Color Blindness or Color Vision Deficiency

Found @ Archimedes Lab

daltonismo (it, es, por), daltonisme (fr), Farbenfehlsichtigkeit (ger), kleurenblindheid (du), 色盲 (ch), 色覚異常 (jap), дальтонизм (ru), עיוורון צבעים (he).

*Color Blindness used to be called “daltonism” thanks to Dalton’s work; however this term is used now to describe a type of color vision deficiency called Deuteranopia.

 

Color blindness is an inaccurate term to describe a lack of perceptual sensitivity to certain colors, a more precise term is Color Vision Deficiency (CVD). Color blindness is, however, the most commonly used term though it is misleading if taken literally, because colorblind people CAN see colors, but cannot make out the difference between some couples of complementary colors. Color vision deficiency is not related to visual acuity at all and is most commonly due to an inherited condition. Red/Green color vision deficiency is by far the most common form, about 99%, and causes problems in distinguishing reds and greens. Another color vision deficiency Blue/Yellow also exists, but is rare and there is no commonly available test for it.
• Color vision deficiency seems to occur in about 8% – 12% of males of European origin and about one-half of 1% of females. Total CVD (seeing in only shades of gray) is extremely rare.
• Another rare form of CVD called unilateral dichromacy affects people who have one normal eye and one colorblind eye.
There is no treatment for color vision deficiency, nor is it usually the cause of any significant disability. Actually, most color deficient persons compensate well for their defect. At one time the U.S. Army found that colorblind persons can spot ‘camouflage‘ colors where those with normal color vision are fooled by them. In fact, a reduction in color signals makes the differences in texture and brightness more apparent (see reverse test)!

 Shinobu Ishihara (石原 忍)
The most commonly used test to detect color vision deficiencies   was developed by the Japanese ophthalmologist Shinobu Ishihara (1879-1963). While working at the Military Medical School he was asked to devise a test to screen military recruits for abnormalities of color vision. His assistant was a colorblind physician who helped him test the plates. A collection of 38 plates filled with colored dots build the base of this test. The dots are colored in different shades and a number is hidden inside with shades of another color.

More color vision deficiency facts and questions…

• What color do color vision deficient people dream in?
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 and white!

• What 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 lemons.

- 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…

- 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.

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.

• Are 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, or dichromatic 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 to people. Cats have the ability to distinguish between blues and greens, but lack the ability to pick out shades of red. However, cats 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 to do.

• Are 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 light.
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 tank.

Read the whole article in the Lab

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