Contributor: Gordon K. Klintworth
An atypical coloboma does not involve the inferior nasal segment of the iris or lens, but another  sector. This type of iris coloboma seems to result from the persistence of  blood vessels at the edge of the optic cup. The defect may extend from the pupil to the periphery or involve only a part of the iris.
Atypical lens colobomas result from localized deficiencies of zonules that usually occur without an apparent cause. An atypical lens coloboma may follow an adjacent medulloepithelioma or other ciliary body tumor or surgery for congenital glaucoma [glaucoma - congenital].