Embryo Flashcards
Arrange the following structures in order of formation of the eye:
- optic pits
- optic cups
- embryonic plate
- optic vesicles
- neural plate
embryonic plate–> neural plate–> optic pits–> optic vesicles –> optic cups
What are the 3 layers that make up the Embryonic Plate?
- Ectoderm
- Mesoderm
- Endoderm
Which layer of the embryonic plate forms the eye and brain?
Ectoderm
What are the 3 layers that make up ectoderm?
- Neural ectoderm
- Surface ectoderm
- Neural crest
What is the blue layer on the figure?
Ectoderm
What is the yellow layer on the figure?
Mesoderm
What is the red layer on the figure?
Ectoderm
What is the central green structure prior to folding of the embryonic plate?
Notochord
What is the analogous structure to the notochord after folding?
Neural Tube
What is the name of the layer of ectoderm indicated?
Neural Plate
Which ectodermal cells migraine into the pockets shown?
Neural crest cells
What does the endoderm fold to form?
Gastrointestinal Tube
The optic pit forms at which day of gestation?
Day 23
What is the optic vesicle?
anterolateral outpouching of primitive brain stem
When does the optic vesicle form the globe?
evaginates on day 25 and becomes the globe
On which day does the optic vesicle induce the lens placode?
Day 25
Name some of the possible disorders that can arise from abnormalities in envagination of the optic vescile.
- anophthalmia
- cyclopia (synophthalmia)
- congenital cystic eye
- congenital nonattachment of the retina
Name 4 disorders that are associated with synopthalmia
Apical forebrain lesions such as synophthalmia are associated with arrhinencephaly, proboscis, ethmocephaly, trisomy 13
How does the optic cup develop?
develops embryologically as an anterolateral evagination of the forebrain
What does the inner layer of the optic cup become?
Inner layer becomes the retina
What does the outer layer of the optic cup become? Outer layer becomes the retinal pigment epithelium
Outer layer becomes the retinal pigment epithelium
What does the potential space between the inner and outer layer of the optic cup become?
Potential space between the two becomes the SUBRETINAL SPACE (which was the cavity of the neural tube)
What do cells at the anterior margin of the optic cup form?
the posterior pigment epithelium of the iris
As the optic cup forms, what do cells between the future iris and the future retina form?
the ciliary body
Name the following structures:
What does the lens pit form before it bcomes the Lens vesicle?
Lens pore
Name the following components of the formation of the optic cup.
where is the embryonic fissure located on the optic cup?
undersurface
When does the embyonic fissure close?
closes on day 33 allowing pressurization of globe
Where does the closure of the embryonic fissure begin?
Closure occurs first in midzone/equator, then extends posteriorly and anteriorly
what embronic tissue uses the embyonic fissure as a portal to enter the eye?
Embronic fissure serves as portal for mesoderm to enter eye (i.e. hyaloid artery)
What is it called when the embyonic fissure fails to close?
Coloboma
What is the inheritance pattern of colobomas?
sporadic or autosomal dominant (AD)
What is the typical quadrant location of a coloboma?
typical (located in inferonasal quadrant)
If a coloboma involves the retina and choroid what other conditions or syndromes can it be associated with?
associated with basal encephalocele, cleft palate, and CHARGE syndrome)
Is eyelid coloboma associated with closure of the embryonic fissure?
No
What do you call a small, abnormal eye with cystic expansion extending postioerly into the orbit?
Microphthalmos with cyst
Where does the cyst in microphthalmos with cyst typically arise?
Arises in area of and external to a choroidal coloboma
What kind of tissues are contained in the cyst with microphthalmos with cyst?
cyst usually contains dysplastic neuroectodermal tissue and may not directly connect with the eye
T/F: an optic pit is a coloboma?
True, an optic pit is considered an atypical coloboma
What abnormality is associated with optic pit?
basal encepholocele
Through wich structure does the hyaloid artery enter the eye?
embryonic fissure
What stucture does the hyaloid artery form?
vasa hyaloidea propria
what does the vasa hyaloidea propria supply blood to?
primary vitreous
At what gestational age does the intravitreal portion of the hyaloid artery regress?
8.5 months
What does the intraneural portion of the hyaloid artery form?
central retinal artery
What supplies blood flow to the posterior lens in embryologic development?
Posterior tunica vasculosa
At what gestational age does retinal vscular devlopement begin?
16th week
what cell type located next to the hyaloid artery form capillary network, then form arteries and veins
mesenchymal cells
in what pattern do retinal vessels grow?
vessels grow centrifugally from optic disc
When do retinal blood vessels reach the ora serrata?
