ABSTRACT
The optic nerve consists of axons of retinal ganglion cells and extends from the optic disc to the optic chiasm. It can be divided into four portions: intraorbital, orbital, intracanalicular and intracranial. The intraorbital portion of the optic nerve includes the optic disc and the portion of the optic nerve within the posterior scleral foramen. Congenital anomalies include aplasia and hypoplasia of the optic nerve, coloboma, optic atrophy, glaucoma, optic pit and tilted disc. Drusen are deposits of a hyaline-like calcific material within the tissue of the optic nerve head. Myelinated nerve fibres are a common congenital abnormality which may be mistaken for disc oedema. Optic nerve hypoplasia may be complete or partial and is typically a sporadic occurrence and asymptomatic. Visual field defects are due to mechanical compression resulting in nerve fibre bundle defects, generalised depression or scotomas, dependent on the area of nerve compressed.
