Embryology of the Eye Structures

Podcast

Play an AI-generated podcast conversation about this lesson

Questions and Answers

What is the correct order of development after fertilization?

Morula, blastocyst, gastrula, bilaminar disc (correct)

Zygote, morula, blastocyst, bilaminar disc

Zygote, morula, gastrula, embryo

Morula, blastocyst, bilaminar disc, gastrula

Which structure forms as a longitudinal groove within the epiblast during gastrulation?

Amnion

Chorion

Primitive streak (correct)

Neural folds

What is the role of the neural crest during embryonic development?

Contributing to structures like the brain

Emerging at the junction with surface ectoderm (correct)

Differentiating into the three germ cell layers

Forming the bilateral elevations called neural folds

When does gastrulation occur in humans?

Day 15 - 20 Signup and view all the answers

Which cells migrate towards the primitive streak to form the mesoderm?

Epiblast cells Signup and view all the answers

What is the purpose of the bilaminar disc during embryonic development?

Forming extraembryonic tissues like amnion and chorion Signup and view all the answers

What determines the size of the lens vesicle?

Contact area of the optic vesicle with surface ectoderm Signup and view all the answers

What can cause the induction of a smaller lens vesicle?

Abnormal orientation of the optic vesicle Signup and view all the answers

What is the lining of the lens vesicle made up of?

Monolayer of cuboidal cells Signup and view all the answers

Which structure promotes primary lens fiber formation?

Retina Signup and view all the answers

What is responsible for the regression of the hyaloid artery?

Production of aqueous humor (AH) by the ciliary body Signup and view all the answers

Which clinical anomaly arises from incomplete regression of the hyaloid artery?

Mittendorf's dot Signup and view all the answers

Which cell type contributes to the formation of the corneal endothelium?

Mesenchymal neural crest cells Signup and view all the answers

What is the role of tight junctions formed by the corneal endothelium?

To form Descemet's membrane Signup and view all the answers

Which structure surrounds and nourishes the lens during early gestation in dogs?

Tunica vasculosa lentis Signup and view all the answers

What contributes to the formation of the anterior chamber, including the pupillary membrane?

Basal lamina of lens vesicle Signup and view all the answers

From which layer of the optic cup do the iris and ciliary body develop?

Nonpigmented layer Signup and view all the answers

What is responsible for the folding of the inner layer of the optic cup, representing early anterior ciliary processes?

Differential growth of epithelial layers Signup and view all the answers

What is the main result of the differential growth during the last trimester of human gestation?

Deepening of the chamber angle and exposure of outflow pathways Signup and view all the answers

Which cells develop first in the retina according to the text?

Retinal ganglion cells Signup and view all the answers

What is the function of primary vitreous according to the text?

Forms between the lens and optic cup Signup and view all the answers

What happens at around day 45 of gestation in dogs regarding retinal development?

RPE cells become hexagonal Signup and view all the answers

Which tissue/tissues are derived from neural crest tissues according to the text?

RPE and sclera Signup and view all the answers

What is one important role of retinal pigment epithelium (RPE) in development?

Proper development of sclera and choroid Signup and view all the answers

Where do neural crest cells migrate beneath during the eye development process?

Surface ectoderm Signup and view all the answers

What is the role of the mesoderm in eye development according to the text?

Develops into the striated myocytes of extraocular muscle Signup and view all the answers

What structure arises from the optic vesicle within the forebrain during eye development?

Ocular connective tissue derivatives Signup and view all the answers

What may cause colobomas in the iris, choroid, or optic nerve during eye development?

Failure of optic fissure to close Signup and view all the answers

Which structure plays a significant role in determining the size of the palpebral fissure and orbital structures?

Optic stalk Signup and view all the answers

What develops from mesenchyme in the optic fissure around day 25 of gestation?

Hyaloid artery Signup and view all the answers

What is the precursor to the vitreous base and lens zonules?

