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Color vision test
Color vision test
Color vision test
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A color vision test is used for measuring color vision against a standard. These tests are most often used to diagnose color vision deficiencies ("CVD", or color blindness), though several of the standards are designed to categorize normal color vision into sub-levels. With the large prevalence of color vision deficiencies (8% of males) and the wide range of professions that restrict hiring the colorblind for safety or aesthetic reasons, clinical color vision standards must be designed to be fast and simple to implement. Color vision standards for academic use trade speed and simplicity for accuracy and precision. Color Vision tests can show the difference. Color Vision Tests

Applications

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Color vision standards are used to evaluate the color vision of a subject. They are most commonly applied to job applicants during pre-job screening. The evaluation may be to select against the color vision deficient for roles where basic color vision is required, or to select for individuals with superior color vision for roles where recognition of subtle color difference is required.[1]

Alterations to color vision are common symptoms of toxicity and eye health, so color vision standards can also be used to detect conditions of the eye or brain or to track the recovery from these conditions.[1]

Pseudoisochromatic plates

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An Ishihara test image as seen by subjects with normal color vision and by those with a variety of color deficiencies

A pseudoisochromatic plate (from Greek pseudo, meaning "false", iso, meaning "same" and chromo, meaning "color"), often abbreviated as PIP, is a style of standard exemplified by the Ishihara test, generally used for screening of color vision defects.[2]

A figure (usually one or more numerals) is embedded in the plate as a number of spots surrounded by spots of a slightly different color. The figure can be seen with normal color vision, but not with a particular color defect. The figure and background colors must be carefully chosen to appear isochromatic to a color deficient individual, but not an individual with normal color vision.[2]

Pseudoisochromatic Plates are used as screening tools because they are cheap, fast and simple, but they do not provide precise diagnosis of CVD, and are often followed with another test if a user fails the PIP standard.[3]

Ishihara plates

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Main article: Ishihara color test

Ishihara plates hide Arabic numerals within PIPs. They are the test most often used to screen for red–green color deficiencies and most often recognized by the public.[4] However, this can be attributed more to its ease of application, and less to do with its precision.[2]

The basic Ishihara test may not be useful in diagnosing young, preliterate children, who can't read the numerals, but larger editions contain plates that showcase a simple path to be traced with a finger, rather than numerals.[5]

HRR plates

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The second most common PIP color vision standard is the HRR color test (developed by Hardy, Rand, and Rittler), which solves many of the criticisms of the Ishihara test. For example, it detects blue-yellow color blindness, is less susceptible to memorization and uses shapes, so it is accessible to the illiterate and young children.[2]

City University test

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City University test contains test plates that can be used to detect all types of color vision deficiencies.[6][7] The test which was derived from Farnsworth D15 color arrangement test,[8] consists of 10 plates, containing a central colored dot surrounded by four peripheral dots of different colors. The subject is asked to choose the dot closest to the central hue, allowing abnormalities to be detected according to the responses.[9]

Arrangement tests

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A Farnsworth–Munsell 100 Hue Test
A Farnsworth D-15 test

Arrangement-style color vision standards comprise a spectrum of colors that must be arranged in an array to minimize the difference between adjacent colors. An error score is calculated from incorrectly positioned colors. Lower error scores denote better color vision. Typically, the subject is asked to arrange a set of colored caps or chips between two anchor caps.[10]

The Farnsworth–Munsell 100 hue test comprises 4 separate color arrays, each representing 20 arrangeable caps and 2 anchor caps. This gives a total of 88 colors, contrary to the standard's name.[11] The standard is sensitive enough that it not only can detect color blindness, but also categorize normal color vision into "low", "average" and "superior" levels based on their error score.[11] It is usually not used for the detection of CVD.

The Farnsworth D-15 is simpler, comprising a single array, which itself comprises 1 end cap and 15 arrangeable caps.[11] It is primarily used for occupational screening of CVD and is the standard of choice in most US/Canadian Police Forces (after screening with Ishihara).[12] About 50% of people who fail the Ishihara are able to pass the D15.[13]

Lanterns

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Lanterns project small colored lights to a subject, who is required to identify the color of the lights. The colors are usually restricted to those of typical signal lights, i.e. red, green and yellow, though some lanterns may project other colors. The main signal light colors also happen to be colors of confusion for red-green CVD.

