. However, limited data exists validating the EHB test to gold standard colour vision testing. EHB and Ishihara colour vision tests were evaluated and compared under simulated colour vision loss through use of image processing software. Images of both tests were processed through ImageJ to 32 bit-grey scale and blue channel under split RBG channel to model total colour vision loss and red-green (R-G) deficiency, respectively. Two colour plates differentiated R-G deficiency from total colour blindness in EHB compared with eight Ishihara plates. Without colour information, correct numerals were identified in 3.5/15 EHB plates converted to 32-bit greyscale, versus 1/16 in Ishihara. We conclude EHB may underestimate colour vision loss severity in persons with normal contrast sensitivity compared to Ishihara. Eye-care providers need to be aware of the potential inconsistency compared to standardised methods, including limitations in differentiating patients with R-G colour deficiencies from total colour blindness.     

A new test for screening color vision: concurrent validity and utility

Recognizing the need for an effective test for screening color vision in young children, we have developed a new pseudoisochromatic (PIC) plate test which is useful for a wide variety of observers at different ages. The test consists of four plates and responses can be used to categorize color vision as normal or as either red-green or blue-yellow defective. Results of this validation study with adults, both color normal and red-green defective, show a high degree of correlation between the new test and the Nagel anomaloscope: there were no false positives and only a few false negatives, which occurred with mild deuteranomalous observers. The validity of the test compares favorably to the Ishihara, F-2, and the AO-HRR screening plates. Results with toddlers (3 to 6 years) indicate that the task demands of the test are well suited for testing young children. The percentage of color defectives identified in the toddler sample using the new test is closer to the adult prevalence than results obtained with the F-2 and AO-HRR screening plates, which gave dramatically higher failure rates. The new test is culture-free and can be administered rapidly to both verbal and nonverbal observers using pointing or preferential looking.     

The C-100:a new dichotomiser of colour vision defectives

This paper evaluates a new instrument (C-100) which employs flicker photometry or silent substitution to determine the type of colour vision defect (protan or deutan). Specifically, this study addresses the unit's capacity to: 1. detect colour vision defects; 2. differentiate protans from deutans; and 3. produce reliable measurements under different viewing conditions. We find that an average of five readings enables protans to be clearly separated from deutans in all cases (p < 0.0001), but that the distinction between these groups and normals is less clear. Dichromats are not distinguished from anomalous trichromats, so the instrument cannot be used as an index of severity. The results are shown to be robust to most of the test conditions likely to be encountered during normal clinical use. A clinical protocol is suggested that utilises the C-100 for classification of colour defective observers. It is concluded that normal, and some anomalous, trichromat settings are performed using flicker photometry, whereas dichromatic observers appear to utilise silent substitution.     

Velhagen Pflügertrident pseudoisochromatic plates in screening congenital red-green vision defects

Red-green colour vision defects were screened in a group of 425 trade school students using Velhagen Pflügertrident pseudoisochromatic plates. Thereafter, the students were examined with the Nagel anomaloscope. Of the 425 students, 31 (7.3%) were found to be colour defectives. Deuteranomalous defects were found in 4.9% of cases; deuteranopic defects, in 0.2%; and protanomalous defects, in 2.1%. There were no protanopic 1 students in the study group. The Velhagen plates found 19 of the 31 defectives (sensitivity, 61.3%); none of the students with normal colour vision were suspected of being colour defectives (specificity, 100%). The sensitivity of the Velhagen plates is not as high as that of other pseudoisochromatic tests. However, the Velhagen Pflugertrident test is easy to use when screening of preschool-aged children is needed.

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Velhagen Pflügertrident pseudoisochromatic plates in screening congenital red-green vision defects

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This study was supported by Finnish Eye Foundation

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Offprint requests to: M. Mantyjärvi     

Orienteers with poor colour vision require more than cunning running

Background: Highly detailed colour coded maps are used in the sport of orienteering to enable competitors to navigate from one check point to another and to provide guidance on the nature of the terrain to be traversed. The colours are defined by the International Orienteering Foundation (IOF) and are said to have been chosen so they will not be confused by competitors who have abnormal colour vision. However, there are anecdotal reports that individuals with colour vision defects do have problems with the colour coding. Method: A Minolta Spectrophotometer CM‐503i was used to measure the CIE x,y chromaticity co‐ordinates and the reflectances of the standard colours recommended by the IOF for the colour coding of orienteering maps, as well as the colours on two maps used in orienteering events. Results: Four pairs of IOF standard colours are likely to be confused by protan observers and four pairs by deutan observers. There were three pairs of colours likely to be confused by both deutan and protan observers on one of the competition maps and one pair likely to be confused by protan observers on the other map. Some of the colours on the actual competition maps differed noticeably from the standard IOF colours. Discussion: Orienteers with more severe forms of abnormal colour vision are likely to be disadvantaged by their inability to differentiate some colours used on orienteering maps. The IOF should choose different colours that are less likely to be confused or should employ a redundant code (such as a pattern or texture). There is need for better quality control of the colours of competition maps to ensure they do conform to the IOF standard colours.     

