Retinal Development Flashcards
Where do the neural folds and the neural groove originate
On the embryonic disc
What happens to the neural folds and the neural groove to form a neural tube
They get “zipped” up
What are the 3 germ layers
Ectoderm
Mesoderm
Endoderm
What kind of structures are the neural crest cells going to be
PNS
What kind of structures are the neural tube going to become
CNS
Are CN CNS or PNS?
All are peripheral except CN2
What are the out pouches of the optic pit
Optic vesicles
What is it called when the neural tube closes
The embryo is in a tube within a tube concept at this point
What is the inner tube of the tube within the tube concept
Neural tube
What is the outer tube of the tube within the tube concept
Surface ectoderm
What lies between the inner and outer tube in the tube within a tube concept
Mesoderm
What are the two evaginations will form off the cranial portion of the neural tube
Optic vesicles
What are the optic vesicles made up of
Neural ectoderm
Formation of the optic cup
The optic vesicle will elongate forming the optic stalk. The end of the stalk will come in close proximity to the outer tube (surface ectoderm)
When the optic vesicle encoutners the surface ectoderm, it will being to fold inward and invaginate.
This infolding will create the optic cup
How does the apex to apex formation occur
As the optic cup folds upon itself, the back of the cup comes into contact with the layer from the front of the cup.
The small space left over by the apex to apex folding is initially called the _______
Intraretinal space
What eventually happens to the intranet in all space
Eventually just becomes a potential space as the layers connect together
What are the apex to apex cells in the most posterior part of the optic cup
Outer layer is the RPE
Inner layer i the neural retina
What is the apex to apex cells in the more anterior part of the optic cup going to become
Outer layer is the PCE
Inner layer is the NPCE
What are the cells that are apex to apex that are most anteriorly in the optic cup
Outer layer is the anterior iris epithelium
Posterior iris epithelium
How many layers are in the RPE
1 cell layer
What is essential for development of the RPE
Apposition of the two layers of the optic cup
What is the first retinal layer to differentiate
RPE
What event forms the RPE
Induction
What is the earliest pigmentation evident in the embryo
RPE
When does the RPE become pigmented
1 month
Base of each RPE cell
Is external toward the developing choroid
Apex of each RPE cell
Internal toward the inner layer if the optic cup
When do the cells of the inner layer of the optic cup proliferate and two zones are evident
Between weeks 4 to 6
When does the neural retina subdivide into two distinct areas
Beginning around weeks 4 to 6
What are the 2 subdivisions of the neural retina at weeks 4 to 6
Outer area: germinating zone (thicker)
Inner area: marginal zone (thinner area)
Other than the neural retina deividing into two subdivisions, what else happens at weeks 4 to 6
A basal lamina is formed that will eventually become the inner limiting membrane of the retina
What happens at week 7
All migration occurs, forming the inner and outer neuroblastic layers, between which lies the transient fiber layer of Chievitz
When do the formation of the inner and outer neuroblastic layers (separated by the transient layer of Chievitz) occur
Week 7
What is a nucleus free zone that lies between the inner and outer neuroblastic layers
Transient fiber layer of Chievitz
The formation of the two neuroblastic layers is complete during the _____ month
3rd
Where does differentiation of the neural retinal cells begin first
In the central retina first and proceeds to the periphery
What develops first, the central or peripheral retina
Central
Layer development of the inner neuroblastic layer
- The ganglion cells migrate, forming a layer close to the basement membrane, and almost immediately send out their axonal processes, which become evident by week 8
- Biomolecular agents guide axonal growth towards termination in the LGN
- Muller cells located rather centrally in the inner neuroblastic layer develop at the same time. The bodies of the muller and amacrine cells remain in the inner neuroblastic layer but move slightly scleral
How do ganglion cells move
Inward
How do the muller and amacrine cells shift
Outward
How do bipolar cells migrate
From the outer neuroblastic layer and settle near the muller and amacrine cells and the horizontal cell follows
When is the fiber layer of Chievitz obliterated
