Dr.Lhacha Wangdi, 1st year resident (Ophthalmology) UMSB,JDWNRH, 2014

Objectives

1. To understand the concept of origin and developmental processes of human eye

2. To know the pathogenesis of congenital anomalies of eye that may occur as a result of defective embryogenesis

Presentation lay outFirst session –

1. Development of primordial structures- general embryology

2. Embryogenesis of anterior segment of eye3. Congenital anomalies

Second session-

1. Embryogenesis of posterior segment of eye2. Congenital anomalies

Introduction The eyeball and its related structures are derived from

following primordia ;

1. Optic vesicle 2. lens placode 3. Mesoderm surrounding the optic vesicles

Derived from germ layers Ectoderm Mesoderm Endoderm

Embryology and regularity factors In embryology various endogenic regulatory factors controls

cellular differentiation, proliferation, cell migration and inductive interaction for the specific organ development.

Three groups of regularity factors are identified

1.Growth factors 2.Homeobox genes/ master genes

3.Neural crest cells

fibroblast growth factors(FGF)

transforming growth factors Bs

insulin like growth factors (IGF-I)

control subordinate genes in regulation of patterns

of anatomical development(morphogenesis) eg. PAX6-marks the

location of lens, HOX ( HOX8.1 –corneal

epethelium,HOX7.1-ciliarybody)

Transient population of

pluripotent cells, originated from neuroectoderm

which latter transforms into

mesenchymal cell

General Embryology 1. To understand the formation of germ layers

2. To know about the origin and formation of ocular primordia

General embryology

After fertilization of ovum it undergoes series of cellular division/cleavage(1st cell division-meiosos followed by mitotic division)

Forms morula ( 16 cell) stage by 4th day

Blastocyst (single cavity cell mass without zona pellucida) by 5th day

Implantation of blastocyst occurs by 6th day after fertilazation

EARLY EMBRYONIC STAGES

24 hours Day 2

Blastocyst-5th day-ready for implantation

Morula-4th day

meiosis mitosis

1st week embryology

Implantation of Blastocyst by 6th day

Fertilization –occurs 24 hours after ovulation at the

ampula of fallopian tube

Bilaminar embryonic disc-8th day

Formation of double layer cell from embryoblast( Inner cell mass)

With the formation of blastocyst , cells are divided into inner cell mass call embryoblast and out cell mass the tropoblast

By 8th day inner cell mass (embryoblast) is divided into two layer ; epiblast and hypoblast- the Bilaminar disc

bilaminar disc- 8th day

HYPOBLAST

GASTRULATION-early 3rd week Process of formation of three germinal

layers

Begins with invagination of epiblastic cells to form primitive streak by 16th day

Primitive streak is a central narrow groove on the surface of epiblast formed by the invagination of epiblastic cells

Cells from epiblast starts migrating towards the primitive streak

GASTRULATION-beginning 3rd week

Primitive streak

GASTRULATION-early 3rd week...

Cells of primitive streak invaginates the hypoblast and forms endoderm,

Cells between epiblast and endoderm forms mesoderm

Cell remaining in epiblast becomes ectoderm

Gastruation-eaqrly 3rd week

Bilaminar embryonic disc with Migrating epiblastic cells

Gartrula with three germ layers

Trilaminar disc- germ layer and ocular derivatives

NSR,RPE, pigmented ciliary epithelium,nonpigmented

ciliary epithelium,pigmented iris epithelium,smooth muscle

of iris,optic nerve,vitreous,corneal stroma

and endothelium,sclera,trabecular

meshwork,ciliary muscle,melanocytes,meningeal

sheath,ciliary ganglion,connective tissue of orbit,lens,lacrimal gland and drainage system,conjunctival

epithelium,connective tissue of orbit, muscle layer and

connective tissue sheaths of all ocular and blood vessels,

cartilage, choroidal stroma,schwann cells

Fibers of extraocular muscle, endothelial lining of all orbit and ocular blood vessels, temporal

portion of sclera, vitreous

Neuraltion and neural tube formation-22th day

Neural tube is an important primitive structure from which ocular primordia-the optic vesicle, the progenitor mesenchymal cell and neural tissue develops

