Embryology of the Eye (Easy to Understand)

Summary

This 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

• 🌱 The embryological development of the eye begins with the formation of the blastula, which is a result of cell multiplication after fertilization.
• 🌀 The blastula differentiates into three germ layers: the ectoderm, mesoderm, and endoderm, with the eye deriving from the ectoderm.
• 👀 The optic vesicle, a part of the developing eye, forms around day 22 of embryonic development and is connected to the surface ectoderm.
• 🔍 The optic grooves develop and grow to reach the surface ectoderm, leading to the formation of the lens placode and the lens itself.
• 🔁 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.
• 👁 The optic cup differentiates into the inner and outer layers of the retina, with the choroid fissure allowing the entry of the hyaloid artery.
• 👶 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.
• 👁️‍🗨️ The optic nerve is not part of the retina but is where all the nerves of the eye converge to transmit visual information.
• 💎 The mesenchyme, a loose connective tissue, differentiates into various structures of the eye, including the choroid and sclera.
• 🌌 The ciliary process develops and is responsible for the production of aqueous humor, which is crucial for eye function.
• 🔗 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

00:00

👀 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.

05:02

🔍 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.

10:05

🌟 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.

15:06

📢 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.

Keywords

💡Embryological development

Embryological development refers to the process by which an organism grows and forms from a fertilized egg into a mature adult form. In the context of the video, it specifically addresses the development of the eye, detailing the stages and structures that form during embryogenesis. The script outlines how the eye develops from the ectoderm layer of the early embryo.

💡Blastula

A blastula is an early stage in embryonic development characterized by a ball of cells resulting from the multiplication of cells following fertilization. The script mentions the blastula as the starting point of the embryological process, where cells begin to differentiate and form the three germ layers.

💡Germ layers

Germ layers are the three primary tissue layers in an early embryo that give rise to all tissues and organs of the body. The script identifies the ectoderm, mesoderm, and endoderm as the three germ layers, each with specific developmental paths and contributions to the body's structures, with a focus on the ectoderm for eye development.

💡Optic vesicle

The optic vesicle is a structure that develops from the ectoderm and eventually forms the retina and other parts of the eye. The script describes the optic vesicle's formation around day 22 of embryonic development and its critical role in the embryology of the eye.

💡Lens placode

The lens placode is a thickened area of the surface ectoderm that will eventually give rise to the lens of the eye. The script explains how the lens placode forms as a result of the optic grooves contacting the surface ectoderm and triggers the formation of the lens.

💡Optic cup

The optic cup is a two-layered structure that forms from the optic vesicle through a folding process. The script describes the optic cup's development and how it contributes to the formation of the retina and other eye structures.

💡Choroid fissure

The choroid fissure is a temporary space within the developing eye that allows the hyaloid artery to enter and nourish the eye. The script mentions the choroid fissure's role in eye development and its eventual closure to form the pupil.

💡Retina

The retina is the light-sensitive tissue at the back of the eye that plays a crucial role in vision. The script explains the retina's development from the optic cup, highlighting its inner neural layer and outer pigmented layer.

💡Mesenchyme

Mesenchyme is a type of loose connective tissue that can differentiate into various structures. In the script, mesenchyme is described as encasing the developing eye and differentiating into important eye structures such as the choroid and sclera.

💡Ciliary body

The ciliary body is part of the eye involved in the production of aqueous humor and the accommodation of the lens. The script details the development of the ciliary body from mesenchyme and its role in eye function.

💡Hyaloid artery

The hyaloid artery is a temporary blood vessel that supplies the developing lens. The script describes the hyaloid artery's role in providing nourishment to the eye during development and its eventual regression.

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

please shoot me a message on Facebook I

try to reply to them and also I've

launched this patreon page it includes

all of the 4k quality electronically

drawn pictures of my summaries behind me

and you get all these bunch of perks as

well I don't care what tier you join you

can contact me and I'll talk to you and

we can do phone calls or whatever if you

want so yeah check that out it's

patreon.com slash doc terminus with a dr

not a doctor reader now okay but if I

read all of the comments that you leave

below I'll try and reply to most of them

I read every single one though so please

leave a comment let me know what you

think I'd love to hear from you you can

add me on instagram @ - so it's at m1

dot n a SS if you have any other

questions shoot a message you can

literally send me stuff you can do

anything that you want just get in

contact with me I would love to hear

from you all the best

you