Lecture 14: Embryology of the Eye Flashcards
Growth factors bind to
receptor sites on target cells
receptor sites on target cells control what
normal development by modulating proliferation, migration, and
differentiation
One particular gene that appears to be important in the
development of ocular structures is the
Pax-6 gene
3rd week of embryonic development: three primary germ layers have formed the embryonic plate
- Ectoderm
- Mesoderm
- Endoderm
what layers will take part in the developing ocular
structures
Only ectoderm and mesoderm
Ectoderm
outer layer
mesoderm
middle layer
endoderm
inner layer (NOT INVOLVED)
what layer thickens to form neural plate
ectoderm
Neural Plate gives rise to
CNS and eye
Longitudinal groove in neural plate
neural groove
Lateral edges of neural groove are brought closer
together and are called
nural folds
Neural folds fuse to give
neural tube (ectoderm)
Neural tube surrounded by
mesoderm
Mesoderm covered dorsally by surface
ectoderm (surface and neural)
As neural folds move towards one another
neural crest cells differentiate
NCs take up a position in mesoderm between
neural tube and surface ectoderm
Mesenchyme =
collective term that includes both neural crest cells + mesoderm
As neural tube is closing
optic pits form on both sides of forebrain
Optic pits form a
diverticulum
diverticulum extend laterally from forebrain and are called
optic vessels
– For a brief time the optic vesicles are in contact with the
surface ectoderm
Soon neural crest cells situate themselves in
mesoderm between the optic
vesicle and surface ectoderm
What happens if inferior optic fissure does not zip
completely?
- Uveal Coloboma with Optic
Nerve involvement - Iris Coloboma “Key Hole
Pupil”
Coloboma
Incomplete closure of the optic fissure may affect
the developing optic cup or stalk, resulting in an
inferior nasal defect in the optic disc, retina, ciliary
body, or iris.
coloboma and can vary from
a slight notch to a
large wedge like defect.
Colobomas affecting the sensory retina and RPE
also involve
the choroid because its differentiation
depends on an intact RPE layer
optic cup resembles a
sphere that has collapsed onto itself
how many layers is the optic cup composed of
2 layers (inner and outer) arranged apex to apex
The optic vesicle was in
contact with the surface
ectoderm. It pulls back inducing
lens placode to
form
Center of the placode
elongates forming
lens pit
Pit invaginates until
forms hollow circular
structure, lens vesicle
lens vesicle is composed of how many cell layers? surrounded by?
Composed of a single layer of cells surrounded by
a basal lamina (future
lens capsule)
lens vesicle takes up position in
future vitreous chamber
lens vesicle is derived from
surface ectoderm
Makes sense because
structures derived from
surface ectoderm continuously
form throughout life (I.e. skin)
All Secondary Lens Fibers are derived from
the Anterior Lens Epithelium
Six crescent fibers are laid down equidistant in a
growth shell
Subsequent fibers are laid down and follow the pattern to give rise to an
Anterior upright Y-suture and a Posterior Inverted Y-suture.
The spectrum of lens opacities that can result from problems during lens development range from
pinpoint densities having no effect on vision to
significant opacities causing extensive loss of vision
If the tissue near the developing lens fails to induce the lens fibers to elongate
and pack together in an orderly way,
the lens fibers will be misaligned, forming a
cataract of the primary fibers.
Hyaloid Vasculature gives rise to
Central Retinal Artery and Vein
Hyaloid Vasculature may leave its mark on the
lens and optic nerve (Bergmeister’s papilla and Mittendorf’s dot)
Choroid is induced by RPE to form
from Mesenchyme
As the optic cup grows, the vitreous cavity is filled with
fibrillar material that
is secreted by embryonic retina, lens,
and hyaloid vasculature which is referred to as primary vitreous
Cup increases in size, secondary vitreous develops from
retina and degenerating
hyaloid = secondary vitreous (what we now have).
Secondary vitreous
pushes primary vitreous
anteriorly
Funnel-shaped tube remnant of
hyaloid vasculature. (Cloquet’s canal is left in the middle)
Optic Stalk is
the precursor
Inferior optic fissure invaginates forming a
two-layered stalk
Outer layer gives
rise to
neuralglial sheath that
surrounds optic nerve.
The inner layer of the optic nerve is destroyed by
apoptosis to make way
for axons of the retinal ganglion cells.
RPE forms from
outer layer of optic cup
what layer is the first layer of the retina to differentiate
RPE
what is the first visible pigmentation in the embryo!
RPE
Apex faces
retina
basal surface faces
Bruch’s membrane.
retina forms
inner layer of optic cup
Photoreceptors continue to develop
well after birth to increase resolution and sensitivity of the visual system
Macula first develops as an area of
increased ganglion cell density lateral to the optic disc
Inner retinal elements become displaced as
cones increase packing density
Henle’s layer (PR inner fibers) develops
obliqueness in fovea
what is the last portion of retina to fully develop
fovea
Lens vesicle induces the formation
cornea
Corneal epithelium is derived from the
surface ectoderm.
Stroma from
mesenchyme
Corneal endothelium from
neural crest cells
Sclera and EOMs originate from
MESENCHYME outside the optic cup
Sclera will envelop the developing
choroid
Connective tissue fibers will pass through the
scleral foramen and optic nerve fibers to form the
lamina cribrosa.
