Encyclopedia of Color Science and Technology

2016 Edition
| Editors: Ming Ronnier Luo

Color Vision Testing

  • Galina V. Paramei
  • David L. Bimler
Reference work entry
DOI: https://doi.org/10.1007/978-1-4419-8071-7_374

Synonyms

Definition

Color vision testing is the assessment of chromatic discrimination ability and the diagnosis of any perceptual deficiency according to its severity and quality (see Paramei and Bimler, “ Protanopia”; Paramei and Bimler, “ Deuteranopia”; Bimler and Paramei, “ Tritanopia”; Rodríguez-Carmona, “ Environmental Influences on Color Vision”). Tests vary in sensitivity, specificity, ease of use, and time required for administration [1, 2, 3, 4]. Many were designed primarily for vocational screening for congenital deficiency, an issue in any occupation where color-coding conveys information (e.g., railways, aviation, electronics) [5, 6]. Testing is also important for assessing and monitoring acquired color abnormality, appearing as a manifestation of visual-system pathology resulting from ophthalmological diseases (e.g., glaucoma, ocular hypertension), systemic or neurological diseases (e.g., diabetes, Parkinson’s), or the effects of medications or exposure to environmental/occupational toxins (see Paramei, “ Color Perception and Environmentally Based Impairments”).

Color vision tests fall into several broad categories [1, 2, 3, 4].  Pseudoisochromatic plates and arrangement tests both directly address an observer’s confusions between color pairs along a given confusion axis. Both types of tests have the advantage of rapid administration and ease of interpretation, making them suitable for field/epidemiological applications. Generally they distinguish between the protan, deutan, and tritan forms of deficiency. Their results emphasize a dichotomous outcome: whether a subject’s color sensitivity is (vocationally) impaired. Versions of the tests exist for testing color vision in children. More recent computerized developments measure variations in color perception along a continuous range. Matching tests and naming (lantern) tests follow different principles. Below, the most widely used tests are described in more detail.

Pseudoisochromatic Tests

Pseudoisochromatic tests (Fig. 1)  Pseudoisochromatic Plates are irregular mosaics of small circles, randomly varying in size and luminance. Color differences among the circles demarcate a foreground design (digits, simple geometric forms, or curved lines), so that for a normal trichromatic observer the design stands out by Gestalt fusion from its background. In diagnostic plates the defining color difference disappears for color-deficient observers, and the design vanishes or is supplanted by an alternative design, demarcated by a different chromatic distinction. The spatial fluctuations in the mosaic mask any residual luminance traces of the normal design.
Color Vision Testing, Fig. 1

Examples of the Ishihara pseudoisochromatic plates used for screening for red-green deficiency (top) and Hardy-Rand-Rittler plates for screening tritan defects (bottom) (Source: Jägle, H., Zrenner, E. Krastel, H., W. Hart. W.: Dyschromatopsias associated with neuro-ophthalmic disease. Ch. 6. In: Schiefer, U., Wilhelm, H., Hart, W. (eds.), Clinical Neuro-Ophthalmology. A Practical Guide (2007), Fig. 6.2. Springer Copyright Clearance Center. Licence Number: 3655300610668)

The Ishihara test, used most widely, is intended for diagnosis of congenital red-green deficiency (“daltonism”), differentiating its two types, protans and deutans, and severity (mild, moderate, or extreme) [6, 7] (see Paramei and Bimler, “ Protanopia”; Paramei and Bimler, “ Deuteranopia”). The Hardy-Rand-Rittler (HRR) test contains additional six plates designed to detect tritan defects and gauge their severity [7, 8]. There also exists a Farnsworth F2 plate designed specifically for revealing tritan abnormality (see Bimler and Paramei, “ Tritanopia”; Paramei, “ Color Perception and Environmentally Based Impairments”).

Color Arrangement Tests

Arrangement/panel tests use a set of color stimuli (“caps”) which sample a color circle (see Green-Armytage, “ Color Circle”) at regular intervals. The subject is requested to arrange them in sequence, so that each color lies between the two colors most similar to it. Transpositions of the caps, departing from a normal trichromat’s sequence, are recorded as errors. These departures can be plotted graphically to measure the angle of the confusion axis (if any) and summed to quantify the severity of any deficit.

