Congenital right optic nerve colobomatous cyst associated with microphthalmos.

Optic nerve coloboma is a congenital defect caused by the incomplete closure of the embryonic fissure. This closure begins around the fifth week of gestation, when the embryo measures approximately 7 to 14 mm. Colobomas may appear as isolated defects or alongside other ocular and systemic abnormalities. They typically occur in the inferonasal quadrant, where the optic vesicle undergoes closure. This closure process starts centrally within the eye and progresses both anteriorly and posteriorly. The distinct nature of these closures can result in an optic nerve coloboma without an associated iris coloboma. The formation of a coloboma can be attributed to external factors affecting the fetus during pregnancy or to a genetic mutation, such as an autosomal dominant mutation in the Pax gene, which is linked to bilateral colobomas. Small colobomas generally require only clinical and radiological observation, whereas larger colobomas may need surgical intervention to remove the cyst and prevent complications related to orbital content development, thereby improving cosmetic outcomes.