COLORBLINDNESS:COLORBLINDNESS: Invisible Disability John Stiles Ruamrudee International School

What is it? Color “blindness” is more correctly known as color “deficiency.” It is the inability to see or identify certain colors of the visible light spectrum. Color “blindness” is more correctly known as color “deficiency.” It is the inability to see or identify certain colors of the visible light spectrum.

How does one “get” it? Dyschromacy is inherited. It is caused by a gene on the “X” chromosome. A male with an affected “X” chromosome will inherit the condition (always inherited from the mother). A female must be born with BOTH “X” chromosomes affected (inherited from both parents). A female with only one affected “X” chromosome will not have the condition, but may pass the gene to one of her children.

“Normal” Female “Carrier” Female “Colorblind” Female

“Normal” Male “Colorblind” Male X Y X Y

What causes it? “Normal sighted individuals have a certain ratio of signals from three types of color cones on the retina of the eye. Those with dyschromacy may have different absorption rates of the cones (reddish perceiving, greenish perceiving, or bluish perceiving).

Normal Vision

Red-Green Deficiency

Blue-Yellow Deficiency (Rare)

Deuteranopia-Normal-Protanopia

Problems in Science

Can colorblindness be “corrected?” Daltonization is a process that analyzes the information in the red/green domains and convert them to changes in blue-yellow coloration or brightness, allowing colorblind persons to see dimensions otherwise invisible (

Daltonized image Simulated image

Ishihara Test Used to check for red/green colorblindness:

Ishihara Test This is what a person with red/green colorblindness might see:

Can colorblind people “see” colors? A red/green color deficiency means that reds and greens are more difficult to distinguish. But as the following photos demonstrate, many other colors are just as distinguishable to a person with a color deficiency as to someone with normal color vision.

Normal Protanope Tritanope

Why does it happen? This resulted from an evolutionary “accident” 40 million years ago after Africa and South America split apart. All old world primates, including humans, have separate red and green receptors. New world primates have a single red-green receptor. Humans apparently are the only Old World primates to have had their color receptors mutate. Apes do not seem to experience color deficiency.

How many people have dyschromacy? Approximately 8% of the population have color difficulties (estimates range from 4- 12%). This means that in a class of 25, one, and possibly more, likely will have difficulty distinguishing colors. Most will be male (Males are 17 times more likely to be colorblind than females).

How can teachers help? Acknowledge the disability as legitimate. Never ask students with dyschromacy to “prove” their disability. Talk to the student and parents. Ask how you can help. Consider alternatives to color coding:

What teachers can do (cont.) Use gray scales or B&W; Use symbols or shapes (this can be in addition to using color codes: a red diamond for example); Label the colors; Consider not using the colors that cause difficulties; Use Black on White instructional sheets.

What teachers can do (cont.) Allow sketches as an alternative to color reproductions; Advocate for early dyschromacy screening (Ishihara test); Let the student(s) know (privately) that you will help if they would like to discuss color deficiency in class; If you are colorblind, talk openly about it with your students.

Online Article Iowa Science Teachers Journal Fall 2005 edition 5/index.html

WEB LINKS FOR MORE INFORMATION Ishihara Test for Color Blindness: Causes of color blindness: Chromosome-based historical information: Howard Hughes Medical Institute Image corrections for colorblindness: Vischeck Comparison examples: <

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