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