EMBRYOLOGY Flashcards
Which structures derive from neuro-ectoderm? (3)
NEURO-ECTODERM –> NERVOUS STRUCTURES –> ROMES.
- Retina (Neurosensory and RPE)
- Optic nerves
- Muscles (smooth) of iris (sphincter and dilator)
- Epithelial lining of iris and ciliary body.
- Secondary and tertiary vitreous
Which structures derive from surface ectoderm?
SURFACE ECTODERM –>
LEVEL surface.
Lens
Epithelium (cornea, conjunctiva, caruncle, skin)
Vitreous
Eyelid skin, eyelashes and gland.
Lacrimal gland / NLD system.
PAX6 is critical for surface ectoderm development.
Which structures derive from Neural Crest?
NEURAL CREST –> Supportive framework and FLOW.
“Some irritated cats and mice took sharp claws everywhere”
Sclera
Iris Stroma
Corneal Stroma and Endothelium
Melanocytes.
Trabecular meshwork
Schwann’s cells / meningeal cells.
Connective tissue of orbit
Extraocular muscle (partially derived)
Ciliary Ganglion
Choroid
Anterior segment dysgenesis occurs with abnormalities relating to neural crest.
What structures are derived from mesoderm?
Mesoderm:
“MESO”
Muscles
Endothelial lining of blood vessels
Sclera (temporal) Schlemm’s canal
Others: Vitreous, suspensory fibres.
Whats the difference between mittendorf’s dot and Bergmeister’s papilla?
Mittendof marks the lens - anterior attachment of hyaloid artery
Bergmeister papilla - posterior attachment of hyaloid artery.
When is the maximal number of axons in the optic nerve achieved?
15 weeks.
Whats the difference between anophthalmia, nanophthalmia and microphthalmia? What mutations are associated?
Anophthalmia: Failure of optic vesicle formation - only extrocular muscle (mesoderm) and lacrimal gland (ectoderm)
Mutations of anophthalmia: RAX and SOX2 and PAX6 (in homozygous)
Nanophthalmia: small eye but basic structures present.
Microphthalmia: Small eye with defects, recognisable elements
Mutations in microphthalmia) : PAX6 (heterozygeous), SOX2
What mutations are involved in cyclopia?
Mutations: SHH and SIX3
What is synophthalmia? What mutation?
Fusion of two eyes due to malformation of mesenchymal tissue of optic vesicles.
Mutation: Chromosome 18
Which week do the three waves of neural crest migration (for form cornea and iris stroma)?
What happens if this is failed?
Week 7.
Pathology: anteiror segment dysgenesis, albinism.
At how many weeks gestation does hyaloid artery enter optic nerve head?
4 weeks.
What order is the extraocular muscle formation (When primordium forms)
Day 26-Day 29: All muscles, then lateral rectus, then superior oblique.
What events happen between weeks 3 and 4? (6)
22nd to 29th day - Optic groove prepares rectus and fissuRes
O: Optic Groove (22nd day)
P: Optic Pit becomes optic vesicle (25th day)
R: Rectus muscles from primordium (26th day), Superior oblique forms last.
F: Embryonic fissure forms (day 27)
R: RPE pigmentation forms (day 28)
What happens in week 5 of embryologic development (3)
Lens Has Very Vital Orbit
1. Lens pit forms from lens vesicle
2. Hyaloid vessels form
3. Vitreous develops
4. Orbital bones begin development
Double V because week 5 (V)
What happens in week 6 embyologically? (6)
Fissures close, Cells, Layers and Vessels Evolve - 6 words
- F - embryonic fissure closes
- C - corneal epithelium connections
- C - Ciliary Ganglion appears
- L - Lens Fibres form
- L - Layers of retina
- V - Vitreous (secondary forms)
- V - vasculature around eye
- E - Eyelid folds and nasolacrimal duct
What happens in week 7 embryologically?
*Some Ganglions Create New Choroidal Tissue
*
1. S - Sclera forms
2. G - Ganglion cells migrate to optic disc
3. C - Choroidal fissure closes which forms pupil
4. N - Nucleus - lens nucleus matures
5. C - Crest Migration (neural crest) Wave 1 - TM, wave 2 - Corneal/scleral stroma, Wave 3 - Iris stroma)
6. T - Tunica vasculosa lentis forms
What happens in month 3 embryologically? (8-12 weeks)
Rods and Chambers Grow SlowLEE
R: Rod/Cone precursors form
A: Anterior chamber appears
C: Ciliary body develops
G: Growth of sclera
S: Sclera condenses
L: Limbus forms
What happens in month 4 embryologically?
