The Formation of Colour Perception in Humans, Colour Blindness and Its Main Types - Literature review Example

Colour Blindness The human eye sees through the stimulation of the retina which is a neuromembrane lining at the back of the eye. This part of the inside eye is made of rods and cones that act as the peripherals for the eyes. The rods give humans the night vision but are not good at the distinction of the colours present. The cones on the other hand are located near the centre of the retina or what biologists term as the macula. The cones also do not give good night vision, but work on letting the human eye perceive colour based on the conditions experienced during the day (Wong 2011a:441). They contain light sensitive pigments that cover different wavelengths. Each of the colours present at different wavelengths is represented from approximately 400 to 700 nm, which the eye can comfortably deduce (Neitz & Neitz 2011: 634). The essence of these visions and light simulation attributes are contained in gene coding instructions within the pigments. If the instructions are wrong, the pigments will be reproduced and offer wrong information. The cones will then be sensitive to the different wavelengths which results into colour deficiency. Therefore, the best way of defining the colours that the eye sees is by terming them as the most sensitive reactions the cones have when exposed to light (Carlson 2007: 142). Graph showing the accepted colour perception spectra (Carlson 2007: 143) Colour blindness, contrary to popular belief, does not imply having a black and white vision. Instead, it only means that the individual has colour vision deficiencies based on gene coding (Neitz & Neitz 2011: 635). Colour blindness varies from one individual to the next, with four main categories defining the colour deficiencies present in the world today: protanopia, deuteranopia, tritanopia and monochromasy. Monochromasy defines an individual who has absence of colour sensation completely, though this is one of the rarest conditions (Wong 2011a:441). Protanopia and deuteranopia are common amongst those with dichromasy, which is a condition that affects those with one or more cones that are wrongly light sensitive. Trichomasy occurs when an individual has a mild colour deficiency and occurs through protanomaly and deuteranomaly sensitivity shifts. As such, identifying these attributes provides a better understanding of the different aspects of the colourblind issues that affect a majority of the people in the world today (Carlson 2007: 145). Before delving deep into the main types of colour blindness, it is important to look at the way human beings see colour. When one looks at an object, the vision starts when the light enters the eye. This allows the cornea and the lens to focus this light into the cornea and offer more chances of using this to project it into the retina. With millions of light-sensitive photoreceptors in the retina, it reflects the light into the rods and cones present there. The eye has approximately 6 million cones compared to 120 million rods (National Institute of Health 2013). Each eye has a different number of each, but the rods are more. These two contain photopigments molecules that undergo a variety of changes when they absorb some light. The chemical change occurring at the back of an eye triggers electricity-like signals that pass through the retina to the visual sensory parts in the brain. The response of the rods and cones to the light is quite different and the difference is in the intensity of the light (Carlson 2007: 149). Figure showing rods and cones in the eye (National Institute of Health 2013) The rods respond best to dim light while the cones respond best to bright light and are most active during the day. Rods also contain only one photo pigment while cones possess one of three different photopigments (Neitz & Neitz 2011: 635). The longer wavelengths that the cones are sensitive to are the red lights, followed by the medium sized green wavelengths, and to the short wavelengths, which are blue in colour. The rich vision that humans have come from this possession of different photopigments that are essential for normal viewing (Wong 2011a:441). Each of the photopigments has a particular part of the visual spectrum and that gives everything its colour. An object will appear as white when it has a reflection of all wavelengths, and black when it appears to absorb all wavelengths. This defines the unusual human view that allows them to have trichomatic vision, whilst most of the mammals have two such as dogs or other animals such as butterflies have more than three (Carlson 2007: 152). Monochromacy As noted, this is the condition of possessing only one channel for conveying colour information to the brain. This does not allow the individual to have