Embryology of the Eye (Easy to Understand)
Summary
TLDRThis video offers a simplified exploration of the embryological development of the human eye. Beginning with the formation of the blastula, it follows the differentiation into germ layers, focusing on the ectoderm's role in eye formation. The optic vesicle's transformation into the optic cup, lens placode's development into the lens, and the intricate process of retina formation are detailed. The script also covers the mesenchyme's differentiation into vital eye structures and the development of the ciliary process and aqueous humor, providing a foundational understanding of ocular embryology.
Takeaways
- đ± The embryological development of the eye begins with the formation of the blastula, which is a result of cell multiplication after fertilization.
- đ The blastula differentiates into three germ layers: the ectoderm, mesoderm, and endoderm, with the eye deriving from the ectoderm.
- đ The optic vesicle, a part of the developing eye, forms around day 22 of embryonic development and is connected to the surface ectoderm.
- đ The optic grooves develop and grow to reach the surface ectoderm, leading to the formation of the lens placode and the lens itself.
- đ The optic vesicle folds to form the two-walled optic cup, which will eventually give rise to the optic stalk and the optic cup structures.
- đ The optic cup differentiates into the inner and outer layers of the retina, with the choroid fissure allowing the entry of the hyaloid artery.
- đ¶ By week 6, the lens vesicle pinches off and becomes its own structure, and the retina develops its inner neural layer and outer pigmented layer.
- đïžâđšïž The optic nerve is not part of the retina but is where all the nerves of the eye converge to transmit visual information.
- đ The mesenchyme, a loose connective tissue, differentiates into various structures of the eye, including the choroid and sclera.
- đ The ciliary process develops and is responsible for the production of aqueous humor, which is crucial for eye function.
- đ The development of the eye includes the formation of the anterior and posterior chambers, the iris, and the lens, all of which are essential for vision.
Q & A
What is the blastula and what is its significance in embryological development?
-The blastula is a stage in embryonic development that results from the multiplication of cells following the fertilization of an egg by a sperm. It is significant because it continues to differentiate and eventually implants into the uterine wall, leading to the formation of three germ layers.
What are the three germ layers formed during gastrulation and what will they eventually become?
-The three germ layers are the ectoderm, mesoderm, and endoderm. The ectoderm will become the skin, nervous tissue, and neural crest; the mesoderm will differentiate into muscles, connective tissue, and gonads among other structures; and the endoderm contributes to the epithelium of the gastrointestinal tract and other organs.
What is the role of the ectoderm in eye development?
-The ectoderm plays a crucial role in eye development as it gives rise to the optic vesicle, which is the precursor to the eye. It also contributes to the formation of the lens placode, which eventually becomes the lens of the eye.
At what stage of embryonic development do the optic grooves begin to form?
-The optic grooves begin to form around day 22 of embryonic development.
What happens when the optic grooves reach the surface ectoderm?
-When the optic grooves reach the surface ectoderm, they trigger the thickening of the surface ectoderm to form the lens placode and initiate the formation of the lens.
What is the optic vesicle and how does it contribute to the formation of the eye?
-The optic vesicle is an outgrowth of the forebrain that eventually folds to form the two-layered optic cup. It contributes to the formation of the eye by differentiating into the optic stalk and the optic cup, which further develops into the retina and other structures of the eye.
What is the choroid fissure and what is its purpose during eye development?
-The choroid fissure is an empty space within the developing eye that allows the hyaloid artery to enter and provide nourishment to the developing eye. It eventually closes off, leaving only its tip open to form the pupil.
What are the two layers of the retina and what are their functions?
-The retina has an outer pigmented layer and an inner neural layer. The pigmented layer provides light absorption and structural support, while the neural layer contains the photoreceptor cells (rods and cones) and other neurons that process visual information.
How does the lens of the eye develop?
-The lens develops from the lens placode, which pinches off from the surface ectoderm and then differentiates and thickens to form the lens. The posterior wall fibers of the lens grow anteriorly, filling the lens with fibers to complete its formation.
What is the role of mesenchyme in eye development?
-Mesenchyme is a loose connective tissue that surrounds the developing eye and differentiates into various structures needed for the eye, such as the sclera, choroid, and ciliary body.
What is the function of the ciliary process and how does it relate to the aqueous humor?
