Most people relate the term color blindness test to the dotted pictures or even to the name Ishihara.

But this is not the only one, not the best one, definitely not the most current one, and most often an unsuitable test which is still used all around the world.

This part of the Color Blind Essentials series focuses on the different possibilities to test color vision, how they work, what they can be used for and lists some of the well-known and used tests. There will be no conclusive enumeration as there are just to many tests around, with a lot of them not available anymore but still in use.

First color blindness tests

Already in the 17th century Turberville found differences in some individuals color naming, which was definitely one of the first color blindness tests. About one hundred years later John Dalton described in detail his color vision and also tested other people with some colored ribbons which had to be named as well. At this time most often color vision deficiency was reported simply by subjective descriptions.

In 1837 August Seebeck used some more advanced technique. He used a set of more than 300 colored papers and let people match or find a closely related color to a sample color. This type of color vision test abandoned the naming of colors, which differs a lot between test persons. Through Seebeck’s color blindness test two different types of red-green color blindness and a broad severity scale were discovered. Holmgren adopted this kind of test in 1877 by using skeins of wool. The Holmgren wool test was widely used and even commercially available more than one hundred years later.

The following two developments happened around the same time. They led to modern color vision deficiency testing.

• John William Strutt Rayleigh developed a precise color matching test. This match—still known as Rayleigh match—is not only the base of modern anomaloscopes but also made him discover dichromatism and anomalous trichromatism.
• Dr. J. Spilling published the first painted set of pseudoisochromatic plates. They were the predecessors of the famous Ishihara plates, which were produced the first time in 1917.

The different color vision deficiency test forms

Anomaloscope

Anomaloscope

The anomaloscope provides the most accurate possibility to test the severity of color blindness and distinguish between dichromats and anomalous trichromats.

It is based on the Rayleigh match: A mixture of red and green light sources has to be matched with a yellow light source. Through the matching range it is possible to discover all different types of red-green color vision deficiency. Some of the anomaloscopes also include the Moreland match (blue-green) to test for tritan defects.

If you are a dichromat you will be able to make a match for all red-green mixture ratios. Anomalous trichromats don’t accept the normal match and the distance of their match indicates the severity of their deficiency. On the other side, if you suffer a protan vision deficiency you will use much more red to match the colors compared to people with a deutan defect, which use more green in their mixture.

In 1907 the Nagel anomaloscope was introduced and is still known as one of the best. Unfortunately it is not produced anymore. Other well known instruments are the Neitz anomaloscope, the HMC (Heidelberg Multi Color) anomaloscope or the Pickford-Nicolson anomaloscope.

Pseudoisochromatic plates

Pseudoisochromatic plates are the most famous type of color blindness test. Most people know them under the name Ishihara plates test, because Dr. Shinobu Ishihara was one of the first persons who designed a very reliable plate test, introduced in 1917. He produced different test sets. Ishihara plates are still widely used all around the world.

The copunctual points build the source for this type of color vision test. The fact that colorblind people can’t distinguish colors along the confusion lines is used to build a pattern of differently colored dots. If you are color blind you won’t spot the dots which are shifted along the confusion lines and therefore numbers, letters, lines or anything else can be hidden from you.

There exist four different type of plates:

• Vanishing design: Only people with good color vision can see the sign. If you are colorblind you won’t see anything.
• Transformation design: Color blind people will see a different sign than people with no color vision handicap.
• Hidden digit design: Only colorblind people are able to spot the sign. If you have perfect color vision, you won’t be able to see it.
• Classification design: This is used to differentiate between red- and green-blind persons. The vanishing design is used on either side of the plate, one side for deutan defects an the other for protans.

Why can colorblind people see something which is not visible for people with perfect color vision?
If you are colorblind you are not distracted by hue differences along the confusion lines. You will be more focused on lightness differences. This two different facts are used to design the hidden or invisible plates.

Besides the most famous Ishihara plates exists in a standard version of 38 plates, a shorter version of 24 plates and a concise test containing 14 plates. Ishihara plates can only be used to classify red-green color vision deficiencies. Tritan defects can not be evaluated by these tests.