Begins by proliferation of the surface ectodermal cells to forms neural crest cells

The crest cell moves medially to form neural groove. Elevation of two side of neuroectoderm forms neural fold and ultimately it fuses to become neural tube

Neuraltion and neural tube formation-22th day Neural

crest cell

Gartrula Neural grove

Neuraltion and neural tube formation-22th day1.Neural

plate

2.Neural grove

3.Neural tube Neural crest cell-

proginater cells for mesenchymal cells

Surface ectoderm

Formation of eye primordia-3rd week

Primitive eye starts in 3rd week of gestation when anterior portion of neural tube is folding

As the neural tube is folding 3 dilatation appears at the anterior portion of neural tube-forebrain, midbrain and hindbrain

Primitive eye originates as Optic pit on either side of midline in venterolateral region of primitive forebrain

eye primordia-3rd week

The optic pit/ocular primordia

forebrain

Formation of optic and lens vesicle Begins with the proliferation of

neuroectodermal cell of neural tube of forebrain.

Neural tube of forebrain grows laterally and forms 2 globular structure at either side called- primary optic vesicle

With the formation of optic vesicle it induce surface ectodermal cells to proliferate

Surface ectoderm in contact with Optic vesicle becomes lens plate/placode.

Ocular primordia

Cross section of neural tube

ectoderm

mesoderm

endoderm

Lateral outgrowth of neuroectoderm forms optic

vesicle

Neural tube

Lens plate

By end of 3rd week gestation Three primordial structure are

formed:

1. Lens placode

2. Optic vesicle

3. Mesoderm surrounding the optic vesicles

Concept of congenital anomalies Developmental anomalies Occurs due to

disturbance in embryonic events by various factors in 1st -3rd months of pregnancy, ocular structures are most at risk in the period of organogenesis from 18 – 60 days

1. Intrinsic factors 2.extrinsic factors(teratogen)Altered, defective or imperfective genes

Impaired cellular induction/proliferation

Defective cell migration

Inadequate differentiation & cell death

Infection (Rubella, syphilis, cytomegalovirus, herpes simplex virus

radiation

Maternal diseases(eg.Diabetes)

Drugs/toxins-alcohol,thalidomide,antiseizure,retinoic acid ets

Anterior segments-development

Development of eye structure are mostly induced with the formation of optic vesicle and lens placode .

Formation of lens Derived from surface

ectoderm With the formation of optic

vesicle the surface ectoderm in contact with optic vesicle thicken and forms lens plate/lens placode-27th day

Eventually the lens plate invaginates and separates from surface ectoderm and forms lens vesicle -33rd day

Lens vesicle Lens vesicle has anterior wall with cuboidal

epithelial cell and posterior columnar epithelial cells

Synthesize type 1v collagen & gylcosaminoglycans to

form lens capsule, maintains homeostatic

fuction of cell and serves as progenitors for 2ndary lens

fibers

Forms primary lens fiber- embryonic nucleus

Cells of posterior wall lengthens and form elongated fiber that projects into the lumen and specific lens protein(crystalline) are synthesized

Posterior cell contributes for most of the growth of lens for first 2 month- embryonic nucleus.

Posterior epithelial cell

Primary lens fiber- embryonic nucleus

From 2nd month the anterior progenitor cells proliferates and produce 2ndary lens fibers also called fetal nucleus

In 3rd month inner most fibere mature with increase in cytoplasmic fibrillar materials and the cell nuclei and organelles decreases

Secondary fibers are displaced inward between the capsule and embryonic nucleus and meets on vertical planes to form Y shape suture anteriorly and inverted Y posteriorly

Lens At birth it weighs 90 mg (adult-255mg) with

thickness of 3.5mm ( adult-5mm) Lens fiber are formed throughout the human life

developing into different layers of lens fibers

Lens anomalies

!1.Congenital aphakia-absence of lens at birthprimary aphakia Secondary aphakia(more common)

Occurs due to failure of surface ectoderm to

proliferate

Occurs due to spontaneous absorption of developing lens

Associated with Alports syndrome-X-linked disease characterized by defective genes for production of

type 1V collagen

Lens anomalies

Most are Idiopathic Herediatery-AD(most common),AR,X linked Genetic and metabolic disorders-Down

syndrome, marfans syndrome,galactosaemia etc.

