Definition of Coloboma

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Coloboma: A congenital malformation (birth defect) in which part of the eye does not form due to failure of fusion of an embryonic feature called the intraocular fissure. The resultant coloboma can be likened to a missing slice from a pie that may involve a number of different structures within the eye including the choroid, iris, lens, optic nerve, and retina.

A coloboma can occur as an isolated defect in an otherwise normal baby, or it can be part of a multiple congenital malformation syndrome such as the cat-eye syndrome (named after the coloboma which gives the eye something of a feline look). Colobomas are also seen in the aniridia-Wilms tumor association (the concurrence of undergrowth of the iris of the eye and Wilms tumor of the kidney); and the trisomy 13 syndrome (a disastrous disease due to an extra chromosome number 13).