Color blindness is a genetic disease affecting color perception. The color blind may for example not see red and green or see only black and white. Types of color blindness, characteristic signs, tests, solutions.
Color blindness is a genetic disease affecting mainly men (8% of men suffer from color blindness against only 0.5% of women). Too often reduced to an inability to see red or green, there are actually several degrees of color blindness. Although this disease is not yet completely curable, people affected generally develop other ways of seeing the world.
Definition
The best known color blindness of dyschromatopsias (disease affecting color perception). Described by the English chemist John Dalton in the 18th century, color blindness is a genetic disease that affects the Y and X sex chromosomes. If the normal eye perceives the three fundamental colors thanks to three types of retinal cells called “cones”, the color blind may suffer from dysfunctional cones or none at all.
Type of color blindness
There are typically three types of color blindness:
Dichromatism: which results in the presence of only 2 cones which can only give a perception of green and blue, red and blue, or red and green only?
Monochromatism (or achromatic): which results in an absence of a cone, the color-blind subject only sees in black and white and in shades of gray. This very rare type affects one in 40,000 people.
Abnormal trichromatism: which results in an abnormal perception of the intensity of colors because of the 3 cones unable to transmit information correctly to the brain? There may be a gap in the perception of red, green, or blue.
Symptoms
In the color blind, one of the transmission channels (the cones) is absent or deficient. It is customary to say that the color blind confuses red and green. In fact, he only really perceives two dominant colors, blue and yellow, but there are many shades. On a daily basis, color blind contacts can be a problem in driving on the road, in particular in the perception of traffic lights, intersections or the rear lights of cars. Dichromate may also be unable to clearly recognize a person’s characteristics (makeup, color of eyes, hair, clothes, etc.) or certain foods (rare or cooked meat, color of fruits and vegetables, difference between certain foods, etc.).
Causes
The transmission of the disease is generally hereditary. In fact, there are naturally three color genes, encoding three different pigments: red, green and blue. In the retina of the human eye exist color-specific receptors. Called photoreceptors, they are stimulated by a very specific wavelength corresponding to a given color: red, green or blue. We then perceive shades of these colors following the simultaneous activation of these receptors. The genes encoding the red and green pigments are found on the X chromosome, the sex chromosome carried in a single copy in men. The gene encoding the blue pigment is found on chromosome 7. This disorder most often affects red and green pigments whose corresponding genes are more likely to mutate. Moreover, since the mutations concern the X chromosome, men are more likely to be affected because they have only one copy of this chromosome (X and Y for men) inherited from their mother. Whereas females have two X chromosomes and therefore must receive the mutation from both parents.
In other, fairly rare cases, color blindness may appear following nerve, eye or brain damage, or exposure to certain chemical substances.
How old?
Since color blindness is an inherited condition, it occurs from birth. From an early age, a child can be detected during an ophthalmological examination.
Transmission
In the vast majority of cases, color blindness is hereditary and depends on chromosome 7 and the sex chromosome X. It is therefore transmitted by one of the two parents or both in very rare cases.
Tests
The most common and well-known test for diagnosing color blindness is the Ishihara test , named after the Japanese ophthalmologist who invented it, Shantou Ishihara. It consists of 38 color plates containing a colored number. The color blind is not able to perceive the number and its color.