计算机控制的Ishihara色觉测试法

目的:研究经计算机控制的Ishihara测试法诊断色盲的可靠性及其与经典Ishihara测试法的一致性,计算机控制的Ishihara测试法的敏感性与特异性;并探讨该测试方法在检测先天性色盲或色弱中的潜在价值。方法:用两种方法测试104名大学生的色觉,年龄20～23岁(中位数21岁)。分别采用经计算机控制的Ishihara色板和经典的Ishihara打印色板显露法对个体色觉进行检查。通过上述两种不同的方法评价每个学生对颜色的感知能力,借此探讨计算机控制的Ishihara测试法的特异性,准确性以及与经典法的一致性。结果:本实验共检测到6位男性色盲患者和1位女性色盲患者。调查该女性学生的家族史,发现其母亲为色盲基因携带者,而其父亲为色盲患者。本实验中男性色盲患病率为13.6%(6/44),女性为1.7%(1/60);整个人群总的患病率为6.7%(7/104)。进行本试验前,这些学生并未意识到自己存在色觉功能缺陷。为探讨这两种方法的一致性,分别对色觉正常和患色盲的学生的测试结果进行比较。结果表明:两种实验方法的特异性及敏感性均为100%,一致性达到100%。结论:计算机控制的Ishihara测试法是数字调控性的,但有关色觉测试的基本概念没有改变。该法总的测试时间和误差计分都已标准化,与手动测试法相比有明显的优势;而且该法与被认为是"金标准"的经典测试法的一致性达到100%。这些特征表明,计算机控制的Ishihara测试法是一种新颖和可靠的方法。     

Screening for congenital colour vision defects

A prospective comparison between the Ohkuma¹ and Ishihara² pseudoisochromatic (PIC) plates was carried out in a group of 400 patients attending a general ophthalmology practice. The sensitivity of the Ohkuma test was compared to the Ishihara test, and the specificity of both was determined by reference to anomaloscopy as a gold standard.
Both tests correctly identified the same group of 24 patients as having a red/green confusion axis, and the Ohkuma test was equally as sensitive as the Ishihara. The grading plates in both tests are unreliable, but the Ohkuma test is quicker, easier to administer, gives less ambiguous responses and has a clearer cut-off score for abnormality. On the basis of this experience the Ohkuma test is recommended as more appropriate for routine colour vision screening than either the 24 or 38 plate Ishihara tests.     

Experimental study of the individual differences in chromatic perception through blue‐yellow metameric matches of a white‐light continuum

A metameric colour matching test was designed to study inter‐observer variability. Blue‐yellow metameric matching to a white‐light continuum was used to define the optimal wavelengths at which each of eight non‐colour‐defective observers achieved a match. The tests involved chromatic stimuli on a 2° bipartite field, with a white‐light continuum presented on the left half, and a mixture of two monochromatic stimuli on the right half. The luminance of these chromatic stimuli was adjusted by the researcher using a staircase method, with the observer providing feedback about the similarity in luminance and chromaticity between the two halves of the field. Two series were performed for each observer, using different fixed yellow wavelengths. Since for each fixed yellow wavelength the match with the target white can be achieved by only one corresponding blue wavelength which is particular for each observer, the initial blue wavelengths were approximations based on the 2° CIE 1931 standard observer. Once the observers had attained an achromatic match, they modified the blue wavelength to achieve a perfect match of both halves. Generally, the observers found this modification of the blue wavelength necessary to achieve the metameric match. Each observer had a particular optimal blue wavelength which differed between the two series. The differences between the deviations from the standard observer for the two series were constant in value among the observers.     

Jan Lovie‐Kitchin

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.     

Spatio-temporal selectivity of loss of colour and luminance contrast sensitivity with multiple sclerosis and optic neuritis

Colour and luminance-contrast thresholds were measured in the presence of dynamic Random Luminance-contrast Masking (RLM) in individuals who had had past diagnoses of optic neuritis (ON) some of whom have progressed to a diagnosis of multiple sclerosis (MS). To explore the spatio-temporal selectivity of chromatic and luminance losses in MS/ON, thresholds were measured using three different sizes and modulation rates of the RLM displays: small checks modulating slowly, medium-sized checks with moderate modulation and large checks modulating rapidly. The colour of the chromatic stimuli used were specified in a cone-excitation space to measure relative impairments in red-green and blue-yellow chromatic channels. These observers showed chromatic thresholds along the L/(L+M) axis that were higher than those along the S-cone axis for all display sizes/modulation rates and both red-green and blue-yellow colour thresholds were higher than luminance-contrast thresholds. The principal change in thresholds with spatio-temporal changes in the display was a reduction in thresholds for L/(L+M) and S-cones with increasing check size and modulation rate. However, luminance contrast thresholds did not change with display size/rate. These results are consistent with MS/ON selectively affecting processing in colour pathways rather than in the magnocellular pathway, and that within the colour pathways neurones with opposed L- and M-cone inputs are more damaged than colour-opponent neurons with input from S-cones.     

Screening of colour vision defects in diabetic patients

The colour vision of 50 diabetic patients was examined with two screening tests, Standard Pseudoisochromatic Plates part 2 (SPP 2) and Farnsworth Panel D 15 (Panel D 15) test and with two diagnostic tests, Nagel anomaloscope and Farnsworth-Munsell 100-hue test. The performance of the diabetic patients in colour vision tests was compared to their performance in colour dependent urine and blood glucose tests. Fourteen of the patients failed the glucose tests, and they failed both of the screening tests as well. The diagnostic tests showed that all of them had a blue-yellow defect and 10 of them also had a red-green defect. The rest of the patients, 36, read the glucose tests correctly, but 17 of them failed the SPP 2 screening test, and 5 failed the Panel D 15 screening test. In diagnostic tests there were 15 patients with normal colour vision, one patient with a red-green defect, 13 patients with a blue-yellow defect, and 7 patients with both a red-green and a blue-yellow defect. The colour vision defect in diabetic patients is most often a blue-yellow defect or a combined blue-yellow and red-green defect. Therefore, the usual pseudoisochromatic plates, e.g. the Ishihara test, are not sufficient in screening because they screen only red-green defects. The screening tests should contain both a red-green and a blue-yellow part.(ABSTRACT TRUNCATED AT 250 WORDS)