-The ciliary process is involved in the production of aqueous humor, which is essential for maintaining the shape of the cornea and providing nutrients to the eye. It is formed from the differentiation of mesenchyme and is connected to the lens via the suspensory ligament.
Outlines
đ Embryological Development of the Eye
This paragraph introduces the embryological development of the human eye, starting from the blastula stage, which is the result of cell multiplication following fertilization. It discusses the formation of the three germ layers: ectoderm, mesoderm, and endoderm, with a focus on the ectoderm as the origin of the eye. The optic vesicle's formation at day 22 is highlighted, along with the optic grooves that eventually become vesicles by day 28, leading to the development of the lens placode and the lens itself. The optic vesicle's transformation into the optic cup and the formation of the optic stalk are also covered, providing a foundational understanding of eye development.
đ Detailed Eye Development and Structure Formation
This section delves deeper into the eye's development, describing the formation of the choroid fissure and its eventual closure to form the pupil. It outlines the differentiation of the optic cup into the optic stalk and optic cup, emphasizing the development of the retina's inner and outer layers. The paragraph also discusses the lens's development from the posterior wall fibers and the retina's neural and pigment layers. Additionally, it covers the encasing of the eye in mesenchyme, which differentiates into various structures, and the formation of the vitreous body from a gelatinous substance. The importance of the Highland vessels and the development of the neural layer with rods and cones as light sensing receptors are also highlighted.
đ Further Development of the Eye's Anterior Segment
The focus shifts to the anterior segment of the eye, detailing the differentiation of mesenchyme into the choroid and sclera, and the formation of the anterior and posterior chambers. The development of the ciliary process, sphincter and dilator pupillae, and ciliary muscles from mesenchymal cells is explained. The paragraph also describes the production of aqueous humor by the ciliary process and its role in lens accommodation. The intricate process of how light interacts with the retina's layers, from rods and cones to bipolar and ganglion cells, forming the optic nerve, is also covered, providing a comprehensive understanding of the eye's light processing capabilities.
đą Conclusion and Engagement Invitation
The final paragraph serves as a conclusion to the video, summarizing the key points of embryological eye development and inviting viewers to engage with the content. It encourages viewers to reach out with questions via social media platforms like Facebook and Instagram, and mentions a Patreon page offering additional resources such as 4K quality illustrations and personalized interactions. The speaker expresses a desire to hear from the audience and promises to read and respond to all comments and messages, fostering a community of learning and discussion around the topic.
Mindmap
Keywords
đĄEmbryological development
đĄBlastula
đĄGerm layers
đĄOptic vesicle
đĄLens placode
đĄOptic cup
đĄChoroid fissure
đĄRetina
đĄMesenchyme
đĄCiliary body
đĄHyaloid artery
Highlights
Introduction to the embryological development of the eye, simplified for beginners.
Explanation of the blastula stage, resulting from the fertilization of an egg by a sperm.
Formation of three germ layers: ectoderm, mesoderm, and endoderm, through gastrulation.
Focus on the ectoderm, the origin of the eye development.
Description of the optic vesicle and its differentiation from the forebrain ectoderm.
Development of the optic grooves and their growth towards the surface ectoderm by day 28.
Formation of the lens placode and the lens from the surface ectoderm.
Folding of the optic vesicle to form the two-walled optic cup.
Development of the choroid fissure and its role in allowing the hyaloid artery to enter.
Formation of the pupil from the tip of the closed choroid fissure.
Differentiation of the inner and outer layers of the retina from the optic cup.
Development of the lens from the posterior wall fibers growing anteriorly.
Formation of the vitreous body from a gelatinous substance.
Differentiation of the mesenchyme into various eye structures including the conjunctival sac and cornea.
Development of the ciliary process, muscles, and the production of aqueous humor.
Explanation of the neural layer of the retina, including rods and cones as light sensing receptors.
Differentiation of the posterior mesenchyme into the choroid and sclera.
Formation of the anterior chamber and the pupillary membrane from anterior mesenchyme.
Involvement of the ectoderm in the development of the sphincter and dilator pupillae muscles.
Offering of high-quality illustrations and additional perks on Patreon for further understanding.