When the bipolar cells migrate along with the horizontal cells
When the bipolar and horizontal cells migrate and the fiber layer of Chievitz all move/ obliterate, what happens to the photoreceptor cells
They remain in the outer neuroblastic layer
What happens in week 12
The photoreceptors are aligned along the outer side of the inner layer of the optic cup and adhering junctions appear between them
When are the photoreceptors aligned along the outer side of the inner layer of the optic cup and adhering junctions appear between them
Week 12
How are the photoreceptors aligned at week 12
Along the outer side of the inner layer of the optic cup with adhering junctions between them
What forms the precursor of the external limiting membrane
Adhering junctions appearing between the photoreceptors aligned along the outer side of the inner layer of the optic cup
What are the last cells of the neural retina to differentiate
Photoreceptor cells
When do the photoreceptors differentiate
Month 5
What photoreceptors differentiates first
Cones
When do rods being to diffentiate
7th month
Which develops first, inner segment of the photoreceptor or the outer segment of the photorecetor
Inner segment develops first
What cells are initially all in the outer retina
Bipolar, horizontal, and PR
After migration, only the PR remain
Where are the horizontal, amacrine, and muller cells developing
In the inner nuclear layer
What is happening in the inner and outer plexiform layer
Filling with neuronal processes
What forms the primitive internal limiting membrane
The fibers of the muller cells appear and extend to the basal lamina, forming the primitive internal limiting membrnae
What does the muller cell provide
A scaffolding for cell development and appears to be involved with guiding the direction of axonal fiber growth
What begins to appear at the same time as the plexiform layers?
Synaptic complexes
What plexiform layer develops first
Inner plexiform
Do cone pedicles or rod spherules develop first
Cone spherules
What is established even before the outer segments of photoreceptors are completed
Photoreceptor synapses with bipolar cells
When is the ganglion cell layer well established
Month 5
What is one of the first layers to be well established
Ganglion cell layer
Describe the horizontal raphe
Because the retinal development is more advances centrally than peripherally, the ganglion axons from the periphery must take an arched route above and below the macular area to reach the nerve head. The line of deviation at the horizontal temporal meridian is termed the horizontal raphe
When does apoptosis of retina cells happen
5th month
Retinal growth after month 6
No further mitosis, retinal growth continues because of cell differentiation, growth, and maturation
When do cones begin to differentiate and accumulation of nuclei in the macula happen
Sixth month
How many rows of ganglion cells are present
Up to 9
What are the three stages of foveal displacement
- Displacement of inner retinal components to form the depression
- Migration of photoreceptors toward the center, which increases cone packing
- Maturation of the photoreceptors
Ganglion cells and the cells of the inner nuclear layer in the seventh month
Begin to move to the periphery of the macula
Fovea after birth
- Still a single layer of ganglion cells and a thin inner nuclear layer across the no-depressed foveal area
- by 4 months postpartum both these layers are displaced to the sloping walls of the fovea, leaving the cones of the outer nuclear layer as the only neural cell bodies in the center of the depression
How long does the foveal depression continue to deepen after birth
Until about age 15 months
What is the last the reach maturity in the developing eye
The foveola
What is different about the cone inner fibers in the fovea
Elongate and adopt an oblique orientation (forming Henles fiber layer) in order to synapse with the cells of the inner nuclear layer, which have been displaced to the sloping walls
VA of infants under one month
20/800 to 20/200
VA of infants 2 months
20/150
VA of infants 4 months old
20/60
VA of infants 6 months old
20/20
What cells start in the inner neuroblastic layer
Ganglion
Amacrine
Muller
What cells being in the outer neurblastic layer
Bipolar
Horizontal
Photoreceptor
Where does the ganglion end up
RNFL
GCL
What cells end up in ther inner nuclear layer
Amacrine
Muller
Bipolar
Horizontal
What layers do the photoreceptors end up occupying
Outer nuclear layer
Photoreceptor layer
