(Jrt)
Color blindness
Color blindness is an anomaly in which one or more of three types of cones of the eye retina responsible for color vision are weak. A colorblind is a person with this condition.
History
The scientific name of the anomaly is color blindness, but it is generally known as color blindness, according to the name of its discoverer. The English chemist John Dalton in fact published the first scientific article on this subject in 1794, "extraordinary facts about color vision", following the completion of its own disabilities to collect colors.
In the twenty-first century, the color blindness is detected early among French youth, at school, during medical visits mandatory. It is detected through testing Ishihara, which consist of a series of images of large groups of colored points. A number is included in the image, designed as a series of points of a color slightly different from the rest of the image. This number can be seen with a complete collection of colors, but not if there is a deficiency of it. Each tests a specific color deficiency and all of these tests can determine the type of color deficiency. These tests can be performed using Beyne lantern.
Presentation
This anomaly occurs sometimes after a nerve, eye, brain, or may even be caused by certain chemicals, but usually a genetic origin is the cause. However, no trend is present in the life of the person, except the decline of color perception normally associated with age among all human beings.
There are several forms of partial color blindness, the most common being the confusion of green and red. Other forms of color blindness are much more rare, such as confusion blue and yellow, the rarest of all being the total deficiency of color perception (achromatopsie), where the subject does not receive as shades of gray.
Types of color blindness
* Deuteranopia: lack of retinal cones receiving green; those affected are unable to differentiate between red and green. This is the most common form of color blindness, the very man who beat John Dalton (The diagnosis of deuteranopia in it was confirmed in 1995, more than 150 years after his death, DNA analysis taken on a its eyeballs preserved until today). Other forms of disability are the colors of color blindness by abuse of language.
* Deuteranomalie presence of a mutation in the pigment of the perception of green; sensitivity to that color is diminished. Constitutes the majority (about half) of congenital anomalies of color vision.
* Protanopia absence of retinal receptors in red color that is undetectable by the subject.
* Protanomalie presence of a mutation in the pigment of red vision; sensitivity to that color is diminished.
* Tritanopia absence receivers Retinal blue, this color is undetectable by the subject.
* Tritanomalie presence of a mutation in the pigment of the vision of blue; sensitivity to that color is diminished.
In fact, color vision and distinction vary from one individual to another, because we also found even for people with color vision called normal, a combination of different types of anomaly by the presence common to both normal pigments and pigments with the mutation, and variability of the relative amount of cones holders of each of these pigments. On the other hand relative rates of holders of each cone pigment may vary during the life of the individual, particularly during childhood when the retina is growing in size and the relative proportion of certain types of cone may increase at the expense other. These proportions may also be affected by certain diseases or infections because the eye is heavily irrigated.
Finally each eye has its own capacity of discernment with a slightly different, and even some areas of the retina do not have a uniform distribution of the different pigments but in this case, the brain, which controls also the movement of the 'Eye, provides a common gum and these local differences, sensitivity to color differences then with increasing duration of exposure.
We are talking about only when some abnormality minimum thresholds are not met for holders of the cone pigments normal. Thus there is almost always between two pairs of color that distinguishes one and the other not. This explains why cases of deuteranomalie are by far the most common (and probably even more frequent than what could measure the usual tests based on a limited set of standardized plates). However anopie cases of interest are extremely rare, and even today are contested: the subjects are rarely devoid of the vision of certain colors, and even know some have in a three dimensional space as when they are even holders of several types of cones with different pigments, even if one is too predominate over all other which makes this distinction more difficult, and learning by comparative methods (or a modification of the lighting) can increase their sensitivity.
That is why research is conducted to create tests more reliable and accurate, capable of measuring defects directly inspection by the substance of the retina by exposure to pulsed lasers colorful very low power and the extent of the sensitivity of different retinal areas by detecting the effect of product on their fluorescent pigments. Other methods use image sequences adjustable by the viewer to determine the threshold from which they can feel more certain differences, but these tests dynamic face retinal persistence that some false results. But they significantly improve the accuracy of anomalies and also to give a more complete profile of the retinal sensitivity to color. Some of these tests have been made to establish calibrated color models used in industry (eg photography, television and printing systems) to provide the public with a richer palette of colors.
