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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.
ENTRIES A–Z
Published in Philip Winn, Dictionary of Biological Psychology, 2003
A term used to refer to either a total or a partial loss of COLOUR VISION which may be either inherited or acquired. The most common inherited colour vision deficiencies are present from birth and produce a partial loss of colour vision in about 8% of men and under 1 % of women. These are forms of DICHROMATIC COLOUR BLINDNESS (PROTANOPIA, DEUTERANOPIA, TRITANOPIA) which arise when one of the three light-absorbing pigments in the cones of the retina is missing, and the milder versions (PROTANOMALY, DEUTERANOMALY, TRITANOMALY) which occur when all three pigments are present but one is anomalous. Much more rarely, colour vision may be absent altogether as a result of an inherited disorder, as in ROD MONOCHROMACY in which all three cone pigments are functionally absent. Acquired colour vision disorders, which onset during the subject's lifetime, have a wide range of causes. They usually produce a relatively mild loss of colour vision, for example due to disease processes or pharmacological agents affecting the retina or optic pathways. These acquired colour vision disorders may affect both red-green and blue-yellow colour OPPONENT PROCESSES, although it is believed that blue-yellow colour vision is more vulnerable when the damage is to the receptoral layers of the retina (KOLLNER'S RULE). A complete loss of colour vision (ACHROMATOPSIA) is very rare and is likely to arise from damage to areas of the temporal lobe of the brain that are specialized for the encoding of colour.
Comparative Study of the Primate Retina
Published in Jon H. Kaas, Christine E. Collins, The Primate Visual System, 2003
Recently, it was shown that prosimians might be as diversified as platyrrhines in terms of color vision. Some species are monochromats,940 others dichromats,11 and still others have a mixed population of di- and trichromatic individuals due to X chromosome-linked polyallelism.12
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
Visual and ocular findings in a family with X-linked cone dysfunction and protanopia
Published in Ophthalmic Genetics, 2021
Dag Holmquist, David Epstein, Monica Olsson, Bernd Wissinger, Susanne Kohl, Jürg Hengstler, Kristina Tear-Fahnehjelm
Prior to molecular genetic testing, blue cone monochromacy (BCM) was suspected due to the clinical findings with marked decreased function of the cones detected by ERG, symptoms of photophobia and decreased visual acuity, and a family history of color vision deficiency. BCM represents the most severe form of impaired L- and M-cone function due to complete (function) loss of L- and M-cone photoreceptors, while in the extremely rare BED some residual L- and/or M-cone function is evident. BCM and BED are both inherited as an X-linked trait, predominantly affecting males, and are caused by mutations at the red and green opsin gene cluster on Xq28. The clinical diagnosis can be confirmed with high confidence by molecular genetic testing.