Maternal infection and toxicity- rubella, CMV,varicella,radiation etc

4.Congenital cataract-etiology

3.Lens coloboma- flattening/notching of lens due to

absence of zonular fibers, associated with defect in iris, optic nerve/ retina as a result of abnormal closure of embryonic fissure

Development of cornea Development of cornea is

induced by lens and optic vesicle formation

With the separation lens vesicle the surface ectodermal cell proliferates to form epithelium of cornea

Basal lamina of epithelium cells secrets collegen fibers and gycosaminoglycans to form primary stroma

Corneal epithelium

Lens vesicle

Surface ectoderm

Corneal embryogenesis-5th week By early 5th week gestation there

are 3 waves of mesenchymal cells migrating towards the corneal epithelium.

1st mesenchymal wave forms the corneal endothelium.

Desment’s membrane is derived from the basal lamina of endothelium

Ctn… 3rd mesenchymal wave

migrates between epithelium and endothelium and forms keratocytes

The keratocytes synthesis type 1 collagen fibers and proteoglycans which are organized as lamellae to form stroma of cornea

Corneal derivatives

Diameter at birth –( 9.5-10.5)mm reaches adult size 12 mm by 2 years

Derived from surface ectoderm

Derived from mesenchyme(neural

crest cell)

Derived from mesenchyme(neural

crest cell)

Developmental anomalies-cornea

Due to fetal arrest of corneal growth in 5th month or related to the overgrowth of anterior tips of optic cup which leaves less space for cornea to develop

Inherits as autosomal dominant/recessive trait

Due to failure of optic cup to grow leaving large space for cornea to fill

Associated with abnormal collagen production-Marfan syndrome

Inherits as X-linked recessive pattern

1.Microcornea:

Corneal diameter is less than 9mm in newborn or less than 10mm in adult

2.MegalocorneaCorneal diameter more tha 12mm at birth or more

than 13mm after 2 years

Disorder of 2nd wave mesenchymal migration

90% bilateral

Sporadic but both autosomal dominant and recessive inheritance pattern are reported

Endothelial dystrophy-Primary dysfunction of 1st mesenchymal wave/corneal endothelial cell degeneration. Autosomal recessive>dominant.

Stromal dystrophy –dysfunction of corneal stroma causing corneal opacity.

3.Sclerocornea-Sclera like clouding of cornea with ill-defined limbus.

Difficult to differentiate cornea and sclera

4.Corneal DystrophyDiffuse,ill defined flaky/featheary/blue-gray ground

glass opacification of cornea. Cornea is clearer peripherally

Corneal thinning and bulging due stromal and epithelium thinning, fragmentation of Bowman’s layer and folds or break in Descement’s membrane

Etiology unknown, usually multifactorial associated with Down syndrome, mental retardation and atopic diseases

5.keratoconus-Condition in which central cornea assume a conical shape

THANK YOUEnd of 1st session

References 1.American Academy of Ophthalmology (BCSC-section 2, 2012-2013)2.Langmans medical embryology3.Oxford Text Book of ophthalmology (volume 11-section2.16.1-Embryology of eye

and orbit by Garry N.Shuttleworth)4.Internet resources

Embryology of eyeSession 11

Recap General embryology

Development of embryoblast from inner cell mass of blastocyst which

differentiate into bilaminar disc (epiblast and hypoblast)

Formation of three germ layers and neuralation

Ocular origin and primordia

Derivatives of ocular structure (ectoderm and mesoderm)

Formation of optic vesicle, lens placode/plate

Embryogenesis of lens and cornea

Developmental anomalies of cornea and lens

Session 11-Outline

Origin and developmental processes of anterior and posterior segment of eye

Developmental anomalies

Anterior chamber and angle formation

By beginning of 3rd week there are three successive in growth of mezenchymal cell surrounding the optic cup

1st wave of mezenchye forms corneal endothelium, 2nd waves forms pupillary membrane and 3rd wave forms the keratocytes of cornea

