Color Vision Screening Test
The perception of color can be exhilarating and motivational. Certain colors give us information such as a red sign when driving. Certain colors can calm us such as a room painted in light blue. Some colors can improve our concentration such as yellow. The perception of color can be varied. Eskimos can perceive many shades of blue. This learned skill helps them understand if the ice that they stand on is becoming thin. Many men (approximately 10%) perceive colors inaccurately. The following information will help to give you a background in understanding color vision.
There are many
types of cells inside of the eye. Cells which help us to perceive light
can generally be divided into cones and rods. Cone cells help us to see
color and during daylight. Rod cells are generally more responsible for
nighttime vision.
There are generally three types of cone cells. They include "red," "green," and "blue." cells. Normally we have all three types. The scientific name for when we have all three color receptors and normal function occurs is trichromaticity. If one type of color receptor is not working properly, the condition is called "anomalous trichromaticity." This person will have reduced sensitivity to a color. For example, they might be able to perceive all color except for green. It might be duller than normal. This is termed color deficiency, not color blindness.
A person that has one of the three pigments missing is called a "dichromat." This means one of the three primary pigments (red, green and blue) is actually missing. This results in no color perception for the missing pigment. Again this is called color deficiency, not color blindness.
It is very rare to be completely color blind or a monochromat (sometimes called achromatopsia). Unfortunately the term color blindness is often used when color vision is slightly deficient.
Examples of School Difficulties because of Color Vision difficulties
1. John is working in his reading workbook. The directions to one item say to draw a line to the red ball. The other ball is brown. Both colors look alike to John, so he guesses. The teacher reminds him not to be careless.
2. A teacher is writing vocabulary words on a green chalk board with yellow chalk in mid-afternoon. There is a glare on the board from unshaded windows. Peter is sitting so that the glare diminishes the figure-ground contrast. The teacher wonders why he is copying from a neighbor's paper.
3. Tommy ordinarily seems to enjoy reading aloud. Today, however, he doesn't volunteer and balks when the teacher calls on him to read. The poem in the reader is printed in blue on a purple background.
4. Susan, a bright and articulate youngster, was asked to go to the front of the class and read from the blue green book on the teachers' desk. She went to the front of the class and just stood there looking at the pile of different colored books. Not knowing which one to pickup, she started to cry.
5. T.J. was very out going in pre-school & kindergarten. He loved to wave his arms and volunteer to answer questions the teacher asked. The only time he did not volunteer answers was when it came to learning or identifying his colors. A lot of the colors looked the same to him. They just had different names.
6. The kindergarten teacher notices the kids during art class teasing Jimmy. The other kids think it is funny that Jimmy's stick people have green faces.
7. The kids at school told the teacher Jeff was cheating during kick ball. They said he would break the rules by kicking the ball when it was out of bounds. They accusingly stated the boundary lines on the green grass were clearly marked with orange chalk. Jeff, rather than admitting he could not see the boundary line, simply quit playing with the other kids during recess.
Inheritance & incidence
Most kinds of congenital colorblindness are caused by defects in the X chromosome (called sex linked). Since females have two X chromosomes and males have an X chromosome and a Y chromosome, colorblindness is much more common in males: females must have defects in both chromosomes before they exhibit colorblindness or deficiency.
A female with the colorblindness defect in one X chromosome is a carrier of colorblindness. Male children of a female carrier are as likely to be colorblind as male children of a male with colorblindness, and male children of a male with colorblindness and a female carrier are extremely likely to be colorblind.
Approximately 5% to 8% of the men and 0.5% of the women of the world are born colorblind. That's as high as one out of twelve men and one out of two hundred women. People who are protans (red weak) and deutans (green weak) comprise 99% of this group.
The following is a genetic diagram or pedigree of a female that is a color blind carrier and her "normal" husband:
Every human has 2 sex chromosomes, women have two X's, men have an X and a Y. The genes for L and M photopigments are located next to each other (tandemly) on the X chromosome. This means that men have one set of L and M genes and that women have two sets. This is why men are more likely to be colorblind; if there is a defect in a man's genes, they are colorblind, a woman's second set of genes often keeps her from being colorblind. A woman can get a "colorblind" X from her father and pass this X on to her children. This woman has a 50% chance of having a colorblind son, and if her husband has normal color vision, her daughters should have normal color vision but have a 50% chance of being carriers for colorblindness. The woman herself is a carrier for colorblindness. If a woman's father is colorblind she is said to be an obligate carrier because she is known to have gotten the colorblind X from her father (if she had gotten the Y, she would be male!). Other genetic options to the above diagram are shown below:
Safety Considerations & Strategies
Having difficulty with color perception will result in exclusion from certain jobs for safety reasons. For example, they cannot be airline pilots, policemen or ship captains. Their everyday lives are also fraught with occasional minor hazards: how to match socks, how to decide whether the power indicator on the stereo is red or green, how to find red golf tees in the grass and how to choose an appropriate color scheme for decorating the house.
If color perception is difficult, there are some strategies that can help.
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Red tint on a single contact lens can help some people - this can be a soft or gas permeable lens. The process is called a "X" chrome contact lens. Since the lens is worn on one eye only, the perception of color is perceived at different speeds between the eyes. This helps the brain to perceive differences.
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Get help to match socks. Safety clip them together during washing to prevent matching problems.