Lanterns are usually used for occupational screening as they are more closely related to the actual safety-related color tasks required in those occupations. For example, the Farnsworth Lantern Test is used extensively by the United States Armed Forces and FAA.[14] This test allows about 30% of individuals who fail the ishihara plates (generally those with mild CVD) to pass.[15]

Anomaloscopes

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Anomaloscope using a Rayleigh Match
Main article: Anomaloscope

Anomaloscopes are very expensive and require expertise to administer, so are generally only used in academic settings. However, they are very precise, being able to diagnose the type and severity of color blindness with high confidence.[16] An anomaloscope designed to detect red–green color blindness is based on the Rayleigh equation, which compares a mixture of red and green light in variable proportions to a fixed spectral yellow of variable luminosity. The subject must change the two variables until the colors appear to match. The values of the variables at match (and the deviation from the variables of a color normal subject) are used to diagnose the type and severity of colorblindness. For example, deutans will put too much green in the mixture and protans will put too much red in the mixture.[17]

Digital tests

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The graduation of color vision tests to the digital space offers several advantages, but is not trivial. Even if the digital tests mimic a traditional test, the digital version must be requalified or validated and every screen it is viewed on must be well-calibrated. Freely available web-based tests suffer from a lack of validation and typical viewing on uncalibrated screens. However, when well controlled, digital tests offer several significant advantages over their analog counterparts:

  • They randomize solutions, which eliminates memorization[18]
  • The test can adapt in real time to the subject's performance (e.g. give more protan questions if the subject appears to be a protan)[18]
  • They don't suffer from color fading like the pigments/dyes in analog tests.
  • The variance in test administration is minimized
  • The tests are immune to mistakes in interpreting the results
  • Test parameters can be dynamic and vary with time

Validated digital tests used for occupational screening include:

An example of a digital, mobile, non-validated test is the Android application "Color Blind Check".

References

[edit]
Revisions and contributorsEdit on WikipediaRead on Wikipedia

Color vision test

View on Grokipedia
from Grokipedia
A color vision test is a diagnostic procedure designed to assess an individual's ability to perceive and discriminate between colors, identifying congenital or acquired deficiencies such as red-green (the most common type, affecting approximately 8% of males and 0.5% of females). These tests are essential for screening in clinical settings, occupational evaluations (e.g., for pilots or electricians), and early detection of underlying conditions like retinal diseases or disorders. Common methods include pseudoisochromatic plate tests, such as the Ishihara plates, where individuals identify numbers or shapes embedded in colored dot patterns under standardized lighting; these are quick, reliable for red-green defects (with screening accuracy up to 95%), and widely used as initial screens. Arrangement tests, like the Farnsworth-Munsell 100-Hue test, require sorting colored caps by hue to measure discrimination ability and severity, providing quantitative error scores that increase with age or defect progression. Lantern tests, such as the Farnsworth Lantern, simulate real-world signal light identification to evaluate practical color recognition, particularly for safety-critical professions. Anomaloscopes, considered the gold standard for classifying red-green anomalies, involve matching bipartite color fields but require specialized equipment and trained examiners. Overall, these tests vary in complexity from simple visual tasks to precise instrumental assessments, ensuring comprehensive evaluation while minimizing false positives through controlled conditions like CIE Illuminant C lighting at 100-650 lux.

Background

Color vision deficiencies

Normal trichromatic color vision in humans relies on three types of cone photoreceptors in the retina: long-wavelength-sensitive (L) cones, primarily responsive to light; medium-wavelength-sensitive (M) cones, responsive to light; and short-wavelength-sensitive (S) cones, responsive to blue light. These cones enable the perception of a wide spectrum of colors through their differential sensitivity to various wavelengths of light. Color vision deficiencies, also known as , occur when one or more types are absent, dysfunctional, or altered, leading to impaired color discrimination. The most common forms are red-green deficiencies, including protanomaly (reduced sensitivity to red light due to anomalous L ) and protanopia (complete absence of L ), as well as deuteranomaly (reduced sensitivity to green light due to anomalous M ) and deuteranopia (complete absence of M ). Less frequent are blue-yellow deficiencies, such as tritanomaly (reduced sensitivity to blue light due to anomalous S ) and tritanopia (complete absence of S ), while represents the rarest and most severe form, involving only one functional type or none, resulting in vision. These deficiencies predominantly affect males, with a global prevalence of approximately 8% in males and 0.5% in females, attributed to X-linked recessive inheritance patterns where the genes encoding the cone pigments are located on the X chromosome. Females, possessing two X chromosomes, are less likely to express the condition unless both carry the mutation. Congenital color vision deficiencies arise from genetic mutations in the opsin genes—OPN1LW for L cones, OPN1MW for M cones, and OPN1SW for S cones—leading to hybrid pigments or absent photopigments. Acquired deficiencies, in contrast, result from non-genetic factors such as cataracts, which scatter light and alter color perception, or diabetes, which can damage retinal cells and impair cone function over time. Color vision tests are essential for identifying these impairments, which can affect daily tasks and occupational safety.