Veins, Cup, Muscles and Membrane, Drain, Eyelids
V: Retinal vasculature,
C: Physiological cup forms
M: Iris muscles and Ciliary body and muscles
M: Bowman’s membrane
D: Drain - canal of schlemm
E: Eyelid glands form.
What happens in month 5 and month 6 embryologically?
*Photoreceptors create functional layers *
P - Photoreceptors differentiate
C - cones differentiate further
F - Folds of eyelids seperate
L - layers thicken in macula (ganglion cell layer)
Also: Dilator pupillae muscle differentiates and nasolacrimal system becomes patent
What happens in month 7 embryologically?
Orderly Choroids Make Nerves Develop Smoothly
O: Ora serrata and orbicularis muscle forms
C: Choroid becomes pigmented
M: Migration of ganglion cells to form nerve fibre layer –> Forms foveal depression.
N: Nerve myelination in optic nerve
D: Differentiatation of circular muscle fibres and orbicularis oculi
S: Shifting position of anterior chamber angle structures, finalising their placement
What happens in months 8-9?
**Finish By Clearing Pupils
F: Final touches to chamber angle
B: Blood vessels form in retina at periphery, Hyaloid vessels disappear
C: Choroid and Pupillary membrane disappear.
What lens structure fills the optic cup?
Lens vesicle
What is the weight of the lens at birth? How much does it increase per year?
90mg at birth, increases 2mg per year.
What is the main embryological development of the cornea?
Cornea: Surface ectoderm (epithelium)
Cornea: Stroma/endothelium (neural crest)
First wave: forms epithelium and lens, forms double layer of cornea endothelium
Second wave: Epithelium and endothelium - contains hyaluronic acid and collagen fibrils
Descemets: 4 months
Bowman’s: 5 months
Corneal nerves: 5 months.
What do the first pharyngeal arches give rise to?
What do the second pharyngeal arches give rise to?
First pharyngeal arch: Muscles of mastication.
second pharyngeal arch (hyoid arch): Cranial nerve 7 –> muscles of facial expression.
Anterior segment dysgenesis reflects embryonic abnormalities relating to which cell line?
Neural crest.
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Which retinal cells are formed from the outer neuroblastic layer?
Which retinal cells are formed from the inner neuroblastic layer?
Outer: Bipolar cells, Horizontal cells, nuclei of rods and cones
Inner: Ganglion cells, amacrine cells, nuclei of Muller cells.
What is the difference between primary vitreous, secondary virreous and tertiary vitreous development?
Primary: Hyaloid system
Secondary vitreous ; vitreous body
Tertiary: Anterior/peripheral involved in development of zonules
Diagram of telencepharlon
At what age does the eyeball stop growing in size?
8 years.
Which corneal layer is the last layer to form?
Bowman’s layer.
Which location does myelination start and finish? WHen is myelination complete?
Starts: Optic chiasm
Finishes: Lamina cribrosa
Retinal nerve fibre layer is not myelinated.
Completed at 1 month after birth.
At what week does the primitive streak appear?
Week 3.
What pharyngeal arches are associated with what structures?
1 - Trigeminal (V2 and V3)
2 - Facial
3- Glossopharyngeal
4- Vagus - superior laryngeal branch
5 - Vagus - recurent laryngeal branch
When does ciliary body formation begin?
What is the last structure of the ciliary body to be made?
Begins at 3 months
Circular ciliary muscle - at 7th month.
Drainage angle embryology
Schlemm’s canal
Trabecular meshwork
- 7 weeks - neural crest cells from peripheral cornea differentiates into chamber angle –> TM pathology is associated with corneal pathology
- 4 months - Schlemm’s canal
- 8 months - Drainage angle complete
- Just before birth - TM formation.
Ciliary Body Embryology.
Ciliary body formation: 3 months
4 months: zonules, longitudinal muscle, ciliary process,
5 months: pars plana, ciliary muscle
7 months: circular ciliary muscle.