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Shop with a friend when buying clothes, paint, carpets and wallpaper.
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Remember that red is always at the top on red/yellow/green traffic lights.
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Artificial light will often distort colors - use natural light when possible.
Review
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Trichromat
Regular vision is Trichromatic - it uses all three color pigments (red/green/blue).
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Anomalous Trichromat (6.3% of males and 0.37% of females)
People with Anomalous Trichromatic vision use all three color receptors but reception of one pigment is misaligned.
Protanomaly: reduced red sensitivity (L or long wavelength cone cell defect). 1.3% of males and 0.02% of females
Deuteranomaly: reduced green sensitivity (M for middle cone cell defect). 5% of males and 0.35% of females
Tritanomaly: reduced blue sensitivity (S for short cone cell defect). 0.0001% of males and 0.0001% of females
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Dichromat (2.4% of males and 0.3% of females)
People with Dichromatic vision use only 2 of the 3 visual pigments - red, green or blue is missing.
Protanopia: unable to receive red (L cone cell absent). 1.3% of males and 0.02% of females
Deuteranopia: unable to receive green (M cone cell absent). 1.2% of males and 0.01% of females
Tritanopia: unable to receive blue (S cone cell absent). 0.01% of males and 0.03% of females
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Monochromat (Achromatopsia - 0.00001% of males and females)
People with Monochromatic vision can only see one color, so their vision contains no 'color'.
Typical Monochromatic: unable to combine colors. Fully grayscale. Also known as Rod Monochromat.
Atypical Monochromatic: very low color recognition. Also known as Cone Monochromat.
Frequently Asked Questions
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Is there a cure for colorblindness? No. Color blindness is almost always caused by an inherited condition that alters the photoreceptors (cone cells) in the eye. There is no way to restore normal function to these cells.
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I need to pass a color blindness test for work. What can I do? Some jobs require their employees to take a color blindness test (often using the Ishihara plates). These tests are required by, among others, the FAA, the coastguard and most military and emergency services. Such tests generally prohibit the use of colored contact lenses or other devices that are claimed to alleviate the effects of color deficiency. Unfortunately, if you really are color blind, there is very little you can do to pass these tests.
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Will my child inherit my color deficiency? Color deficiency is usually caused by a problem in a gene carried on the X chromosome. Men do not pass their X chromosomes onto their sons, so a color deficient man cannot pass his color deficiency onto his son. Women, having two X chromosomes, can carry the color deficiency gene and never know it. If there are men on the mother's side of the family who are color deficiency, there is a chance that her child will inherit this gene. It will usually only cause color deficiency if the child is a boy. Very rarely, a mother will have color deficiency herself. This means that she has two 'color deficient X chromosomes. If she has a boy, he is almost certain to be color deficient. The fact that the color deficiency gene is on the X chromosome is reason why men are about ten to twenty times more likely to be color deficient than women.
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According to a color test I'm red-green color blind, but I can tell the difference between red and green- how can this be? It is certainly possible to have a red-green color deficit but still be able to distinguish many shades of 'red' from many shades of 'green'. In fact, color tests carefully select specific shades of red and green that are indistinguishable to people with a color deficit. Also, there are various degrees of color deficiency. Someone with a mild deficit would be able to distinguish more reds and greens than someone with a more severe deficit.
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Will a color deficit prevent me from becoming a pilot? Good color vision is important for recognizing various lights and signals important to a pilot, especially at night. In the United States, the FAA requires all pilots to have 'the ability to perceive those colors necessary for the safe performance of airman duties.
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I work on a computer - is there a way that I can determine the various colored graphics or letters? There is a new product called eyePilot that might help you. It is a software program that takes a picture of your screen and allows you to manipulate various colors. You can download the program and try it for a free period of time. This is technology worth trying if you work on a computer.
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How can teachers help if a child has a color deficiency?
a. Label a picture with words or symbols when the response requires color recognition.
b. Label coloring utensils (crayons, colored pencils, and pens) with the name of the color red.
c. Use white chalk, not colored chalk, on the board to maximize contrast. Avoid yellow, orange, or light tan chalk on green chalkboards.
d. 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 deficient students.
e. Assign a classmate to help color deficient students when assignments require color recognition. Example - color coding different countries on a world map.
f. Teach color deficient students the color of common objects. Knowing what color things are can help them in their daily tasks. Example: when asked to color a picture, they will know to use the crayon "labeled" green for the grass, blue for the sky, and light tan for Lincoln's face.
g. Try teaching children "all" the colors. Remember, most color deficient children can identify pure primary colors. It is normally just different shades or tints that give them problems. If they can not learn certain colors, let them know you understand some colors look the same to them and it is "OK".
h. Make sure a child's color vision has been tested before they have to learn their colors or color-enhanced instructional materials are used.
Links
Concepts in Color Vision
Appearances to the Color
Deficient
Color Vision & Pilots
Color Vision Simulator
Another Color Vision
Simulator
More Frequently Asked Questions
PC program for Color Blindness
Color Vision Testing Made
Easy - Pediatric Color Vision test
Waggoner HRR and Quick Six Color Vision tests
Farnsworth-Lanthony Combined D-15 Test
Farnsworth Lantern Flashlight
Neitz
Test of Color Vision
Richmond
Products - major distributor for a number of tests
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Thousand Oaks, CA 91362
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