Transcripts
hey guys my name is - and today we're
going to be talking about the
embryological development of the eye and
as usual I've broken it down at the most
simple steps possible so that if you
have no idea what embryology is you will
by the end of this short video and as
usual we're going to begin at the
beginning with the blastula the blastula
is a result of multiplication of a bunch
of cells from when a sperm fertilizes an
egg now this ball of cells continues to
differentiate it goes in from the
uterine tube and it goes into the
uterine canal and it plants into the
uterine wall and a process of
gastrulation will form three germ layers
these germ layers are the ectoderm
mesoderm and endoderm
and you might have seen this pancake
structure before this is an
oversimplification for this where we
have in blue the ectoderm which will
become skin nervous tissue and even lies
the mesoderm in red which has three
paths a paraxial mesoderm which are
muscles or thermite's
the intermediate mesoderm which forms
gonads in kidneys and the lateral plaits
in green we have the endoderm and the
endoderm contributes epithelium to the
GI T among other things but for today's
focus we're only going to be talking
about ectoderm because that's whether
our eyes derive from okay so if you've
seen my previous video on embryology of
the CNS you'll know that the CNS is one
long tube the central nervous system
from ectoderm and it's open at the top
and at the bottom and eventually in a
normal situation this tube has to close
at the top and close at the bottom so
when this occurs at around day 22 that's
when we first start noticing the eye
being developed so around day 22 if we
look at this picture
don't let this scare you if we have this
fetus or embryo that is curled up like
this imagine I'm the embryo and we were
looking at it this way
and we slice it right here at the optic
vesicle and look at it this way this is
what we'll have all right wait a second
looking at this we have an optic
vesical that's where the focus of this
video will be because this has to do
with embryology of the eye we also have
a otic vesicle not to be confused with
the optic vesicle the otic vesicle is a
subject for another video development of
the ear but let's leave that for now and
only focus on the optic vesicle so we
slice this embryo here and looking at it
this way we will have this so again
slice pull and day 22 we have the
forebrain in purple which is still
ectoderm and we have surfaced ectoderm
which is essentially akin to skin let's
just think about it as skin surface
ectoderm so what happens is that at day
22 at around day 22 optic grooves will
start to form so we this is step 1 step
2 step 3 let's keep it simple what
happens the optic grooves continue to
grow until they reach the surface
ectoderm at around day 28 the grooves
will become vesicles and when they
contact the surface ectoderm it sets off
this chain reaction that thickens the
surface ectoderm making it the lens
placode and triggers the formation of
the lens so what happens in the next
stage is that the optic vesicle where it
was a single wall initially will fold
and form two walls at the same time the
lens placode which is surface ectoderm
differentiates thickens and digs in to
the optic vesicle what does this mean
for eye embryology let's have a look
over here over here we have the optic
stalk and the optic cup what is this
from this is from this the optic vesicle
will form the optic cup by folding on
itself forming a two old structure the
lens placode
pinches in and eventually will fall
the lens let's only look at this week
six optic cup for now we will notice
that the optic cup where it was the
optic vesicles has two walls and this is
let's just say if we pull this out and
place it here this is what the optic cup
will look like looking at it this way
through the middle we have this choroid
fissure it's an empty space the purpose
of which is to allow the higher loyd
artery to enter its destination and
reach its destination to continue to
provide sustenance to the eye the to the
developing I eventually the choroid
fissure will close off and fuse and only
leave its tip open and that will form
the pupil all right if we were to slice
this optic cup right through here and
look at it this way and let's pull it
here this is what we'll have we will
have a choroid fissure here with a
highland artery going right through it
we will have an inner layer and an outer
layer in a layer an outer layer of what
inner layer and outer layer of the
retina the outer layer is a pigmented
layer and the inner layer is the neural
layer and we will go into that in a
moment first let's have a look at what
happens in eye development in week 7 so
we have an eye imagine you take my eye
here slice it in half and look at it
this way this is what we have if I was
the week six week seven embryo in blue
we still have ectoderm that's all the
surface ectoderm this is the eyelid we
notice that the lens where we had this
lens placode pinching in digging in into
this optic cup you know pinches off and
becomes its own structure so this one
being week seven let's rewind back to
week six focusing here this view is
looking at it like this if I was to take
this optic cut cut and slice it this way
so let's cut this optic cup that way
this way we will have this around week
six we notice surface ectoderm and the
pinched off or dug in lens vesicle the
lens vesicle has its circuits its blood
supply sustenance from the hi Lloyd
artery we notice in this view that we
have an intro retinal space and this is
only a temporary space that lies between
