The optic nerve and its disorders

Published on April 27, 2016   24 min
The subject of this talk is The Optic Nerve and Its Disorders. And over the course of this talk, we will explain the anatomy of the optic nerve, the pathology that can affect this nerve, and the consequences in terms of disease. The talk will be presented by Dr. Simon Skalicky from the University of Melbourne and myself. My name is Keith Martin. I'm Professor of Ophthalmology at the University of Cambridge.
Thinking embryologically, the optic vesicle and cup develop as an out-pouch of the developing forebrain. These develop into the oculus structures, including retina and optic nerve. And this is why the optic nerve is part of the central nervous system. Its histology and pathological responses and behavior resemble a central nervous system white matter tract. This is in contrast to all other cranial nerves, which are peripheral nerves. Peripheral and central nerves differ in terms of their glial cells. Like the rest of the central nervous system, the optic nerve is surrounded by three meningeal layers. Finally, unlike peripheral nerves, the optic nerve has a limited capacity to regenerate axons after injury, which is similar to other central nervous system white matter tracts.
The optic nerve consists of the axons of 1.2 million ganglion cells. These are initially found in the inner most retinal layer, nerve fiber layer, and converge on the optic nerve head. At the optic nerve head, the axons form neuroretinal rim around the empty cup. The neuro tissue is supported by the lamina cribrosa, a thin, perforated area of sclera that allows the extra ocular passage of axons. This may be the reasons why it is more susceptible to high intraocular pressure than the rest of the sclera. The optic nerve travels through the orbit from the lamina cribrosa to the optic canal. Its length is somewhat longer than the orbit providing some laxity to prevent tethering of the globe on movement and some protection against mechanical stretch during proptosis. The optic nerve then passes through the sphenoid bone in the optic canal where its dura is firmly attached to the bone. Consequently, this portion of the optic nerve is more susceptible to sharing forces in trauma. As it enters the cranial cavity, the optic nerve travels posteriorly, dorsally, and medially to meet the contralateral optic nerve at the optic chiasm.