Exploring Color Vision Deficiency

Posted Jul 31, 2005
Last Updated Jun 21, 2012
EXPLORING COLOR VISION DEFICIENCY (COLORBLINDNESS)
By Arlene Evans

Black fingerpaint was Jim Doane's choice when he was in kindergarten. "Nobody wanted black," he explained, "so it was always available." In first grade he was sent to the principal's office because he didn't follow the red line to the cafeteria. He learned reading and arithmetic well in spite of color-coded workbooks. He was humiliated in high school by passing a ball to a member of the team with the red jersey instead of to his own team member with the green jersey. He wanted to be a physician but was told that doctors couldn't be colorblind.

Doane is far from alone. Approximately eight to ten percent of the worldwide population has some degree of color vision deficiency (CVD) or colorblindness.. This includes 1:12 males and 1:200 females. Although the condition is more common in those with European ancestry, it exists in people of all races and ethnic origins. Doane also isn't blind to color, so CVD is a more accurate term.

A sex-linked recessive condition, CVD is carried on the X chromosome. Females have two X chromosomes, so if one is affected, the unaffected chromosome will dominate and she will be a carrier. Males, on the other hand, have one X and one Y, so if their X is affected, they will have CVD. A male passes his Y chromosome to his sons who have typical color vision. He passes his affected X chromosome to his daughters who are then carriers. With each pregnancy, a carrier has a 50 percent chance of passing her affected X on. The daughters who inherit it will, like their mothers, be carriers. The boys who inherit it will have CVD. For a female to be affected, she must inherit an X from each of her parents.

Most people have trichromatic color vision. They use three primary colors of light -- red, green and blue -- that blend in a variety of ways that allow them to see all the colors of the rainbow.

CVD is often called "red-green colorblindness" because red and green are the colors most often confused. Colors with red and/or green in them are also often confused with each other and with other colors, such as gray.

Although people with reduced color vision may see colors differently from each other, CVD can be classified into two main groups:

Anomalous trichromacy. Those with anomalous trichromacy also use three colors of light to match all colors, but in different proportions. Three types of anomalous tricromacy are:

*Protonomaly. Red colors are seen more weakly by this person.

*Deuteranomaly. Green is seen more weakly, which is the most common type of CVD.

*Tritanomaly. Sometimes called "blue-yellow," although blue and yellow are not confused. Confusions are between blue and green and yellow-green and violet. This rare condition is autonomic dominant and affects males and females equally.

People mildly affected with anomalous trichromacy may have no difficulty with a saturated color, but may confuse pale shades even in excellent light. Distinguishing blue from light shades of purple is difficult if red is seen faintly. If green is seen weakly, people confuse tans and browns with dull green. However, they may notice no difficulty with tasks that require typical color vision.

Color confusions increase as the extent of the CVD increases. Those who are severely affected usually know they see color differently, have various challenges in their lives, and have color vision similar to those with the condition discussed next: dichromacy.

Dichromacy. People with dichromatic vision require two colors of light -- either red or green plus blue -- to match the color spectrum as they see it. Types are:

*Protanopia (no red color vision). Red and green not only appear the same, but may look identical to gray or black.

*Deuteranopia (no green color vision). These people have similar color vision as those with protanopia. Red, orange, green and yellow all appear as one color (yellow). Violet, lavender and purple appear as another (blue).

Education and Nursing Interventions
Ideally, children should be tested for CVD in pre-school or as they enter kindergarten, where there's a heavy emphasis on color. This emphasis is helpful for most children, but not for the approximate 2:100 males and the rare female with severe CVD. When children are tested early, parents and teachers can make appropriate accommodations.

When early testing is not possible, those who are referred by teachers or parents should be tested. Also, a color vision test should be part of an evaluation for students with learning difficulties. Children have been accused of "not paying attention" when they don't respond appropriately to a parent or teacher's directions. When children confuse colors, they have been suspected of having language problems.