Anterior chamber is first recognized as split like space between developing corneal endothelium and iris epithelium as a result of selective mezenchymal cell atrophy/cleavage

Anterior chamber and angle formation

1stMesenchymal wave form corneal

endothelium

2nd wave forms pupillary membrane

3rd wave forms keratocytes of

cornea

Primitive anterior

chamber-slitlike space

By 15th week of gestation corneal endothelial cells extend into the angle recess and meets with iris epithelium

By 3rd month angle recess deepens and forms iridocorneal angle

In 7th week – the angle of the anterior chamber is occupied by the mesenchymal cells of neural crest origin- forms trabecular meshwork

Schlemm canal develops from small plexus of venous canaliculi of endodermal origin and forms uveoscleral outflow/tract.

Trabecular meshwork

The anterior chamber angle continuous to recede until 6-12 month after birth when it become adult type appearance.

Anterior chamber depth is 2.3-2.7 mm at birth (adult-3mm) In the final week gestation the

trabecular meshwork undergoes fenestration and communicates with anterior chamber

Congenital glaucoma may occur as a result of defect in terminal differentiation of trabecular tissue leading to excessive formation of meshwork collegen preventing formation of iridocorneal angle

Ciliary body and iris- outline By 3rd week gestation there is

extension of 2 layers of neuroectoderm from the edge of optic cup

Its has outer pigmented epithelium(PE) and inner non pigmented epithelium(NPE)

Distal part of advancing neuroectoderm becomes an iris

Proximal part of neuroectoderm extension becomes the ciliary body

Ciliary body-ctn..

Cellular proliferation of proximal 2 layers of neuroectoderm forms longitudinal indentation of outer pigmented epithelium

By 12 weeks Inner non pigmented layer forms radial fold(75) and become ciliary processes

At 10 week mezenchymal cells get condensed at its anterior surface to form the stroma of ciliary body

At 12 weeks there is Myofillament proliferation of mezenchyme and forms smooth muscles of ciliary body by 5th month

Ciliary muscle continues to develop for at least 1year after birth.

Ciliary body By 4th month ciliary body is

functional and secrets aqueous humour which fills up anterior and posterior chamber

Ciliary epithelium synthesis collagen fibers which becomes suspensory ligament/zonules of lens

Development of iris-3rd month Developed from 2 layers;

1. Mesenchyme-anterior stroma

2.Neuroectoderm of optic cup–

- iris pigment epithelium

-sphinchte and dilater muscles

Iris begins to develop by condensation of 2nd wave mezenchymal to form Pupillary membrane

Formation of pupillary membrane-early 3rd month Pupillary membrane is formed by Condensation of 2nd wave

mesenchymal cell forms pupilary membrane

Lens vesicle

Optic cup

Condensation of mesenchymal cells

corneaPupillarey membrane

Iris epithelium-end of 3rd month

2 layers of neuroectoderm from the edge of optic cup extend to the posterior surface of pupillary membrane.

Three structures(PE,NPE and pupillary membrane) ultimately fuses to become an iris

Pupillary membrane

Iris- 3rd month

At 3rd month Cells of anterior epithelium layer differentiates into myofobrills and forms sphincter and dilator muscles of an iris

Pupillary Membrane(PM)-cells of PM differentiates into fibroblast like cell and secrets collegen fibrills & extracelluler matrix which is incorporated with PE to form the anterior stroma of an iris

pigmentation of posterior epithelial cell occurs begins at the pupillary margin at midterm , by 7th month iris is fully pigmented

Iris and pupil-8th month gestation

Pupillary membrane begins to degenerate at about 8th months of gestation

Opening in the central part of iris forms the pupil

Iris stroma and dilator muscle is still immature at birth-pupil appears miotic at birth

Iris anomalies

Can be Associated with syndromic presentation like trisomy 13, klinefelter,turner, CHARGE association(ocular coloboma,heart defects, choanal atresia, mental retardation, genitourinary and ear anomalies)

1.Hypoplasia/absence of an irisInadequate inductive interactive between optic cup, surface ectoderm and neural crest cell due to Defect in PAX6 genes Occurs as sporadic or autosomal dominant