a complete distinction of the any colours and perception are only variations in brightness rather than the colours viewed from a spectrum. It occurs in two main ways. The rod monochromacy is one of the main issues affect the eyes where the cones do not contain any cells in them. This means that the functions of the eye that depend on the cones are missing. Colour discrimination is impossible and the vision in lights of normal intensity becomes a hurdle as well. Though this is considered a rare occurrence, about 10% of the population in the Federated States of Micronesia has it (Carlson 2007: 152-3). The other form is the cone monochromacy that implies a condition with both rods and cones, but only one of the cones is present. This means that the other two are absent and the pattern f visions during the day is normal. The only difference is that it will not be distinguished using the hues that are present amongst those with all the cones. One could have the X chromosome or blue cone monochromacy where the green and red cones are missing. The sensitive spectrum sensitivities are all in the blue region or near the 440 nm level. People with this condition have light sensitivity, near sightedness, reduced visual acuity or nystagmus (Goldstein 2007: 223). Figure showing the blue cones of monochromats (Goldstein 2007: 225). This form of colour blindness shows a complete inability to make any distinctions between the different colours in the world. It also brings about severe light sensitivity, long-sightedness and near sightedness. People in this category are taught how to associate the colours with objects and differentiate the colours based on their brightness (Xin Bei, Chan, & Chuan 2014: 5). This condition is based on an autosomal recessive inheritance and is equally distributed amongst the men and women, with occurrences noted between 1 in every 300000 and 1 in every 50,000. It is one of the most common types of complete colour blindness despite the small number of people noted in that occurrence ratio (National Institute of Health 2013). Dichromacy This category involves people who have colour visions that allow them to see colours based on two main primary colours. This is unlike the normal human being who has an ability of seeing the three primary colours and distinguishing them (Neitz & Neitz 2011: 647). These individuals understand that they have this problem and it affects their daily lives and interactions (Nevid 2011: 46). This also makes it difficult for them to distinguish between certain colours such as red, orange, green and yellow, meaning that the different shades of a similar colour can be quite difficult to deal with for some. This condition involves those with protanopia, triatanopia, and deuteranopia (Xin Bei, Chan, & Chuan 2014: 7; Wise 2013: 123). Protanopia involves the lack of a long-wavelength sensitive retinal cone and the condition makes it difficult for an individual to differentiate between colours that are in the yellow-green-red region. This means that the wavelength reaching the eye is limited to 492 nm that defines a cyan-like wavelength (Xin Bei, Chan, & Chuan 2014: 6-7). For these individuals, it is difficult to distinguish between colours in this wavelength from white. The brightness of yellow, orange or red is reduced to a normal view, compared to that of the normal eye that defines the brightness from far (Bonilla-Silva 2013: 210; Catanese 2011: 410). The hue difference may not be strength to them, but they could distinguish between red and yellow based on the lightness and brightness of the colours. To them, purple, violet and lavender have no difference from shades of blue due to the reddish components that many see as invisible (Sembulingam & Sembulingam 2012: 58). Figure showing normal view on the left and protanopic view on the right (Xin Bei, Chan, & Chuan 2014: 9) Deuteranopia defines the lack of the medium-wavelength cones that does not allow the affected person to distinguish the colours that are between the green-red-yellow spectra (Dunkel 2013: 154). The neutral point for these individuals forms at the 498 nm wavelength, which is considered more of a greenish hue of cyan. These individuals suffer hue discrimination problems as noted by the protanopia individuals, though normal dimming separates the two (Tovee 2008: 58). Tritanopia affects individuals who lack the short wavelength cones. These individuals only have the shorter wavelengths in their vision and that means they can only view blue, indigo and a violet spectral (Ashe 2014: 22). The colours are drastically dimmed, and some of the colours even seem like they are black. They cannot distinguish between pink and yellow, and the purple colours seem like different shades of red. Unlike the other two forms of colour blindness that are common amongst the males, this one is not