color vision deficiency facts and questions...
does a man/woman affected by CVD perceive this
Click on: Red/Green or Blue/Yellow color
filter (Be patient, the filter activation may take
a minute or so...).
color do color vision deficient people dream
We only dream of what we know... People who become
blind after birth can see colors and images in their
dreams. People who are born blind do not see any images,
but have dreams equally vivid involving their other
senses of sound, smell, touch and emotion. It is hard
for a seeing person to imagine it. So, colorblind people
dream in the color set they see in real life... However,
a full 12% of sighted people dream exclusively in black
a color deficient person experience 3D movies
or stereoscopic images?
It depends on the color vision deficiency, and the
degree of severity. A color vision deficient person
can see recent 3D movies which are devised to be seen
with glasses using crossed polaroid lenses,
but not the old style 3D movies devised to be seen
wearing anaglyph (red-green) glasses. Redgreen colorblind
people do sometimes have difficulties with red-green anaglyph
images since although the colors appear
similar, the intensities are rather different - the
red image typically looks darker than the green.
do color vision deficient persons perceive a colorwheel?
over this standard colorwheel to see it as a colorblind
person might see it.
color blindness test
Color vision deficient people have a tendency to better
night vision and, in some situations, they can perceive
variations in luminosity that color-sighted
people could not. In fact, most color blind people
can easily read what is written in the picture below...
That means, if you fail the test, you probably have
the full range of color sensitivity that is attributed
to color-sighted people. Anyway, this test is not to
be considered by itself sufficient to determinate defective
(Highlight answer: NO)
taken from Sarcone's book Puzzillusions
bothers colorblind people most?
- When grilling a piece of meat, a red deficient individual
cannot tell whether it is raw or well done. Many cannot
tell the difference between green and ripe tomatoes
or between ketchup and chocolate syrup! Many others
are always buying and biting into unripe bananas -
they cannot tell if they are yellow or green, and the
matt, natural material makes it even harder to distinguish.
- Some food may look definitely disgusting to color
vision deficient individuals: a plate full of spinach,
for instance, just appears to them like cow pat.
- They can however distinguish some citrus fruits.
Oranges seem to be of a brighter yellow than that of
- A colorblind person is generally unable to interpret
the chemical testing kits for swimming pool water,
test strips for hard water, soil or water pH tests
because they rely on subtle color differences.
- Many colorblind people cannot tell whether a woman
is wearing lipstick or not. More difficult to handle
for some is the inability to make the difference between
a blue-eyed blonde and a green-eyed redhead.
- Color vision deficiencies bother affected children
from the earliest years. At school, coloring can become
a difficulty when one has to take the blue crayon -
and not the pink one - to color the ocean.
- Bi-color and tri-color LEDs (Light Emitting Diodes):
is that glowing indicator light red, yellow, or green?
Same problem with the traffic lights...
personal experiences of being a color blind
If you are a color blind person you may want to help
us by answering these two
need to pass a color blindness test for work.
What can I do?
Some jobs require their employees to take a color vision
deficiency test (often using the Ishihara plates above).
For instance, good color vision is vital for recognizing
various lights and signals important to pilots, especially
at night. These tests are required by, among others,
the coast-guard and most military and emergency services.
Unfortunately, if you really are colorblind, there
is very little you can do to pass these tests.
However, the CAA UK
and the FAA US
are currently reviewing the color vision requirements
for professional flight crew. Many documents and papers
over the last 20 years have stated the need for new
color vision tests that are more appropriate to the
tasks that pilots carry out. That is the reason why
a new range of tests has been developed by Applied
Vision Research Centre. For the few subjects
that fail or are judged borderline from the results
of the first CVD screening test, then a second program
will measure the subject's chromatic sensitivity for
stimulus conditions that are considered important experimentally.
The results from this will then make it possible to
judge whether the subject's performance meets the minimum
color vision requirements that yield acceptable visual
performance in the tasks investigated.
No cure exists yet for inherited color deficiency.
However, the researchers Jay
Neitz and his wife have developed and
therapy to restore color vision in two
adult male squirrel monkeys that have been unable to
distinguish between red and green hues since birth
- raising the hope of curing color blindness and other
visual disorders in humans.
They introduced the human form of the red-detecting ‘opsin’ gene
into a viral vector, and injected the virus behind
the retina of the monkeys. The researchers then assessed
the monkeys’ ability to find colored patches
of dots on a background of grey dots by training them
to touch colored patches on a screen with their heads.
After 20 weeks, the monkeys’ color skills improved
dramatically. The insertion of the red-detecting ‘opsin’ gene
gave rise to new color perception stimuli and, in fact,
their brain started to react on this new visual information.
Gaining this new dimension of color vision becomes
a simple (!) matter of splitting the preexisting "blue-yellow" pathway
into two systems, one for "blue-yellow" and
a second for "red-green" color vision.
The Neitz’s are still in the middle of clinical
trials. Actually, they are not only looking for a cure,
but also trying to develop a test that can help forecast
the severity of someone’s color blindness.