2.Persistant pupillary membraneMost common congenital iris anomaliesFailure to atrophy pupillary membrane

3.Iris ColobomaFailure of embryonic fissure to close in 5th week gestationPupil appears like inverted tear drop usually at the inferonasal quadrantCan be associated wit coloboma of choroid, retina, ciliary body and optic nerve

Iris anomalies…

7.Conginatal mydriasis

Mlafoamation of iris sphincter muscle

4.polycoria -Accessory iris openingAssociated with Axenfeld-Reiger Syndrome ( autosomal dominant disorder) due to mutation of PAX and FOXC1 genePresent with ,malformation of face, teeth, skeletal system

5.Corectopia-Displacement of pupilAssociated with sector iris hypoplasia or colobomatous lession or lens subluxation(ectopia lentis et pupillae)

6.microcoria-congenital miosisOccurs due to malformation of dilator pupillae muscleCan be associated with microcornea,lens subluxation, iris atrophy and glaucoma

Posterior chamber

Develops as a slit in the mesenchyme posterior to the developing iris and anterior to the developing lens

Anterior and posterior communicates when the pupillary membrane disappears and the pupil is formed

Aqueous humor fills these two chamber

Embryogenesis-Posterior segment

Retina Optic nerve Vitreous Choroid Sclera Vascular system

Retina-originates from ectoderm

Neurosensory retina- originates from the inner layer

of neuroectodermal cell of optic cup

Retinal pigment epithelium- Originates from the outer

neuroectodermal cell of an optic cup

Neurosensory layer-1st month(3-4 rows of cells) Anterior 1/5th – forms the posterior

surface of developing ciliary and iris Posterior 4/5th forms the primordial

sensory retina Mitotic cellular differentiation at

primordial retina forms two 2 distinct layers by 7th week

Outer 2/3rd –primitive nuclear zone has rows of nucleated cells which will forms neural cells

Inner 1/3rd- marginal zone has cells devoid of nucleus which will form nerve fiber layers)

Neurosensory(NSR) retina

NSR begins to develop from outer primitive nuclear zone(PNZ)

Cellular proliferation of PNZ forms nuclear and glial cells which are organized as 2 distinctive zones

1. Outer neuroblastic layer(forms photoreceptors)

2. Inner neuroblastic layer(Ganglion cell layers)

3. Two neuroblastic layer are seperated by transient nerve fiber layer of Chievitz which become inner plexiform layer by 9th week gestation

Primitive nerve fiber

NSR formation…ctn… Differentiation of outer neuroblastic layers

occurs(ONL)by 5th week and form photoreceptors(rods and cones)

Cellular differentiation of ONL also forms bipolar, amacrine, horizontal cells and form inner nucleated layers of retina

Ganglion cell appears in inner neuroblastic layers and form ganglion cell layer

Axons from ganglion cell develops at 6th week and form primitive nerve fiber layers

Retina-cells and synapses formation

Optic cup

Primitive nuclear zoneInner marginal

zone forms nerve fiber layers

Inner neuroblastic

layer

Outer neuroblastic

layer

Primitive neurosensory retina

Cellular proliferation and melanogenesis of outer wall of optic cup begins by 6th week and forms retinal pigment epithelium

By 15 week gestation all cells types , synapses and intercellular junction of neurosensory retina are formed

Fovea is formed by thinning of ganglion and inner nucleated layer by 24 weeks

Retina by 5th week Retinal pigment epithelium

developed from outer layer of an optic cup

Outer segment-photoreceptors

Outer nucleated layers retina

Outer plexiform layers

Inner nucleated layers

Inner plexifor layers

Ganglion layer Nerve fiber layer

Derived from outer

neuroblastic layer

Derived from inner

neuroblastic layer

Optic nerve Develops from optic

stalk(connection between optic vesicle and forebrain)

Initially optic stalk has two layers

1. Inner neuroectodermal cells layer

2. Outer undifferentiated neural crest cells layer

Optic nerve formationLate in 6th week, cells of inner layer of optic nerve degenerates and become vacuolated

Nerve fibers (axons) from the ganglion cells migrates through the vacuolated space of optic stalk

By 33 weeks it establishes an adult type optic nerve of 1.1 million of axons

Few cells of inner layer differentiated into glial cell which forms lamina cribosa by 8th week.

