00:01
Let me now move from the iris to the ciliary
body shown here in the diagram.
00:06
It has got a number of components, which I
would like to explain to you. First of
all the ciliary muscle is the bulk of what
you see on the top left-hand side
of this picture. Ciliary muscle is very
important because when it contracts or
relaxes, it affects the dimensions of the lens
because the ciliary processes which
you see there, they have an epithelium on them.
There's two epithelial layers there and again the
extensions on the neural part of the retina.
Those epithelial cells closest to
the posterior chamber or the vitreous actually
make these little fibres and
those fibres extend to the lens. And as we
will see in a moment when the ciliary
muscles contract or relax, that changes of
tension on those fibres extending into
the lens and, therefore, the shape of the
lens. So the ciliary process is very
important for that and also the
epithelial cells produce the aqueous
humor that I will explain in a moment.
So let's just go back and look at the image
on the right-hand side. Let us look very carefully.
You can see some of these zones with
fibres extending from the ciliary processes.
They are very hard to see in
sections because often when you section
through the eye, it does not have to be
lucky enough to get the zonular fibres,
but some are shown here if you look very
very finely and top of the lens are
shown up in the top left hand side of
this particular image. And there is a
ciliary muscle there in the corner and
on the right-hand side of that, the dark
green structure is going to be the sclera.
You are looking right at the junction
between the cornea and the sclera in an area
we call the limbus. Let us just go back a
step before we continue with those zonular
fibres and the lens and have a closer
look at this double epithelium that lines
the ciliary processes. You can see
two epithelia here
adjacent or facing the posterior chamber or
the vitreous is the non-pigmented ciliary
epithelial cells, the cuboidal cells and
then below them are the pigmented ciliary
epithelial cells and then below those
cells is going to be the stroma of the
ciliary body. And again let me
remind you that this
double epithelial layer is a nonneural
extension of the retina. Back in the
posterior part of the retinal course, there
are going to the photoreceptor cells and
also this pigmented epithelium. Right
between the two cell layers is the ciliary
channel, which is an important collection
site when the process of these cells
are making the aqueous humor. And if you look
very very carefully at the top part of the
epithelium, the nonpigment epithelium, you
can see a very fine line running across
the surface of those cells. That happens to
be the basal lamina, the basement
membrane of this epithelial layer. The
basement epithelium of the pigmented epithelium
is adjacent to the stroma.
03:41
So really that ciliary channel you see
labelled there has both the apical surfaces of
the non-pigmented epithelium and also
the apical surfaces of the pigmented
epithelial cells. And we are going to
see in a moment that basal lamina
on the surface, on the non-pigmented
layer are going to be the component that
anchors the zonula fibres that extend
then to equator of the lens.
04:14
Here is a diagram explaining that double
epithelium that I indicated to you in the
previous slide. I actually like this
diagram. I like the colour in that.
04:27
So congratulations to the artist. Let us
focus on the bottom part of the diagram, you
can see a fenestrated capillary. That is
the stroma component of the ciliary
processes in the ciliary body and just
above that is the pigmented epithelial
cell. Then the ciliary channel and then the
non-pigmented epithelial cells. And then
you can see the basal lamina on the
non-pigmented ciliary epithelial cells
and extending from that basal lamina
are the zonula fibres that are going to go
the equator of the lens. And then above
that it just tells you really the
components of the aqueous humor. They
are produced, those components, by
the epithelial cells particularly the
non-pigmented cells. They are very very busy.
05:25
They are very easily processing various
components coming up from those
fenestrated capillaries. They're actively
processing materials. So they have lots
of sodium and potassium pumps etc and a
very busy epithelium that makes up this
layer. Busy because not only producing
the aqueous humor, but they are also producing
those zonula fibres as well.
05:54
So they are busy cells. And that aqueous
humor is going to circulate through the
anterior and posterior chambers of the eye.
Now I can show you the canal of
Schlemm which sits in the limbus that I
pointed out earlier. There is a corneal
epithelium coming around to join the
conjunctiva and the cornea is
continuous with the sclera and there's
the canal of Schlemm on the left hand side
in low magnification and on the right
hand side in the centre at high
magnification. This is the network that
is going to allow that aqueous humor to
drain into it and finds its way into
the venous system. Here is a diagram
explaining that, the pictures on the left-hand
side and the diagram just follow
the sequence.
06:48
One, the epithelial cells produce the aqueous
humor that circulates from the
posterior chamber through the little
valve created by the iris into
the anterior chamber and then into the
canal of Schlemm and then to the venous
system. That is constantly being produced and
it maintains a certain pressure in
the anterior and posterior chamber of the eye.
If there's some reason that there is a blockage in
that canal or over production, then the
pressure increases and that is a
condition that we call glaucoma and is quite
a common eye disease that needs to
be treated. The vitreous cavity shown in the
very bottom part of the diagram is a gel-like
component. It is a large component. Its
job being a gel is to maintain the shape
of the eye, but it is also a shock
absorber. When you do
sudden eye movements, the vitreous protects
the retina the very sensitive retina
from vibrations caused
by those rapid eye movements. You can see the
lens there and you can see the zonular fibres
extending from the epithelium are described
earlier to the equator of the
lens. Again let me remind you that post
lens fibres or zonular fibers are
produced by the epithelial cells that
produce the aqueous humor.