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Albinism: Ocular Albinism
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Albinism is a disorder of amino acid metabolism that results in a congenital hypopigmentation of ocular and systemic tissues. Cellular pigmentation is dependant upon a cell’s ability to manufacture and sequester the pigment melanin. This is accomplished within organelles called melanosomes which reside inside cells called melanocytes. The melanocytes that originate in the neural crest provide pigment for the skin (including eyelids), hair, uvea, conjunctiva, stroma of the iris, ciliary body and choroid. The melanocytes that supply pigment for the retinal pigment epithelium (RPE) are derived from neuroectoderm. Inside the melanosome, melanin is synthesized from the amino acid tyrosine through the actions of the enzyme tyrosinase.
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Albinism is an inherited condition in which eyes, hair and/or skin have less than normal amounts of pigment. Some children and adults with albinism (albinos) can have a total lack of pigment with white skin and hair and pink-colored eyes. Others have only mildly decreased amounts of pigmentation. One form, Ocular Albinism, affects mostly the eyes, leaving the skin and hair pigmentation nearly normal. In most cases of albinism the eye's central vision area, the macula, does not develop properly, resulting in poor vision.
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In Ocular Albinism, the skin and hair are relatively normal but are quite fair. Heightened sensitivity to light (photophobia) and the visual abnormalities of Oculocutaneous Albinism are typically present. There may be patchy degeneration of the retina (retinal mosaicism) in the eyes.
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Albinism of just the eyes ... occurs. This is called ocular albinism type 1 (OA1) and can be inherited via either an X-linked or an autosomal recessive process. In this form of albinism, skin color is usually normal and eye color may be in the normal range. However, examination of the eye will show that there is no pigment in the retina.
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Ocular Albinism (OA) is divided into two types according to the inheritance pattern: [A]utosomal recessive OA occurring equally in males and females, and X-linked OA with symptoms occurring primarily in males. In the X-linked cases, mothers carry the gene and pass it to their sons. Although the mothers usually have normal vision, they have subtle eye changes that can be identified by an ophthalmologist. If a woman does carry the gene, with each pregnancy there is a one in two chance of having a son with X-linked ocular albinism. For specific information, families should seek the advice of a qualified genetic counselor.
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Albinism is caused by the loss of melanin pigment in areas of normal pigmentation such as the skin, eyes, and hair. Aside from the hypopigmentation that these patients suffer, melanin pigment is needed for normal vision. The lack of melanin pigment in the skin predisposes these patients to many types of skin cancers. Broadly speaking, albinism is divided into two main types: ocular and oculocutaneous, with oculocutaneous type more common than ocular types.
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Ocular Albinism