A lantern color vision test for the rail industry.

BACKGROUND: Correct identification of wayside signal colors is critical for safe operation of railway equipment. However, evaluating color discrimination using just a screening test may not be occupationally relevant. METHODS: A lantern test (CNLAN) was designed to provide a functional assessment of color discrimination for the rail industry. It was validated against a simulated field trial. 81 individuals with normal color vision and 74 individuals with congenital red-green defects participated. Color vision was classified using the Nagel Anomaloscope. RESULTS: Using a criterion based on the worst-normal performance, 97% of the individuals with a color vision defect failed both the CNLAN and simulation trial. This value is slightly lower than the 100% who failed both the Ishihara test and simulation. However, the Ishihara test also failed 3.7% of the color-normals who passed both the simulation and lantern, whereas by definition none of the color-normals failed the lantern. CONCLUSIONS: This lantern test provides a reasonable functional assessment of one's ability to identify rail signal colors; especially when a strict failing criterion is applied to screening tests.

Detection of color vision defects in chloroquine retinopathy.

OBJECTIVE: The effect of chloroquine toxicity on color vision is unclear. The authors identified the color defects seen in chloroquine retinopathy and determined the sensitivity and specificity of clinical color vision tests for detecting the presence of previously diagnosed chloroquine retinopathy. DESIGN: Case-control study. PARTICIPANTS: Chloroquine retinopathy was defined using previously published criteria. Data from 30 patients with retinopathy and 25 patients using chloroquine but with no evidence of retinal toxicity were collected. METHODS: All patients were tested with the following six clinical color vision tests: Ishihara, Farnsworth D-15, and Adams Desaturated-15 (Dsat-15), City University 2nd Edition (CU), Standard Pseudoisochromatic Plates Part 2 (SPP-2), and American Optical Hardy Rand Rittler (AO HRR). MAIN OUTCOME MEASURES: The number of failures was determined for each test. The types of color vision defects were classified as blue-yellow (BY), red-green (RG), or mixed RG and BY (mixed). RESULTS: Of the 30 patients with retinopathy, 28 (93.3%) of 30 patients failed at least 1 color vision test, demonstrating predominantly mixed defects. Five (25%) of 25 of the control subjects failed at least 1 test, and these defects were predominantly BY. The sensitivity and specificity of the tests are as follows: SPP-2 (93.3%, 88%), AO HRR (76.7%, 88%), Ishihara (43.3%, 96%), Dsat-15 (33.3%, 84%), D-15 (16.7%, 96%), and CU (20%, 92%). CONCLUSIONS: Color vision can be affected by chloroquine and should be tested routinely with a color vision test designed to detect both mild BY and protan RG defects to maximize sensitivity for toxicity. The SPP-2 and AO HRR are two tests that meet these criteria. The Ishihara has a low sensitivity, as do the D-15 tests and CU. All of the tests have similar specificity for chloroquine toxicity. If color vision defects are detected in patients at risk of developing chloroquine retinopathy, additional testing is indicated to rule out toxicity.

Comparison of the D-15 and City University (second) color vision tests.

This study examines the equivalence of the City University color vision test (CUT) to the Farnsworth Munsell D-15 (D-15). This information is important because a number of occupations require individuals to pass either the D-15 of the CUT. Using two or more major crossings on the D-15 as failure, our results indicate that agreement between tests can be improved if the failing criterion for the CUT is either > or = 5 total errors, or > or = 2 errors on the large circles. Our preference is to use the criterion based on the large circles because there is a marginal improvement in agreement between the two tests for protanopes.

Validity of the Holmes-Wright lantern as a color vision test for the rail industry.

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.

Long wavelength pass filters designed for the management of color vision deficiencies.

This study reports on the effectiveness of long wavelength pass filters dispensed as tinted spectacles as an aid for individuals with congenital red-green color vision deficiencies. The effectiveness of the filters was evaluated by the performance on a series of clinical color vision tests and a questionnaire after the subjects had tried the lenses for 1 week. The lenses improved performance on color vision tests that required discrimination between large color differences, particularly between red and green hues. However, performance was degraded on tests which required fine color discrimination or used colors that were located parallel to the tritan confusion axis. The improved performance on certain tests was primarily based on brightness artificats induced by the filters, whereas the degraded performance on the other tests was due to the absorption of short- to midwavelength light by the filters. A slight majority (56%) of the subjects rated the filters as being moderate to highly effective in improving their color discrimination. Nevertheless, only 17% were interested in actually purchasing a pair. Common reasons for rejecting the filters were the color distortions produced by the red filters and fewer colors were actually perceived when wearing the filters.

Comparison of the standard pseudoisochromatic plates--Parts 1 and 2--As screening tests for congenital red-green color vision deficiencies.

