Color blindness or color vision deficiency is the inability or decreased ability to see color, or perceive color differences, under lighting conditions when color vision is not normally impaired. "Color blind" is a term of art; there is no actual blindness but there is a fault in the development of either or both sets of retinal cones that perceive color in light and transmit that information to the optic nerve. The gene that causes color blindness is carried on the X chromosome, making the handicap far more common among men (who have just one X chromosome) than among women (who have two, so must inherit the gene from both parents).
The symptoms of color blindness also can be produced by physical or chemical damage to the eye, optic nerve, or the brain generally. These are not true color blindness, however, but they represent conditions of limited actual blindness. Similarly, a person with achromatopsia, although unable to see colors, is not "color blind" per se but they suffer from a completely different disorder, of which atypical color deficiency is only one manifestation.
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The image below can be used as a simple, non-medical test for red-green colorblindness in children. Originally published in Field and Stream magazine, the test was intended for potential hunters. However, the animal shapes can usually be identified by young children who may not yet be able to read numbers, which are used in standard colorblindness tests.
A larger version of the image, which can be printed on plain white paper (or photo paper), can be found here.
The image should be presented to a child in private. The child can be asked if they see any animals. There should be no prompting. The key for what can be seen with differing color vision can be seen below:
Past use of this test indicates the following:
Children with normal vision can see the bear, deer, rabbit, and squirrel. They cannot see the fox.
Children with a red-green color vision deficiency see a cow (instead of the deer), a fox (in the lower left), and usually the rabbit and squirrel. They cannot see the bear. Red-green colorblindness apparently occurs in varying degrees--mild to severe. Children with severe red-green color vision deficiency may have difficulty seeing the rabbit and/or squirrel. Generally, anyone with a red-green color deficiency cannot see the bear, but can see the fox.
Children (and adults) with a red-green color deficiency have difficulty differentiating shades of the following colors from each other:
red from green
green from brown (especially beige)
blue from purple
pink from gray
Note that most color deficient children can identify pure primary colors.
In each of these cases, the color red (found in red, brown, purple, and pink) cannot be discerned, making the distinction difficult. Thus children see purple azalea or crepe myrtle blossoms as blue. They have difficulty seeing the browned pine needles among the green ones. A flashing traffic light could be red or amber. Green traffic lights look white.
Because of the shift in the color vision of those with red-green colorblindness, those with the deficiency can more readily differentiate yellow and blue from green. Yellow and/or blue are frequently the “favorite colors” of those with a red-green color deficiency.
Obviously once identified, tact must be used when informing a child of this vision issue. Care must also be shown when dealing with such children in a group setting, so as not to call undue attention or create a reason for discrimination or ridicule.
Given the frequency of this condition, it is surprising that testing is not done on all children prior to entering pre-school or school. This condition should be identified early, so that parents, caregivers, and teachers can address it with understanding, patience, and respect.