Epidemiology
The red-green color blindness is mainly male, genes control the color receptors located on the X chromosome that men possess a single copy (XY) and women in two (XX). This gene is recessive, women are color blind if their two X chromosomes are weak, while men will be reached when their single X chromosome is. Women can be carriers of color blindness gene and pass it on to his children, but not reaching the disorder. Women are more prone to have 3 types of cones, allowing a full three colors.
The red-green color blindness is transmitted from one man reached through his daughters (who are healthy carriers) to her grandchildren males. His own son will not be affected, since they receive his Y chromosome and not deficient X chromosome.
The blue color blindness (tritanopia) is divided equally between men and women: the gene encoding the information receiver blue is located on chromosome 7. A mutation in this receptor causes tritanomalie.
Statistics vary among populations. Among the North American population, approximately 10% of men suffer from some form or another deficiency in color vision. In France, the proportion of color blindness is about 8% for men and 0.45% among women.
Although rare, the complete color blindness (monochrome vision) is very common on the atoll of Pingelap (Pohnpei, Micronesia): nearly one-twelfth of the population is affected.
Testing
Several types of tests can be performed for screening. The color blindness do not receive one or more colors. To detect the disorder of vision, so use tests based on the colors are not collected. There are dozens of tests, the most important and most famous are:
* The Ishihara test. The test is composed of many color plates containing a number, a color as the colorblind concerned protanopia here, do not collect or color, or the difference in color seen here For example, gray on green.
* The test Holmgren. In this test, the person who should be closer to the color strands of wool as hue, and on a gray background.
* The Anomaloscope of Nagel. This test is intended to protanomal at deutéranomal, and tritanomal. This test is a screening of two circles of light, forming a third. The topic should resolve itself proportions, to restore color as it is perceived. If it adds red, it is protanomal. If it adds green, it is deuteranomal, and it adds blue, then it is tritanomal.
* The test Farnsworth. It was designed by Dean Farnsworth in 1943. It was used for selection of workers in American industry. The test consists of fifteen tokens including a black colored dot. The test is to rank in order of colors ranging from bluish to gradually reddish.
* Tests for children. An examination of color vision can be practiced from the age of three years, using specific tests. The most common are:
o The child Ishihara test for children four to six years. It consists of 8 plates representative of shapes: circles, squares, lines, rods, boats, ...
o Verriest The test consists of colored tokens that the child must meet like dominos.
Note
Some animals have less or no cones (most mammals, as are dichromates cats, with only 2 types of cones, but the rat is monochromatic with only one type of cones), and others have as much or more than humans (most birds are Tristimulus with exceptions such as pigeon, for example, which is pentachromate through 5 types of cones).
Color blindness is often seen as a handicap, but in certain situations, the opposite. Compared to the hunter "banal", some color blind hunters (depending on the type of color blindness) better identify their prey in a confused environment. The soldiers also discovered that color blindness can sometimes detect a camouflage who delude anyone else. Some architecture firms also looking for color blindness for their ability to better visualize the space. Moreover, in return for the lack of sensitivity to color, sensitivity to light, better than a person not met, would improve night vision.
There are also variations "inverse" Ishihara tests that only people with color blindness can resolve. They are based on differences in contrast points up the image (and not on differences of tone between these points as in the tests Ishihara). An individual suffering from color blindness see something, thinking that what he sees is the same color. But for a non-color, different colors are more obvious contrasts close, so she said nothing to see.
Color blindness is usually discovered at the age of 6 to 12 years when the child becomes more communicative. It even happens that people realize much later.
Color blindness is usually not a problem for the person who is reached. It's just like not see ultraviolet or infrared, no awareness of their existence. It becomes embarrassing when the individual reaches must make a distinction between colors, sometimes to comply with the distinctions drawn by the non-affected persons (Conventions of colors in different areas, such as electronics).
wikipedia
