Eye Anatomy


hello everyone!
in this video we’re gonna cover the structures of the eye and we are also
going to talk about their functions. first let’s talk about the accessory
structures of the eye. We have the eyebrows over here. This is basically a
structure that helps make facial expression more obvious and also it does
play a minor role in protecting the eyes. so when you sweat, your sweat does get
trapped in your eyebrows and it prevents it from entering your eyes. Eyelids! This is
basically the anatomical term for eyelids, this is called the palpebra. so
we have the superior palpebral and the inferior palpebra! lacrimal caruncle is this little pink structure over here Let’s see if I could draw this thing.
This structure over here this is going to be the lacrimal carunlce. Which basically produces some sweat , and some substances that lubricate the eye. There are gonna be some sebaceous glands and modified sweat glands in this area that produce those substances. So when you wake up with in the morning with those sandy things in your eyes. That’s
what is produced by the lacrimal caruncle. T They tend to accumulate
at night time when you’re sleeping. Eyelashes! so in between the eyelashes
are going to have tarsal glands, and tarsal glands are basically modified sebaceous
glands. They are also going to produce this lubricating substance that’s going
to prevent the eyelids from getting attached to each other. There are muscles
around the eye that help move the eye. I’m going to go over it in the next
slide. We also have a lacrimal gland and lacrimal gland is actually lateral.
So it’s gonna be around maybe this area over here. we’ll take a better look. It’s
gonna be lateral. keep that in mind. That’s important to remember when when
it comes to naming the muscles. Lacrimal gland is responsible for producing tears,
and keeping in mind tears are always being produced, not just when you’re crying. And
that’s important for basically keeping the eye lubricated and hydrated. And then
there’s gonna be adipose tissue. There’s gonna be a lot of fat around the eye
that basically cushion the eye. Here we could see the muscles around the eye. There are six muscles that move the eye Four of them are going be your rectus
muscles. Rectus means straight. And two are going to be oblique muscles. Here’s
the superior rectus, inferior rectus, the medial rectus, lateral rectus. Again
rectus means straight so these muscles are basically going straight back.
Their muscle fibers are straight. And then we also have two oblique muscles
that move the eye. Superior oblique, up here, means diagonal. And inferior
oblique. These are the six muscles that are going to move the eye. you might ask
me how would I know the difference between the lateral rectus and medial
rectus? well, you have to look for the lacrimal gland gland.
It’s not obvious on this picture over here, but if you look at models
there is going to be a little lacrimal gland like this over here. You’ll see it
attached so whatever is on this side, the muscle that is on the side, is going to
be the lateral rectus. And the muscle that is on the opposite side is going to
be the medial rectus. And we will take a look at that in another video. I go over
the models in my lab videos so make sure to take a look at those before you take
your lab practical. Now let’s go over some structures from the anterior view.
okay so lacrimal gland is going to be lateral. These little ducts here are the
excretory ducts, so they basically going to move tears over the eye. Lacrimal gland is
going to produce tears and they’re basically going to move over the eye by
the excretory lacrimal glands. They’re gonna wash over the eyes. So it’s going
to wash over the eyes, going this way, and they’re going to drain right here by the
lacrimal canals. This is a lacrimal canal right here.
And here’s another lacrimal canal. Another term, by the way, to keep in mind
is the lacrimal canaliculi. I’ve also heard them referred to as the lacrimal
canaliculi. As a matter of fact that’s the term I prefer to use. So this is the
superior lacrimal canaliculi. This is the inferior lacrimal canaliculi. And there’s
going to be opening here, on the inner eyelid area. So there’s this little
opening here. This is usually not visible on the models. But it is there! This is
the opening that allows the tear to move into the canaliculi.
Right here! Next the tears are gonna pour into the sac here called the lacrimal
sac. Now keep in mind it is called lacrimal sac on top. When it moves
down, it becomes narrow, this is called the nasolacrimal duct. So this connects
between your nasal cavity. This lacrimal sac becomes narrow and connects to your
nasal cavity. And that’s why when you cry, you get runny nose. I also want
to briefly talk about the commissure, even though it’s not labeled on this video.