Nasal: 8 months
Temporal: 1-2 months later
what percentage of normal neonates have a patent hyaloid artery?
3%
Name the 4 remnants of hyaloid vasculature system
- Bergmeister Papillae
- Peripapillary Loop
- Mittendorf’s Dot
- Peristent Pupillary membrane
Where is a Bergmeister papillae located?
At the optic nerve head
Describe how the bergmeister papillae interacts with the hyaloid artery-glial sheath of Bergmeister envelops posterior third of hyaloid artery and begins to atrophy during 7th month
glial sheath of Bergmeister envelops posterior third of hyaloid artery and begins to atrophy during 7th month
What is seen if the glial sheath of the bergmeister papillae does not fully regress?
epipapillary veil
From what structure does the peipapillar loop extend?
optic nerve head
What ocular conditions is one at increased risk for if a Peripapillary loop is present?
risk of artery obstruction or vitreous hemorrhage
Where is a mittendorf’s dot located?
at the posterior lens capsule
what does the mittendorf’s dot represent?
location where the hyaloid artery is attached to posterior tunica vasculosa lentis
what does a persistent pupillary membrane represent?
remnants of anterior tunica vasculosa lentis
Which cells eventually form the optic disc?
Primative epithelial papillae- cells from inner layer of optic cup at superior end of embryonic fissure
Axons of which cell type grow through the primartive epithelial papillae?
ganglion cells
Does myelination of the optic nerve start centrally or peripherally?
centrally
At what gestational age does myelination of the optic nerve reach the chiasm?
7.5 months
At what gestational age does myelination of the optic nerve reach the lamina cribrosa?
birth
At what gestational age is myelination of the optic nerve complete?
approximately 1 month after birth
What is the embronic structure that is contiguous with the retinal ILM that covers the optic nerve?
Inner limiting membrane of Elschnig
Why can newborns optic nerves appear exaggeratedly cupped initially?
ON may show deceptively exaggerated cupping because nerve fibers posterior to lamina cribrosa are incompletely myelinated at birth
What systemic condition is associated with optic nerve hypoplasia?
DeMorsier’s Syndrome
What percentage of patient’s with DeMorsier’s Syndrome have pituitary abnormalities?
13%
Which 3 ocular strutures produce the vitreous?
- lens
- retina
- walls of the hyaloid artery
What type of embyonic cells are contained in the vitreous?
mysechymal cells
What forms the primary vitreous?
hyaloid vascular system
what blood vessels system make up the hylaloid vascular system (aka vasa hyaloidea propria)?
hyaloid canal
hyaloid vessels
posterior portions of tunica vasculosa lentis
What eventually replaces the primary vitreous?
secondary vitreous
What is the disease state caused by failure of the primary vitreous to regress?
persistent hyperplastic primary vitreous (PHPV)
By which ocular structure is the secondarty vitreous formed?
the retina
What is the name of the area that extends from the disc into the vitreous?
Area of Martegiani
What does the Area of Martegiani become?
Cloquet’s canal
What is does Cloquet’s canal represent?
junction of primary and secondary vitreous
What ocular strutures important to cataract surgery make up the tertiary vitreous?
zonule fibers
Which ocular structures from the tertiary vitreous?
ciliary processes and lens capsule
Name the embryologic space directly behind the lens
Berger’s space
Of which embryologic tissue is teh retina derived?
neuroectoderm
When does retinal vascularization begin?
4 months
Which area of the retina is the last to become vascularized?
termporal periphery
At what age is development of the fovea complete?
4 weeks after birth
What is the condition called in which there is an abnormal proliferation of developing retina produces tubular structures with a rosette-like appearance?
Retinal dysplasia
How does retinal dysplasia occur?
It is a nonspecific response to disorganizing influence during development
There are 8 conditions associated with retinal dysplasia, name at least 4 of them
- materal LSD use
- Patau syndrome (trisomy 13)
- microphthalmos
- congenital gluacoma
- Peter’s anomaly
- uveal and optic nerve colobomas
- cycloplia
- synophthalmia
What ocular structure/cell type does the choroid require for development?
From which embryologic tissue is the stromal choroid derived?
neural crest cells
From which embrologic tissue is the vascular endothelium derived?
mesoderm
From which embryologic tissue are choroidal blood vessel walls derived?
neural crest cells
From which embryologic tissues is the scelra derived?
nerual crest cells
mesoderm (temporal aspect)
Why do babies have a blueish hue to their sclera at birth?
due to thinness (seeing the underlying uveal pigment)
From which embryologic tissue is the cornea derived?
neural crest cells (2 waves)
Between which 2 ocular tissues does the first wave of neural crest cell migration occur to form a duble layer of corneal endothelium?
epithelium and the lens
Between which two ocular tissues does the 2nd wave of neural crest migration occur?
epithelium and endothelium
The second wave of neural crest cell migration in conreal formation is rich in which biochemicals?
hyaluonic acid and collagen fibrils
At which gestational age does Descemet’s membrane develop?
