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.
Blue cone monochromacy is a severe condition in which the cones sensitive to red or green light are missing or defective, and only S-cones sensitive to blue light and rods which are responsible for night (scotopic) vision are functional.
However, interaction of the blue cones and rod photoreceptors in mesopic vision (twilight) may enable some level of dichromacy.
Once the molecular biological basis of BCM was understood, the more descriptive term Blue cone monochromacy became dominant in the literature.
[9] Furthermore, only 7 of these dimorphic sites lead to a functional difference between the genes, i.e. that tune the opsin's spectral sensitivity.
The first detailed description of achromatopsia was given in 1777, where the subject of the description: ...could never do more than guess the name of any color; yet he could distinguish white from black, or black from any light or bright color...He had 2 brothers in the same circumstances as to sight; and 2 brothers and sisters who, as well as his parents, had nothing of this defect.In 1942, Sloan first distinguished typical and atypical achromatopsia, differentiated mainly on the inheritance patterns.
[20] In 1953, Weale theorized that the atypical achromatopsia must stem from cone-monochromatism, but estimated a prevalence of only 1 in 100 million.
[22][23] A significant discovery was announced in 1989 (and 1993) by Nathans et al.[1][2] who identified the genes which cause Blue cone monochromacy.