China
Africa
Explore chapters and articles related to this topic
Impairment of visual functions
Published in Ramar Sabapathi Vinayagam, Integrated Evaluation of Disability, 2019
Normal persons (trichromats) are sensitive to red, green, and blue light. Dichromats, with two photoreceptors, can recognize two colors. Most of the dichromats are red and green color deficient. Yellow and blue color deficient persons are rare. Monochromats with a single photoreceptor are color blind as they cannot recognize any color signal. They perceive only grayscale between black and white. Persons with achromatopsia (13) (monochromats) are deprived of the full experience of color perception in their environment, and this may interfere with activities of daily living. They also find it difficult to identify the color signal in a traffic light, and can drive only by locating the illumination of upper, middle, or lower lights. Thus, they have the risk of being involved in an accident. Furthermore, color discrimination is significantly important in certain occupations requiring critical safety tasks, such as in air, marine, road, and train transport systems as well as in certain trades. Hence, they may not be eligible for occupations such as a pilot, train engineer, railroad worker, firefighter, and signalman on railways. In dichromatopsia and those with anomalous color vision, there is an inaccurate recognition of the actual color and the perception of the reduced intensity of color may further augment the difficulty in identifying standard colors at a regular distance or in the presence of mist, smoke, or during rain. Thus, the quality of life is at a low ebb in persons with impairment of color vision.
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
One of the most interesting results of comparative studies about the primate visual system was the discovery by John Mollon, James Bowmaker, and Gerald Jacobs that platyrrhines, in contrast to catarrhines, have several normal color vision pheno-types.5 Together with a chromosome 7 gene that codes the S-cone opsin, several diurnal platyrrhines possess a single locus in the X chromosome that codes for M-or L-cone opsins. However, due to the existence of a polyallelism of the X chromosome opsin gene, there are several possible color vision phenotypes. All males and some females are dichromats, whereas the majority of females are trichromats. The number of di- and trichromatic phenotypes, as well as the proportion of females that are di- or trichromats, depends on the number of alleles present in the population. In some platyrrhines, such as Ateles, there are only two alleles; in others such as Cebus, Saimiri, Callithrix, and Saguinus, there are three alleles; whereas in some others, such as Callicebus, there are up to five alleles (reviewed by Jacobs6). There is at least one exception to this pattern among diurnal platyrrhines. The Alouatta has color vision similar to catarrhines, with two loci in the X chromosome coding M and L opsins, respectively, and a single allele for each locus.67× Another exception is the nocturnal, monochromatic Aotus. It lacks a functioning gene on chromosome 7 and has a single allele for the X chromosome, coding for a M-cone opsin.6,8
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
Despite the limited benefits of CCLs in patients with protan defects, all CCLs equally (Violet 3 included) improved the mean number of recognised symbols in patients with deutan defects. Swarbrick et al.2001 reported there was no difference in the number of recognised symbols between a normal trichromat and a dichromat after the insertion of CCLs in eyes with deutan defects. Similarly, in the present study, while the number of recognised symbols was lower in patients with medium rather than strong deutan defects at baseline, the numbers of recognised symbols of the two groups were similar after the insertion of CCLs. This study analysed the results in detail according to the type and extent of congenital red‐green CVD.