The other well known pseudoisochromatic test plates are the 24 HRR plates by Hardy, Rand and Ritter. This test was first produced in 1954 and can be used the classify all three different forms of color vision deficiency. There also exist a lot more of such tests but none of them is widely used. Even some electronic vision test equipments include certain pseudoisochromatic plates as a quick color vision test. But none of them is very accurate to get a concise test result.

Arrangement tests

Arrangement tests are also based on the theory of copunctual points. In contrast to the static pseudoisochromatic plates where you have to spot a path or number, an arrangement test is dynamic.

D-15 Color Arrangement Test

Every such test consists of a certain number of colored discs or plates which have to be arranged in the correct order, starting from a pilot plate. The colors are chosen around the white point and because colorblind people can not distinguish colors along certain lines they will arrange the discs completely different compared to somebody with normal color vision.

The most well known test was introduced by Fransworth in the forties of the last century and is called Farnsworth D-15 arrangement test. As the names suggests this test includes 15 colored plates which have to be arranged in the correct order. You can try an online version of this test right here at Colblindor: Color Arrangement Test.

Some other well known tests in this category are the Lanthony desaturated D-15 test, which is used to classify milder forms of color blindness and the Farnsworth-Munsell 100 hue test. This test includes 100 different plates which have to be arranged in batches of 20 plates. Unfortunately the results are not that better compared to the 15 plates versions.

Lanterns

The last well known type of tests was introduced by railway companies which discovered, that some of their employees couldn’t distinguish certain signal lights. Lantern tests are specially designed to simulate signals and are therefore most often used as vocational tests.

Compared to the other tests with lanterns you are testing the required ability directly. They are robust and have a high practical value. On the other side you can’t reveal much of the nature and severity of the color vision defect.

• Holmes-Wright lanterns: This lantern includes two different green, two red and a white light. Lights are shown in pairs of two, low or high brightness, either vertically or horizontally aligned. The test person is asked to name the colors.
• Farnsworth lantern (Falant): This is the standard test in the US. It is comparable to the Holmes-Wright lantern but is specially designed to pass people with a mild form of color vision deficiency.
• Beyne lantern: France.
• Giles-Archer lanterns: UK.
• Edridge-Green lantern: UK.

The following table shows an overview of the different main test types for color blindness and compares them in certain dimensions. Every test type is graded from (-) not capable to (+++) excellent capability.

Unfortunately Ishihara plates are used much to often to check for occupational suitability. Lanterns or certain arrangement tests would be much better in this case. And if you like to have a precise diagnosis of your color vision deficiency there is no way around an anomaloscope.

The future of color vision testing

Today in our digital world one might think, why don’t we have some simple computer based color blindness test. Unfortunately this is not as simple as it looks like. There are two main problems:

1. Computers displays just make use of three main colors red, green and blue (RGB). Every other color gets mixed from those three colors. The anomaloscope and lantern tests use different light sources which can’t be simulated by a display.
2. Every computer display has a different color range it covers, little differences in light sources, different brightness and more. This causes different test results. Only calibrated computers can be used to perform such computer based tests.

The City University in London developed a computer based color vision test which is also based on the same principal as pseudoisochromatic plates and arrangement tests. The main difference is that the colors are constantly changing which gives some really good results. Just recently they used their test to check color vision in pilot candidates and it looks like as the Color Assessment & Diagnosis Test (CAD Test) could become a standard screening instrument for color vision testing. At least for certain professions, where color vision is critical but people with a mild form of color vision still perform perfectly.

There are also some genetic screenings available. But even such a simple impairment as color blindness is not easy to detect in the genes. So every genetic test always needs some physical tests in parallel to get a proper and concise test result.

Color naming would be a very simple test to identify color blindness. But for most cases this is just to simple, to unspecific and not reliable enough. Therefore color naming can be used to check if you have a moderate to strong color vision deficiency but not for a detailed classification of your color vision deficiency.