Outer neural crest cells differentiates into (1)pia, (2)arachnoid and (3)dura matter which form optic nerve sheath by 4th month

Optic nerve

Ganglion cell layer

Axons from ganglion cells

Optic disc

Optic nerve

Optic anomalies 1.Morning glory disc anomalyAppears as funnel shaped excavation of the posterior fundus that incorporates the disc.Occurs due to abnormal closure of embryonic fissure

2.Coloboma of optic nerve.May occurs as a part of chorioretinal coloboma or solitary abnormalityDue to failure of embryonic fissure to closeCan be associated with systemic abnormalities-CHARGE association

3.

Formation of vitreous Develops between lens and optic cup

Mostly derived from mesoderm with minimal contribution from ectoderm

Formation of vitreous occurs in three stages ;

❶ Primary vitreous ❷Secondary vitreous ❸Tertiary vitreous

Primary vitreous-1st month of gestation

Network of delicate cytoplasmic process which occupy the space between lens vesicle and inner layer of optic cup

It is composed of fibrils (ectoderm) and mesenchymal cells(mesoderm) which constitutes primary vitreous

Supplied by hyaloid vessels and its branches

Secondary vitreous- 2nd month of gestation

By 2nd month the hyaloid system regresses and primary vitreous cell differentiates into hyalocytes which synthesis type 11 collagen and hyaluronic acid which constitutes secondary vitreous

2nd vitreous is avascular gel like substances occupying the space between primary vitreous and retina

By 5th-6th month primary vitreous and Hyaloid vessels undergoes atrophy.

Atrophied hyaloid vessels become hyaloid cannal which remain throughout the life as Cloquet canal

Primary vitreous

Tertiary vitreous-3rd month

It is Formation of zonular fiber between the ciliary body and lens capsule

Collagen fibrils synthesized by ciliary epithelium becomes more condensed and extends to the lens equator and become zonular fiber of lens which constitutes the tertiary vitreous

Persistent hyperplastic primary vitreous(PHPV)

Presents as leukocoria-white pupillary reflex

Its occurs due to failure of primary vitreous and hyaloid vessels to regress

None hereditary and not associated with systemic defects.

Choroid Vascular endothelium and the haemopoietic cells of

choroid are derived from endoderm Choroidal stroma ( vascular pericytes, smooth muscles,

melanocytes and collagenous components) of choroid are derived from ectoderm.

Choroidal development is associated with the condensation of neural crest cells around the optic cup

Choroid..cntn Differentiation of neural crest

cells form choroidal stroma by the end of 3rd month gestation

Endothelium line blood vessels appears in the choroid stroma and forms choriocapillary

By 4the week Choriocapillary begins to differentiate and by 2nd month it anastomosis with short ciliary artery

By 8th month final arterial circulation of choroid is established after anastomosis with vessels of ciliary body and iris

Sclera Sclera is mostly ectodermal (neural crest) in origin,

however posterior region are mesoderm in origin

Sclera begins to develop by condensation of mesenchymal cells around the anterior rim of optic cup

Mesenchymal cells proliferates and deposits glycosaminoglycans, collagen and elastin fibrils and forms stroma of sclera

By 5th month sclera is relatively well formed

Vascular system of eye- overview

Arterial wall has three layers;

1. Tunica adventitia(connective tissue)

2. Tunica media(smooth muscle layer)

3. Tunica intima( endothelium)

Tunica adventitia and tunica media of ocular vessels are derived from neural crest cells(ectoderm)

Tunica intima is derived from endoderm

Primitive orbital vessels During early embryonic life

untill 8th month, the developing ocular structure is nourished by three transient vessels originating from internal carotid artery;

A. Ventral ophthalmic artery

B. Dorsal ophthalmic artery

F. Stapedial artery

Ventral artery later atrophy and only a portion remain as long posterior nasal ciliary artery

Dorsal ophthalmic artery become definitive ophthalmic artery Stapedial artery becomes Middle meningeal artery

