Achromatopsia

Achromatopsia (ACHM), is a medical syndrome that exhibits symptoms relating to at least five separate individual disorders. Although the term may refer to acquired disorders such as cerebral achromatopsia also known as color agnosia, it typically refers to an autosomal recessive congenital color vision disorder, the inability to perceive color and to achieve satisfactory visual acuity at high light levels (typically exterior daylight). The syndrome is also present in an incomplete form which is more properly defined as dyschromatopsia. The only estimate of its relative occurrence of 1:33,000 in the general population dates from the 1960s or earlier.

There is some discussion as to whether achromats can see color or not. As illustrated in The Island of the Colorblind by Oliver Sacks, some achromats cannot see color, only black, white, and shades of grey. With five different genes currently known to cause similar symptoms, it may be that some do see marginal levels of color differentiation due to different gene characteristics. With such small sample sizes and low response rates, it is difficult to accurately diagnose the 'typical achromatic conditions'. If the light level during testing is optimized for them, they may achieve corrected visual acuity of 20/100 to 20/150 at lower light levels, regardless of the absence of color. One common trait is hemeralopia or blindness in full sun. In patients with achromatopsia, the cone system and fibres carrying colour information remain intact. This indicates that the mechanism used to construct colours is defective.