13 - Optic Disc and Optic Nerve

Abstract

This chapter provides an overview of optic disc and optic nerve. The axons of the ganglion cells converge on the optic disc, which is approximately 1.5 mm in diameter. The optic disc, which is devoid of photoreceptors, is a pale pink color and is often slightly lighter temporally than nasally, as there are fewer blood vessels on the temporal side. The nerve fibers, making up the optic nerve, normally become myelinated immediately behind the lamina cribrosa. Congenital swelling of the optic nerve is a physiological variation of the norm frequently seen in patients with axial hypermetropia. Colobomas of the optic nerve head are often associated with choroidal or iris colobomas. Sometimes remnants of the posterior portion of the hyaloid artery remain, or glial sheets persist, and cover the optic nerve. In children, gliomas of the optic nerve are frequently associated with neurofibromatosis. These tumors are relatively slow-growing and do not normally require removal. The most common secondary tumors of the optic nerve head in that age group are leukaemic infiltrations.