Congenital Optic Nerve Head Abnormalities
Optic disc colobomas are uncommon congenital defects that develop as a result of defective closure of the fetal fissure (Fig. 6.3.1). Colobomas can be associated with peripapillary retinal detachments or schisis. In posterior segment colobomas, histological and OCT studies show that a tissue called the intercalary membrane overlies the area affected by the defect. OCT allows a qualitative assessment of the vitreous in eyes with optic disc colobomas, documenting the degree of vitreous condensation and adhesion in the area of the optic disc, especially with the three-dimensional reconstruction. OCT can potentially reveal retinal breaks on the optic disc margin. Retinal detachments and schisis associated with the optic disc colobomas can also be visualized on OCT scanning.
Figure 6.3.1 Color photograph of an optic disc coloboma of the right eye. There is minimal retinal involvement with pigmentation and scarring temporal to the disc. A line scan shows a deep cavitary depression within the optic nerve that is significantly more exaggerated than what is seen in normal optic nerve cupping. There are associated hyporeflective cystic changes within the nerve fiber layer (arrow). There is shadowing due to overhanging of the nasal optic nerve rim with loss of the underlying OCT signal (arrowhead). The blue line (inset) shows the position of the B-scan.