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UNIVERSITY OF MANCHESTER INSTITUTE OF SCIENCE AND TECHNOLOGY
Have you ever had trouble matching your socks? Do you often pick out a necktie that makes your
friends laugh at the way that tie clashes with your shirt? As a kid, did you wonder what
everybody in science class was talking about when they said there was a number in that circle full
of Colored dots? If so, you might be color blind.
"Color blindness" is the term commonly applied to a genetic defect that causes the inability to
distinguish certain colors or shades of colors. A better term for the problem might be "color
vision deficiency" because almost all color blind individuals see in color - they just can't tell
some colors apart. (Totally color blind persons, called monochromats, see only black, white, and
shades of gray - but this condition is extremely rare.) The most common type of color vision
deficiency affects red-green perception. This condition doesn't mean the person affected by it
can't tell red from green; it means he or she has problems distinguishing colors such as green
from brown (brown is composed of red and green) or blue from purple (purple is composed of
red and blue).
Color vision is the responsibility of cone cells that are part of the retina of the eye. There are a
few different types of cones and each type is sensitive to a different set of colors (reds, greens, or
blues). The cones absorb light rays that bounce off objects and relay information on the color of
that light to the brain. Color blind people generally are missing at least one type of cone and so
can't perceive certain colors. This doesn't mean they can't see the color entirely, however--the
ability to perceive a color is also based on factors such as intensity, hue of the color, and the
amount of light available.
It is estimated that about 8 percent of men and .5 percent of women are color blind. Color
blindness is a sex-linked genetic trait carried on the X-chromosome and therefore passed from
mothers to sons. About half of the male offspring from a woman who has the "defective" gene
will probably be color blind. For a woman to have the trait, both parents need to have been
carriers of the color blindness gene. That's why the problem is much more common for men.
It's a good idea to have a child's color vision checked at an early age, since problems
distinguishing colors can cause the child to be a source of ridicule during childhood. Because of
widespread misunderstandings about color blindness, people with an "undiagnosed" color
blindness problem might be uncomfortable or defensive when discussing the topic.
A thorough color blindness test is offered by the University of Manchester Institute of Science
and Technology . The test is a series of 10 screens that prompt you to match a colored dot with
other dots of similar colors. If you give the correct answer, you proceed to the next screen in the
test. If you give the wrong answer, you are told you have made a protanomalous,
deuteranomalous, or tritanomalous matching error. Sound dangerous? Don't be alarmed. The
terms mean "red-weakness," "green-weakness," and "blue-weakness," respectively. At the end of
the test, a summary explains the results. The site makes it clear that the test is not definitive.
However, you can use it as an indicator of sight problems that should be checked by an
optometrist or opthamologist.
COLOR PERCEPTION ISSUES
This is a lengthy article by Diane Wilson about the use of color in Web design; it's thorough and
contains much detailed information about color blindness. Graphics illustrate how colors tend to
be perceived by color blind people. Wilson's main paint is that you should not assume your
audience (whether you're designing for the Web or creating a color-filled presentation for your
boss) has normal color perception. She suggests providing other cues, in addition to color, to help
people understand a Web page, chart, or graph; otherwise, you might lose part of your audience.
ASK A BIOLOGIST
Created by the Arizona State University's Life Sciences Visualization Group, Ask a Biologist
offers a page on color blindness designed for students and teachers of grades K through 12. A
color blindness test is provided (a set of five Ishahara test charts) along with brief,
straightforward explanations about color blindness. The information is presented clearly and
succinctly - perfect for students. So, if you want to avoid difficult terms like "deutanomolous,"
this site is a good primary resource. Terms are defined throughout the site. and links are listed
within a general biology index.
Colorblindness - Eye Resources and Information
Here's another excellent resource on color blindness well worth visiting.
COLOR BLINDNESS
If for no other reason, you should see this site just to check out the color scheme and the
multitude of blinking eye balls. Webmaster Mark Melnick is color blind, and his personal
testimonial expresses many of the frustrations experienced by individuals labeled as such. ("Oh,
you're color blind! What color is my shirt?") Like many color blind people, Melnick did not
realize he was color blind until he was an adult and finally able to identify the source of his
difficulties with color. There's much personal and scientific information here along with
excellent links.
COLOR BLINDNESS CHECK
This site contains a testimonial from a color blind individual, along with six Ishahara color
blindness tests. (Ishahara tests, named after their inventor are circles made up of multicolored
dots, some of which are grouped to form numbers.) The tests are not an exact science. In theory,
a person with normal color vision will see one number, and a color blind person will see another
number - although color blind people often don't see any number in the circles! The tests,
however; call indicate a possible problem that should be checked with an eye doctor.
COLORVISIONTEST.COM
Once you pick the French or English version, this site is easy to navigate. The home Page is a list
of questions that link to pages offering extracts from a CD-ROM the organization has for sale. If
you're interested in learning more about color blindness, order the CD-ROM for US $15.95.
Unfortunately, this site tends.to speak in absolutes-as though all color blind people see exactly
the Same way - and some of the information might be considered by people who experience
color blindness to be inaccurate. There are no links to other sites.
Get free information to help solve what ails you. This site provides a wealth of resources from medical experts, including links to articles about health and disease, companies that provide specialized health care services, health care organizations (such as hospitals and drug manufacturers), and related publications. There's also information about medical education, opportunities to buy health and fitness books, and feature articles on health topics.
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