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It is hypothesized that if blue is signalled more slowly than red in the visual system, and if integration time is longer for blue than for red, then a tritan defect should be apparent for normal observers. Data from short-exposure viewing of the City University Colour Vision Test indicate that, at 3.75 msec. a significant tritan error occurs.
A simulated field test was designed to determine whether the Holmes-Wright A lantern (HWA) is a valid color vision test for the rail industry. The simulation replicated viewing rail signal lights at 0.8 km distance under daylight conditions. Using the worst-normal as the maximum number of allowable errors on the simulation, 94% of the color-defectives failed both tests on the first trial and 92% failed at the second session. The HWA had a higher false negative rate than a false alarm rate. The majority of individuals who had discrepancies on the two tests were mild deutans. Results from the Ishihara test were marginally better at predicting performance on the simulation.
In children with a visual handicap, colour vision testing may provide additional cues to diagnosis. Some information is given by pseudo-isochromatic plates. More informative are the arrangement tests, especially the Panel D-15. These tests can be used also in cases with severely reduced visual acuity. In suspected achromatopsia, the scotopic spectral sensitivity can be revealed by the D-15 test, the anomaloscope, or measuring the spectral sensitivity.
From our results we can be sure that the colour test disk is at least as reliable for mass testing for colour blindness as the Ishihara isochromatic colour plates. In practice the test disk has the advantage of constancy of testing conditions and easy and quick procedure. If it is necessary to differentiate between protopia and deuteropia the colour test disk is significantly better Ishihara's colour plates.
Psychophysical measurements were performed with a view to providing an assessment of early neural functional integrity in the presence of no or minimal diabetic retinopathy (DR). The investigations were carried out on a normal group and a number of age- and sex-matched non-insulin dependent diabetic groups with different levels of DR. Results were considered in terms of the presence of functional changes relative to the severity of DR and the duration of diabetes. Significant deficits were found for visual acuity (VA), contrast sensitivity (CS) and colour vision. Both CS and colour vision measurements differentiated between non-diabetics and those with diabetes but without DR. However, none of the tests reliably distinguished diabetics without DR from those with early retinal changes although VA and colour vision (especially along a blue-yellow colour axis) were sensitive to more substantial retinal changes. This finding suggests such tests may be useful as screening tests for more advanced levels of background DR.
The color of an object, when part of a complex scene, is determined not only by its spectral reflectance but also by the colors of all other objects in the scene (von Helmholtz, 1886; Ives, 1912; Land, 1959). By taking global color information into account, the visual system is able to maintain constancy of the color appearance of the object, despite large variations in the light incident on the retina arising from changes in the spectral content of the illuminating light (Hurlbert, 1998; Maloney, 1999). The neural basis of this color constancy is, however, poorly understood. Although there seems to be a prominent role for retinal, cone-specific adaptation mechanisms (von Kries, 1902; Pöppel, 1986; Foster and Nascimento, 1994), the contribution of cortical mechanisms to color constancy is still unclear (Land et al., 1983; D'Zmura and Lennie, 1986). We examined the color perception of 27 patients with defined unilateral lesions mainly located in the parieto-temporo-occipital and fronto-parieto-temporal cortex. With a battery of clinical and specially designed color vision tests we tried to detect and differentiate between possible deficits in central color processing. Our results show that color constancy can be selectively impaired after circumscribed unilateral lesions in parieto-temporal cortex of the left or right hemisphere. Five of 27 patients exhibited significant deficits in a color constancy task, but all of the 5 performed well in color discrimination or higher-level visual tasks, such as the association of colors with familiar objects. These results indicate that the computations underlying color constancy are mediated by specialized cortical circuitry, which is independent of the neural substrate for color discrimination and for assigning colors to objects.
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A cheap, portable automated scorer for the Farnsworth-Munsell (FM) 100 hue test has been developed. It consists of a light pen, a series of omni-directional bar-codes attached to the reverse of the FM 100 hue caps and a small micro-computer. The print-out includes patient details, a linear histogram of the partial errors by cap position, indication of the peak error positions for congenital colour vision deficiencies and appropriate statistical analysis of the total error score. All the results are available within four minutes of completing the testing procedure.
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.