BACKGROUND: The Standard Pseudoisochromatic Plates-Part 2 (SPP-2) are designed primarily as a screening test for acquired color vision deficiencies. However, results from several studies suggest that the SPP-2 may also be effective as a screening test for congenital red-green color vision defects. METHODS: In this study, the screening effectiveness of the SPP-2 was compared with the Standard Pseudoisochromatic Plates-Part 1 (SPP-1) to determine whether clinicians must use both tests: the SPP-1 to screen for congenital color vision defects and the SPP-2 to screen for acquired color vision defects. RESULTS: The results showed that, when using the recommended scoring criterion for the SPP-1, the SPP-2 test is slightly more sensitive in detecting congenital red-green defects. CONCLUSIONS: Clinicians can use the SPP-2 to screen for both congenital and acquired color vision defects.

Colorimetric analyses of various light sources for the D-15 color vision test.

Colorimetric analyses were performed in both normal trichromatic and dichromatic color spaces to determine whether several light sources were suitable illuminants for the Farnsworth-Munsell Panel D-15 (D-15) color vision test. Results for fluorescent lamps showed that lamps with a correlated color temperature (CCT) of 7200 degrees K and a general color rendering index (GCRI) of at least 90 are acceptable substitutes for illuminant C. Predictions for filtered tungsten light indicated that lights with a color temperature near 5000 degrees K are unsuitable because of nonuniformities in the glass daylight filter transmittance. Conclusions based on these analyses are conservative because, with exception of the GCRI, color adaptation effects were not taken into account.

Tinted lenses and the ANSI standards for traffic signal transmittances.

The transmittance properties of 96 tinted lenses were examined to determine whether these lenses met the American National Standards Institute (ANSI) Z80.3 standards for traffic signal transmittances and color shifts. Transmission functions of the lenses were measured using a Zeiss Spectrophotometer, and the luminous transmittances and color shifts were calculated according to the ANSI guidelines. Approximately 50% of the sampled tinted lenses failed to meet at least 1 of the ANSI requirements. Lenses that failed to meet several ANSI requirements were often special purpose sun lenses. Although the special purpose tinted lenses do not have transmittance requirements for traffic signals, it is not always clear from the manufacturers' brochures that the lenses may be unsuitable for driving.

Normative data for the standard pseudoisochromatic plates--Part 2.

The Standard Pseudoisochromatic Plates--Part 2 are designed as a screening test for acquired color vision deficiencies. In order to control for age-related changes in color vision, it is necessary to establish norms for this test. Results from this study suggest that, disregarding one figure on the first test plate, one or more blue-yellow errors indicate a blue-yellow color vision defect for patients between 20 and 60 years, whereas two or more blue-yellow errors are indicative of a blue-yellow color vision defect for patients under 20 years and over 60 years. For modified red-green test figures, one or more errors are suggestive of a red-green defect for patients under 60 years, whereas two or more errors indicate red-green vision defect for patients over 60 years. Asking patients to judge which figure is more distinct on each test plate is not useful in comparing responses between patients.

Physical characteristics and perceptual effects of "blue-blocking" lenses.

The transmission-optical properties of a "blue-blocking" lens and its influence on several aspects of human visual performance were assessed. Results showed that the lens was effective in absorbing ultraviolet and blue wavelengths and that its effects on contrast sensitivity and visual evoked potentials (VEP's) were similar to those produced by an equivalent neutral density (ND) filter. Although the lens did not alter stereopsis, it did produce severe color discrimination losses for normal and dichromatic subjects.

Dichoptic opponent hue cancellations.

Relative to monoptic opponent hue cancellations, dichoptic cancellations, which were possible over most of the visible spectrum, generally required more blue or less yellow to cancel the opponent yellow or blue response and less green to cancel the opponent red response. Differences between dichoptic and monoptic red-to-cancel-green functions were wavelength dependent. These data were approximately predicted by a model in which monoptic cancellations are based at the receptor level, whereas dichoptic cancellations are based upon cancellations of postreceptor opponent hue responses at a central level in the visual system. The model also makes reasonable predictions of other dichoptic hue-matching data.

Review of dichoptic color mixing.

Dichoptic color mixing has been a controversial issue for nearly two centuries. The first dispute arose from the fact that dichoptic color mixtures occur only under certain conditions. A later controversy arose over the implications of dichoptic color mixtures to color vision theories. The present consensus is that dichoptic color mixtures occur under conditions which apparently minimize chromatic differences between the two monocular impressions. However, dichoptic mixtures do not match the corresponding monoptic mixtures. Dichoptic mixtures appear dimmer, and if a green light is mixed with either a red or violet light, then the dichoptic mixture appears greener relative to the monoptic mixture.

Comparison of the Standard Pseudoisochromatic Plates to the Ishihara color vision test.

The Standard Pseudoisochromatic Plates (SPP) color vision test was compared to the Ishihara color vision test with respect to screening validity, digit confusion errors, and individual plate efficiency. Results from 315 1st and 3rd grade males confirmed previous reports that the SPP is an effective screening test. Moreover, the SPP test was superior to the Ishihara test with respect to digit confusion errors. Color normal children made about 5 to 7 times as many errors on the Ishihara test as on the SPP. Screening inefficiency values of individual plates of both tests were calculated. A high inefficiency value of a SPP plate was usually caused by its inability to detect color defective subjects.