Anomaloscope Research Articles

Color vision assessment‐2: Color assessment outcomes using single and multi‐test protocols

AbstractThe main purpose of this study was to produce reliable, color assessment outcomes to examine the extent to which single and multi‐test protocols in use meet current clinical and occupational needs. The latter include the detection of small changes in chromatic sensitivity as the earliest signs of retinal and/or systemic disease, and the need to assess the class of color vision in congenital deficiency and to quantify severity of loss. Color vision was assessed using Ishihara (IH), Farnsworth Munsell D‐15, City University (CU, 2nd ed.) and Holmes‐Wright type A (HW‐A) lantern tests. All subjects also carried out Colour Assessment and Diagnosis and Nagel anomaloscope tests. The sample included 350 normal trichromats, 1012 deutans and 465 protans (age 31.1 ± 12.4, range 10‐65 years). The results reveal the trade‐off between sensitivity and specificity, depending on the number of errors accepted as a pass on the IH test. The D‐15 and CU tests pass all normals and almost 50% of subjects with color vision deficiency. The HW‐A lantern passes all normals, 22% of deutans and 1% of protans. The multi‐test protocols designed to identify protans and to pass only subjects with mild color loss, pass over 50% of protans and deutans. Many of the subjects who fail exhibit less severe loss of color vision than others who pass. When high sensitivity for detection of congenital deficiency is achieved, single‐test protocols fail many normal trichromats. Multi‐test protocols produce large variability and fail to achieve desired aims.

Color vision assessment‐1: Visual signals that affect the results of the Farnsworth D‐15 test

AbstractThe Farnsworth D‐15 test (D‐15) is commonly used to screen for moderate to severe congenital color vision deficiency. The aim of this study was to establish reliable D‐15 statistics for normal, deutan and protan subjects, and to investigate the different visual signals one can use to carry out the test, even in dichromats and rod monochromats. Six hundred and seventy‐four subjects were examined using the D‐15, the Colour Assessment and Diagnosis test and the Nagel anomaloscope. A rod monochromat and five dichromats were tested using the standard D‐15 protocol before the caps were separated into two groups and subjects were asked to repeat the task. D‐15 spectral radiance data, measured under D65 illumination, were used to estimate differences in photoreceptor excitations for each of the caps. When no crossings and up to two adjacent transpositions on the D‐15 results diagram are accepted as a pass, 100% of normal trichromats, 54% of deutans and 43% of protans pass the D‐15. A rod monochromat and two protanopes and deuteranopes were able to complete the D‐15 when the caps were separated into two groups, despite severe loss or even complete absence of color vision. When up to two adjacent transpositions are accepted 50% of color deficient subjects, some with severe red/green loss, pass the D‐15. While the D‐15 is normally used to screen for moderate to severe color deficiency, subjects with severe loss can still use combined, residual red/green, yellow/blue and luminance signals to pass.

