An apparent absence or defect of some ocular tissue, usually due to failure of a part of the fetal fissure to close; it may affect the choroid, ciliary body, eyelid (palpebral coloboma, coloboma palpebrale), iris (coloboma iridis), lens (coloboma lentis), optic nerve or retina (coloboma retinae). Colobomas of the choroid are common in cattle, and have been observed in miniature swine. Colobomas of the optic disk are an inherited defect in several breeds of cattle.
- atypical c. — on occurring at a location other than the fetal fissure.
- iris c. — a full thickness defect in the iris. When it occurs at the base of the iris, it is called iridodiastasis.
- optic nerve c. — part of the scleral ectasia syndrome in dogs; also seen in Basenji dogs and Charolais cattle.
- typical c. — one occurring in or near to the fetal cleft.
