General Guide for Testing Color Vision
Here you will get to learn, how to access a person's color vision and availability of different types of test to check color blindness.
Last updated
Here you will get to learn, how to access a person's color vision and availability of different types of test to check color blindness.
Last updated
[Author : Admin | Date : 6, April 2023 | Reading time : 5 min]
One of the first methods of color blindness test was to compare the individual color naming of everyday objects with that of a normal person. This was the method used by Turberville (1684) and several later researchers.
Dalton (1798) has gave a detailed report of his own perceptions and his brother (both protanopes) and near about 20 other people.
Then, the next advancement in testing was made by Seebeck (1837), where observer need to select from a wide range of colored samples were those that matched or most closely resembled a selected test sample.
The task was completed and inspected without naming colors. Holmgren (1877) developed varieties of color blind by skeins of wool; by Abney (1906), Oliver (1902) and Edridge-Green (1920) using small beads or pellets; and by Fridenberg (1903) with small square pieces of colored cardboard.
The Holmgren wool test is based on the principles of Helmholtz's theory of color perception. Helmholtz (1866) had tentatively suggested that color blindness could manifest itself in three forms: red, green, or violet blindness, depending on the nature of the missing color receptor (one for red, one for green, and one for violet).
Although this position was subsequently abandoned by Helmholtz as erroneous, Holmgren adhered to it and selected three standard wool skeins (red, green and purple) specifically designed to detect the three proposed types of color blindness.
As a result, Holmgren's test relies on an incorrect and misleading set of color blindness categories and an unwise selection of test and combination strands.
It is possible to design appropriate task-specific field tests in order to establish the color vision requirements of different jobs, but such a job-by-job analysis would be inefficient and expensive.
On the other hand, selecting an available clinical color vision test for a particular application is not simple.
First, information concerning the merits of these tests relative to each other and to various job requirements has not been readily available.
Second, clinical color vision tests are not designed for the scaling of performance or for multiple cutoff criteria; the scoring standard for most clinical tests is stated in terms of a single pass/fail score.
Third, the classification of color discrimination ability by clinical tests might not predict performance in a real-life situation (Kinney et al., 1979).Many experts feel that to generalize from a clinical test to a job requirement is inappropriate at best and meaningless at worst.
Fourth, the determinants of performance on each test are sufficiently complex, ranging from colorimetric design to motivational factors, that no test can be considered to provide a single metric of color vision.
In the absence of good population studies that relate job performance measures to test scores in batteries of color vision tests, these problems might be essentially insolvable.
However, an understanding of the existing color vision tests may help an employer who is familiar with the job requirements to decide whether to use a clinical test or to have field tests designed to his specifications.
This report surveys the existing clinical tests of color vision and gives some general indications as to their design and use.
Anomaloscopes are optical instruments in which the observer must manipulate stimulus control knobs to match two colored fields in color and brightness.
The anomaloscope is the standard instrument for the diagnosis of color vision defects. When supplemented by information from other color vision tests, the results provided by this instrument permit the accurate classification of all color deficiencies.
A variety of instruments were available in the past, but currently the Nagel, the Neitz, and the Pickford-Nicolson anomaloscopes are commercially available in the United States.
Of all of the color vision tests described here, anomaloscopes are the most difficult to use.
Extensive training of examiners is necessary if anomaloscopes are to be used validly and efficiently; hence, these instruments are most often found in research settings.
However, when used by a skilled examiner, the anomaloscope has advantages as a diagnostic instrument that far outweigh any inconveniences in training.
In a plate test, the observer must identify a colored symbol embedded in a background (most pseudoisochromatic plates); identify which of four colors is most similar to a standard color, (City University Test); or identify which circle matches a gray rectangle (Sloan Achromatopsia Test).
There are many types of pseudoisochromatic tests (e.g., American Optical Hardy-Rand-Rittler, Ishihara, Dvorine, Tokyo Medical College). All provide efficient screening (90 to 95%) of congenital red-green defects.
Basically these tests consist of a series of cards on which colored dots of discs of various sizes are printed to form a multicolored figure against a multicolored background.
The figure is some easily identifiable letter, arabic numeral, or geometric configuration (e.g., a circle, triangle, or cross). The only systematic difference between the figure and background dots is in color: the figure is composed of dots of one or more colors, and the background is composed of dots of different color or colors.
Variations in the size, lightness, and saturation of the dots may be employed so that identification of the intended figure by cues other than hue is less likely.
Observers with normal color vision can detect the hue difference between figure and background and consequently can easily read the figures, but observers with defective color vision may fail to distinguish between figure and background colors and hence fail to read the figures.