Cone mosaic characteristics in red-green colour deficiency: a comparative study

ObjectiveTo compare photoreceptor cone characteristics using adaptive optics (AO) technology between congenital colour blind patients and healthy age-matched controls. DesignCross-sectional. Participants21 eyes (21 cases) with congenital red-green colour blindness and 21 eyes of age-matched controls (21 controls), all having a best-corrected visual acuity of 20/20 and normal ophthalmological examination, were recruited. MethodsColour vision testing was done using the Farnsworth–Munsell 100-Hue test and Nagel anomaloscope. Imaging of fovea was done using rtx1 AO retinal camera with a sampling window size of 4° × 4°. Peak cone density, intercone spacing, cone regularity, and cone dispersion were determined using AOdetect Mosaic software. ResultsOverall, mean cone characteristics at 2° off fixation in cases and controls, respectively, were density 26 587 ± 1328/26 448 ± 687 cells/mm2 (p = 0.67), spacing 6.69 ± 0.17/6.75 ± 0.11 μm (p = 0.19), regularity 94.36 ± 2.56/94.83 ± 1.28% (p = 0.46), dispersion 10.22 ± 1.21/11.68 ± 0.79% (p = 0.0001), and hexagonality 50.62 ± 4.21/49.52 ± 2.45% (p = 0.31). No significant difference was noted in various cone metrics except dispersion, which was markedly decreased in colour-deficient individuals. At 4° off fixation, the cone characteristics were not significantly different between cases and controls: density 16 521 ± 1230/16 930 ± 678 cells/mm2 (p = 0.37), spacing 8.60 ± 0.29/8.46 ± 0.17 μm (p = 0.19), regularity 92.68 ± 2.83/92.6 ± 3.05% (p = 0.95), dispersion 13.43 ± 3.48/13.65 ± 2.38% (p = 0.87), and hexagonality 45.22 ± 3.8/45.21 ± 5.5% (p = 0.99). A significant reduction in cone density, regularity, and hexagonality was associated with corresponding increase in spacing and dispersion as we moved from 2° to 4° off fixation in both cases and controls. ConclusionCone photoreceptor characteristics are anatomically well preserved in young colour-deficient individuals except cone dispersion.

A Comparison of Nagel Anomaloscope and Farnsworth Munsel 100-hue in Congenital Color Vision Deficiency

A Comparison of Nagel Anomaloscope and Farnsworth Munsel 100-hue in Congenital Color Vision Deficiency

Color Vision Tests in Pilots' Medical Assessments.

The aim of this study was to evaluate the ability of eight color vision tests to screen for and accurately measure hereditary color-deficiency in order to improve color vision assessment methods for aircraft pilots. This prospective study included 29 color-deficient subjects and 23 healthy subjects. All performed the following tests: Ishihara plates, Farnsworth D15, Lanthony desaturated 15 Hue, Munsell 100 Hue, Beyne and Fletcher-Evans CAM lanterns, Nagel anomaloscope, and the Color Assessment and Diagnosis (CAD) test. The sensitivity and specificity of color-deficiency diagnosis were evaluated for each test, as well as the test's relevance for assessing aircraft pilots. The Ishihara plate test demonstrated a sensitivity of 0.97 and a specificity of 1.00 for color-deficiency screening. The CAD test and anomaloscope showed both a sensitivity and specificity of 1.00. The Beyne lantern, Fletcher lantern, Farnsworth D15, and the Lanthony 15 Hue tests all showed a specificity of 1.00 and sensitivities of, respectively, 0.69, 0.97, 0.58, and 0.79. During aircraft pilot selection tests, the CAD test classified 10% of color-deficient subjects as safe to fly, the anomaloscope 17%, and the Beyne and Fletcher lantern tests, respectively, 31% and 3%. The discrepancy in results confirms that current color vision test protocols need to be reassessed. The CAD test could be an interesting alternative to the series of tests used to assess flight crew, but it seems more selective than current tests.Marechal M, Delbarre M, Tesson J, Lacambre C, Lefebvre H, Froussart-Maille F. Color vision tests in pilots' medical assessments. Aerosp Med Hum Perform. 2018; 89(8):737-743.

Test/retest and inter‐test agreement of color aptitude measures

AbstractThe color discrimination capacity of color vision normal observers can be assessed using color aptitude tests (CATs), although data on the test/retest reliability and inter‐test agreement of such tests using appropriate statistical measures is limited. In this study, 32 color vision normal observers twice performed each of five CATs, being the Farnsworth‐Munsell 100 hue test, HVC Color Vision Skills Test, inter‐Society Color Council Color Aptitude Test, the Nagel Anomaloscope (Nagel), and a custom designed two‐color discrimination test. Two methods of determining the Nagel matching range were used based on the initially accepted matching range or on repeated measures. The test/retest performance of each test was determined using the method outlined by Bland and Altman[Lancet 1986;1:307–310] and the inter‐test agreement was analyzed using the same method, after converting test scores into z score units. No test was found to have a significant systematic alteration in test performance between test and retest. Test/retest performance was generally poor, indicating that tests can only reliably classify observers into very broad performance bands. All tests failed to show inter‐test agreement, and our data indicate a primary reason for this: as test/retest performance is generally poor, inter‐test agreement must also be poor as no test can agree more with another test than it agrees with itself. © 2014 Wiley Periodicals, Inc. Col Res Appl, 40, 224–231, 2015

