Monochromacy
Monochromacy | |
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owl monkeys and some other animals. | |
Specialty | Ophthalmology |
Monochromacy (from
Humans
Human vision relies on a
Most humans have three classes of cones, each with a different class of
- Anomalous trichromacy, when all three cones are functional, but one or more is altered in its spectral sensitivity.
- Dichromacy, when one of the cones is non-functional and one of the red-green or blue-yellow opponent channels are fully disabled.
- Cone monochromacy, when two of the cones are non-functional and both chromatic opponent channels are disabled. Vision is reduced to blacks, whites, and greys.
- Rod Monochromacy (Achromatopsia), when all three of the cones are non-functional and therefore photopic vision (and therefore color vision) is disabled.
Monochromacy of photopic vision is a symptom of both Cone Monochromacy and Rod Monochromacy, so these two conditions are typically referred to collectively as monochromacy.[1][2]
Rod monochromacy
Rod monochromacy (RM), also called
Cone monochromacy
Cone monochromacy (CM) is a condition defined by the exhibition of only one class of cones. A cone monochromat can have good pattern vision at normal daylight levels, but will not be able to distinguish hues.
As humans typically exhibit three classes of cones, cone monochromats can hypothetically derive their photopic vision from any one of them, leading to three categories of cone monochromats:[4]
- Blue cone monochromacy (BCM), also known as S-cone monochromacy, is an X-linked cone disease.[5] It is a rare congenital stationary cone dysfunction syndrome, affecting less than 1 in 100,000 individuals, and is characterized by the absence of L- and M-cone function.[6] BCM results from mutations in a single red or red–green hybrid opsin gene, mutations in both the red and the green opsin genes or deletions within the adjacent LCR (locus control region) on the X chromosome.[3]
- Green cone monochromacy (GCM), also known as M-cone monochromacy, is a condition where the blue and red cones are absent in the fovea. The prevalence of this type of monochromacy is estimated to be less than 1 in 1 million.
- Red cone monochromacy (RCM), also known as L-cone monochromacy, is a condition where the blue and green cones are absent in the fovea. Like GCM, the prevalence of RCM is also estimated at less than 1 in 1 million.
Cone Monochromats with normal rod function can sometimes exhibit mild color vision due to conditional dichromacy. In mesopic conditions, both rods and cones are active and opponent interactions between the cones and rods can afford slight color vision.[7]
According to
Mammals
Until the 1960s, popular belief held that most
Two mammalian orders containing marine mammals exhibit monochromatic vision:
- Pinnipeds (including seals, sea lions and walruses)
- Cetaceans(including dolphins and whales)
Unlike the
The light available in an animal's habitat is a significant determiner of a mammal's color vision.
A recent study using through PCR analysis of genes OPN1SW, OPN1LW, and PDE6C determined that all mammals in the cohort Xenarthra (representing sloths, anteaters and armadillos) developed rod monochromacy through a stem ancestor.[11]
See also
- Achromatopsia
- Blue cone monochromacy
- Cone dystrophy
- Dichromacy
- Trichromacy
- Tetrachromacy
References
External links
- Rossi, Ethan (February 2013). "Visual Function and Cortical Organization in Carriers of Blue Cone Monochromacy". PLOS ONE. 8 (2): e57956. PMID 23469117.
- Weleber, Richard (June 2002). "Infantile and childhood retinal blindness: A molecular perspective (TheFranceschetti Lecture)". Ophthalmic Genetics. 23 (2): 71–98. S2CID 30741530.