Drualt's bundle Signup and view all the answers

Which component has been identified in developing zonules and Descemet's membrane?

Elastin Signup and view all the answers

What contributes to lens expansion?

Traction of zonules Signup and view all the answers

What can lead to a flattened area inaccurately referred to as a lens coloboma?

Localized absence of zonules Signup and view all the answers

What does Doppler ultrasound biomicroscopy document related to hyaloid regression between birth and postnatal day 13 in mice?

Decrease in blood velocity Signup and view all the answers

Where do axons from developing ganglion cells traverse during their development?

Through vacuolated cells in the inner wall of the optic stalk Signup and view all the answers

What is Bergmeister's papilla a remnant of?

Glial cells around the hyaloid artery Signup and view all the answers

Where do glial cells form a sheath as they surround the hyaloid artery?

Around the hyaloid artery itself Signup and view all the answers

What initiates myelinization of the optic nerve and progresses toward the eye?

The chiasm Signup and view all the answers

What is the origin of glial cells surrounding the optic nerve and forming part of the lamina cribrosa?

Neural ectoderm Signup and view all the answers

Study Notes

Tertiary Vitreous

Forms as a thick accumulation of collagen fibers between the lens equator and the optic cup, known as Drualt's bundle
Precursor to the vitreous base and lens zonules
Early lens zonular fibers appear to be continuous with the inner membrane of the non-pigmented epithelial layer
Elastin and emulin have been identified in developing zonules and Descemet's membrane
Traction of zonules contributes to lens expansion, and localized absence of zonules can lead to a flattened area of the lens, inaccurately referred to as a lens coloboma

Optic Nerve

Axons from developing ganglion cells traverse through vacuolated cells in the inner wall of the optic stalk
Glial cells form a sheath around the hyaloid artery
As the artery regresses, the space between it and the glial sheath expands
Bergmeister's papilla is a remnant of glial cells around the hyaloid artery
Glial cells migrate into the optic nerve and establish the primitive optic disc
Glial cells surrounding the optic nerve and those forming part of the lamina cribrosa originate from the inner layer of the optic stalk, derived from neural ectoderm
Subsequently, a mesenchymal portion of the lamina cribrosa develops from neural crest origin
Myelinization of the optic nerve initiates at the chiasm, progresses toward the eye, and reaches the optic disc after birth

Ocular Embryology and Congenital Malformations

Gastrulation and neurulation:
- Fertilization → zygote → morula (cluster of 12-16 cells)
- Morula becomes blastocyst, which contains a fluid-filled cavity
- Cells of the blastocyst form embryo proper and extraembryonic tissues (amnion and chorion)
- Embryo bilaminar disc: hypoblast and epiblast
Gastrulation: process where blastocyst becomes gastrula, forming mesodermal germ layer
Day 10 in dogs, day 7 in mice, and day 15-20 in humans
Primitive streak forms as a longitudinal groove within epiblast (future ectoderm)
Epiblast cells migrate towards primitive streak, invaginate to form mesoderm
Results in the 3 classic germ cell layers: Ectoderm, mesoderm, and endoderm
Gastrulation proceeds in cranial-to-caudal progression, with cranial surface ectoderm proliferating to form bilateral elevations called neural folds (forming the brain)

Formation of the Optic Vesicle and Optic Cup

Optic vesicle development starts with the emergence of optic sulci, which are paired outgrowths of the forebrain neural ectoderm
Optic sulci are paired evaginations of forebrain neural ectoderm, around day 13 of gestation in dogs
Concurrent with the closure of the neural tube, the optic sulci transform into optic vesicles
Optic vesicle enlarges and approaches the basal lamina underlying the surface ectoderm
Optic vesicle and optic stalk invaginate through growth and infolding
Surface ectoderm in contact with optic vesicle thickens to form lens placode, which then invaginates with underlying neural ectoderm