linked to any, and occurs in either (Crow 2008: 52: Goes 2013: 45). Figure: Testing the colour conditions amongst patients using a web chart (Crow 2008: 53) Trichomacy Commonly referred to as anomalous trichomacy, this condition is seen as the least severe condition of colour deficiency (Kunii 2012: 139). This category is divided into three main parts, which are protanomaly, tritanomaly and deuteranomaly (Stein, Stein & Freeman 2012: 125). These here differ in the colour matches from the normal individual. The protanomalous individuals require more of the red light in a red and green mixture for them to match a given light in the yellow spectra compared to the normal observers (Jones, Shim, He & Zhuang 2011: 501). The deuteranomalous individuals require more green light (Levine 2013: 45). As such, it is very easy for these two types of observers to do their normal jobs as they work on their daily attributes. It can be diagnosed as an instrument of anomaloscope, which mixes the spectral green, and red lights in various compositions for comparison with the fixed yellow spectral (Albrecht 2010: 770). This allows one to understand the type of anomaly in his or her vision, generating a renewed interest in meeting the main problems affecting the people within the society. The important thing is to get as much from the observations and understand the importance of making things better for the sake of the practical assistance of those diagnosed with the problem (Simunovic 2010: 751). Protanomaly implies having a long wavelength that is mutated and the peak of the light sensitivity is at the shorter wavelength in the retina. These individuals will have a red light sensitivity that is lesser than the normal individuals are (Sommers, & Norton 2006: 120). This implies the inability to discriminate colours and do not have the ability to see the mixed lights as the normal observers do (Jones, Shim, He & Zhuang 2011: 503). These individuals also report having a problem with the darkening of the red spectrum’s end, which results in the reduction of the intensity to almost a point where the end of the spectrum seems like black. It occurs within the X chromosome; hence, is an inherited genetic modification from this particular chromosome (Cole & Harris 2009: 423). Deuteranomalous individuals experience a mutation of the medium wavelength that covers the green pigment. This condition shifts the green spectral towards the end of the spectrum resulting to a reduction in the sensitivity to the green light (Norton, Vandello & Darley 2004: 821). The intensity remains unchanged though. It is one of the most common colour blindness conditions present, affecting at least 6% of the male and 0.4% of the females (Mollon & Cavonius 2012: 184). When talking about weakening green spectral, it implies that an individual with this condition will view dark green cars in the evening as black. Discrimination of colours is also difficult and that makes it difficult to differentiate the hues within the green, orange, red, and yellow spectra. Brightness remains part of their vision unlike the protanomalous individuals who have a dimming effect (Wong 2011b: 443). Tritanomaly is a rare condition for both genders, and indicates a mutation of the blue pigment, which is the short wavelength (Potnik & Kouyoumdjian 2012: 28). The short wavelength in this case is shifted to the end that has the green spectrum and individuals have a problem differentiating hues falling in this area. The mutation, unlike the other two, is formed within chromosome 7. Chart showing the wavelengths noted by trichromats (Cole & Harris 2009: 425) Achromatopsia This is defined as the total inability to see any colour. It is in reference to the congenital vision disorders where colours are absent to the individual’s eye. Even though the eye can distinguish the colours, it becomes difficult for this individual to differentiate the colours and perceive their existence (Neitz & Neitz 2011: 647). Image showing how an achromatopsic individual views the traffic lights (Neitz & Neitz 2011: 648). References Albrecht, M. (2010) "Colour blindness," Nature Methods vol. 7, no. 10, pp. 765–775 Ashe, T. (2014) Colour management & quality output: working with colour from camera to display to print. Washington, D.C.: CRC Press. Bonilla-Silva, E. (2013) Racism without racists: colour-blind racism and the persistence of racial inequality in America, Princton: Rowman & Littlefield Publishers Carlson, N.R. (2007) Psychology: the science of behaviour, New Jersey, USA: Pearson Education. Catanese, B.W. 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Xin Bei, V., Chan, G.S. & Chuan, T.N. (2014) "Subjects with colour vision deficiency in the community: What do primary care physicians need to know?" Asia Pacific Family Medicine vol. 13, no. 1, pp. 1-20. Read More