Purpose and applications

Color vision tests are primarily employed to screen for congenital and acquired color vision deficiencies, quantify the severity of these impairments, and inform targeted interventions such as monitoring disease progression or recommending corrective therapies. Congenital deficiencies, often genetic and stable from birth, and acquired ones, resulting from conditions like or medication toxicity, can be detected early to prevent functional limitations. In clinical practice, these tests form a standard component of routine eye examinations, where they help identify subtle abnormalities in color perception that may signal underlying ocular or systemic diseases, such as or . Pre-surgical assessments utilize color vision testing to establish baseline function, particularly for procedures involving the or , enabling clinicians to evaluate potential postoperative changes and tailor interventions accordingly. Occupational applications emphasize safety and performance in roles demanding precise color discrimination. In aviation, the Federal Aviation Administration requires computerized color vision screening for all new pilot medical certificate applicants effective January 1, 2025, supplanting legacy methods like Ishihara plates to standardize evaluation and mitigate risks in interpreting color-coded signals and instruments. Military branches, including the U.S. Army, Navy, and Air Force, mandate color vision testing for visually intensive positions such as piloting or signal operation to ensure operational readiness. In electrical work, testing verifies the ability to differentiate color-coded wiring, a critical safety measure despite the absence of federal mandates, while design professions like graphic arts rely on it to confirm accurate hue perception for professional output.

History

Early developments

The scientific study of color vision deficiencies began with the personal account of English chemist , who in 1794 described his own inability to distinguish certain colors, such as confusing scarlet with green and pink with blue, in a paper presented to the Manchester Literary and Philosophical Society. This description, later published in 1798, marked the first documented case of what became known as and sparked broader interest in the phenomenon among scientists and physicians. In 1876, Swedish physiologist Alarik Frithiof Holmgren introduced the first practical color vision screening test in response to the Lagerlunda train collision of November 1875, where poor color discrimination by the engineer was suspected to have contributed to the accident. The test used skeins of colored wool that test subjects were asked to match to reference yarns. The test quickly gained adoption for screening railway and maritime personnel across and , as it provided a simple, non-instrumental method to identify individuals unable to differentiate key signal colors like and green. Advancing beyond yarn-based matching, Japanese ophthalmologist introduced pseudoisochromatic plates in 1917 specifically to screen military recruits for the during . These plates consisted of dotted patterns forming numerals visible to those with normal but obscured or altered for those with red-green deficiencies, offering a more portable and standardized alternative to earlier methods. Ishihara's innovation built on prior pseudoisochromatic concepts but achieved greater reliability through careful color calibration, leading to its widespread use in medical and occupational settings. Despite these foundational advances, early color vision tests like the Holmgren wool test and Ishihara plates suffered from inherent limitations, including high subjectivity in interpretation—such as reliance on verbal matching or examiner judgment—and an inability to quantify the severity or type of deficiency beyond basic detection. The Holmgren test, in particular, was criticized for its reliance on outdated color confusion theories and potential for false positives due to non-color factors like lighting variations. Similarly, Ishihara plates excelled at screening but provided limited diagnostic depth, often failing to differentiate mild anomalies from severe . These shortcomings influenced the development of more precise arrangement and matching tests in subsequent decades.