Lens Formation

Surface ectoderm becomes competent to respond to lens inducers
Anterior neural plate produces inductive signals to give this area of ectoderm a "lens-forming bias"
Optic vesicle then adheres to lens placode, ensuring alignment of lens and retinal in the visual axis
Lens placode invaginates, forming a hollow sphere = lens vesicle
Size of lens vesicle is determined by contact area of optic vesicle with surface ectoderm and ability of surface ectoderm to respond to induction of growth signals
Abnormal orientation of optic vesicle can cause induction of a smaller lens vesicle
Lens vesicle detachment leads to anterior chamber formation
Induction of small lens vesicle that does not separate normally from surface ectoderm can lead to anterior segment dysgenesis

Vascular Development

Hyaloid artery is the termination of the primitive ophthalmic artery, which branches off the internal ophthalmic artery
Remains within the optic cup following closure of the optic fissure
Branches round the posterior lens capsule and anastomoses with vessels in the pupillary membrane
Hyaloid vascular network forms around the lens, providing nutrition to the lens and anterior segment
Venous drainage occurs near the equatorial lens area, with no discrete hyaloid vein present
Ciliary body begins to produce aqueous humor, which nourishes the lens, and the hyaloid artery starts to regress
Regression of the hyaloid vasculature allows for the development of retinal vessels, primarily mediated by vascular endothelial growth factor (VEGF)-A

Development of the Cornea and Anterior Chamber

After detachment of the lens vesicle, the anterior margins of the optic cup extend beneath the surface ectoderm, initiating corneal development
Surface ectoderm above the optic cup secretes a thick matrix (primary stroma)
Mesenchymal neural crest cells migrate between the surface ectoderm and the optic cup, using the basal lamina of the lens vesicle as a substrate
Induction of corneal endothelium requires the presence of an adjacent lens vesicle
Dehydration leads to a 50% reduction in stromal thickness, aided by the corneal endothelium, which develops tight junctions and forms Descemet's membrane
Transparency of the cornea is achieved by the end of gestation in dogs, with subsequent postnatal changes in corneal thickness observed after eyelid opening

Development of the Iris, Ciliary Body, and Iridocorneal Angle

The two layers of the optic cup are neuroectoderm in origin
The iris and ciliary body develop from the anterior aspect of the optic cup, while the retina develops from the posterior aspect
Optic vesicle is organized with all cell apices directed towards the center, so during invagination, apices of inner and outer epithelial layers become adjacent
Both pigmented and nonpigmented epithelial cells develop apical cilia and show increased Golgi complexes and vesicles around day 40 of gestation in dogs
Nonpigmented and pigmented epithelium of the iris and ciliary body originates from the neural ectoderm of the optic cup
Stroma comes from neural crest cell origin (mesenchymal tissue)
Differential growth of optic cup epithelial layers causes folding of the inner layer, representing early anterior ciliary processes

Retina and Optic Nerve Development

The infolding of the neuroectodermal optic vesicle leads to the formation of a bilayered optic cup
The outer layer of the optic cup, which originates from the optic vesicle, becomes cuboidal and develops melanin granules, forming the retinal pigment epithelium (RPE)
The inner layer of the optic cup gives rise to the neurosensory retina
Bruch's membrane, the basal lamina of the RPE, appears during this time, coinciding with the development of the choriocapillaris
RPE cells adopt a hexagonal shape by day 45 in dogs and develop microvilli that interdigitate with projections from photoreceptors
At the time of lens placode induction, the retinal primordium consists of an outer nuclear zone and an inner marginal (anuclear) zone
Retinal histiogenesis involves cell proliferation in the nuclear zone, migration into the marginal zone, and differentiation into inner and outer neuroblastic layers

Studying That Suits You

Use AI to generate personalized quizzes and flashcards to suit your learning preferences.

Description

Explore the development of eye structures during embryology, including the secretion of primary stroma above the optic cup and the migration of mesenchymal neural crest cells. Learn about the induction of corneal endothelium and the role of adjacent lens vesicle in this process.