0:00
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.
0:24
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.
1:10
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.
