Ishihara Color Blindness Test

Shinobu Ishihara (石原 忍)
The most commonly used test to detect color vision deficiencies was developed by the Japanese ophthalmologist Shinobu Ishihara (1879-1963). While working at the Military Medical School he was asked to devise a test to screen military recruits for abnormalities of color vision. His assistant was a colorblind physician who helped him test the plates. A collection of 38 plates filled with colored dots build the base of this test. The dots are colored in different shades and a number is hidden inside with shades of another color.

• What color do color vision deficient people dream in?
We only dream of what we know... People who become blind after birth can see colors and images in their dreams. People who are born blind do not see any images, but have dreams equally vivid involving their other senses of sound, smell, touch and emotion. It is hard for a seeing person to imagine it. So, colorblind people dream in the color set they see in real life... However, a full 12% of sighted people dream exclusively in black and white!

• How do color vision deficient persons perceive a colorwheel?

Mouse over this standard colorwheel to see it as a colorblind person might see it.

• Reverse color blindness test
Color vision deficient people have a tendency to better night vision and, in some situations, they can perceive variations in luminosity that color-sighted people could not. Only color blind people can actually read what is written in the picture below... That means, if you fail the test, you probably have the full range of color sensitivity that is attributed to color-sighted people. (highlight answer: NO)

Image taken from Sarcone's book Puzzillusions

• What bothers colorblind people most?
- When grilling a piece of meat, a red deficient individual cannot tell whether it is raw or well done. Many cannot tell the difference between green and ripe tomatoes or between ketchup and chocolate syrup!
- Some food may look definitely disgusting to color vision deficient individuals: a plate full of spinach, for instance, just appears to them like cow pat.
- They can however distinguish some citrus fruits. Oranges seem to be of a brighter yellow than that of lemons.
- A colorblind person is generally unable to interpret the chemical testing kits for swimming pool water, test strips for hard water, soil or water pH tests because they rely on subtle color differences.
- Many colorblind people cannot tell whether a woman is wearing lipstick or not. More difficult to handle for some is the inability to make the difference between a blue-eyed blonde and a green-eyed redhead.
- Color vision deficiencies bother affected children from the earliest years. At school, coloring can become a difficulty when one has to take the blue crayon - and not the pink one - to color the ocean.
- Bi-color and tri-color LEDs (Light Emitting Diodes): is that glowing indicator light red, yellow, or green? Same problem with the traffic lights...

• I need to pass a color blindness test for work. What can I do?
Some jobs require their employees to take a color vision deficiency test (often using the Ishihara plates above). For instance, good color vision is vital for recognizing various lights and signals important to pilots, especially at night. These tests are required by, among others, the coast-guard and most military and emergency services. Unfortunately, if you really are colorblind, there is very little you can do to pass these tests.

• How can colorblind people compensate for their deficient color vision?
While there are no cures for color blindness, there are many possibilities to help control the annoyance of this disease. A possible treatment for color vision deficiency is to use special glasses with red-orange filters to make it easier to interpret colors or actually to better see contrasts. Another way to control symptoms is to use what is called the X-Chrom lens. The X-Chrom lens is a red contact lens worn on the non-dominant eye of color deficient people and which helps some to better interpret colors or contrasts. The X-Chrom lens does not restore normal color vision, it just allows some colorblind individuals to distinguish colors better.

• How can I create a colorblind friendly website?
Apart from its aesthetic appeal, seeing many different colors allows us to distinguish things in the world. However, remember that there are always colorblind people among your audience and readers. Actually, there could be more than TEN colorblind people per 250 people visiting your site.
Then, we, the web community, must create an atmosphere which makes it easier for colorblind individuals to differentiate between text and background along with images! There are 2 ways that we can make information in pictures available to colorblind people:
1) The simplest way is to increase the red/green contrast in the images.
2) We can also convert the variations in red and green colors into variations in brightness and/or blue/yellow coloration.
One way to test your website for colorblind usability is by using these tools:
- Colorblind Web Page Filter,
- Vischeck.
Each tool will show a copy of your web page as if it was seen as a select type of color vision deficiency.
Firefox also has a great add-on which allows webmasters to see color contrasts:
- Color Contrast Analyser Firefox Extension.

• How can teachers help if a student has a color vision deficiency?
1) Always use white chalk, not colored chalk, on the board to maximize contrast. Avoid yellow, orange, or light tan chalk on green chalkboards.
2) Xerox parts of textbooks or any instructional materials printed with colored ink. Black print on red or green paper is not safe. It may appear as black on black to some color vision deficient students.

• I am colorblind and work on a computer - is there a way that I can determine the various colored graphics or letters?
Yes, there is a new product called eyePilot that might help you. It is an interactive software program that takes a picture of your screen and allows you to manipulate various color.

• What is the relation between colorectal cancer and color deficiency?
Men are statistically more likely to die of colorectal cancer than women, and it is thought that one reason for this is that they are more likely than women to be color vision deficient. The link is that if you are red colorblind, when you look at a piece of used toilet paper it may all look the same color, even though there is red and brown on there. Hopefully, the other symptoms will prompt the color deficient person to seek medical attention (source: h2g2).

• Are there 'false' colorblind persons?
There is a type of color vision deficiency that is caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina. This kind of color vision deficiency is called "cerebral achromatopsia". People affected with cerebral achromatopsia are perfectly aware of their visual experiences; however, they are unable to imagine or remember colors. They see the world like a black & white television where everything is a shade of gray. They cannot chromatically order or discriminate hue but they can distinguish color contrasts like a normal person. 'Transient achromatopsia' is a temporary loss of colour vision caused by a short-lived vascular insufficiency in the occipital cortex.

• Are cats and dogs color vision deficient?
Yes, we can compare man’s best friends’ vision with the vision of human being suffering from red or green color vision defiency (protanope, deuteranope, see fig. below). Dogs do see in color, but have two-color, or dichromatic vision, that is, they cannot distinguish between red, orange, yellow or green. They can see various shades of blue and can differentiate between closely related shades of grey that are not distinguishable to people. Cats have the ability to distinguish between blues and greens, but lack the ability to pick out shades of red. However, cats and dogs are primed to see "motion", rather than defining the world through sight alone. They use a blend of senses such as smell and hearing with their vision to do what we humans use our eyes alone to do.