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Specialist Applications and Multispectral Imaging
Published in Adrian Davies, 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.
Comparative Study of the Primate Retina
Published in Jon H. Kaas, Christine E. Collins, 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
Published in Philip Winn, 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.
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.
Dalton's pseudo‐isochromatic plates and congenital colour vision deficiency
Published in Clinical and Experimental Optometry, 2020
Anuradha Narayanan, Mohan Venkadesan, Sruthi Sree Krishnamurthy, Jameel R Hussaindeen, Krishna Kumar Ramani
Dalton PIP was found to have high sensitivity and specificity. This could be attributed to the selection of those numerals with lower percentage of errors in the vanishing plates from the 38‐plate edition of Ishihara PIP. This selection could have effectively separated normal trichromats from the colour vision deficient.2012 Earlier studies comparing smartphone‐based applications to Ishihara's booklet have demonstrated a good sensitivity and specificity with few applications (Eye2Phone)2015 and a relatively poor specificity (colour vision test) with few other applications.2016 This difference was attributed to the technologies involved like the property of display, screen size and corresponding test plate size, glare and reflections from the smartphone screen. The Dalton PIP overcomes the disadvantages of these applications. Its construction and the procedure of testing red‐green colour deficiency closely resembles the standard Ishihara PIP.2012
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