achromatopsia

n. Inability to distinguish colors (color blindness). It is also known as monochromatism. Congenital achromatopsia (daltonism or maskun) is a hereditary vision defect found in 1/33,000 persons in the United States (incidence is different in different world areas). People may have congenital achromatopsia as a result of having a low number of cells, an absence of cells, or morphologically malformed cone cells. Individuals who have achromatopsia may be either totally color-blind or almost totally color-blind; visual acuity is poor. Different subtypes are distinguished: complete rod mono- chromats, incomplete rod monochromats, and blue cone monochromats. Achromatopsia appearance requires two recessive genes and it is more frequently found in men than in women. Achromatopsia can also be due to an acquired brain condition (acquired or cerebral achromatopsia), associated with stroke, trauma, or some other cause. Persons who develop cerebral achromatopsia report that they only can see shades of gray. Usually, ventro-medial occipital lobe damage involving the lingual and fusiform gyri is observed in patients who have acquired achromatopsia.     - AA