00:01
The eyelid is a structure
that protects the eye. We saw the
conjunctival surface, a continuation of
the corneum very early on.
00:12
Remember the junction is protected by
that mesh of stem cells that provide
additional cells accordingly when they are
lost and it prevents the cell lining
the conjunctiva from being part of that
epithelium. The conjunctiva is a
wet mucous surface. There are a number of
different glands associated
with the eyelid,
the meibomian glands secrete large amounts
of secretions. They secrete an oily
component and that oily component mixes
with the tears that are secreted by the
lacrimal gland and also small lacrimal
glands in the eyelid. And that will prevent
the very rapid vapourization of the tears
and therefore maintains the protection
of our eye particularly the corneum. The big large
oculi that's in the centre of the eyelid. That is one of
the very small muscles of facial expression
and then there is a very dense
piece of connective tissue running through
the eyelid called the tarsal
plate that gives the eyelid a certain
structural rigidity or support.
01:31
The lacrimal gland
is just like any other compound gland. I
described the structure of compound
glands in another lecture, but as you see
on the left-hand side under very low
magnification, you can see clusters of
glandular units called lobules. And
within those lobules on the right-hand side,
you can see secretory ascinii,
little grape or berry shaped cells. They are serous
secreting. They secrete a watery fluid with
some material in it that helps to be
antimicrobial, in other words it stops
bacteria and stuff and other material from
colonizing on the surface of the eye.
02:17
They are surrounded in the interstitial
component by plasma cells that secrete
antibodies through those tears again onto
eye to protect it. And the rather
large circular structure you see on the
right-hand side is the duct lined by
almost a columnar epithelium. But I won't say
any more about the lacrimal gland
because as I've mentioned before it is covered
in lectures I've have given in this
course on the exocrine glands.
02:48
In summary then, make sure you understand now
the structure of the cornea and the lens
and how those two major components then focus
the light on the retina. Understand
the macula lutea. It is the yellow
pigmented area of about 5-1/2
millimeters in diameter I mentioned. And
the fovea centralis with the very
central fovelial, that is where the light
is focused when we want to have
discrimination of detail and also very
fine color vision. It is where the
concentration of cons only. And then there's
the optic nerve containing all the ganglion cells,
axons projecting back to the brain. There's
the retina that I've have described or the
photoreceptors there and the very
complex supporting cells and other
neuroglial cells, neurons and conducting
neurons within that retina. And then
there is the production of the aqueous
humor by the ciliary epithelium and the
production is zonular fibres that
extend to the lens and then the
importance of the ciliary muscle when
it contracts and relaxes, it changes the
shape of the lens and, therefore, allows
us to focus distant objects and near
objects on the retina. So I hope you
now understand a bit more about the eye
particularly histological structures
of the eye and thank you very much for
listening to this lecture.