More info at http://www.neitzvision.com/content/genetherapy.html
can colorblind people compensate for their deficient
While there are no cures for color blindness, there
are many possibilities to help control the annoyance
of this disease. A possible treatment for color vision
deficiency is to use special
glasses with particular color filters
to make it easier to interpret colors or actually to
better see contrasts. Another way to control symptoms
is to use what is called the X-Chrom
lens. The X-Chrom lenses are red contact
lenses worn on the non-dominant eye of color
deficient people and which helps some to better interpret
colors or contrasts. The X-Chrom lens does not restore
normal color vision, it just allows some colorblind
individuals to distinguish colors better.
can I create a colorblind friendly website?
Apart from its aesthetic appeal, seeing many different
colors allows us to distinguish things in the world.
However, remember that there are always colorblind
people among your audience and readers. Actually, there
could be more than TEN colorblind people per 250 people
visiting your site.
Then, we, the web community, must create an atmosphere
which makes it easier for colorblind individuals to
differentiate between text and background along with
images! There are 2 ways that we can make information
in pictures available to colorblind people:
1) The simplest way is to increase the red/green contrast
in the images.
2) We can also convert the variations in red and green
colors into variations in brightness and/or blue/yellow
One way to test your website for colorblind usability
is by using these tools:
Web Page Filter,
Each tool will show a copy of your web page as if it
was seen as a select type of color vision deficiency.
Firefox also has a great add-on which allows webmasters
to see color contrasts:
Contrast Analyser Firefox Extension.
is a proposal of a color range selection that may
be unambiguous both to color vision deficient people
and normal sighted persons.
Some useful hints: when combining colors from this
pallet, try to use 'warm' and 'cool' colors alternatively.
Avoid combination of colors with low saturation or
of colors unambiguous to color vision deficients
and to normal sighted persons
CMJN % 0,0,0,100.
CMJN % 15,41,93,1.
CMJN % 66,16,4,0.
CMJN % 81,15,62,2.
CMJN % 15,6,79,0.
CMJN % 90,49,12,1.
CMJN % 17,71,96,5.
CMJN % 26,62,12,0.
color vision deficients may see our corporate
CMJN % 18,54,95,3.
CMJN % 81,15,62,2.
CVD resulting from insensitivity to red light,
causing confusion of greens, reds, and yellows.
Deuteranopia: CVD resulting from insensitivity
to green light, causing confusion of greens, reds,
Tritanopia: a rare form of CVD resulting
from insensitivity to blue light, causing confusion
of greens and blues.
can teachers help if a student has a color vision
1) Always use white chalk, not colored chalk, on the
board to maximize contrast. Avoid yellow, orange, or
light tan chalk on green chalkboards.
2) 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 vision deficient students.
am colorblind and work on a computer - is there
a way that I can determine the various colored
graphics or letters?
Yes, there is a new product called Visolve that
might help you. It is an interactive software program
that takes a picture of your screen and allows you
to manipulate various color.
is the relation between colorectal cancer and
Men are statistically more likely to die of colorectal
cancer than women, and it is thought that one reason
for this is that they are more likely than women to
be color vision deficient. The link is that if you
are red colorblind, when you look at a piece of used
toilet paper it may all look the same color, even though
there is red and brown on there. Hopefully, the other
symptoms will prompt the color deficient person to
seek medical attention (source: h2g2).
there 'false' colorblind persons?
There is a type of color vision deficiency that is
caused by damage to the cerebral cortex of the brain,
rather than abnormalities in the cells of the eye's
retina. This kind of color vision deficiency is called "cerebral
achromatopsia". People affected with
cerebral achromatopsia are perfectly aware of their
visual experiences; however, they are unable to imagine
or remember colors. They see the world like a black & white
television where everything is a shade of gray. They
cannot chromatically order or discriminate hue but
they can distinguish color contrasts like a normal
person. 'Transient achromatopsia' is a temporary loss
of colour vision caused by a short-lived vascular insufficiency
in the occipital cortex.
cats and dogs color vision deficient?
Yes, we can compare man’s best friends’ vision
with the vision of human being suffering from red or
green color vision defiency (protanope, deuteranope,
see fig. below). Dogs do see in color, but have two-color,
vision, that is, they cannot distinguish
between red, orange, yellow or green. They can see
various shades of blue and can differentiate between
closely related shades of grey that are not distinguishable
have the ability to distinguish between blues and
greens, but lack the ability to pick out shades of
red. They have a wider field of view — about
200 degrees, compared with humans' 180-degree view.
So, cats have a greater range of peripheral vision.
They also are crepuscular, that means they are active
at dawn and dusk. Their night vision is far superior
to that of humans: cats' eyes have 6 to 8 times more
rod cells, which are more sensitive to low light
What a Cat Sees].
and dogs are primed to see "motion", rather
than defining the world through sight alone. They
use a blend of senses such as smell and hearing with
their vision to do what we humans use our eyes alone
goldfish color vision deficient?
The common goldfish is not colorblind. It seems that
it can see a very wide range of the spectrum both infra-red
and ultra-violet and has the largest range so far discovered.
In that sense, it is tetrachromatic because
its color vision is based on four types of cones (ultraviolet,
short, medium and long wavelength-sensitive). Goldfish
are actually the only animals that can discriminate,
under certain conditions, both infra-red and ultra-violet
Since they have greater sensitivity to light than we
do, it is important then to protect your goldfish from
bright lights and sudden movements, and to spend a
little time working out the right location for their