Optic disc coloboma

Findings

A posterior protrusion of vitreous is seen in the left globe, at the insertion of the optic nerve head. There is no hemorrhage, retrobulbar colobomatous cyst, or optic nerve atrophy. The right globe is normal.

Differential diagnosis:
- Coloboma (chorioretinal or optic disc)
- Peripapillary staphyloma
- Morning glory disc anomaly (MGDA)
- Buphthalmos (ox eye)


Diagnosis: Optic disc coloboma


Key points

Coloboma (Greek koloboun, "to mutilate") is the result of incomplete closure of the choroidal fissure.
Funnel or cone-shaped protrusion from the posterior aspect of the globe, often involving the optic nerve head insertion.
Two general types: Optic disc coloboma (ODC = excavated/everted region involves the posterior globe at the optic disc insertion only). Chorioretinal colobomas are more broad-based, extending beyond the margins of the optic disc.
May be associated with large retrobulbar colobomatous cysts (apparently encapsulated outpouchings of vitreous) which may be larger than the actual globe, may cause significant proptosis, or even globe atrophy / microphthalmia.
Majority of colobomas are sporadic and unilateral.
Associated with midline craniocerebrofacial clefting, choanal atresia, basal (particularly sphenoidal) encephalocele, corpus callosal agenesis, olfactory hypoplasia, cardiac anomalies, retardation, genital hypoplasia, and ear anomalies.

Differential diagnosis:
- Peripapillary staphyloma – more diffuse / broad based than coloboma, must feature posterior uveoscleral thinning and lack enhancement.
- Morning glory disc anomaly – fundoscopic description of ODC. Funnel or square shaped posterior defect at the optic nerve head.
- Buphthalmos ("ox eye") – 2/2 congenital glaucoma. Assoc. with Marfan's, NF-1, Sturge-Weber. Entire globe enlarged.