Question of the Week

August 10, 2009


Depending on the students and their backgrounds, the chances of having a student in class who has some form of color blindness will vary.

"Red-green color vision defects are the most common form of color vision deficiency. This condition affects males more often than females. Among populations with Northern European ancestry, it occurs in about 8 percent of males and 0.5 percent of females. Red-green color vision defects have a lower incidence in almost all other populations studied. Blue-yellow color vision defects affect males and females equally. This condition occurs in fewer than 1 in 10,000 people worldwide. Complete achromatopsia affects an estimated 1 in 30,000 people. This condition is much more common among Pingelapese islanders, who live on one of the Eastern Caroline Islands of Micronesia. Five percent to 10 percent of this population have a total absence of color vision."

With so many different ways for someone to be affected by a color vision deficiency, even the phrase "color blindness" can be confusing.

"Color blindness is a common eye condition that makes it difficult to distinguish certain colors. A person that is color blind often experiences problems determining colors like yellow, red, blue or green. Color blindness refers to a deficiency in the way you see color, and not any form of blindness. ... The problem is caused by a cell defect in the retina of the eye. The light absorbing tissue in the back of the eye that transforms what we see into signals to the brain partly contains cells that distinguish colors. When these cells in the retina are not working correctly color blindness occurs. ... If you experience any difficulty in seeing color we recommend you visit your local eye doctor for a proper eye examination."

While most people with color blindness can learn to adapt fairly easily, there is still one area that those with red-green color blindness can still have difficulties: driving. Most stoplights have the red light on top and the green light on the bottom. When this is the case, those who are color blind can often interpret the traffic light by using brightness and location, rather than color. When the traffic lights are horizontal, or when there are other factors that make detecting brightness difficult, interpreting the signal can become more complicated.

"In the fall of 2002, the Minnesota Department of Transportation (Mn/DOT) received a complaint from a color-blind citizen concerning his ability to properly perceive the new LED indications. Under direct sunlight conditions, especially near the spring and fall equinox, the color-blind individual could not determine which indication, either red or green, was illuminated. ... Both color-blind and non-color-blind subjects were driven through the test intersections, and interviews were conducted at each intersection. The study determined that:

  • There is a difference in green LED perceptions between color-blind and non-color-blind people.
  • There are different impacts on perceptions from different signal indication designs. The green-tinted lens was better for the color-blind, but the clear lens was better for the non-color-blind.
  • The best solutions are very different for color-blind versus non-color-blind travelers. The brand and the design of the head (high LED count versus low LED count) that was best was different for color-blind versus non-color-blind."

For pictures of the traffic lights as seen by people with various types of color blindness, visit the above link. For a color blindness simulation which helps those without color vision deficiencies to see how those with different deficiencies would see the same image, visit:

If you think that you, or someone you know, may have a color vision deficiency, "Feel free to test your eyesight in our color blindness online test below to determine your color perception."

If you would like a professional vision assessment, "Eye doctors (and some school nurses) test for color blindness by showing a picture made up of different colored dots... If a person can't see the picture or number within the dots, he or she may be color-blind. Boys are far more likely to be color-blind. In fact, if you know 12 boys, one of them is probably at least a little color-blind."

Questions of the Week:
Why is it important for those with and without color vision deficiencies to understand color blindness? How might color vision deficiencies affect a person's job choice? How might red-green color blindness affect how a person learns to interpret traffic signals and other color-based indicators? What other aspects of a person's life might be affected by color visions deficiencies?

Please email me with any ideas or suggestions.
Note: Due to increasing amounts of SPAM sent to this account, please include "QOW" in the subject line when sending me email.

I look forward to reading what you have to say.

Health Community Coordinator
Access Excellence @ the National Health Museum

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