4 months
At which gestational age does Bowman’s membrane develop?
5 months
From which embryologic tissue is the angle derived?
neural crest cells from peripheral cornea differentiate into chamber angle
At which gestational age does the angle develop?
7th week
At which gestational age does Schlemm’s canal develop?
4th month
At which gestational age does the angle move posteriorly?
7th month
At which gestational is the formation of the angle complete?
8th month
At which gestational agedoes the trabecular meshwork appear?
just before birth
At which gestational age does the lens begin to form?
27 days
What tissues begin to form the lens?
surface ectoderm adjacent to optic vesicle enlarges to form lens placode
Describe the steps involved in the development of the lens outlined in the drawing:
- Circular indentation occurs on lens plate, forming lens pit, which invaginates the wall of the optic vesicle until it closes to form a sphere
- Basement membrane of the surface ectoderm forms the surface of the sphere (the lens vesicle) and subsequently becomes the lens capsule
- Lens epithelial cells on posterior aspect of this sphere elongate and migrate first (primary lens fibers)
- At 7 weeks, anterior cells migrate toward equator and proliferate to form secondary lens fibers that encase the embryonal nucleus and form the Y sutures
At what gestational age do the posterior lens epithelial cells fill the core of the lens to form the embryonal nucleus?
40 days
What do the Y sutures represent?
the meeting of embryonal and fetal nuclei
Describe the orientation of the “Y” of the Y suture in the anterior lens and posterior lens
upright anteriorly, inverted posteriorly
At which gestational age does the lens placode form?
3 weeks
From which embryologic tissue does the lens placode form?
surface ectoderm
At which gestational age does the lens vesicle form?
6 weeks
Further development of the lens vesicle requires which ocular tissue to be normal to proceed?
Normal neuroretina
At which gestational age does the tunica vasculosa lentis form?
12 weeks
At which gestational age does the tunica vasculosa lentis degenerate?
28-38 weeks
Why would the anterior chamber of a newborn appear more shallow than an adult?
Lens of a newborn is more spherical than that of an adult
How does the iris form?
rim of optic cup grows around lens and forms iris
From which embryologic strucutre does the Iris pigment epithelium develop?
from inner and outer layers of the optic cup
Describe the pigmentation status of the anterior and posterior iris pigment epitheliumanterior pigmented and posterior nonpigmented
anterior pigmented and posterior nonpigmented
From which embryologic tissue do the IPE layers develop?
neuroectoderm
Iris pigment epithelium forms which important ocular divide?
blood-aqueous barrier
At which gestational age does the iris stroma form from neural crest cells?
7th week
At which gestational age does the sphincter and dilator muscles form?
7th week
From which embryologic tissues are the sphincter and dilator muscles derived?
neuroectoderm
At which gestational age blood vessels enter the iris?
7th month
At which gestational age does the tunica vaculosa lentis disappear?
9th month
What color is the typical pigmentation of the newborn iris?
grey-blue
How does the final color of the iris develop?
stromal chromatophores (dendritic melanocytes from neural crest) complete their migration into uvea shortly after birth
Why do newborns have relative miosis in infancy?
Iris dilator muscle is immature
which two tissues form the outer layer of the optic cup?
RPE and posterior iris pigment epithelium
why does the outer layer of the optic cup have matuer pigmentation?
pigment granules develop very early in gestation
when does the formation of the ciliary body begin?
3rd month
what becomes the epithelial layers of the ciliary processes?
folds in the optic cup
At which gestational age do ciliary body filaments from surface cells form zonules; the major arterial circle of the iris (located in CB), the longitudinal ciliary muscle, and the ciliary processes develop?
4th month
At which gestational age does the pars plana, ciliary body stroma and ciliary muscle develop?
5th month
From whcih embryologic tissues does the paras plana, ciliary muscle and ciliary body stroma develop?
neural crest cells adjacent to cornea
At which gestational age do the circular fibers of the ciliary muscle differentiate?
7th month
How can you tell how old a person is by looking at their ciliary body?
Patient’s age can be determined by analysis of CB cellularity
At which gestational age does the nasolacrimal system begin to develop?