Internal carotid artery

Primitive ocular vesselsEmbryonic intraocular vasculature system has two components;1.Anterior system- supplies anterior segment formed in iris and pupillary membrane formed by the branches of ophthalmil artery- anterior ciliary artery and posterior long ciliary artery

2.Posterior system- supplies posterior segment formed within the vitreous formed by hyaloid vascular system

Anterior artery system Anterior artery system is formed by

posterior long,short ciliary artery and anterior ciliary artery which are the branches of dorsal opthalmic artery

Anastomosis of ciliary arteries forms major arterial circle at the root of iris

Vascular twigs from major arterial cicle and annular vessels forms the pupialiary arcade

With the disappearance of pupillary membrane pupilliary arcade remain peripherally as minor artery circle which supply iris

Posterior ciliary artery

Anterior ciliary artery

Posterior arterial system

Hyaloid artery nourishes the developing eye globe until the 8th month of gestation

Hyaloid artery is the branch of primitive dorsal ophthalmic artery

Later the Hyaloid artery regresses and become central retinal artery

Atrophied ventral artery

Dorsal artery

Hyaloid system…. As the optic vesicle develops there

is incomplete folds in its inferior portion of cup and stalk called embryonic fissure

Embryonic fissure allows hyaloid system to be incorporated within the eye.

In 3rd week Hyaloid artery enters the embryonic fissure of optic stalk.

With the fusion of fissure the hyaloid system are enclosed within the eye

Clinical application

Failure to close embryonic fissure causes colobomatous deformaties of an iris, choroid, retina and optic nerve

Hyaloid system

Branches of the hyaloid artery supplies developing lens, vitreous, optic nerve

Anastomosis of branches of hyaloid artery forms 3 arterial arcades called Tunica vasculosa Lentis

1.Anterior vascular capsule

2.Capsulopupialary portion

3.Posterior vascular capsule

Valsa hyaloida propria(small capillary branches)

Hyaloid artery

Retinal circulation By 4th month the hyaloid artery bud of to from

central retinal artery Hyaloid artery system atrophy and regresses in

3rd trimester Retinal artery vascularizes the retinal Nasal retina completes vascularization prior to

temporal retina By 8th month all retinal part are vascularized

except for portion of peripherals temporal retina which completes 3 months after birth

Retinal circulation

Atrophied hyaloid system

Retinal vessels buds from hyaloid artery and vascularizes retina

Vascularization reaches nasal ora serrata by 8th month and temporal ora serrata by 2 month after birth

Retinopathy of prematurity

Ischemia triggers abnormal vessel formation called neovascularization-retinopathy of prematurity

Premature baby has incomplete vascularization of retina

Hyperoxia(supplementary oxygenation) causes vasoconstriction

Vasoconstriction causes ischemia in the incompletely developed retinal periphery

Summary-Derivatives Ocular structures Derivatives

Cornea

Ectoderm

Ectoderm

Ectoderm and neural crest cells

Vitreous

Ectoderm Ciliary body

Neural crest cell(ectoderm)Trabecular meshwork

Lens

Iris

Choroid

ectodermRetina

Ectoderm and mesoderm

ectodermOptic nerve

Ectoderm & mesodermSclera

Ectoderm

Mesoderm & ectoderm Ocular vessels

Human eye at birth and after birth Eye grows rapidly during first 2 years of life

until puberty Most young children are hyperopic of 3.0 D

because of less axial length of eye( at birth 17mm, adult 24mm)

Corneal diameter is 9.5-10.5 at birth and 12 mm in adults

Radius of corneal curvature is 6.6-7.4 mm at birth and 7.4-8.4 in adults

…………continue

Newborn has miotic pupil because dilator pipillae muscle is not well form at birth

Visual development Pupillary light reflux-present after 31 week of gestationBlink reflex to light- several days after birth6 weeks-maintain eye contact and react with facial expression2-3months –preferential to bright objects

References 1. American Academy of Ophthalmology (BCSC-section 2-fundamentas and principles

of ophthalmology BCSC-section6-pediatric ophthalmology)2.Langmans medical embryology3.Oxford Text Book of ophthalmology4.Internet resources