Modern standardization

Following , significant advancements in color vision testing emerged to meet the demands of military and aviation applications, emphasizing more reliable detection and classification of deficiencies. In the 1940s, Dean Farnsworth developed the Farnsworth-Munsell 100 Hue test, a arrangement-based assessment designed to quantify color discrimination abilities, initially for screening U.S. Navy personnel involved in tasks requiring precise color identification, such as signaling and navigation. By the early 1950s, LeGrand Hardy, Gertrude Rand, and M. Catherine Rittler introduced the Hardy-Rand-Rittler (HRR) pseudoisochromatic plates, which improved upon earlier designs by incorporating both red-green and blue-yellow screening capabilities through vanishing and diagnostic configurations, and were adopted by the U.S. Air Force in 1953 for medical evaluations to ensure pilot safety in color-coded environments. In the , refinements to anomaloscope technology enhanced the precision of color matching assessments, building on precursors like the Nagel anomaloscope. The Pickford-Nicolson anomaloscope, introduced in 1960, allowed for more accurate measurement of anomalous by enabling finer adjustments in spectral primaries and brightness, facilitating quantitative diagnosis of defects in clinical and occupational settings. International standardization efforts in the mid-20th century established consistent lighting conditions to minimize variability in test outcomes. The (ISO) and (ANSI), in collaboration with the Commission Internationale de l'Éclairage (CIE), defined guidelines for illuminants in , recommending CIE C—an approximation of average daylight with a of about 6774 K—for viewing pseudoisochromatic plates and other tests to ensure reproducible results across global clinical practices. By the 2000s, the transition to digital platforms revolutionized color vision testing, offering automated administration, higher sensitivity, and reduced subjective bias compared to traditional methods. Tests like the Colour Assessment and Diagnosis (CAD) system, developed in the early 2000s, utilized computer-generated stimuli to isolate chromatic pathways and quantify deficiency severity, while the Cambridge Colour Test provided adaptive algorithms for precise discrimination thresholds. This shift culminated in regulatory adoption, with the U.S. Federal Aviation Administration (FAA) mandating approved computerized tests for pilot medical examinations effective January 1, 2025, to standardize screening and improve detection accuracy in aviation.

Pseudoisochromatic plate tests

Ishihara test

The , developed by Japanese ophthalmologist in 1917, is a pseudoisochromatic plate test designed to screen for congenital red-green deficiencies. It remains one of the most widely used color vision screening tools globally, valued for its simplicity and effectiveness in detecting protan and deutan defects despite its age. The test comprises plates made of numerous small colored dots of varying hues, saturations, and brightness levels arranged on a neutral background. In the full edition, there are 38 plates, though common variants include 24-plate, 16-plate, and 14-plate versions for shorter administrations. These plates form numerals (for literate individuals) or winding paths (for children or illiterates) that are visible to those with normal trichromatic vision but typically obscured, altered, or invisible to individuals with red-green color deficiencies, exploiting the confusion between red and green tones. The plates are categorized into demonstration types (to explain the task), screening types (to detect deficiencies), and transformation types (to distinguish protan from deutan defects). The procedure requires viewing the plates binocularly at a standardized distance of 75 cm under daylight illumination (Illuminant C or equivalent artificial light adjusted to match), with each plate held perpendicular to the patient's . The patient verbally identifies the embedded figure within 3 seconds per plate, starting with demonstration plates to confirm comprehension. Transformation plates, such as those where normals see "35" but protans see "5" and deutans see "3," help differentiate defect types by revealing specific misperceptions. Testing typically takes 3–5 minutes and is conducted in a well-lit environment to minimize external influences. Interpretation relies on the number of correctly identified plates: for the 38-plate version, normal vision is indicated by 4 or fewer errors, a deficiency by 8 or more errors, and borderline results (5–7 errors) warrant confirmatory testing with more precise methods like anomaloscopy. The 24-plate and 16-plate variants use thresholds of 2 or fewer errors for normal and 6 or 4 errors for deficient, respectively. Its strengths include rapid administration, high screening sensitivity for red-green deficiencies ( = 0.95–1.00), and broad acceptance by occupational and regulatory bodies. Limitations encompass inability to detect tritan defects, only qualitative (not quantitative) assessment of severity, and inconsistent reliability ( = 0.10–0.70), with potential for legibility errors in some cases.