The classical example is the Farnsworth-Munsell 100-Hue (FM100) test [1, 2, 3, 4, 8, 9], consisting of 85 caps, which takes 20–30 min to complete. Errors (transpositions) peak in the sectors of the color circle running tangential to the protan, deuten, or tritan confusion axis (Fig. 2). Performance on the FM100 improves with repetition, and as well as measuring color discrimination, it is affected by general nonverbal intelligence [10].
Color Vision Testing, Fig. 2

Example of the Farnsworth-Munsell 100 Hue test scoring sheet indicating a moderate color discrimination defect (Source: Jameson, K.A. Human potential for tetrachromacy. Glimpse Journal: The Art + Science of Seeing 2.3 (2009), Online Supplementary Material, p. 4, Figure 3; http://www.glimpsejournal.com/2.3-KAJ.html. Copyright (2009) Kimberly A. Jameson, All Rights Reserved)

Two shorter versions, the Farnsworth Dichotomous D-15 test and the Lanthony Desaturated D-15d, each contain only 15 movable caps plus a fixed “pilot cap” as the start of the sequence [9] and take about 5 min to complete. The D-15 is designed to diagnose moderate to severe color defects. The D-15d test uses color samples that are lighter and paler [11]. It was designed specifically to capture mild or subclinical color defects in observers who pass the standard D-15 test. Errors can include diametrical circle-crossing transpositions, indicating the protan, deuten, or tritan confusion axis when plotted graphically (see Fig. 1 in Paramei, “ Color Perception and Environmentally Based Impairments”). Outcomes of both tests can be summarized as a color confusion index (CCI), where 1.0 corresponds to perfect color arrangement and CCI values greater than 1.0 indicate progressive impairment of color discrimination. These tests are often used in conjunction, though the more sensitive D-15d is widely employed for early detection of mild acquired dyschromatopsias.

The Lanthony New Color Test [3, 4] comprises four panels of 15 caps each at four levels of saturation, to examine color similarities at four different scales. Like the D-15d, it can be used to track the progression of acquired dyschromatopsias.

Although not strictly an arrangement test, the City University Test [2, 3, 4] is derived from the D-15. It is a forced-choice test consisting of 10 panels, each presenting four colored dots in a quincunx around a central dot; the subject has to indicate which of the four colors most closely resembles the central one. The colors are selected so that protan, deutan, or tritan deficiencies affect which dot is subjectively most similar to the center.

Anomaloscopes

Within color-matching tests, the “gold standard” of color deficiency diagnosis are anomaloscopes, which present colors as monochromatic light rather than on a computer monitor or via reflective pigments. Compared to the pseudoisochromatic and panel tests, anomaloscopy requires a skilled examiner.

The Nagel anomaloscope is intended for assessment of red-green discrimination (Fig. 3). The observer views a 2° hemipartite circle, where one half is yellow light (589 mm), while the other half-circle mixes red (666 nm) and green light (549 nm) – known as the Rayleigh equation [1, 2, 3]. These wavelengths differ only in their relative stimulation of L- and M- cones (S-cones being unresponsive in this spectral range) (see Stockman, “ CIE Physiologically Based Color Matching Functions and Chromaticity Diagrams”). A normal trichromat’s setting is characterized by a green/red ratio around 41 (on the scale between 0 and 73) and a very narrow range of such settings upon retest. Anomalous trichromats accept a wider than normal range of mixed lights as indistinguishable from the yellow, with the range – from narrow to very broad – characterizing mild, moderate, or extreme impairment. A dichromat can match any red/green ratio to the yellow light by adjusting the luminance of the latter, which a protanopic dichromat dims if the mixed light is mainly red whereas a green-dominated light requires a more luminant yellow; the opposite is observed for a deuteranope (see Paramei and Bimler, “ Protanopia”; Paramei and Bimler, “ Deuteranopia”).
Color Vision Testing, Fig. 3

Rayleigh spectral matching in the Nagel anomaloscope (Source: Jägle, H., Zrenner, E. Krastel, H., W. Hart. W.: Dyschromatopsias associated with neuro-ophthalmic disease. Ch. 6. In: Schiefer, U., Wilhelm, H., Hart, W. (eds.), Clinical Neuro-Ophthalmology. A Practical Guide (2007), Fig. 6.5. Springer Copyright Clearance Center. Licence Number: 3655300610668)

The Moreland anomaloscope serves to assess tritan discrimination. One half of the 2° hemipartite circle is a cyan standard (480 nm light tinged with a small admixture of 580 nm), which must be matched by mixing indigo (436 nm) and green lights (490 nm) in the other half-circle, known as the Moreland equation [12]. Decreasing discrimination along the tritan confusion lines increases the range of mixtures which perceptually match the standard. Notably, at 8° only complete tritanopes accept the full range of color mixtures as a match to the cyan standard (see Bimler and Paramei, “ Tritanopia”).