The next part of the Color Blind Essentials series focuses on how color blindness can affect your everyday life.

Color Assessment & Diagnosis Test

Because of the lack of reliable, standardised tests and the absence of information on the specific colour vision needs of professional flight crew, the UK Civil Aviation Authority supported by the US Federal Aviation Administration initiated this study.

A team around Prof Barbur from the Applied Vision Research Center in London was mandated to find the minimum color vision requirements for modern flight crew, and a new color assessment and diagnosis test. This was the last part of the study after The Use of Colour Signals and the Assessment of Colour Vision Requirements in Aviation and a Task Analysis which included two operating case studies: the Airbus A321 and Boeing 757.

Dr Sally Evans, Chief Medical Officer at the CAA, says:

“The current diversity in colour vision testing methods and standards demonstrates the need to adopt more objective assessment techniques internationally. If the assessment methods and limits derived from this study were applied as minimum requirements for professional flight crew, 35 per cent of colour deficient applicants would be eligible for medical certification as a professional pilot. The CAA intends to promote this research internationally with a view to gaining acceptance of the CAD test and its incorporation in world-wide medical standards for pilots.”

This sounds very promising for all colorblind pilot applicants! So let us have a closer look at what this new color blindness test is all about and how they reached this new results.

Color Assessment & Diagnosis Test

The current procedures within JAA for pilot applicants are unsatisfactory for at least two reasons.

1. There is no guarantee that the deutan subjects that pass secondary tests can cope with safety-critical, color-related tasks, since the severity of their color vision loss remains unquantified.
2. Many color deficient subjects that can carry out such tasks safely fail the lantern tests and will not therefore be allowed to fly.

This findings and many detailed studies on color vision deficiency resulted in a new color blindness test, the color assessment & diagnosis test (CAD test). The subject’s task is to report the direction of motion of a colored square on a gray square background with dynamic luminance contrast noise. This new developed color vision test has shown in a broad study to be very accurate in identifying type and severity of one’s color blindness.

The subject’s color vision severity is measured in Standard Normal units (SN units). If your result would show a red-green threshold of 2 SN units this would mean, that you need a twice as strong color signal compared to a average standard CAD observer. This threshold can be quit different for deuteranomalous and protanomalous observers as a limit to pass the PAPI test. Details on this are shown in the conclusions.

PAPI Test

The Precision Approach Path Indicator (PAPI) was indicated as the most important, safety-critical task that relies largely on color vision. On this basis a PAPI simulator test was developed to quantify the severity of a pilots color vision deficiency which is still safe to fly. This simulator can be used in controlled laboratory environments.

PAPI Test Simulator

The simulator reproduces both the photometric and the angular subtense of the real lights under demanding viewing conditions when the lights are viewed against a dark background. Since other color-related tasks such as seeing the color of the parking lights or the discrimination of runway, center-line, red and white lights are less demanding, it is assumed that the pilot will also be able to perform correctly these tasks.

The aim was to identify type and severity of color vision deficiency which cause problems with the PAPI test and correlate those results to the CAD test results. In principle, this approach should make it possible to recommend pass/fail limits based on the observer’s ability to carry out the most safety-critical and demanding PAPI task.

Principal conclusions

The very promising results suggest that subjects with minimum color blindness that does not exceed 6 SN units for deuteranomalous observers and 12 SN units for protanomalous observers perform the PAPI test as well as normal trichromats. If these findings were adopted as pass/fail limits for pilots ~35% of color deficient applicants would be classed as safe to fly.

• When the ambient level of light adaptation is adequate, normal aging does not affect significantly either red-green or yellow-blue thresholds below 60 yrs of age.
• Analysis of PAPI results shows that the use of a modified white light results in significant, overall improvements in PAPI performance.The modified white is achieved simply by adding a color correction filter.
• 43 of the 77 deuteranomalous subjects failed the PAPI test. 29 out of the remaining 34 subjects that passed the PAPI test had CAD thresholds < 6 SN units.
• 20 of the 40 protanomalous subjects failed the PAPI test. 13 out of the remaining 20 subjects that passed the PAPI test had CAD thresholds < 12 SN units.

