Contributor. Gordon K. Klintworth
A coloboma commonly results from incomplete closure of the embryonic fissure (5-8 weeks of gestation) and is usually located nasally in the area of the embryonic fissure. Sometimes it is found in a different location. A coloboma may be complete or partial and can involve the iris [coloboma - iris], retina [coloboma - retina], choroid [coloboma - choroid] and/or the optic disc [coloboma - optic nerve]. Colobomas are divided into typical colobomas (those that occur at the site of the embryonc fissure)[coloboma - typical]. and atypical colobomas (that do not ocur at the site if the embronic fissure)[coloboma - atypical]. Ocular colobomas may be associated with several syndromes, including  CHARGE syndrome, and specific mutations in the SHH gene.