Retinal Development Flashcards by Sarah Heath

Where do the neural folds and the neural groove originate

On the embryonic disc

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What happens to the neural folds and the neural groove to form a neural tube

They get “zipped” up

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What are the 3 germ layers

Ectoderm
Mesoderm
Endoderm

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What kind of structures are the neural crest cells going to be

PNS

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What kind of structures are the neural tube going to become

CNS

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Are CN CNS or PNS?

All are peripheral except CN2

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What are the out pouches of the optic pit

Optic vesicles

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What is it called when the neural tube closes

The embryo is in a tube within a tube concept at this point

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What is the inner tube of the tube within the tube concept

Neural tube

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What is the outer tube of the tube within the tube concept

Surface ectoderm

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What lies between the inner and outer tube in the tube within a tube concept

Mesoderm

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What are the two evaginations will form off the cranial portion of the neural tube

Optic vesicles

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What are the optic vesicles made up of

Neural ectoderm

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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

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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.

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The small space left over by the apex to apex folding is initially called the _______

Intraretinal space

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What eventually happens to the intranet in all space

Eventually just becomes a potential space as the layers connect together

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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

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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

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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

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How many layers are in the RPE

1 cell layer

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What is essential for development of the RPE

Apposition of the two layers of the optic cup

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What is the first retinal layer to differentiate

RPE

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What event forms the RPE

Induction

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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

1. 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 2. Biomolecular agents guide axonal growth towards termination in the LGN 3. 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

1. Displacement of inner retinal components to form the depression 2. Migration of photoreceptors toward the center, which increases cone packing 3. 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