Computerized Tests

More recently, computerized equivalents of pseudoisochromatic tests have become common, displaying a series of colored mosaics in which the elements vary in luminance spatially as well as dynamically to leave only chromatic cues. Employed on a calibrated monitor under strict psychophysical protocols, the tests allow precise measurement of chromatic sensitivity.

In the Cambridge Colour Test (CCT) [13] (Fig. 4a) the design in each display is a stylized letter “C” with a four-way choice for the orientation for the letter’s open side (see Paramei and Bimler,  Protanopia; Paramei and Bimler, “ Deuteranopia”; Bimler and Paramei, “ Tritanopia”). The magnitude of the color difference demarcating each design (i.e., the difficulty of the choice) varies interactively in response to the observer’s ongoing performance, to specify the direction in the color plane of elevated thresholds, and to “bracket” their discrimination in the frame of the CIE (u’v’) 1976 chromaticity diagram (see Schanda, “ CIE u′, v′ Uniform Chromaticity Scale Diagram and CIELUV Color Space”). Outcomes are chromatic discrimination thresholds along the protan, deutan, and tritan confusion lines (Trivector subtest (Fig. 4b)) and elongation/orientation parameters for three MacAdam ellipses (Ellipses subtest (Fig. 4c)). CCT normative data for normal trichromats for eight life decades track the impact of age upon chromatic discrimination [14]. The CCT has been employed in numerous clinical studies for differential diagnostics of relative damage to chromatic pathways (e.g., [15]).
Color Vision Testing, Fig. 4

The Cambridge Colour Test. (a) An illustration of chromatic targets, Landolt “C,” embedded in the luminance noise background. (b) Confusion vectors (in CIE 1976 u’v’ chromaticity diagram) along which the chromaticity is varied in the CCT Trivector test: Protan (red), Deutan (green), and Tritan (blue). The origin of the vectors indicates chromaticity coordinates of the neutral background (u’ = 0.1977, v’ = 0.4689). (c) Examples of chromatic discrimination ellipses for normal trichromats: Ellipse 1 (middle), Ellipse 2 (top), Ellipse 3 (bottom); crosses indicate raw discrimination vectors, fitted ellipses are shown by solid lines (Figures 3a, c: Source: Mollon, J.D., Regan, B.C.. Cambridge Colour Test. Handbook (Cambridge Research Systems Ltd., 2000), p. 4. Permission has been obtained from Prof. John D. Mollon, who holds the copyright)

The Colour Assessment and Diagnosis (CAD) test [5, 6] employs spatiotemporal luminance contrast masking. Direction-specific, color-defined moving stimuli must be detected against a background of random, dynamic luminance contrast (Fig. 5, right). Chromatic sensitivity is measured in 16 color directions in the CIE (x,y) 1931 chromaticity diagram. From these, mean thresholds are computed for thresholds of the red-green and blue-yellow systems (Fig. 5, left),  Color Vision, Opponent Theory to diagnose accurately the subject’s class of color vision (i.e., normal, protan-, deutan-, tritan-like congenital loss or acquired color deficiency). The CAD test has been extensively applied for screening in occupations with color-intensive visually demanding tasks, in particular in aviation [5, 6]. The CAD units of chromatic sensitivity are based on the mean thresholds measured in 333 young normal trichromats. CAD data on protan, deutan, and tritan thresholds for normal trichromats across the lifespan have recently been obtained (in press).
Color Vision Testing, Fig. 5

An illustration of the Colour Assessment and Diagnosis (CAD) test (right). Direction-specific, color-defined moving stimuli must be detected against a background with random, dynamic luminance contrast (Source: Barbur, J.L., Rodríguez-Carmona, M.: Variability in normal and defective colour vision: consequences for occupational environments. In: Best, J. (ed.) Colour Design: Theories and Application, pp. 24–82. Woodhead Publishing, Philadelphia (2012). P. 52, Fig. 2.13(a, b). The authors hold the copyright; permission has been obtained from Prof. John Barbur)

Cross-References

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Copyright information

© Springer Science+Business Media New York 2016

Authors and Affiliations

  1. 1.Department of PsychologyLiverpool Hope UniversityLiverpoolUK
  2. 2.School of PsychologyMassey UniversityPalmerston, NorthNew Zealand