commissure is where the eyelids come together. So right here this area. This
little area right here where the upper eyelid and the lower eyelid come
together, this is called the lateral commissure. And
this little area where the eyelids come together, it’s called the medial commissure. This is on the medial side. This is from the lateral side. I want you to be
careful not to mix up the medial commissure with the caruncle. This is a gland-like
structure. Commissure is where the two eyelids meet. Another
structure on the anterior side of the eye is the conjunctiva. This is sort of like a mucous
like membrane. It’s a thin transparent layer that covers your eyes, so it’s like
a sheet. Right here! You can’t really see this in any of the models. None of the model i’ve seen in our labs have this. But, it’s important to know what it is, and
what what it does. So this is basically, like a thin mucous-membrane that
covers the eye. I if this layer gets inflamed or
infected, that’s when you get pink eye! so this part. We could see that it’s a
sheath basically. The part that goes over the inner eyelids, right here, this is
called the palpebral conjunctiva. And again it’s continuous. So it’s gonna move over the eyes When it moves over the eyes, it is called the bullbar conjunctiva. so it’s one sheath
sort of like a mucous membrane that covers your eyes and
folds into the inner eyelids. We’re gonna talk about the layers of the eye. So
we are going to go over the structures one layer at a time. This is
supposed to be outer,by the way! There’s a typo here. We have the outer fibrous
tunic, the middle vascular tunic, and the inner neural tunic. We’re going to start
with the eye with the outer fibrous tunic. Two structure
that make the fibrous tunic are sclera and a cornea. The sclera is basically
that white part of your eye. When you look at your eye, the outer white part,
that’s gonna be the sclera. The purpose of sclera is to maintain the shape of
the eye. And of course it’s very fibrous. It’s a hard tick layer. Cornea is made
out of several layers of squamous epithelium. It is transparent. we’re gonna
see that inside the inner portion of the cornea is going to
contain aqueous fluid. And the cornea doesn’t have any blood vessels.
It’s actually nourished by the aqueous humor, that is inside. The cornea is
basically like a window. It’s a transparent part of your eye, so when you
look at your eyes, that transparent part is gonna be the cornea. It’s important!
There has to be something there to protect the eye; however, it
needs to be transparent to allow light in. If light is not allowed into your
eyes, then vision would not be possible. So let’s look at these structures. So all of this right here! this is the sclera. And this glassy membrane right here, is going
to be the cornea. It is really important to remember these terms, be able to
identify them, and know their function. So the sclera and the cornea together,
because they are continuous, make the fibrous tunic. The middle vascular layer! We
have the choroid, iris, pupil, and lens. This will make the vascular part. So
we are going a layer in. I know it’s not perfect
we’re gonna talk about them more. This is the choroid. So starting out here. This
white layer, this is the sclera! Here’s the cornea, the transparent fibrous
structure. Now moving in, from the sclera, you have the choroid here. This is
going to be vascular and pigmented. Here’s the iris. Right here, basically the colored
part of your eye. Here’s the ciliary body, I’ll talk about it more in a second. And here
is the pupil, this is the opening to the eye. So, this is basically a sagittal cut of the
eye. The choroid is a highly vascular. layer. The main function of the choroid
is to provide blood flow to the eye. The choroid is also going to be pigmented.
It is a pigmented layer and that’s important, because it prevents light from
scattering in the eye. You’ll see in a second that when light enters the eye,
for a vision to become possible, the light has to basically focus on a
particular spot. So we don’t want that light to be bouncing around in the eye,
and that’s why the choroid is pigmented; to prevent the light from scattering. Okay. Again! Let’s take another look. Here
is the choroid over here so right below sclera you have the choroid; this vascular,
pigmented layer. The iris is basically the colored part of the eye. It is going
to be vascular and pigmented. And the main function of the iris is
actually to control the amount of light entering in the eye. The iris is going to
have a muscles. There’s going to be muscles inside the iris: the radial
muscle and the circular muscle. These two muscles are both made out of smooth
muscle. Because remember this is involuntary. So they’re made out of
smooth muscle. Let’s take a look. Here’s the choroid, right here. And here, the colored
part, of the eye is the iris. And the pupil is going to be the opening. We want
to make sure that we also identify this in a sagittal place.
So choroid right here. Here is the iris. and here is the pupil. These are the two
muscles in the iris area. We have the circular muscle, which helps with
constriction of the pupil. And also the radial muscle, this is the radial one,
which will help with dilation of the pupil. So the pupil is the opening of the
eye. It can be dilated or constricted. with radial and circular
muscles. So the pupil basically is the structure that allows light to enter the
eye. The lens is made of layers of crystalline fibers. It is very hard. It looks
like a marble. If you’ve ever dissected a cow eyeball you’ll see that there’s this
marble like structure in there, it’s transparent. and if there is buildup
of calcified compounds, it causes cataract. Ciliary body is basically made of muscles that are going to be on the inner portion of the
eye. Relaxing and constricting of the ciliary body is what helps change the
shape of the lens. And I’ll show you guys suspensory ligaments in just a second. so
let’s see. This is the lens over here. this is going to be the ciliary body
right here. They contain muscles and processes. And they’re going to attach
and directly to the lens by these fibers here called the suspensory ligaments. So
the suspensory ligaments are going to attach the ciliary body to the lens. and
the ciliary body has muscles that are going to relax or constrict to change
the shape of the lens. Let’s look at it on an actual model. This is one of the
important models to remember. This is the lens right here. Now this area, right here, this is going to be these ciliary body.