Predicting chromatic sensitivity in normal trichromats and in subjects with congenital deficiency

AbstractPurpose Differences between M‐ and L‐class variant pigments arise largely because amino acid substitutions in M‐class pigments contribute less to the corresponding shifts in spectral responsivity. Other factors such as the relative numbers of L and M cones, their optical density and the midpoint between their spectral peaks can also contribute to the subject’s overall, red/green (RG) chromatic sensitivity. The purpose of this study was to examine how these differences affect chromatic sensitivity in normal trichromats and in subjects with deutan‐ and protan‐like deficiency.Methods RG thresholds were measured in 269 deutans, 132 protans and 330 normal trichromats using the CAD test. The colour vision of every subject was also examined using the Nagel anomaloscope. Classification into normal, deutan and protan classes was based on the results obtained on CAD and anomaloscope tests.Results RG thresholds measured within each group were ranked in increasing order. Samples equal to the number of subjects within each group were taken from a single Gaussian distribution, in the case of normal trichromats, or from more than one distribution in the case of deutan and protan groups. The distribution parameters were optimised to predict the rank order of the measured RG thresholds in each group.Conclusion The rank order of thresholds measured in normal trichromats can be predicted by a single Gaussian distributions. Deutans produced the most complex rank order which could only be predicted adequately with a minimum of four Gaussians. In contrast, the rank order for the protan group was much simpler and could be predicted well with only two or at most three Gaussian distributions.

Processing of color signals in female carriers of color vision deficiency

The aim of this study was to assess the chromatic sensitivity of carriers of color deficiency, specifically in relation to dependence on retinal illuminance, and to reference these findings to the corresponding red-green (RG) thresholds measured in normal trichromatic males. Thirty-six carriers of congenital RG color deficiency and 26 normal trichromatic males participated in the study. The retinal illuminance was estimated by measuring the pupil diameter and the optical density of the lens and the macular pigment. Each subject's color vision was examined using the Color Assessment and Diagnosis (CAD) test, the Ishihara and American Optical pseudoisochromatic plates, and the Nagel anomaloscope. Carriers of deuteranopia (D) and deuteranomaly (DA) had higher RG thresholds than male trichromats (p < 0.05). When referenced to male trichromats, carriers of protanomaly (PA) needed 28% less color signal strength; carriers of D required ∼60% higher thresholds at mesopic light levels. Variation in the L:M ratio and hence the absolute M-cone density may be the principal factor underlying the poorer chromatic sensitivity of D carriers in the low photopic range. The increased sensitivity of PA carriers at lower light levels is consistent with the pooling of signals from the hybrid M' and the M cones and the subsequent stronger inhibition of the rods. The findings suggest that signals from hybrid photopigments may pool preferentially with the spectrally closest "normal" pigments.

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.

