00:02
Now let's take a closer look at
the optic nerve, cranial nerve II.
00:07
Here we see the sphenoid bone
and its relationship to the optic
nerve coming from the eyeball.
00:14
As it moves posteriorly,
it's going to pass through the
opening of the sphenoid bone
known as the optic canal.
00:20
Before it interacts with
its contralateral side
at the optic chiasm.
00:25
Before continuing on more
posteriorly into the brain
as the optic tract.
00:31
When we look at the retina,
which is the sensory
apparatus of vision,
we can divide it into
medial and lateral parts.
00:38
We also call it the
nasal and temporal parts
because the medial part
is closer to the nose
and the temporal part is closer
to the temporal area of the skull.
00:48
It turns out,
when we're looking
at a particular area
or a visual field,
the temporal aspect
of the visual field
is actually received by the
nasal aspect of the retina
and vice versa.
01:03
The temporal aspect of a retina
is picking up the nasal
aspects of the visual field.
01:09
As you can see by the color
coding in this image here.
01:13
Furthermore,
the fibers that carry those
visual field informations
travel in different aspects,
so the temporal fibers,
again those are carrying
information from the nasal fields
stay somewhat laterally,
whereas the nasal fibers,
seeing somewhat more medially,
will actually cross over
at the optic chiasm.
01:39
And this is clinically
important because
this area of the optic chiasm
happens to be right near
the pituitary gland.
01:46
So, when the pituitary gland
becomes abnormally enlarged,
such as with a
pituitary adenoma,
it may compress
this optic chiasm.
01:56
And again, this is where those
nasal fibers are crossing.
02:00
And again, keeping in
mind that nasal fibers
carry the temporal fields,
leading to a particular type of vision
loss called bitemporal hemianopsia.
02:12
In fact,
when you see this type
of visual field loss,
it helps you target
a potential pathology
related to the pituitary gland.
02:25
Now let's take a look at
how the orbit interacts
with the middle cranial fossa.
02:31
Here we see the optic nerve
reaching the optic chiasm
or that crossing point.
02:38
Beyond which,
it becomes the optic tracts
as they go to the
visual processing areas.
02:44
And the optic canal
is a passageway
through the sphenoid bone.
02:50
The superior orbital fissure,
also a feature of
the sphenoid bone
carries multiple cranial nerves:
III, IV, V1 and VI.
03:00
One thing that does not carry is
the maxillary
division of trigeminal
that goes through
the foramen rotundum.