Now the ciliary body can be divided into two parts. There is a ciliary
muscle. So here in this area could see the muscle. All of this. And there’s also
ciliary processes. The processes are going to be these
extensions. These finger-like extensions are going to be the ciliary
processes. So both the ciliary processes and the
ciliary muscle are part of the ciliary body. Here, these little lines here, are going to be the suspensory ligaments or the ciliary zonules.
They’re going to attach to the lens. And basically this is what allows the
ciliary body to control the shape of the lens. It is either going to make it more
flat or make it bulge; and that’s important because it needs to do that in
order for lights to be focused on the right place in your eyes. Okay! Here’s a
close-up. So I’m going to go over this just one more time. Let’s see if I could pick a
better color. So all of the area over here, this whole area, is
the ciliary body. Right here, see these muscles, these are the ciliary
muscles. So the ciliary muscles belong to the ciliary body. And then these
extensions here, these finger-like extensions, are the
ciliary processes. And right here we have these fiber-like structures. These are
called the suspensory ligaments or the ciliary zonules.
These are going to attach the ciliary body to the lens, and in this way the
ciliary body can change the shape of the lens as needed. So if you’re trying
to focus on an object that is far away, the lens will become more flat to focus
light on the right place. If you’re trying to focus on something that is
nearby, the lens will bulge. This is one of the
important things to remember for your exam. I do want to know howthe shape of the lens changes if you’re trying to focus on something that’s far
away or nearby. okay! I want you guys for a minute or two go ahead and
stop this video, and I label this picture over here. And make sure you’re getting
everything correctly. Oka,y so let’s go ahead and check everything. Number one,
the colored part of your eye is the iris. Number two, is the pupil right here.
Number three, this is gonna be the cornea. Remember the glassy membrane. It was
removed on top. Number four is the sclera, the white part of the eye.
Number five is actually the opening to the pupil. I think that’s what this
picture is supposed to represent here. I think two and five pretty much the same
thing. Number six, this is the choroid, the pigmented layer of the eye. Okay! now
we’re gonna move into the neural tunic. This is the innermost layer of the eye.
The retina is basically going to be this thin, very delicate sheath, that’s
covering the innermost layer of the eye. So here, this layer that you see here,
this is the retina. As we’ve said it’s going to be a very delicate layer. The retina
contains photoreceptor cells; therefore, this is the layer that actually makes
vision possible. So in order to have clear vision, light coming in to
the eye it needs to converge on the macula. The macula is actually an area
inside the eyes on the retina that is filled with photoreceptor cells. There’s
going to be a high concentration of photoreceptor cells on the macula. For
vision to be clear, light coming into the eye needs to converge on that spot. If
light doesn’t converge on the macula, then vision will become blurry. So that’s what
happens when you’re getting blurry vision, is that light coming into your
eye is not converging on the macula. Now this could be due to the shape of your
eyeball or it could be due to flexibility of the lens itself. I want to
make sure I show this to you guys on the model. This is where the macula is, right
here, in this area. So naming the layers. This is the sclera,
this is the choroid, the yellow part this is the retina. And retina is actually two
layers technically, I’m not going to talk about it in detail in this video. But
in this part of the retina there’s going to be a concentration of photoreceptor
cells and this is where light needs to be focused on. It needs to converge on
this spot over here. Again, if it converges
on the right spot, you have normal vision. If it doesn’t, if it’s off for whatever
reason, you’re going to have blurry vision. The reason that the lens
changes shapes, becomes flat or bulges, is to allow focusing of light on the
macula. If the lens cannot become flat enough or bulge enough you will have
blurry vision, and that’s why we have contacts or lenses to basically help
focus the light on optic disc. Optic disc is basically your blind spot. It is
right on the optic nerve. It’s a blind spot because there’s no photoreceptor
cells found in this area. We don’t notice the blind spot because one eye
is kind of like helping the other. You know you have both eyes working together
and the optic nerves do cross. We can’t see them. I don’t have a picture. But
they do cross so that allows full vision. So one kind of compensates for the other. So let’s look Right here, this area this is going
to be the optic disc. Right here, this is the optic nerve right, in front of it you have the optic disc. This is where there is
basically no photoreceptor cells. I want to make sure you guys could see it on
