Achromatopsia

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(Redirected from Maskun)

**Achromatopsia**
*Classifications and external resources*
ICD-10	H 53.5
ICD-9	368.54
OMIM	216900 262300
DiseasesDB	83
MeSH	D003117

Achromatopsia is the inability to see color. Although the term may refer to acquired disorders such as color agnosia and cerebral achromatopsia, it typically refers to congenital color vision disorders (i.e. more frequently rod monochromacy and less frequently cone monochromacy).

1 Classification
2 Acquired achromatopsia (Cerebral achromatopsia)
3 Congenital / inherited achromatopsia
- 3.1 Complete / typical achromatopsia (Rod monochromacy)
- 3.2 Incomplete / atypical achromatopsia
4 References
5 External links

[edit] Classification

Acquired achromatopsia (Cerebral achromatopsia)
Congenital/inherited achromatopsia

Complete/typical achrompatopsia (Rod monochromacy)
Incomplete/atypical achromatopsia

[edit] Acquired achromatopsia (Cerebral achromatopsia)

Cerebral achromatopsia is a form of acquired color blindness that is caused by damage to the cerebral cortex of the brain, rather than abnormalities in the cells of the eye's retina.

[edit] Congenital / inherited achromatopsia

[edit] Complete / typical achromatopsia (Rod monochromacy)

Typical achromatopsia, also known as complete achromatopsia<ref name="Michaelides"/><ref name="Typical achromatopsia">"Typical achromatopsia". Drugs.com. Accessed October 5, 2006.</ref> or rod monochromatism<ref name="Michaelides"/>, is associated with absent color vision, nystagmus, reduced visual acuity, and light aversion.<ref name="Complete achromatopsia">"Complete achromatopsia". Drugs.com. Accessed October 4, 2006.</ref>

Rod monochromacy, also known as total color blindness<ref name="Deeb">Deeb SS. "Molecular genetics of colour vision deficiencies." Clin Exp Optom. 2004 Jul;87(4-5):224-9. PMID 15312026.</ref>, achromatopsia<ref name="Deeb"/>, typical monochromacy<ref name="Alpern">Alpern M. "What is it that confines in a world without color?" Invest Ophthalmol. 1974 Sep;13(9):648-74. PMID 4605446.</ref>, or complete achromatopsia<ref name="Pokorny">Pokorny J, Smith VC, Pinckers AJ, Cozijnsen M. "Classification of complete and incomplete autosomal recessive achromatopsia." Graefes Arch Clin Exp Ophthalmol. 1982;219(3):121-30. PMID 6983472.</ref>, is a rare, nonprogressive inability to distinguish any colors as a result of absent or nonfunctioning retinal cones. It is associated with light sensitivity (photophobia), involuntary eye oscillations (nystagmus), and poor vision.<ref name="Cassin">Cassin, B. and Solomon, S. Dictionary of Eye Terminology. Gainsville, Florida: Triad Publishing Company, 1990.</ref>

Rod monochromatism is also known as achromatopsia<ref name="Windsor">Windsor RL, Windsor RK. "Understanding Achromatopsia." Accessed October 4, 2006. [1]</ref>, complete achromatopsia<ref name="Michaelides">Michaelides M, Hunt DM, Moore AT. "The cone dysfunction syndromes." Br J Ophthalmol. 2004 Feb;88(2):291-7. PMID 14736794.</ref><ref name="Ben Simon">"Ben Simon GJ, Abraham FA, Melamed S. "Pingelapese achromatopsia: correlation between paradoxical pupillary response and clinical features." Br J Ophthalmol. 2004 Feb;88(2):223-5. PMID 14736779.</ref><ref name="Complete achromatopsia"/>, and typical achromatopsia.<ref name="Michaelides"/><ref name="Complete achromatopsia"/>

Rod monochromacy is characterized by a low or nonexistent cone cell count or morphologically malformed cone cells; these are the light receptors responsible for color perception. Those with the condition have difficulty seeing in bright daylight because their rod cells (the receptors responsible for detecting brightness) are saturated. People with normal color vision do not perceive things in the same way as those with rod monochromacy, because they depend on color more than on luminosity to identify objects and patterns, whereas achromatopics depend almost entirely on luminosity to identify patterns. The closest that normal-sighted persons can come to experiencing rod monochromatic-type vision is in the dark, when the rod cells become the predominant receptors for vision due to their sensitivity to variations in brightness. Achromatopsia can vary in its severity from being mild enough that it is not diagnosed to causing near blindness. It is a relatively rare condition requiring two recessive genes (CNGA3 and CNGB3). In the United States, it affects approximately 1 in 33,000 people. The condition is generally stable over the course of one's life. Many achromats function normally with the aid of darkened lenses, while others use guide dogs, canes, and are considered legally blind.

Rod monochromacy is endemic on the atoll of Pingelap (where it is called maskun, literally "not see", by the locals) and was described by Oliver Sacks in The Island of the Colour-blind.[2] Sacks went there with Knut Nordby, a Norwegian man who had maskun, and the book narrates his experiences on the island.

[edit] Incomplete / atypical achromatopsia

Atypical achromatopsia, also known as incomplete achromatopsia<ref name="Michaelides"/><ref name="Atypical achromatopsia">"Atypical achromatopsia". Drugs.com. Accessed October 5, 2006.</ref>, is associated with normal visual acuity and absence of nystagmus.<ref name="Atypical achromatopsia"/>