The school nurse can alert teachers and parents to signs indicating CVD: coloring objects strange colors; ignoring puzzles that are based primarily on color rather than on shape; inability to recognize optical illusions that other children see easily.

A favorite color for flannel boards is black. However, children who have severe CVD may confuse red and green with black, so a better color is a pastel blue.

Eventually, people with CVD learn to tell some colors apart by their lightness, darkness, or luster. Through language, such as "leaves are green" and "fire engines are red," they pick up other clues.

Parents and teachers can label objects like "Bear" for brown or "Leaves" for green to help children learn color names. Children can be taught the first letter of color names printed on crayon wrappers to help them distinguish one color from the next.

Even though they may understand their reduced color vision, people often hide their dissimilarity instead of asking for help when they need it. The nurse needs to be attuned to the psychological aspects of the disorder.

Testing
School nurses are familiar with pseudoisochromatic plates such as the Ishihara and the H-R-R (Hardy-Rand-Rittler). Young children can use a dry paint brush or cotton-tipped applicator to trace the numbers or geometrical shapes. Older students can name them. Even students who are "legally blind" can successfully complete the testing because the tests rely on color, not on visual acuity.

Pseudoisochromatic plates include "transformation" designs. People with severe CVD see figures or paths that others don't see. Colors that may appear the same to most viewers may actually have a subtle difference. This may explain why people with CVD are able to see camouflage better than those with typical color vision.

If a child fails testing, there's no need for further evaluation unless another visual problem exists. However, if a child gives conflicting answers, the nurse should test each eye individually. A discrepancy between the two eyes might indicate a neurological problem.

The nurse can assure parents the condition remains the same throughout life. Often, when a boy fails testing, he has a maternal grandfather or maternal uncle with the same CVD. He can talk with the older family member regarding tips in handling the disorder.

Presently, Jim Doane is re-working his city's colorful bicycle map. He said the map, as well as many Web sites, are "mush" to him. "People don't realize to what extent they use colors," he observed.

Arlene Evans, R.N. wrote the only book available for children on CVD: Seeing Color: It's My Rainbow, Too. For older readers, she wrote: Color is in the Eye of the Beholder. Visit her Web site at: www.CVDbooks.com. She also wrote a novel Dinner for Two, a romantic-comedy-adventure with a colorblind hero!


Bibliography
Birch, Jennifer, Diagnosis of Defective Colour Vision, Butterworth Heinemann, Oxford Auckland Boston Johannesburg Melbourne New Delhi, Butterworth-Heinemann, Linacre House, Jordan Hill, Oxford OX2 SDP, 225 Wildwood Avenue, Worbourn, MA 01801-2041, second edition 2001.

McIntyre, Donald, Colour Blindness: Causes and Effects, Dalton Publishing, 33 Eaton Rd., Chester CH4 7EW, UK, 2002.

Olsen, Mary Margaret and Harris, Kenneth R., Color Vision Deficiency and Color Blindness: An Introduction to the Problem, Fern Ridge Press, 1927 McLean Blvd., Eugene, Oregon 97405, 1989.

Sachs, Oliver, The Island of the Colorblind, Alfred A. Knoph, 1977.

Trevor-Roper, Patrick, The World Through Blunted Sight, The Bobbs-Merrill Co, Inc., Indianapolis-New York, 1970

Websites:
The Achromatopsia Network: www.achromat.org

Many sites are devoted to CVD. A few are:

All About Vision: www.allaboutvision.com

Color Vision Deficiency: www.firelily.com/opinions/color.html

Color Vision Store: www.colorblind.to

Colour Group of Great Britain: www.city.ac.uk/colourgroup/

Simulating CVD vision: www.vischeck.com

Tests for Color vision (not to be used for diagnosis or career planning)
www.toledo-bend.com/colorblind/ishihara.html
http://members.aol.com/nocolorvsn/color.htm

Links: www.toledo-bend.com/colorblind/links.htm






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