Coloboma of the optic nerve is a congenital eye abnormality in which the optic nerve (which carries images of what the eye sees to the brain) is not completely formed. The condition may occur in one or both eyes. The degree of visual impairment varies widely depending on the severity and structures involved. Detachments of the retina may occur in in people who have Coloboma of optic nerve. Other associated symptoms may include a small eye (microphthalmia) with or without a cyst; small cornea (microcornea); or coloboma of other eye structures. Although the condition is present from birth, diagnosis may be delayed since the coloboma is inside the eye and not visible by simple inspection. Coloboma of the optic nerve may occur sporadically, may be due to a genetic change and be inherited, or may occur as a feature of an underlying syndrome or other genetic condition.