6 weeks
What is the first sign of the formation of the nasolacrimal system?surface ectoderm is buried in mesoderm, between maxillary and lateral nasal processes
surface ectoderm gets buried in mesoderm, between maxillary and lateral nasal processes
At what gestational age does the nasaolacrimal system canalize?
3rd month
What defects can result from problems in canalization of the nasolacrimal system?
may result in imperforate valve of Hasner; rarely, absent puncta or canaliculi
At what gestational age does the eyelids begin to form?
8 weeks
The fusion of which tissues form the upper eyelids?
medial and lateral frontonasal processes
The fusion of which tissues form the lower eyelids?
maxillary processes and medial nasal processes
At what gestational age do eyelid folds fuse?
12 weeks
At what gestational age do eyelids begin to seperate?
24 weeks
do eyelids begin to seperate from the nasal or lateral side?
nasal
From which embryologic tissue does the sensory retina develop?
Neural ectoderm
From which embryologic tissue does the RPE develop?
Neural ectoderm
From which embryologic tissue does nonpigmented ciliary body epithelium develop?
Neural ectoderm
From which embryologic tissue does the the pigmented CB epithelium develop?
Neural ectoderm
The pigmeneted CB epithelium is an extension of which tissue?
RPE
From which embryologic tissue does the IPE develop?
Neural ectoderm
From which embryologic tissue does the iris sphincter and dilator muscle develop?
neural ectoderm
From which embryologic tissue does the optic nerve (glial and neural elements) develop?
Neural ectoderm
From which embryologic tissue does the sympathetic ganglion and lateral geniculare body develop?
neural ectoderm
From which embryologic tissue does ocular pigment granules develop? (RPE, CB, IPE)
neural ectoderm
From which embryologic tissue do the peripheral nerves related to eye function develop?
neural ectoderm
From which embryologic tissue do the erector pili muscle associated with hair follicles of the skin develop?
neural ectoderm
From which embryologic tissue does the crystalline lens develop?
Surface ectoderm
From which embryologic tissue does the corneal and conjunctival epithelium develop?
surface ectoderm
From which embryologic tissue does the eyelid epithelium develop?
surface ectoderm
From which embryologic tissue does the lacrimal gland develop?
surface ectoderm
From which embryologic tissue does the nasolacrimal system develop?
surface ectoderm
From which embryologic tissue does the vitreous develop?
surface and neural ectoderm
From which embryologic tissue do the zonules develop?
surface and neural ectoderm
From which embryologic tissue does the corneral stroma and endothelium develop?
neural crest cells
From which embryologic tissue does the iris stroma develop?
neural crest cells
From which embryologic tissue does the trabecular meshwork develop?
neural crest cells
From which embryologic tissue does Schlemm’s canal develop?
neural crest cells
From which embryologic tissue does the sclera (except temporal portion) develop?
neural crest cells
From which embryologic tissue does the sheaths and tendons of extraocular muscles develop?
neural crest cells
From which embryologic tissue does the ciliary muscle (nonpigmented layer of the ciliary body) develop?
neural crest cells
From which embryologic tissue does the choroidal stroma develop?
neural crest cells
From which embryologic tissue do melanocytes develop?
neural crest cells
From which embryologic tissue domeningeal sheaths develop?
neural crest cells
From which embryologic tissue dothe orbital bones develop?
neural crest cells
From which embryologic tissue does the connective tissue of the orbit develop?
neural crest cells
From which embryologic tissue do the musclar and connective tissue layers of the blood vessels develop?
neural crest cells
What stain is specific for neural crest derived structures?
S-100 stain
What what gestational age do the 3 waves of Neural crest cell migration occur?
7th week
Name 3 ocular structures that are forme dby the waves of neural crest cell migration
- corneal and TM endothelium
- keratocytes (corneal stroma)
- iris stroma
Name the 5 conditions that can be caused by abnormal neural crest migration.
- congenital glaucoma
- posterior embryotoxin
- Axenfield-Reiger syndrome
- Peter’s anomaly
- sclerocornea
Which ocular syndromes result from an abnormal proliferation of neural crest cells?
iridocorneal endothelial (ICE) syndromes
Which ocular conditions result from an abnormal terminal induction of neural crest cells?
corneal endothelial dystrophies
From which embryologic tissue does the blood vessel endothelium develop?
mesoderm
From which embryologic tissue does the anterior chamber angle outflow apparatus develop?
mesoderm
From which embryologic tissue does the small temporal area of the sclera develop?
mesoderm
From which embryologic tissue do the extraocular muscles develop?
From which embryologic tissue does the primative connective tissue develop?
mesenchyme
From which embryologic tissues does mesenchyme originate?
neural crest cells and mesoderm
Reference of timeline for Ocular Development:
