- Disabilities & the Disabled
Color blindness: Through their Eyes
The term Color blindness means the gradual decrease of capacity to identify the exact difference between several colors which is easily distinguished by ordinary people. Though color blindness is of genetic nature, the problem happens because of some damage of eye, brain or nerve or even due to some exposure to some chemical matters. After perceiving his own problem, John Dalton, an English chemist, published his scientific publication in the year 1798 on the subject concerned. The problem color blindness was also termed ‘daltonism’ because of the work of John Dalton. Now days, this problem is categorised as a kind of color blindness termed deuteranopia. However, color blindness is a mild disability. Some scientific investigations claim that color blind people are able to perceive certain colors better than others.
Background of color blindness
The retina of a normal human being bears 2 types of light cells. They are rod cells which are active in low lights and the other is cone cells which are active in regular daylight. In an average, there are 3 types of cones each of them contain a pigment of different type. While pigments absorb light, the cones are activated. Spectral sensitivities of the respective cones are different: one remains highest sensitive to the wave length of short distance, another is to medium wave length and the other is to wave length of long distances. They have sharp sensitivity to blue, yellow-green, and yellow area of spectrum respectively. The visible spectrum depends on the three systems of their absorption spectra. For short, medium and long distance wave length the receptors are termed as S, M and L clones. They are also termed as blue, green and red cones respectively. I spite of being referred as blue, green and red receptors, this is not an accurate terminology, because the red receptor has the highest sensitivity in the yellow area. Normal color vision sensitivity depends upon overlap between absorption spectra of these 3 systems. While various kinds of cones are stimulated to various degrees, various colors can be recognized. For example, the red light can stimulate long wave length cones much higher and much more than the others and thus can reduce the wave length causing the two others systems being gradually stimulated. This happens to cause an active change in hue. Other factors involved in the concern are X chromosome. Thus male color blindness are more frequent than females as male bear one X chromosome while females bear two.
Inherited color blindness is classified into three categories: Monochromacy, dichromacy and anomalous trichromacy.
Monochromacy: This is the state of total color blindness. In this blindness the person lacks the capacity to distinguish colors. This class occurs while all cones pigments happen to be missing. In this state lightness vision and color are reduced to single dimension.
Dichromacy: This is severe color blindness in which any of the 3 basic colors mechanisms is not functioning or is absent. This kind of blindness occurs when one of cone pigment is absent and the color happens to be reduced to 2 dimensions.
Anomalous Trichromacy: This is a usual kind of color blindness. This happens when one of three cone pigments happen to be altered. The result is an impaired and three dimensional color vision.
There are several sub classes like: Protanopia, Deuteranopia and Tritanopia.
Color Blindness Tests
Causes of color blindness
Color blindness is a genetic cause. It is inherited from mutations on X chromosomes. Investigation has shown that there are number of causative mutations that are able to cause color blindness. According to the database of JohnHopkinsUniversity, color blindness is caused from 19 different chromosomes and other 56 genes. There are inherited diseases that play vital role to cause color blindness. These are: cone dystrophy, achromatopsia, cone-rod dystrophy, blue cone monochromatism and retinitis pigmentosa.
Color blindness that is caused from inheritance may be from birth. It may also step in during childhood or adulthood. This may continue throughout a person’s whole life. It is also progressive. While progressive, it deteriorates one’s retina as well as other parts of eye.
Other causes are brain or retinal damage which are caused by shaken baby syndrome or accidents causing the swelling of brains and damaging of retina. Sometimes color blindness I caused by diabetes.
The most usual test is the Ishihara color test. Consisting of a series of images of spots, this test is widely used to diagnose the deficiencies of red-green color. When taken the image, a number of slightly different color spots are visible. The entire tests display enormous color combinations. This test is also very fruitful while testing young children. Besides this test, the US Army and US Navy also permit the color testing with Farnsworth Lantern Test. The test shows normal deficiency.
Misconceptions and Compensations:
.Regarding color blindness there are some misconceptions. Dichromats sometimes make confusion with red and green items. They find it difficult to separate a Braeburn apple from Granny Smith. Sometimes, they confuse with the red and green traffic lights. They also suffer while working with color printers. The thing is that there are not enough difference between red lights. They also suffer while distinguishing the sodium street lights from Grubby while lamps. Really this is highly risky while speedy driving on undulating roads and where angular info is absent. That is why British Railway department use bright and more easily visible colors: red is blood red, green is bluish. InCanadatraffic lights of horizontally-mounted region are differentiated by shape to identify the exact signals for the color blind people.