A large surface Panel D-15 Test, specially designed for low vision patients, is presented. The value of the test is compared to the one of other standard colour vision tests in such patients.
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The term "color blind" is encountered frequently in areas pertaining to health, commerce, art, and entertainment, but in these cases it is generally not appropriate. Complete color blindness or achromasy is rare, but weakness or absence of discrimination to certain colors can be found in at least 8% of the male population. The most useful description of these color defects is in terms of hue and saturation, thresholds of which can be plotted as polar coordinates on a circular diagram. Plotting color thresholds with the chromagraph reveals more clearly than other clinical systems the true nature of color defects, as well as some inconsistencies in the traditional terminology and test methods. Fifty strongly color-defective subjects were tested by five different methods and the results compared. Normal values are also indicated.
A 45 year old man was studied who was previously diagnosed as a typical achromat. Increment spectral sensitivity measurements on white and several colored backgrounds showed that he possessed a rod system, a cone system sensitive in the short wavelength region (blue cones) and a cone system sensitive in the long wavelength region (red cones). This investigation shows that rather extensive testing is required to classify incomplete achromats.
BACKGROUND: Screening tests of visual functions using the Internet are theoretically possible. To use these tests as a screening test, they must deliver comparable results with conventional test procedures. A web-based color vision test was developed based on pseudoisochromatic color plates. METHOD: The web-based color vision test was developed according to the pseudoisochromatic color plates by Velhagen and Broschmann using the programming-languages HTML, Java, and Perl. Sixty-five voluntary subjects, including nine color-deficient subjects, were examined by luminescence color plates (via web-based color vision test) and pigment color plates (via book). The statistical analysis was performed by determining the correspondence and the 95%-confidence interval. RESULTS: The correspondence of the test results for all subjects was 0.98 and the 95%-confidence interval was within 0.91 and 0.99. The correspondence of the test results in the group of color-deficient subjects was 1.0 and because of the limited number the 95%-confidence interval was within 0.71 and 1.0. CONCLUSIONS: The web-based color vision test with luminescence color plates for color-efficient and color-deficient subjects delivers test results comparable to pigment color plates under standardized examination conditions. Further studies are needed to examine if the web-based color vision test can also be used as an Internet screening test.
AIMS: This paper describes a novel test of colour vision using a standard personal computer, which is simple and reliable to perform. METHODS: Twenty healthy individuals with normal colour vision and 10 healthy individuals with a red/green colour defect were tested binocularly at 13 selected points in the CIE (Commission International d'Eclairage, 1931) chromaticity triangle, representing the gamut of a computer monitor, where the x, y coordinates of the primary colour phosphors were known. RESULTS: The mean results from individuals with normal colour vision were compared to those with defective colour vision. Of the 13 points tested, five demonstrated consistently high sensitivity in detecting colour defects. CONCLUSION: The test may provide a convenient method for classifying colour vision abnormalities.
The Roth 28-hue test, first described in 1966, uses every third color cap from the Farnsworth-Munsell 100-hue (85-color-cap) test. Protans, deutans, and tritans exhibit slightly different confusion axes on the Roth 28-hue test and the Farnsworth D-15 test. These axes are illustrated on a CIE chromaticity diagram. The little-used Roth 28-hue test may be a good compromise between the D-15 and 100-hue tests, but clinical trials for verification are needed.
This paper reports a survey of the lantern tests that have been or are used to evaluate the color vision of people who wish to enter occupations that require the ability to recognize colored signal lights reliably. The origin of each lantern is traced and the principal features of each are described. The available data concerning failure rate of normals, the failure rate of people with defective color vision, and the extent to which scores on lantern tests correlate with field trials are summarized. Despite the fact that lantern tests have been used since the turn of the century and that some lanterns have been in use for more than 30 years and some for much longer periods, the available validation data are incomplete and sometimes conflicting. However, the data do indicate that some lanterns may fail a significant proportion of normals and that there is considerable variation between lanterns in the proportion of color vision defectives that will fail. It is noted that most lanterns will pass some protanomals despite their reduced sensitivity to red light and correspondingly short visual range for red signals. The view of Cameron is supported that a more rational approach would be to made a clinical diagnosis of the type of color vision defect, to reject protanopes, deuteranopes, and protanomals and to use a lantern test only to determine which deuteranomals should be accepted.