the model. So right here, this is going to be the optic disc. There are, by the way,
fluids that fill the eye. So we’re going to talk about those fluids. The posterior
segment of the eye, the posterior cavity of the eye, it’s filled with a fluid
called the vitreous humor. If you’ve ever dissected a cow eyeball, it
looks like gel. like you’ve filled that posterior cavity of the eye with
gel. And that gel is called the vitreous humor. The function of vitreous humor is
to maintain intra-ocular pressure of the eye. But also one of the important
functions is to make sure that this retina stays pressed against the walls
of the eye. As we saw in one of those previous slides, the retina is going to
be very delicate. You want to have something there keeping it attached to
the walls. Okay, so here’s the lens. What makes the
posterior cavity, is basically everything behind the lens. So the anterior cavity
or segment right here, is in front of the lens. Posterior cavity
or segment is behind the lens. So behind the lens. And in this posterior cavity
you’re going to have vitreous humor. That’s what this fluid here is supposed
to represent. And this is the fluid that basically is going to help keep the
retina attached and pressed against the walls of the eye. So here’s the lens. And
portion here right here, all of this, is going to be filled with the vitreous
humour. But keep in mind this is only behind the lens. Now about aqueous humor, I didn’t really get the chance to talk
about the aqueous humor a lot. I want to go ahead and talk about that.
So aqueous humor is actually gonna be in front of the lens. Right here. So the
posterior segment of the eye or posterior cavity of the eye it’s gonna
be filled with vitreous humor. And anterior cavity, that’s going to be
everything in front of the lens. Let’s see if I could draw that in. So it would be basically from here to
here. So in front of the lens you’re going to have this portion here, it’s
gonna be filled with aqueous humor. The aqueous humor helps make sure
that he is not sclera is nourished, but also it helps maintain the
intraocular pressure of the eye. So if you have been to the eye doctor, you
sit at this machine, and they tell you to look at an image. And this little
machine puffs into your eyes. That machine is for testing your intraocular
pressure. it is important to have the right intraocular pressure in the eye. If
the pressure is too high it could potentially cause blindness. Now let’s
talk about photoreceptor cells. We know that these
cells are contained on the retina. We have the cones and the rods. These
skinny long ones are gonna be rods so, they basically looked like rods. Rods are gonna be more for detecting night vision.
so it’s involved in black and white vision. And the cones right here are for
day vision or colored vision. You have more rods than you have cones. okay the other cells in the retina are ganglion cells. These
form the innermost layer of the retina. And these are the first cells
that are going to be stimulated by light. So right here, this is the innermost part
of the eye. So the light is going to come this way.
these are the ganglion cells right here We also have bipolar cells. They are the
cells that receive and send out signals. They receive signals from ganglion cells
and sent them out to photoreceptor cells. So take a look. Here are the ganglion cells.
They’re gonna receive, they’re going to be the first one stimulated, and
they’re gonna send signals. Here are the bipolar cells, and the bipolar cells are
gonna send them (signals) to the photoreceptor cells. Here you could see a rod. Right
here, The skinny long one. And the ones that
have this cone shape are going to be the cones. Okay let’s
briefly talk about vision again. This has to do with the ability of the lens to focus
light. But also the shape of your eye does influence vision.
Emmetropia is proper vision. Myopia is nearsightedness. And hyperopia is
farsightedness. As you can see, these could be influenced by this shape of
your eyeball. Usually if you start wearing glasses at a young age, it has to
do with the shape of your eye. But if you have normal vision all throughout your
life, and as you age notice that your vision is becoming blurry, that’s usually
due to the flexibility of the lens. So here, you have
myopia, a short eyeball. Normal right here. And hyperopia this is the eyeball. that’s basically longer than it
needs to be. So with myopia, this is near sightedness over here. You could see
this is someone who has like a normal eye shape. But this
person who has myopia probably has an eyeball that is short so the focusing of
light doesn’t happen on the retina, where it needs to be. It focuses (converges) before it hits
the retina. So a person who has myopia, they could see objects that are nearby,
but they have trouble seeing far away objects. farsightedness. This is typically where
the eyeball is longer than it needs to be. So the focus of light goes past the retina. It doesn’t focus it on the retina, it tries to go past it. So people who have
this problem are able to see faraway objects, but they can’t see close objects
very well.

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