Chorioretinal Coloboma

Coloboma is a term used to describe defects seen in various ocular structures due to incomplete embryologic development. Fundus coloboma specifically is due to failure of the embryonal fissure to close, which typically occurs by 5-7 weeks gestation. Posterior colobomas, involving the retina, choroid, and optic nerve, are more likely to be visually significant. In choroidal coloboma, both choroid and retinal pigment epithelium (RPE) are absent in the coloboma. A major complication of chorioretinal coloboma is a retinal detachment (RD) in up to 50% of large coloboma. In such cases the detachment is challenging to treat as the retinal break often occurs within the fibrotic intercalary membrane overlying the coloboma. Given the lack of RPE within the coloboma, laser or cryotherapy cannot induce an adhesion to treat the retinal break. Pars plana vitrectomy with silicone oil tamponade and endolaser on the coloboma margin, where RPE is present, has demonstrated modest surgical success. Depicted is a severe coloboma with optic disc involvement and variable RPE hyperplasia on the edge of the coloboma. The fovea (arrow) is visible within the coloboma but does not support good vision due to the lack of RPE.