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From Biology-Online Dictionary | Biology-Online Dictionary
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noun, plural: colobomas or colobomata

A defect especially of the eye, such as the presence of a hole in the eye due to some structures missing or that which is caused by an incomplete fusion of the intraocular fissure


A coloboma refers to any defect, especially of the eye, wherein a hole is present. The hole in the eye is caused by a gap (an intraocular fissure). The eye structures that may be affected are iris, retina, choroid, and optic disc. The most common form is the one affecting the iris.

In congenital conditions, the eye of the newborn would have a gap due to the incomplete fusion of the foetal intraocular fissure during gestation. If only one eye is affected, it is described as unilateral. If both eyes are affected, the condition is described as bilateral. Individuals with colobama usually have no problems with their sight. Blindness does occur when the condition is severe (e.g. lacking in optic nerve). Possible causes of congenital colobamas are associated with genetic mutations. One possible cause is a mutation in the PAX2 gene. Colobamas may also manifest as one of the symptoms in some genetic disorders. For example, the cat eye syndrome is a genetic disorder caused mainly by the extra copy of chromosome 22 (trisomic or tetrasomic). The condition derived its name from the manifestation of an iris coloboma. A hole in the iris results in an eye resembling that of a cat.

Word origin: Greek koloboma ("defect")

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