The study also concluded that the administration of the CAD test eliminates the need to use any other primary or secondary tests. When one includes normal trichromats, ~94% of all applicants will pass the so called fast-CAD screening test and be classified as safe to fly. This process is very efficient since the fast-CAD test is simple to carry out and takes less than 30 seconds to complete.

Official CAA news:
CAA research paves the way for more people with CVD to become pilots
CAA Paper 2009/04:
Minimum Colour Vision Requirements for Professional Flight Crew

Jay Neitz from the Neitz Color Vision Lab could just recently cure some colorblind monkeys and also developed a genetic color vision test. Building upon this basis in this new partnership they want to develop a new standard for color blindness tests and possibly have a breakthrough in curing color deficient patients.

Matt Lemelin, the founder and CEO of Genevolve:

“Our goal is to establish a new world standard for color vision testing and to increase public safety while providing a diagnosis that doctors may discuss with their patients. With this process, we can now diagnose the type of colorblindness and the extent of deficiency with amazing accuracy and precision.”

Lemelin also lists some of the reasons, why such a genetic color blindness test is a need today:

• Age: Todays color blindness tests often require a minimal age of at least 5 years. This could potentially affect a child’s development.
• Memorizing: Persons can memorize a test and alter the result. This could be very dangerous for some specific jobs.

I personally believe that a genetic test is only needed because people themselves want to have something fool-prove. A test which tells them the truth about their color vision, which is not influenced by some doctors judgment. Of course a fool-prove test also makes the testers feel more safe. But I don’t really think that the above two statements are true:

• Children don’t have to be tested much earlier. They can’t grasp the concept of color yet and don’t need special assistance in daily life until they recognize it themselves.
• Arrangement tests, anomaloscopes and lanterns can’t really be memorized. And even a plates test only needs a shuffle to unmask any potential cheater.

Anyway, the colorblind community is definitely looking forward to get an accurate color vision test which can be used as a standard for many job specific vision tests and as a matter of course a gene therapy to cure color blindness. We will wait patiently for further news…

You can read the whole article from the NMSU here: DNA lab at NMSU partners with company to fight colorblindness. And don’t miss the latest breakthrough in color blindness gene therapy of monkeys.

Yves contacted and told me about this error. What happened? I forgot to perform the chromatic adaptation from D50 to D65 for the sRGB color space. This means I actually assume the XYZ values were taken under a white-blueish D65 light while in reality they were measured under D50 which is white-yellowish. This means I have overestimated the red and underestimated the blue.

Today I updated the test with the new values. The used colors should now be correct and ready to try out: Online D-15 Color Arrangement Test.

I you’ve taken the test previously the result won’t change that much as the colors are just slightly shifted in the color space. My results were still very unpromising: Strongly color blind!

Just the other day I took a picture of a rainbow. It was such a beautiful one, but I couldn’t see the color spectrum so I had to ask my son, if it is really a nice one where you can spot the whole color spectrum. The same would happen if I would work as a professional in the film industry: Either I could ask somebody for help or I just would fail. My color blindness is just to strong to deliver good work.

Truelight Color
Vision Test

FilmLight is a leading company in the film industry and provides a simple online color blindness test on their website. This way you can perform a first check if you are ready to work with moving pictures. Can you spot the T? Check out their website to see the whole Truelight color vision test picture.

This color blindness test picture consists of three lines each showing six T’s. Four of them should be visible and you should be able to tell their orientation. You should also be able to guess the fifth correctly and the sixth is just visible under perfect conditions. The three lines of T’s relate to the three different types protan, deutan, and tritan color vision defects. The test is based on the color blindness confusion lines.

You can’t see anything? — No worries. I can only spot two T’s in the last line. Only if I bend my laptop display back and forth I see two more T’s, but not more.

If you did like this kind of test make sure to check out my color blindness tests or have a look at some other color vision tests online available.