In this sense the colors of the plates appear isochromatic only to the defective observer.
Hardy, Rand, and Rittler (1945) characterized four types of pseudoisochromatic design: the vanishing design, the qualitatively diagnostic plate, the transformation plate, and the hidden defect design.
The vanishing design contains a figure that is easily read by the normal trichromat but not by the color-defective observer.
The qualitatively diagnostic plate is a vanishing plate that permits the differentiation of a protan from a deutan observer.
In the transformation plate, two figures are embedded in the background: one figure with the appropriate color and lightness contrast to be read by the normal trichromat, and the other with the appropriate color and lightness contrast to be read by the color defective.
In the hidden digit design, the plate is a vanishing plate for normal trichromats, but the figure is seen by the color-defective observer. Lakowski (1965b, 1966, 1969, 1976) has analyzed the colorimetric properties of several of the pseudoisochromatic plate tests.
The City University Test was designed to detect color confusions (i.e., colors that appear quite different to the normal observer but appear similar to the defective observer), and the Sloan Achromatopsia Test was designed to detect achromatopsia (i.e., the inability to differentiate any of the rainbow hues or their intermediaries other than on the basis of lightness).
There are certain advantages in the use of plate tests. They are rapidly and easily administered by inexperienced personnel; they are readily available; they are relatively inexpensive; and they can be used on naive subjects, illiterates, and children.
There are, however, certain disadvantages.
First, the spectral quality of the light source illuminating the plates affects the reading of the figures; the plates must be exhibited under the standard viewing conditions for which they were designed.
Second, the success of the plates depends mainly on the careful selection of confusion colors. Often, for technical reasons, the best confusion colors for diagnostic purposes are not available.
Third, even when a set of colors is chosen, individual variation in the eye lens and in coloration of the back of the eye means that a single choice of colors will not be optimal for all observers.
Finally, no accurate scoring criteria for classifying defects on the basis of test performance are available; the number of errors on pseudoisochromatic tests tells us little about the type or extent of a color vision defect.
Pseudoisochromatic tests should be used primarily as screening tests to divide people into normal and color-defective populations; their diagnostic value is limited.
Caution should be used in extracting more detailed information about color discrimination from them. At present it is always better to look on information from pseudoisochromtic plate tests as providing a probable but not certain diagnosis.
In arrangement tests, the observer is required to arrange color samples by similarity in a sequential color series. Usually the colors are mounted in caps, which are numbered on the back and can be moved about freely during performance.
Arrangement tests may be designed for evaluation of fine hue discrimination (FM 100-hue test); for evaluation of color confusion (Farnsworth Panel D-15, Lanthony Desaturated Panel, Lanthony New Color Test); for evaluation of neutral zones or colors seen as gray (Lanthony New Color Test); and for evaluation of saturation discrimination (Sahlgren Saturation Test, ISCC Color Aptitude Test).
Arrangement tests are easy to administer and can be used with naive subjects. Such tests require manual dexterity, patience, concentration, and the understanding of abstract ordering. Hence, they are less suitable for young children.
The Farnsworth Panel D-15 and the Lanthony Desaturated Panel provide rapid tests of gross color confusions but are not designed for fine color screening.
The FM 100-hue test is more time-consuming, but it is acknowledged to be a sensitive indicator of aptitude for hue discrimination. Both the Panel D-15 and the 100-hue tests differentiate among protan, deutan, and tritan defects by the axes along which confusions are made.
The ISCC test takes 45 to 90 minutes to complete and does not provide specific information about color defects.
Disadvantages of arrangement tests include the fact that some manual dexterity is required. For tests using colored papers, the observer should wear a glove to avoid soiling the colored pigments. The specified illuminant must be used.
Lantern tests were designed as practical means for measuring the ability of seamen, railway personnel, and airline pilots to identify and discriminate navigational aids and signals. Accordingly these tests emphasize correct color recognition as the important testing variable.
The design of lantern tests is straightforward, necessitating neither the construction of complex optical systems (as do anomaloscopes) nor the development of complicated color printing procedures (as for pseudoisochromatic plate tests).
Lantern tests simply require that a system be developed for presenting colored lights (duplicating signal lights) to the observer for identification. Several different models of lanterns are available: Giles-Archer, Edridge-Green, Martins, Sloan Color Threshold Tester, and Farnsworth Lantern.
Lantern tests are easy to administer. Their value lies in their simulation of the working condition. Lantern tests do not specifically screen for color defect, although it is expected that color-defective observers will not perform as well as observers with normal color vision.