Chromatic VEP in colour deficient children

Abstract Purpose To compare chromatic VEP response to isoluminant red‐green stimulus in children with congenital red‐green colour deficiency with a control group of 30 children with normal colour vision. Methods 15 children (7‐18 years) with congenital colour vision deficiency (8 in deutan and 7 in protan axis) and 30 healthy children (7‐19 years) were included in the study. Colour vision was assessed with Ishihara plates, Nagel Anomaloscope, Mollon‐Reffin Minimalist test, Farnsworth‐Munsell D‐15 saturated and desaturated test and Farnsworth‐Munsell hue 100 test. VEP were recorded to isoluminant red‐green stimulus. The stimulus was a 7 deg large circle composed of horizontal sinusoidal gratings, with spatial frequency 2 cycles/deg and 90 % chromatic contrast. VEP were recorded from Oz (mid occipital) position. Children were tested binocularly. Latency and amplitude of positive (P) and negative (N) wave were measured and so was mean amplitude (N‐P wave). Results N wave was present in 24/30 children with normal colour vision (110 ± 25.1 ms; 9.7 ± 4.8 μV) and only in 1/15 child with colour vision deficiency (93 ms; 3.2 μV). P wave was present in 30/30 children with normal colour vision (138 ± 21.1 ms; 21.1 ± 13.5 μV) and in 13/15 children with colour vision deficiency (131.9 ± 6.1 ms; 19.4 ± 10.7 μV). In healthy children waveform changed from predominantly positive to negative wave with increasing age, whereas in colour deficient children no obvious waveform changes were observed. Conclusion VEP response to isoluminant chromatic stimulus showed different characteristics in children with congenital colour vision deficiency compared to children with normal colour vision. manca.tekavcic‐pompe@guest.arnes.si

Failure of concordance of the Farnsworth D15 test and the Nagel anomaloscope matching range in anomalous trichromatism

The Farnsworth D15 test (D15) was developed for use in occupational guidance. People with significant color deficiency, including all dichromats are expected to fail and people with slight color deficiency are expected to pass. Pass is a circular results diagram and fail an interlacing pattern with one or more red-green isochromatic errors (Farnsworth, 1947). The Nagel anomaloscope is a "gold standard" reference test for identifying and classifying red-green color deficiency. The matching range on the red/green mixture scale indicates the severity of the discrimination deficit. Pass/fail results for the D15 are presented for 107 protanomalous and 410 deuteranomalous trichromats and compared with the anomaloscope matching range. Thirty-six percent of the subjects examined failed the D15. Protanomalous trichromats are able to utilize perceived luminance contrast to obtain good results on the D15 but 42% of these subjects failed the D15 compared with 35% of deuteranomalous subjects. Failure of the D15 was clearly related to the Nagel matching range in deuteranomalous trichromatism but not in protanomalous trichromatism. For example, 84% of deuteranomalous subjects with matching ranges > 30 scale units failed the D15 but only 2% with matching ranges 15 scale units and 33% of subjects with matching ranges < 5 scale units were unsuccessful. Protanomalous trichromats with apparently minimal color deficiency are therefore shown to have poor practical hue discrimination ability as measured with this test.

Which color vision test should be used in progressive cone dystrophy?

Abstract Purpose: The early manifestation of progressive cone dystrophy (COD) can remain unrecognized due to the relatively normal macular appearance. Color vision testing can be very useful as a first diagnostic step. The many available color vision tests have different benefits and shortcomings. We aimed to identify which test would be preferred to use in a clinical setting as a first step towards diagnosis of COD. Methods: We compared patients (n=18) derived from the ophthalmogenetic unit of Erasmus Medical Center and University Medical Center Nijmegen, with various levels of cone dysfunction. Golden Standard for diagnosis of COD was a diminished photopic ERG and a relative central scotoma on Goldmann perimetry. Controls (n=33) were patients from these clinics with other diagnoses or healthy companions of COD patients. We estimated sensitivity and specificity of the Ishihara test, Lanthony Desaturated and Saturated Panel D15 test, the Hardy‐Rand‐Rittler (HRR) pseudo‐isochromatic plates, and the Nagel anomaloscope. We analyzed sensitivity, specificity and the predictive value with receiver operating characteristic curve (ROC). Results: The HRR test had the highest sensitivity and specificity for protan and deutan axes. HRR and Ishihara had the highest predictive value. Lanthony Panel D15 test did not have an additional predictive value for severe color vision defects. The Nagel anomaloscope was not reliable due to low specificity. Its results showed high variations among both healthy and afflicted individuals. Conclusions: The HRR test was the most useful for COD. This test had the highest sensitivity in detecting early dysfunction of all three cone types, and it adequately quantifies the level of cone dysfunction in the course of the disease.