Hardy-Rand-Rittler test

The Hardy-Rand-Rittler (HRR) test, first published in 1955 by the based on research from the mid-1940s, represents a significant advancement in pseudoisochromatic plate testing for deficiencies. The current 4th edition, available since the early 2000s, is the most widely used version and has been validated for improved detection of acquired dyschromatopsia. Developed by LeGrand H. Hardy, Gertrude Rand, and M. Catherine Rittler, it incorporates 6 screening plates (4 for red-green defects and 2 for blue-yellow defects), 14 diagnostic plates (10 for red-green and 4 for tritan or blue-yellow defects), and uses geometric shapes such as crosses, circles, and triangles embedded in pseudoisochromatic dot patterns to minimize reliance on numeracy or language skills. In the procedure, the test is administered at a viewing distance of approximately 75 cm under controlled illumination of 100-650 , with patients asked to identify the geometric symbols on each plate within 2-3 seconds per plate. The screening plates first determine if a deficiency is present; if errors occur, the diagnostic plates follow to classify the type (protan, deutan, or tritan) and grade severity based on the progression of errors in increasingly difficult plates—for red-green defects, mild if limited to plates 7-11, medium extending to 12-14, and strong including 15-16; a similar scale applies to blue-yellow defects—allowing for quantitative assessment of defect extent. Key advantages of the HRR test include its ability to detect all major congenital and acquired color vision deficiencies, including rare tritan defects that confound many other plate tests, while providing severity grading that supports clinical monitoring and differentiation between mild and severe cases. It also demonstrates greater reliability across varying lighting conditions compared to earlier tests, reducing false positives or negatives in non-standard environments, and its use of simple shapes makes it particularly suitable for pediatric and non-verbal populations. In clinical settings, the HRR test is preferred over the for comprehensive assessments due to its broader detection capabilities and diagnostic depth, especially in practices evaluating optic neuropathies, dystrophies, or occupational fitness where tritan defects or severity grading are relevant.

City University test

The City University Colour Vision Test (CUT), developed by Robert Fletcher at City University London in the 1970s with its second edition published in 1980, is a pseudoisochromatic plate test designed to detect and differentiate moderate to severe red-green (protan and deutan) and blue-yellow (tritan) color vision deficiencies. It builds on pseudoisochromatic principles by exploiting color confusions where hues that appear distinct to normal observers are similar for those with deficiencies. The test uses Munsell colors derived from the Farnsworth-Munsell D-15 arrangement, presented in a format that allows classification of defect types beyond the red-green focus of earlier tests like Ishihara. The test comprises 11 plates: one demonstration plate and 10 test plates, each featuring a central test spot surrounded by four comparison spots of varying chroma and hue. Under controlled daylight illumination of approximately 600 at a viewing of 35 cm, the observer uses a soft-tipped pointer to indicate the comparison spot most similar to the central one within 3 seconds per plate. Responses are recorded in columns corresponding to normal vision, protan, deutan, or tritan classifications, with scores computed as the fraction of correct identifications out of 10 to determine pass/fail and defect type. The third edition, released in 1998, incorporates desaturated colors and smaller disc sizes (5 mm for screening, 8 mm or 5 mm for diagnostics) to enhance detection of milder defects and tritan confusions, dividing the test into a four-plate screening phase and a six-plate diagnostic phase for severity assessment. This design emphasizes sensitivity to blue-yellow deficiencies and milder red-green anomalies, which are often missed by saturation-heavy plates in standard tests, making it suitable for screening acquired conditions like those from retinal pathology or medication effects. For instance, it achieves 96% accuracy in classifying dichromatic defects and shows high agreement (AC1 = 0.90) with the Ishihara for red-green screening while providing tritan-specific plates absent in many alternatives. Compared to the Hardy-Rand-Rittler test's geometric shapes and path-tracing for broad typing, the CUT prioritizes hue matching with desaturated stimuli to isolate subtle tritan and mild protan/deutan errors. However, limitations include reduced specificity for very mild defects (19-25% of passers may fail the D-15) and potential misclassification of protans as deutans in about 50% of cases, alongside a administration time of around 5-10 minutes that exceeds rapid screeners.

Arrangement tests

Farnsworth-Munsell 100 Hue test

The Farnsworth-Munsell 100 Hue test was developed in by Dean Farnsworth as an exploratory method for evaluating through hue arrangement. The test utilizes 85 removable colored caps distributed across four trays or quadrants, each covering a portion of the Munsell hue circle at constant value and chroma, with fixed anchor caps at the ends to guide the sequence. These caps are presented on a non-reflecting black background under standard daylight illumination, such as CIE illuminant C or D65, to ensure consistent color perception. In the procedure, the participant arranges the randomized in each quadrant into perceived order of hue progression, starting from one fixed end and matching to the other, typically taking 2-3 minutes per quadrant for a total of 15-30 minutes. The test can be administered monocularly or binocularly, with encouragement to work quickly but accurately, and retests are recommended after hours or days to account for practice effects. This task quantifies subtle differences in hue by revealing patterns of confusion along color axes. Scoring involves calculating the total error score (TES) as the sum of the square roots of adjacent mismatches, where for each cap with number CC placed between adjacent caps LL and RR, the contribution is (C−L)2+(C−R)2\sqrt{(C - L)^2 + (C - R)^2}
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