Anomalous Trichromacy - An individual with faulty trichromatic vision will be colour blind to some degree. All 3 cone types are used to perceive light colours but one type of cone perceives light slightly out of sequence, so there will be three different types of effects depending which cone is faulty. As an example, an anomalous observer might have a blue, reddish-green and blue cone sensors and so would have reduced green light sensitivity.
The different types of Anomalous Trichromacy are:
Protanomaly- Reduced sensitivity to red light. Blue, green and greenish red cones are present for anomalous protanope observers. Or, there is no red sensitivity at all (green and blue cones only) for pure protanopes.
Deuteranomaly - Reduced sensitivity to green light. Red, reddish green and blue cones are present for anomalous deuteranope observers. Or, there is no green sensitivity at all (blue and red cones only) for pure deuteranopes. People with Deuteranomaly and Protanomaly are collectively known as red/green colour blind and have problems distinguishing between reds, greens browns and oranges and will confuse types of blue and purple. This is the most common type of colour blindness effecting 6% of males, 0.4% of females.
Tritanomaly - Reduced sensitivity to blue light (blue cone missing). Blue colour blindness affects both men and women equally because it is carried on a non-sex chromosome (Chromosome 7). Will have difficulty identifying blue and yellow, violet and red, blue and green. They see most red, pink, black, white, grey and turquoise.
Many cases of Tritanomaly are recorded as non-genetic. An injury to the front or back of the head can lead to blue/yellow colour blindness. Organic solvents, even at low concentrations can impair the vision and alcoholics are at risk of poor colour discrimination particularly the blue/green colour range. These can be reversible unlike the genetic condition.
Within these groups there are an infinite numbers of variations depending on the degree of defective or mutated cones.
Red-Green Colour Blindness
Deuteranomaly and Protanomaly are collectively known as red-green colour blind. This is by far the most common form of colour inherited blindness.
Deuteranopia (green weakness); where the eye does not respond to green light. For example, in low light, dark green appears as black. They are poor at differentiating the hues in red,orange, yellow and green. Deuteranomalous individuals are fortunate in that they do not have the loss of brightness issue. Quite common affecting 6% of males and 0.4% females.
Protanopia (red weakness ); where the eyes is less sensitive to red light, there is also a darkening of the red end if the spectrum. Thus causing reds to be interpreted as black. Brightness of colours is much reduced. Much less common and affecting about 1% of the males and 0.01% females.
(Tetra="four" chroma="intensity of distinctive hue") is a condition where a person possesses four sets of cone cells for conveying colours.
It appears that the same defective cone that causes colour blindness is probably responsible for the mutant fourth cone in a tetrachromat. Women carry two X chromosomes so it is possible that she will have a normal X chromosome carrying genes for red and green and the other X chromosome carrying an abnormal gene. This combination of the two chromosomes results in a fourth cone.
The fourth cone, somewhere between red and green, appears to be in the orange/yellow range. In theory, the extra 100 shades would enable this person to see around 100 million colours.
Although in the animal/birds/fish/reptile and insect world, tetrachromacy is common, in humans it is very rare and recent research indicates that only women are affected. An average person (Trichromat) with three cones for red, green and blue can see 1 million colours. A woman with tetrachromacy can see in region of 100 million colours.
Paintings by Australian artist Concetta Antico. One of the few people confirmed with Tetrachromacy. These paintings give us an insight into the world of colour and light that she sees.
"COLOR BLINDNESS MAY SOON BE TREATABLE WITH A SINGLE INJECTION"
"SPECIAL GLASSES GIVE PEOPLE SUPERHUMAN COLOUR VISION"
New Scientist - 21st March 2017
Daily Mail Online - 22nd March 2017
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Ishihara Testing for Colour Vision Deficiency