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Colour Blindness – Dichromacy (Protanopia, Deuteranopia, Tritanopia)

Protanopes, deuteranopes and tritanopes are dichromats. They can reproduce any colour they see in any combination of two primary colours. The normal eye bulb can produce any colour by combining all three primary colors. The majority of this people know that they have some sort of problem with their sight, they have to live with for the rest of their lifes. A percentage of about 2% of the men, have very hard time perceiving the colours red, orange, yellow and green. Generally a hue is perceived by the normal eye in a very different way, and this means that the end result that the two eyes will perceive will have a different colour feeling and stimulus.

By: Samuel Johnson

Protanopia

Protanopia appears at about 1% of men approximately. Its symptoms is the lack of sensitive in the long waves from the cones of the retina. Therefore is difficult to distinguish between the colours of green, yellow, and red of the colour spectrum. The neutral point in their sight is a cyanic colour with wave length of about 492nm, and this means that they can’t distinguish the white light as truly white.

The red, yellow and orange rays they distinguish them at a reduced length compared to a normal eye. This problem is sometimes so intense that some red and orange waves to be perceived by them as black or as tones of gray. It has been observed that in some cases the red traffic lights are completely unperceived. After practice people with protanopia can learn to distinguish red from the yellow hues, by distinguishing the difference in the luminosity or in the brightness of the hues.

The problem though is not only on these hues. In colours like mauve they can’t distinguish only some shades of blue. Also the red percentages in the violet waves are not easily perceivable by them. There are very few people though in which we can have a normal eye and one that is affected by protanopia. In the unilateral dichromacy with open only the affected eye the person can only perceive colours below the neutral point like blue, while above that as yellow. This is the most rare form of dyschromatopsia.

Deuteranopia

Deuteranopia appears only in 1% of the men approximately. It is also called Daltonism, after the examination of John Dalton’s [1] eye DNA, 150 years after his death. The diagnosis was that he was affected by deuteranopia. The symptoms of deuteranopia are the lack of sensitivity in the cones of the retina, which are responsible for the process of middle waves of the colour spectrum.

The neutral point in that case has a bit bigger wavelength and is established at 498nm, comparing to protanopia it has a more greenish hue. The affected in this case has the same issues of distinguishing hues, like the ones with protanopia, but without losing the saturation of the colours. Violet hues are not being perceived as hues opposite of those in the visible spectrum but almost normally perceived. The affected by deuteranopia, and more specifically unilateral dichromacy, with the affected eye open, they see wave lengths below the neutral point as blue and higher than the neutral point as yellow.

Tritanopia

Tritanopia appears in a percentage smaller than 1% in both men and women. Here we notice lack of cones sensitivity to perceive short wave lengths like blue and violet hues. In some instances the perception of these hues is so pale that the affected people perceive these hues like black. They can hardly tell between yellow and white, and they perceive most violet colours as shades of red. Tritanopia is gender independent.

The following boards represent human vision through the forms of dichromacy:

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Supplementary info:

[1] John Dalton

John Dalton was born into a Quaker family at Eaglesfield, near Cockermouth, Cumberland, England. The son of a weaver, he joined his older brother Jonathan at age 15 in running a Quaker school in nearby Kendal. Around 1790 Dalton seems to have considered taking up law or medicine, but his projects were not met with encouragement from his relatives – Dissenters were barred from attending or teaching at English universities – and he remained at Kendal until, in the spring of 1793, he moved to Manchester. Mainly through John Gough, a blind philosopher and polymath to whose informal instruction he owed much of his scientific knowledge, Dalton was appointed teacher of mathematics and natural philosophy at the “New College” in Manchester, a dissenting academy. He remained in that position until 1800, when the college’s worsening financial situation led him to resign his post and begin a new career in Manchester as a private tutor for mathematics and natural philosophy.

Dalton’s early life was highly influenced by a prominent Eaglesfield Quaker named Elihu Robinson, a competent meteorologist and instrument maker, who got him interested in problems of mathematics and meteorology. During his years in Kendal, Dalton contributed solutions of problems and questions on various subjects to the Gentlemen’s and Ladies’ Diaries, and in 1787 he began to keep a meteorological diary in which, during the succeeding 57 years, he entered more than 200,000 observations. He also rediscovered George Hadley‘s theory of atmospheric circulation (now known as the Hadley cell) around this time. Dalton’s first publication was Meteorological Observations and Essays (1793), which contained the seeds of several of his later discoveries. However, in spite of the originality of his treatment, little attention was paid to them by other scholars. A second work by Dalton, Elements of English Grammar, was published in 1801.

In 1794, shortly after his arrival in Manchester, Dalton was elected a member of the Manchester Literary and Philosophical Society, the “Lit & Phil”, and a few weeks later he communicated his first paper on “Extraordinary facts relating to the vision of colours”, in which he postulated that shortage in colour perception was caused by discoloration of the liquid medium of the eyeball. In fact, a shortage of colour perception in some people had not even been formally described or officially noticed until Dalton wrote about his own. Since both he and his brother were colour blind, he recognized that this condition must be hereditary.

Although Dalton’s theory lost credence in his own lifetime, the thorough and methodical nature of his research into his own visual problem was so broadly recognized that Daltonism became a common term for colour blindness.Examination of his preserved eyeball in 1995 demonstrated that Dalton actually had a less common kind of colour blindness, deuteroanopia, in which medium wavelength sensitive cones are missing (rather than functioning with a mutated form of their pigment, as in the most common type of colour blindness, deuteroanomaly). Besides the blue and purple of the spectrum he was able to recognize only one colour, yellow, or, as he says in his paper,

“that part of the image which others call red appears to me little more than a shade or defect of light. After that the orange, yellow and green seem one colour which descends pretty uniformly from an intense to a rare yellow, making what I should call different shades of yellow”

This paper was followed by many others on diverse topics on rain and dew and the origin of springs, on heat, the colour of the sky, steam, the auxiliary verbs and participles of the English language and the reflection and refraction of light.