Using clinical tests of colour vision to predict the ability of colour vision deficient patients to name surface colours

To determine the predictive power of commonly used tests for abnormal colour vision to identify patients who can or cannot name surface colours without error. The colour vision of 99 subjects with colour vision deficiency (CVD) was assessed using the Ishihara, the Richmond HRR (2002), the Farnsworth D15, the Medmont C100 and the Nagel anomaloscope. They named 10 surface colours (red, orange, brown, yellow, green, blue, purple, white, grey and black), which were presented in two shapes (lines and dots) and three sizes. The surface colours were also named by an age-matched group of 20 subjects with normal colour vision. The performance of the clinical tests to predict the CVD subjects who made no colour naming errors and those who made errors is expressed in terms of the predictive value of a pass P((P)) and the predictive value of a fail P((F)). The P((P)) values of the tests were between 0.59 and 0.70 and P((F)) values were between 0.77 and 1.00. A 'mild' classification with the Richmond HRR test, especially if no more than two errors are made on the HRR diagnostic plates, identifies patients with abnormal colour vision who are able to name surface colour codes without error or only the occasional error. A pass of the Farnsworth D15 test identifies patients who will make no or few (up to 6%) errors with a 10 colour code, but who will be able to name the colours of a seven colour code that does not include orange, brown and purple. If protans are excluded, the predictive value for a pass P((P)) for the Farnsworth D15 is improved from 0.59 to 0.70. The anomaloscope is not an especially good predictor of those who can recognise surface colour codes. However, an anomaloscope range >35 units identifies those who have difficulty in recognising surface colour codes, as does a fail at the Farnsworth D15 test.

A low-power, LED-based, high-brightness anomaloscope

Color matches made with a Nagel anomaloscope are used in the differentiation of color vision deficiencies. When these color matches are made over a wide range of retinal illuminances, the changes in the color match provide information about the regeneration kinetics and the absorption spectra of the middle- and long-wavelength cone photopigments. These steady-state color matches vary with a variety of conditions, and may have value in screening for eye disease. Recently, high-brightness LEDs have become available that allowed us to construct a LED-based, high-brightness anomaloscope. We used inexpensive, low-energy components to replicate an earlier instrument, getting a maximum retinal illuminance over 5.6 log Trolands.

Evaluation of the New Web-Based “Colour Assessment and Diagnosis” Test

The purpose of the study was to determine the sensitivity, specificity, and repeatability of the web-based Colour Assessment and Diagnosis (CAD) test in comparison to current tests of color vision. Thirty color normals and 30 color deficients, identified and diagnosed by the Nagel anomaloscope, were tested. The results of the CAD test were compared with standard tests like Nagel anomaloscope, Ishihara (concise version, 2001), Hardy, Rand and Rittler (HRR; 4 ed) pseudoisochromatic test, and the Farnsworth Munsell 100 (FM-100) hue test. Using the Nagel anomaloscope as the "gold standard," the sensitivity with the CAD test was 93.33%, Ishihara 96%, HRR 100%, and the FM-100 hue 100%. The specificity was 100% with CAD and the Ishihara color plates, whereas it was 33% with the HRR and 83% with the FM-100 hue test. The concurrent validity of the CAD test for color normals was 93.75%. The concurrent validity of CAD test for color deficiency was 100%. Thus, anyone failing the CAD test has a color defect. The coefficient of agreement for the Nagel anomaloscope and the CAD test was 0.93, with Ishihara it was 0.96, with the HRR it was 0.33, and with FM-100 hue it was 0.83. These results showed that the CAD test is a valid test for identifying congenital red-green color deficiency. Further testing is required in a larger population of anomalous trichromats.

The Nagel anomaloscope: its calibration and recommendations for diagnosis and research.

