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The four pigments in a bird's cone cells (in this example, estrildid finches) extend the range of color vision into the ultraviolet. [1]Tetrachromacy (from Greek tetra, meaning "four" and chroma, meaning "color") is the condition of possessing four independent channels for conveying color information, or possessing four types of cone cell in the eye.
There are about six to seven million cones in a human eye (vs ~92 million rods), with the highest concentration being towards the macula. [1] Cones are less sensitive to light than the rod cells in the retina (which support vision at low light levels), but allow the perception of color.
Blue cone monochromacy (BCM) is an inherited eye disease that causes severe color blindness, poor visual acuity, nystagmus, hemeralopia, and photophobia due to the absence of functional red (L) and green (M) cone photoreceptor cells in the retina. BCM is a recessive X-linked disease and almost exclusively affects XY karyotypes.
Cone dystrophy; Fundus of a 45 year-old patient with cone rod dystrophy segregating with a loss-of-function mutation (E1087X) in ABCA4. Note the presence of various-shaped pigment deposits in the posterior pole with atrophy of the retina, while the retina appears less damaged in periphery (upper part of the photograph). Specialty: Ophthalmology
Trichromatic color vision is the ability of humans and some other animals to see different colors, mediated by interactions among three types of color-sensing cone cells. The trichromatic color theory began in the 18th century, when Thomas Young proposed that color vision was a result of three different photoreceptor cells .
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.
The mantis shrimp has 16 color-receptive cones in their eyes. Humans have only three. The spectrum of colors we see comes from three base colors: green, blue and red.
By comparison, every color in a trichromat's gamut can be evoked with a combination of monochromatic light and white light. Dichromacy in humans is a color vision deficiency in which one of the three cone cells is absent or not functioning and color is thereby reduced to two dimensions. [1]