Comparative Study of the Primate Retina
Jon H. Kaas, Christine E. Collins in The Primate Visual System, 2003
The presence of three cone classes in the retina does not guarantee the joy of trichromacy. In addition to the correct number of cone classes, the retina should also have the appropriate postreceptoral mechanisms to process the cone signals. It has been proposed that primate color vision evolved in two steps.31 Ancient mammals were nocturnal, possessed a single M/L cone, and thus were monochromats. The ancient form of color vision appeared when mammals acquired S cones, initially to enlarge their spectral sensitivity, and then developed the neural circuitry for blue-yellow color opponency.31 This circuit comprises the appropriate synapses between S cones, H2 horizontal cells, S-cone bipolar cells, and small bistratified cells. All the neural elements of this circuit have been found both in diurnal catarrhines32-31
ENTRIES A–Z
Philip Winn in Dictionary of Biological Psychology, 2003
The principle of trichromacy is exploited in colour technology because it allows any colour to be specified in terms of the proportions of three primary lights required to match it, providing a convenient means of quantifying a colour and allowing its exact replication. Furthermore, the manufacture of colour television also relies on this property of human vision since only three light emitting phosphors (red, green and blue) are required to generate to the satisfaction of the normal human visual system a full range of naturally occurring colours. It is important to note that the mixture of three primaries is not physically identical to the light being matched, since the two matching test fields have different spectral power functions. Rather, the identity between the two is a perceptual one, arising because they set up an equivalence in the visual system of the observer. Such an identity is called a METAMERIC MATCH. The colour-mixing experiments are governed by the rules of linear algebra (GRASSMANN'S LAWS), and because of this they imply the presence of three underlying receptoral mechanisms in human vision. Subsequent physiological and behavioural experiments have identified these as the three types of light-absorbing CONES of the human retina. Each cone type has a different spectral sensitivity, absorbing light from a slightly different but overlapping regions of the VISIBLE SPECTRUM. They are termed the short wavelength (S), medium wavelength (M) and long wavelength (L) absorbing cones. Coloured surfaces or lights usually stimulate all three cone types, but to different relative degrees. Thus each colour is coded uniquely in the nervous system by its own special ratio of activity in the L, M and S cone mechanisms.
Specialist Applications and Multispectral Imaging
Adrian Davies in Digital Ultraviolet and Infrared Photography, 2017
The colour receptors (cones) of different animals are sensitive to different wavelengths, meaning they see the world in completely different ways. Most humans can see red, green and blue (trichromats), while most other mammals can’t see the difference between red and green (dichromats). It is likely that smaller mammals see further into UV than humans do.
Masking Colour Blindness: A Case Report
Published in Neuro-Ophthalmology, 2023
Antonia Kartika, Raisha Pratiwi Indrawati, Angga Kartiwa, Rusti Hanindya Sari, Dianita Veulina Ginting, Prettyla Yollamanda
Colour vision is important for some occupations that need good colour discrimination. Identification of colours requires normal function of photoreceptors containing visual pigment responsible for short (blue), medium (green), and long (red) wavelengths, which are the S-cones, M-cones, and L-cones, respectively. Normal colour vision is known as trichromacy.4 However, if one of this photoreceptors is absent or defective, dysfunction in colour perception will be present. Anomaly of a photoreceptor is known as anomalous trichromacy, absence of one of the photoreceptor cones is called dichromacy, and absence of two of the photoreceptor cones is called monochromacy. Anomalous trichromacy can cause tritanomaly, deuteranomaly, or protanomaly. Dichromacy can cause tritanopia, deuteranopia, or protanopia. Monochromacy, which is caused by the absence of red and green cones, is called blue cone monochromacy. The absence of all cones is called achromatopsia or total colour vision loss.1,2,5 Red-green colour deficiency is the most prevalent form of CVD. Red-green CVD is caused by the absence of M-cones or L-cones, causing deuteranopia and protanopia, respectively.6 In this condition, there are overlapping of green and red wavelength bands received by cone photoreceptors, causing abnormality of deutan and protan colour perception.
Identification of colorblindness among selected primary school children in Hararghe Region, Eastern Ethiopia
Published in Alexandria Journal of Medicine, 2018
Temesgen Tola Geletu, Manikandan Muthuswamy, Tamiru Oljira Raga
Colorblindness is hereditary defect and can be grouped as monochromacy, dichromacy and trichromacy. Monochromacy is the total colorblindness that is very rare and it is manifested when two or all three of the cone pigments are not functioning or missing. However, dichromacy includes protanopia which is caused as a result of the complete absence of red retinal color receptors, and deuteranopia which results from the absence of green retinal color receptors and tritanopia which occurs when blue retinal photoreceptors are completely absent. In abberant trichromacy one of the three retinal photoreceptors is altered in its spectral sensitivity and results in protanomaly, deuteranomaly and tritanomaly in which the spectral specificity of the red, green and blue or yellow receptors is not functioning well. Achromatopsia is the most severe and rarest type of color vision impairment which occurs when an individual is unable to see any color due to absence of all the three retinal photoreceptors.11 The most common type of CVD is termed as Red-green CVD, which is also known as Daltonism.10
The effect of the ChromaGen contact lens system on visual performance
Published in Clinical and Experimental Optometry, 2020
Cagri Ilhan, Mehmet A Sekeroglu, Sibel Doguizi, Pelin Yilmazbas
There are three types of cone photoreceptors in trichromats that respond best to either small (S cone), medium (M cone), or long (L cone) wavelength light.1972 These cones encode the information for red‐green, and blue‐yellow components of colour vision and luminance. The ganglion cell axons carry encoded information as action potentials. L and M cones mainly project to the parvocellular layers of the lateral geniculate nucleus and this projection is important for red‐green colour vision. A smaller portion of the L and M cones project magnocellular layers of the lateral geniculate nucleus and luminance information is carried by this projection. Ganglion cells which increase their firing rate proportionally with S cone inactivation project to the koniocellular layers of the lateral geniculate nucleus and provide blue‐yellow colour vision.2019 Thus, all three types of cone photoreceptors must serve as appropriate signals for normal colour vision. The loss of function in any type of cone photoreceptor causes congenital colour vision deficiency (CVD). Congenital CVD is seen in eight per cent of males and 0.5 per cent of females.2010 The most common form of congenital CVD is associated with the reduced ability to discriminate red‐green (protan‐deutan defect) and is inherited as X‐linked recessive.2011 It is characterised by the defect in functions of cone photoreceptors, which respond best to either the long or medium wavelength light. Blue‐yellow congenital CVD (tritan defect) is extremely rare and this is characterised by the defect in functions of a cone photoreceptor that responds best to small wavelength light, inherited in autosomal dominant fashion.2014