The Nagel anomaloscope Model I is the definitive clinical instrument for classifying phenotypic variations in X-linked color-vision disorders. Its system of classification is based on the Rayleigh equation: the relative amounts of red and green primary lights required to match a yellow primary. Our aim was to characterize how changes in mains voltage and ambient temperature influence the wavelength and intensity of each primary and alter the Rayleigh matches of normal and anomalous trichromats. A Nagel Model I anomaloscope was calibrated in wavelength and intensity while varying the temperature of its prism housing and the mains voltage. Three normal, three protanomalous and three deuteranomalous trichromats made Rayleigh matches at various temperatures and voltages. The intensities of the green and red primaries show an exponential growth with mains voltage. Additionally, the wavelengths and intensities of all three primaries change with prism housing temperature. As a result, the R-G match midpoints of normal and anomalous trichromats shift with increasing mains voltage, and more markedly with increasing prism housing temperature, to higher R-G settings. Rayleigh matches obtained with the Nagel I anomaloscope are sensitive to changes in voltage supply and prism housing temperature, arising largely from thermal effects of the internal light sources. However, the instrument may still be safely used for diagnostic and research purposes provided that: (1) a stable voltage supply is used; (2) it is kept at a constant temperature; and (3) the match midpoint of the reference population has been established under identical conditions.

Variety of genotypes in males diagnosed as dichromatic on a conventional clinical anomaloscope

The hypothesis that dichromatic behavior on a clinical anomaloscope can be explained by the complement and arrangement of the long- (L) and middle-wavelength (M) pigment genes was tested. It was predicted that dichromacy is associated with an X-chromosome pigment gene array capable of producing only a single functional pigment type. The simplest case of this is when deletion has left only a single X-chromosome pigment gene. The production of a single L or M pigment type can also result from rearrangements in which multiple genes remain. Often, only the two genes at the 5' end of the array are expressed; thus, dichromacy is also predicted to occur if one of these is defective or encodes a defective pigment, or if both of them encode pigments with identical spectral sensitivities. Subjects were 128 males who accepted the full range of admixtures of the two primary lights as matching the comparison light on a Neitz or Nagel anomaloscope. Strikingly, examination of the L and M pigment genes revealed a potential cause for a color-vision defect in all 128 dichromats. This indicates that the major component of color-vision deficiency could be attributed to alterations of the pigment genes or their regulatory regions in all cases, and the variety of gene arrangements associated with dichromacy is cataloged here. However, a fraction of the dichromats (17 out of 128; 13%) had genes predicted to encode pigments that would result in two populations of cones with different spectral sensitivities. Nine of the 17 were predicted to have two pigments with slightly different spectral peaks (usually < or = 2.5 nm) and eight had genes which specified pigments identical in peak absorption, but different in amino acid positions previously associated with optical density differences. In other subjects, reported previously, the same small spectral differences were associated with anomalous trichromacy rather than dichromacy. It appears that when the spectral difference specified by the genes is very small, the amount of residual red-green color vision measured varies; some individuals test as dichromats, others test as anomalous trichromats. The discrepancy is probably partly attributable to testing method differences and partly to a difference in performance not perception, but it seems there must also be cases in which other factors, for example, cone ratio, contribute to a person's ability to extract a color signal from a small spectral difference.

Does the Farnsworth D15 test predict the ability to name colours?