the inner and outer layer so between the
two layers of the retina the inner and
outer layer okay so let's go
fast-forward back to week seven we have
here the lens and how the lens develops
is that from the posterior wall fibers
continue to grow anteriorly towards the
front until it's filled with fiber
essentially breaking it down simply it
gets filled and then the lens will be
formed what else do we have here we have
the retina which has the inner layer the
neural layer and the pigment layer on
the outside the optic nerve is on the
furthermost
inside of the of the retina it's not
part of the retina but the when we go
through this we will notice how all of
the nerves of the whole eye go through
the optic nerve over here and if we
focus right on this one from here we
will notice that this whole eye is
encased in this mesenchyme where it's
white everywhere that I haven't filled
its mesenchyme
now what missing chyme is it's a loose
connective tissue that can be come
anything so it can differentiate into
whatever the eye needs and what does
that mean so this eye is encased in
tissues cells all around it which will
develop into the various important
structures that we will see here so
again this is a slice looking at it this
way
we have the conjunctival sack with
further development of the surface
the cornea in the front which is also
continuous with the sclera we will
notice that now we have a vitreous body
and how that develops is that there is a
gelatinous substance that infiltrates
the eye into this intricate interstitial
network network filling it up and
becoming the vitreous body the Highland
vessels will eventually degenerate
leaving behind a Highland canal in
orange here we have the neural layer
this is the neural layer otherwise known
as pars
optica retina at the most posterior
aspect of the neural layer we have the
rods and cones these are your light
sensing receptors so the light enters
this way and the nerves go that way so
when the light comes in through this way
it activates the rods and cones and then
the electrical stimulus is sent back
down so we have the first layer which is
the rods and cones the second one which
is the outer nuclear layer so that is
the nucleus of the rods and cones and
then there is the inner nuclear layer
with the bipolar cells and then the
final layer is that ganglion cells which
have all of their nerve fibers going
from the inner part of this eye where
it's orange going to the optic nerve so
the combination of all of these ganglion
cell fibers will eventually form the
optic nerve okay let's focus over here
again let's talk about the Mezen kind
there is both a posterior mesenchyme so
the white bits like the loose tissue and
a anterior mesenchyme the posterior
mesenchyme has an inner layer which is
continuous with the pia mater and that
is the choroid vessels so the choroid
vessels
and it has an outer layer which is
continuous with the dura mater and that
will be the sclera so if we were
actually going to make so this is the
inner layer the vascular the coid layer
would be this one in red and then the
outer layer would be the sclera here so
for the posterior part of the Mezen kind
that's what it differentiates into
however for the anterior part the this
part of the eye the loose connective
tissue that it was blank here will
differentiate into other really
important structures so one of them
being the anterior chamber and how it
was packed full of cells over here the
anterior chamber is formed when these
cells are hollowed out forming a chamber
so this chamber sits in front of the
lens and also more mesenchyme
differentiates which will become the
e-reader pupillary membrane which sits
in front right here so it has both
anterior and posterior chambers the
aqueous humor is produced by the ciliary
process now let's talk about the ciliary
process ciliary body just over here
let's zoom in and look over here this is
the development of the ciliary process
the sphincters and the ciliary muscles
initially we have in our orange here
this neuronal layer and then we have
this layer on top and mesenchyme
surrounding it the mesenchyme like we
said the loose connective tissue the
undifferentiated cells will
differentiate into a sphincter pupil the
dilated pupil a-- and the ciliary
muscles the ciliary process is what
creates the aqueous humor so the aqueous
humor so if we're just looking over here
coming back up we notice that the
ciliary Buc process is connected
the lens with the suspensory ligament
and this is what controls contraction of
the lens which will adapt to certain
lights among other things
notice again let's just go over what we
just spoke about let's take this here
zoom in we have the ciliary process here
which is shown by the folding there is
the pigment layer and the it the which
is the outer layer of the retina and the
inner layer of the retina which will
become here on this side in the most
anterior aspect the ciliary process with
aqueous humor is formed okay
and as we grow we differentiate into the
sphincter pupil a-- and the dilator
pupil a-- and these are from ectoderm
from the mesenchymal intiated cells will
produce this type of tissue including
the ciliary muscles thanks for watching
my video I'm gonna leave it it there
there's a lot of high yield points but
it's clearly not enough for a high level
understanding of embryology of the eye
this is just so that you get a great
introduction to embryology so that you
understand all of your lectures and your
textbooks if you have any questions
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you
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