Background: The Farnsworth D15 test is designed to categorise colour vision deficiency as severe or moderate. The level of difficulty of the test was set so that those who passed it should be able to recognise surface colour codes, such as those used for electrical wiring. The test is widely used to provide advice to patients with abnormal colour vision and is often used for occupational selection when reliable recognition of surface colour codes is required. However, there has been only one previous study of the correlation between performance at the D15 test and the naming of surface colour codes and there has been no study of whether a person who passes the D15 can reliably name surface colours. Methods: One hundred and two people aged 11 to 65 years with abnormal colour vision were recruited from consecutively presenting optometric patients and were asked to name the colours of fabric, paint and cotton thread samples. There were 10 colours in each class of material and the samples were presented in a large (five to 10 degree angular subtense) and small size (2.5 deg and a single thread). The errors made were compared to those made by an age‐matched control group of equal size with normal colour vision. Results: The correlations between the Farnsworth D15 colour confusion index and colour naming errors were 0.62 for the large stimuli and 0.73 for the small stimuli. Its sensitivity and specificity identifymg those who made more errors than the worst performing colour normal person were 0.80 and 0.69 (large stimuli) and 0.75 and 0.71 (small stimuli). A Nagel anomaloscope range of less than 35 scale units provides essentially the same sensitivity and specificity. Conclusions: About 40 per cent of those with abnormal colour vision can name the main colours correctly under good visibility conditions. The D15 test is an imperfect predictor of those who can name surface colour codes correctly but it does provide useful information for general counselling. It is not suitable as a single test for occupational selection because it will pass 20 per cent who cannot name surface colours correctly and fail 30 per cent who can. In occupations in which recognition of surface colour codes is of critical importance, it may be best not to select people with abnormal colour vision because of the lack of a colour vision test that is a perfect predictor of the ability to recognise surface colours.

A new mass screening test for color-vision deficiencies in children

Five thousand one hundred and twenty-nine Wis- consin children, ages 4 -12 years, were tested for color- vision deficiencies using a newly devised, precisely cali- brated paper-and-pencil test. The disposable 1-page test consisted of 1 demonstration and 8 test panels. Thousands of copies of the test were produced, and they were distrib- uted and administered in classrooms by teachers. Children wrote directly on the test and were allowed to trace over the symbols with a pencil or crayon, if they had difficulty. Performance on the paper-and-pencil color vision test was compared with that on conventional tests of color vision including Ishihara's tests, the American Optical-Hardy Rand and Rittler (AO-HRR) plate test, and the APT-5 Color Vision Tester. Older children were also tested on the Nagel Anomaloscope. All the children who were classified as having a color vision deficiency by the paper-and-pencil test also failed one or more of the conventional tests. Likewise, among children who passed the paper-and-pencil test, none were classified as having a color-vision defect from the results on the conventional tests. In the sample of all males, 7.5% were classified as having a color-vision deficiency, which is consistent with what has been observed previously in large population studies. Children who were classified as having color vision deficiencies were examined further us- ing a new minimalist genetic test that was shown to be accurate and reliable. Genetic material derived from buccal swabs was used to determine the type of deficiency, protan vs. deutan, and to provide added information about severity. Among the subjects for whom type could be determined, 27% were protans, consistent with large population studies in which approximately 25% of red-green deficiencies have been found to be of the protan type. Classification of the severity of the deficiencies determined from the paper-and- pencil test plus minimal genetics were in good agreement with classification based on a battery of conventional tests. In conclusion, we found the methods used here to be rapid, efficient, and reliable for testing color vision in children.

Can clinical colour vision tests be used to predict the results of the Farnsworth lantern test?

Clinicians usually do not have access to a lantern test when making an occupational assessment of the ability of a person with defective colour vision to recognise signal light colours: they must rely on the results of ordinary clinical tests. While all colour vision defectives fail the Holmes Wright Type B lantern test and most fail the Holmes Wright Type A lantern, 35% of colour vision defectives pass the Farnsworth lantern. Can clinical tests predict who will pass and fail the Farnsworth lantern? We find that a pass (less than two or more diametrical crossings) at the Farnsworth Panel D 15 Dichotomous test has a sensitivity of 0.67 and specificity of 0.94 in predicting a pass or fail at the Farnsworth lantern test; a Nagel range of >10 has a sensitivity of 0.87 and a specificity of 0.57. We conclude that neither the D 15 nor the Nagel Anomaloscope matching range are satisfactory predictors of performance on the Farnsworth Lantern.